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Mohammadalinejad G, Afsharipour B, Yacyshyn A, Duchcherer J, Bashuk J, Bennett E, Pearcey GEP, Negro F, Quinlan KA, Bennett DJ, Gorassini MA. Intrinsic motoneuron properties in typical human development. J Physiol 2024; 602:2061-2087. [PMID: 38554126 DOI: 10.1113/jp285756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 03/06/2024] [Indexed: 04/01/2024] Open
Abstract
Motoneuron properties and their firing patterns undergo significant changes throughout development and in response to neuromodulators such as serotonin. Here, we examined the age-related development of self-sustained firing and general excitability of tibialis anterior motoneurons in a young development (7-17 years), young adult (18-28 years) and adult (32-53 years) group, as well as in a separate group of participants taking selective serotonin reuptake inhibitors (SSRIs, aged 11-28 years). Self-sustained firing, as measured by ΔF, was larger in the young development (∼5.8 Hz, n = 20) compared to the young adult (∼4.9 Hz, n = 13) and adult (∼4.8 Hz, n = 8) groups, consistent with a developmental decrease in self-sustained firing mediated by persistent inward currents (PIC). ΔF was also larger in participants taking SSRIs (∼6.5 Hz, n = 9) compared to their age-matched controls (∼5.3 Hz, n = 26), consistent with increased levels of spinal serotonin facilitating the motoneuron PIC. Participants in the young development and SSRI groups also had higher firing rates and a steeper acceleration in initial firing rates (secondary ranges), consistent with the PIC producing a steeper acceleration in membrane depolarization at the onset of motoneuron firing. In summary, both the young development and SSRI groups exhibited increased intrinsic motoneuron excitability compared to the adults, which, in the young development group, was also associated with a larger unsteadiness in the dorsiflexion torque profiles. We propose several intrinsic and extrinsic factors that affect both motoneuron PICs and cell discharge which vary during development, with a time course similar to the changes in motoneuron firing behaviour observed in the present study. KEY POINTS: Neurons in the spinal cord that activate muscles in the limbs (motoneurons) undergo increases in excitability shortly after birth to help animals stand and walk. We examined whether the excitability of human ankle flexor motoneurons also continues to change from child to adulthood by recording the activity of the muscle fibres they innervate. Motoneurons in children and adolescents aged 7-17 years (young development group) had higher signatures of excitability that included faster firing rates and more self-sustained activity compared to adults aged ≥18 years. Participants aged 11-28 years of age taking serotonin reuptake inhibitors had the highest measures of motoneuron excitability compared to their age-matched controls. The young development group also had more unstable contractions, which might partly be related to the high excitability of the motoneurons.
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Affiliation(s)
- Ghazaleh Mohammadalinejad
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Babak Afsharipour
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Alex Yacyshyn
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Jennifer Duchcherer
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Jack Bashuk
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Erin Bennett
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Gregory E P Pearcey
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St John's Canada and Physical Therapy & Human Movement Sciences, Northwestern University, Chicago, IL, USA
| | - Francesco Negro
- Clinical and Experimental Sciences, Universita degli Studi di Brescia, Brescia, Italia
| | - Katharina A Quinlan
- George and Anne Ryan Institute for Neuroscience, Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - David J Bennett
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB, Canada
| | - Monica A Gorassini
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
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2
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Yildiz N, Cecen S, Sancar N, Karacan I, Knikou M, Türker KS. Postsynaptic potentials of soleus motor neurons produced by transspinal stimulation: A human single motor unit study. J Neurophysiol 2024. [PMID: 38656134 DOI: 10.1152/jn.00077.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2024] [Accepted: 04/17/2024] [Indexed: 04/26/2024] Open
Abstract
Transspinal (or transcutaneous spinal cord) stimulation is a non-invasive, cost-effective, easily applied method with great potential as a therapeutic modality for recovering somatic and non-somatic functions in upper motor neuron disorders. However, how transspinal stimulation affects motor neuron depolarization is poorly understood, limiting the development of effective transspinal stimulation protocols for rehabilitation. In this study, we characterized the responses of soleus α motor neurons to single pulse transspinal stimulation using single motor unit discharges as a proxy given the 1:1 discharge activation between the motor neuron and the motor unit. Peristimulus time histogram, peristimulus frequencygram and surface electromyography (sEMG) were used to characterize the postsynaptic potentials of soleus motor neurons. Transspinal stimulation produced short-latency excitatory postsynaptic potentials (EPSPs) followed by two distinct phases of inhibitory postsynaptic potentials (IPSPs) in most soleus motor neurons and only IPSPs in others. Transspinal stimulation generated double discharges at short interspike intervals in a few motor units. The short-latency EPSPs were likely mediated by muscle spindle group Ia and II afferents, and the IPSPs via excitation of group Ib afferents and recurrent collaterals of motor neurons leading to activation of diverse spinal inhibitory interneuronal circuits. Further studies are warranted to understand better how transspinal stimulation affects depolarization of α motor neurons over multiple spinal segments. This knowledge will be seminal for developing effective transspinal stimulation protocols in upper motor neuron lesions.
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Affiliation(s)
- Nilgün Yildiz
- Faculty of Dentistry, Physiology, & Health Sciences, Istanbul Gelisim University, Istanbul, Turkey
| | - Sepril Cecen
- Department of Physiology, Hamidiye Medical School, Istanbul, Turkey
| | - Nuray Sancar
- Faculty of Dentistry & Physiology, Istanbul Gelisim University, Istanbul, Turkey
| | - Ilhan Karacan
- Physical Medicine & Rehabilitation, Bagcilar Training & Research Hosptial, Istanbul, Turkey
| | - Maria Knikou
- Graduate Center, Department of Physical Therapy, Collaborative Neuroscience Program, City University of New York, Staten Island, NY, United States
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3
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Yeung D, Negro F, Vujaklija I. Adaptive HD-sEMG decomposition: towards robust real-time decoding of neural drive. J Neural Eng 2024; 21:026012. [PMID: 38479007 DOI: 10.1088/1741-2552/ad33b0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2023] [Accepted: 03/13/2024] [Indexed: 03/22/2024]
Abstract
Objective. Neural interfacing via decomposition of high-density surface electromyography (HD-sEMG) should be robust to signal non-stationarities incurred by changes in joint pose and contraction intensity.Approach. We present an adaptive real-time motor unit decoding algorithm and test it on HD-sEMG collected from the extensor carpi radialis brevis during isometric contractions over a range of wrist angles and contraction intensities. The performance of the algorithm was verified using high-confidence benchmark decompositions derived from concurrently recorded intramuscular electromyography.Main results. In trials where contraction conditions between the initialization and testing data differed, the adaptive decoding algorithm maintained significantly higher decoding accuracies when compared to static decoding methods.Significance. Using "gold standard" verification techniques, we demonstrate the limitations of filter re-use decoding methods and show the necessity of parameter adaptation to achieve robust neural decoding.
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Affiliation(s)
- Dennis Yeung
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy
| | - Ivan Vujaklija
- Department of Electrical Engineering and Automation, Aalto University, Espoo, Finland
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Kirk EA, Sauerbrei BA. Accessing populations of motor units. eLife 2024; 13:e94764. [PMID: 38175188 PMCID: PMC10766347 DOI: 10.7554/elife.94764] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2024] Open
Abstract
A new device improves the way scientists can record the activity of motor units in a wide range of animals and settings.
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Affiliation(s)
- Eric A Kirk
- Department of Neurosciences, School of Medicine, Case Western Reserve UniversityClevelandUnited States
| | - Britton A Sauerbrei
- Department of Neurosciences, School of Medicine, Case Western Reserve UniversityClevelandUnited States
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Kwon M, Christou EA. Visual Information Processing in Older Adults: Force Control and Motor Unit Pool Modulation. J Mot Behav 2023; 56:330-338. [PMID: 38155098 PMCID: PMC11006344 DOI: 10.1080/00222895.2023.2298888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 12/19/2023] [Indexed: 12/30/2023]
Abstract
Increased visual information about a task impairs force control in older adults. To date, however, it remains unclear how increased visual information changes the activation of the motor unit pool differently for young and older adults. Therefore, this study aimed to determine how increased visual information alters the activation of the motor neuron pool and influences force control in older adults. Fifteen older adults (66-86 years, seven women) and fifteen young adults (18-30 years, eight women) conducted a submaximal constant force task (15% of maximum) with ankle dorsiflexion for 20 s. The visual information processing was manipulated by changing the amount of force visual feedback into a low-gain (0.05°) or high-gain (1.2°) condition. Older adults exhibited greater force variability, especially at high-gain visual feedback. This exacerbated force variability from low- to high-gain visual feedback was associated with modulations of multiple motor units, not single motor units. Specifically, increased modulation of multiple motor units from 10 to 35 Hz may contribute to the amplification in force variability. Therefore, our findings suggest evidence that high-gain visual feedback amplifies force variability of older adults which is related to increases in the activation of motor neuron pool from 10 to 35 Hz.
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Affiliation(s)
- MinHyuk Kwon
- Department of Kinesiology and Health Promotion, California
State Polytechnic University, Pomona, CA, USA
- Department of Applied Physiology and Kinesiology,
University of Florida, Gainesville, FL, USA
| | - Evangelos A Christou
- Department of Applied Physiology and Kinesiology,
University of Florida, Gainesville, FL, USA
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Cohen JW, Vieira TM, Ivanova TD, Garland SJ. Regional recruitment and differential behavior of motor units during postural control in older adults. J Neurophysiol 2023; 130:1321-1333. [PMID: 37877159 DOI: 10.1152/jn.00068.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Revised: 10/23/2023] [Accepted: 10/23/2023] [Indexed: 10/26/2023] Open
Abstract
Aging is associated with neuromuscular system changes that may have implications for the recruitment and firing behaviors of motor units (MUs). In previous studies, we observed that young adults recruit subpopulations of triceps surae MUs during tasks that involved leaning in five directions: common units that were active during different leaning directions and unique units that were active in only one leaning direction. Furthermore, the MU subpopulation firing behaviors [average firing rate (AFR), coefficient of variation (CoVISI), and intermittent firing] modulated with leaning direction. The purpose of this study was to examine whether older adults exhibited this regional recruitment of MUs and firing behaviors. Seventeen older adults (aged 74.8 ± 5.3 yr) stood on a force platform and maintained their center of pressure leaning in five directions. High-density surface electromyography recordings from the triceps surae were decomposed into single MU action potentials. A MU tracking analysis identified groups of MUs as being common or unique across the leaning directions. Although leaning in different directions did not affect the AFR and CoVISI of common units (P > 0.05), the unique units responded to the leaning directions by increasing AFR and CoVISI, albeit modestly (F = 18.51, P < 0.001). The unique units increased their intermittency with forward leaning (F = 9.22, P = 0.003). The mediolateral barycenter positions of MU activity in both subpopulations were found in similar locations for all leaning directions (P > 0.05). These neuromuscular changes may contribute to the reduced balance performance seen in older adults.NEW & NOTEWORTHY In this study, we observed differences in motor unit recruitment and firing behaviors of distinct subpopulations of motor units in the older adult triceps surae muscle from those observed in the young adult. Our results suggest that the older adult central nervous system may partially lose the ability to regionally recruit and differentially control motor units. This finding may be an underlying cause of balance difficulties in older adults during directionally challenging leaning tasks.
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Affiliation(s)
- Joshua W Cohen
- School of Kinesiology, Western University, London, Ontario, Canada
- Faculty of Health Sciences, School of Physical Therapy, Western University, London, Ontario, Canada
| | - Taian M Vieira
- Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
| | - Tanya D Ivanova
- Faculty of Health Sciences, School of Physical Therapy, Western University, London, Ontario, Canada
| | - S Jayne Garland
- Faculty of Health Sciences, School of Physical Therapy, Western University, London, Ontario, Canada
- Collaborative Specialization in Musculoskeletal Health Research, Bone and Joint Institute, Western University, London, Ontario, Canada
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7
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Wansbrough K. A novel protocol for indirectly evaluating entrainment during tACS in humans. J Physiol 2023; 601:4663-4664. [PMID: 37804075 DOI: 10.1113/jp285465] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 09/28/2023] [Indexed: 10/08/2023] Open
Affiliation(s)
- Kym Wansbrough
- School of Psychology, College of Health and Education, Murdoch University, Western Australia, Australia
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Hug F, Avrillon S, Sarcher A, Del Vecchio A, Farina D. Correlation networks of spinal motor neurons that innervate lower limb muscles during a multi-joint isometric task. J Physiol 2023; 601:3201-3219. [PMID: 35772071 DOI: 10.1113/jp283040] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 06/22/2022] [Indexed: 11/08/2022] Open
Abstract
Movements are reportedly controlled through the combination of synergies that generate specific motor outputs by imposing an activation pattern on a group of muscles. To date, the smallest unit of analysis of these synergies has been the muscle through the measurement of its activation. However, the muscle is not the lowest neural level of movement control. In this human study (n = 10), we used a purely data-driven method grounded on graph theory to extract networks of motor neurons based on their correlated activity during an isometric multi-joint task. Specifically, high-density surface electromyography recordings from six lower limb muscles were decomposed into motor neurons spiking activity. We analysed these activities by identifying their common low-frequency components, from which networks of correlated activity to the motor neurons were derived and interpreted as networks of common synaptic inputs. The vast majority of the identified motor neurons shared common inputs with other motor neuron(s). In addition, groups of motor neurons were partly decoupled from their innervated muscle, such that motor neurons innervating the same muscle did not necessarily receive common inputs. Conversely, some motor neurons from different muscles-including distant muscles-received common inputs. The study supports the theory that movements are produced through the control of small numbers of groups of motor neurons via common inputs and that there is a partial mismatch between these groups of motor neurons and muscle anatomy. We provide a new neural framework for a deeper understanding of the structure of common inputs to motor neurons. KEY POINTS: A central and unresolved question is how spinal motor neurons are controlled to generate movement. We decoded the spiking activities of dozens of spinal motor neurons innervating six muscles during a multi-joint task, and we used a purely data-driven method grounded on graph theory to extract networks of motor neurons based on their correlated activity (considered as common input). The vast majority of the identified motor neurons shared common inputs with other motor neuron(s). Groups of motor neurons were partly decoupled from their innervated muscle, such that motor neurons innervating the same muscle did not necessarily receive common inputs. Conversely, some motor neurons from different muscles, including distant muscles, received common inputs. The study supports the theory that movement is produced through the control of groups of motor neurons via common inputs and that there is a partial mismatch between these groups of motor neurons and muscle anatomy.
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Affiliation(s)
- François Hug
- LAMHESS, Université Côte d'Azur, Nice, France
- Laboratory 'Movement, Interactions, Performance' (EA 4334), Nantes University, Nantes, France
- Institut Universitaire de France (IUF), Paris, France
| | - Simon Avrillon
- Legs + Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, IL, USA
- Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA
- Neuromechanics & Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London, UK
| | - Aurélie Sarcher
- Laboratory 'Movement, Interactions, Performance' (EA 4334), Nantes University, Nantes, France
| | - Alessandro Del Vecchio
- Neuromuscular Physiology and Neural Interfacing Group, Department of Artificial Intelligence in Biomedical Engineering, Faculty of Engineering, Erlangen-Nuremberg, Friedrich-Alexander University, Erlangen, Germany
| | - Dario Farina
- Neuromechanics & Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London, UK
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Rungta S, Murthy A. Context-specific early recruitment of small motor units in the shoulder muscle reflects a reach movement plan. J Neurophysiol 2023; 129:1094-1113. [PMID: 36988205 DOI: 10.1152/jn.00522.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/30/2023] Open
Abstract
Understanding how motor plans are transformed into appropriate patterns of muscle activity is a central question in motor control. While muscle activity during the delay period has not been reported using conventional EMG approaches, we isolated motor unit activity using a high-density surface EMG signal from the anterior deltoid muscle to test whether heterogeneity in motor units could reveal early preparatory activity. Consistent with our previous work (Rungta et al., 2021), we observed early selective recruitment of small-amplitude size motor units during the delay period for hand movements like early recruitment of small-amplitude motor units in neck muscles of non-human primates performing delayed saccade tasks. This early activity was spatially specific and increased with time and resembled an accumulation to threshold model that correlated with movement onset time. Such early recruitment of ramping motor units was observed at the single trial level as well. In contrast, no such recruitment of large amplitude size motor units, called non-rampers, was observed during the delay period. Instead, non-rampers became spatially specific and predicted movement onset time after the delay period. Interestingly, spatially specific delay period activity was only observed for hand movements but was absent for isometric force-driven cursor movements. Nonetheless, muscle activity was correlated with the time it took to initiate movements in both task conditions for non-rampers. Overall, our results reveal a novel heterogeneity in the EMG activity which allows the expression of early motor preparation via small amplitude size motor units which are differentially activated during initiation of movements.
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Affiliation(s)
- Satya Rungta
- IISc Mathematics Initiative, Indian Institute of Science Bangalore, Bangalore, Karnataka, India
- Centre for Neuroscience, Indian Institute of Science Bangalore, Bangalore, India
| | - Aditya Murthy
- Centre for Neuroscience, Indian Institute of Science Bangalore, Bangalore, India
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10
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Beauchamp JA, Pearcey GEP, Khurram OU, Chardon M, Wang YC, Powers RK, Dewald JPA, Heckman CJ. A geometric approach to quantifying the neuromodulatory effects of persistent inward currents on individual motor unit discharge patterns. J Neural Eng 2023; 20:016034. [PMID: 36626825 PMCID: PMC9885522 DOI: 10.1088/1741-2552/acb1d7] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 12/11/2022] [Accepted: 01/10/2023] [Indexed: 01/11/2023]
Abstract
Objective.All motor commands flow through motoneurons, which entrain control of their innervated muscle fibers, forming a motor unit (MU). Owing to the high fidelity of action potentials within MUs, their discharge profiles detail the organization of ionotropic excitatory/inhibitory as well as metabotropic neuromodulatory commands to motoneurons. Neuromodulatory inputs (e.g. norepinephrine, serotonin) enhance motoneuron excitability and facilitate persistent inward currents (PICs). PICs introduce quantifiable properties in MU discharge profiles by augmenting depolarizing currents upon activation (i.e. PIC amplification) and facilitating discharge at lower levels of excitatory input than required for recruitment (i.e. PIC prolongation).Approach. Here, we introduce a novel geometric approach to estimate neuromodulatory and inhibitory contributions to MU discharge by exploiting discharge non-linearities introduced by PIC amplification during time-varying linear tasks. In specific, we quantify the deviation from linear discharge ('brace height') and the rate of change in discharge (i.e. acceleration slope, attenuation slope, angle). We further characterize these metrics on a simulated motoneuron pool with known excitatory, inhibitory, and neuromodulatory inputs and on human MUs (number of MUs; Tibialis Anterior: 1448, Medial Gastrocnemius: 2100, Soleus: 1062, First Dorsal Interosseus: 2296).Main results. In the simulated motor pool, we found brace height and attenuation slope to consistently indicate changes in neuromodulation and the pattern of inhibition (excitation-inhibition coupling), respectively, whereas the paired MU analysis (ΔF) was dependent on both neuromodulation and inhibition pattern. Furthermore, we provide estimates of these metrics in human MUs and show comparable variability in ΔFand brace height measures for MUs matched across multiple trials.Significance. Spanning both datasets, we found brace height quantification to provide an intuitive method for achieving graded estimates of neuromodulatory and inhibitory drive to individual MUs. This complements common techniques and provides an avenue for decoupling changes in the level of neuromodulatory and pattern of inhibitory motor commands.
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Affiliation(s)
- James A Beauchamp
- Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, IL, United States of America
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
| | - Gregory E P Pearcey
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s, NL, Canada
| | - Obaid U Khurram
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, MN, United States of America
| | - Matthieu Chardon
- Northwestern Argonne Institute for Science and Engineering (NAISE), Northwestern University, Evanston, IL, United States of America
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
| | - Y Curtis Wang
- Department of Electrical and Computer Engineering, California State University, Los Angeles, Los Angeles, CA, United States of America
| | - Randall K Powers
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, WA, United States of America
| | - Julius P A Dewald
- Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, IL, United States of America
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
| | - CJ Heckman
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States of America
- Shirley Ryan AbilityLab, Chicago, IL, United States of America
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11
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Abstract
It has been shown that when humans lean in various directions, the central nervous system (CNS) recruits different motoneuron pools for task completion; common units that are active during different leaning directions, and unique units that are active in only one leaning direction. We used high-density surface electromyography (HD-sEMG) to examine if motor unit (MU) firing behavior was dependent on leaning direction, muscle (medial and lateral gastrocnemius; soleus), limits of stability, or whether a MU is considered common or unique. Fourteen healthy participants stood on a force platform and maintained their center of pressure in five different leaning directions. HD-sEMG recordings were decomposed into MU action potentials and the average firing rate (AFR), coefficient of variation (CoVISI), and firing intermittency were calculated on the MU spike trains. During the 30°-90° leaning directions both unique units and common units had higher firing rates (F = 31.31, P < 0.0001). However, the unique units achieved higher firing rates compared with the common units (mean estimate difference = 3.48 Hz, P < 0.0001). The CoVISI increased across directions for the unique units but not for the common units (F = 23.65, P < 0.0001). Finally, intermittent activation of MUs was dependent on the leaning direction (F = 11.15, P < 0.0001), with less intermittent activity occurring during diagonal and forward-leaning directions. These results provide evidence that the CNS can preferentially control separate motoneuron pools within the ankle plantarflexors during voluntary leaning tasks for the maintenance of standing balance.NEW & NOTEWORTHY In this study, we demonstrate that the different subpopulations of motor units within the three muscles comprising the ankle plantarflexors behave differently during multidirectional leaning. Our results suggest that the central nervous system has the capability to control distinct subpopulations of motor units to meet the force requirements necessary for leaning. This may allow for a precise, efficient, and flexible control strategy for the maintenance of standing balance.
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Affiliation(s)
- Joshua W Cohen
- School of Kinesiology, Western University, London, Ontario, Canada.,Collaborative Specialization in Musculoskeletal Health Research, Bone and Joint Institute, Western University, London, Ontario, Canada
| | - Taian M Vieira
- Laboratorio di Ingegneria del Sistema Neuromuscolare (LISiN), Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Turin, Italy
| | - Tanya D Ivanova
- Physical Therapy, Faculty of Health Sciences, Western University, London, Ontario, Canada
| | - S Jayne Garland
- Physical Therapy, Faculty of Health Sciences, Western University, London, Ontario, Canada.,Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
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12
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Lin YT, Chen YC, Chang GC, Hwang IS. Failure to improve task performance after visuomotor training with error reduction feedback for young adults. Front Physiol 2023; 14:1066325. [PMID: 36969593 PMCID: PMC10030953 DOI: 10.3389/fphys.2023.1066325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 02/22/2023] [Indexed: 03/29/2023] Open
Abstract
Visual feedback that reinforces accurate movements may motivate skill acquisition by promoting self-confidence. This study investigated neuromuscular adaptations to visuomotor training with visual feedback with virtual error reduction. Twenty-eight young adults (24.6 ± 1.6 years) were assigned to error reduction (ER) (n = 14) and control (n = 14) groups to train on a bi-rhythmic force task. The ER group received visual feedback and the displayed errors were 50% of the real errors in size. The control group was trained with visual feedback with no reduction in errors. Training-related differences in task accuracy, force behaviors, and motor unit discharge were contrasted between the two groups. The tracking error of the control group progressively declined, whereas the tracking error of the ER group was not evidently reduced in the practice sessions. In the post-test, only the control group exhibited significant task improvements with smaller error size (p = .015) and force enhancement at the target frequencies (p = .001). The motor unit discharge of the control group was training-modulated, as indicated by a reduction of the mean inter-spike interval (p = .018) and smaller low-frequency discharge fluctuations (p = .017) with enhanced firing at the target frequencies of the force task (p = .002). In contrast, the ER group showed no training-related modulation of motor unit behaviors. In conclusion, for young adults, ER feedback does not induce neuromuscular adaptations to the trained visuomotor task, which is conceptually attributable to intrinsic error dead-zones.
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Affiliation(s)
- Yen-Ting Lin
- Department of Ball Sport, National Taiwan University of Sport, Taichung City, Taiwan
| | - Yi-Ching Chen
- Department of Physical Therapy, College of Medical Science and Technology, Chung Shan Medical University, Taichung City, Taiwan
- Physical Therapy Room, Chung Shan Medical University Hospital, Taichung City, Taiwan
| | - Gwo-Ching Chang
- Department of Information Engineering, I-Shou University, Kaohsiung City, Taiwan
| | - Ing-Shiou Hwang
- Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan City, Taiwan
- Institute of Allied Health Sciences, College of Medicine, National Cheng Kung University, Tainan City, Taiwan
- *Correspondence: Ing-Shiou Hwang,
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13
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Yokoyama H, Kaneko N, Sasaki A, Saito A, Nakazawa K. Firing behavior of single motor units of the tibialis anterior in human walking as non-invasively revealed by HDsEMG decomposition. J Neural Eng 2022; 19. [PMID: 36541453 DOI: 10.1088/1741-2552/aca71b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Accepted: 11/29/2022] [Indexed: 12/02/2022]
Abstract
Objective.Investigation of the firing behavior of motor units (MUs) provides essential neuromuscular control information because MUs are the smallest organizational component of the neuromuscular system. The MUs activated during human infants' leg movements and rodent locomotion, mainly controlled by the spinal central pattern generator (CPG), show highly synchronous firing. In addition to spinal CPGs, the cerebral cortex is involved in neuromuscular control during walking in human adults. Based on the difference in the neural control mechanisms of locomotion between rodent, human infants and adults, MU firing behavior during adult walking probably has some different features from the other populations. However, so far, the firing activity of MUs in human adult walking has been largely unknown due to technical issues.Approach.Recent technical advances allow noninvasive investigation of MU firing by high-density surface electromyogram (HDsEMG) decomposition. We investigated the MU firing behavior of the tibialis anterior (TA) muscle during walking at a slow speed by HDsEMG decomposition.Main results.We found recruitment threshold modulation of MU between walking and steady isometric contractions. Doublet firings, and gait phase-specific firings were also observed during walking. We also found high MU synchronization during walking over a wide range of frequencies, probably including cortical and spinal CPG-related components. The amount of MU synchronization was modulated between the gait phases and motor tasks. These results suggest that the central nervous system flexibly controls MU firing to generate appropriate force of TA during human walking.Significance.This study revealed the MU behavior during walking at a slow speed and demonstrated the feasibility of noninvasive investigation of MUs during dynamic locomotor tasks, which will open new frontiers for the study of neuromuscular systems in the fields of neuroscience and biomedical engineering.
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Affiliation(s)
- Hikaru Yokoyama
- Institute of Engineering, Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan.,Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan
| | - Naotsugu Kaneko
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan.,Japan Society for the Promotion of Science, Tokyo 102-0083, Japan.,Department of Neuropsychiatry, Keio University School of Medicine, Tokyo 160-8582, Japan
| | - Atsushi Sasaki
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan.,Japan Society for the Promotion of Science, Tokyo 102-0083, Japan.,Graduate School of Engineering Science, Department of Mechanical Science and Bioengineering, Osaka University, Osaka 560-8531, Japan
| | - Akira Saito
- Center for Health and Sports Science, Kyushu Sangyo University, Fukuoka 813-8503, Japan
| | - Kimitaka Nakazawa
- Department of Life Sciences, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan
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14
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Sarto F, Stashuk DW, Franchi MV, Monti E, Zampieri S, Valli G, Sirago G, Candia J, Hartnell LM, Paganini M, McPhee JS, De Vito G, Ferrucci L, Reggiani C, Narici MV. Effects of short-term unloading and active recovery on human motor unit properties, neuromuscular junction transmission and transcriptomic profile. J Physiol 2022; 600:4731-4751. [PMID: 36071599 PMCID: PMC9828768 DOI: 10.1113/jp283381] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Accepted: 08/26/2022] [Indexed: 01/12/2023] Open
Abstract
Electrophysiological alterations of the neuromuscular junction (NMJ) and motor unit potential (MUP) with unloading are poorly studied. We aimed to investigate these aspects and the underlying molecular mechanisms with short-term unloading and active recovery (AR). Eleven healthy males underwent a 10-day unilateral lower limb suspension (ULLS) period, followed by 21-day AR based on resistance exercise. Quadriceps femoris (QF) cross-sectional area (CSA) and isometric maximum voluntary contraction (MVC) were evaluated. Intramuscular electromyographic recordings were obtained during 10% and 25% MVC isometric contractions from the vastus lateralis (VL). Biomarkers of NMJ molecular instability (serum c-terminal agrin fragment, CAF), axonal damage (neurofilament light chain) and denervation status were assessed from blood samples and VL biopsies. NMJ and ion channel transcriptomic profiles were investigated by RNA-sequencing. QF CSA and MVC decreased with ULLS. Increased CAF and altered NMJ transcriptome with unloading suggested the emergence of NMJ molecular instability, which was not associated with impaired NMJ transmission stability. Instead, increased MUP complexity and decreased motor unit firing rates were found after ULLS. Downregulation of ion channel gene expression was found together with increased neurofilament light chain concentration and partial denervation. The AR period restored most of these neuromuscular alterations. In conclusion, the human NMJ is destabilized at the molecular level but shows functional resilience to a 10-day unloading period at least at relatively low contraction intensities. However, MUP properties are altered by ULLS, possibly due to alterations in ion channel dynamics and initial axonal damage and denervation. These changes are fully reversed by 21 days of AR. KEY POINTS: We used integrative electrophysiological and molecular approaches to comprehensively investigate changes in neuromuscular integrity and function after a 10-day unilateral lower limb suspension (ULLS), followed by 21 days of active recovery in young healthy men, with a particular focus on neuromuscular junction (NMJ) and motor unit potential (MUP) properties alterations. After 10-day ULLS, we found significant NMJ molecular alterations in the absence of NMJ transmission stability impairment. These findings suggest that the human NMJ is functionally resilient against insults and stresses induced by short-term disuse at least at relatively low contraction intensities, at which low-threshold, slow-type motor units are recruited. Intramuscular electromyography analysis revealed that unloading caused increased MUP complexity and decreased motor unit firing rates, and these alterations could be related to the observed changes in skeletal muscle ion channel pool and initial and partial signs of fibre denervation and axonal damage. The active recovery period restored these neuromuscular changes.
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Affiliation(s)
- Fabio Sarto
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly
| | - Daniel W. Stashuk
- Department of Systems Design EngineeringUniversity of WaterlooOntarioCanada
| | - Martino V. Franchi
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly,CIR‐MYO Myology CenterUniversity of PadovaPadovaItaly
| | - Elena Monti
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly
| | - Sandra Zampieri
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly,CIR‐MYO Myology CenterUniversity of PadovaPadovaItaly,Department of SurgeryOncology, and GastroenterologyUniversity of PadovaPadovaItaly
| | - Giacomo Valli
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly
| | - Giuseppe Sirago
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly
| | - Julián Candia
- Longitudinal Studies SectionTranslational Gerontology BranchNational Institute of AgingNational Institutes of HealthBaltimoreMDUSA
| | - Lisa M. Hartnell
- Longitudinal Studies SectionTranslational Gerontology BranchNational Institute of AgingNational Institutes of HealthBaltimoreMDUSA
| | - Matteo Paganini
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly
| | - Jamie S. McPhee
- Department of Sport and Exercise SciencesManchester Metropolitan University Institute of SportManchesterUK
| | - Giuseppe De Vito
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly,CIR‐MYO Myology CenterUniversity of PadovaPadovaItaly
| | - Luigi Ferrucci
- Longitudinal Studies SectionTranslational Gerontology BranchNational Institute of AgingNational Institutes of HealthBaltimoreMDUSA
| | - Carlo Reggiani
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly,Science and Research Center KoperInstitute for Kinesiology ResearchKoperSlovenia
| | - Marco V. Narici
- Department of Biomedical SciencesUniversity of PadovaPadovaItaly,CIR‐MYO Myology CenterUniversity of PadovaPadovaItaly,Science and Research Center KoperInstitute for Kinesiology ResearchKoperSlovenia
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15
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Zicher B, Ibáñez J, Farina D. Beta inputs to motor neurons do not directly contribute to volitional force modulation. J Physiol 2022. [PMID: 36222347 DOI: 10.1113/jp283398] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 09/30/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS It has been previously proposed that beta (13-30Hz) common inputs to a motor neuron pool may have a nonlinear effect in voluntary force control. The needed strength of beta oscillations to modulate forces has not been analysed yet. Based on computer simulations, we show that sustained beta inputs to a spinal motoneuron pool at physiologically reported levels have minimal effect on force. Levels of sustained beta rhythmic activity that can cause a significant change in force are not compatible with experimental observations of intramuscular coherence in human skeletal muscles. ABSTRACT Neural oscillatory activity in the beta band (13-30 Hz) is prominent in the brain and it is transmitted partly linearly to the spinal cord and muscles. Multiple views on the functional relevance of beta activity in the motor system have been proposed. Previous simulation work suggested that pools of spinal motoneurons (MNs) receiving a common beta input could demodulate this activity transforming it into low-frequency neural drive that could alter force production in muscles. This may suggest that common beta inputs to muscles have a direct role in force modulation. Here we report the experimental average levels and ranges of common beta activity in spinal MNs projecting to single muscles and use a computational model of a MN pool to test if the experimentally observed beta levels in MNs can influence force. When beta was modelled as a continuous activity, the amplitude needed to produce non-negligible changes in force corresponded to beta representation in the MN pool that was far above the experimental observations. On the other hand, when beta activity was modelled as short-lived events (i.e., bursts of beta activity separated by intervals without beta oscillations), this activity approximated levels that could cause small changes in force with estimated average common beta inputs to the MNs compatible with the experimental observations. Nonetheless, bursting beta is unlikely to be used for force control due to the temporal sparsity of this activity. It is therefore concluded that beta oscillations are unlikely to contribute to the voluntary modulation of force. Abstract figure legend This work studied a potential role of beta oscillatory activity (13-30Hz) on force production. Through simulation of different patterns of beta inputs to a spinal motoneuron pool, we looked at how force production can be affected by this oscillatory activity. The levels of beta, quantified with intramuscular coherence measures, were compared to experimental values. The results suggest that beta oscillatory activity is unlikely to contribute to voluntary force modulation. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Blanka Zicher
- Department of Bioengineering, Imperial College, London, United Kingdom
| | - Jaime Ibáñez
- Department of Bioengineering, Imperial College, London, United Kingdom.,BSICoS, IIS Aragón, Universidad de Zaragoza, Zaragoza, Spain.,Department for Clinical and movement neurosciences, Institute of Neurology, University College London, United Kingdom
| | - Dario Farina
- Department of Bioengineering, Imperial College, London, United Kingdom
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16
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Del Vecchio A, Jones RHA, Schofield IS, Kinfe TM, Ibáñez J, Farina D, Baker SN. Interfacing Motor Units in Nonhuman Primates Identifies a Principal Neural Component for Force Control Constrained by the Size Principle. J Neurosci 2022; 42:7386-7399. [PMID: 35999052 PMCID: PMC9525173 DOI: 10.1523/jneurosci.0649-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 06/10/2022] [Accepted: 07/16/2022] [Indexed: 11/21/2022] Open
Abstract
Motor units convert the last neural code of movement into muscle forces. The classic view of motor unit control is that the CNS sends common synaptic inputs to motoneuron pools and that motoneurons respond in an orderly fashion dictated by the size principle. This view, however, is in contrast with the large number of dimensions observed in motor cortex, which may allow individual and flexible control of motor units. Evidence for flexible control of motor units may be obtained by tracking motor units longitudinally during tasks with some level of behavioral variability. Here we identified and tracked populations of motor units in the brachioradialis muscle of two macaque monkeys during 10 sessions spanning >1 month with a broad range of rate of force development (1.8-38.6 N · m · s-1). We found a very stable recruitment order and discharge characteristics of the motor units over sessions and contraction trials. The small deviations from orderly recruitment were fully predicted by the motor unit recruitment intervals, so that small shifts in recruitment thresholds happened only during contractions at a high rate of force development. Moreover, we also found that one component explained more than ∼50% of the motor unit discharge rate variance, and that the remaining components represented a time-shifted version of the first. In conclusion, our results show that the recruitment of motoneurons is determined by the interplay of the size principle and common input and that this recruitment scheme is not violated over time or by the speed of the contractions.SIGNIFICANCE STATEMENT With a new noninvasive high-density electromyographic framework, we show the activity of motor unit ensembles in macaques during voluntary contractions. The discharge characteristics of brachioradialis motor units revealed a relatively fixed recruitment order and discharge characteristics across days and rate of force developments. These results were further confirmed through invasive axonal stimulation and recordings of intramuscular electromyographic activity from 16 arm muscles. The study shows for the first time the feasibility of longitudinal noninvasive motor unit interfacing and tracking of the same motor units in nonhuman primates.
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Affiliation(s)
- Alessandro Del Vecchio
- Department Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University (FAU), 91058 Erlangen, Germany
| | - Rachael H A Jones
- Medical Faculty, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Ian S Schofield
- Medical Faculty, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Thomas M Kinfe
- Division of Functional Neurosurgery and Stereotaxy, Friedrich-Alexander University (FAU), 91054 Erlangen, Germany
| | - Jaime Ibáñez
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
- UCL Queen Square Institute of Neurology, University College London, London WC1E 6BT, United Kingdom
- BSICoS Group, Instituto de Investigación Sanitaria Aragón (IIS Aragón), 50009 Zaragoza, Spain
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Stuart N Baker
- Medical Faculty, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
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17
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Bräcklein M, Barsakcioglu DY, Del Vecchio A, Ibáñez J, Farina D. Reading and Modulating Cortical β Bursts from Motor Unit Spiking Activity. J Neurosci 2022; 42:3611-3621. [PMID: 35351832 PMCID: PMC9053843 DOI: 10.1523/jneurosci.1885-21.2022] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 02/01/2022] [Accepted: 02/27/2022] [Indexed: 11/21/2022] Open
Abstract
β Oscillations (13-30 Hz) are ubiquitous in the human motor nervous system. Yet, their origins and roles are unknown. Traditionally, β activity has been treated as a stationary signal. However, recent studies observed that cortical β occurs in "bursting events," which are transmitted to muscles. This short-lived nature of β events makes it possible to study the main mechanism of β activity found in the muscles in relation to cortical β. Here, we assessed whether muscle β activity mainly results from cortical projections. We ran two experiments in healthy humans of both sexes (N = 15 and N = 13, respectively) to characterize β activity at the cortical and motor unit (MU) levels during isometric contractions of the tibialis anterior muscle. We found that β rhythms observed at the cortical and MU levels are indeed in bursts. These bursts appeared to be time-locked and had comparable average durations (40-80 ms) and rates (approximately three to four bursts per second). To further confirm that cortical and MU β have the same source, we used a novel operant conditioning framework to allow subjects to volitionally modulate MU β. We showed that volitional modulation of β activity at the MU level was possible with minimal subject learning and was paralleled by similar changes in cortical β activity. These results support the hypothesis that MU β mainly results from cortical projections. Moreover, they demonstrate the possibility to decode cortical β activity from MU recordings, with a potential translation to future neural interfaces that use peripheral information to identify and modulate activity in the central nervous system.SIGNIFICANCE STATEMENT We show for the first time that β activity in motor unit (MU) populations occurs in bursting events. These bursts observed in the output of the spinal cord appear to be time-locked and share similar characteristics of β activity at the cortical level, such as the duration and rate at which they occur. Moreover, when subjects were exposed to a novel operant conditioning paradigm and modulated MU β activity, cortical β activity changed in a similar way as peripheral β. These results provide evidence for a strong correspondence between cortical and peripheral β activity, demonstrating the cortical origin of peripheral β and opening the pathway for a new generation of neural interfaces.
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Affiliation(s)
- Mario Bräcklein
- Neuromechanics and Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London W12 0BZ, United Kingdom
| | - Deren Y Barsakcioglu
- Neuromechanics and Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London W12 0BZ, United Kingdom
| | - Alessandro Del Vecchio
- Department Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen 91052, Germany
| | - Jaime Ibáñez
- Neuromechanics and Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London W12 0BZ, United Kingdom
- Biomedical Signal Interpretation and Computational Simulation (BSICoS), Instituto de Investigación Sanitaria Aragón, Universidad de Zaragoza, Zaragoza 50018, Spain
- Department of Clinical and Movement Disorders, Institute of Neurology, University College London, London WC1N 3BG, United Kingdom
| | - Dario Farina
- Neuromechanics and Rehabilitation Technology Group, Department of Bioengineering, Faculty of Engineering, Imperial College London, London W12 0BZ, United Kingdom
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18
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Rossato J, Tucker KJ, Avrillon S, Lacourpaille L, Holobar A, Hug F. Less common synaptic input between muscles from the same group allows for more flexible coordination strategies during a fatiguing task. J Neurophysiol 2022; 127:421-433. [PMID: 35020505 DOI: 10.1152/jn.00453.2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study aimed to determine whether neural drive is redistributed between muscles during a fatiguing isometric contraction, and if so, whether the initial level of common synaptic input between these muscles constrains this redistribution. We studied two muscle groups: triceps surae (14 participants) and quadriceps (15 participants). Participants performed a series of submaximal isometric contractions and a torque-matched contraction maintained until task failure. We used high-density surface electromyography to identify the behavior of 1874 motor units from the soleus, gastrocnemius medialis (GM), gastrocnemius lateralis(GL), rectus femoris, vastus lateralis (VL), and vastus medialis(VM). We assessed the level of common drive between muscles in absence of fatigue using a coherence analysis. We also assessed the redistribution of neural drive between muscles during the fatiguing contraction through the correlation between their cumulative spike trains (index of neural drive). The level of common drive between VL and VM was significantly higher than that observed for the other muscle pairs, including GL-GM. The level of common drive increased during the fatiguing contraction, but the differences between muscle pairs persisted. We also observed a strong positive correlation of neural drive between VL and VM during the fatiguing contraction (r=0.82). This was not observed for the other muscle pairs, including GL-GM, which exhibited differential changes in neural drive. These results suggest that less common synaptic input between muscles allows for more flexible coordination strategies during a fatiguing task, i.e., differential changes in neural drive across muscles. The role of this flexibility on performance remains to be elucidated.
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Affiliation(s)
- Julien Rossato
- Nantes Université, Laboratory "Movement, Interactions, Performance" (EA 4334), Nantes, France
| | - Kylie J Tucker
- The University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia
| | - Simon Avrillon
- Legs + Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, IL, United States.,Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, United States
| | - Lilian Lacourpaille
- Nantes Université, Laboratory "Movement, Interactions, Performance" (EA 4334), Nantes, France
| | - Ales Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Slovenia
| | - François Hug
- Nantes Université, Laboratory "Movement, Interactions, Performance" (EA 4334), Nantes, France.,Institut Universitaire de France (IUF), Paris, France.,Université Côte d'Azur, LAMHESS, Nice, France
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19
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Formento E, Botros P, Carmena JM. Skilled independent control of individual motor units via a non-invasive neuromuscular-machine interface. J Neural Eng 2021; 18. [PMID: 34727532 DOI: 10.1088/1741-2552/ac35ac] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Accepted: 11/02/2021] [Indexed: 11/11/2022]
Abstract
Objective.Brain-machine interfaces (BMIs) have the potential to augment human functions and restore independence in people with disabilities, yet a compromise between non-invasiveness and performance limits their relevance.Approach.Here, we hypothesized that a non-invasive neuromuscular-machine interface providing real-time neurofeedback of individual motor units within a muscle could enable independent motor unit control to an extent suitable for high-performance BMI applications.Main results.Over 6 days of training, eight participants progressively learned to skillfully and independently control three biceps brachii motor units to complete a 2D center-out task. We show that neurofeedback enabled motor unit activity that largely violated recruitment constraints observed during ramp-and-hold isometric contractions thought to limit individual motor unit controllability. Finally, participants demonstrated the suitability of individual motor units for powering general applications through a spelling task.Significance.These results illustrate the flexibility of the sensorimotor system and highlight individual motor units as a promising source of control for BMI applications.
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Affiliation(s)
- Emanuele Formento
- Department of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, CA 94720, United States of America
| | - Paul Botros
- Department of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, CA 94720, United States of America
| | - Jose M Carmena
- Department of Electrical Engineering and Computer Sciences, University of California Berkeley, Berkeley, CA 94720, United States of America.,Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA 94720, United States of America
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20
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Rungta S, Basu D, Sendhilnathan N, Murthy A. Preparatory activity links the frontal eye field response with small amplitude motor unit recruitment of neck muscles during gaze planning. J Neurophysiol 2021; 126:451-463. [PMID: 34232741 DOI: 10.1152/jn.00141.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A hallmark of intelligent behavior is that we can separate intention from action. To understand the mechanism that gates the flow of information between motor planning and execution, we compared the activity of frontal eye field neurons with motor unit activity from neck muscles in the presence of an intervening delay period in which spatial information regarding the target was available to plan a response. Although spatially specific delay period activity was present in the activity of frontal eye field neurons, it was absent in motor unit activity. Nonetheless, motor unit activity was correlated with the time it took to initiate saccades. Interestingly, we observed a heterogeneity of responses among motor units, such that only units with smaller amplitudes showed a clear modulation during the delay period. These small amplitude motor units also had higher spontaneous activity compared with the units which showed modulation only during the movement epoch. Taken together, our results suggest the activity of smaller motor units convey temporal information and explains how the delay period primes muscle activity leading to faster reaction times.NEW & NOTEWORTHY This study shows that the temporal aspects of a motor plan in the oculomotor circuitry can be accessed by peripheral neck muscles hundreds of milliseconds before the instruction to initiate a saccadic eye movement. The coupling between central and peripheral processes during the delay time is mediated by the recruitment pattern of motor units with smaller amplitude. These findings suggest that information processed in cortical areas could be read from periphery before execution.
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Affiliation(s)
- Satya Rungta
- IISc Mathematics Initiative, Indian Institute of Science, Bengaluru, India.,Centre for Neuroscience, Indian Institute of Science, Bengaluru, India
| | - Debaleena Basu
- Centre for Neuroscience, Indian Institute of Science, Bengaluru, India
| | | | - Aditya Murthy
- Centre for Neuroscience, Indian Institute of Science, Bengaluru, India
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21
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Affiliation(s)
- Marin Manuel
- SPPIN - Saints-Pères Paris Institute for the Neurosciences, Université de Paris, CNRS, Paris, F-75006, France
| | - Daniel Zytnicki
- SPPIN - Saints-Pères Paris Institute for the Neurosciences, Université de Paris, CNRS, Paris, F-75006, France
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22
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Ibáñez J, Del Vecchio A, Rothwell JC, Baker SN, Farina D. Only the Fastest Corticospinal Fibers Contribute to β Corticomuscular Coherence. J Neurosci 2021; 41:4867-4879. [PMID: 33893222 PMCID: PMC8260170 DOI: 10.1523/jneurosci.2908-20.2021] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/04/2021] [Accepted: 03/15/2021] [Indexed: 01/09/2023] Open
Abstract
Human corticospinal transmission is commonly studied using brain stimulation. However, this approach is biased to activity in the fastest conducting axons. It is unclear whether conclusions obtained in this context are representative of volitional activity in mild-to-moderate contractions. An alternative to overcome this limitation may be to study the corticospinal transmission of endogenously generated brain activity. Here, we investigate in humans (N = 19; of either sex), the transmission speeds of cortical β rhythms (∼20 Hz) traveling to arm (first dorsal interosseous) and leg (tibialis anterior; TA) muscles during tonic mild contractions. For this purpose, we propose two improvements for the estimation of corticomuscular β transmission delays. First, we show that the cumulant density (cross-covariance) is more accurate than the commonly-used directed coherence to estimate transmission delays in bidirectional systems transmitting band-limited signals. Second, we show that when spiking motor unit activity is used instead of interference electromyography, corticomuscular transmission delay estimates are unaffected by the shapes of the motor unit action potentials (MUAPs). Applying these improvements, we show that descending corticomuscular β transmission is only 1-2 ms slower than expected from the fastest corticospinal pathways. In the last part of our work, we show results from simulations using estimated distributions of the conduction velocities for descending axons projecting to lower motoneurons (from macaque histologic measurements) to suggest two scenarios that can explain fast corticomuscular transmission: either only the fastest corticospinal axons selectively transmit β activity, or else the entire pool does. The implications of these two scenarios for our understanding of corticomuscular interactions are discussed.SIGNIFICANCE STATEMENT We present and validate an improved methodology to measure the delay in the transmission of cortical β activity to tonically-active muscles. The estimated corticomuscular β transmission delays obtained with this approach are remarkably similar to those expected from transmission in the fastest corticospinal axons. A simulation of β transmission along a pool of corticospinal axons using an estimated distribution of fiber diameters suggests two possible mechanisms by which fast corticomuscular transmission is achieved: either a very small fraction of the fastest descending axons transmits β activity to the muscles or, alternatively, the entire population does and natural cancellation of slow channels occurs because of the distribution of axon diameters in the corticospinal tract.
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Affiliation(s)
- J Ibáñez
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
- Department of Clinical and Movement Disorders, Institute of Neurology, University College London, London WC1N 3BG, United Kingdom
| | - A Del Vecchio
- Department Artificial Intelligence in Biomedical Engineering, Friedrich-Alexander University, Erlangen-Nürnberg, Erlangen 91052, Germany
| | - J C Rothwell
- Department of Clinical and Movement Disorders, Institute of Neurology, University College London, London WC1N 3BG, United Kingdom
| | - S N Baker
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - D Farina
- Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom
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Wen Y, Avrillon S, Hernandez-Pavon JC, Kim SJ, Hug F, Pons JL. A convolutional neural network to identify motor units from high-density surface electromyography signals in real time. J Neural Eng 2021; 18. [PMID: 33721852 DOI: 10.1088/1741-2552/abeead] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 03/15/2021] [Indexed: 11/11/2022]
Abstract
OBJECTIVES This paper aims to investigate the feasibility and the validity of applying deep convolutional neural networks (CNN) to identify motor unit (MU) spike trains and estimate the neural drive to muscles from high-density electromyography (HD-EMG) signals in real time. Two distinct deep CNNs are compared with the convolution kernel compensation (CKC) algorithm using simulated and experimentally recorded signals. The effects of window size and step size of the input HD-EMG signals are also investigated. APPROACH The MU spike trains were first identified with the CKC algorithm. The HD-EMG signals and spike trains were used to train the deep CNN. Then, the deep CNN decomposed the HD-EMG signals into MU discharge times in real time. Two CNN approaches are compared with the CKC: 1) multiple single-output deep CNN (SO-DCNN) with one MU decomposed per network, and 2) one multiple-output deep CNN (MO-DCNN) to decompose all MUs (up to 23) with one network. MAIN RESULTS The MO-DCNN outperformed the SO-DCNN in terms of training time (3.2 to 21.4 s/epoch vs. 6.5 to 47.8 s/epoch, respectively) and prediction time (0.04 vs. 0.27 s/sample, respectively). The optimal window size and step size for MO-DCNN were 120 and 20 data points, respectively. It results in sensitivity of 98% and 85% with simulated and experimentally recorded HD-EMG signals, respectively. There is a high cross-correlation coefficient between the neural drive estimated with CKC and that estimated with MO-DCNN (range of r-value across conditions: 0.88-0.95). SIGNIFICANCE We demonstrate the feasibility and the validity of using deep CNN to accurately identify MU activity from HD-EMG with a latency lower than 80 ms, which falls within the lower bound of the human electromechanical delay. This method opens many opportunities for using the neural drive to interface humans with assistive devices.
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Affiliation(s)
- Yue Wen
- Legs and Walking Lab, Shirley Ryan AbilityLab, 355 East Erie Street, Chicago, Illinois, 60611-2654, UNITED STATES
| | - Simon Avrillon
- Shirley Ryan AbilityLab, 355 E Erie St, Chicago, Illinois, 60601, UNITED STATES
| | - Julio Cesar Hernandez-Pavon
- Department of Physical Medicine and Rehabilitation, Northwestern University Feinberg School of Medicine, 251 E Huron St, Chicago, Illinois, 60611, UNITED STATES
| | - Sangjoon Jonathan Kim
- Shirley Ryan AbilityLab, 355 E Erie St, Chicago, Illinois, 60611-2654, UNITED STATES
| | - Francois Hug
- Laboratoire 'Motricite, Interactions, Performance', Universite de Nantes, JE 2438 UFRSTAPS,, 25 bis Guy Mollet BP 72206, Nantes, F-44000 France, Nantes, 72206, FRANCE
| | - Jose Luis Pons
- Bioengineering Group, Spanish Research Council, Serrano 117, Arganda del Rey (Madrid), 28006, SPAIN
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24
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Habeych ME, Trinh T, Issar T, Kwai NCG, Krishnan AV. Motor unit number estimation of facial muscles using the M Scan-Fit method. Muscle Nerve 2020; 62:555-558. [PMID: 32564387 DOI: 10.1002/mus.27010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 06/16/2020] [Accepted: 06/17/2020] [Indexed: 11/06/2022]
Abstract
INTRODUCTION M Scan-Fit, an automated method for motor unit number estimation (MUNE), was assessed in muscles innervated by the facial nerve. METHODS Healthy volunteers were recruited. M Scans were recorded twice from nasalis and depressor anguli oris (DAO) muscles, and then fitted to a probabilistic model. RESULTS Twenty-one subjects were evaluated; 38% were females and 62% were males, with a mean age of 34.71 years. The average number of MUs was 38.57 on both testing occasions (t ≤ 0.0001; P = 1.0) for the nasalis. For the DAO, results were 20.62 MUs for the first and 23.48 for the second (t = -2.12; P = .04). Pearson's interrater correlation coefficients were 0.96 (P < .0001) for nasalis and 0.87 (P ≤ .01) for DAO. Intraclass correlation coefficients were 0.88 (P ≤ .01) for nasalis and 0.39 (P = .37) for DAO. DISCUSSION M Scan-Fit MUNE is an automated, accurate, reliable method of estimating MU number and size from facial muscles.
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Affiliation(s)
- Miguel E Habeych
- Prince of Wales Clinical School, University of New South Wales, Sydney, New South Wales, Australia
| | - Terry Trinh
- Prince of Wales Clinical School, University of New South Wales, Sydney, New South Wales, Australia
| | - Tushar Issar
- Prince of Wales Clinical School, University of New South Wales, Sydney, New South Wales, Australia
| | - Natalie C G Kwai
- School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Arun V Krishnan
- Prince of Wales Clinical School, University of New South Wales, Sydney, New South Wales, Australia
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25
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O'Halloran KD, Smith BK. Diaphragm remodelling following cervical spinal cord injury: Can intrinsic neural plasticity be harnessed to improve respiratory motor function? J Physiol 2020; 598:2049-2050. [PMID: 32266973 DOI: 10.1113/jp279707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Accepted: 03/30/2020] [Indexed: 11/08/2022] Open
Affiliation(s)
- Ken D O'Halloran
- Department of Physiology, School of Medicine, College of Medicine & Health, University College Cork, Cork, Ireland
| | - Barbara K Smith
- Departments of Physical Therapy and Pediatrics, University of Florida, Gainesville, FL, 32610-0154, USA
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26
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Geijo-Barrientos E, Pastore-Olmedo C, De Mingo P, Blanquer M, Gómez Espuch J, Iniesta F, Iniesta NG, García-Hernández A, Martín-Estefanía C, Barrios L, Moraleda JM, Martínez S. Intramuscular Injection of Bone Marrow Stem Cells in Amyotrophic Lateral Sclerosis Patients: A Randomized Clinical Trial. Front Neurosci 2020; 14:195. [PMID: 32265627 PMCID: PMC7105864 DOI: 10.3389/fnins.2020.00195] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 02/24/2020] [Indexed: 12/11/2022] Open
Abstract
Background Preclinical studies suggest that stem cells may be a valuable therapeutic tool in amyotrophic lateral sclerosis (ALS). As it has been demonstrated that there are molecular changes at the end-plate during the early stages of motorneuron degeneration in animal models, we hypothesize that the local effect of this stem cell delivery method could slow the progressive loss of motor units (MUs) in ALS patients. Methods We designed a Phase I/II clinical trial to study the safety of intramuscularly implanting autologous bone marrow mononuclear cells (BMMCs), including stem cells, in ALS patients and their possible effects on the MU of the tibialis anterior (TA) muscle. Twenty-two patients participated in a randomized, double-blind, placebo-controlled trial that consisted of a baseline visit followed by one intramuscular injection of BMNCs, follow-up visits at 30, 90, 180, and 360 days, and an additional year of clinical follow-up. In each patient, one TA muscle was injected with a single dose of BMMCs while the contralateral muscle was given a placebo; the sides were selected randomly. All visits included a complete EMG study of both TA muscles. Results Our results show that (1) the intramuscular injection of BMMCs is a safe procedure; (2) ALS patients show heterogeneities in the degree of TA injury; (3) a comparison of placebo-injected muscles with BMMC-injected muscles showed significant differences in only one parameter, the D50 index used to quantify the Compound Muscle Action Potential (CMAP) scan curve. This parameter was higher in the BMMC-injected TA muscle at both 90 days (placebo side: 29.55 ± 2.89, n = 20; experimental side: 39.25 ± 3.21, n = 20; p < 0.01) and 180 days (placebo side: 29.35 ± 3.29, n = 17; experimental side: 41.24 ± 3.34, n = 17; p < 0.01). Conclusion This procedure had no effect on the TA muscle MU properties, with the exception of the D50 index. Finding differences in just this index supports the fact that it may be much more sensitive than other electrophysiological parameters when studying treatment effects. Given the low number of patients and their heterogeneity, these results justify exploring the efficacy of this procedure in further patients and other muscles, through Phase II trials. Clinical Trial Registration www.clinicaltrials.gov (identifier NCT02286011); EudraCT number 2011-004801-25.
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Affiliation(s)
| | - Carlos Pastore-Olmedo
- Institute of Neurosciences, Universidad Miguel Hernández-CSIC, Alicante, Spain.,Clinical Neurophysiology Service, San Juan University Hospital, Alicante, Spain
| | - Pedro De Mingo
- Service of Clinical Neurophysiology, Virgen de la Arrixaca University Clinical Hospital, Murcia, Spain
| | - Miguel Blanquer
- Hematopoietic Stem Cell Transplant and Cell Therapy Unit, Hematology Service, Virgen de la Arrixaca University Hospital, University of Murcia, Murcia, Spain.,Institute for Bio-Health Research of Murcia (IMIB-Arrixaca), Murcia, Spain
| | - Joaquín Gómez Espuch
- Hematopoietic Stem Cell Transplant and Cell Therapy Unit, Hematology Service, Virgen de la Arrixaca University Hospital, University of Murcia, Murcia, Spain
| | - Francisca Iniesta
- Hematopoietic Stem Cell Transplant and Cell Therapy Unit, Hematology Service, Virgen de la Arrixaca University Hospital, University of Murcia, Murcia, Spain.,Institute for Bio-Health Research of Murcia (IMIB-Arrixaca), Murcia, Spain
| | - Natalia García Iniesta
- Hematopoietic Stem Cell Transplant and Cell Therapy Unit, Hematology Service, Virgen de la Arrixaca University Hospital, University of Murcia, Murcia, Spain.,Institute for Bio-Health Research of Murcia (IMIB-Arrixaca), Murcia, Spain
| | - Ana García-Hernández
- Hematopoietic Stem Cell Transplant and Cell Therapy Unit, Hematology Service, Virgen de la Arrixaca University Hospital, University of Murcia, Murcia, Spain.,Institute for Bio-Health Research of Murcia (IMIB-Arrixaca), Murcia, Spain
| | | | - Laura Barrios
- Department of Applied Statistics, SGAI-CSIC, Madrid, Spain
| | - José M Moraleda
- Hematopoietic Stem Cell Transplant and Cell Therapy Unit, Hematology Service, Virgen de la Arrixaca University Hospital, University of Murcia, Murcia, Spain.,Institute for Bio-Health Research of Murcia (IMIB-Arrixaca), Murcia, Spain
| | - Salvador Martínez
- Institute of Neurosciences, Universidad Miguel Hernández-CSIC, Alicante, Spain.,Institute for Bio-Health Research of Murcia (IMIB-Arrixaca), Murcia, Spain
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27
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Wernbom M, Aagaard P. Muscle fibre activation and fatigue with low-load blood flow restricted resistance exercise-An integrative physiology review. Acta Physiol (Oxf) 2020; 228:e13302. [PMID: 31108025 DOI: 10.1111/apha.13302] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 05/12/2019] [Accepted: 05/17/2019] [Indexed: 12/13/2022]
Abstract
Blood flow-restricted resistance exercise (BFRRE) has been shown to induce increases in muscle size and strength, and continues to generate interest from both clinical and basic research points of view. The low loads employed, typically 20%-50% of the one repetition maximum, make BFRRE an attractive training modality for individuals who may not tolerate high musculoskeletal forces (eg, selected clinical patient groups such as frail old adults and patients recovering from sports injury) and/or for highly trained athletes who have reached a plateau in muscle mass and strength. It has been proposed that achieving a high degree of muscle fibre recruitment is important for inducing muscle hypertrophy with BFRRE, and the available evidence suggest that fatiguing low-load exercise during ischemic conditions can recruit both slow (type I) and fast (type II) muscle fibres. Nevertheless, closer scrutiny reveals that type II fibre activation in BFRRE has to date largely been inferred using indirect methods such as electromyography and magnetic resonance spectroscopy, while only rarely addressed using more direct methods such as measurements of glycogen stores and phosphocreatine levels in muscle fibres. Hence, considerable uncertainity exists about the specific pattern of muscle fibre activation during BFRRE. Therefore, the purpose of this narrative review was (1) to summarize the evidence on muscle fibre recruitment during BFRRE as revealed by various methods employed for determining muscle fibre usage during exercise, and (2) to discuss reported findings in light of the specific advantages and limitations associated with these methods.
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Affiliation(s)
- Mathias Wernbom
- Center for Health and Performance, Department of Food and Nutrition and Sport Science University of Gothenburg Gothenburg Sweden
- Department of Health and Rehabilitation, Institute of Neuroscience and Physiology, Sahlgrenska Academy University of Gothenburg Gothenburg Sweden
| | - Per Aagaard
- Department of Sports Sciences and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC) University of Southern Denmark Odense M Denmark
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28
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Puttaraksa G, Muceli S, Gallego JÁ, Holobar A, Charles SK, Pons JL, Farina D. Voluntary and tremorogenic inputs to motor neuron pools of agonist/antagonist muscles in essential tremor patients. J Neurophysiol 2019; 122:2043-2053. [PMID: 31509467 PMCID: PMC6998026 DOI: 10.1152/jn.00407.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pathological tremor is an oscillation of body parts at 3–10 Hz, determined by the output of spinal motor neurons (MNs), which receive synaptic inputs from supraspinal centers and muscle afferents. The behavior of spinal MNs during tremor is not well understood, especially in relation to the activation of the multiple muscles involved. Recent studies on patients with essential tremor have shown that antagonist MN pools receive shared input at the tremor frequency. In this study, we investigated the synaptic inputs related to tremor and voluntary movement, and their coordination across antagonist muscles. We analyzed the spike trains of motor units (MUs) identified from high-density surface electromyography from the forearm extensor and flexor muscles in 15 patients with essential tremor during postural tremor. The shared synaptic input was quantified by coherence and phase difference analysis of the spike trains. All pairs of spike trains in each muscle showed coherence peaks at the voluntary drive frequency (1–3 Hz, 0.2 ± 0.2, mean ± SD) and tremor frequency (3–10 Hz, 0.6 ± 0.3) and were synchronized with small phase differences (3.3 ± 25.2° and 3.9 ± 22.0° for the voluntary drive and tremor frequencies, respectively). The coherence between MN spike trains of antagonist muscle groups at the tremor frequency was significantly smaller than intramuscular coherence. We predominantly observed in-phase activation of MUs between agonist/antagonist muscles at the voluntary frequency band (0.6 ± 48.8°) and out-of-phase activation at the tremor frequency band (126.9 ± 75.6°). Thus MNs innervating agonist/antagonist muscles concurrently receive synaptic inputs with different phase shifts in the voluntary and tremor frequency bands. NEW & NOTEWORTHY Although the mechanical characteristics of tremor have been widely studied, the activation of the affected muscles is still poorly understood. We analyzed the behavior of motor units of pairs of antagonistic wrist muscle groups in patients with essential tremor and studied their activity at voluntary movement- and tremor-related frequencies. We found that the phase relation between inputs to antagonistic muscles is different at the voluntary and tremor frequency bands.
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Affiliation(s)
| | - Silvia Muceli
- Department of Bioengineering, Imperial College London, London, United Kingdom.,Division of Signal Processing and Biomedical Engineering, Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden
| | - Juan Álvaro Gallego
- Neural and Cognitive Engineering Group, Centre for Automation and Robotics, Spanish National Research Council, Arganda del Rey, Spain
| | - Ales Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Steven K Charles
- Department of Mechanical Engineering and Neuroscience Center, Brigham Young University, Provo, Utah
| | - Jose L Pons
- Legs & Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, Illinois.,Department of Physical Medicine & Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Department of Biomedical Engineering and Department of Mechanical Engineering, McCormick School of Engineering, Northwestern University, Chicago, Illinois.,Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council, Madrid, Spain
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London, United Kingdom
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29
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Fogarty MJ. Strong links in a weak chain: skeletal muscle fibres in amyotrophic lateral sclerosis. J Physiol 2019; 597:3799-3800. [PMID: 31206712 DOI: 10.1113/jp278331] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Matthew J Fogarty
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN, 55905, USA
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30
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Bello-Rojas S, Istrate AE, Kishore S, McLean DL. Central and peripheral innervation patterns of defined axial motor units in larval zebrafish. J Comp Neurol 2019; 527:2557-2572. [PMID: 30919953 DOI: 10.1002/cne.24689] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 03/20/2019] [Accepted: 03/25/2019] [Indexed: 02/06/2023]
Abstract
Spinal motor neurons and the peripheral muscle fibers they innervate form discrete motor units that execute movements of varying force and speed. Subsets of spinal motor neurons also exhibit axon collaterals that influence motor output centrally. Here, we have used in vivo imaging to anatomically characterize the central and peripheral innervation patterns of axial motor units in larval zebrafish. Using early born "primary" motor neurons and their division of epaxial and hypaxial muscle into four distinct quadrants as a reference, we define three distinct types of later born "secondary" motor units. The largest is "m-type" units, which innervate deeper fast-twitch muscle fibers via medial nerves. Next in size are "ms-type" secondaries, which innervate superficial fast-twitch and slow fibers via medial and septal nerves, followed by "s-type" units, which exclusively innervate superficial slow muscle fibers via septal nerves. All types of secondaries innervate up to four axial quadrants. Central axon collaterals are found in subsets of primaries based on soma position and predominantly in secondary fast-twitch units (m, ms) with increasing likelihood based on number of quadrants innervated. Collaterals are labeled by synaptophysin-tagged fluorescent proteins, but not PSD95, consistent with their output function. Also, PSD95 dendrite labeling reveals that larger motor units receive more excitatory synaptic input. Collaterals are largely restricted to the neuropil, however, perisomatic connections are observed between motor units. These observations suggest that recurrent interactions are dominated by motor neurons recruited during stronger movements and set the stage for functional investigations of recurrent motor circuitry in larval zebrafish.
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Affiliation(s)
- Saul Bello-Rojas
- Interdepartmental Neuroscience Postbaccalaureate Research Education Program, Northwestern University, Evanston, Illinois
| | - Ana E Istrate
- Masters Program in Neurobiology, Northwestern University, Evanston, Illinois
| | - Sandeep Kishore
- Department of Neurobiology, Northwestern University, Evanston, Illinois
| | - David L McLean
- Interdepartmental Neuroscience Postbaccalaureate Research Education Program, Northwestern University, Evanston, Illinois.,Masters Program in Neurobiology, Northwestern University, Evanston, Illinois.,Department of Neurobiology, Northwestern University, Evanston, Illinois
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31
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Lai AKM, Biewener AA, Wakeling JM. Metabolic cost underlies task-dependent variations in motor unit recruitment. J R Soc Interface 2018; 15:rsif.2018.0541. [PMID: 30464057 DOI: 10.1098/rsif.2018.0541] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 10/23/2018] [Indexed: 11/12/2022] Open
Abstract
Mammalian skeletal muscles are comprised of many motor units, each containing a group of muscle fibres that have common contractile properties: these can be broadly categorized as slow and fast twitch muscle fibres. Motor units are typically recruited in an orderly fashion following the 'size principle', in which slower motor units would be recruited for low intensity contraction; a metabolically cheap and fatigue-resistant strategy. However, this recruitment strategy poses a mechanical paradox for fast, low intensity contractions, in which the recruitment of slower fibres, as predicted by the size principle, would be metabolically more costly than the recruitment of faster fibres that are more efficient at higher contraction speeds. Hence, it would be mechanically and metabolically more effective for recruitment strategies to vary in response to contraction speed so that the intrinsic efficiencies and contraction speeds of the recruited muscle fibres are matched to the mechanical demands of the task. In this study, we evaluated the effectiveness of a novel, mixed cost function within a musculoskeletal simulation, which includes the metabolic cost of contraction, to predict the recruitment of different muscle fibre types across a range of loads and speeds. Our results show that a metabolically informed cost function predicts favoured recruitment of slower muscle fibres for slower and isometric tasks versus recruitment that favours faster muscles fibres for higher velocity contractions. This cost function predicts a change in recruitment patterns consistent with experimental observations, and also predicts a less expensive metabolic cost for these muscle contractions regardless of speed of the movement. Hence, our findings support the premise that varying motor recruitment strategies to match the mechanical demands of a movement task results in a mechanically and metabolically sensible way to deploy the different types of motor unit.
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Affiliation(s)
- Adrian K M Lai
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | | | - James M Wakeling
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
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32
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Mani D, Almuklass AM, Hamilton LD, Vieira TM, Botter A, Enoka RM. Motor unit activity, force steadiness, and perceived fatigability are correlated with mobility in older adults. J Neurophysiol 2018; 120:1988-1997. [PMID: 30044670 DOI: 10.1152/jn.00192.2018] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The purpose of our study was to examine the associations between the performance of older adults on four tests of mobility and the physical capabilities of the lower leg muscles. The assessments included measures of muscle strength, muscle activation, and perceived fatigability. Muscle activation was quantified as the force fluctuations-a measure of force steadiness-and motor unit discharge characteristics of lower leg muscles during submaximal isometric contractions. Perceived fatigability was measured as the rating of perceived exertion achieved during a test of walking endurance. Twenty participants (73 ± 4 yr) completed one to four evaluation sessions that were separated by at least 3 wk. The protocol included a 400-m walk, a 10-m walk at maximal and preferred speeds, a chair-rise test, and the strength, force steadiness, and discharge characteristics of motor units detected by high-density electromyography of lower leg muscles. Multiple-regression analyses yielded statistically significant models that explained modest amounts of the variance in the four mobility tests. The variance explained by the regression models was 39% for 400-m walk time, 33% for maximal walk time, 42% for preferred walk time, and 27% for chair-rise time. The findings indicate that differences in mobility among healthy older adults were partially associated with the level of perceived fatigability (willingness of individuals to exert themselves) achieved during the test of walking endurance and the discharge characteristics of soleus, medial gastrocnemius, and tibialis anterior motor units during steady submaximal contractions with the plantar flexor and dorsiflexor muscles. NEW & NOTEWORTHY Differences among healthy older adults in walking endurance, walking speed, and ability to rise from a chair can be partially explained by the performance capabilities of lower leg muscles. Assessments comprised the willingness to exert effort (perceived fatigability) and the discharge times of action potentials by motor units in calf muscles during submaximal isometric contractions. These findings indicate that the nervous system contributes significantly to differences in mobility among healthy older adults.
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Affiliation(s)
- Diba Mani
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Awad M Almuklass
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado.,College of Medicine, King Saud bin Abdulaziz University for Health Sciences , Riyadh , Saudi Arabia
| | - Landon D Hamilton
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Taian M Vieira
- LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Turin , Italy
| | - Alberto Botter
- LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Turin , Italy
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
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Abstract
The control of motor unit firing behavior during fatigue is still debated in the literature. Most studies agree that the central nervous system increases the excitation to the motoneuron pool to compensate for decreased force contributions of individual motor units and sustain muscle force output during fatigue. However, some studies claim that motor units may decrease their firing rates despite increased excitation, contradicting the direct relationship between firing rates and excitation that governs the voluntary control of motor units. To investigate whether the control of motor units in fact changes with fatigue, we measured motor unit firing behavior during repeated contractions of the first dorsal interosseous (FDI) muscle while concurrently monitoring the activation of surrounding muscles, including the flexor carpi radialis, extensor carpi radialis, and pronator teres. Across all subjects, we observed an overall increase in FDI activation and motor unit firing rates by the end of the fatigue task. However, in some subjects we observed increases in FDI activation and motor unit firing rates only during the initial phase of the fatigue task, followed by subsequent decreases during the late phase of the fatigue task while the coactivation of surrounding muscles increased. These findings indicate that the strategy for sustaining force output may occasionally change, leading to increases in the relative activation of surrounding muscles while the excitation to the fatiguing muscle decreases. Importantly, irrespective of changes in the strategy for sustaining force output, the control properties regulating motor unit firing behavior remain unchanged during fatigue. NEW & NOTEWORTHY This work addresses sources of debate surrounding the manner in which motor unit firing behavior is controlled during fatigue. We found that decreases in the motor unit firing rates of the fatiguing muscle may occasionally be observed when the contribution of coactive muscles increases. Despite changes in the strategy employed to sustain the force output, the underlying control properties regulating motor unit firing behavior remain unchanged during muscle fatigue.
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Affiliation(s)
| | - John Letizi
- Delsys and Altec Inc. , Natick, Massachusetts
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Asmussen MJ, von Tscharner V, Nigg BM. Motor Unit Action Potential Clustering-Theoretical Consideration for Muscle Activation during a Motor Task. Front Hum Neurosci 2018; 12:15. [PMID: 29445332 PMCID: PMC5797735 DOI: 10.3389/fnhum.2018.00015] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 01/12/2018] [Indexed: 11/13/2022] Open
Abstract
During dynamic or sustained isometric contractions, bursts of muscle activity appear in the electromyography (EMG) signal. Theoretically, these bursts of activity likely occur because motor units are constrained to fire temporally close to one another and thus the impulses are "clustered" with short delays to elicit bursts of muscle activity. The purpose of this study was to investigate whether a sequence comprised of "clustered" motor unit action potentials (MUAP) can explain spectral and amplitude changes of the EMG during a simulated motor task. This question would be difficult to answer experimentally and thus, required a model to study this type of muscle activation pattern. To this end, we modeled two EMG signals, whereby a single MUAP was either convolved with a randomly distributed impulse train (EMG-rand) or a "clustered" sequence of impulses (EMG-clust). The clustering occurred in windows lasting 5-100 ms. A final mixed signal of EMG-clust and EMG-rand, with ratios (1:1-1:10), was also modeled. A ratio of 1:1 would indicate that 50% of MUAP were randomly distributed, while 50% of "clustered" MUAP occurred in a given time window (5-100 ms). The results of the model showed that clustering MUAP caused a downshift in the mean power frequency (i.e., ~30 Hz) with the largest shift occurring with a cluster window of 10 ms. The mean frequency shift was largest when the ratio of EMG-clust to EMG-rand was high. Further, the clustering of MUAP also caused a substantial increase in the amplitude of the EMG signal. This model potentially explains an activation pattern that changes the EMG spectra during a motor task and thus, a potential activation pattern of muscles observed experimentally. Changes in EMG measurements during fatiguing conditions are typically attributed to slowing of conduction velocity but could, per this model, also result from changes of the clustering of MUAP. From a clinical standpoint, this type of muscle activation pattern might help describe the pathological movement issues in people with Parkinson's disease or essential tremor. Based on our model, researchers moving forward should consider how MUAP clustering influences EMG spectral and amplitude measurements and how these changes influence movements.
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Affiliation(s)
| | | | - Benno M Nigg
- Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
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Almuklass AM, Davis L, Hamilton LD, Vieira TM, Botter A, Enoka RM. Motor unit discharge characteristics and walking performance of individuals with multiple sclerosis. J Neurophysiol 2018; 119:1273-1282. [PMID: 29357453 DOI: 10.1152/jn.00598.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Walking performance of persons with multiple sclerosis (MS) is strongly influenced by the activation signals received by lower leg muscles. We examined the associations between force steadiness and motor unit discharge characteristics of lower leg muscles during submaximal isometric contractions with tests of walking performance and disability status in individuals who self-reported walking difficulties due to MS. We expected that worse walking performance would be associated with weaker plantar flexor muscles, worse force steadiness, and slower motor unit discharge times. Twenty-three individuals with relapsing-remitting MS (56 ± 7 yr) participated in the study. Participants completed one to three evaluation sessions that involved two walking tests (25-ft walk and 6-min walk), a manual dexterity test (grooved pegboard), health-related questionnaires, and measurement of strength, force steadiness, and motor unit discharge characteristics of lower leg muscles. Multiple regression analyses were used to construct models to explain the variance in measures of walking performance. There were statistically significant differences (effect sizes: 0.21-0.60) between the three muscles in mean interspike interval (ISI) and ISI distributions during steady submaximal contractions with the plantar flexor and dorsiflexor muscles. The regression models explained 40% of the variance in 6-min walk distance and 47% of the variance in 25-ft walk time with two or three variables that included mean ISI for one of the plantar flexor muscles, dorsiflexor strength, and force steadiness. Walking speed and endurance in persons with relapsing-remitting MS were reduced in individuals with longer ISIs, weaker dorsiflexors, and worse plantar flexor force steadiness. NEW & NOTEWORTHY The walking endurance and gait speed of persons with relapsing-remitting multiple sclerosis (MS) were worse in individuals who had weaker dorsiflexor muscles and greater force fluctuations and longer times between action potentials discharged by motor units in plantar flexor muscles during steady isometric contractions. These findings indicate that the control of motor unit activity in lower leg muscles of individuals with MS is associated with their walking ability.
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Affiliation(s)
- Awad M Almuklass
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado.,College of Medicine, King Saud bin Abdulaziz University for Health Sciences , Riyadh , Saudi Arabia
| | - Leah Davis
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Landon D Hamilton
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Taian M Vieira
- LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Turin , Italy
| | - Alberto Botter
- LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Turin , Italy
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
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Liu TH, Chiao CC. Mosaic Organization of Body Pattern Control in the Optic Lobe of Squids. J Neurosci 2017; 37:768-80. [PMID: 28123014 DOI: 10.1523/JNEUROSCI.0768-16.2016] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Revised: 11/05/2016] [Accepted: 11/28/2016] [Indexed: 11/21/2022] Open
Abstract
Cephalopods in nature undergo highly dynamic skin coloration changes that allow rapid camouflage and intraspecies communication. The optic lobe is thought to play a key role in controlling the expansion of the chromatophores that generate these diverse body patterns. However, the functional organization of the optic lobe and neural control of the various body patterns by the optic lobe are largely unknown. We applied electrical stimulation within the optic lobe to investigate the neural basis of body patterning in the oval squid, Sepioteuthis lessoniana Most areas in the optic lobe mediated predominately ipsilateral expansion of chromatophores present on the mantle, but not on the head and arms; furthermore, the expanded areas after electrical stimulation were positively correlated with an increase in stimulating voltage and stimulation depth. These results suggest a unilaterally dominant and vertically converged organization of the optic lobe. Furthermore, analyzing 14 of the elicited body pattern components and their corresponding stimulation sites revealed that the same components can be elicited by stimulating different parts of the optic lobe and that various subsets of these components can be coactivated by stimulating the same area. These findings suggest that many body pattern components may have multiple motor units in the optic lobe and that these are organized in a mosaic manner. The multiplicity associated with the nature of the neural controls of these components in the cephalopod brain thus reflects the versatility of the individual components during the generation of diverse body patterns. SIGNIFICANCE STATEMENT Neural control of the dynamic body patterning of cephalopods for camouflage and intraspecies communication is a fascinating research topic. Previous studies have shown that the optic lobe is the motor command center for dynamic body patterning. However, little is known about its neural organization and the mechanisms underlying its control of body pattern generation. By electrically stimulating the optic lobe of the oval squids and observing their body pattern changes, surprisingly, we found that there is no somatotopic organization of motor units. Instead, many of these components have multiple motor units within the optic lobe and are organized in a mosaic manner. The present work reveals a novel neural control of dynamic body patterning for communication in cephalopods.
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Udina E, Putman CT, Harris LR, Tyreman N, Cook VE, Gordon T. Compensatory axon sprouting for very slow axonal die-back in a transgenic model of spinal muscular atrophy type III. J Physiol 2017; 595:1815-1829. [PMID: 27891608 DOI: 10.1113/jp273404] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Accepted: 11/15/2016] [Indexed: 01/13/2023] Open
Abstract
KEY POINTS Smn+/- transgenic mouse is a model of the mildest form of spinal muscular atrophy. Although there is a loss of spinal motoneurons in 11-month-old animals, muscular force is maintained. This maintained muscular force is mediated by reinnervation of the denervated fibres by surviving motoneurons. The spinal motoneurons in these animals do not show an increased susceptibility to death after nerve injury and they retain their regenerative capacity. We conclude that the hypothesized immaturity of the neuromuscular system in this model cannot explain the loss of motoneurons by systematic die-back. ABSTRACT Spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans and is the leading genetic cause of infantile death. Patients lack the SMN1 gene with the severity of the disease depending on the number of copies of the highly homologous SMN2 gene. Although motoneuron death in the Smn+/- transgenic mouse model of the mildest form of SMA, SMA type III, has been reported, we have used retrograde tracing of sciatic and femoral motoneurons in the hindlimb with recording of muscle and motor unit isometric forces to count the number of motoneurons with intact neuromuscular connections. Thereby, we investigated whether incomplete maturation of the neuromuscular system induced by survival motoneuron protein (SMN) defects is responsible for die-back of axons relative to survival of motoneurons. First, a reduction of ∼30% of backlabelled motoneurons began relatively late, at 11 months of age, with a significant loss of 19% at 7 months. Motor axon die-back was affirmed by motor unit number estimation. Loss of functional motor units was fully compensated by axonal sprouting to retain normal contractile force in four hindlimb muscles (three fast-twitch and one slow-twitch) innervated by branches of the sciatic nerve. Second, our evaluation of whether axotomy of motoneurons in the adult Smn+/- transgenic mouse increases their susceptibility to cell death demonstrated that all the motoneurons survived and they sustained their capacity to regenerate their nerve fibres. It is concluded the systematic die-back of motoneurons that innervate both fast- and slow-twitch muscle fibres is not related to immaturity of the neuromuscular system in SMA.
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Affiliation(s)
- Esther Udina
- Neuroscience and Mental Health Institute, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2.,Institute of Neurosciences and Department of Cell Biology, Physiology and Immunology, Universitat Autònoma de Barcelona, and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), Bellaterra, Spain
| | - Charles T Putman
- Neuroscience and Mental Health Institute, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2.,Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada, T6G 2H9
| | - Luke R Harris
- Neuroscience and Mental Health Institute, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2.,Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada, T6G 2H9
| | - Neil Tyreman
- Neuroscience and Mental Health Institute, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2
| | - Victoria E Cook
- Neuroscience and Mental Health Institute, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2.,Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, Edmonton, AB, Canada, T6G 2H9
| | - Tessa Gordon
- Neuroscience and Mental Health Institute, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2.,Division of Rehabilitation and Physical Medicine of the Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada, T6G 2S2
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Silva MF, Dias JM, Pereira LM, Mazuquin BF, Lindley S, Richards J, Cardoso JR. Determination of the motor unit behavior of lumbar erector spinae muscles through surface EMG decomposition technology in healthy female subjects. Muscle Nerve 2016; 55:28-34. [PMID: 27170098 DOI: 10.1002/mus.25184] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Revised: 04/30/2016] [Accepted: 05/09/2016] [Indexed: 11/06/2022]
Abstract
INTRODUCTION The aims of this study were to determine the motor unit behavior of the erector spinae muscles and to assess whether differences exist between the dominant/nondominant sides of the back muscles. METHODS Nine healthy women, aged 21.7 years (SD = 0.7), performed a back extension test. Surface electromyographic decomposition data were collected from both sides of the erector spinae and decomposed into individual motor unit action potential trains. The mean firing rate for each motor unit was calculated, and a regression analysis was performed against the corresponding recruitment thresholds. RESULTS The mean firing rate ranged from 15.9 to 23.9 pps and 15.8 to 20.6 pps on the dominant and nondominant sides, respectively. However, the early motor unit potentials of the nondominant lumbar erector spinae muscles were recruited at a lower firing rate. CONCLUSIONS This technique may further our understanding of individuals with back pain and other underlying neuromuscular diseases. Muscle Nerve 55: 28-34, 2017.
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Affiliation(s)
- Mariana Felipe Silva
- Laboratory of Biomechanics and Clinical Epidemiology, PAIFIT Research Group, Universidade Estadual de Londrina, Londrina, PR, Brazil
| | - Josilainne Marcelino Dias
- Laboratory of Biomechanics and Clinical Epidemiology, PAIFIT Research Group, Universidade Estadual de Londrina, Londrina, PR, Brazil
| | - Ligia Maxwell Pereira
- Laboratory of Biomechanics and Clinical Epidemiology, PAIFIT Research Group, Universidade Estadual de Londrina, Londrina, PR, Brazil
| | - Bruno Fles Mazuquin
- Allied Health Research Unit, University Central of Lancashire, Preston, Lancashire, United Kingdom
| | - Steven Lindley
- Allied Health Research Unit, University Central of Lancashire, Preston, Lancashire, United Kingdom
| | - Jim Richards
- Allied Health Research Unit, University Central of Lancashire, Preston, Lancashire, United Kingdom
| | - Jefferson Rosa Cardoso
- Laboratory of Biomechanics and Clinical Epidemiology, PAIFIT Research Group, Universidade Estadual de Londrina, Londrina, PR, Brazil
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Marker RJ, Campeau S, Maluf KS. Psychosocial stress alters the strength of reticulospinal input to the human upper trapezius. J Neurophysiol 2016; 117:457-466. [PMID: 27832595 DOI: 10.1152/jn.00448.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 10/31/2016] [Indexed: 11/22/2022] Open
Abstract
Psychosocial stress has been shown to influence several aspects of human motor control associated with the fight-or-flight response, including augmentation of upper trapezius muscle activity. Given the established role of the reticular formation in arousal, this study investigated the contribution of reticulospinal activation to trapezius muscle activity during exposure to an acute psychosocial stressor. Twenty-five healthy adults were exposed to startling acoustic stimuli (SAS) while performing a motor task during periods of low and high psychosocial stress. Acoustic startle reflexes (ASRs) were recorded in the upper trapezius during low intensity contractions using both surface and intramuscular electromyography. Exposure to the stressor increased subjective and physiological measures of arousal (P < 0.01). The majority of participants demonstrated inhibitory ASRs, whereas a small subgroup with significantly higher trait anxiety (n = 5) demonstrated excitatory ASRs in the low stress condition. Changes in synaptic input for inhibitory ASRs were confirmed by decreases in the discharge rate of single motor units in response to the SAS. ASRs decreased in magnitude for all participants during exposure to the acute psychosocial stressor. These findings suggest that the reticular formation has predominately inhibitory effects on the human upper trapezius during an ongoing motor task and that disinhibition caused by psychosocial stress may contribute to augmentation of trapezius muscle activity. Further research is required to investigate mechanisms underlying the complex ASRs characterized by this study, particularly the phase reversal to excitatory responses observed among more anxious individuals. NEW & NOTEWORTHY This study is the first to quantify stress-evoked changes in the acoustic startle reflex in the upper trapezius muscle of humans, and our findings reveal a complex pattern of inhibitory and facilitatory responses consistent with observations in nonhuman primates. We further demonstrate that psychosocial stress consistently reduces the amplitude of these responses. These findings have implications for the control of motor behaviors in response to stress.
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Affiliation(s)
- Ryan J Marker
- Rehabilitation Science Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado
| | - Serge Campeau
- Department of Psychology and Neuroscience, University of Colorado Boulder, Boulder, Colorado; and
| | - Katrina S Maluf
- Rehabilitation Science Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado; .,School of Exercise and Nutritional Sciences, San Diego State University, San Diego, California
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Contessa P, De Luca CJ, Kline JC. The compensatory interaction between motor unit firing behavior and muscle force during fatigue. J Neurophysiol 2016; 116:1579-1585. [PMID: 27385798 DOI: 10.1152/jn.00347.2016] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 07/05/2016] [Indexed: 11/22/2022] Open
Abstract
Throughout the literature, different observations of motor unit firing behavior during muscle fatigue have been reported and explained with varieties of conjectures. The disagreement amongst previous studies has resulted, in part, from the limited number of available motor units and from the misleading practice of grouping motor unit data across different subjects, contractions, and force levels. To establish a more clear understanding of motor unit control during fatigue, we investigated the firing behavior of motor units from the vastus lateralis muscle of individual subjects during a fatigue protocol of repeated voluntary constant force isometric contractions. Surface electromyographic decomposition technology provided the firings of 1,890 motor unit firing trains. These data revealed that to sustain the contraction force as the muscle fatigued, the following occurred: 1) motor unit firing rates increased; 2) new motor units were recruited; and 3) motor unit recruitment thresholds decreased. Although the degree of these adaptations was subject specific, the behavior was consistent in all subjects. When we compared our empirical observations with those obtained from simulation, we found that the fatigue-induced changes in motor unit firing behavior can be explained by increasing excitation to the motoneuron pool that compensates for the fatigue-induced decrease in muscle force twitch reported in empirical studies. Yet, the fundamental motor unit control scheme remains invariant throughout the development of fatigue. These findings indicate that the central nervous system regulates motor unit firing behavior by adjusting the operating point of the excitation to the motoneuron pool to sustain the contraction force as the muscle fatigues.
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Affiliation(s)
| | - Carlo J De Luca
- Delsys Incorporated, Natick, Massachusetts; and Department of Biomedical Engineering, Boston University, Boston, Massachusetts
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Kaczmarek D, Łochyński D, Everaert I, Pawlak M, Derave W, Celichowski J. Role of histidyl dipeptides in contractile function of fast and slow motor units in rat skeletal muscle. J Appl Physiol (1985) 2016; 121:164-72. [PMID: 27197862 DOI: 10.1152/japplphysiol.00848.2015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Accepted: 05/18/2016] [Indexed: 11/22/2022] Open
Abstract
The physiological role of the muscle histidyl dipeptides carnosine and anserine in contractile function of various types of muscle fibers in vivo is poorly understood. Ten adult male Wistar rats were randomly assigned to two groups: control and supplemented for 10 wk with beta-alanine, the precursor of carnosine (∼640 mg·kg body wt(-1)·day(-1)). Thereafter, contractile properties and fatigability of isolated fast fatigable (FF), fast resistant to fatigue (FR), and slow motor units (MUs) from the medial gastrocnemius were determined in deeply anaesthetized animals. The fatigue resistance was tested with a 40-Hz fatigue protocol followed by a second protocol at 40 Hz in fast and 20 Hz in slow units. In the supplemented rats, histidyl dipeptide concentrations significantly increased (P < 0.05) by 25% in the red portion of the gastrocnemius, and carnosine increased by 94% in the white portion. The twitch force of FF units and maximum tetanic force of FR units were significantly increased (P < 0.05), and the half-relaxation time was prolonged in slow units (P < 0.05). FF units showed less fatigue during the first 10 s, and FR units showed higher forces between 10 and 60 s during the 40-Hz fatigue test. In slow units, forces declined less during the first 60 s of the 20-Hz test. In conclusion, this in vivo experiment demonstrates that an elevation in muscle histidyl dipeptide content elicits beneficial changes in MU contractile characteristics and fatigue resistance. Carnosine and anserine seem to play an important yet divergent role in various MUs.
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Affiliation(s)
- Dominik Kaczmarek
- Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland; Department of Physiology, Biochemistry and Hygiene, Poznan University of Physical Education, Poznań, Poland;
| | - Dawid Łochyński
- Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland; Department of Motor Rehabilitation, Poznan University of Physical Education, Poznań, Poland; and
| | - Inge Everaert
- Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium
| | - Maciej Pawlak
- Department of Physiology, Biochemistry and Hygiene, Poznan University of Physical Education, Poznań, Poland
| | - Wim Derave
- Department of Movement and Sports Sciences, Ghent University, Ghent, Belgium
| | - Jan Celichowski
- Department of Neurobiology, Poznan University of Physical Education, Poznań, Poland
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Dideriksen JL, Holobar A, Falla D. Preferential distribution of nociceptive input to motoneurons with muscle units in the cranial portion of the upper trapezius muscle. J Neurophysiol 2016; 116:611-8. [PMID: 27226455 DOI: 10.1152/jn.01117.2015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 05/18/2016] [Indexed: 11/22/2022] Open
Abstract
Pain is associated with changes in the neural drive to muscles. For the upper trapezius muscle, surface electromyography (EMG) recordings have indicated that acute noxious stimulation in either the cranial or the caudal region of the muscle leads to a relative decrease in muscle activity in the cranial region. It is, however, not known if this adaption reflects different recruitment thresholds of the upper trapezius motor units in the cranial and caudal region or a nonuniform nociceptive input to the motor units of both regions. This study investigated these potential mechanisms by direct motor unit identification. Motor unit activity was investigated with high-density surface EMG signals recorded from the upper trapezius muscle of 12 healthy volunteers during baseline, control (intramuscular injection of isotonic saline), and painful (hypertonic saline) conditions. The EMG was decomposed into individual motor unit spike trains. Motor unit discharge rates decreased significantly from control to pain conditions by 4.0 ± 3.6 pulses/s (pps) in the cranial region but not in the caudal region (1.4 ± 2.8 pps; not significant). These changes were compatible with variations in the synaptic input to the motoneurons of the two regions. These adjustments were observed, irrespective of the location of noxious stimulation. These results strongly indicate that the nociceptive synaptic input is distributed in a nonuniform way across regions of the upper trapezius muscle.
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Affiliation(s)
- Jakob L Dideriksen
- Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - Ales Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia; and
| | - Deborah Falla
- School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
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Dakin CJ, Héroux ME, Luu BL, Inglis JT, Blouin JS. Vestibular contribution to balance control in the medial gastrocnemius and soleus. J Neurophysiol 2015; 115:1289-97. [PMID: 26683068 DOI: 10.1152/jn.00512.2015] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Accepted: 12/16/2015] [Indexed: 12/17/2022] Open
Abstract
The soleus (Sol) and medial gastrocnemius (mGas) muscles have different patterns of activity during standing balance and may have distinct functional roles. Using surface electromyography we previously observed larger responses to galvanic vestibular stimulation (GVS) in the mGas compared with the Sol muscle. However, it is unclear whether this difference is an artifact that reflects limitations associated with surface electromyography recordings or whether a compensatory balance response to a vestibular error signal activates the mGas to a greater extent than the Sol. In the present study, we compared the effect of GVS on the discharge behavior of 9 Sol and 21 mGas motor units from freely standing subjects. In both Sol and mGas motor units, vestibular stimulation induced biphasic responses in measures of discharge timing [11 ± 5.0 (mGas) and 5.6 ± 3.8 (Sol) counts relative to the sham (mean ± SD)], and frequency [0.86 ± 0.6 Hz (mGas), 0.34 ± 0.2 Hz (Sol) change relative to the sham]. Peak-to-trough response amplitudes were significantly larger in the mGas (62% in the probability-based measure and 160% in the frequency-based measure) compared with the Sol (multiple P < 0.05). Our results provide direct evidence that vestibular signals have a larger influence on the discharge activity of motor units in the mGas compared with the Sol. More tentatively, these results indicate the mGas plays a greater role in vestibular-driven balance corrections during standing balance.
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Affiliation(s)
- Christopher J Dakin
- School of Kinesiology, University of British Columbia, Vancouver, Canada; Institute of Neurology, University College London, London, United Kingdom
| | - Martin E Héroux
- School of Kinesiology, University of British Columbia, Vancouver, Canada; Neuroscience Research Australia, Sydney, Australia
| | - Billy L Luu
- School of Kinesiology, University of British Columbia, Vancouver, Canada; Neuroscience Research Australia, Sydney, Australia
| | - John Timothy Inglis
- School of Kinesiology, University of British Columbia, Vancouver, Canada; David Mowafaghian Center for Brain Health, University of British Columbia, Vancouver, Canada; International Collaboration for Repair Discoveries, University of British Columbia, Vancouver, Canada; and
| | - Jean-Sébastien Blouin
- School of Kinesiology, University of British Columbia, Vancouver, Canada; David Mowafaghian Center for Brain Health, University of British Columbia, Vancouver, Canada; Institute for Computing Information and Cognitive Systems, University of British Columbia, Vancouver, Canada
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Contessa P, Puleo A, De Luca CJ. Is the notion of central fatigue based on a solid foundation? J Neurophysiol 2015; 115:967-77. [PMID: 26655823 DOI: 10.1152/jn.00889.2015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Accepted: 12/02/2015] [Indexed: 11/22/2022] Open
Abstract
Exercise-induced muscle fatigue has been shown to be the consequence of peripheral factors that impair muscle fiber contractile mechanisms. Central factors arising within the central nervous system have also been hypothesized to induce muscle fatigue, but no direct empirical evidence that is causally associated to reduction of muscle force-generating capability has yet been reported. We developed a simulation model to investigate whether peripheral factors of muscle fatigue are sufficient to explain the muscle force behavior observed during empirical studies of fatiguing voluntary contractions, which is commonly attributed to central factors. Peripheral factors of muscle fatigue were included in the model as a time-dependent decrease in the amplitude of the motor unit force twitches. Our simulation study indicated that the force behavior commonly attributed to central fatigue could be explained solely by peripheral factors during simulated fatiguing submaximal voluntary contractions. It also revealed important flaws regarding the use of the interpolated twitch response from electrical stimulation of the muscle as a means for assessing central fatigue. Our analysis does not directly refute the concept of central fatigue. However, it raises important concerns about the manner in which it is measured and about the interpretation of the commonly accepted causes of central fatigue and questions the very need for the existence of central fatigue.
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Affiliation(s)
- Paola Contessa
- Delsys Incorporated, Natick, Massachusetts; Department of Physical Therapy and Athletic Training, Boston University, Boston, Massachusetts
| | - Alessio Puleo
- Delsys Incorporated, Natick, Massachusetts; Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy; and
| | - Carlo J De Luca
- Delsys Incorporated, Natick, Massachusetts; Department of Biomedical Engineering, Boston University, Boston, Massachusetts
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Laine CM, Martinez-Valdes E, Falla D, Mayer F, Farina D. Motor Neuron Pools of Synergistic Thigh Muscles Share Most of Their Synaptic Input. J Neurosci 2015; 35:12207-16. [PMID: 26338331 DOI: 10.1523/JNEUROSCI.0240-15.2015] [Citation(s) in RCA: 92] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
UNLABELLED Neural control of synergist muscles is not well understood. Presumably, each muscle in a synergistic group receives some unique neural drive and some drive that is also shared in common with other muscles in the group. In this investigation, we sought to characterize the strength, frequency spectrum, and force dependence of the neural drive to the human vastus lateralis and vastus medialis muscles during the production of isometric knee extension forces at 10 and 30% of maximum voluntary effort. High-density surface electromyography recordings were decomposed into motor unit action potentials to examine the neural drive to each muscle. Motor unit coherence analysis was used to characterize the total neural drive to each muscle and the drive shared between muscles. Using a novel approach based on partial coherence analysis, we were also able to study specifically the neural drive unique to each muscle (not shared). The results showed that the majority of neural drive to the vasti muscles was a cross-muscle drive characterized by a force-dependent strength and bandwidth. Muscle-specific neural drive was at low frequencies (<5 Hz) and relatively weak. Frequencies of neural drive associated with afferent feedback (6-12 Hz) and with descending cortical input (∼20 Hz) were almost entirely shared by the two muscles, whereas low-frequency (<5 Hz) drive comprised shared (primary) and muscle-specific (secondary) components. This study is the first to directly investigate the extent of shared versus independent control of synergist muscles at the motor neuron level. SIGNIFICANCE STATEMENT Precisely how the nervous system coordinates the activity of synergist muscles is not well understood. One possibility is that muscles of a synergy share a common neural drive. In this study, we directly compared the relative strength of shared versus independent neural drive to synergistically activated thigh muscles in humans. The results of this analysis support the notion that synergistically activated muscles share most of their neural drive. Scientifically, this study addressed an important gap in our current understanding of how neural drive is delivered to synergist muscles. We have also demonstrated the feasibility of a novel approach to the study of muscle synergies based on partial coherence analysis of motor unit activity.
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Woods MJ, Nicholas CL, Semmler JG, Chan JKM, Jordan AS, Trinder J. Common drive to the upper airway muscle genioglossus during inspiratory loading. J Neurophysiol 2015; 114:2883-92. [PMID: 26378207 DOI: 10.1152/jn.00738.2014] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 09/14/2015] [Indexed: 12/14/2022] Open
Abstract
Common drive is thought to constitute a central mechanism by which the efficiency of a motor neuron pool is increased. This study tested the hypothesis that common drive to the upper airway muscle genioglossus (GG) would increase with increased respiratory drive in response to an inspiratory load. Respiration, GG electromyographic (EMG) activity, single-motor unit activity, and coherence in the 0-5 Hz range between pairs of GG motor units were assessed for the 30 s before an inspiratory load, the first and second 30 s of the load, and the 30 s after the load. Twelve of twenty young, healthy male subjects provided usable data, yielding 77 pairs of motor units: 2 Inspiratory Phasic, 39 Inspiratory Tonic, 15 Expiratory Tonic, and 21 Tonic. Respiratory and GG inspiratory activity significantly increased during the loads and returned to preload levels during the postload periods (all showed significant quadratic functions over load trials, P < 0.05). As hypothesized, common drive increased during the load in inspiratory modulated motor units to a greater extent than in expiratory/tonic motor units (significant load × discharge pattern interaction, P < 0.05). Furthermore, this effect persisted during the postload period. In conclusion, common drive to inspiratory modulated motor units was elevated in response to increased respiratory drive. The postload elevation in common drive was suggestive of a poststimulus activation effect.
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Affiliation(s)
- Michael J Woods
- Melbourne School of Psychological Sciences, The University of Melbourne, Melbourne, Victoria, Australia; and
| | - Christian L Nicholas
- Melbourne School of Psychological Sciences, The University of Melbourne, Melbourne, Victoria, Australia; and
| | - John G Semmler
- School of Medical Sciences, The University of Adelaide, Adelaide, South Australia, Australia
| | - Julia K M Chan
- Melbourne School of Psychological Sciences, The University of Melbourne, Melbourne, Victoria, Australia; and
| | - Amy S Jordan
- Melbourne School of Psychological Sciences, The University of Melbourne, Melbourne, Victoria, Australia; and
| | - John Trinder
- Melbourne School of Psychological Sciences, The University of Melbourne, Melbourne, Victoria, Australia; and
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Vieira TM, Botter A, Minetto MA, Hodson-Tole EF. Spatial variation of compound muscle action potentials across human gastrocnemius medialis. J Neurophysiol 2015; 114:1617-27. [PMID: 26156382 DOI: 10.1152/jn.00221.2015] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 06/26/2015] [Indexed: 12/14/2022] Open
Abstract
The massed action potential (M wave) elicited through nerve stimulation underpins a wide range of physiological and mechanical understanding of skeletal muscle structure and function. Although systematic approaches have evaluated the effect of different factors on M waves, the effect of the location and distribution of activated fibers within the muscle remains unknown. By detecting M waves from the medial gastrocnemius (MG) of 12 participants with a grid of 128 electrodes, we investigated whether different populations of muscle units have different spatial organization within MG. If populations of muscle units occupy discrete MG regions, current pulses of progressively greater intensities applied to the MG nerve branch would be expected to lead to local changes in M-wave amplitudes. Electrical pulses were therefore delivered at 2 pps, with the current pulse amplitude increased every 10 stimuli to elicit different degrees of muscle activation. The localization of MG response to increases in current intensity was determined from the spatial distribution of M-wave amplitude. Key results revealed that increases in M-wave amplitude were detected somewhat locally, by 10-50% of the 128 electrodes. Most importantly, the electrodes detecting greatest increases in M-wave amplitude were localized at different regions in the grid, with a tendency for greater stimulation intensities to elicit M waves in the more distal MG region. The presented results indicate that M waves recorded locally may not provide a representative MG response, with major implications for the estimation of, e.g., the maximal stimulation levels, the number of motor units, and the onset and normalization in H-reflex studies.
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Affiliation(s)
- Taian M Vieira
- Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Turin, Italy; Escola de Educação Física e Desportos, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Alberto Botter
- Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica e Telecomunicazioni, Politecnico di Torino, Turin, Italy;
| | - Marco A Minetto
- Division of Endocrinology, Diabetology and Metabolism, Department of Medical Sciences, University of Turin, Turin, Italy; Division of Physical Medicine and Rehabilitation, Department of Surgical Sciences, University of Turin, Turin, Italy; and
| | - Emma F Hodson-Tole
- School of Healthcare Sciences, Manchester Metropolitan University, Manchester, United Kingdom
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Kubin L, Jordan AS, Nicholas CL, Cori JM, Semmler JG, Trinder J. Crossed motor innervation of the base of human tongue. J Neurophysiol 2015; 113:3499-510. [PMID: 25855691 DOI: 10.1152/jn.00051.2015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Accepted: 04/06/2015] [Indexed: 12/15/2022] Open
Abstract
Muscle fibers of the genioglossus (GG) form the bulk of the muscle mass at the base of the tongue. The motor control of the tongue is critical for vocalization, feeding, and breathing. Our goal was to assess the patterns of motor innervation of GG single motor units (SMUs) in humans. Simultaneous monopolar recordings were obtained from four sites in the base of the tongue bilaterally at two antero-posterior levels from 16 resting, awake, healthy adult males, who wore a face mask with airway pressure and airflow sensors. We analyzed 69 data segments in which at least one lead contained large action potentials generated by an SMU. Such potentials served as triggers for spike-triggered averaging (STA) of signals recorded from the other three sites. Spontaneous activity of the SMUs was classified as inspiratory modulated, expiratory modulated, or tonic. Consistent with the antero-posterior orientation of GG fibers, 44 STAs (77%) recorded ipsilateral to the trigger yielded sharp action potentials with a median amplitude of 52 μV [interquartile range (IQR): 25-190] that were time shifted relative to the trigger by about 1 ms. Notably, 48% of recordings on the side opposite to the trigger also yielded sharp action potentials. Of those, 17 (29%) had a median amplitude of 63 μV (IQR: 39-96), and most were generated by tonic SMUs. Thus a considerable proportion of GG muscle fibers receive a crossed motor innervation. Crossed innervation may help ensure symmetry and stability of tongue position and movements under normal conditions and following injury or degenerative changes affecting the tongue.
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Affiliation(s)
- Leszek Kubin
- School of Psychological Sciences, University of Melbourne, Melbourne, Australia;
| | - Amy S Jordan
- School of Psychological Sciences, University of Melbourne, Melbourne, Australia
| | | | - Jennifer M Cori
- School of Psychological Sciences, University of Melbourne, Melbourne, Australia
| | - John G Semmler
- School of Medical Sciences, University of Adelaide, Adelaide, Australia
| | - John Trinder
- School of Psychological Sciences, University of Melbourne, Melbourne, Australia
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Abstract
Over the past 3 decades, various algorithms used to decompose the electromyographic (EMG) signal into its constituent motor unit action potentials (MUAPs) have been reported. All are limited to decomposing EMG signals from isometric contraction. In this report, we describe a successful approach to decomposing the surface EMG (sEMG) signal collected from cyclic (repeated concentric and eccentric) dynamic contractions during flexion/extension of the elbow and during gait. The increased signal complexity introduced by the changing shapes of the MUAPs due to relative movement of the electrodes and the lengthening/shortening of muscle fibers was managed by an incremental approach to enhancing our established algorithm for decomposing sEMG signals obtained from isometric contractions. We used machine-learning algorithms and time-varying MUAP shape discrimination to decompose the sEMG signal from an increasingly challenging sequence of pseudostatic and dynamic contractions. The accuracy of the decomposition results was assessed by two verification methods that have been independently evaluated. The firing instances of the motor units had an accuracy of ∼90% with a MUAP train yield as high as 25. Preliminary observations from the performance of motor units during cyclic contractions indicate that during repetitive dynamic contractions, the control of motor units is governed by the same rules as those evidenced during isometric contractions. Modifications in the control properties of motoneuron firings reported by previous studies were not confirmed. Instead, our data demonstrate that the common drive and hierarchical recruitment of motor units are preserved during concentric and eccentric contractions.
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Affiliation(s)
- Carlo J De Luca
- NeuroMuscular Research Center, Boston University, Boston, Massachusetts; Department of Biomedical Engineering, Boston University, Boston, Massachusetts; Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts; Department of Neurology, Boston University, Boston, Massachusetts; Department of Physical Therapy, Boston University, Boston, Massachusetts; and Delsys, Natick, Massachusetts
| | | | - Serge H Roy
- NeuroMuscular Research Center, Boston University, Boston, Massachusetts; Department of Physical Therapy, Boston University, Boston, Massachusetts; and
| | - Joshua C Kline
- NeuroMuscular Research Center, Boston University, Boston, Massachusetts
| | - S Hamid Nawab
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts; Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts
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Suresh AK, Hu X, Powers RK, Heckman CJ, Suresh NL, Rymer WZ. Changes in motoneuron afterhyperpolarization duration in stroke survivors. J Neurophysiol 2014; 112:1447-56. [PMID: 24920018 DOI: 10.1152/jn.01091.2012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hemispheric brain injury resulting from a stroke is often accompanied by muscle weakness in limbs contralateral to the lesion. In the present study, we investigated whether weakness in contralesional hand muscle in stroke survivors is partially attributable to alterations in motor unit activation, including alterations in firing rate modulation range. The afterhyperpolarization (AHP) potential of a motoneuron is a primary determinant of motoneuron firing rate. We examined differences in AHP duration in motoneurons innervating paretic and less impaired (contralateral) limb muscles of hemiparetic stroke survivors as well as in control subjects. A novel surface EMG (sEMG) electrode was used to record motor units from the first dorsal interosseous muscle. The sEMG data were subsequently decomposed to derive single-motor unit events, which were then utilized to produce interval (ISI) histograms of the motoneuron discharges. A modified version of interval death rate (IDR) analysis was used to estimate AHP duration. Results from data analyses performed on both arms of 11 stroke subjects and in 7 age-matched control subjects suggest that AHP duration is significantly longer for motor units innervating paretic muscle compared with units in contralateral muscles and in units of intact subjects. These results were supported by a coefficient of variation (CV) analysis showing that paretic motor unit discharges have a lower CV than either contralateral or control units. This study suggests that after stroke biophysical changes occur at the motoneuron level, potentially contributing to lower firing rates and potentially leading to less efficient force production in paretic muscles.
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Affiliation(s)
- Aneesha K Suresh
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois;
| | - Xiaogang Hu
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois
| | - Randall K Powers
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington
| | - C J Heckman
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Department of Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, Illinois; Department of Physiology, Northwestern University, Chicago, Illinois; and
| | - Nina L Suresh
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois
| | - William Zev Rymer
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Department of Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, Illinois; Department of Biomedical Engineering, Northwestern University, Chicago, Illinois
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