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Mesquita RNO, Taylor JL, Trajano GS, Holobar A, Gonçalves BAM, Blazevich AJ. Effects of jaw clenching and mental stress on persistent inward currents estimated by two different methods. Eur J Neurosci 2023; 58:4011-4033. [PMID: 37840191 DOI: 10.1111/ejn.16158] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 08/25/2023] [Accepted: 09/13/2023] [Indexed: 10/17/2023]
Abstract
Spinal motoneuron firing depends greatly on persistent inward currents (PICs), which in turn are facilitated by the neuromodulators serotonin and noradrenaline. The aim of this study was to determine whether jaw clenching (JC) and mental stress (MS), which may increase neuromodulator release, facilitate PICs in human motoneurons. The paired motor unit (MU) technique was used to estimate PIC contribution to motoneuron firing. Surface electromyograms were collected using a 32-channel matrix on gastrocnemius medialis (GM) during voluntary, ramp, plantar flexor contractions. MU discharges were identified, and delta frequency (ΔF), a measure of recruitment-derecruitment hysteresis, was calculated. Additionally, another technique was used (VibStim) that evokes involuntary contractions that persist after cessation of combined Achilles tendon vibration and triceps surae neuromuscular electrical stimulation. VibStim measures of plantar flexor torque and soleus activity may reflect PIC activation. ΔF was not significantly altered by JC (p = .679, n = 18, 9 females) or MS (p = .147, n = 14, 5 females). However, all VibStim variables quantifying involuntary torque and muscle activity during and after vibration cessation were significantly increased in JC (p < .011, n = 20, 10 females) and some, but not all, increased in MS (p = .017-.05, n = 19, 10 females). JC and MS significantly increased the magnitude of involuntary contractions (VibStim) but had no effect on GM ΔF during voluntary contractions. Effects of increased neuromodulator release on PIC contribution to motoneuron firing might differ between synergists or be context dependent. Based on these data, the background level of voluntary contraction and, hence, both neuromodulation and ionotropic inputs could influence neuromodulatory PIC enhancement.
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Affiliation(s)
- Ricardo N O Mesquita
- Department of Electrical Engineering, Chalmers University of Technology, Gothenburg, Sweden
- Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Perth, Western Australia, Australia
- Neuroscience Research Australia, Sydney, New South Wales, Australia
| | - Janet L Taylor
- Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Perth, Western Australia, Australia
- Neuroscience Research Australia, Sydney, New South Wales, Australia
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences and Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Basílio A M Gonçalves
- Neuromechanics Research Group, Centre for Sport Science and University Sports, University of Vienna, Vienna, Austria
| | - Anthony J Blazevich
- Centre for Human Performance, School of Medical and Health Sciences, Edith Cowan University, Perth, Western Australia, Australia
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Khurram OU, Pearcey GEP, Chardon MK, Kim EH, García M, Heckman CJ. The Cellular Basis for the Generation of Firing Patterns in Human Motor Units. ADVANCES IN NEUROBIOLOGY 2022; 28:233-258. [PMID: 36066828 DOI: 10.1007/978-3-031-07167-6_10] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Motor units, which comprise a motoneuron and the set of muscle fibers it innervates, are the fundamental neuromuscular transducers for all motor commands. The one to one relationship between a motoneuron and its innervated muscle fibers allow motoneuron firing patterns to be readily measured in humans. In this chapter, we summarize the current understanding of the cellular basis for the generation of firing patterns in human motor units. We provide a brief review of landmark insights from classic studies and then proceed to consider the features of motor unit firing patterns that are most likely to be sensitive estimators of motoneuron inputs and properties. In addition, we discuss recent advances in technology for recording human motor unit firing patterns and highly realistic computer simulations of motoneurons. The final section presents our recent efforts to use the power of supercomputers for implementation of the motoneuron models, with a goal of achieving a true "reverse engineering" approach that maximizes the insights from motor unit firing patterns into the synaptic structure of motor commands.
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Affiliation(s)
- Obaid U Khurram
- Departments of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Gregory E P Pearcey
- Departments of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
- Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Matthieu K Chardon
- Departments of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
- Northwestern-Argonne Institute of Science and Engineering, Evanston, IL, USA
| | - Edward H Kim
- Departments of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Marta García
- Northwestern-Argonne Institute of Science and Engineering, Evanston, IL, USA
- Computational Science Division, Argonne National Laboratory, Lemont, IL, USA
| | - C J Heckman
- Departments of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
- Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
- Physical Therapy and Human Movement Sciences, Northwestern University, Chicago, IL, USA.
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3
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Binder MD, Powers RK, Heckman CJ. Nonlinear Input-Output Functions of Motoneurons. Physiology (Bethesda) 2020; 35:31-39. [PMID: 31799904 PMCID: PMC7132324 DOI: 10.1152/physiol.00026.2019] [Citation(s) in RCA: 67] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 09/09/2019] [Accepted: 09/09/2019] [Indexed: 12/19/2022] Open
Abstract
All movements are generated by the activation of motoneurons, and hence their input-output properties define the final step in processing of all motor commands. A major challenge to understanding this transformation has been the striking nonlinear behavior of motoneurons conferred by the activation of persistent inward currents (PICs) mediated by their voltage-gated Na+ and Ca2+ channels. In this review, we focus on the contribution that these PICs make to motoneuronal discharge and how the nonlinearities they engender impede the construction of a comprehensive model of motor control.
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Affiliation(s)
- Marc D Binder
- Department of Physiology & Biophysics, University of Washington School of Medicine, Seattle, Washington
| | - Randall K Powers
- Department of Physiology & Biophysics, University of Washington School of Medicine, Seattle, Washington
| | - C J Heckman
- Departments of Physiology, Physical Medicine & Rehabilitation, Physical Therapy & Human Movement Sciences, Northwestern University Feinberg School of Medicine, Chicago, Illinois
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Pereira HM, Schlinder-DeLap B, Keenan KG, Negro F, Farina D, Hyngstrom AS, Nielson KA, Hunter SK. Oscillations in neural drive and age-related reductions in force steadiness with a cognitive challenge. J Appl Physiol (1985) 2019; 126:1056-1065. [PMID: 30817244 DOI: 10.1152/japplphysiol.00821.2018] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
A cognitive challenge when imposed during a low-force isometric contraction will exacerbate sex- and age-related decreases in force steadiness, but the mechanism is not known. We determined the role of oscillations in the common synaptic input to motor units on force steadiness during a muscle contraction with a concurrent cognitive challenge. Forty-nine young adults (19-30 yr; 25 women, 24 men) and 36 old adults (60-85 yr; 19 women, 17 men) performed a cognitive challenge (counting backward by 13) during an isometric elbow flexion task at 5% of maximal voluntary contraction. Single-motor units were decomposed from high-density surface EMG recordings. For a subgroup of participants, motor units were matched during control and cognitive challenge trials, so the same motor unit was analyzed across conditions. Reduced force steadiness was associated with greater oscillations in the synaptic input to motor units during both control and cognitive challenge trials ( r = 0.45-0.47, P < 0.01). Old adults and young women showed greater oscillations in the common synaptic input to motor units and decreased force steadiness when the cognitive challenge was imposed, but young men showed no change across conditions (session × age × sex, P < 0.05). Oscillations in the common synaptic input to motor units is a potential mechanism for altered force steadiness when a cognitive challenge is imposed during low-force contractions in young women and old adults. NEW & NOTEWORTHY We found that oscillations in the common synaptic input to motor units were associated with a reduction in force steadiness when a cognitive challenge was imposed during low-force contractions of the elbow flexor muscles in young women and old men and women but not young men. Age- and sex-related muscle weakness was associated with these changes.
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Affiliation(s)
- Hugo M Pereira
- Department of Health and Exercise Science, University of Oklahoma , Norman, Oklahoma
| | | | - Kevin G Keenan
- Department of Kinesiology, University of Wisconsin-Milwaukee , Milwaukee, Wisconsin
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Università degli Studi di Brescia , Brescia , Italy
| | - Dario Farina
- Department of Bioengineering, Imperial College London, Royal School of Mines , London , United Kingdom
| | | | - Kristy A Nielson
- Department of Psychology, Marquette University , Milwaukee, Wisconsin
| | - Sandra K Hunter
- Department of Physical Therapy, Marquette University , Milwaukee, Wisconsin
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5
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Chimenti RL, Frey-Law LA, Sluka KA. Author Response. Phys Ther 2018; 98:817-818. [PMID: 30169805 DOI: 10.1093/ptj/pzy102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Ruth L Chimenti
- Department of Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, Iowa
| | - Laura A Frey-Law
- Department of Physical Therapy and Rehabilitation Science, University of Iowa
| | - Kathleen A Sluka
- Department of Physical Therapy and Rehabilitation Science, University of Iowa
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Helou LB, Rosen CA, Wang W, Verdolini Abbott K. Intrinsic Laryngeal Muscle Response to a Public Speech Preparation Stressor. JOURNAL OF SPEECH, LANGUAGE, AND HEARING RESEARCH : JSLHR 2018; 61:1525-1543. [PMID: 29922837 PMCID: PMC6195061 DOI: 10.1044/2018_jslhr-s-17-0153] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 11/30/2017] [Indexed: 05/09/2023]
Abstract
PURPOSE Research suggests that abnormal levels of intrinsic laryngeal muscle (ILM) contraction is a potential causal factor in stress-induced voice disorders. This study seeks to characterize the ILM stress response in a cohort of vocally healthy women. METHOD The authors used an unblinded, nonrandomized, repeated-measures design. Forty vocally healthy female adults were subjected to a stressful speech preparation task. Measurements of heart rate, blood pressure, trapezius muscle (positive control) activation, and tibialis muscle (negative control) activation were obtained from 37 participants before and during stressor exposure, in a nonvoice and nonspeaking task paradigm, to confirm physiological stress response compared to baseline. Fine wire electromyography of the ILMs (posterior cricoarytenoid, thyroarytenoid/lateral cricoarytenoid muscle complex, and cricothyroid) was performed simultaneously so that the activity of these muscles could be measured prior to and during stressor exposure. RESULTS The protocol successfully elicited the typical and expected physiological stress responses. Findings supported the hypothesis that, in some individuals, the ILMs significantly increase in activity during stress reactions compared to baseline, as do the control muscles. CONCLUSIONS This study characterizes ILM responses to psychological stress in vocally healthy participants. Some of the female adults in this study appeared to be "laryngeal stress responders," as evidenced by increased activity of the ILMs during a silent (i.e., nonvocal, nonspeech) speech preparation task that they considered to be stressful.
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Affiliation(s)
- Leah B. Helou
- Department of Communication Science and Disorders, University of Pittsburgh, PA
| | - Clark A. Rosen
- Department of Communication Science and Disorders, University of Pittsburgh, PA
| | - Wei Wang
- Department of Communication Science and Disorders, University of Pittsburgh, PA
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Johnson MD, Thompson CK, Tysseling VM, Powers RK, Heckman CJ. The potential for understanding the synaptic organization of human motor commands via the firing patterns of motoneurons. J Neurophysiol 2017; 118:520-531. [PMID: 28356467 DOI: 10.1152/jn.00018.2017] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 03/07/2017] [Accepted: 03/21/2017] [Indexed: 12/19/2022] Open
Abstract
Motoneurons are unique in being the only neurons in the CNS whose firing patterns can be easily recorded in human subjects. This is because of the one-to-one relationship between the motoneuron and muscle cell behavior. It has long been appreciated that the connection of motoneurons to their muscle fibers allows their action potentials to be amplified and recorded, but only recently has it become possible to simultaneously record the firing pattern of many motoneurons via array electrodes placed on the skin. These firing patterns contain detailed information about the synaptic organization of motor commands to the motoneurons. This review focuses on parameters in these firing patterns that are directly linked to specific features of this organization. It is now well established that motor commands consist of three components, excitation, inhibition, and neuromodulation; the importance of the third component has become increasingly evident. Firing parameters linked to each of the three components are discussed, along with consideration of potential limitations in their utility for understanding the underlying organization of motor commands. Future work based on realistic computer simulations of motoneurons may allow quantitative "reverse engineering" of human motoneuron firing patterns to provide good estimates of the relative amplitudes and temporal patterns of all three components of motor commands.
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Affiliation(s)
- Michael D Johnson
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois;
| | | | - Vicki M Tysseling
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
| | - Randall K Powers
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington
| | - Charles J Heckman
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
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8
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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] [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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9
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Kudina LP, Andreeva RE. Triplet firing origin in human motor units: emerging hypotheses. Exp Brain Res 2015; 234:837-44. [PMID: 26661335 DOI: 10.1007/s00221-015-4514-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 11/25/2015] [Indexed: 12/12/2022]
Abstract
A specific feature of motor unit (MU) firing behaviour is rhythmic trains of single discharges at low rate resulting from the prolonged motoneuronal afterhyperpolarization. However, some MUs exhibit occasional doublets with uniquely short interspike intervals (2.5-20.0 ms). Motoneuronal delayed depolarization is commonly accepted to be doublet underlying mechanism. Apart from doublets, much scarcer MU triple discharges were described, but their mechanisms are disputable. The aim of the present study was to analyse MU triplet firing origin in healthy humans. MU triple discharges occasionally arising during gentle voluntary muscle contractions were compared with those arising in axons during motor nerve stimulation. Firing pattern was analysed in 109 MUs of four muscles: the tibialis anterior, the flexor carpi ulnaris, the abductor pollicis brevis, and the abductor digiti minimi. Our findings present evidence that during voluntary contractions two kinds of MU triplet firing can be occasionally observed: "true" motoneuronal triplets (interspike intervals of 3.6-17.3 ms) with the delayed depolarization as the possible underlying mechanism and axonal triple discharges including the M-response and F-wave. The findings can be useful not only for understanding mechanisms of the very rare motoneuronal firing in healthy humans but also for estimation of pathological triplet firing origin.
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Affiliation(s)
- Lydia P Kudina
- Institute for Information Transmission Problems (Kharkevich Institute), Russian Academy of Sciences, 19, Bol'shoi Karetnyi pereulok, Moscow, Russia, 127994.
| | - Regina E Andreeva
- Institute for Information Transmission Problems (Kharkevich Institute), Russian Academy of Sciences, 19, Bol'shoi Karetnyi pereulok, Moscow, Russia, 127994
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Søgaard K, Olsen HB, Blangsted AK, Sjøgaard G. Single motor unit firing behavior in the right trapezius muscle during rapid movement of right or left index finger. Front Hum Neurosci 2014; 8:881. [PMID: 25404907 PMCID: PMC4217388 DOI: 10.3389/fnhum.2014.00881] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 10/13/2014] [Indexed: 11/15/2022] Open
Abstract
Background: Computer work is associated with low level sustained activity in the trapezius muscle that may cause development of trapezius myalgia. Such a low level activity may be attention related or alternatively, be part of a general multi joint motor program providing stabilization of the shoulder joint as a biomechanical prerequisite for precise finger manipulation. This study examines single motor unit (MU) firing pattern in the right trapezius muscle during fast movements of ipsilateral or contralateral index finger. A modulation of the MU firing rate would support the existence of a general multi joint motor program, while a generally increased and continuous firing rate would support the attention related muscle activation. Method: Twelve healthy female subjects were seated at a computer work place with elbows and forearms supported. Ten double clicks (DC) were performed with right and left index finger on a computer mouse instrumented with a trigger. Surface electromyographic signals (EMG) was recorded from right and left trapezius muscle. Intramuscular EMG was recorded with a quadripolar wire electrode inserted into the right trapezius. Surface EMG was analyzed as RMS and presented as %MVE. The intramuscular EMG signals were decomposed into individual MU action potential trains using a computer algorithm based on signal shape recognition and manual editing. Instantaneous firing rate (IFR) was calculated as the inverse of each inter-spike interval (ISI). All ISI shorter than 20 ms were defined as doublets. For all MU IFR was spike triggered averaged across the 10 DC to show the modulation during DC as well as for calculation of the cross correlation coefficient (CCC). Results: All subjects showed surface EMG activity in both right and left trapezius ranging from 1.8 %MVE to 2.5 %MVE. Regarding intramuscular EMG during right hand DC a total of 32 MUs were identified. Four subjects showed no MU activity. Four showed MU activity with low mean firing rate (MFR) with weak or no variations related to the timing of DC. Four subjects showed firing patterns with large modulation in IFR with a clear temporal relation to the DC. During left hand DC 15 MUs were identified in four subjects, for two of the subjects with IFR modulations clearly related to DC. During both ipsi- and contralateral DC, doublets occurred sporadically as well as related to DC Conclusion: In conclusion, DC with ipsi- and contralateral fast movements of the index finger was found to evoke biomechanically as well as attention related activity pattern in the trapezius muscle. Doublets were for three of the subjects found as an integrated part of MU activation in the trapezius muscle and for one subject temporarily related to DC.
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Affiliation(s)
- Karen Søgaard
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense Denmark
| | - Henrik B Olsen
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense Denmark
| | | | - Gisela Sjøgaard
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense Denmark
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Ritter LK, Tresch MC, Heckman CJ, Manuel M, Tysseling VM. Characterization of motor units in behaving adult mice shows a wide primary range. J Neurophysiol 2014; 112:543-51. [PMID: 24805075 DOI: 10.1152/jn.00108.2014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The mouse is essential for genetic studies of motor function in both normal and pathological states. Thus it is important to consider whether the structure of motor output from the mouse is in fact analogous to that recorded in other animals. There is a striking difference in the basic electrical properties of mouse motoneurons compared with those in rats, cats, and humans. The firing evoked by injected currents produces a unique frequency-current (F-I) function that emphasizes recruitment of motor units at their maximum force. These F-I functions, however, were measured in anesthetized preparations that lacked two key components of normal synaptic input: high levels of synaptic noise and neuromodulatory inputs. Recent studies suggest that the alterations in the F-I function due to these two components are essential for recreating firing behavior of motor units in human subjects. In this study we provide the first data on firing patterns of motor units in the awake mouse, focusing on steady output in quiet stance. The resulting firing patterns did not match the predictions from the mouse F-I behaviors but instead revealed rate modulation across a remarkably wide range (10-60 Hz). The low end of the firing range may be due to changes in the F-I relation induced by synaptic noise and neuromodulatory inputs. The high end of the range may indicate that, unlike other species, quiet standing in the mouse involves recruitment of relatively fast-twitch motor units.
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Affiliation(s)
- Laura K Ritter
- McCormick Biomedical Engineering Department, Northwestern University, Evanston, Illinois
| | - Matthew C Tresch
- McCormick Biomedical Engineering Department, Northwestern University, Evanston, Illinois; Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
| | - C J Heckman
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; and
| | - Marin Manuel
- Laboratoire de Neurophysique et Physiologie, Université Paris Descartes, Institut des Neurosciences et de la Cognition, Centre National de la Recherche Scientifique UMR 8119, Paris, France
| | - Vicki M Tysseling
- Department of Physiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; and
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12
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Marker RJ, Stephenson JL, Kluger BM, Curran-Everett D, Maluf KS. Modulation of intracortical inhibition in response to acute psychosocial stress is impaired among individuals with chronic neck pain. J Psychosom Res 2014; 76:249-56. [PMID: 24529046 PMCID: PMC9288141 DOI: 10.1016/j.jpsychores.2013.12.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Revised: 12/01/2013] [Accepted: 12/02/2013] [Indexed: 11/26/2022]
Abstract
OBJECTIVE Psychosocial stress has been associated with a variety of chronic pain disorders although the mechanisms responsible for this relationship are unknown. The purpose of this study was to compare the excitability of intracortical and corticospinal pathways to the trapezius muscle in individuals with and without chronic neck pain during exposure to low and high levels of psychosocial stress. METHODS Single and paired-pulse transcranial magnetic stimulation was used to assess motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) during mental math performed in the presence and absence of social evaluative threat. RESULTS All participants demonstrated higher amplitude MEPs in the high stress compared to the low stress condition (p < 0.01). Participants with chronic neck pain had significantly greater SICI than healthy participants in the low stress condition (p = 0.03). During exposure to the stressor, healthy participants showed an increase in SICI, whereas participants with neck pain showed no change (group difference for change in SICI, p < 0.01). CONCLUSIONS These findings suggest that individuals with chronic neck pain inhibit motor output to the trapezius in the presence of minor stressors, and are unable to compensate for additional stress-evoked increases in corticospinal excitability through further modulation of SICI. This observation has potential implications for the management of patients who have difficulty relaxing painful muscles during times of stress.
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Affiliation(s)
- Ryan J. Marker
- Rehabilitation Science Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Jennifer L. Stephenson
- Clinical Science Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Benzi M. Kluger
- Department of Neurology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Douglas Curran-Everett
- Division of Biostatistics and Bioinformatics, National Jewish Health, Denver, CO, USA and Department of Biostatistics and Informatics, Colorado School of Public Health, University of Colorado Denver, Denver, CO, USA
| | - Katrina S. Maluf
- Rehabilitation Science Program, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
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13
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Harwood B, Rice CL. Short interspike intervals and double discharges of anconeus motor unit action potentials for the production of dynamic elbow extensions. J Neurophysiol 2014; 111:2039-46. [PMID: 24554783 DOI: 10.1152/jn.00412.2013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Incidence of double discharges (DDs; >100 Hz) and short interspike intervals (ISIs; >50 to <100 Hz) is reported to vary widely among different muscles and tasks, with a higher incidence in motor unit (MU) trains of fast muscles and for the production of fast contractions in humans. However, it is unclear whether human muscles with a large composition of slower motor units exhibit DDs or short ISIs when activated with maximal synaptic drive, such as those required for maximal velocity dynamic contractions. Thus the purpose of this study was to determine the effect of increasing peak contraction velocity on the incidence of DDs and short ISIs in the anconeus muscle. Seventeen anconeus MUs in 10 young males were recorded across dynamic elbow extensions ranging from low submaximal velocities (16% of maximal velocity) up to maximal velocities. A low incidence of DDs (4%) and short ISIs (29%) was observed among the 583 MU trains recorded. Despite the low incidence in individual MU trains, a majority (71% and 94%, respectively) of MUs exhibited at least one DD or short ISI. The number of short ISIs shared no variance with MU recruitment threshold (R(2) = 0.02), but their distribution was skewed toward higher peak velocities (G = -1.26) and a main effect of peak elbow extension velocity was observed (P < 0.05). Although a greater number of short ISIs was observed with increasing velocity, the low incidence of DDs and short ISIs in the anconeus muscle is likely related to the function of the anconeus as a stabilizer rather than voluntary elbow extensor torque and velocity production.
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Affiliation(s)
- B Harwood
- Canadian Centre for Activity and Aging, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; and
| | - C L Rice
- Canadian Centre for Activity and Aging, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; and Department of Anatomy and Cell Biology, The University of Western Ontario, London, Ontario, Canada
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14
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Piotrkiewicz M, Sebik O, Binboğa E, Młoźniak D, Kuraszkiewicz B, Türker KS. Double discharges in human soleus muscle. Front Hum Neurosci 2013; 7:843. [PMID: 24367319 PMCID: PMC3856367 DOI: 10.3389/fnhum.2013.00843] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2013] [Accepted: 11/19/2013] [Indexed: 11/13/2022] Open
Abstract
Double discharges (doublets) were recorded from human soleus (SOL), where they have never been reported before. The data analyzed in this study were collected from 12 healthy volunteers. The subjects were recruited for other studies, concerning: (1) estimation of motoneurons' (MNs) afterhyperpolarization (AHP) duration and (2) analysis of motor unit responses to nerve stimulation, and were not trained to voluntarily evoke doublets. The majority of intradoublet intervals fell into the commonly accepted range 2-20 ms. However, two SOL MNs from one presented exceptional doublets of intradoublet interval about 37 ms. This interval was virtually identical with the interval between second and third discharge in the few triplets recorded from another subject. It is hypothesized that triplets are generated by the delayed depolarization with the second narrow hump, which is the same as the hump responsible for exceptional doublets.
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Affiliation(s)
- Maria Piotrkiewicz
- Polish Academy of Sciences, Department of Engineering of Nervous and Muscular System, Nałęcz Institute of Biocybernetics and Biomedical Engineering, Warsaw Poland
| | - Oğuz Sebik
- Laboratory of Neuromuscular Research, Koç University School of Medicine, Istanbul Turkey
| | - Erdal Binboğa
- Faculty of Medicine, Department of Biophysics, Ege University, Izmir Turkey
| | - Dariusz Młoźniak
- Polish Academy of Sciences, Department of Engineering of Nervous and Muscular System, Nałęcz Institute of Biocybernetics and Biomedical Engineering, Warsaw Poland
| | - Bożenna Kuraszkiewicz
- Polish Academy of Sciences, Department of Engineering of Nervous and Muscular System, Nałęcz Institute of Biocybernetics and Biomedical Engineering, Warsaw Poland
| | - Kemal S Türker
- Laboratory of Neuromuscular Research, Koç University School of Medicine, Istanbul Turkey
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15
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Abstract
Movement is accomplished by the controlled activation of motor unit populations. Our understanding of motor unit physiology has been derived from experimental work on the properties of single motor units and from computational studies that have integrated the experimental observations into the function of motor unit populations. The article provides brief descriptions of motor unit anatomy and muscle unit properties, with more substantial reviews of motoneuron properties, motor unit recruitment and rate modulation when humans perform voluntary contractions, and the function of an entire motor unit pool. The article emphasizes the advances in knowledge on the cellular and molecular mechanisms underlying the neuromodulation of motoneuron activity and attempts to explain the discharge characteristics of human motor units in terms of these principles. A major finding from this work has been the critical role of descending pathways from the brainstem in modulating the properties and activity of spinal motoneurons. Progress has been substantial, but significant gaps in knowledge remain.
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Affiliation(s)
- C J Heckman
- Northwestern University, Evanston, Illinois, USA.
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16
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Kudina LP, Andreeva RE. Delayed depolarization and firing behavior of human motoneurons during voluntary muscle contractions. Front Hum Neurosci 2013; 7:793. [PMID: 24302909 PMCID: PMC3831088 DOI: 10.3389/fnhum.2013.00793] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 10/30/2013] [Indexed: 11/30/2022] Open
Affiliation(s)
- Lydia P. Kudina
- Department of Bioinformatics, Institute for Information Transmission Problems (Kharkevich Institute), Russian Academy of SciencesMoscow, Russia
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17
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Kudina LP, Andreeva RE. Motoneuron double discharges: only one or two different entities? Front Cell Neurosci 2013; 7:75. [PMID: 23734101 PMCID: PMC3660662 DOI: 10.3389/fncel.2013.00075] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2013] [Accepted: 05/06/2013] [Indexed: 11/13/2022] Open
Affiliation(s)
- Lydia P. Kudina
- Institute for Information Transmission Problems Kharkevich Institute, Russian Academy of SciencesMoscow, Russia
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18
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Bensoussan L, Duclos Y, Rossi-Durand C. Modulation of human motoneuron activity by a mental arithmetic task. Hum Mov Sci 2012; 31:999-1013. [PMID: 23159444 DOI: 10.1016/j.humov.2012.02.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2011] [Revised: 02/06/2012] [Accepted: 02/15/2012] [Indexed: 10/27/2022]
Abstract
This study aimed to determine whether the performance of a mental task affects motoneuron activity. To this end, the tonic discharge pattern of wrist extensor motor units was analyzed in healthy subjects while they were required to maintain a steady wrist extension force and to concurrently perform a mental arithmetic (MA) task. A shortening of the mean inter-spike interval (ISI) and a decrease in ISI variability occurred when MA task was superimposed to the motor task. Aloud and silent MA affected equally the rate and variability of motoneuron discharge. Increases in surface EMG activity and force level were consistent with the modulation of the motor unit discharge rate. Trial-by-trial analysis of the characteristics of motor unit firing revealed that performing MA increases activation of wrist extensor SMU. It is suggested that increase in muscle spindle afferent activity, resulting from fusimotor drive activation by MA, may have contributed to the increase in synaptic inputs to motoneurons during the mental task performance, likely together with enhancement in the descending drive. The finding that a mental task affects motoneuron activity could have consequences in assessment of motor disabilities and in rehabilitation in motor pathologies.
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Affiliation(s)
- Laurent Bensoussan
- Pôle de Médecine Physique et de Réadaptation, Aix-Marseille Université, Assistance publique des Hopitaux de Marseille, CHU Timone, Marseille, France
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19
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Revill AL, Fuglevand AJ. Effects of persistent inward currents, accommodation, and adaptation on motor unit behavior: a simulation study. J Neurophysiol 2011; 106:1467-79. [PMID: 21697447 DOI: 10.1152/jn.00419.2011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Motor neurons are often assumed to generate spikes in proportion to the excitatory synaptic input received. There are, however, many intrinsic properties of motor neurons that might affect this relationship, such as persistent inward currents (PICs), spike-threshold accommodation, or spike-frequency adaptation. These nonlinear properties have been investigated in reduced animal preparation but have not been well studied during natural motor behaviors because of the difficulty in characterizing synaptic input in intact animals. Therefore, we studied the influence of each of these intrinsic properties on spiking responses and muscle force using a population model of motor units that simulates voluntary contractions in human subjects. In particular, we focused on the difference in firing rate of low-threshold motor units when higher threshold motor units were recruited and subsequently derecruited, referred to as ΔF. Others have used ΔF to evaluate the extent of PIC activation during voluntary behavior. Our results showed that positive ΔF values could arise when any one of these nonlinear properties was included in the simulations. Therefore, a positive ΔF should not be considered as exclusive evidence for PIC activation. Furthermore, by systematically varying contraction duration and speed in our simulations, we identified a means that might be used experimentally to distinguish among PICs, accommodation, and adaptation as contributors to ΔF.
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Affiliation(s)
- Ann L Revill
- Department of Physiology, College of Medicine, PO Box 210093, University of Arizona, Tucson, AZ 85721-0093, USA
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20
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Stephenson JL, Maluf KS. Dependence of the paired motor unit analysis on motor unit discharge characteristics in the human tibialis anterior muscle. J Neurosci Methods 2011; 198:84-92. [PMID: 21459110 PMCID: PMC3718290 DOI: 10.1016/j.jneumeth.2011.03.018] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Revised: 03/18/2011] [Accepted: 03/23/2011] [Indexed: 11/19/2022]
Abstract
The paired motor unit analysis provides in vivo estimates of the magnitude of persistent inward currents (PIC) in human motoneurons by quantifying changes in the firing rate (ΔF) of an earlier recruited (reference) motor unit at the time of recruitment and derecruitment of a later recruited (test) motor unit. This study assessed the variability of ΔF estimates, and quantified the dependence of ΔF on the discharge characteristics of the motor units selected for analysis. ΔF was calculated for 158 pairs of motor units recorded from nine healthy individuals during repeated submaximal contractions of the tibialis anterior muscle. The mean (SD) ΔF was 3.7 (2.5)pps (range -4.2 to 8.9 pps). The median absolute difference in ΔF for the same motor unit pair across trials was 1.8 pps, and the minimal detectable change in ΔF required to exceed measurement error was 4.8 pps. ΔF was positively related to the amount of discharge rate modulation in the reference motor unit (r² = 0.335; P<0.001), and inversely related to the rate of increase in discharge rate (r² = 0.125; P<0.001). A quadratic function provided the best fit for relations between ΔF and the time between recruitment of the reference and test motor units (r² = 0.229, P<0.001), the duration of test motor unit activity (r² = 0.110, P<0.001), and the recruitment threshold of the test motor unit (r² = 0.237, P<0.001). Physiological and methodological contributions to the variability in ΔF estimates of PIC magnitude are discussed, and selection criteria to reduce these sources of variability are suggested for the paired motor unit analysis.
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Affiliation(s)
- Jennifer L Stephenson
- Department of Physical Medicine & Rehabilitation, University of Colorado Denver, School of Medicine, Aurora, CO 80045, USA
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21
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Stephenson JL, Christou EA, Maluf KS. Discharge rate modulation of trapezius motor units differs for voluntary contractions and instructed muscle rest. Exp Brain Res 2010; 208:203-15. [PMID: 21063691 DOI: 10.1007/s00221-010-2471-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2010] [Accepted: 10/19/2010] [Indexed: 10/18/2022]
Abstract
This study examined discharge rate modulation at respiratory (0-0.5 Hz) and beta (16-32 Hz) frequencies in trapezius motor units active during voluntary contractions and during periods of instructed rest under conditions of low and high psychosocial stress. In separate sessions, single motor unit activity was recorded from the trapezius muscle of healthy women during low-intensity voluntary contractions and during periods of instructed muscle rest that followed voluntary contractions. The level of psychosocial stress during periods of instructed muscle rest was manipulated using a verbal math task combined with social evaluative threat which increased perceived anxiety, heart rate, and blood pressure (P ≤ 0.002). Discharge rate modulation was quantified by the mean power of motor unit discharge rate profiles within frequency bands of interest. Under low stress conditions, motor units active during instructed rest had greater power at 0-0.5 Hz (P = 0.002) and less power at 16-32 Hz (P = 0.009) compared to those active during voluntary contraction. Exposure to the stressor increased the amount of motor unit activity during instructed rest (P = 0.021) but did not alter the power of discharge rate modulation at 0-0.5 Hz (P = 0.391) or 16-32 Hz (P = 0.089). These results indicate that sustained motor unit activity during periods of instructed muscle rest has a lesser contribution from inputs at beta frequencies and a greater contribution from inputs at respiratory frequencies than present during low-intensity voluntary contractions. Furthermore, increases in motor unit activity when exposed to stressors during periods of instructed rest are not caused by changes in inputs at respiratory or beta frequencies.
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Affiliation(s)
- Jennifer L Stephenson
- Department of Physical Medicine & Rehabilitation, Applied Neuromuscular Physiology Lab, Physical Therapy Program, University of Colorado Denver School of Medicine, Aurora, CO 80045, USA
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