1
|
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.
Collapse
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
| |
Collapse
|
2
|
Torell F. Evaluation of stretch reflex synergies in the upper limb using principal component analysis (PCA). PLoS One 2023; 18:e0292807. [PMID: 37824570 PMCID: PMC10569523 DOI: 10.1371/journal.pone.0292807] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Accepted: 09/28/2023] [Indexed: 10/14/2023] Open
Abstract
The dynamic nature of movement and muscle activation emphasizes the importance of a sound experimental design. To ensure that an experiment determines what we intend, the design must be carefully evaluated. Before analyzing data, it is imperative to limit the number of outliers, biases, and skewness. In the present study, a simple center-out experiment was performed by 16 healthy volunteers. The experiment included three load conditions, two preparatory delays, two perturbations, and four targets placed along a diagonal path on a 2D plane. While the participants performed the tasks, the activity of seven arm muscles were monitored using surface electromyography (EMG). Principal component analysis (PCA) was used to evaluate the study design, identify muscle synergies, and assess the effects of individual quirks. With PCA, we can identify the trials that trigger stretch reflexes and pinpoint muscle synergies. The posterior deltoid, triceps long head, and brachioradialis were engaged when targets were in the direction of muscle shortening and the perturbation was applied in the opposite direction. Similarly, the pectoralis and anterior deltoid were engaged when the targets were in the direction of muscle shortening and the perturbation was applied in the opposite direction. The stretch reflexes were not triggered when the perturbation brought the hand in the direction of, or into the target, except if the muscle was pre-loaded. The use of PCA was also proven valuable when evaluating participant performance. While individual quirks are to be expected, failure to perform trials as expected can adversely affect the study results.
Collapse
Affiliation(s)
- Frida Torell
- Physiology Section, Department of Integrative Medical Biology, Umeå University, Umeå, Sweden
| |
Collapse
|
3
|
Hodgson DD, King JA, Darici O, Dalton BH, Cleworth TW, Cluff T, Peters RM. Visual feedback-dependent modulation of arousal, postural control, and muscle stretch reflexes assessed in real and virtual environments. Front Hum Neurosci 2023; 17:1128548. [PMID: 37082148 PMCID: PMC10110857 DOI: 10.3389/fnhum.2023.1128548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Accepted: 03/14/2023] [Indexed: 04/07/2023] Open
Abstract
IntroductionThe mechanisms regulating neuromuscular control of standing balance can be influenced by visual sensory feedback and arousal. Virtual reality (VR) is a cutting-edge tool for probing the neural control of balance and its dependence on visual feedback, but whether VR induces neuromodulation akin to that seen in real environments (eyes open vs. closed or ground level vs. height platform) remains unclear.MethodsHere we monitored 20 healthy young adults (mean age 23.3 ± 3.2 years; 10 females) during four conditions of quiet standing. Two real world conditions (eyes open and eyes closed; REO and REC) preceded two eyes-open virtual ‘low’ (ground level; VRL) and ‘high’ (14 m height platform; VRH) conditions. We measured arousal via electrodermal activity and psychosocial questionnaires rating perceived fear and anxiety. We recorded surface electromyography over the right soleus, medial gastrocnemius, and tibialis anterior, and performed force plate posturography. As a proxy for modulations in neural control, we assessed lower limb reflexive muscle responses evoked by tendon vibration and electrical stimulation.ResultsPhysiological and perceptual indicators of fear and anxiety increased in the VRH condition. Background soleus muscle activation was not different across conditions; however, significant increases in muscle activity were observed for medial gastrocnemius and tibialis anterior in VRH relative to REO. The mean power frequency of postural sway also increased in the VRH condition relative to REO. Finally, with a fixed stimulus level across conditions, mechanically evoked reflexes remained constant, while H-reflex amplitudes decreased in strength within virtual reality.DiscussionNotably, H-reflexes were lower in the VRL condition than REO, suggesting that these ostensibly similar visual environments produce different states of reflexive balance control. In summary, we provide novel evidence that VR can be used to modulate upright postural control, but caution that standing balance in analogous real and virtual environments may involve different neural control states.
Collapse
Affiliation(s)
| | - Jordan A. King
- Biomedical Engineering, University of Calgary, Calgary, AB, Canada
| | - Osman Darici
- Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
| | - Brian H. Dalton
- School of Health and Exercise Sciences, University of British Columbia Okanagan, Kelowna, BC, Canada
| | | | - Tyler Cluff
- Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
| | - Ryan M. Peters
- Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
- Biomedical Engineering, University of Calgary, Calgary, AB, Canada
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- *Correspondence: Ryan M. Peters,
| |
Collapse
|
4
|
Spinal Cord Circuits: Models and Reality. NEUROPHYSIOLOGY+ 2022. [DOI: 10.1007/s11062-022-09927-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
|
5
|
Dimitriou M. Human muscle spindles are wired to function as controllable signal-processing devices. eLife 2022; 11:78091. [PMID: 35829705 PMCID: PMC9278952 DOI: 10.7554/elife.78091] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 06/29/2022] [Indexed: 12/26/2022] Open
Abstract
Muscle spindles are encapsulated sensory organs found in most of our muscles. Prevalent models of sensorimotor control assume the role of spindles is to reliably encode limb posture and movement. Here, I argue that the traditional view of spindles is outdated. Spindle organs can be tuned by spinal γ motor neurons that receive top-down and peripheral input, including from cutaneous afferents. A new model is presented, viewing γ motor activity as an intermediate coordinate transformation that allows multimodal information to converge on spindles, creating flexible coordinate representations at the level of the peripheral nervous system. That is, I propose that spindles play a unique overarching role in the nervous system: that of a peripheral signal-processing device that flexibly facilitates sensorimotor performance, according to task characteristics. This role is compatible with previous findings and supported by recent studies with naturalistically active humans. Such studies have so far shown that spindle tuning enables the independent preparatory control of reflex muscle stiffness, the selective extraction of information during implicit motor adaptation, and for segmental stretch reflexes to operate in joint space. Incorporation of advanced signal-processing at the periphery may well prove a critical step in the evolution of sensorimotor control theories.
Collapse
Affiliation(s)
- Michael Dimitriou
- Physiology Section, Department of Integrative Medical Biology, Umeå University, Umeå, Sweden
| |
Collapse
|
6
|
Affiliation(s)
- David Burke
- Department of Neurology, Royal Prince Alfred Hospital and The University of Sydney, New South Wales, 2006, Australia
| |
Collapse
|
7
|
Affiliation(s)
- Michael Dimitriou
- Physiology Section, Department of Integrative Medical Biology, University of Umeå, Umeå, Sweden
| |
Collapse
|