Contrôle de la contraction musculaire volontaire après un traumatisme médullaire cervical : Etude de la réorganisation des activations musculaires et corticales

The realization of a motor action involves simultaneous activation of both agonist and antagonist muscles controlled by the central nervous system. Following spinal cord injury, damage to the spinal cord causes both a loss of motor efficiency and changes in the control of muscle activations. In the present work, we studied the reorganization of muscle activations, cortical activations and corticomuscular interactions (ICM) in spinal cord injured (SCI) and able-bodied (AB) participants during voluntary isometric contractions in flexion and extension around the elbow joint. In extension, our results showed altered capacity of maximum force production in SCI participants, associated with increased muscle activations, similar cortical activation and decreased involvement of M1 in the control of muscle activations when compared to AB participants. In flexion, the force capacities, cortical activations and ICM were similar between SCI and AB participants, but the activation of antagonistic muscles and the difficulty to inhibit the contraction were greater in SCI participants. For all participants in flexion, ICM were different depending on the function of the muscle groups. Taken together, these results suggest an alteration of the cortical control of spinal inhibitory mechanisms following a spinal cord injury, but suggest that the motor cortex remain functional to control a motor act despite the atrophy of the extensor muscles. These results could find clinical applications for the development of neuroprotheses involving simultaneous control of different muscle groups.La réalisation d'une action motrice implique l'activation simultanée des muscles agonistes et antagonistes contrôlés par le système nerveux central. Suite à un traumatisme médullaire, la détérioration de la moelle épinière entraine à la fois une perte d'efficience motrice et des modifications du contrôle des activations musculaires. Dans le cadre de ce travail de thèse, nous avons étudié la réorganisation des activations musculaires, des activations corticales et des interactions cortico-musculaires (ICM) d'un groupe traumatisé médullaire cervical (SCI) et d'un groupe contrôle (AB) lors de contractions isométriques volontaires en flexion et en extension autour de l'articulation du coude. En extension, nos résultats ont mis en évidence une altération des capacités de force maximale chez les participants SCI, associée à une augmentation des activations musculaires, une activation corticale identique au groupe AB et une diminution de l'implication du M1 dans le contrôle des activations musculaires. En flexion, la force développée, les activations corticales et les ICM étaient similaires chez les participants SCI et AB, mais l'activation des muscles antagonistes et la difficulté à inhiber la contraction étaient plus importantes chez les participants SCI. Pour l'ensemble des participants, les ICM en flexion étaient différentes selon la fonction des groupes musculaires. L'ensemble de ces résultats suggèrent une altération du contrôle cortical des mécanismes inhibiteurs spinaux de la contraction musculaire suite à une lésion médullaire mais indiquent que le cortex moteur est toujours activable et fonctionnel pour contrôler un acte moteur malgré l'atrophie des muscles extenseurs. Ces résultats pourraient trouver des applications cliniques pour l'élaboration de neuroprothèses nécessitant un contrôle simultané de différents groupes musculaires

Control of voluntary muscle contraction after a spinal cord injury : neuro-biomechanical study of the reorganization of muscular and cortical activations

La réalisation d’une action motrice implique l’activation simultanée des muscles agonistes et antagonistes contrôlés par le système nerveux central. Un traumatisme médullaire détériore la moelle épinière, entrainant une déficience motrice et des modifications du contrôle des activations musculaires. Ce travail étudie la réorganisation des activations musculaires, des activations corticales et des interactions corticomusculaires (ICM) d’un groupe traumatisé médullaire cervical (SCI) et d’un groupe contrôle (AB) lors de flexions et d'extensions isométriques autour de l’articulation du coude. En extension, nos résultats ont mis en évidence une altération des capacités de force maximale chez les SCI, associée à une augmentation des activations musculaires, une activation corticale identique aux AB et une diminution de l’implication du M1 dans le contrôle des activations musculaires. En flexion, la force développée, les activations corticales et les ICM étaient similaires chez les SCI et AB, mais les activations antagonistes et la difficulté à inhiber la contraction étaient plus importantes chez les SCI. Pour l’ensemble des participants, les ICM en flexion étaient différentes selon la fonction des groupes musculaires. Ces résultats suggèrent une altération du contrôle cortical des mécanismes inhibiteurs spinaux de la contraction musculaire après un traumatisme médullaire mais indiquent que le cortex moteur reste fonctionnel pour contrôler un acte moteur malgré l’atrophie des muscles extenseurs. Ces résultats pourraient trouver des applications cliniques pour l’élaboration de neuroprothèses nécessitant un contrôle simultané de différents groupes musculaires.The realization of a motor action involves simultaneous activation of both agonist and antagonist muscles controlled by the central nervous system. Following spinal cord injury, damage to the spinal cord causes both a loss of motor efficiency and changes in the control of muscle activations. In the present work, we studied the reorganization of muscle activations, cortical activations and corticomuscular interactions (ICM) in spinal cord injured (SCI) and able-bodied (AB) participants during voluntary isometric contractions in flexion and extension around the elbow joint. In extension, our results showed altered capacity of maximum force production in SCI participants, associated with increased muscle activations, similar cortical activation and decreased involvement of M1 in the control of muscle activations when compared to AB participants. In flexion, the force capacities, cortical activations and ICM were similar between SCI and AB participants, but the activation of antagonistic muscles and the difficulty to inhibit the contraction were greater in SCI participants. For all participants in flexion, ICM were different depending on the function of the muscle groups. Taken together, these results suggest an alteration of the cortical control of spinal inhibitory mechanisms following a spinal cord injury, but suggest that the motor cortex remain functional to control a motor act despite the atrophy of the extensor muscles. These results could find clinical applications for the development of neuroprotheses involving simultaneous control of different muscle groups

Corticomuscular Coherence and Motor Control Adaptations after Isometric Maximal Strength Training

International audienceStrength training (ST) induces corticomuscular adaptations leading to enhanced strength. ST alters the agonist and antagonist muscle activations, which changes the motor control, i.e., force production stability and accuracy. This study evaluated the alteration of corticomuscular communication and motor control through the quantification of corticomuscular coherence (CMC) and absolute (AE) and variable error (VE) of the force production throughout a 3 week Maximal Strength Training (MST) intervention specifically designed to strengthen ankle plantarflexion (PF). Evaluation sessions with electroencephalography, electromyography, and torque recordings were conducted pre-training, 1 week after the training initiation, then post-training. Training effect was evaluated over the maximal voluntary isometric contractions (MVIC), the submaximal torque production, AE and VE, muscle activation, and CMC changes during submaximal contractions at 20% of the initial and daily MVIC. MVIC increased significantly throughout the training completion. For submaximal contractions, agonist muscle activation decreased over time only for the initial torque level while antagonist muscle activation, AE, and VE decreased over time for each torque level. CMC remained unaltered by the MST. Our results revealed that neurophysiological adaptations are noticeable as soon as 1 week post-training. However, CMC remained unaltered by MST, suggesting that central motor adaptations may take longer to be translated into CMC alteration

Increased intensity of unintended mirror muscle contractions after cervical spinal cord injury is associated with changes in interhemispheric and corticomuscular coherences

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Effect of training status on beta-range corticomuscular coherence in agonist vs. antagonist muscles during isometric knee contractions

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Altered corticomuscular coherence after cervical spinal cord injury

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Does the force level modulate the cortical activity during isometric contractions after a cervical spinal cord injury?

IF=2.98International audienceObjective: This study investigated the effects of a cervical spinal cord injury (SCI) on the modulation of cortical desynchronization (ERD) during isometric contractions at different force levels. Methods: For 8 able-bodied (AB) and 6 cervical SCI participants, the net joint moment and electroencephalographic activities were recorded during isometric contractions of the right elbow in flexion and in extension at 3 force levels, that is, during intact and altered muscle contractions for SCI participants. The mean net moment and similar to 20 Hz ERD from C3 electroencephalographic electrode were compared between AB and SCI participants. Results: In flexion, that is, during intact contractions for all participants, the mean net moment and the ERD increased with the required force level. In extension, that is, during altered contractions, the mean net moment increased for 3 SCI participants while it was almost zero for 3 other SCI participants. The associated ERD increased with the required force level for all participants. Conclusion: The cortical desynchronization was modulated by the intent to modulate the force level rather than the actual modulation of the force production. Significance: These results provide a better understanding of the modulation of the cortical desynchronization following SCI. Potential applications could include the control of neuroprostheses. (C) 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved