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

Mirror contractions refer to unintended contractions of the contralateral homologous muscles during voluntary unilateral contractions or movements. Exaggerated mirror contractions have been found in several neurological diseases and indicate dysfunction or lesion of the cortico-spinal pathway. The present study investigates mirror contractions and the associated interhemispheric and corticomuscular interactions in adults with spinal cord injury (SCI) - who present a lesion of the cortico-spinal tract - compared to able-bodied participants (AB). Eight right-handed adults with chronic cervical SCI and ten age-matched right-handed able-bodied volunteers performed sets of right elbow extensions at 20% of maximal voluntary contraction. Electromyographic activity (EMG) of the right and left elbow extensors, interhemispheric coherence over cerebral sensorimotor regions evaluated by electroencephalography (EEG) and corticomuscular coherence between signals over the cerebral sensorimotor regions and each extensor were quantified. Overall, results revealed that participants with SCI exhibited (1) increased EMG activity of both active and unintended active limbs, suggesting more mirror contractions, (2) reduced corticomuscular coherence between signals over the left sensorimotor region and the right active limb and increased corticomuscular coherence between the right sensorimotor region and the left unintended active limb, (3) decreased interhemispheric coherence between signals over the two sensorimotor regions. The increased corticomuscular communication and decreased interhemispheric communication may reflect a reduced inhibition leading to increased communication with the unintended active limb, possibly resulting to exacerbated mirror contractions in SCI. Finally, mirror contractions could represent changes of neural and neuromuscular communication after SCI.

Temporal Dynamics of Corticomuscular Coherence Reflects Alteration of the Central Mechanisms of Neural Motor Control in Post-Stroke Patients.

The neural control of muscular activity during a voluntary movement implies a continuous updating of a mix of afferent and efferent information. Corticomuscular coherence (CMC) is a powerful tool to explore the interactions between the motor cortex and the muscles involved in movement realization. The comparison of the temporal dynamics of CMC between healthy subjects and post-stroke patients could provide new insights into the question of how agonist and antagonist muscles are controlled related to motor performance during active voluntary movements. We recorded scalp electroencephalography activity, electromyography signals from agonist and antagonist muscles, and upper limb kinematics in eight healthy subjects and seventeen chronic post-stroke patients during twenty repeated voluntary elbow extensions and explored whether the modulation of the temporal dynamics of CMC could contribute to motor function impairment. Concomitantly with the alteration of elbow extension kinematics in post-stroke patients, dynamic CMC analysis showed a continuous CMC in both agonist and antagonist muscles during movement and highlighted that instantaneous CMC in antagonist muscles was higher for post-stroke patients compared to controls during the acceleration phase of elbow extension movement. In relation to motor control theories, our findings suggest that CMC could be involved in the online control of voluntary movement through the continuous integration of sensorimotor information. Moreover, specific alterations of CMC in antagonist muscles could reflect central command alterations of the selectivity in post-stroke patients.

Behavioural and cerebral asymmetries of mirror movements are specific to rhythmic task and related to higher attentional and executive control.

Mirror movements (MM) refer to the involuntary movements or contractions occurring in homologous muscles contralateral to the unilateral voluntary movements. This behavioural manifestation increases in elderly. In right-handed adults, some studies report asymmetry in MM production, with greater MM in the right dominant hand during voluntary movements of the left non-dominant hand than the opposite. However, other studies report contradictory results, suggesting that MM asymmetry could depend on the characteristics of the task. The present study investigates the behavioural asymmetry of MM and its associated cerebral correlates during a rhythmic task and a non-rhythmic task using low-force contractions (i.e., 25 % MVC). We determined the quantity and the intensity of MM using electromyography (EMG) and cerebral correlates through electroencephalography (EEG) in right-handed healthy young and middle-aged adults during unimanual rhythmic vs. non-rhythmic tasks. Overall, results revealed (1) behavioural asymmetry of MM specific to the rhythmic task and irrespective of age, (2) cerebral asymmetry of motor activations specific to the rhythmic task and irrespective of age and (3) greater attentional and executive activations in the rhythmic task compared to the non-rhythmic task. In line with our hypotheses, behavioural and cerebral motor asymmetries of MM seem to be specific to the rhythmic task. Results are discussed in terms of cognitive-motor interactions: greater attentional and executive control required in the rhythmic tasks could contribute to the increased occurrence of involuntary movements in both young and middle-aged adults.

Spastic co-contraction is directly associated with altered cortical beta oscillations after stroke.

OBJECTIVE: Spastic co-contraction is a motor-disabling form of muscle overactivity occurring after a stroke, contributing to a limitation in active movement and a certain level of motor impairment. The cortical mechanisms underlying spastic co-contraction remain to be more fully elucidated, the present study aimed to investigate the role of the cortical beta oscillations in spastic co-contraction after a stroke. METHOD: We recruited fifteen post-stroke participants and nine healthy controls. The participants were asked to perform active elbow extensions. In the study, multimodal analysis was performed to combine the evaluation of three-dimensional elbow kinematics, the elbow muscles electromyographic activations, and the cortical oscillatory activity. RESULTS: The movement-related beta desynchronization was significantly decreased in post-stroke participants compared to healthy participants. We found a significant correlation between the movement-related beta desynchronization and the elbow flexors activation during the active elbow extension in post-stroke participants. When compared to healthy participants, post-stroke participants exhibited significant alterations in the elbow kinematics and greater muscle activation levels. CONCLUSIONS: Cortical beta oscillation alterations may reflect an important neural mechanism underlying spastic co-contraction after a stroke. SIGNIFICANCE: Measuring the cortical oscillatory activity could be useful to further characterize neuromuscular plasticity induced by recovery or therapeutic interventions.

Spastic co-contraction, rather that spasticity, is associated with impaired active function in adults with acquired brain injury: A pilot study.

OBJECTIVE: To elucidate the adverse consequences of spasticity and spastic co-contraction of elbow flexors on motor impairment and upper limb functional limitation. DESIGN: A pilot case-controlled prospective observational study. SUBJECTS: Ten brain-injured adults, and 10 healthy controls. METHODS: The co-contraction index was computed from electromyographic recordings of elbow flexors during sub-maximal (25% Maximal Voluntary Contraction) isometric elbow extension. Spasticity was assessed with the Tardieu scale, upper limb limitation using a goniometer during active elbow extension, motor selectivity with the Fugl-Meyer Assessment for the upper limb, and motor function with the Action Research Arm Test. RESULTS: Greater co-contraction occurred in patients with brain injury compared with controls. In contrast to spasticity, strong associations were found between the co-contraction index, the limitation of active elbow extension, the Fugl-Meyer Assessment, and the Action Research Arm Test. CONCLUSION: This pilot study suggests that spastic co-contraction rather than spasticity is an important factor in altered upper limb motricity in subjects with brain injury, leading to abnormal restricting arm movement patterns in subjects with more severe motor impairment. Practical applications directly concern the pre- and post-therapeutic evaluation of treatments aimed at improving motor skills in subjects with brain injury.

Lateralized inhibition of symmetric contractions is associated with motor, attentional and executive processes.

Mirror movements (MM) refer to involuntary contractions occurring in homologous muscles contralateral to the voluntary movements. In right-handers, greater MM occur in the right hand during movements of the non-dominant left hand than conversely. However, it remains to know if such behavioural asymmetry of MM relies only on motor processes or if it is also related to attentional and executive processes. This study explores MM behavioural asymmetry and its cerebral correlates with electroencephalography in 14 right-handed healthy adults. We investigated the quantity and the intensity of MM and the associated task-related power changes in the beta band over central regions (motor processes), in the alpha band over the parietal regions (attentional processes) and in the theta band over frontal regions (executive processes). Behavioural results revealed greater MM in the right hand when the left hand was active than the reverse. This behavioural asymmetry was associated with asymmetry in the cortical activations over motor areas. Greater MM in the right hand correlated with activation over the contralateral left motor region, revealing that selective inhibition of one hand induced activation of the motor cortex leading to MM. In addition, increased cortical activations over parietal and fronto-mesial regions suggest that an increase of attentional and executive processes is required to inhibit one hand, independently of its side. All in all, this study highlights that side-specific motor and non-side-specific attentional and executive processes are associated to the MM asymmetry.

Mirror Movements are Linked to Executive Control in Healthy and Brain-injured Adults.

It has been shown that brain-injured patients (BIP) have exacerbated mirror movements (MM). MM are involuntary contractions occurring in homologous muscles contralateral to voluntary movements, particularly in distal upper limb muscles. Attentional and inhibitory processes have been proposed as key factors to explain the level of MM. However, the link between MM and attentional/inhibitory processes has never been formally tested. The present study aims to test this link in 24 right-handed healthy adults and eight chronic BIP. We investigated the link between the amount/intensity of MM and attentional/inhibitory functions. For each participant, MM produced on each limb were assessed with two tasks, and the attentional and inhibitory functions were assessed with six neuropsychological tests. Our results showed (1) a greater amount and intensity of MM and (2) a selective deficit in sustained attention in BIP compared to healthy adults. Moreover, (3) in all participants - independent of the type of task used to evaluate MM - the amount and intensity of MM was predicted by the level of executive control, assessed by the Trail Making Test. High level of MM was associated with weak executive control abilities. This study is the first to highlight the link between MM and executive functioning, which may have implications for rehabilitation in BIP.