Overactivation of the supplementary motor area in chronic stroke patients

Stroke induces a loss of neural function, but it triggers a complex amount of mechanisms to compensate the associated functional impairment. The present study aims to increase our understanding of the functional reshape of the motor system observed in chronic stroke patients during the preparation and the execution of movements. A cohort of 14 chronic stroke patients with a mild-to-moderate hemiparesis and 14 matched healthy controls were included in this study. Participants were asked to perform a bimanual reaction time task synchronizing alternated responses to the presentation of a visual cue. We used Laplacian-transformed EEG activity (LT-EEG) recorded at the locations Cz and C3/C4 to study the response-locked components associated with the motor system activity during the performance of this task. Behaviorally, patients showed larger variable errors than controls in synchronizing the frequency of execution of responses to the interstimulus interval, as well as slower responses compared with controls. LT-EEG analysis showed that whereas control participants increased their supplementary motor area (SMA) activity during the preparation of all responses, patients only showed an increment of activity over this area during their first response of the sequence. More interestingly, patients showed a clear increment of the LT-EEG activity associated with SMA shortly after motor responses as compared to the control participants. Finally, patients showed a hand-dependent inhibitory activity over motor areas ipsilateral to the response hand. Overall, our findings reveal drastic differences in the temporal dynamics of the LT-EEG components associated with the activity over motor and premotor cortices in chronic stroke patients compared with matched control participants during alternated hand responses.