Interhemispheric Pathways Are Important for Motor Outcome in Individuals with Chronic and Severe Upper Limb Impairment Post Stroke

Figure 1

TMS-evoked TCI. (a) A schematic diagram of TMS-evoked TCI. Participants maintain a unilateral voluntary background muscle contraction in the arm ipsilateral to the TMS coil. A single TMS pulse is delivered to the motor cortex. The TMS pulse activates transcallosal pathways which transmit an inhibitory signal (─) to the active motor cortex. This elicits a transient quiescence in the background EMG in the active muscle. In the present example, TMS is delivered over the contralesional hemisphere to elicit the contra-iSP. TCI was also evoked with TMS delivered over the ipsilesional hemisphere to elicit the ipsi-iSP. (b) and (c) Rectified EMG data collected during a TMS session from a representative participant with mild to moderate impairment. (b) The motor evoked potential collected from the contralateral ECR muscle during the TCI procedure. (c) The EMG activity and iSP collected simultaneously from the ipsilateral ECR muscles. The iSP_mean ratio was calculated as: iSP mean EMG (blue line)/prestimulus mean EMG (red line). For ease of viewing, only 150 ms of the total 450 ms recording window is displayed. (d) and (e) Representative TCI output from the cohort of individuals with severe arm impairment. (d) The output from an individual when TCI was present. (e) The output from an individual when TCI was not present.

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