Transcallosal inhibition does not influence subacute motor recovery in mild-to-moderate stroke

After stroke, upper extremity (UE) motor recovery may be mediated in part by transcallosal projections between hemispheres. The interhemispheric competition model posits that transcallosal inhibition (TI) from the contralesional hemisphere is abnormally strengthened following stroke and interferes with motor recovery. This model has recently been questioned. In this longitudinal study, we aimed to definitively confirm or refute a maladaptive role of contralesional TI in subacute motor recovery. We assessed 30 mild-to-moderately impaired subjects over the 6 months following ischaemic stroke. We tracked contralesional TI and motor functions in the proximal and distal segments of the paretic UE. We used transcranial magnetic stimulation to examine the ipsilateral silent period in an arm and hand muscle. We used quantitative and clinical testing to examine deficits in muscle strength, motor control and individuation; UE segmental impairment; and UE activity limitation. We assessed the relationships of contralesional TI to motor functions in the subacute period. Despite recovery of most motor functions in the proximal and distal UE, contralesional TI was largely static and unrelated to recovery of any motor function. There were inconsistent associations between stronger TI, less hand impairment, and less activity limitation in the subacute period overall. We found no compelling evidence to suggest a maladaptive role of contralesional TI in UE motor recovery in mild-to-moderately impaired stroke subjects. The scattered associations between stronger TI and better levels of paretic UE function suggest a potential supportive role rather than a limiting one. These findings challenge the validity of the interhemispheric competition model in the subacute recovery period, and prompt reconsideration of neuromodulatory strategies that subacutely target contralesional TI.