Transcallosal inhibition in chronic subcortical stroke.

Movements of the paretic hand in patients with chronic subcortical stroke are associated with high interhemispheric inhibition (IHI) targeting the motor cortex in the lesioned hemisphere relative to healthy controls. The purpose of this investigation was to determine whether this abnormality also involves IHI operating during movements of the non-paretic hand. Here, we studied IHI in the process of generation of voluntary index finger movements by the paretic and non-paretic hands in a simple reaction time paradigm in a group of patients with chronic subcortical stroke. With movements of the non-paretic index finger, IHI targeting the contralateral primary motor cortex ((c)M1) decreased progressively to turn into facilitation at around movement onset, similar to healthy controls. In contrast, movements of the paretic index finger resulted in significantly deeper inhibition at all premovement timings relative to the non-paretic hand. In conclusion, these results document a deeper premovement IHI with paretic than non-paretic hand movements of patients with chronic subcortical stroke, a possible mechanism underlying deficits in motor control.