Influence of Interhemispheric Interactions on Paretic Hand Movement in Chronic Subcortical Stroke

Abstract

In patients with chronic stroke, the primary motor cortex of the intact hemisphere (M1_intact) may influence functional recovery, possibly through transcallosal effects exerted over Ml in the lesioned hemisphere (Ml_lesioned). Here, we studied interhemispheric inhibition (IHI) between Ml_intact and M1_lesioned in the process of generation of a voluntary movement by the paretic hand in patients with chronic subcortical stroke and in healthy volunteers. IHI was evaluated in both hands preceding the onset of unilateral voluntary index finger movements (paretic hand in patients, right hand in controls) in a simple reaction time paradigm. IHI at rest and shortly after the Go signal were comparable in patients and controls. Closer to movement onset, IHI targeting the moving index finger turned into facilitation in controls but inhibition still continued in patients, a finding that correlated with poor motor performance. IHI targeting the resting finger remained deep all through the reaction time. In case of intact hand movement, IHI targeting the moving fingers showed similar facilitation with that in control subjects. These results suggest an abnormally high interhemispheric inhibitory drive from M1_intact to M1_lesioned in the paretic hand movement. It is conceivable that this abnormality could adversely influence motor recovery in some patients with subcortical stroke.