Influence of interhemispheric interactions on motor function in chronic stroke

TLDR

In chronic stroke patients, the intact primary motor cortex may influence recovery through transcallosal effects on the lesioned hemisphere. The study examined interhemispheric inhibition between the intact and lesioned M1 during voluntary index‑finger movements of the paretic hand in chronic subcortical stroke patients and healthy controls. IHI was measured before and after the Go signal in a simple reaction‑time paradigm. At rest and shortly after the Go signal, IHI was comparable in patients and controls, but just before movement onset the intact hemisphere’s inhibition turned into facilitation in controls while remaining strong in patients, correlating with poorer motor performance and indicating an abnormally high inhibitory drive that could hinder recovery.

Abstract

Abstract In patients with chronic stroke, the primary motor cortex of the intact hemisphere (M1 intact hemisphere ) may influence functional recovery, possibly through transcallosal effects exerted over M1 in the lesioned hemisphere (M1 lesioned hemisphere ). Here, we studied interhemispheric inhibition (IHI) between M1 intact hemisphere and M1 lesioned hemisphere 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 remained deep in patients, a finding that correlated with poor motor performance. These results document an abnormally high interhemispheric inhibitory drive from M1 intact hemisphere to M1 lesioned hemisphere in the process of generation of a voluntary movement by the paretic hand. It is conceivable that this abnormality could adversely influence motor recovery in some patients with subcortical stroke, an interpretation consistent with models of interhemispheric competition in motor and sensory systems.