The relationship between the severity of motor impairment and motor cortical excitability in the unaffected hemisphere after unilateral stroke

The present study has investigated the relationship between the severity of motor impairment and motor cortex excitability in the unaffected hemisphere (UH) after unilateral stroke. Forty-four patients with hemiparesis after single event of unilateral stroke were investigated. We used paired conditioning-test transcranial magnetic stimulation (TMS) to investigate intracortical inhibition (ICI) and intracortical facilitation (ICF) in the UH. Responses from the patients with reliable motor-evoked potentials (MEP) on the affected side (mild group) were compared with those of patients without MEP (severe group) and those of a population of 15 control subjects. ICI at interstimulus interval (ISI) of 1 and 5 ms was significantly reduced in the affected hemisphere in comparison to the control group. We found that ICF at ISI of 20 ms was significantly reduced in the UH of patients compared with control group. ICI at ISI of 1 ms was significantly reduced in the UH only in the mild group with cortical lesion. Motor cortex disinhibition and reduced facilitation may occur after unilateral hemispheric stroke. This change was demonstrated only in patients with mild cortical lesion, which suggests that motor cortex disinhibition is indicative of compensatory mechanisms.