Facilitation of Motor Evoked Potentials by Voluntary Muscle Contraction in Post-stroke Patients

Objective: To identify interhemispheric differences of facilitation of motor evoked potentials (MEPs) from the affected and unaffected hemispheres after stroke and to correlate the differences with their motor functions. Method: MEPs induced by cortical stimulation were obtained at both thenar muscles in 28 post-stroke patients. Motor cortex was stimulated with 110% and 130% intensity of threshold during rest, minimal and moderate voluntary muscle contraction. We analyzed the MEP amplitude or area in 130% threshold intensity at rest (Rmax) and on moderate contraction (Fmax). The ratio of Fmax in both hemispheres (interhemispheric facilitation ratio, FR) and the ratio of Fmax to Rmax (facilitation index, PI) were also analyzed. Pinch strength, Brunnstrom stage, and Jebsen hand function test were included evaluating their motor functions. Results: MEPs could not be evoked in cases whose Brunnstrom stage of hand was under 3. In response group, amplitude and area of Fmax of unaffected side were significantly larger than those of affected side (p 0.5, PI of unaffected side was significantly greater than that of affected side (p