Side of lesion influences bilateral activation in chronic, post-stroke hemiparesis.

OBJECTIVE To determine how stroke lesion side and ipsilateral motor pathways influence motor performance in bimanual tasks. METHODS Stroke subjects and age-matched controls participated in two data collection sessions: (1) motor behavior was examined during a movement task performed in unimanual, bimanual symmetric, and bimanual asymmetric conditions and (2) transcranial magnetic stimulation was used to examine the excitability of ipsilateral and contralateral motor pathways during isometric unilateral and bilateral muscle activation. RESULTS Subjects with left hemiparesis and controls demonstrated a performance differential between symmetric and asymmetric motor tasks compared to subjects with right hemiparesis. Contralateral motor pathway excitability decreased and ipsilateral pathway excitability increased during bilateral compared to unilateral activation in control subjects and in the non-affected arm of stroke subjects. Responses in the affected arm were similar to controls in subjects with left hemiparesis but not right. CONCLUSIONS Changes in motor pathway excitability during bilateral activation may promote more stable performance of symmetric movements. In individuals with hemiparesis, the side of lesion influences neural and behavioral aspects of bimanual tasks. Those with injuries to the right hemisphere exhibit coupling that is more similar to age-matched controls. SIGNIFICANCE The efficacy of bilateral training interventions may be different between people with lesions in the left and right hemispheres.