Right in Comparison to Left Cerebral Hemisphere Damage by Stroke Induces Poorer Muscular Responses to Stance Perturbation Regardless of Visual Information.

OBJECTIVE: Fast and scaled muscular activation is required to recover body balance following an external perturbation. An issue open to investigation is the extent to which the cerebral hemisphere lesioned by stroke leads to asymmetric deficits in postural reactive responses. In this experiment, we aimed to compare muscular responses to unanticipated stance perturbations between individuals who suffered unilateral stroke either to the right or to the left cerebral hemisphere.

METHODS: Stance perturbations were produced by releasing a load attached to the participant's trunk, inducing fast forward body oscillation. Electromyography was recorded from the gastrocnemius medialis and biceps femoris muscles. Muscular activation from age-matched healthy individuals was taken as reference.

RESULTS: Analysis indicated that damage to the right hemisphere induced delayed activation onset, and lower rate and magnitude of activation of the proximal and distal muscles of the paretic leg. Those deficits were associated with stronger activation of the nonparetic leg. Comparisons between left hemisphere damage and controls showed deficits limited to activation of the biceps femoris of the paretic leg. Manipulation of visual information led to no significant effects on muscular responses.

CONCLUSIONS: These results suggest that right cerebral hemisphere damage by stroke leads to more severe deficits in the generation of reactive muscular responses to stance perturbation than damage to the left cerebral hemisphere regardless of visual information.