Movement related potentials in acutely induced weakness and stroke

Weakness is a common symptom of neurological illness, and recovery may occur via restorative or compensatory mechanisms. Functional imaging studies have shown varied patterns of activity in motor areas following recovery from stroke. Movement related potentials (MRP) reflect the activity in primary and non-primary motor areas. We recorded MRPs in association with index finger abduction in six normal volunteers before and after induced weakness of a hand muscle and in six stroke patients with subcortical lesions and weakness affecting the arm. In both groups of subjects the greatest change was observed in the motor potential component of the MRP. On average, the motor potential had its greatest amplitude and duration at the time of the greatest weakness and became smaller with recovery. In artificially-induced weakness, the MRP had an earlier onset latency (P=0.042) and a greater early BP component (P=0.05) for the weakened finger. For the stroke subjects overall, the peak and NS′ amplitudes were largest for the initial study and declined thereafter. Similar but smaller changes were present for movements of the clinically unaffected side. The increased motor potential is therefore consistent with increased activity in the motor cortex, and this may occur as compensation for weakness in both normals and after stroke.