Recovery of hypermetria after a cerebellar stroke occurs as a multistage process

In a prospective study, we repeatedly recorded fast goal-directed wrist movements of 8 patients who had experienced an acute cerebellar hypermetria due to a stroke and who had subsequently recovered clinically. Movements and the associated agonist and antagonist electromyographic (EMG) activities were recorded before and after addition of inertial loads. Four stages characterized the recovery process. At stage 1, hypermetria was present in the basal state and was not modified by the addition of inerital loads. At stage 2, hypermetria, which was present in the basal state, was enlarged by mass addition. At stage 3, hypermetria was absent in the basal state, but was revealed by an inertial load increase. At stage 4, as in healthy subjects, there was no hypermetria without or with addition of inertial loads. At stage 1, the patients presented several defects. (1) Facing an increased inertia, they could not increase their agonist EMG activity. (2) The onset latency of their antagonist EMG activity was delayed. (3) Facing an increased inertia, they could not increase their antagonist EMG activity. Among these three defects, the first disappeared at stage 2, the second at stage 3, and the third at stage 4.