ANALYSIS OF BALLISTIC MOVEMENTS IN ATAXIC HEMIPARESIS FOLLOWING A PONTINE STROKE

Although cerebellar-like ataxia is a well known component of the ataxi c hemiparesis (AH), the mechanism of hypermetria in AH has not been es tablished. We describe a patient presenting a left AH following a righ t pontine infarction. We investigated the ballistic flexion movements of both wrists and the associated agonist and antagonist electromyogra phic (EMG) activities, before and after addition of inertial loads. At the time of motion analysis, neurological examination showed cerebell ar-like dysmetria of the left side but the patient had recovered a nor mal strength. In the basal state (without addition of loads), movement s of the left wrist were hypermetric. The duration of the agonist EMG activity was prolonged and the onset latency of the antagonist EMG act ivity was not delayed. Moreover, when a mass was added, the hypermetri a was unchanged because the patient was unable to adapt appropriately neither the agonist, nor the antagonist EMG activity. We suggest that the hypermetria was due to an imbalance between the duration of the ag onist EMG activity(the launching force) and the duration of the antago nist EMG activity (the braking force).