ROLE OF THE STRIATUM, CEREBELLUM AND FRONTAL LOBES IN THE AUTOMATIZATION OF A REPEATED VISUOMOTOR SEQUENCE OF MOVEMENTS

Recently, Doyon et al. [20] demonstrated that lesions to both the stri atum and to the cerebellum in humans produce a similar deficit in the learning of a repeated visuomotor sequence, which occurs late in the a cquisition process. We now report the results of two experiments that were designed to examine whether this impairment was due to a lack of automatization of the repeating sequence of finger movements by using a dual-task paradigm and by testing for long-term retention of this sk ill. In Experiment 1, the performance of groups of patients with Parki nson's disease, or with damage to the cerebellum or to the frontal lob es, was compared to that of matched control subjects on the Repeated S equence Test (primary task) and the Brooks' Matrices Test (secondary t ask). These two tests were administered concomitantly in both early an d late learning phases of the visuomotor sequence. Overall, the groups did not differ in their ability to execute the primary task. By contr ast, in accordance with the predictions, patients in Stages 2-3 of Par kinson's disease or with a cerebellar lesion failed to reveal the expe cted increase in performance on the secondary task seen with learning, suggesting that the latter groups of patients did not have access to the same level of residual cognitive resources to complete the matrice s compared to controls. In Experiment 2, the same groups of patients a nd control subjects were retested again 10-18 months later. They were given four blocks of 100 trials each of the repeating sequence task, f ollowed by a questionnaire and a self-generation task that measured th eir declarative knowledge of that sequence. The results revealed a lon gterm retention impairment only in patients who changed from Stage I t o Stage II of the disease (suggesting further striatal degeneration) d uring the one-year interval, or who had a cerebellar lesion. By contra st, performance of the three clinical groups did not differ from contr ols on declarative memory tests. These findings suggest that both the striatum and the cerebellum participate to the automatization process during the late (slow) learning stage of a sequence of finger movement s and that these structures also play a role in the neuronal mechanism subserving long-term retention of such a motor sequence behavior. (C) 1998 Elsevier Science Ltd. All rights reserved.