Procedural visuo-motor learning in Parkinson's disease and cerebellar degeneration

Abstract

The purpose of this study was to evaluate the contributions of basal ganglia and cerebellum to procedural visuo-motor learning. We studied 19 medicated patients with Parkinson's disease (PD), 10 with cerebellar cortical atrophy (CCA), 5 with olivopontocerebellar atrophy (OPCA), and 30 age-matched normal volunteers (NV). Subjects were seated in front of a computer screen and a keyboard with four marked response keys. An asterisk appeared in one of four positions spaced horizontally on the screen and aligned above the response keys. The subjects had to push the key aligned with the asterisk that appeared. The asterisk did not disappear until the correct button was pushed, upon which the next stimulus appeared. Each subject completed seven blocks of 100 trials. In blocks 1, 2, and 7, the sequence of asterisk positions was random. Block 1 was considered practice and discarded from further analysis. In blocks 2-6 a 10-trial sequence of asterisk positions repeated itself 10 times. The subjects were not told that a repeating sequence was being presented. Nevertheless, 5 patients with PD (26%), 1 with CCA(10%), 1 with OPCA(20%), and 8 NV(27%) detected the repeating sequence and were able to reproduce at least 5 consecutive positions. These findings are considered to reflect declarative learning. PD patients and NV who did not detect the repeating sequence showed an equivalent, progressive shortening of reaction time (RT) and decrease in error rate (ER) across blocks 2-6. (p<0.001), and a rebound increase in RT and ER in block 7 (p<0.001). These findings were considered to reflect procedural learning. In CCA and OPCA patients who did not detect the repeating sequence, RT and ER remained constant across all blocks. These results demonstrate impairment of procedural visuo-motor learning in cerebellar degeneration and add to the evidence for a role of the cerebellum in different types of implicit memory function.