ASSOCIATIVE LEARNING IN DEGENERATIVE NEOSTRIATAL DISORDERS - CONTRASTS IN EXPLICIT AND IMPLICIT REMEMBERING BETWEEN PARKINSONS AND HUNTINGTONS DISEASES

The performances of 12 patients with Parkinson's disease (PD), 16 with Huntington's disease (HD), and young and old healthy controls were as sessed on a number of tests of verbal and nonverbal declarative memory , on a test of nonmotor conditional associative learning (words and co lors), and on a number of reaction time (RT) tasks. The RT tasks consi sted of cued simple and choice reactions. The relationship between the precue and the imperative stimulus in the S1-S2 paradigm was nonarbit rary in the first series and arbitrary in the second series. The serie s with arbitrary S1-S2 associations was repeated across two successive blocks of trials. The rationale of the study was to investigate the f unction of the basal ganglia ''complex loop,'' and it was postulated t hat HD patients would show greater deficits because of greater involve ment of the caudate nucleus. The patients with HD had the slowest RTs. Across the two blocks with arbitrary S1-S2 associations, the patients with HD but not PD nevertheless showed evidence of learning in their precued RTs. In contrast, the patients with PD were better able to rem ember the associations in free recall than were the HD patients. It is concluded that patients with PD have relatively greater deficits in p rocedural learning, whereas those with HD have relatively more impairm ents in declarative memory, and the greater level of cognitive impairm ent in HD overall is interpreted as being due to more serious damage t o the caudate loop.