ROLE OF THE STRIATUM, CEREBELLUM, AND FRONTAL LOBES IN THE LEARNING OF A VISUOMOTOR SEQUENCE

This study was designed to examine the role of the striatum, cerebellu m, and frontal lobes; in the implicit learning of a visuomotor sequenc e. The performance of patients with idiopathic Parkinson's disease (PD ), with damage to the cerebellum, or with a circumscribed lesion to th e frontal lobes was thus compared to that of separate groups of matche d normal control subjects on an adapted version of the Repeated Sequen ce Test. This paradigm consists of a visual reaction-time task with a fixed embedded sequence of finger movements to he performed based on p resentation of visual stimuli. Subjects received four blocks of trials (i.e., 40 presentations of a 10-item sequence) per day over 6 trainin g days. Following the last experimental session, subjects were also gi ven two tests measuring their declarative knowledge of the sequence. O nly PD patients with a bilateral striatal-dysfunction or patients with lesions to the cerebellum failed to improve their performance in the last three training sessions, hence suggesting an impairment late in t he acquisition process, Further analyses revealed that such impairment was mainly implicit in nature, and that it could not be ascribed to a general decline in cognitive functioning, to mood disturbances, or to the severity of the motor symptoms. By contrast, the level of declara tive knowledge of the sequence did not differ between the three clinic al groups and their respective groups of normal subjects. These findin gs suggest that, unlike declarative memory the incremental acquisition of a new visuomotor skill depends upon the integrity of both the stri atum and the cerebellum, but not of the frontal lobes. (C) 1997 Academ ic Press.