Dissociating sequence learning performance in Parkinson's disease: Visuomotor sequence acquisition and pattern judgment on a serial reaction time task

In this study, the sequence learning performance of 16 non-demented patients with Parkinson's disease (PD) was compared with 18 age-matched healthy controls on a verbal version of the serial reaction time (SRT) task intended to encapsulate both visuomotor- and judgment-linked learning processes. Visuomotor sequence performance in PD patients was closely related to baseline response speed, with robust learning demonstrated by patients who responded with comparable speed to controls but severely impaired performance in patients who responded slowly. In contrast, both fast- and slow-responding PD patients were able to successfully categorise patterns according to their sequential status, a performance that was linked to declarative memory for the sequence. The findings highlight the important role of event timing in SRT performance and are in accord with the hypothesis that, despite the important role played by the basal ganglia in motor sequence learning, basal ganglionic dysfunction may not substantially impair sequence order learning so much as the translation of sequence knowledge into rapid motor performance for some PD patients. Intact pattern judgment on the SRT experiment suggests that the integrity of the neostriatum is not essential for learning judgment-linked categorical information about sequences of temporal stimulus movement.