Provision of external cues and movement sequencing in Parkinson's disease

The basal ganglia (BG) may play a part in motor sequencing. Individuals with Parkinson's disease (PD) may exhibit progressive slowing (sequence effect) during motor sequences such as writing (micrographia) and gait. In the present study, a serial two-way choice reaction time (CRT) task was employed, in which advance information about each next movement was not provided until the participant began moving, thereby assessing the participant's ability to utilize advance information. Participants were 13 individuals with idiopathic PD and 13 age-matched controls. Both PD subjects and controls showed a significant sequence effect in the absence of advance information, possibly reflecting difficulty in initiating and maintaining movement without external cues. PD subjects and controls both exhibited a sequence effect at moderate levels of advance information. At high levels of advance information, PD subjects showed the effect but controls did not, suggesting that controls, unlike PD subjects, were able to use the extra information to facilitate performance, perhaps reflecting more frontal aspects of impairment in PD.