The movement speed/accuracy operator in Parkinson's disease.

This study examined the effects of Parkinson's disease (PD) and its treatment on the speed of rapid arm movements to different target sizes in a simple reaction time task in 8 PD and 9 normal subjects. Testing in PD subjects occurred after an overnight fast from their medications and 1 hour after their usual 1st dose. They had longer reaction and movement times, both of which shortened following medication. Like normal subjects, PD subjects had decreased movement times to larger targets, but without drug were unable to maximize speed within the range of target sizes tested whereas PD subjects taking drug and normal subjects could. These findings suggest that a speed/accuracy operator is functioning in PD but at reduced initial gain and at an offset towards longer movement times.