Cognitive speed in nondemented Parkinson's disease

Studies of speed of cognitive processing in Parkinson's disease (PD) have yielded mixed results. This may relate in part to a differential effect on cognitive speed by the type of information to be processed. In the present study, we compared medication fasted, nondemented individuals with mild idiopathic PD (N = 26) with age-matched controls (N = 12) on a test requiring easy and hard same-different discriminations for verbal, quantitative, and spatial information, as well as on a traditional memory scanning paradigm. A voice-activated relay rather than a key press was used to eliminate the need for limb and finger movements. Simple reaction time and movement time were also measured in a task requiring subjects to move a hand held stylus to a designated target. The PD group performed as fast as the control group across all tasks except movement time. Thus, in our paradigm, the presence of PD alone does not predict cognitive slowing in the presence of motor slowing.