Perseveration for novel stimuli in Parkinson's disease: an evaluation based on event-related potentials topography

Event-related potential topography produced by novel and target stimuli was used to detect dysfunction of mental switching (perseveration) in nondemented patients with Parkinson's disease. The study participants were 15 patients with Parkinson's disease and 13 age-matched healthy control patients. Ten percent of the novelty tones with pitches of 125 and 500 Hz were added to 20% of the target tones that had a pitch of 1000 Hz. Patients were instructed to count the target tones. The modified Wisconsin Card Sorting Test was used to evaluate frontal lobe function. Patients with Parkinson's disease showed a significant decrease in the achieved categories and an increase in perseverative errors in the Wisconsin Card Sorting Test. These results indicate that the cognitive impairment of patients with Parkinson's disease can be characterized as failure of mental switching related to frontal lobe dysfunction based on basal ganglia disturbance. As compared with the control patients, patients with Parkinson's disease had shorter P3 latencies to the novel stimuli and a more frontal distribution on the P3 map, especially for the 125-Hz stimuli. This characteristic of P3 to novel stimuli in the patients with Parkinson's disease, but not in the control patients, is categorized by P3a (novelty P3). Our findings suggest that decreased mental switching causes lack of novelty P3 habituation in patients with Parkinson's disease and that it is related to learning disabilities based on dysfunction of the frontal lobe and basal ganglia.