Kazumi Aragane

Electrophysiological analysis of cognitive slowing in Parkinson's disease

To analyze chronometrically the evidence for possible cognitive slowing in Parkinsons disease, we measured visual event-related potentials (ERPs) and reaction times (RTs) in 29 patients with nondemented Parkinsons disease and 19 age-equivalent normal controls during the performance of semantic discrimination tasks. The components of the N1, P2, NA, N2 and P3 and simple and GO/NOGO RTs were observed. The N2 was measured from difference waveforms, subtracting the ERPs to frequent stimuli from those to infrequent stimuli in the discrimination task. Difference waveforms were also derived to delineate NA by subtracting the ERPs in the simple RT task from those of the frequent stimuli of the discrimination task. The N2 and P3 latencies and GO/NOGO RT in patients with Parkinsons disease were significantly longer than those in the controls, although there were no differences in N1, P2 and NA latencies or simple RT between the two groups. The results are interpreted as electrophysiological signs of cognitive slowing, particularly with respect to stimulus classification and attention processes in Parkinsons disease, independent of sensory problems. As for the automatic/controlled processes, the present results suggest that the automatic processing stage associated with NA may be less impaired than the attention-controlled processing reflected by N2 in patients with Parkinsons disease.

Age-related changes in event-related potentials in visual discrimination tasks.

Visual event-related potentials and reaction times in physical and semantic discrimination tasks were studied in 29 normal subjects between the ages of 21 and 74 years. The NA, N2 and P3 components of the evoked potential, and simple and GO/NOGO reaction times were observed in both kinds of discrimination. Significant age-related slowing of the GO/NOGO reaction time was observed only in the semantic discrimination task. The N2 and P3 latencies elicited by both the physical and semantic stimuli were significantly and positively correlated with age, although there was no significant correlation between the NA latency and age. The interpeak latency between N2 and P3 showed no age-related changes. The decline of cognitive information processing with advancing age was evident from the classification of a perceived event as reflected by the N2 component.

Chronometrical analysis of event-related potentials and reaction time in patients with multiple lacunar infarcts.

We measured the visual event-related potentials (ERPs) and reaction time (RT) in 31 patients with multiple lacunar infarcts and 18 age-equivalent normal subjects. The N2 and RT latencies of the patients were significantly longer than those of normal subjects, although P2 and P3 latencies did not differ between the two groups. However, the time from N2 to RT did not differ between the two groups. These observations suggest that the impairment of cognitive information processing in these patients arises from an uncertainty in classifying the perceived event, while motor organization time is relatively well preserved. In addition, the N2 latency may be more sensitive in detecting cognitive impairment in such patients.