Abstract
Event-related potentials (ERPs) occurring in response to attended and unattended stimuli were studied in 31 patients with Parkinson's disease (mean age: 66.9 years), 9 patients with Alzheimer's disease (mean age: 73.6 years) and 37 normal subjects (mean age: 47.5 years). Of the 31 patients with Parkinson's disease, 6 met the criteria for dementia in DSM-III-R. ERPs were recorded during the performance of visual discrimination tasks using three kinds of stimuli: frequent non-target (62%), infrequent non-target (19%) and infrequent target (19%) stimuli. The P3a and P3b were identified as the components of the P3 (P300) responses to infrequent nontarget stimuli and infrequent target stimuli. Both the P3a and P3b latencies were significantly prolonged with normal aging. Nine of the Parkinson's disease patients showed a P3b latency above the 95% confidence limit of the age estimated regression line, while only one patient showed a prolonged P3a latency. There was no significant correlation between the P3a and P3b latencies in the patients with Parkinson's disease, although a significant correlation was found in the normal subjects. There was a significant correlation between the P3b latency and Hasegawa's dementia scale (HDS) score although the P3a latency showed no correlation with HDS score. These results indicate that the P3a and P3b components have some differences. In demented patients with Parkinson's disease, the P3b latency was significantly longer than that in 15 age-matched normal subjects, although no significant difference was found in the P3a latency. On the other hand, patients with Alzheimer's disease showed a significant prolongation of both P3a and P3b latencies compared to the age-matched normal subjects. Furthermore, there was a significant difference in P3a latency between demented patients with Parkinson's disease and those with Alzheimer's disease. There were no significant differences in any of the amplitudes among these three groups. These results suggest that the automatic processing stage, as reflected by P3a, may be less impaired than attentional controlled processing reflected by P3b in patients with Parkinson's disease, and further indicate that there may be some differences in the changes of the cognitive process between patients with Parkinson's disease and those with Alzheimer's disease.
