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Electrical field changes of event-related potentials (ERPs) were investigated in 26 patients with dementia of Alzheimer's type (DAT) and 12 age-matched normal subjects. The patients were assessed with the Clinical Dementia Rating and Mini-Mental State. Each patient selected had only mild to moderate mental disability. Auditory oddball stimulation was presented at 1.5 s intervals and 1,000 Hz for the nontarget and 2,000 Hz for the target tones, both at 85 dB. The target tones were 20% of all the tones. The reference-independent data (latency, global field power: GFP, dissimilarity index: DISS and location of centroids) were obtained and analyzed for each ERP component. The momentary electric strength or 'hilliness' of the ERPs landscape was indicated by GFP. The patients showed prolonged latencies and decreased P300 GFP amplitudes and of N100 GFP. These findings suggest that the abnormal electrical field of ERP may reflect abnormal information processing following the attentional process for target stimuli in DAT patients.

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The purpose of our study was to demonstrate impaired allocation of processing resources in non-demented patients with early-stage mild Parkinson's disease (PD) using a multimodal event-related potential (ERP) paradigm. The multimodal ERP paradigm was performed in 18 non-demented medicated patients with early-stage PD (Mini-Mental State Examination Score >26) and 16 matched normal controls, the Global Field Power (GFP) was employed for ERP components analysis, and the new modified Wisconsin Card Sorting Test (WCST) was used to evaluate frontal lobe function. Patients with PD did not exhibit novelty P3s, and P3 latency to non-target novel stimuli in visual and auditory modalities was significantly longer in PD patients than in controls. P3 amplitude for the target stimuli (P3b) was higher in PD in both auditory and visual modalities; however, P3b latency was not different between the two groups. Patients with PD showed a significantly lower score of achieved categories and made more perseverative errors in WCST as compared to controls. Our results showed that there were no natural novelty P3s in patients with PD; this finding suggests that non-demented patients with mild PD do not have sufficient mental resources to allocate to the central executive, due to dysfunction of the frontal lobe.