Visual and auditory event-related potential comparisons between Parkinson's disease with dementia and Alzheimer's disease

Visual hallucinations (VHs) are relatively common in Parkinson's disease patients with dementia (PDD), while auditory ones are quite rare. To investigate whether VHs in PDD are associated with specific involvement in visual cognitive functions, we compared visual P3 event-related potential (VP3) latencies among patients with PDD with (VH) and without VHs (NH), and Alzheimer's disease (AD), with consideration of auditory P3 (AP3) latencies. The subjects consisted of 11 PDD-VH, 6 PDD-NH and 20 AD patients, and 19 healthy volunteers (C). The mean ages and MMS scores of the three patient groups were comparable. To elicit VP3s and AP3s, a visual paradigm with human faces and a conventional auditory oddball paradigm were used, respectively. The three patient groups had significantly longer VP3 latencies than the C group. The mean VP3 latencies were longer in the order of PDD-VH, PDD-NH, and AD group, and a significant difference was observed between PDD-VH and AD group, while the mean AP3 latencies did not differ significantly. These findings suggest that visual cognitive functions are more markedly impaired in PDD-VH patients than in AD patients. Our findings also suggest that VHs might be associated in part with predominating visual cognitive impairments in PDD patients.