Variability of P300 in elderly patients with dementia during a single day

We recorded P300 sequentially during a single day in nine patients with dementia in a health care facility. The variability of the P300 response and the relationship between P300 and the Revised Hasegawa Dementia Scale were investigated. The sequential P300 latency and amplitude measurements varied significantly during the day, but the value changes were not related to the scheduled programs in the facility. Although there was no correlation between the values of latency or amplitude and Revised Hasegawa Dementia Scale (HDS-R), the variability index of the P300 latency correlated with the HDS-R score. Variability in the P300 response was considerable and the reproducibility was poor in elderly patients with dementia during the day, although the P300 latency was consistently prolonged. These results suggested that the variability of P300 was not due to transient changes in the level of consciousness, but was related to the latent pathology of fluctuating cognitive functions in patients with dementia.