P300 latency reflects the degree of cognitive decline in dementing illness.

An auditory discrimination paradigm was employed to elicit the P3 component of the event-related brain potential (ERP) from 39 demented patients (mean age = 71 years). Component latency was longer in patients who were diagnosed as having primary degenerative dementia and other cognitive impairment disorders compared to age-matched controls. Neurologist ratings of cognitive impairment were significantly correlated with P3 latency values, although no differences in mean latency were obtained between the various categories of dementia. ERP measurement techniques and the interpretation of P3 latency as in index of dementing illness are discussed.