[Topographical analysis of endogenous evoked potentials in depressed old people and in patients with Alzheimer's type dementia]. / Analyse topographique des potentiels évoqués endogènes chez des sujets âgés déprimés et chez des sujets atteints de démence de type Alzheimer.

Latencies, amplitudes and localization of the maximum of the peaks of late onset evoked responses have been studied in 3 groups of elderly people: normal, depressed and demented (probable dementia of Alzheimer type DAT) at the early stage of the disease. Evoked responses with an auditory oddball paradigm have been recorded with 16 electrodes in 2 situations: counting the target sounds, and motor response with measurement of the reaction time. No difference in amplitude was observed between the 3 groups. Only a significant difference for P3 latency was observed between the DAT and the depressed groups and only in the counting situation. The maximum P3 response was most often found on the anterior areas in the DAT group and in the posterior areas in the normal and depressed groups. The topographic localization of the P3 peak could therefore be of some help in the characterize of subjects with probable DAT at the early stage of the disease.