Electrophysiological assessment of semantic memory in Alzheimer's disease.

This paper used the Event Related Evoked Potentials (ERPS) to study the ele ctroencephalographic activity of a group of patients with dementia of the A lzheimer's type (DAT). Ten patients with DAT and 10 elderly control subject s participated in a semantic categorization task using pictures as stimulus . The task was conformed by 118 pairs of pictures of common objects and ani mals where 50 % of the pairs of pictures pertained to the same semantic cat egory (e.g.guitar-violin) and conformed the congruent trials. The other 50 % of the pairs of pictures pertained to different categories (e.g. helmet-v iolin) and conformed the incongruent trials. The analysis of the ERPs of bo th groups showed a significant reduction of the N400 component in the DAT p atients. This reduction was due to the great positivity of the electrical a ctivity of the incongruent trials. The reduction of the N400 in DAT patient s supports the hypothesis of a failure to access and use the semantic infor mation in a proper manner.