Electrophysiological assessment of semantic memory in Alzheimer's disease.

This paper used the Event Related Evoked Potentials (ERPS) to study the electroencephalographic activity of a group of patients with dementia of the Alzheimer's type (DAT). Ten patients with DAT and 10 elderly control subjects participated in a semantic categorization task using pictures as stimulus. The task was conformed by 118 pairs of pictures of common objects and animals where 50 % of the pairs of pictures pertained to the same semantic category (e.g.guitar-violin) and conformed the congruent trials. The other 50 % of the pairs of pictures pertained to different categories (e.g. helmet-violin) and conformed the incongruent trials. The analysis of the ERPs of both groups showed a significant reduction of the N400 component in the DAT patients. This reduction was due to the great positivity of the electrical activity of the incongruent trials. The reduction of the N400 in DAT patients supports the hypothesis of a failure to access and use the semantic information in a proper manner.