Defective inhibition in the visual system of patients with early-stage Alzheimer disease

Abstract

To assess the visual system excitability of patients with Alzheimer disease (AD) with the paired-pulse flash-evoked potential (paired F-VEP) technique. We studied 14 patients with early-stage probable AD. Twenty-two normal subjects of similar age and sex acted as controls. We recorded F-VEPs from occipital electrodes. Stimuli were single flashes, intermingled to flash pairs at the internal frequency of 8, 16, 20, 30, and 60 Hz. Recordings were done with closed eyes. The single F-VEP was split into a “main complex” and a “late response,” which were measured separately. As to paired stimuli, the “test” F-VEP emerged from electronic subtraction of the single F-VEP to the paired F-VEP. Grouped data were analyzed by means of analyses of variance (ANOVA). The normal inhibition of the “main complex” of the test F-VEP was replaced by a paradoxical facilitation, significant at the frequency of 16 Hz (p