TEMPORAL FREQUENCY DEFICIT IN PATIENTS WITH SENILE DEMENTIA OF THE ALZHEIMER-TYPE - A VISUAL-EVOKED POTENTIAL STUDY

To study the temporal aspect of visual processing of senile dementia o f the Alzheimer type (SDAT), we recorded the steady-state visual evoke d potentials (VEPs) to LED goggle stimulation at five different tempor al frequencies in 14 patients with SDAT and 14 control subjects. For c omparison, we also studied 14 patients with vascular dementia (VD). Al l subjects were women, and their ages were closely matched. Temporal f requencies were 5, 10, 15, 20, and 30 Hz. The steady-state VEPs were F ourier analyzed, and both the amplitude and phase of the first and sec ond harmonic responses were obtained. There was a significant differen ce in the amplitude across the three groups for stimulation at 15, 20, and 30 Hz, but no difference at a stimulation of 5 and 10 Hz. Multipl e comparison tests revealed that patients with SDAT had a significantl y smaller amplitude than normal controls. Patients with VD had lower a mplitudes than normal subjects, but this was not statistically signifi cant. In the phase data, there were also no statistically significant differences across the three groups for any of the temporal frequencie s. These results indicate that a temporal frequency deficit exists in SDAT. This phenomenon may be explained by the pathology that affects t he early stage of visual signal processing.