ABNORMAL FUNCTIONAL CONNECTIVITY IN ALZHEIMERS-DISEASE - INTRAHEMISPHERIC EEG COHERENCE DURING REST AND PHOTIC-STIMULATION

Electroencephalography (EEG) coherence provides a measure of functiona l correlations between two EEG signals. The present study was conducte d to examine intrahemispheric EEG coherence at rest and during photic stimulation (PS; 5, 10 and 15 Hz) in ten unmedicated patients with pre senile dementia of the Alzheimer type (AD; mean age at onset 56 years) . In the resting EEG, the AD patients had significantly lower coherenc e than gender- and age-matched control subjects in the alpha-1, alpha- 2 and beta-1 frequency bands. The EEG analysis during PS also showed t hat the patients had significantly lower coherence in the frequency co rresponding to PS at 10 and 15 Hz. In this study, the changes in coher ence from the resting state to the stimulus condition (i.e. PS-related coherence reactivity) were examined. The patients were found to show significantly smaller coherence reactivity to PS at 5 and 15 Hz. These findings suggest that, in addition to the resting state, AD patients have an impairment of intrahemispheric functional connectivity during PS. They also suggest that AD shows a failure of PS-related functional reorganization.