Topographic EEG analysis of photic driving responses in patients with dementia of the Alzheimer type

The present study performed topographic analysis of EEGs recorded at rest and during photic stimulation (PS; 5, 10, and 15 Hz) in unmedicated patients with presenile Alzheimer's disease (AD) and sex-and age-matched controls. In the resting EEG, the AD patients had significantly lower alpha-2 (9.0-12.8 Hz) and beta band power, as well as a significant increase in Delta (2.0-3.8 Hz) and Theta band power (4.0-7.8 Hz) as compared with the normal controls. EEG analysis during PS showed that the patients generally had lower EEG power for the Theta (4.8-5.2 Hz), alpha (9.8-10.2 Hz) and beta bands (14.8-15.2 Hz) corresponding to each stimulus frequency. Significant topographic differences were found mainly over the parieto-occipital regions, and there was no posterior predominance of photic driving responses in the patients. In addition, the control subjects had an increased EEG power in association with PS, whereas the patients showed significantly less EEG reactivity mainly over the posterior regions. These findings indicate that AD patients have diminished EEG responses to PS, suggesting an impairment of visual functioning in AD.