Periodic photic stimuli across the entire electroencephalographic (EEG) frequency range were used in an attempt to assess EEG functional differences between chronic schizophrenic patients and control subjects. The EEG responses to these photic stimuli were significantly attenuated in the schizophrenic patients, specifically at the frequencies within the EEG alpha range. The schizophrenic patients also showed an alpha range attenuation in the "no stimulus" EEG alpha measure, such that there was a significant correlation across subjects between the "stimulus" and "no stimulus" EEG alpha range abnormalities. These abnormalities are discussed with reference to possible dysfunctional thalamic mechanisms involved in the pacing of EEG alpha activity and the gating of information through the cerebral cortex.

Quantitative scalp EEG from 32 channels and the cerebral glucose metabolic rate from the 32 underlying cortical positions as assessed by positron emission tomography (PET) with 18F-2-deoxyglucose (FDG) were obtained on 36 patients with mild to moderate senile dementia of the Alzheimer type and 17 age- and sex-matched normal control subjects. Subjects performed a verbal memory task during uptake of FDG. There were significant correlations between both delta amplitude and metabolic rate and memory performance during FDG uptake. Patients with Alzheimer's disease had significantly greater left temporal delta amplitude and lower glucose metabolic rates. Both EEG delta in microvolts and metabolic rate had similar diagnostic sensitivity, but PET had fewer false positives among normals. The left amygdala had the highest sensitivity and percent correct diagnosis of any brain area. Temporal lobe EEG delta activity showed higher correlations with hippocampal metabolic rate than metabolic rate directly under the electrode.