Electroencephalographic coherence in Alzheimer's disease: comparisons with a control group and population norms.

Previous research from independent laboratories has shown reduced electroencephalographic coherence in patients diagnosed with dementia of the Alzheimer type (DAT). This study added to this work by comparing interhemispheric and intrahemispheric coherence in nonmedicated DAT patients (n = 35) with that of a normal control group (n = 30), as well as with a data bank of population norms. Raw and Z-score transformed values showed reduced coherence, interhemispherically (in delta, theta, alpha, and beta bands) and intrahemispherically (delta and theta bands) in DAT patients with both comparison procedures. Discriminant analysis correctly classified 73% to 75% of patients. The results are discussed in relation to earlier research, "trait" versus "state" factors, the cholinergic system, and cognitive processes in dementia.