Quantified electroencephalographic correlates of depression in Alzheimer's disease.

While depression is one of the most frequent psychiatric problems among patients with probable Alzheimer's disease (AD), its mechanism is not well known. We performed quantified EEGs in a consecutive series of seven patients with mild dementia and depression, six patients with mild dementia and no depression, eight patients with moderate dementia and depression, and eight patients with moderate dementia and no depression. Regardless of the severity of dementia, depressed patients had a significantly higher percent theta in posterior brain areas. Moreover, depressed patients with mild AD showed a similar theta frequency as non-depressed patients with moderate AD. These findings suggest that the presence of depression may contribute to the qEEG changes of AD.