In elderly patients who suffer from depressive symptoms and cognitive impairment the clinical decision between the diagnoses of depression and dementia may be difficult. In addition, patients with dementia and depressed patients frequently show a disturbance of sleep. Sleep EEG registration in depression revealed a characteristic sleep EEG profile concerning distinct alterations of sleep architecture and REM-sleep (reduction of SWS, increase and advance of REM-sleep). In dementia polysomnographic assessment has been done less intensively, mainly in patients with dementia of Alzheimer type (DAT). The most significant polysomnographic finding in DAT is a reduction of REM-sleep, which may reflect impaired cholinergic neurotransmission. Therefore, predominantly REM-sleep variables clearly differ between depressed patients and patients with DAT.

In this presentation polysomnographic data and data of cognitive performance in dementia and depression will be reviewed. In addition, own long term studies in patients with different types of dementia and in depressed patients will be presented. The polysomnographic findings of these studies will be discussed with respect to differential diagnosis, prediction of treatment response and the long term course of both diseases. In addition, the results will be related to the current knowledge of the neurochemical and neuroendocrine regulation of sleep.