Electroencephalographic sleep, aging, and psychopathology: new data and state of the art.

Dysregulation of sleep-wake function is an important problem in both normal aging and in the two most common neuropsychiatric disorders of old age, depression and primary degenerative dementia. Since considerable overlap of symptoms in depression and dementing disorders (e.g., sleep disturbance, dysphoria, and cognitive impairment) often results in patients with a "mixed" syndrome, the development of specific, objective indicators as diagnostic markers, using electroencephalographic sleep patterns, was undertaken. Patients with dementia showed significantly less sleep continuity disturbance than patients with depression, less rapid eye movement activity, a different temporal distribution of REM density, and a longer REM latency. A discriminant function analysis using three variables (REM latency, REM density, and scaled sleep maintenance) correctly identified eight of nine depressives and six of nine dementing patients (78%) (k = 0.56, p = 0.008). These differences in REM sleep timing and density may be related to several factors: (i) defects in acetylcholine production in dementia; (ii) cholinergic mechanisms of REM sleep; and (iii) increased cholinergic induction of REM sleep in depression. The data suggest the utility of EEG sleep measures in the differential diagnosis of dementia and depression in the elderly.