Sleep electroencephalography in depressive illness. A collaborative study by the World Health Organization.

Eight WHO research centres from Europe, North America and Asia took part in a WHO study aimed at assessing the reliability and consistency of sleep-EEG abnormalities in major depression. Each centre was asked to include in the study ten depressed patients aged 20-65 years meeting the Research Diagnostic Criteria for a major depressive disorder, and to match them by age and gender with ten controls. There were 67 patients and 66 controls included in the study. Compared with controls, depressed patients showed sleep-continuity disturbances such as increase in sleep-onset latency, and decrease in total sleep time and in sleep efficiency. Stages 2 and 3, as percentages of total sleep time, were reduced in depressed patients, REM latency was shortened and REM density increased. These findings confirm the presence of specific sleep-EEG abnormalities in major depression.