Neurophysiological "markers"--EEG sleep measures.

Although a number of neurophysiological "markers" have been suggested as potential correlates of depression, the most promising set has been based on the electroencephalographic (EEG) measurement of sleep in affective disorders. Our knowledge, based on episodic biological correlates of depression, has attained considerable consensus in demonstrating specific findings for EEG sleep and depression. While there are some controversial issues remaining, the available evidence suggests that EEG sleep correlates can certainly be used as a state measure in affective disorders. A second phase of inquiry is now concerned with two issues--whether there are any specific markers during remitted phases of depression, and how the data base can help us understand some of the key theoretical biological issues in affective states.