EEG Sleep Changes in Recurrent Depression

Abstract

A few years ago we presented data pointing to the possible role of electroencephalographic (EEG) sleep patterns as a biological correlate in affective disorders. At that time we argued that although the notion of biological markers was becoming an increasingly prominent one their definition remained unclear and their application was often inappropriate. Any discussion of biological markers should begin, therefore, with the criteria for a valid biological marker and a minimum portrait delineating two types of marker. The first, the episodic (so-called state) marker appears during a clinically definable episode of illness but is not apparent at the completion of an episode when the patient is in remission. It was assumed that the marker was not present before the episode, and that it will present during the course of any future episodes. The second type of marker is viewed as a trait marker, not a so-called marker of the present state. It may be apparent in one of several blends: premorbidly or during, between, or only at the conclusion of an episode. A final point is that the same biological marker may be incorporated in both types (episodic/trait) of marker.