Slow wave sleep redistribution and rem sleep eye movement density in depression: Towards the adaptive function of rem sleep

In depressed patients EM density in REM sleep and Slow Wave Sleep (SWS) are often redistributed. The goal of the present investigation was to analyze the relationships between these variables. - Twenty-four depressed patients underwent two or three consecutive polysomnography studies before treatment. Polysomnograms (PSG) were divided into two groups: Group I in which SWS were concentrated in the 3^rd or 4^th cycles, while group II (51 PSGs) included all other PSGs. In group I Eye Movement Density (EMD) in REM sleep periods which preceded the enhancement of slow wave sleep was found to be higher in all cases compared to the EMD in the previous REM sleep periods; REM sleep latency was shorter than in group II. In group II EMD was not regularly increased from cycle to cycle. In group II the first REM sleep period was the longest one while group I followed the normal tendency of REM sleep periods to increase from cycle to cycle. Only in group I does the improvement of mood from evening to morning have a strong positive correlation with EM density in the 4th cycle. The increased phasic activity of the REM sleep in depression may reflect an adaptive activity of REM sleep, which creates a condition for slow wave sleep to appear.