Endogenous depression improvement and REM pressure

In the treatment of endogenous depression by rapid eye movement (REM) sleep deprivation, depression improvement, measured on Hamilton and Global scales, correlated positively and significantly (P less than .05) with REM pressure (increase of REM sleep stimulated by REM sleep deprivation). This dose-response relationship suggests that (1) REM pressure was an indicator of a process that mediated the antidepressant effects of REM sleep deprivation, and (2) since improvement varied with stimulation of REM sleep, an unknown stimulus of REM sleep is a naturally occurring, endogenous antidepressant.