 Major depressive disorder is associated with several sleep Polysomnograph PSG findings: 1 impaired sleep continuity; 2 non-REM NREM changes; and 3 enhanced rapid eye movement REM sleep. The first two patterns are common in other psychiatric disorders, while the REM pattern is very characteristic in depression, so the phase-advance theory was accepted by most of psychiatrists. Many researchers have focused on the biological rhythm to investigate the etiological and pathophysiology of depression, and they think depression can be cured if its sleep abnormality is ameliorated. 