Men sleep shorter and go to bed and get up later than women, thus they are laterchronotypes. This difference between the sexes is most pronounced betweenpuberty and menopause indicating the possibility that morningness is subject tosexual dimorphism related to reproductive aspects. The objective of the studywas to compare the sleep-wake behavior of women with their actual partners andwith their preferred partners. As a hypothesis, we expect some assortment inmating concerning chronotype (with the actual partner), but we also expect ahigher synchronization with a preferred ideal partner. 167 women were analyzedin this study (mean age: 23.0 ± 2.57 (SD) years).Mated women were earlier chronotypes than their partners (t= –2.051, p = .042,d = .34) but the difference was small (11:02 min± 1:04 min). The results of the present study showed women preferringa partner synchronized to their own sleep-wake-rhythm more than their actualpartners were. The above result was true either for single facets of thesleep-wake rhythm (e.g. bed time, sleep onset) or for midpoint of sleep on freedays – an indicator of actual chronotype: women’s andtheir partners’ correlation of midpoint of sleep was lower(r = .513) than women’s and their idealpartners’ correlation (r = .855). Amongstvarious sleep-wake measures, women particularly preferred a partner going to bedat the same time. Assortative mating according to sleep-wake rhythm exists, butwomen for long-term pair-bonds would like their partners far moresynchronized.

Abnormalities of circadian rhythms in depressed patients have been noted, including decreased amplitude, distorted waveform, day-to-day instability, and unusual 48 hour periods. Consistent electroencephalographic sleep recording in these patients show a shortened rapid eye movement latency and slow-wave sleep (stages 3 and 4), resulting in an increase in rapid eye movement sleep. This phenomenon appears to be a dependable, measurable marker for diagnosing primary depression. Total sleep deprivation appears to significantly improve mood in a high percentage of depressed patients. Current pharmacological research suggests that drug treatment such as lithium would not affect the intra sleep cycles of the REM stagebut would shift the phase backward and lithium would also shift the phase of circadian rhythm of the daytime sleepiness backward. This paper highlights some of the new approaches for investigating the molecular substrate for the control of circadian rhythmicity and sleep in man and critically examines the hypothesis of the alteration of this mechanism in psychopathology, particularly depression. What is known of the endogenous clock mechanism is discussed with known molecular circadian mechanisms with a view towards understanding how circadian information is transmitted to the rest of the central nervous system and how it is affected in depression.