To clarify disturbances in sleep regulation in patients with delayed sleep
phase syndrome (DSPS), we studied three patients with DSPS and seven health
y controls. Sleep propensity and melatonin rhythms after 24-h sleep depriva
tion were investigated under dim light condition by using the ultra-short s
leep-wake schedule. The sleep propensity curves displayed clear differences
between DSPS patients and the controls. During the subjective day when mel
atonin was not produced, recovery sleep after the sleep deprivation did not
occur in DSPS patients, while recovery sleep occurred during the subjectiv
e day in controls, This: suggests that DSPS may involve problems related to
the homeostatic regulation of sleep after sleep deprivation.