Schlafregulation

Circadian rhythmicity and sleep homeostasis both contribute to sleep timing and sleep structure in animals and humans. The circadian process and the sleep homeostat interact to consolidate the sleep-wake cycle and, thus, establish wakefulness and sleep. The circadian process generates a sleep-wake propensity rhythm that is timed to oppose homeostatic changes in sleep drive. Disruption of this fined-tuned interaction can lead to performance decrements, daytime sleepiness, and sleep problems, which are often found in shift workers, jet lag, in older people, and patients suffering from delayed or advanced sleep phase syndrome. Recent progress in molecular biology and cell physiology has led to the following conclusions regarding these two processes and their impact on the neurobiology of sleep: The suprachiasmatic nuclei (SCN), located in the anterior hypothalamus, represent the master circadian pacemaker. There is a feedback to the SCN via the neurohormone melatonin. The ventrolateral preoptic area (VLPO) is particularly important for the initiation of sleep. Adenosine triggers the VLPO. An ultradian oscillator located in the mesopontine brainstem region controls the regular cycling between non-REM and REM sleep. The sleep-wake cycle and the NREM-REM sleep cycle induce regularly occurring neuromodulatory changes in forebrain structures.