摘要
Sleep is not just the absence of wakefulness but a regulated process with an important restorative function. Based on electroencephalographic recordings and characteristic patterns and waveforms we can distinguish wakefulness and five sleep stages grouped into light sleep, deep sleep, and rapid-eye-movement (REM) sleep. In orderto explore the functions of sleep and sleep stages, we investigated the dynamics of sleep stages overthe night and of heart-rate variability duringthe different sleep stages. Sleep stages and intermediate wake states have different distributions oftheir duration and this allows us to create a modelforthe temporalsequence of sleep stages and wake states. Heart rate is easily accessed with a high precision by the recording and analysis ofthe electrocardiogram (ECG). Heart-rate regulation is part ofthe autonomous nervous system and sympathetic tone is strongly influenced bythe sleep stages. © 2003 Nature Publishing Group.