VARIATION OF ELECTROENCEPHALOGRAPHIC ACTIVITY DURING NON-RAPID EYE-MOVEMENT AND RAPID EYE-MOVEMENT SLEEP WITH PHASE OF CIRCADIAN MELATONIN RHYTHM IN HUMANS

1. The circadian pacemaker regulates the timing, structure and consoli dation of human sleep. The extent to which this pacemaker affects elec troencephalographic (EEG) activity during sleep remains unclear. 2. To investigate this, a total of 1.22 million power spectra were computed from EEGs recorded in seven men (total, 146 sleep episodes; 9 h 20 mi n each) who participated in a one-month- long protocol in which the sl eep-wake cycle was desynchronized from the rhythm of plasma melatonin, which is driven by the circadian pacemaker. 3. In rapid eye movement (REM) sleep a small circadian variation in EEG activity was observed. The nadir of the circadian rhythm of alpha-activity (8.25-10.5 Hz) coi ncided with the end of the interval during which plasma melatonin valu es were high, i.e. close to the crest of the REM sleep rhythm. 4. In n on-REM sleep, variation in EEG: activity between 0.25 and 11.5 Hz was primarily dependent on prior sleep time and only slightly affected by circadian phase, such that the lowest values coincided with the phase of melatonin secretion. 5. In the frequency range of sleep spindles, h igh-amplitude circadian rhythms with opposite phase positions relative to the melatonin rhythm were observed. Low-frequency sleep spindle ac tivity (12.25-13.0 Hz) reached its crest and high-frequency sleep spin dle activity (14.25-15.5 Hz) reached its nadir when sleep coincided wi th the phase of melatonin secretion. 6. These data indicate that the c ircadian pacemaker induces changes in EEG activity during REM and non- REM sleep. The changes in non-REM sleep EEG spectra are dissimilar fro m the spectral changes induced by sleep deprivation and exhibit a clos e temporal association with the melatonin rhythm and the endogenous ci rcadian phase of sleep consolidation.