Circadian variation of EEG power spectra in NREM and REM sleep in humans: Dissociation from body temperature

Sep 4, 1999Journal of sleep research

Daily changes in brain wave patterns during deep and dream sleep in humans that differ from body temperature rhythms

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Abstract

EEG power spectra in NREM and REM sleep differ significantly between circadian phases despite identical body temperatures of 36.72 degrees C.

EEG power spectra in NREM sleep showed marked enhancement in low frequency spindle activity after the evening increase in plasma melatonin compared to the morning phase.
For REM sleep, significant differences in power spectra, particularly in the alpha range, were noted between these two circadian phases.
The findings suggest that variations in EEG power spectra during sleep are not primarily caused by changes in body temperature.
Results are inconsistent with the hypothesis that circadian variations in EEG power spectra are driven by temperature fluctuations.

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In humans, EEG power spectra in REM and NREM sleep, as well as characteristics of sleep spindles such as their duration, amplitude, frequency and incidence, vary with circadian phase. Recently it has been hypothesized that circadian variations in EEG spectra in humans are caused by variations in brain or body temperature and may not represent phenomena relevant to sleep regulatory processes. To test this directly, a further analysis of EEG power spectra - collected in a forced desynchrony protocol in which sleep episodes were scheduled to a 28-h period while the rhythms of body temperature and plasma melatonin were oscillating at their near 24-h period - was carried out. EEG power spectra were computed for NREM and REM sleep occurring between 90-120 and 270-300 degrees of the circadian melatonin rhythm, i.e. just after the clearance of melatonin from plasma in the 'morning' and just after the 'evening' increase in melatonin secretion. Average body temperatures during scheduled sleep at these two circadian phases were identical (36.72 degrees C). Despite identical body temperatures, the power spectra in NREM sleep were very different at these two circadian phases. EEG activity in the low frequency spindle range was significantly and markedly enhanced after the evening increase in plasma melatonin as compared to the morning phase. For REM sleep, significant differences in power spectra during these two circadian phases, in particular in the alpha range, were also observed. The results confirm that EEG power spectra in NREM and REM sleep vary with circadian phase, suggesting that the direct contribution of temperature to the circadian variation in EEG power spectra is absent or only minor, and are at variance with the hypothesis that circadian variations in EEG power spectra are caused by variations in temperature.

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Circadian variation of EEG power spectra in NREM and REM sleep in humans: Dissociation from body temperature

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