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Summary
Great toe temperature elevation, previously linked to sleep onset, was found to be uncorrelated with electroencephalogram (EEG) determined sleep. This finding suggests toe temperature changes may reflect metabolic adjustments during early slow-wave sleep.
Area of Science:
- Sleep Science
- Physiology
- Neuroscience
Background:
- Previous research suggested toe temperature elevation indicates "vegetative preparedness for sleep" due to lowered sympathetic tone.
- Toe temperature elevation has also been used as an indicator of anesthesia levels sufficient for major surgery.
Purpose of the Study:
- To investigate toe temperature as a "physiological" measure of sleep onset.
- To compare toe temperature changes with electroencephalogram (EEG) criteria for sleep onset.
Main Methods:
- Monitored great toe temperature in 166 women (aged 21-45) across insomniac and control groups over 166 sleeper-nights.
- Compared the timing of toe temperature elevation with sleep onset determined by EEG.
Main Results:
- The mean latency of toe temperature elevation was uncorrelated with EEG-determined sleep onset.
- Significant toe temperature elevations were observed but were not consistently present across all subjects and nights.
Conclusions:
- Toe temperature elevation is not a reliable indicator of sleep onset based on EEG criteria.
- Toe temperature changes may instead reflect metabolic adjustments associated with the onset of the first period of slow-wave sleep.