A fall in body temperature due to circadian rhythms causes drowsiness and increases the propensity to sleep from the evening to midnight. As one of the sources of declining body temperature, the occipital region was cooled with a water pillow in this study, and the effect of this cooling technique on the sleep process and subjective ratings of sleep was analyzed. Seven university students whose sleep latency was more than 30 min slept using a pillow with a surface temperature 16°C (iced water condition) or 26°C (room temperature water condition), respectively. The iced water decreased the axilla temperature faster than the water at room temperature. A polysomnogram analysis indicated that sleep latency was significantly shorter when iced water was used compared to when cool water at room temperature was used. In addition, the iced water improved the participants’ subjective quality of sleep, including falling asleep and sleep maintenance. These results suggest that cooling the occipital region might be effective in promoting sleep onset and sleep maintenance.
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Setokawa, H., Hayashi, M. & Hori, T. Facilitating effect of cooling the occipital region on nocturnal sleep. Sleep Biol. Rhythms 5, 166–172 (2007). https://doi.org/10.1111/j.1479-8425.2007.00270.x