A paper by Keith Studholme and colleagues suggests that a drop in body temperature brought on by changes in nocturnal ambient light may play a role in the induction of sleep. In an article titled “Brief light stimulation during the mouse nocturnal activity phase simultaneously induces a decline in core temperature and locomotor activity followed by EEG-determined sleep,” Mr. Studholme and his colleagues described the results of experiments showing that changes in body temperature are implicated in sleep regulation in ways that have not been fully appreciated.
Prior research has shown that there is a relationship between the sleep/wake cycle and changes in body temperature. It is known, for example, that temperature is high during the active phase, low during the sleep phase, and just before humans go to sleep their core body temperature drops. Whether or not this temperature change contributes to sleep onset is uncertain. This study, while not resolving all the questions involved, used a unique research paradigm to provide new information about how change in ambient light may affect both body temperature and sleep.
In a series of carefully controlled experiments, the researchers exposed mice to light during the night, when nocturnal rodents are most active. In one experiment they observed that soon after the exposure to even brief flashes (milliseconds) of light, the mice stopped moving about, their core body temperature dropped precipitously, and they went to sleep. Analysis of the results showed that the drop in body temperature occurred simultaneously with the suppression of locomotion but recovered in advance of the resumption of activity, indicating that the drop in body temperature is a direct effect of exposure to light and not explained simply by the reduction in activity.
As the result of this and other experiments, the researchers concluded that nocturnal light induces sleep coincident with a drop in body temperature. The results raise the question of whether the effect of light on other measures, such as circadian rhythm phase, is caused or permitted by the associated lower temperature. The ability to induce sleep with brief nocturnal light may provide a convenient and expeditious means for studying sleep onset and regulation, as well as serving as a proxy for studying the effects of light on circadian rhythms.
The paper was published in the American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, on January 30, 2013. The work was done in chronobiology lab of Lawrence Morin, PhD, with assistance from Heinrich S. Gompf, PhD, of the Harvard Medical School. The project was funded by an award from the National Institutes of Health to Dr. Morin.
