Humans spend around one-third of their life sleeping. Sleep plays a huge role in memory consolidation, waste removal, cellular repair, and much more. Poor quality sleep is associated with problems such as dementia and CVD. Even with sleep playing such a big role in our lives, most of us neglect sleep, getting about 3 and a half ultradian sleep cycles or even less. Sleep is heavily regulated by many factors, with temperature being one of the biggest factors. In order for humans to fall asleep, their core temperature must drop by 1–3 °F. The timing of sleep is controlled by a circadian clock, the suprachiasmatic nucleus (SCN) in humans, and lateral posterior clock neurons (LPNs) in Drosophila. These structures are strongly influenced by temperature, and as they receive temperature information, they release signals that regulate sleep.
Daniel J. Cavanaugh’s paper, “The cell-intrinsic circadian clock is dispensable for lateral posterior clock neuron regulation of Drosophila rest-activity rhythms,” written by Charlene Y.P. Guerrero et al., examines the role of LPNs in Drosophila circadian and sleep regulation. LPNs receive input from thermosensory pathways, which is essential for circadian rhythm regulation. Guerrero reports that reduced LPN excitability causes a slight reduction in sleep. However, when LPNs are silenced using CRISPR, total sleep is reduced, sleep becomes fragmented, and sleep bouts become shorter. Researchers then used CRISPR to delete clock genes (per and tim) inside LPNs, which normally create a 24-hour cycle acting as an internal clock. The flies with their LPN clock genes deleted still received timing information from other clock neurons with functional per and tim cycles, maintaining a normal 24-hour rhythm. This shows that LPNs do not set their own time but instead receive timing from other structures, functioning as driven oscillators. Guerrero’s article demonstrates that LPNs are important for regulating sleep but do not require their own internal clocks. This knowledge may lead to therapeutic strategies for circadian rhythm disorders.
In a study by Roy J. E. M. Raymann et al. titled “Skin deep: enhanced sleep depth by cutaneous temperature manipulation,” Raymann discusses how skin temperature controls sleep quality in humans. Small increases in skin temperature have significant effects on sleep. Raymann et al. argue that adjusting the thermostat in a room has limited impact on sleep, while manipulating skin temperature has powerful effects. Previous experiments show that even a 0.4–1.0°C increase in skin temperature affects sleep. Researchers used slight skin warming and adjustments to the bedding microclimate to observe how it influenced sleep. They recorded sleep onset time, deep sleep duration, interruptions, and comfort. Participants also slept in cool and hot rooms to test whether air temperature made a difference. Results showed that in hot rooms, deep sleep decreased, wakefulness increased, and overall sleep quality worsened. When skin temperature was raised independently of room temperature, results changed dramatically: participants fell asleep faster, experienced more deep sleep, and had overall more restorative sleep. The study concludes that skin temperature plays a larger role in sleep quality than room temperature.
Together, these findings show that temperature plays a major role in regulating sleep. In Drosophila, LPNs integrate thermosensory information to regulate sleep even without their own internal clocks. In humans, manipulation of skin temperature affects sleep more strongly than room temperature. Both articles highlight that sleep systems depend heavily on how the brain interprets thermal information. As research in this field continues, new strategies and treatments for sleep and circadian rhythm disorders may emerge.
References
1.) Guerrero, C. Y. P., Lam, V. H., Cusumano, P., Van Doren, M., & Cavanaugh, D. J. (2025). The cell-intrinsic circadian clock is dispensable for lateral posterior clock neuron regulation of Drosophila rest–activity rhythms. Neurobiology of Sleep and Circadian Rhythms. https://doi.org/10.1016/j.nbscr.2025.100198
2.) Raymann, R. J. E. M., Swaab, D. F., & Van Someren, E. J. W. (2008). Skin deep: Enhanced sleep depth by cutaneous temperature manipulation. Brain, 131(2), 500–513. https://doi.org/10.1093/brain/awm315
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