Length of REM sleep linked to body temperature
Warm-blooded animal groups with a lower body temperature have faster eye movement (REM) sleep, while those with a higher body temperature have less REM sleep. This is according to new research from Jerome Siegel, a professor at the University of California, Los Angeles (UCLA), who said his research suggests that REM sleep acts as a “thermostatically controlled brain heater.”
REM sleep first occurs about 90 minutes after falling asleep. Behind closed eyelids, your eyes dart quickly back and forth. The activity of mixed-frequency brainwaves is closer to the activity seen in wakefulness. Your breathing becomes faster and more irregular, and your heart rate and blood pressure rise to near waking levels. Most of your dreams take place during REM sleep, although some can occur in non-REM sleep as well. Your arm and leg muscles become temporarily paralyzed, preventing you from fulfilling your dreams. As you get older, less of your time is spent sleeping in REM sleep.
Siegel says the findings point to a previously unobserved relationship between body temperature and REM sleep, a sleep period when the brain is highly active. Recently published in Lancet Neurologythe study is written by prof. Siegel, who directs the Center for Sleep Research at the Jane and Terry Semel Institute for Neuroscience and Human Behavior at UCLA.
Birds have the highest body temperature of any warm-blooded or homeothermic animal groups at 41°C (106°F), while getting the least REM sleep of 0.7 hours per day. Next are humans and other placental mammals (37°C/99°F), 2 hours REM sleep), marsupials (35°C/95°F, 4.4 hours REM sleep) and monotremes (31°C/88 °F, 7.5 hours of REM sleep).
Brain temperature falls in non-REM sleep and then rises in the REM sleep that usually follows. With this pattern, “homeothermic mammals can conserve energy in non-REM sleep without the brain becoming so cold that it becomes unresponsive to threat,” Siegel said.
Humans’ amount of REM sleep isn’t high or low compared to other homeothermic animals, “undermining some popular beliefs that suggest REM sleep plays a role in learning or emotional regulation,” he said.
Reference: “Sleep Function: An Evolutionary Perspective” by Jerome M Siegel, PhD, Oct. 1, 2022, The Lancet Neurology.
Siegel’s research is supported by grants from the National Institutes of Health (HLB148574 and DA034748) and the Department of Veterans Affairs’ Medical Research Service. He declared no competing interests.
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