Summary Prospective epidemiological studies in industrial societies indicate that 7 h of sleep per night in people aged 18 years or older is optimal, with higher and lower amounts of sleep predicting shorter lifespan . Humans living a hunter-gatherer lifestyle (e.g., tribal groups) sleep 6 to 8 h per night, with the longest sleep duration in winter. The prevalence of insomnia in hunter-gatherer populations is low (around 2%) compared to the prevalence of insomnia in industrial societies (around 10-30%). Sleep deprivation studies, which are done to obtain information about sleep function, are often confused with the effects of stress . Consideration of the duration of spontaneous daily sleep across mammalian species, which ranges from 2 h to 20 h, may provide important insights into the function of sleep without the stress of deprivation. Sleep duration is not related to brain size or cognitive ability. Rather, sleep duration across species is associated with their ecological niche and foraging requirements , indicating a role for sleep-wake balance in food acquisition and energy conservation. Brain temperature drops from waking levels during non-rapid eye movement (non-REM) sleep and rises during REM sleep. The average daily REM sleep time of homeothermic orders is negatively correlated with average body and brain temperature, with the greatest amounts of REM sleep in egg-laying mammals (monotreme), moderate amounts in pouched mammals (marsupials), larger amounts low in placental mammals and lower amounts in birds. REM sleep could therefore play a key role in regulating brain temperature and metabolism during sleep and facilitating alert awakening. |
Comments
Groups of warm-blooded animals with higher body temperatures have lower amounts of rapid eye movement (REM) sleep, while those with lower body temperatures have more REM sleep, according to new research from UCLA professor Jerome Siegel. , who said their study suggests that REM sleep acts as a "thermostatically controlled brain heater."
The study in Lancet Neurology suggests a previously unobserved relationship between body temperature and REM sleep, a period of sleep in which the brain is very active, said Siegel, who directs the Sleep Research Center at the Jane and Terry Institute. Semel of Neuroscience and Human Behavior at UCLA.
Birds have the highest body temperature of any group of warm-blooded or homeothermic animals at 41 degrees while having the least amount of REM sleep at 0.7 hours per day. They are followed by humans and other placental mammals (37 degrees, 2 hours of REM sleep), marsupials (35 degrees, 4.4 hours of REM sleep), and monotremes (31 degrees, 7.5 hours of REM sleep).
Brain temperature drops during non-REM sleep and then rises during the REM sleep that usually follows. This pattern “allows homeothermic mammals to save energy in non-REM sleep without the brain becoming so cold that it becomes unresponsive to threats,” Siegel said.
The amount of REM sleep in humans is neither high nor low compared to other homeothermic animals, "undermining some popular views that suggest a role for REM sleep in learning or emotional regulation," he said.
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. She declared no competing interests.
