The hibernation habits of lemurs have the potential to allow humans to travel deep into space.
Fat-tailed dwarf lemurs, from Madagascar, hibernate for up to seven months of the year to conserve energy during the island's long winter dry season, during which little food and water is available.
Researchers from Duke University said these lemurs may provide an insight into human sleep, as they are the closest genetic relative to humans that are known to hibernate.
Why people sleep is still a mystery to scientists. Explanations include energy conservation, the processing of information and memories and removing toxins from the body that build up during waking hours.
Andrew Krystal, lead author of the study, said: "If we spend nearly a third of our lives doing it, it must have some specific purpose."
Fat-tailed dwarf lemurs hibernate in a state known as torpor, where the regulation of body temperature stops and the metabolism slows down. These lemurs are able to reduce their heart rate from 120 beats-per-minute to just six during hibernation.
During torpor, the lemur's bodies heated up and cooled down with the temperature of the outside air - rather than maintaining a steady body temperature. During one day, the lemur body temperature could fluctuate up to 25C. Normally in mammals, just a few degrees change in body temperature can be life-threatening.
The researchers say fat-tailed lemur hibernation is a way to conserve energy and tested how they sleep during torpor.
They attached electrodes to the scalps of wild lemurs during hibernation and non-torpid animals sleeping in captivity.
Findings showed that the lemurs went for days without the slow-wave, low-amplitude activity associated with deep sleep. They had periods of rapid eye movement (REM) sleep, when dreaming is thought to occur, but only when temperatures rose above 25C.
The researchers believe the lemur hibernating habits supports the idea that sleep plays a role in regulating body temperature and metabolism, and may lead to scientists being able to induce hibernation-like states in humans.
They say being able to put humans into a "standby mode" by reducing their brain activity and heart rate, doctors could better help patients who had suffered head trauma or heart attacks. Researchers could also extend the shelf life of transplant organs and potentially make way for long-distance space travel.