The fat-tailed dwarf lemur, native to the marvelous isolated ecosystem of Madagascar, is the closest human relative known to hibernate. After studying the sleeping behavior of both captive and wild lemur specimens, scientists at Duke University have discovered a great deal about how hibernation works in lemurs. The key discovery is that they can go for days without the  deepest part of sleep, along with other insights related to body temperature and metabolism. Hopefully coupled with further knowledge to be gained in the future, scientists might one day devise a method that will also allow humans to hibernate – the only for humans to survive a trip from Earth to neighboring solar systems using conventional propulsion methods.

A young fat-tailed dwarf lemur living at the Duke Lemur Center shows the characteristic calorie-packed tail the animal uses to fuel up to 7 months of hibernation. CREDIT : David Haring, Duke Lemur Center

A young fat-tailed dwarf lemur living at the Duke Lemur Center shows the characteristic calorie-packed tail the animal uses to fuel up to 7 months of hibernation. CREDIT : David Haring, Duke Lemur Center

Why do we sleep? You might find this funny, but the key function of sleep is still rather poorly understood. What’s certain is that it’s important, otherwise our bodies, as well as those of most complex organisms, wouldn’t dedicate a third of their lifespan to it. We know sleep is important for regulating body temperature. For instance, during the body’s peak surface temperature, sleep is warranted and this is when we actually get sleepy, seduced by melatonin which starts bathing the brain. At the end of the sleep cycle, the body is the coldest. Also, studies have shown that it is during sleep that most of the information we gather during waking life is processed and memories are consolidated. Finally, sleep plays a role in regulating the metabolism. How, what are the mechanisms and whether indeed these occur due to sleep in the first place are questions that have so far been answered in mixed opinions.

The theory that sleep is vital to temperature and metabolism regulation is supported by the recent study by Duke scientists of the Madagascar lemurs –  a squirrel-sized primate. These tiny primates live up to seven months each year in a physiological state known as torpor (a form of hibernation), where the regulation of body temperature stops and metabolism slows down. Amazingly, the lemurs can  drop their heart rate from 120 beats per minute to a mere 6, and breath extremely crawled. You haven’t heard the best part yet. We humans, like most mammals, have organisms deeply dependent on body temperature. It’s enough for a variation of 2 degrees Celsius to kill most of us, yet the lemurs’  bodies heat up and cool down with the temperature of the outside air, fluctuating by as much as 25 degrees in a single day!

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That may be extreme for humans, but for lemurs the skill is paramount to survival during the long  winter dry season (not that cold for most of us – 10°C and even lower during the night), a time of year when food and water are in short supply.

The researchers then wanted to know what happens when the lemurs sleep, so they attached electrodes to the animals’ scalps and returned them to their nests for monitoring. The researchers also measured oxygen intake and other vital signs. Duke scientists measured periods of brain activity consistent with the phase of sleep known as rapid eye movement (REM) sleep — when most dreaming is believed to occur — but only when winter temperatures rose above 25 degrees Celsius. Interestingly, the lemurs went for days without the slow-wave when in torpor – the  low-amplitude brain activity associated with deep sleep.  People who use poliphasic sleep (sleeping in cycles of say 1 hour every 4 hours) also typically get lees deep sleep, while still feeling rested (not a sleep pattern for the faint of heart, though!).

Next, the researchers plan on studying other hibernating mammals – a family of small hedgehog-like animals called tenrecs. Hibernating would not only help humans actually travel through interstellar space, but also pose practical solutions in present day. Being able to push humans into standby mode by temporarily reducing heart rate and brain activity could buy time for patients who have suffered head trauma or heart attacks, extend the shelf life of transplant organs.

Krystal AD, Schopler B, Kobbe S, Williams C, Rakatondrainibe H, et al. (2013) The Relationship of Sleep with Temperature and Metabolic Rate in a Hibernating Primate. PLoS ONE 8(9): e69914. doi:10.1371/journal.pone.0069914

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