September 5, 2013
Hibernating Lemurs Offer Clues About Purpose Of Sleep
Brett Smith for redOrbit.com - Your Universe Online
By studying a tiny primate that is a distant relative of humans, researchers at Duke University said they are gaining new insights into the purpose of sleep.
According to the researchers’ report published this week in the journal PLOS ONE, observations of the fat-tailed dwarf lemur during its sleep and hibernation cycles indicate that sleep has a function in the regulation of body temperature and metabolism.
Lead study author Andrew Krystal, a sleep researcher at Duke, said the findings provide new information about the value of sleep, which has largely remained a mystery despite decades of research.
"If we spend nearly a third of our lives doing it, it must have some specific purpose," he said.
The lemurs are the closest genetic relatives to humans that are known to hibernate. Spending up to seven months each year in a state known as 'torpor,' the primates’ regulation of their body temperature stops and their metabolism slows down.
The torpid lemurs are also known to lower their heart rate from 120 beats per minute to just 6 and slow their breathing correspondingly. Instead of keeping a stable body temperature like most mammals, lemurs in torpor allow their bodies to sync with the temperature of the outside air, sometimes changing by as much as 25 degrees in one day.
For most mammals, this type of dramatic shift in body temperature would be life-threatening. However, by not maintaining an internal body temperature, the fat-tailed dwarf lemur conserves energy during Madagascar's dry winter season, when food and water are scarce.
To find out whether thermoregulation is one of the functions of sleep, the team hooked up electrodes to the animals' scalps and then placed them back into their nests. The team investigated both dwarf lemurs hibernating in the wilds of Madagascar and non-hibernating primates sleeping at the Duke Lemur Center. The researchers also recorded the lemurs’ oxygen intake and other vital signs.
The team said they observed two different patterns of brain activity during torpor.
"We carried out the first brain electrical activity recordings in a hibernating primate and found ultra-low voltage signals during hibernation at lower ambient temperatures indicative of minimal brain activity, but at higher ambient temperatures we observed brain activity and eye movements suggestive of a REM sleep like state,” Krystal said.
“The findings suggest that hibernation is not a state of dormancy but that sleep may occur; confirm a link between temperature, metabolic rate, and sleep; and indicate that the fat-tailed dwarf lemur may serve as an alternative model for studying sleep, temperature, and metabolism which may be uniquely relevant to understanding human physiology and improving treatments for conditions such as obesity traumatic injury stroke and rabies," he added.
To expand on their findings, the researchers said they are returning to Madagascar to study a family of small hedgehog-like animals called tenrecs that also hibernate. The team suggested that their findings could one day lead to the ability to induce a hibernation-like state in humans which could be useful for trauma patients, extending the shelf life of transplant organs, or even long-distance space travel.