By Mollie Bloudoff-Indelicato. Originally published on September 4, 2013 in National Geographic online. View the original here.

Pictured: A fat-tailed dwarf lemur peeks out of a tree in Madagascar. Photograph by Frans Lanting, National Geographic.

A fat-tailed dwarf lemur peeks out of a tree in Madagascar. Photograph by Frans Lanting, National Geographic NationalGeographic_1370398


Ever wished you could hibernate? Ask a fat-tailed dwarf lemur how it’s done.

These mini-primates have a talent that could help save human lives. Fat-tailed dwarf lemurs are the only primates that can hibernate, according to a new study published in the journal PLoS ONE. And lemurs are unique in that they can go the entire hibernation period—up to eight months—without fully sleeping.

Because lemurs are genetically very similar to humans, these animals may one day teach us how to hibernate, opening up new possibilities for space travel, modern medicine, and warfare.

“We’ve always known that fat-tailed dwarf [lemurs] are pretty incredible,” said Chris Smith, a conservationist at the Duke Lemur Center in Durham, North Carolina.

Hibernation Could Extend Life

Hibernation immediately conjures up images of bears slumbering in caves. But hibernation doesn’t necessarily mean sleep. In fact, hibernation simply refers to the seasonal bodily changes that occur in some animals—slower heart rates, decreased oxygen intake, and a reduced ability to regulate body temperature. The entire process is extraordinary from a biological point of view. If humans could do it, the practical applications would be limitless.

Consider terminally ill patients who will die without an organ transplant, Smith said. With every breath, every heartbeat, they are slipping away. But during hibernation, a lemur’s breathing can slow to one inhalation every 20 minutes, and its heart rate drops from a normal 200 beats per minute to just 4 beats per minute. Do the same thing for a human, and a patient could remain in this suspended state until a donor is found.

“We [could] induce their body into a hibernation-like state, where there’s little body function, to preserve life,” Smith said. “Six months down the road, when we do have an organ donor, we [would] bring them out of the hibernation state and conduct a transplant.”

The same thing applies to soldiers wounded in the field. Or astronauts who need to travel for years to reach their destinations and are unable to bring large quantities of food to sustain themselves during the trip. The ability to hibernate could even increase a human’s life span.

“Hibernators do live longer than non-hibernators,” said Andrew Krystal, a sleep medicine physician with the Duke University School of Medicine and co-author of the study. “It looks like the time [the lemurs] are hibernating is added onto their lives.”

Lemur Dreams

While lemurs can hibernate, surviving three-quarters of a year without deep sleep, humans aren’t so lucky. The longest a human has ever been recorded going without sleep is allegedly 18 days, 21 hours, and 40 minutes, according to a University of California, Berkeley, website.

But since severely sleep-deprived humans have a tendency to fall asleep for seconds at a time, it’s hard to prove such claims without brain monitoring. What we do know is that lack of sleep raises the risk of mood problems, obesity, diabetes, and cardiovascular disease.

“Why do we sleep?” Krystal said. “We spend a third of our time sleeping. Obviously there must be some great reason why we do it, and interestingly, we don’t fully understand what it’s for.”

In humans, there are two different types of sleep: rapid eye movement (REM) sleep—which is when we dream—and non-REM sleep. Non-REM sleep is vital. When you fall into bed after pulling an all-nighter, it’s that deep, non-REM sleep that you want. Scientists believe that non-REM sleep has a replenishing effect on our bodies. Humans can’t go long without this type of sleep, and neither can most animals.

A 1989 study by sleep scientist Allan Rechtschaffen from the University of Chicago demonstrated the lethal consequences of sleep deprivation. When the researcher kept ten rats awake, depriving them of non-REM sleep, they developed skin lesions, lost weight, and experienced an erosion of their gastrointestinal tracts. After 32 days, all of the rats were dead.  

However, when lemurs hibernate, scientists speculate that they experience only REM sleep. Though no one can prove whether lemurs actually dream, these primates exhibit all the telltale signs of a full night’s REM sleep such as increased brain activity, rapid eye movements, and muscle paralysis.

But because REM sleep does not have the supposed replenishing effects of non-REM sleep, Krystal said, it’s like the lemurs aren’t sleeping at all.

“If you completely deprive animals of [non-REM] sleep, then they die,” Krystal said. “And yet the lemurs that hibernate appear to be able to go for months without sleep…and they’re not dying.”

What Triggers Hibernation?

Krystal has been studying how and why fat-tailed lemurs hibernate since 2006. But his initial attempts at measuring lemur brain activity did not go as planned.

“I assumed I’d be able to record their brain activity,” Krystal said, “and it turned out [the lemurs] were running around and biting. They were able to avoid us easily.”

Lemurs in captivity often don’t hibernate, so Krystal and his team visited the primates in their natural habitat—Madagascar. Unfortunately, the measurements there weren’t much easier.

“Some of [the lemurs hibernated] 40 feet off the ground in the middle of the forest in coastal Madagascar,” Krystal said.

By placing the lemurs in special nesting boxes and attaching EEGs to their tiny foreheads while they hibernated, Krystal was able to record their vital signs. He found that when it was warm outside, close to 72 degrees Fahrenheit (22 degrees Celsius), the primates would only hibernate in REM sleep.

The next step is to replicate the study with more than just six lemurs and follow the primates for a month, rather than only five days. The research could lead Krystal and his team closer to the answers they’ll need to someday replicate the results in humans.

“There’s a lot of mystery left. It raises this great question: Can [lemurs] really go that long and survive without non-REM sleep?” Krystal said. “The idea that you could have an animal that doesn’t sleep and survives—it’s surprising.”