Hot Heads: Why Mammals Need R.E.M. Sleep

Sleeping fur seals toggle between two mind patterns: one whereas at sea, the opposite on land. Researchers recommend that R.E.M. sleep serves to heat the mind.

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Fur seals can swap on and off R.E.M. sleep after they’re within the sea and on land, a sample by no means seen earlier than. Scientists imagine it would imply R.E.M. sleep helps generate warmth in our skulls, like shivering for the mind.CreditMickrick, through Getty Images

On a December night in 1951, Eugene Aserinsky, a physiologist on the University of Chicago, positioned electrodes on the scalp of his Eight-year-old son, Armond, earlier than placing him to mattress. Then the scientist retired to a different room to watch a row of pens quiver across a rolling sheet of paper, recording exercise within the boy’s facial muscle mass.

Hours later, the pens began to swing wildly. To decide from the chart, it appeared as if Armond had been awake, his eyes darting concerning the room. But when Aserinsky seemed in on him, his son was quick asleep.

Aserinsky had found R.E.M. sleep.

Eventually he and different researchers discovered that in this state, the mind shifts from low-frequency to high-frequency electrical waves, like these produced in waking hours. When Aserinsky woke his topics from R.E.M. sleep, they usually reported vivid goals.

Almost all mammals expertise R.E.M. sleep, however even right now researchers debate why it exists. On Thursday, a crew of American and Russian researchers reported that fur seals might present an essential clue.

While they swim, fur seals swap off R.E.M. sleep solely. It returns after they come again to land — a sample by no means seen earlier than.

Jerome M. Siegel, a sleep knowledgeable on the University of California, Los Angeles, and a co-author of the brand new examine printed Thursday in Current Biology, stated that the seals present proof that our brains switch to R.E.M. sleep from time to time to generate heat in our skulls.

“R.E.M. sleep is like shivering for the brain,” he stated.

Many scientists have argued that our brains require R.E.M. sleep every evening to perform correctly. One clue comes from experiments through which researchers deprive rats of R.E.M. sleep for a number of days.

As quickly because the rats can sleep usually once more, they expertise a “rebound,” spending extra time every evening in R.E.M. — as if they should catch up.

Some research have urged that the mind wants R.E.M. sleep to maintain its metabolism in steadiness. Rats disadvantaged of R.E.M. will eat extra, and but in addition they will shed some pounds.

This disruption might be deadly. “If you deprive rats of R.E.M. sleep, they’ll die in two weeks,” stated Dr. Siegel.

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But different findings have raised doubts concerning the significance of R.E.M. Certain kinds of antidepressant medicine scale back R.E.M. sleep in customers, for instance, with out proof of hurt.

R.E.M. isn’t even important for dreaming. Researchers have discovered that folks additionally dream during times of so-called slow-wave sleep.

Some of probably the most puzzling proof about R.E.M. sleep has come from the ocean.

In the 1970s, a Russian biologist named Lev M. Mukhametov positioned electrodes on the heads of dolphins. He found that they’ll put one aspect of the mind to sleep as they swim whereas the opposite aspect stays alert. Then they’ll swap, placing the opposite hemisphere to sleep.

But as onerous as Dr. Mukhametov and his colleagues seemed, they by no means discovered a dolphin in R.E.M. sleep.

In the 1990s, Dr. Siegel and Dr. Mukhametov began collaborating on research of family of dolphins and located the hemisphere-switching sleep sample in different species, akin to grey whales.

More lately, the scientists questioned what they may discover in the event that they checked out a species between the 2 ends of the spectrum: a mammal that frequently slept each at sea and on land.

The researchers determined to check 4 fur seals. The animals spend weeks or months swimming within the ocean, however they arrive on land to mate and rear their younger.

Oleg I. Lyamin, a neuroscientist who splits his time between U.C.L.A. and the Severtsov Institute of Ecology and Evolution in Moscow, implanted electrodes within the seals and strapped knowledge recorders to their backs.

The fur seals lived in a pool the place they may swim round or haul themselves onto a dry platform. After two days of recordings, the researchers took away the platform.

For as much as two weeks, the seals might solely swim within the pool. Then the researchers put the platform again, permitting the fur seals to doze out of the water once more.

On the platform, the researchers discovered, the fur seals slept a lot as land mammals do. Their whole brains slipped into slow-wave sleep, interrupted every so often by intervals of R.E.M.

But when the seals needed to sleep within the water, the mind patterns resembled these of dolphins. Only one hemisphere of their mind slept at a time. What’s extra, the fur seals skilled virtually no R.E.M. sleep.

“The R.E.M. sleep pretty much goes to zero and stays there as long as they’re in the water,” stated Dr. Siegel.

When the seals obtained again on the platform, atypical R.E.M. sleep returned. Their lengthy spell of R.E.M.-free sleep did them no obvious hurt, and so they didn’t expertise any R.E.M.-sleep rebound.

The outcomes undermine the concept that R.E.M. sleep is important to mammals, like meals and water, Dr. Siegel stated. In reality, the sooner research on R.E.M. deprivation won’t have been as compelling as they as soon as appeared.

In these earlier research, researchers saved animals from going into R.E.M. sleep by waking them up. “In some experiments, they wake up the animals a thousand times a day,” Dr. Siegel stated.

Fur seals in numerous states of repose on the Pribilof Islands in Alaska. When they sleep within the water, their mind patterns resemble these of dolphins, however after they sleep on land, R.E.M. sleep returns.CreditEnrique R. Aguirre Aves, through Getty Images

The stress of being woke up again and again might have carried out the animals hurt, somewhat than simply the shortage of R.E.M. sleep particularly.

A extra telling clue about R.E.M. sleep might be present in human conduct, Dr. Siegel thinks. When folks get up on their very own, they have a tendency to maneuver out of R.E.M. sleep and develop into alert. Those woke up from slow-wave sleep are groggy and disoriented.

Dr. Siegel and his colleagues suggest that the mind cools throughout slow-wave sleep. To maintain the mind from getting too chilly, nevertheless, the mind periodically unleashes a torrent of exercise. Oxygen-rich blood flows into the mind to gas the exercise, warming the mind within the course of.

“It keeps the brain temperature within a functional limit by cycling on and off the same way your heater in your house might do at night,” Dr. Siegel stated.

Carl Zimmer’s earlier reporting on sleep

This rationalization might additionally account for why dolphins don’t expertise R.E.M. sleep — and why seals don’t as they swim.

These marine mammals have advanced a half-brain model of sleeping, maybe as a strategy to stay alert sufficient to keep away from predators and drowning.

Because a part of the mind is at all times lively, it’s at all times heat. As a outcome, it by no means triggers R.E.M. sleep. Only when fur seals return to land and swap to sleeping with their whole brains do the organs cool sufficient to flick the swap.

Niels C. Rattenborg, a sleep knowledgeable on the Max Planck Institute for Ornithology in Seewiesen, Germany, stated the brand new examine is “another compelling piece of evidence questioning the importance of R.E.M. sleep.”

He discovered Dr. Siegel’s brain-shiver idea intriguing. But he wished to see it put to the take a look at.

Neuroscientists have recognized a clump of neurons within the mind stem because the swap that activates R.E.M. sleep. Dr. Siegel’s idea predicts that in fur seals the mind stem stays heat at sea however cools on land.

“Until we have that test, it’s an interesting idea but remains unproven,” Dr. Rattenborg stated.

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