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.
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 Photographs
On a December night in 1951, Eugene Aserinsky, a physiologist on the College 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 observe a row of pens quiver throughout a rolling sheet of paper, recording exercise within the boy’s facial muscle tissue.
Hours later, the pens began to swing wildly. To evaluate from the chart, it appeared as if Armond had been awake, his eyes darting concerning the room. However when Aserinsky regarded in on him, his son was quick asleep.
Aserinsky had found R.E.M. sleep.
Ultimately he and different researchers realized 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.
Virtually all mammals expertise R.E.M. sleep, however even at this time researchers debate why it exists. On Thursday, a crew of American and Russian researchers reported that fur seals might present an essential clue.
Whereas they swim, fur seals swap off R.E.M. sleep totally. It returns after they come again to land — a sample by no means seen earlier than.
Jerome M. Siegel, a sleep skilled on the College of California, Los Angeles, and a co-author of the brand new examine printed Thursday in Present Biology, mentioned that the seals present proof that our brains swap to R.E.M. sleep every so often to generate warmth in our skulls.
“R.E.M. sleep is like shivering for the mind,” he mentioned.
Many scientists have argued that our brains require R.E.M. sleep every night time 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 night time in R.E.M. — as if they should catch up.
Some research have prompt that the mind wants R.E.M. sleep to maintain its metabolism in stability. Rats disadvantaged of R.E.M. will eat extra, and but in addition they will drop extra pounds.
This disruption may be deadly. “Should you deprive rats of R.E.M. sleep, they’ll die in two weeks,” mentioned Dr. Siegel.
[Like the Science Times page on Facebook. | Sign up for the Science Times newsletter.] However different findings have raised doubts concerning the significance of R.E.M. Sure varieties of antidepressant medicine cut 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 in periods of so-called slow-wave sleep.
A few of the most puzzling proof about R.E.M. sleep has come from the ocean.
Within 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.
However as exhausting as Dr. Mukhametov and his colleagues regarded, they by no means discovered a dolphin in R.E.M. sleep.
Within the 1990s, Dr. Siegel and Dr. Mukhametov began collaborating on research of family members of dolphins and located the hemisphere-switching sleep sample in different species, comparable to grey whales.
Extra 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 usually slept each at sea and on land.
The researchers determined to review 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 might 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 total brains slipped into slow-wave sleep, interrupted every so often by intervals of R.E.M.
However when the seals needed to sleep within the water, the mind patterns resembled these of dolphins. Just one hemisphere of their mind slept at a time. What’s extra, the fur seals skilled nearly no R.E.M. sleep.
“The R.E.M. sleep just about goes to zero and stays there so long as they’re within the water,” mentioned Dr. Siegel.
When the seals acquired again on the platform, unusual 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 R.E.M. sleep is crucial to mammals, like meals and water, Dr. Siegel mentioned. In actual fact, the sooner research on R.E.M. deprivation may not have been as compelling as they as soon as appeared.
In these earlier research, researchers stored animals from going into R.E.M. sleep by waking them up. “In some experiments, they get up the animals a thousand instances a day,” Dr. Siegel mentioned.
Fur seals in varied states of repose on the Pribilof Islands in Alaska. After 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 Photographs
The stress of being woke up time and again might have carried out the animals hurt, relatively than simply the dearth of R.E.M. sleep particularly.
A extra telling clue about R.E.M. sleep may be present in human conduct, Dr. Siegel thinks. When individuals get up on their very own, they have a tendency to maneuver out of R.E.M. sleep and change into alert. These 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, nonetheless, 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 retains the mind temperature inside a useful restrict by biking on and off the identical approach your heater in your own home would possibly do at night time,” Dr. Siegel mentioned.
Carl Zimmer’s earlier reporting on sleep
This clarification 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 developed a half-brain type of sleeping, maybe as a solution to stay alert sufficient to keep away from predators and drowning.
As a result of a part of the mind is all the time lively, it’s all the time heat. In consequence, it by no means triggers R.E.M. sleep. Solely when fur seals return to land and swap to sleeping with their total brains do the organs cool sufficient to flick the swap.
Niels C. Rattenborg, a sleep skilled on the Max Planck Institute for Ornithology in Seewiesen, Germany, mentioned the brand new examine is “one other compelling piece of proof questioning the significance of R.E.M. sleep.”
He discovered Dr. Siegel’s brain-shiver principle intriguing. However 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 principle predicts that in fur seals the mind stem stays heat at sea however cools on land.
“Till we now have that take a look at, it’s an attention-grabbing thought however stays unproven,” Dr. Rattenborg mentioned.