Reindeer can activate sleep mode while eating

Close-up of a reindeer in a snowy field in Norway.

Reindeer put their brains into sleep mode while they chew their food, reducing their need for deep sleep.Credit: Henry Lo/500px via Getty

Summer is a long way off for Arctic reindeer, but those who gorged themselves during these bountiful months will be well equipped to survive the winter. A study published today in Current biology1 reports that reindeer can put their brains into a sleep state while they chew, meaning they are able to maximize their meal time during Arctic summers.

“Reindeer can meet both their digestive needs and their sleep needs,” says Melanie Furrer, first author of the study and a neuroscientist at the University of Zurich, Switzerland.

Like a cow, a reindeer has four chambers in its stomach and it uses the first to store grass for later regurgitation and chewing – a process known as rumination.

The need to sleep

Researchers made electroencephalogram (EEG) recordings of captive Eurasian tundra reindeer (Rangifer tarandus tarandus) in Tromsø, Norway, monitoring their brain activity during the autumnal equinox in September, the summer solstice in June, and the winter solstice in December.

They found that during rumination, the reindeer brain exhibits increased slow waves and rhythmic bursts of activity – patterns typically associated with non-REM sleep. Although they do not always have their eyes closed, ruminating reindeer have also shown sleep-like behaviors. They sat and stood quietly and reacted less to the noises made by the other reindeer.

The more they chewed the cud, the less sleep the reindeer seemed to need. When researchers reduced reindeer’s usual sleep time by two hours by talking loudly, petting them, and enticing them with fresh food, the team observed an increase in slow-wave activity in the reindeer’s brain. reindeer, suggesting increased sleep pressure. the normal biological drive to sleep.

But if the reindeer ruminated, their subsequent sleep showed less slow-wave activity than reindeer who did not ruminate. “The need to sleep decreases with rumination. This is probably the case because reindeer can “sleep” during rumination,” says Furrer.

She believes it is a response to the Arctic’s turbulent environment, characterized by lush, grassy summers and snowy winters. “This is a strategy to ensure enough time in summer for near-constant feeding, to fatten up for the Arctic winter with very low food availability.”

Furrer says that, surprisingly, total sleep duration – measured as time spent in inactive states detected by EEG signals – did not change throughout the year. The team expected that reindeer would sleep less in summer and more in winter, when the animals are much less active and need to conserve energy.

“These results are particularly interesting because we know that there are animals that decrease their sleep time depending on environmental conditions, but this does not seem to be the case in reindeer,” explains Furrer. “This shows how essential sleep is and that it is very tightly regulated in reindeer.”

Jerome Siegel, a neurobiologist at the University of California, Los Angeles, says the study complements other work.2 in animals, including marine mammals, showing that the way an animal sleeps is a function of its environment. Several studies have found brain wave patterns resembling non-REM sleep during rumination in sheep, cattle, and small mouse deer (Tragulus canchil). However, the current study explored for the first time how sleep-like brain activity during rumination modifies the need for deep sleep.


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