New research found reindeer might be more rested in winter because their brains go into power-saving mode while chewing their cud.
A study published Thursday by researchers in Norway found brainwaves observed in reindeer during mimic brainwaves present during non-REM sleep, which suggests reindeer are more rested after ruminating.
Rumination, commonly known as chewing cud, is the act of regurgitating food and chewing it again to absorb more nutrients.
Researchers speculated this restive state during rumination might help reindeer get enough sleep during the summer months when food is abundant in preparation for the long and food-sparse arctic winter.
"We think it's very important that they are able to save time and cover their sleep and digestive needs at the same time, especially during the summer months," said first author and neuroscientist Melanie Furrer of the University of Zurich.
To investigate the influence of shifting seasonal light-dark cycles on reindeer sleep patterns, the researchers used noninvasive surface electrodes to monitor the brainwaves of Eurasian tundra reindeer during the autumn equinox, summer solstice and winter solstice.
The reindeer were part of a captive herd at UiT The Arctic University of Norway in Tromsø, and the experiments were conducted in indoor stables with controlled lighting, unlimited food and constant temperature.
Researchers found the reindeer slept the same amount during the winter, summer and autumn despite being more active in the summer.
"The fact that reindeer sleep the same amount during winter and summer implies that they must have other strategies to cope with limited sleep time during the arctic summer," Furrer said.
Other ruminants, such as domestic sheep, goats and cattle, were previously observed to develop sleep-like brainwaves during rumination, but it's been unclear whether rumination serves a similar reenergizing function to sleep.
Sleeping and ruminating reindeer also displayed similar behavior, researchers said. Ruminating reindeer were less responsive to disturbances, such as neighboring reindeer sitting down or getting up, in a similar pattern to sleeping reindeer.
The research team also tested whether or not rumination could reduce a reindeer's drive to sleep by depriving them of sleep for two hours and then measuring their brainwaves before and after sleep deprivation. According to the findings, the reindeer showed increased slow-wave activity, which implies an unconscious drive for more and deeper sleep. The more reindeer ruminated, however, the more slow-wave activity decreased.
"This suggests that rumination reduces sleep pressure, which could benefit the reindeer because it means they don't have to compromise on sleep recovery when they spend more time ruminating," Furrer said, adding rumination also increases nutrient absorption, making it crucial for reindeer to spend the summer months eating and ruminating to gain weight and be well-rested for winter.
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