The reindeer puts its brain in sleep mode while chewing its food, which reduces its need for deep sleep. This brain state helps increase food intake during the abundant summer months in the Arctic.
The Need for Sleep
Researchers conducted electroencephalography (EEG) recordings of Eurasian reindeer held in Tromsø, Norway, tracking their brain activity during the autumnal equinox in September, the summer solstice in June, and the winter solstice in December.
The Impact on Sleep
Researchers found that the reindeer’s brains exhibited increased slow waves and bursts of rhythmic activity during the digestive process, patterns usually associated with non-rapid eye movement sleep. Although they do not always close their eyes, reindeer chewing their food exhibited sleeping-like behavior. They sat and stood quietly, responding less to sounds made by other reindeer.
The Effect of Digestion on Sleep
The more intense the digestion, the less the reindeer’s actual need for sleep. When researchers reduced the reindeer’s usual sleep time by two hours by speaking loudly, petting them, and enticing them with fresh food, the team noted an increase in slow wave activity in the reindeer’s brains, indicating an increase in sleep pressure – the natural biological drive for sleep.
Reindeer Response to the Environment
Researcher Melanie Furrer believes this response is a reaction to the polar environment, which fluctuates between lush summer and snow-covered winter. “It’s a strategy to ensure adequate time in the summer for continuous feeding, and to fatten the reindeer for the polar winter when food availability is very low.”
The Importance of Sleep for Reindeer
Melanie Furrer notes that total sleep time – measured as the time reindeer spend in detected states of inactivity by EEG signals – did not change throughout the year. The team expected that sleep hours would decrease in summer and increase in winter when the animals are less active and need to conserve energy.
Previous Research
Jerome Siegel, a neuroscientist at the University of California, Los Angeles, states that the study complements other work in animals, including marine mammals, showing that how an animal sleeps is a function of its environment. Several studies have found brainwave patterns resembling non-rapid eye movement sleep during the digestive process in sheep, cows, and mousedeer (Tragulus kanchil). However, the current study is the first to explore how sleep-like brain activity during digestion affects the need for deep sleep.
References:
Furrer, M. et al. Curr. Biol. https://doi.org/10.1016/j.cub.2023.12.012 (2023).
Siegel, J. M., Nature Reviews Neuroscience 10, 747–753 (2009) https://doi.org/10.1038/nrn2697
Source: https://www.nature.com/articles/d41586-023-04034-x
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