If your non-stop feasting at Christmas leaves you exhausted, it might be worth taking inspiration from reindeer: research suggests the animals can sleep while they chew.
During the summer months, reindeer spend most of their time munching on leaves – an important food-giving activity that can be scarce in winter. However, a study suggests that one way they balance their need to consume with the need to sleep is through multitasking.
“We speculate that in nature the ruminant can take over an important part of the sleep cover,” said Prof Gabriela Wagner, a co-author of the research from the Norwegian Institute for Bioeconomy Research in Tromsø. Norway.
Write in the journal Current Biologyreport the team collected data on brain activity from four adult female reindeer, using non-invasive electrodes taped to their scalps – a method known as EEG.
The data were collected over four days in each of the winter, summer and autumn seasons during which the animals were respectively exposed to constant darkness, constant light and a natural change between day and night.
Analysis of the EEG data revealed that, on average, the reindeer spent the same amount of time asleep regardless of the season, with the amount of time spent in each stage of sleep – whether or not it was in rapid eye movement (REM) sleep -REM sleep is. – also steady over winter, summer and autumn.
Among other things, the team carried out experiments in which they disrupted the reindeer’s sleep for two-hour periods, and found that this led to an increase in slow wave activity in the animals’ brains – indicating that the animals had the need to sleep
“This suggests that the reindeer brain has an “idea” of how much sleep the reindeer needs to function well – just like ours,” said Wagner. “It’s not like that in all animals.”
However, the team discovered that after the reindeer spent time chewing the cud, this slow-wave activity decreased—suggesting that the sleepiness had lifted.
“It was the opposite of what we saw when we kept them awake,” said Dr Melanie Furrer, first author of the study from the University of Zurich.
Indeed, analysis of the EEG data, as well as behavioral observations, by the team revealed that during rumination, the reindeer entered a state similar to non-REM sleep.
The researchers say the reindeer spent, on average, the same amount of time in this ruminative sleep state throughout the seasons – likely due to the captive environment of the study where easily digestible food was provided. However, Furrer noted that individual reindeer that ruminated more had less additional non-REM sleep.
The team suggests that the findings could have important implications for reindeer in the wild.
“We think the ability to sleep while digesting may be particularly important during the short summer when the reindeer are active all day to eat enough food [and] storing fat in anticipation of the food cart winter months,” Wagner said.
