MIAMI.- Researchers have discovered that the more time reindeer spend ruminating, the less time they spend in non-rapid eye movement (non-REM) sleep, according to a study published in the journal ‘Current Biology’.
EEG recordings revealed that the reindeer’s brain waves during rumination resemble the brain waves present during non-REM sleep, and these brain wave patterns suggest that the reindeer are more “rested” after ruminating. The researchers speculate that this multitasking could help the reindeer get enough sleep during the summer months, when food is plentiful and the reindeer are fed nearly 24/7 in preparation for the long, lean season. arctic winter
“The more reindeer ruminate, the less additional non-REM sleep they need,” explains first author and neuroscientist Melanie Furrer of the University of Zurich in Switzerland.
Light-dark cycles are absent in the Arctic during winter and summer, and previous studies have shown that Arctic-dwelling reindeer do not show circadian behavioral rhythms during these seasons, although they tend to be more active during the day in the Arctic. spring and autumn equinoxes, when light-dark cycles are present. However, it was unknown whether these seasonal differences also influenced how much and how reindeer sleep.
To investigate the influence of seasonal light-dark cycles on reindeer sleep patterns, researchers performed non-invasive electroencephalography (EEG) on Eurasian tundra reindeer (‘Rangifer tarandus tarandus’) in Tromso, Norway (69° N), during the autumn equinox, the summer solstice and the winter solstice. The reindeer, all adult females, were part of a captive herd at UiT, the Arctic University of Norway, in Tromso, and the experiments were carried out in indoor stables with controlled lighting, unlimited feeding and constant temperature.
They found that the reindeer slept approximately the same in winter, summer and autumn, despite being much more active in summer. This contrasts with other species that change the amount of sleep in response to environmental conditions. On average, reindeer spent 5.4 hours in non-REM sleep, 0.9 hours in REM sleep, and 2.9 hours ruminating during a given 24-hour period, regardless of season.
“The fact that reindeer sleep the same amount in winter and summer means that they must have other strategies to cope with the limited sleep time during the Arctic summer,” says Furrer.
One possible strategy is the opportunity to rest during rumination, that is, the re-chewing of partially digested food, which is an important component of digestion for reindeer and other ruminants. It had previously been observed that domestic sheep, goats, cattle and deer mice produce sleep-like brain waves during rumination, but it was unclear whether rumination could have a sleep-like restorative function.
The researchers found that the reindeer’s EEG readings during rumination resembled brain wave patterns indicative of non-REM sleep, such as increased slow wave activity and sleep spindles. Sleeping and ruminating reindeer also showed similar behavior, tending to sit or stand up quietly during both activities, and reacted less to perturbations such as a neighboring reindeer sitting or standing up: the reindeer responded directly to these perturbations (looking towards the neighboring reindeer) 45% of the time if they were awake, but only 25% of the time if they were ruminating, and 5% of the time if they were in non-REM sleep.
Next, the researchers tested whether rumination could reduce the reindeer’s drive to sleep by depriving them of sleep for 2 hours and measuring their brain waves during sleep before and after this deprivation. Following sleep deprivation, the reindeer’s EEG readings showed an increase in slow wave activity, which is indicative of an increase in “sleep pressure” – the unconscious biological drive to sleep longer and deeper. suggesting that reindeer experience deeper sleep after sleep deprivation.
However, when the reindeer ruminated, this slow wave activity decreased during subsequent sleep, and the more they ruminated, the more the slow wave activity decreased.
This is especially important during the summer, because the more they eat, the more time the reindeer need to ruminate. “Rumination increases nutrient absorption, so it is crucial that reindeer spend enough time ruminating during the summer to gain weight for the winter,” he adds.
Since reindeer appear to sleep while ruminating only part of the time, follow-up studies should compare the impact of rumination while sleeping with that of rumination while awake, and ideally also measure reindeer behavior and sleep. in more natural outdoor conditions, the researchers say. However, these measurements would require surgical implantation of EEG sensors instead of the non-invasive surface electrodes used in this study.
“Another thing we could add is to look at young reindeer,” says Furrer. “We know that the need for sleep is much greater in young children and babies than in adults, so it would be interesting to look at sleep in reindeer.” younger”.
Source: EUROPA PRESS
