Researchers report December 22 within the journal Present Biology that the extra time reindeer spend ruminating, the much less time they spend in non-rapid eye motion (non-REM) sleep. EEG recordings revealed that reindeer’s brainwaves throughout rumination resemble the mind waves current throughout non-REM sleep, and these brainwave patterns counsel that the reindeer are extra “rested” after ruminating. The researchers speculate that this multitasking would possibly assist reindeer get sufficient sleep in the course of the summer season months, when meals is considerable and reindeer feed nearly 24/7 in preparation for the lengthy and food-sparse arctic winter.
“The extra reindeer ruminate, the much less further non-REM sleep they want,” says first creator and neuroscientist Melanie Furrer of the College of Zurich. “We predict it is essential that they’re able to save time and canopy their sleep and digestive wants on the identical time, particularly in the course of the summer season months.”
Mild-dark cycles are absent within the Arctic throughout winter and summer season, and former research confirmed that Arctic-dwelling reindeer do not show circadian behavioral rhythms throughout these seasons, although they are typically extra energetic in the course of the daytime in the course of the spring and autumn equinox, when light-dark cycles are current. Nonetheless, it was unknown whether or not these seasonal variations additionally impacted how a lot — and the way properly — reindeer sleep.
To analyze the affect of seasonal light-dark cycles on reindeer sleep patterns, the researchers carried out non-invasive electroencephalography (EEG) on Eurasian tundra reindeer (Rangifer tarandus tarandus) in Tromsø, Norway (69°N), in the course of the autumn equinox, summer season solstice, and winter solstice. The reindeer, who have been all grownup females, have been a part of a captive herd at UiT The Arctic College of Norway in Tromsø, and the experiments have been performed in indoor stables with managed lighting, limitless meals, and fixed temperature.
They discovered that reindeer slept roughly the identical quantity throughout winter, summer season, and autumn, although they have been rather more energetic in the course of the summer season. That is in distinction to different species who change the quantity they sleep in response to environmental situations. On common, the reindeer spent 5.4 hours in non-REM sleep, 0.9 hours in REM sleep, and a pair of.9 hours ruminating throughout a given 24-hour interval, no matter season.
“The truth that reindeer sleep the identical quantity throughout winter and summer season implies that they will need to have different methods to deal with restricted sleep time in the course of the arctic summer season,” says Furrer.
One attainable technique is the chance for relaxation throughout rumination — the re-chewing of partially digested meals, which is a crucial part of digestion for reindeer and different ruminants. Home sheep, goats, cattle, and Lesser mouse-deer have all been beforehand noticed to supply sleep-like mind waves throughout rumination, however it was unclear whether or not rumination might serve an identical restorative operate to sleep.
The researchers discovered that the reindeer’s EEG readings throughout rumination resembled brainwave patterns which can be indicative of non-REM sleep together with elevated slow-wave exercise and sleep spindles. Sleeping and ruminating reindeer additionally displayed comparable conduct, tending to quietly sit or stand throughout each actions, and have been much less reactive to disturbances equivalent to a neighboring reindeer sitting down or getting up — reindeer straight responded to those disturbances (by wanting towards the neighboring reindeer) 45% of the time in the event that they have been awake, however solely 25% of the time in the event that they have been ruminating, and 5% of the time in the event that they have been in non-REM sleep.
Subsequent, the researchers examined whether or not rumination might scale back the reindeer’s drive to sleep by depriving the reindeer of sleep for two hours and measuring their mind waves throughout sleep earlier than and after this deprivation. Following sleep deprivation, the reindeer’s EEG readings confirmed elevated slow-wave exercise, which is indicative of a build-up of “sleep strain” — the unconscious organic drive for extra and deeper sleep — suggesting that reindeer expertise deeper sleep following sleep deprivation.
Nonetheless, when the reindeer ruminated, this slow-wave exercise was decreased throughout subsequent sleep, and the extra they ruminated, the extra the slow-wave exercise decreased. “This means that rumination reduces sleep strain, which may gain advantage the reindeer as a result of it means they do not need to compromise on sleep restoration after they spend extra time ruminating,” says Furrer.
That is particularly essential in the course of the summer season, as a result of the extra they eat, the extra time the reindeer have to spend ruminating. “Rumination will increase nutrient absorption, so it is essential for reindeer to spend sufficient time ruminating in the course of the summer season with a purpose to acquire weight in anticipation of winter,” says Furrer.
Since reindeer seem to sleep whereas ruminating solely a number of the time, follow-up research ought to evaluate the influence of rumination whereas sleeping with rumination whereas awake and would additionally ideally measure reindeer conduct and sleep in additional pure out of doors situations, the researchers say. Nonetheless, such measurements would require surgically implanted EEG sensors quite than the non-invasive floor electrodes used on this examine.
“One other factor we might add is to take a look at younger reindeer,” says Furrer. “We all know sleep want is way increased in younger youngsters and infants in comparison with adults, so it will be attention-grabbing to take a look at sleep in youthful reindeer.”
This analysis was supported by the Swiss Nationwide Science Basis and UiT The Arctic College of Norway.