New research shows that northern fur seals are able to go without rapid eye movement sleep for two weeks while out at sea without facing problems. Since fur seals spend most of their time in the water, they spend their time going with non-REM sleep in only one brain hemisphere at a time.
Dolphins are other animals that are able to go without REM sleep while spending time in the water.
Lack Of REM Sleep
An international team of researchers from Russia, U.S., and Switzerland published their findings about the sleep of the northern fur seal in the journal Current Biology. Researchers found that just like whales and dolphins, fur seals are able to sleep with only one brain hemisphere being asleep so that they could sleep while they are at sea.
For the study, researchers used four captive northern fur seal. Activity in their brains, eyes, muscles, and hearts was tracked by equipping the seals with electrodes that recorded electric activity. To allow or prevent the fur seals from sleeping on land or in their pool, they raised and lowered the level of the water. This would expose or hide a platform that the seals used to rest.
When the northern fur seals slept in the water they experienced little or no REM sleep. When they were able to sleep on the platform they are able to resume REM sleep without having to make up for their lack of REM sleep. Other studies done with rats have shown that the rats needed more time to recover when they were deprived of REM sleep.
During this time when they weren't able to get REM sleep, the northern fur seals suffer from any adverse effects.
Warm Brain During Sleep
Like in other animals, northern fur seals' brains during REM sleep become warmer. Researchers found that when the northern fur seals slept on land, their brains alternated between REM and non-REM sleep like other animals. Researchers say that this is done in order to keep their brains from getting too cold.
Thomas Wehr, former Chief of the US National Institute of Mental Health's Clinical Psychology told Nature, that the northern fur seals may be able to sleep without the REM because their brains are able to alternate activity between both halves.