you're reading...


Sleeping with one eye open: fur seals may help us understand sleep patterns

Source: Lyamin, O. I., Kosenko, P. O., Korneva, S. M., Vyssotski, A. L., Mukhametov, L. M., & Siegel, J. M. (2018). Fur Seals Suppress REM Sleep for Very Long Periods without Subsequent Rebound. Current Biology, 28, 1–6. http://doi.org/10.1016/j.cub.2018.05.022


I love my sleep. Keep me from getting my usual 8 hours, and I am worthless the next day. And I’m not alone- when we routinely skip out on sleep, we become cognitively impaired and can put our health at risk. Other animals rely on sleep too. Most mammals and birds spend their nights moving between two types of sleep: slow wave sleep , and rapid eye movement (REM) sleep (the time at night when you dream). Mammals deprived of REM sleep have shown some pretty troubling physical symptoms. For example, after about a week of sleep deprivation, mice suffer from skin lesions, hypothermia, weight loss, and even possible death.

Yet, some marine mammals like whales and dolphins do not seem as reliant on sleep. In fact, scientists have never even recorded REM sleep in whales or dolphins! Instead, these marine mammals rest half their brain in a stage of slow wave sleep while the other hemisphere of their brain is active, switching which half of the brain is resting or active. This may allow whales and dolphins to continually regulate their breathing since they have to voluntarily take breaths at the surface (as opposed to humans and other land mammals that involuntarily breathe without having to constantly think about taking a breath). But this is just one hypothesis, and without knowing exactly what REM sleep does in mammals in the first place, scientists are not able to definitively explain why whales and dolphins can get along so well without it.

A fur seal snoozing on land (image from wikimedia commons)

To unravel the mystery of REM sleep, scientists turned to a semi-aquatic mammal – the northern fur seal (Callorhinus ursinus). Northern fur seals spend most of their life at sea. When they come to land during the summer breeding season, the seals will alternate between staying on land for several days and going out to sea to forage for up to two weeks at a time. After the breeding season is done, the fur seals will spend about 10 months at sea completing a predominately solitary migration.

Scientists have been able to study the sleep patterns of fur seals by observing the habits of individuals in captivity. For this study, scientists monitored four individual seals in simulated environmental conditions in a tank to see how their sleep patterns changed on land versus out at sea. The scientists hooked electrodes up to the seals, allowing them to continuously measure their brain waves (electroencephalogram) from both halves (“hemispheres”) of their brain, heart rate (electrocardiogram), and eye (electrocculogram) and muscle (electromyogram) movement during the experiment. First, the seals were given access to a platform, which could be used to get out of the water, (to simulate land) for two days. Then, the water level was increased in the tank and the platform was removed to simulate being at sea. The seals were kept “at sea” for 10-14 days before the water level in the tank was lowered and the platform was returned to allow the seals access to “land”. During this entire timeline, the scientists observed how the seals slept.

While on land, the seals went through periods of both slow wave and REM sleep, averaging about 80 min of sleep a day. But while at sea, the fur seals did not go through much, if any, REM sleep cycles and averaged only 3 min of REM sleep a day. Instead, the seals transitioned into a mode of slow wave sleep similar to that seen in whales and dolphins- one hemisphere of their brain remained active while the other one rested. The seals only nodded off into REM sleep for very short periods of time. After only 10 days at sea, this reduction in REM sleep added up to over 12.8 fewer hours of REM sleep than the seal would have had during its normal sleep cycles on land. Overall, these seals lost way more REM sleep than the mice that were put through sleep deprivation studies mentioned earlier, and yet, the seals were fine!

While at sea, fur seals can rest by switching from REM sleep cycles to resting half of their brain at a time. (Image from pixabay)

After their 10-14 days at sea, the seals showed no physical signs of stress, weight or appetite loss, and acted completely normal. Most mammals subjected to sleep deprivation try to make up for their lost sleep afterwards (yes, exactly like you sleeping in on the weekends to make up for all those early workdays) so the scientists continued to monitor the seals’ sleep patterns for two days. The seals immediately transitioned back into their normal REM sleep cycle, resting both halves of their brain at the same time. While two of the seals spent far more time in REM sleep than they had prior to REM deprivation, it was nowhere near the level of recuperation typically required by mammals after losing out on REM sleep.

It makes sense that the seals would avoid REM sleep while at sea since, just like wales and dolphins, they need to stay at the surface and control their breathing. Dipping into a deeper REM sleep state could also spell disaster for these solitary seals if they are not alert enough to look for predators at all times. By resting only half of their brain at a time, the seals (as well as whales and dolphins) are able to continue swimming, stay more alert, and (literally) sleep with one eye open.

But the researchers think there may be another reason seals are able to forgo REM sleep without showing the typical negative side effects of sleep deprivation. They propose that REM sleep may be a way to warm up the brain stem after it has cooled down during slow wave sleep. It is possible that because the seals only rest half of their brain at a time while they are at sea, the other, active half of the brain is able to keep the brain stem warm enough; thereby preventing the need of a warming REM stage. The researchers, of course, will need to conduct further studies to prove if this is actually a major function of REM sleep and if the seals can retain brain heat sufficiently while only resting half of their brain at a time.  By studying how fur seals respond when switching between sleeping modes on land and at sea, researchers hope to discover the underlying purpose of REM sleep.


No comments yet.

Post a Comment


  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 6 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 9 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 10 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 11 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com