Unihemispheric Sleep And Sleep Deprivation

Picture Source - Pexels (CC0)

There has been a difference in opinion regarding the importance of sleep after it was discovered that a sleep-deprived fruit fly, particularly a male fruit fly, can live as long as an average fruit fly which has been getting a proper duration of sleep or what we thought as the act of sleeping. We can't be sure if a certain action taken by flies can be regarded as the perceived action, for example, if they were static for a certain duration, we perceived them to be sleeping. Technically speaking, there are a few reasons why they could act the way they did, for example, cleaning themselves, eating and any associated micro moving behaviour but it can be useful to us to understand certain aspects of pathology or in this case, the fact that sleeping gives an insignificant contribution to their longevity.

A sleep-deprived male fruit fly bears the same lifespan of a normal male fruit fly and a sleep-deprived female fruit fly lives three days shorter than a normal female fruit fly which constitutes approximately 6 to 7% of their total lifespan. This is a particularly shocking result as we used to think that animals need to sleep the same way they need to eat food to survive. So how is this thing relevant for us? Well, for starters, even though we aren't really sure how sleep deprivation can kill us, we do know that it can reduce productivity, creativity and other things which are necessary to produce a good outcome. Think about your value if you can't consolidate your memory properly by getting enough sleep or you can't really find a solution to a specific problem as your brain was craving sleep more than anything else. People who were sleeping after a period of learning were found to have 2.5 times the insight of people who are sleep-deprived to solve a complex problem.

It's undeniable that sleep is one of the most important aspects of longevity as getting a sufficient amount of it can act as natural prophylaxis against certain chronic diseases. Think about diabetes mellitus, one of the most popular chronic diseases associated with sleep deprivation. Studies have shown as we are getting sleep deprived, the level of ghrelin, a hunger hormone, increases which motivate us to take lots of food in an effort to replace the energy that can be obtained by sleeping; only we can't really replace anything by eating except if you were aiming for a fat belly. We don't really get much energy or any specific form of energy source from sleeping but it does reduce fatigues which is essential in productivity and creative thinking. There are some animals in the animal kingdom which have been modifying the way they were sleeping in order to achieve its physiological benefits.

Let's take a look at some of the example of animals which can be regarded as having an inappropriately short duration of sleep or some kind of impressive sleep pattern but is able to keep up with their predicted lifespan. A few animals have the capability of sleeping and at the same time being conscious of their surrounding by deactivating just a single hemisphere to initiate a contralateral sleep; this is simply translated into an act of sleeping of just one side of the body. If they deactivate their left hemisphere, their right side of the body would rest while their left side would keep awake vice versa.

Ducks

Picture Source - Pixabay (CC0)

Even if there is no direct evidence that could have suggested the role of deactivating a single hemisphere to achieve a much better outcome in doing something, we can hypothesise that certain animals could be adopting a different approach of sleeping to accomplish their own target goals and at the same time, reap the physiological benefit of sleep. Let's take mallard duck for example; this is one of the few known birds which adopt a special tactic of sleeping for various reasons. Be it social, safety and saving energy, there are a few ways a duck can sleep and most of the time, in a potentially hazardous territory, they were sleeping with one of their eyes open! A journal which was published in 1999 in Nature has found that, in order to protect themselves from danger, they can choose whichever brain to deactivate while letting the one stay awake, monitoring the surrounding and if necessary, snoozing itself to run from imminent danger.

Unlike humans, ducks usually sleep more as they age. In humans, one of the natural reason why we sleep less as we age is due to reduce melatonin production. Melatonin is a hormone which various benefits including putting ourselves into sleep at night, protect our body from the action of various oxidants etc. As the production decline with age, an elderly usually sleep for 4-6 hours per day which is less than the recommended duration to achieve optimal health. Ducks, however, sleep and groom longer as they age. Being old is tiring for them, give me 12 hours to sleep.

Dolphins

This is one of the most interesting mammals ever studied as it is not only able to sleep by deactivating just a single hemisphere of its brain but also is capable of transmitting any information received during the period of deactivation to the deactivated brain so that they could recognise things even without any exposure to it. Compared to ducks, dolphins have no much option other than to adopt this sleeping pattern all the time. They need to come to the surface periodically to get some air, so cuddling at the bottom of the ocean is not a possible or even a relevant behaviour. In 2009, a group of scientist from the U.S. Navy Marine Mammal Program conducted an experiment to test a dolphin (named Say) keen senses and whether it is affected by its unusual sleep pattern. There are two senses which were being tested which are hearing and visual.

I don't want to get into details regarding how the experiment was carried out but if you were interested you can click here. Based on the result of the experiment, even with sleep deprivation or even if they weren't using the other hemisphere to learn about a piece of certain information, they were able to adapt and function just as good as they were. There is no ill-effect related to sleep deprivation which can be found to suggest negative consequences.

Crocodiles

Picture Source - Pxhere (CC0)

It's kinda scary to think that this vicious predator is capable of inducing sleep and the state of wakefulness at the same time; why they need to do that? Most of the animals were being cautious (predators) or trying to breath when they were living underwater but this particular predator can live on land and they rarely have predators except if we were talking about humans or a much bigger crocodile. Unlike the dolphin, crocodiles were mostly sleeping with both of their eyes closed but on certain occasions, they did open one of their eyes. Is there anything to be cautious about? Are they detecting potential predators or preys? Are they really sleeping or just pretending to be sleeping? It's funny that we know so little about this prehistoric fella.

Fatal Familial Insomnia (FFI)

If we were thinking of human diseases to illustrate the negative consequence of sleep deprivation, this might be one of the most brutal examples I can provide to illustrate the effect of sleep-deprivation or in this case, none of the sleeping time. What do you think that causes them to succumb to their own pathology? Is it the fact that they were having a lack of sleep or is it the fact that they were stressed out by their inability to fall asleep? Unlike other diseases which either can be caused by genetics or external factors, FFI is classified as prion disease. If you know anything about prion diseases, you would know that people who were affected would have a long asymptomatic period but once symptoms have set in, they would have less time to live as they can easily and rapidly deteriorate.

The commonest presentation of this particular disease is insomnia although in some cases, people might present with memory problems which worsened progressively. People who experienced insomnia as their primary chief complaint would often deteriorate progressively until coma, primarily due to mental and physical exhaustion. Although we have a few other symptoms which can be used to identify people with FFI for early intervention, most of them are constitutional. FFI is extremely rare thus it would be difficult (very) to identify people who are at risk of dying from sleep deprivation.

Even though I have given a few examples of animals which adopted a different way of sleeping without risking themselves being ambushed by predators, they sleep nonetheless. Unless we have the mean of sleeping unihemispherically, we ought to get at least 8-9 hours of sleep for an optimal benefit. It would be best if we can sleep in between 10 pm to 2 am; this time duration is associated with the most melatonin production which could exert an optimal antioxidant effect.

References and further reading materials

• If fruit flies live without sleeping, why can't I?. Retrieved on March 7th, 2019.
• Beware: Animals That Sleep With One Eye Open. Retrieved on March 7th, 2019.
• Birds engage in all types of sleep in flight, but in remarkably small amounts. Retrieved on March 7th, 2019.
• Duck Sleeping Habits. Retrieved on March 7th, 2019.
• Dolphins Keep an Eye Out While Sleeping. Retrieved on March 7th, 2019.
• Animals' Extraordinary Sleeping Strategy. Retrieved on March 7th, 2019.
• Fatal Familial Insomnia. Retrieved on March 7th, 2019.

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