A Good Night’s Sleep Clears Your Mind — Literally

by Bryan Dewhurst on May 12, 2020

Getting a good night’s sleep is one of the simplest and greatest pleasures in life. 

Most people you will meet in your lifetime would agree, but do we know exactly why? REM Sleep and Narcolepsy co-discoverer William Dement said “As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy.” 

Yes, essentially, we sleep simply because we’re sleepy. Surely, there’s a lot more to sleep that meets the eye, and we’re about to break it down for you. Keep reading!

Web-toon XKCD

Photo courtesy of popular web-toon XKCD

 Sleep isn’t just about closing your eyes and counting backwards. It’s much more complicated than that. 

Although you are in a state of relaxation and temporary unconsciousness, your brain is very much active. It may be unresponsive to external stimuli, but  still reactive to internal stimuli.

The exact purpose of sleep has not been discovered yet, but through the years, four prominent and widely popular sleep theories emerged. They are as follows:

 

Repair and Restoration Theory of Sleep

Perhaps the most popular sleep theory of all, The Repair and Restoration Theory is based on the long-held notion that sleep is crucial to the restoration of the body’s immune system. 

Simply put, each activity we do while we’re awake needs to be replaced by sleep. Several experiments suggest that a good night’s sleep allows the body’s immune system to function better. In fact, one experiment showed that people who had less than 7 hours of sleep were more likely to get sick when exposed to the common cold virus than those who had 8+ hours of sleep every night. It doesn’t stop there. 

Further research found that a number of major bodily restorative functions mostly only take action during sleep. These functions include tissue repair, protein synthesis, muscle growth, and growth hormone release.

More than the body, brain functions are also restored during sleep. This sleep theory also supports the idea that sleep has a substantial effect on the body’s ability to produce adenosine; a chemical in the brain heavily involved in the initiation of sleep. 

On the flipside, consuming caffeine promotes energy and wakefulness by blocking the actions of adenosine. It is only when you’re asleep that this chemical can take effect and eventually clear out of your system when it’s time to wake up, leaving you alert, energetic, and ready to get on with your day.

 

Evolutionary Theory of Sleep

Also widely known as the Inactivity Theory, the Evolutionary Theory is one of the earliest theories to emerge. This sleep theory suggests that periods of sleep throughout the day is a form of adaptation which served as a survival measure for animals to avoid danger during times of vulnerability.  

In addition, animals that were able to stay quiet and still during those times of vulnerability had a greater chance of survival than those who were active. In a nutshell, the Evolutionary Theory believes that sleep exists for safety mainly because accidents and impulsive actions usually take place in the dark.

Despite being widely known, many people don’t particularly agree with this sleep theory. Some argue that when animals are sleeping, it will be much more difficult to respond promptly to potential predators, which will do them more harm than good.

Energy Conservation Theory

The Energy Conservation Theory suggests that the sole purpose of sleep is to save energy. The primary function of sleep is to lower the demand for energy so that your body can expend the ample amount when needed, particularly when it doesn’t have enough to look for food.

If you take a blast from the past, this sleep theory actually makes a lot of sense. Our ancestors used to struggle to find sustenance, which is why they had to use sleep to reduce their energy consumption and make most of their limited supply of food.

Research shows that a person’s metabolism is significantly lowered by approximately 10% during sleep. Despite being a very sensible sleep theory, some researchers consider this idea to be part of the evolutionary theory of sleep, which we’ve discussed earlier. Furthermore, they doubt that this kind of reduction (10% drop in energy metabolism) can make a significant change in a person’s overall energy consumption.

 

Brain Plasticity Theory

The term brain plasticity was coined to refer to the brain's ability to evolve throughout a person's life. The Brain Plasticity Theory is one of the more recent theories of sleep, and suggests that sleep contributes a great deal to the processes of brain plasticity. It also believes that a person sleeps so that the brain can consolidate new information and memories that happened during the day. 

In short, when you sleep, your brain is never idle. Instead, it uses this time to absorb and process everything that took place when you were awake. These thoughts and memories are then turned into long-term memories. 

Therefore, a lack of sleep may have an extremely negative impact on your brain, particularly to retain information. This is why our parents used to tell us to get ample sleep the night before an exam or a major event — to retain all the information our brains have collected from hours of studying or practicing. 

For instance, one experiment was conducted wherein the volunteers were given an aptitude test. Half of them were shown the patterns during the morning session, and the other half during the evening session. Sure enough, the researchers found that the group who had a good night’s sleep before taking the test had better recollection of the test patterns.

Similarly in babies, sleeping for 13-14 hours daily allows their brains to process everything they’ve explored throughout the day. So if you have babies with you at home, don’t disrupt their sleep; you might be messing with a crucial cognitive developmental process.

So which among these theories are most likely to be correct? 

Honestly, they all could be. There are compelling arguments in all of them. 

To help you arrive at a conclusion, researchers used a technique called two-photon microscopy, a fluorescence imaging technique that allows fluorescent dyes to be activated by two photons in the infrared range, which penetrates further into tissue.

The result: during sleep the brain cells significantly reduce in size ( 60%), creating more space for the cerebro-spinal fluid (CSF) to provide basic mechanical and immunological protection by allowing blood to flow and waste products to be flushed out.

University of Rochester Medical Center Brain Scans

Brain scans showing the substantially greater flow of cerebro-spinal fluid in the brain of a sleeping mouse (left), as opposed to a mouse that they had just woken up by “gently moving its tail”. Different-coloured dyes were injected at different stages to tell them apart (University of Rochester Medical Center)

Similarly, research shows that during sleep, levels of beta amyloid decline in the human brain. This supports the belief that the brain is technically “clear” when one is asleep. However, some doubt this claim due to the fact that diseases associated with Dementia are linked to sleeping disorders.

There are many theories surrounding sleep, but one clear takeaway is that sleep supports many brain functions – mainly healing and restoration. Whichever sleep theory you decide to believe, it’s safe to say sleep can only do amazing things for your mind and body. With that being said, manage your time and have a good night’s sleep!

 

References:

https://lostinscience.wordpress.com/2014/04/11/a-good-nights-sleep-literally-clears-your-head/

https://sleepopolis.com/education/why-do-we-sleep/

http://healthysleep.med.harvard.edu/healthy/glossary/g-j#growth-hormone

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