Sleep. We all need it and we all do it. But why? Where do we go?
Sleep is obviously important as we, as human beings spend, on average, one-third of our lives asleep. The amount you need every night does vary, but most adults need between 7 and 9 hours a night.
Some individuals spend much less time than this asleep, but they do follow a strict sleep regime regardless of the amount they actually get.
However much sleep you personally get, it is a significant amount of your time, so much so, that sleep is widely recognized as a very important practice for most organisms.
Sleep appears to be important for a number of brain functions, including helping nerve cells (neurons) communicate with each other. Research suggests that sleep allows the body to remove toxicants in the brain that build up while you are awake. In fact, sleep appears to affect almost every type of tissue and system in the body — from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance.
According to research on the subject, almost every organism on the planet appears to sleep to some degree. Interestingly, however, there are some animals that appear to not need any sleep at all — but these are the exception, not the rule.
Since it is so ubiquitous in nature, it follows that it must be a vital part of survival. If you think otherwise, see how long you could last without it (in all seriousness, please do not do this).
What then, if anything, can science tell us about sleep?
As it turns out, science can provide insight — at least in part. However, research on sleep, like many disciplines of science, is a constantly developing field with new discoveries popping up and old theories overturned all the time. With that in mind, here are some of the things science currently has to say about the wonderful world of sleep.
What do your brain and body do when you are sleeping?
The sleep process is a widely studied phenomenon in science. While a lot is still unknown, and probably always will be, scientists have been able to decipher at least some of the basic biomechanical processes that occur.
What has been gleaned, according to sites like The National Sleep Foundation, is that when we sleep, a distinctive pattern of brain activity occurs. Technically called sleep architecture, our brains follow a pattern of REM (rapid eye movement) and non-REM (non-rapid eye movement) phases.
This sequence generally follows a series of 90-minute cycles throughout a typical night's sleep.
Non-REM is by far the largest component of sleep cycles and constitutes somewhere in the order of 75% of your time asleep. This phase can further be subdivided into 1 of 3, or sometimes 4, stages.
- N1, or stage 1, is the phase between being awake and falling asleep. This is by far, the lightest form of sleep.
- N2, or stage 2, is when true "sleep" really begins. As you enter this stage, you begin to become disengaged from your surroundings, your heart rate downregulates, and body temperature tends to drop. It's for this reason that it is usually advised that sleeping in a cool room will help you to fall asleep quicker.
- N3, or stages 3 and 4, is the deepest and most restorative phase. Blood pressure drops, breathing slows, muscles relax and blood flow increases to most tissues of the body. This is the phase in which most tissue repair occurs, and hormones are released (like the very important human growth hormone).
REM is the smallest component of the overall sleep cycle and makes up the remaining 25%, or so of a normal night's sleep. It first occurs after about 90 minutes of falling asleep and recurs roughly every 90 minutes.
Interestingly, this phase also tends to get longer as sleep progresses throughout the night. REM sleep tends to combine increased energy provision to the brain and body, and so, this is generally when dreams occur.
As the name suggests, during REM, your eyes move rapidly from side to side behind closed eyelids and brain wave activity becomes closer to that seen in wakefulness. Breathing becomes faster and irregular, and heart rate and blood pressure increase to near waking levels. During REM, your body is usually immobile and relaxed. Normally during this phase, your muscles are disabled.
Another interesting discovery is the connection between some common hormones and our sleep cycles. For example, levels of the stress hormone cortisol have been shown to dip at bedtime and then gradually increase until morning. This indicates that cortisol has some connection to inducing sleep and awakeness.
This hormone, as it turns out, is created in the HPA axis of the brain, which is also fundamental to coordinating our sleep cycles.
Poor nutrition, chronic stress, illness, and other issues that impact cortisol levels can throw your sleep cycles off-kilter. In extreme circumstances, it can even cause insomnia and other sleep disturbances.
So, make sure you get plenty of it! Your future mental health might just depend on it.
Where does consciousness go when we sleep?
According to the Oxford English Dictionary, consciousness is generally defined as, "the state of being aware of and responsive to one's surroundings." When we sleep, as you are probably more than aware, our state of awareness is temporarily disabled or the very least suppressed.
In reality, when we sleep, we become both disconnected and reconnected, for all intents and purposes, from the outside world through our senses (like sight, hearing, touch, etc). Rather than being completely turned off for the hours you sleep, your connection to the outside world actually rises and falls in predictable patterns.
One moment the sleeper might be ever so slightly aware of things going on around, another they will be"dead to the world". Interestingly, some experts suggest that the highest levels of consciousness, or alertness, during sleep occur when we dream. So much so that our dreams can be affected by stimuli around us like noises, music playing, or a film we've left running when we dropped off to sleep.
To some extent, you can even attempt to have a conversation with someone who is asleep.
While there are some uncommon circumstances when people can be engaged in conversation, their answers are normally complete nonsense, farcical even. For the rest of us, you might as well talk to a brick wall or the cat.
Others, especially deeper sleepers are also able to remain asleep in the noisiest of environments. This may be because they have conditioned themselves not to respond even if a conversation is perceived.
On the subject of deep sleepers, some research indicates that those with "busier brains" tend to sleep more soundly at night. Make of that what you will.
However, for most individuals, you can, at any point, be roused from sleep by loud noises or other stimuli — depending on the stage of sleep you are in.
Interestingly though, other studies seem to indicate that our brains are still receiving and processing stimuli even in the deepest stages of sleep. For instance, researchers in Switzerland have shown that new words can be learned, and retained, when exposed to them during deep sleep.
From this perspective, consciousness is with you all the time, so it doesn't really "go" anywhere. Depending on where you are in the sleep cycle, it is just that little bit harder to "rouse".
What happens to your body when we sleep at night?
As we have previously mentioned, various processes happen to your body (and mind) while you are asleep. While your mind has the liberty of connecting and disconnecting from the outside world, your body needs to be kept alive throughout the process if you want to wake up again.
Basic autonomic functions like breathing clearly need to be maintained through the sleep process. While usually reduced in degree and frequency while asleep, your body continues to respire and conduct other basic autonomic processes to keep your organs alive and well. Waste is processed and your heart continues to pump blood around the body.
So, we can see that, during sleep, your body is far from at rest, per se. As Scientific American explains, "trillions of neurons light up. The endocrine system kicks into overdrive. The bloodstream is flooded with a potent cocktail of critically vital hormones."
For your brain, the sleep process appears to be vitally important not only for rest and restoration. but may also serve other interesting purposes. For example, according to some sleep experts, the act of sleeping may provide a "safe place" of sorts to engage with situations and emotions that cropped up during the waking hours.
It is, in a sense, a kind of simulation space for your mind, and appears to be a necessary process for organizing experiences and saving memories. Others have speculated that sleep may also be a time when your brain rids itself of unwanted feelings and emotions — a kind of neurological defragmentation process.
Sleep helps your brain "spring clean" itself from the previous day
Another important part of sleep can be likened to a form of brain "spring cleaning".
Throughout the day, your brain builds up a chemical called adenosine in its tissues. This chemical is a kind of molecular waste product from cell activity, and when it reaches a certain concentration, we begin to feel sleepy.
While asleep, the brain takes the opportunity to rid itself of any built-up adenosine to ready up for the next day. Called the glymphatic system, this is a vital part of sleep and one reason why chronic sleep disruption increases the chances of developing ailments like Alzheimer's.
Interestingly, if you rely heavily on caffeine to stay awake, this can disrupt the natural response to adenosine build-up in your brain, and levels will continue to build up until you have no choice but to sleep.
It is for this reason that most health practitioners will advise you not to drink any caffeinated drinks at least an hour before bedtime.
Sleep may be very important for dealing with emotional and physical trauma
There are some other studies that suggest sleeping helps to deal with both emotional and physical pain. Researchers at the University of Berkeley, for example, recently discovered that sleep deprivation is linked with higher pain sensitivity.
Their study discovered that the neural mechanism that detects, evaluates, and responds to pain is disrupted if you don't get a good night's sleep. This, in their view, indicates that sleep is vitally important in improving a person's ability to cope with pain.
Other studies have also shown that sleep is a vital component in maintaining things like healthy blood pressure. In fact, a 60-minute power nap during the day can reduce systolic blood pressure by several mm of mercury.
As interesting as this all is, ultimately, scientists are still not entirely sure why we sleep.
Many theories abound for its evolutionary development, with ideas ranging from protecting us from nocturnal predators (i.e. you're not moving around) to energy conservation in a resource-limited environment.
While we may never find out exactly why so many animals, including humans, sleep, lack of it severely impacts our physical and emotional health. Especially for infants and children.
The need for sleep developed for a reason, so make sure you get a good's night sleep regularly. You will reap the benefits in the long run.