What happens to the brain during the different stages of sleep? The answer to this question will take you closer to understanding how the amazing brains of humans work.

Sleep is boring, right? Well, yes and no. On the one hand, you close your eyes, everything goes black and then a few hours later, you wake. If you’re lucky, you might be able to recall a snippet or two of a dream in which you ride a unicorn to victory in the Kentucky Derby, or maybe eat a big bit of cheese. That’s about it!

On the other hand, just because your eyes are closed and you’re unconscious, it doesn’t mean that your brain isn’t doing fascinating things. In fact, as you slumber away, your brain goes through multiple different stages of sleep, each with their own unique quirks.

Below we take a quick look at what happens to your brain during each of these stages of sleep.

Light Sleep

During the night, we go through several sleep cycles that alternate between deep and light sleep. Each of these cycles can be further broken down into four stages of sleep. The first two of these stages are what’s known as light wave sleep, or to give you their more technical names, NREM1 & NREM2.

NREM is shorthand for non-rapid eye movement sleep. NREM1 occurs quickly after we fall asleep and usually only lasts for a very short time, maybe ten minutes or so. During this period, it is very easy for us to be awoken and to return to full alertness.

During this first stage, our blood pressure drops, our breathing slows and the temperature of our brain begins to fall. After a further ten minutes or so, we will enter the second stage of light sleep, NREM2. This is pretty much a continuation of NREM1. The heart rate continues to slow down, body temperature continues to drop, metabolic functions slow down considerably. All this means that it begins to become much harder to wake up.

It’s during NREM2 that the brain begins to emit much larger waves. Researchers believe that we spend the majority of the night in this state, by some estimates, up to 45%.

Slow Wave Sleep

After the first two stages of sleep comes NREM3. It is here the body enters the so-called Slow Wave Sleep (SWS) or even Delta Sleep. This is the beginning of the good stuff.

It’s during SWS that we are at our most difficult to wake up. If our slumber is rudely interrupted at this stage of sleep, we will feel the most groggy and disoriented.

The name Slow Wave Sleep refers to what is happening to our brain at this stage. Electroencephalograms show that in this stage of our sleep cycle, our brain waves have slowed considerably and have become much larger.

It’s thought that SWS is when the mind processes explicit information recorded during the day. That’s new facts, new names and ‘declarative’ memories such as events of the day or topics covered in say class or a meeting.

SWS is a very important stage of the night. It is when we get the truly rejuvenating rest that will power us through the next day. If you find yourself regularly waking up groggy, it’s probably because your SWS is being broken.

If this is the case you should take whatever measures you can to improve the quality of your rest. Maybe change up your pre-bed routines, avoid caffeine and alcohol, invest in the best mattress you can, and above all, avoid screens in the evening.

REM Sleep

After the three NREM stages of sleep comes the Rapid Eye Movement stage that the first three derive their name from. REM is the final stage of the sleep cycle and it generally takes your sleeping brain at least 90 minutes to reach this point.

The name Rapid Eye Movement comes from the continuous darting movement our eyes make during this stage of sleep. For a long time, the reason for this nocturnal ocular dance remained unclear. To some extent, it’s still an uncertain area.

However, one recent study published in Nature Communications appears to back up the belief that the movement is related to dreaming. Researchers suggest that each flicker of the eye is related to the brain switching between a different mental image.

REM is the deepest stage of sleep and tends to be where the most powerful dreams occur. It is where the other weird sleep-related stuff can also happen, such as sleepwalking and bedwetting. Heart and respiration rates also rise during this period.

The time we spend in REM sleep is hugely important as it’s during this period that the encoding of ‘procedural’ memories occurs. That’s things relating to the creative problem-solving and motor control such as walking, talking, dancing, juggling, etc.

REM = ‘Paradoxical Sleep’

Researchers sometimes refer to REM sleep as “paradoxical sleep”. The reason for this rather strange moniker is that although you’re fully unconscious, the scans of your brain waves during this period will look almost identical to those that can be recorded while you are wide awake.

So, even though your muscles are effectively paralyzed and your eyes firmly shut, your brain is firing on all cylinders. Hence the paradox. Pretty interesting, right? That’s something for you to think about while you’re fast asleep tonight!

So, there you have it. You may have previously thought lying in bed with your eyes closed was a boring way to spend a third of your life. But hopefully, reading this article has changed your mind a little. The brain is an endlessly fascinating thing and we are only just beginning to scratch the surface of what is happening in there during the different stages of sleep.


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