The Science
of sleep

Smiling Face - Science of sleep

We spend on average 25 years of our lives sleeping. Our sleep affects our health on a daily basis and impacts heavily on our quality of life. We can even die without it, but after decades of study, scientists still don’t truly know why sleep is such an integral part of our lives.

What scientists do know is what happens to us physiologically when we put our heads down for the night. Our bodies and minds undergo some very strange processes during sleep that all help sort information, recover lost energy and repair damage. Let’s examine a typical night’s sleep.


Sleep and wakefulness are governed by your brain. Different brainwaves are produced during different stages of sleep. Before we venture into Dreamland, let’s look at what your brain output waves consist of - click on the brain and brainwaves to find out more about them:

Beta Wave
Theta Wave
Human Brain Brain waves
Alpha Wave
Delta Wave


Sleep can be broken down into two main categories:

  • NREM (non-rapid eye movement)
  • REM (rapid eye movement)

Within these, there are five stages that we continuously cycle through during the night. We spend the vast majority of our time asleep in NREM – the deepest kind of sleep.

Sleeping Person
Sleeping Person


This is where you become drowsy, beginning to drift off to sleep. You can still be easily awakened at this point and your brain activity is still quite high – but your brainwaves are moving away from the Beta and into the Alpha spectrum, becoming more irregular than when fully awake and alert. Towards the end of this stage, your brainwaves become more amplified and feature more Theta waves.

Theta Wave



While you can still be woken up easily at this stage, you have descended into a light NREM sleep. Your body is most prone to sleep twitches at this point, as you transition from a semi-waking state to light sleep. As you’re still semi-conscious, you can still be easily woken.

Your Theta brainwaves start to spike in what are called “sleep spindles” – bursts of activity lasting a second or so. At the end of this stage, K-complex waves are emitted by the brain and you become disengaged from your surroundings. Your heart and breathing rates stay the same, but your body temperature begins to drop (sleeping in a cooler room can help you get to sleep).

Alpha Wave


In Stage 3, bodily movement is reduced as your muscles begin to relax. As this stage progresses, you become more and more difficult to wake up. Your body temperature lowers further and your brainwaves stop producing sleep spindles. You’re about to enter the deepest sleep when your brainwaves transition into Delta waves – high-amplitude, low-frequency waves where the brain is incredibly active; more so than when you’re awake. Females across most species, not just humans, have been shown to have higher Delta wave activity than males.

Beta Wave


Delta Wave


This is the deepest stage of sleep you can enter. You are extremely difficult to wake as your brain output consists almost exclusively of Delta waves. Your blood pressure falls and blood flow to your muscles reaches its peak. Your heart rate and breathing slow down. If you’re a snorer, this is when snoring occurs.

This stage is one of the most important: it’s where cell and tissue repair takes place and your immune system is at its strongest. Hormones are released to promote growth and muscle repair. Energy is restored to the brain and body.

Human Heart Cleaned
Human Pulse Rate

But strange things can happen in Stage 4 that make it a less serene state than described – sleepwalking, sleep-talking and night terrors included.

Recently, Stages 3 and 4 have been merged into one (called Stage N3 Slow-Wave Sleep) as they are essentially one process – but it is still held that Stage 3 sleep contains less than 50% Delta wave activity and that Stage 4 is anything over 50%.


This is the normal, waking state of your brain activity. It’s characterized by high levels of random activity, where you have full awareness of all your senses.


As you become more disconnected, Theta waves become a greater feature of your brain output. This is where the unconscious mind is accessed, some say, with meditation.


These waves are believed to function as a barrier to external stimuli, like sounds or pressure on the skin that the brain doesn’t consider a sign of danger.


As you enter lighter sleep or are just drifting off, your brainwaves feature Alpha waves, associated with a relaxed yet aware state.


Produced during deep sleep, Delta waves indicate complete isolation from your surroundings. Brain activity is high, but it is not consciously known.

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