The 5 stages of sleep: what happens when you sleep?

You might have heard the common saying “to sleep on a problem”.

It turns out, that’s exactly how your brain works during sleep.

Sleep consolidates information you’ve collected. It sifts through information gathered during your waking hours, consolidates the valuable stuff and tosses out the other stuff we don’t need.

On a good night, you’ll experience several stages of sleep, four or five times. Each of the five stages of sleep has its own particular qualities and purpose.

  1. Stage 1 of your sleep cycle only lasts about five minutes. It happens moments after you lay down in bed. The neurons in your brain that are frantically busy when you’re awake, slow down. And you drift off to sleep.
  1. In Stage 2, a series of electric sparks zap your cerebral cortex. This is the pleated grey matter covering the outer layer of the brain. It’s the home of language and consciousness. These ‘zaps’ are called spindles.

 The theory is that these spindles stimulate the cortex, helping to preserve recently acquired information. They also help establish long-term memory.

Your brain doesn’t distinguish between good or bad memories. Research into post-traumatic stress disorder suggests that soldiers experiencing a major ordeal, should be kept awake for six to eight hours after the event. That way, they might avoid storing those negative experiences as a long-term memory.

Lasting for up to 50 minutes, it’s during Stage 2 of your sleep cycle that your heart rate slows and your body temperature drops. You’ll be unaware of your external environment at this stage.

  1. Stage 3 signals the beginning of deep sleep. It’s when your body’s cells start to recuperate from their busy day. During this deep sleep stage, your cells produce growth hormone. This is essential to service your bones and muscles throughout your life. Your brain goes through a bit of housekeeping as spinal fluid washes away metabolic waste.
  1. During Stage 4, there’s little mental activity going on in your brain. It’s a bit like being in a coma. It only lasts about 30 minutes, but stage 4 is important for its recuperative and restorative function. We do not dream during this stage.

It’s common to wake up several times during the night. Mostly, within seconds, we drop back to sleep without noticing.

  1. Stage 5 is when we experience REM sleep – that’s Rapid Eye Movement. Around 20% of your night is spent in REM sleep. It’s often been referred to as the time when we literally ‘go mad’.

Discovered in 1953, it’s the period when you dream and your brain is ‘fully active’.

Sleep experts still argue about the significance of dreams. Some believe they’re the result of a ‘chaotic firing of neurons’, and mean little. Others give dreams a larger significance and seek to analyse them for a deeper meaning.

REM sleep is associated with learning and the embedding of memories. That might explain why babies spend 50% of their sleep-time in REM sleep. They’re learning new things every day.

Good sleep is as important as food

Sleep is as essential to our bodies as food. It helps maintain a healthy immune system, body temperature and blood pressure. Sleep helps regulate our moods.

Good quality sleep helps to reduce our risk of disease, including dementia, Alzheimer’s disease and many other health conditions associated with ageing.

Without it, we simply can’t survive.


REFERENCE: National Geographic, August 2018, Want to Fall Asleep? Read this story by Michael Finkel.