Your brain on sleep

There’s more than the occasional parkrun-PB dream going on in your grey matter when you’re under the duvet. The bumps on the graph (right) depict your brain’s activity over the course of an average night. ‘We can identify four main stages of sleep,’ says sleep specialist Dr Sophie Bostock. ‘A sleep cycle is made up of the body passing through the three stages of non-rapid eye movement (NREM) sleep and into

REM sleep, before beginning the next cycle,’ she explains. Let’s give it a spin.

Stage one

‘In this stage, where you’re just losing consciousness, it’s very easy to wake up again,’ says Bostock. When you’re tucked up in bed, you’ll probably spend about 10 minutes in this very light sleep before falling into stage two, then further, into stage three, and then into REM sleep.

Stage two

The stage where your heart and breathing rates slow and your body temperature drops until you fully lose consciousness. ‘It’s probably where you’ll spend most of your time asleep,’ says Bostock, with between 20 and 30 mins typically spent in this phase until you go on to the next.

Stage three

This stage is the most physically restorative type of sleep; stage three is referred to by scientists as slow-wave sleep (SWS). You might be out for the count, but your brain is secreting human growth hormone (HGH), helping cells to re-energise and repair. If you’ve done a long run that day, you’ll require more of this kind of slumber.

REM sleep

REM (rapid eye movement) sleep, is so called because your eyes flick about during this phase. It is the stage associated with dreaming, when your brain is highly active.

‘The electrical brain activity of someone who’s awake is actually very similar to that of someone in REM sleep,’

says Bostock.

And...repeat

Rather than just progressing consecutively from SWS to

REM, you reverse through the NREM phases, transitioning from light sleep to

REM before starting the next cycle back in stage one.