During a typical night’s sleep, the brain’s activity fluctuates. The first three stages of sleep are characterised by three types of brainwaves: alpha waves, theta waves and delta waves. The former are typically recorded when we’re in the process of falling asleep, whereas the latter two come about during sleep.

Once we pass into the REM or rapid-eye-movement stage, our brainwaves speed up and reflect those that are present when we’re awake, which is why this is the stage when most dreaming occurs. Your brain’s active state during REM sleep also explains why you’re more likely to remember dreams when you wake up in the middle of an REM period – your brain is already functioning at the same frequency as when you’re awake.

For now, however, let’s take a closer look at the slow brainwaves that arise as we sleep.

What are alpha waves?

When you’re in a chilled-out, relaxed state – eg when you’re relaxing in bed before you turn out the lights – your brain will be home to alpha waves.

“These waves are associated with calm, wakeful states, such as when we’re quietly reflecting or meditating,” Dr Walker explains.

This is what goes on inside your brain when you’re sleeping, according to a neuroscientist