What causes us to fall asleep?

Does a change take place inside our brains when we drop off?
16 January 2018



What actually governs the transition between being awake and being asleep?


Chris Smith put this tiresome query to sleep expert Nick Oscroft...

Nick - Within the brain, there are neural networks that promote wakefulness, and there are neural networks that promote sleep. To demonstrate that, in everyday life, we’re all aware that certain antihistamines can make you sleepy. They block the histamine system in the brain and that makes you sleepy. We know that histamine is one of the alerting systems within the brain, and there is this switch within the brain just as you’re getting drowsy, trying to drop off to sleep where the alerting systems and the systems promoting sleep inhibit each other. It’s almost like a switch where you switch between one and the other one to initiate sleep.

We can measure that in a sleep lab looking at brain waves. We measure EEG and that shows that you actually start with quite a high-frequency brain waves and as you drift off to sleep, go into the state 1 non-rapid eye movement sleep which is generally the first stage of sleep you go into, they start to reduce in frequency.

Then you go into stage 2 sleep where there are some very specific things we can see on the EEG; things called sleep spindles; things called K complexes. Then, as you get deeper into non-REM sleep, you’ll go into a very higher amplitude, but lower frequency slow wave, where you can see slow waves in the sleep, which is what we call them. And then REM sleep actually is a very active state of mind where your brain’s active and your eyes are flicking around.

So, as you’re dropping off to sleep we can see it happening as you’re getting drowsy on the EEG signal, but it’s really this switch that really takes you over the edge.

Chris - Any tips for giving people a good night’s kip - just a few bullet points?

Nick - My top tip would be routine: going to bed at the same time every day and getting up at the same time every day really gives your body a chance to allow all the hormonal changes and other changes that need to happen to happen, to aid sleep onset, and natural waking in the morning.

Giving yourself sufficient time in the current environment is also very important. Most of the population tends to be slightly sleep deprived and that really doesn’t help both in dietary terms, energy intake. It all has negative effects if you’re sleep deprived.


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