Thursday 24 October 2019

Why sleep is key to brain health, and how to sleep better, by Professor Matt Walker

Professor Matt Walker
Professor Matt Walker

We know that your brain, like your body, has a sewage system. In the body it's called the' lymphatic system', but in the brain it's called the 'glymphatic system'. The brain's sewage system is not always on high-flow volume across the 24-hour clock. It is only when we go into deep sleep, what we call deep non-rapid eye movement or NREM sleep, that the brain kicks that sewage system into high gear and it cleanses the brain of all of the metabolic detritus that has been building up during the day.

Why is this related to Alzheimer's disease? One of the toxic metabolic by-products that we build up during the day is a protein called beta amyloid; beta amyloid plaques are one of the leading mechanisms underlying Alzheimer's.

If you're not getting deep sleep at night, you're not giving that power cleanse to the brain to wash away all of that toxic protein and so more builds up. And it's a causal relationship. If you selectively deprive humans of deep, slow wave sleep for one single night, you will see an immediate rise in that protein.

It's also a two-way relationship. Amyloid protein will disrupt your sleep. If you look at where this protein builds up, it is not all over the brain homogeneously. Some parts of the brain accumulate Alzheimer's protein amyloid far more significantly than others.

Unfortunately, the parts of the brain that suffer that Alzheimer's assault are the very same regions that generate deep sleep and it becomes a vicious cycle - if you're not getting deep sleep, more of that protein builds up. Where does that protein build up? In the deep sleep generating regions. So you start to get even less deep sleep. The less deep sleep that you have, the more protein builds up. It's this downward vicious cycle that leads to the escalation of Alzheimer's disease.

The discovery that sleep is related to memory decline and ageing and Alzheimer's disease is potentially exciting because we could do something about that. One way we are approaching this at the Center of Human Sleep Science is by developing electric brain centre stimulation. We're trying to amplify the amount of deep sleep in older adults and those with dementia and trying to restore back some healthy quality of deep sleep. In doing so we are trying to salvage aspects of learning and memory function - that's my real hope now.

Sleep and memory

1 You need sleep before you learn so as to prepare your brain, almost like a dry sponge ready to soak up new information. Without sleep, the memory systems and circuits in the brain, particularly a memory region called 'the hippocampus', get shut down and, as a consequence, any incoming memory files just get bounced. Without sufficient sleep, you can't commit new memories effectively.

2 You also need sleep after learning - as a way to hit the 'save' button on new memories so you don't forget. Sleep after learning is about cementing the new facts into the neural architecture of the brain. That's what we call 'consolidation'.

3 Sleep not only strengthens individual memories, it actually goes on to take all those fresh new memories you've acquired and it starts interconnecting them with your back catalogue of information. It's a little bit like informational alchemy, where sleep will start to collate all this information and test out new associations, novel potential combinations and, as a consequence, you wake up the next day with a revised mind-wide-web of information. By way of those new connections, you can devise novel solutions to previously impenetrable problems. In other words, sleep is key for creativity.

4 keys to better sleep

1 Give yourself at least an eight-hour opportunity in bed each night.

2 Be regular in your habits - go to bed at the same time, get up at the same time, no matter whether it is the weekend or a weekday. Even if you've had a bad night of sleep.

3 Abstain from alcohol and caffeine. Alcohol is used as a sleep aid but it's misunderstood - alcohol is a sedative and will block your dream sleep, or rapid eye movement sleep, but also make you wake up many more times throughout the night. Caffeine is to be avoided - caffeine has a quarter life of 12 hours. If you have a cup of coffee at noon, a quarter of that caffeine is still in your brain at midnight while you're trying to sleep and it's not going to work out very well because caffeine is a stimulant.

4 Don't stay in bed if you're awake. Your brain starts to learn that your bed is about staying awake rather than about being asleep. If it's more than 20 minutes, get out of the bed. Sit somewhere with dim light and just read a book. Don't eat, don't look at a screen, and only when you're sleepy should you return to bed. That way your brain will re-learn the association that your bed is a place for going to sleep and feeling sleepy.

Matthew Walker is Professor of Neuroscience and Psychology at the University of California in Berkeley, and director of the Centre of Human Sleep Science. He is also author of the best-selling 'Why We Sleep: The New Science of Sleep and Dreams' (Penguin).

Prof Matthew Walker

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