Sleep better and remember more! Top neuroscientist reveals why it is vital to get a good night’s rest (and how it can stave off dementia)
- Sleep disturbance precedes onset of Alzheimer’s by several years and may be early warning sign
- Lack of deep sleep affects night-time power cleanse of brain of metabolic waste
- Sleep helps memory retention by effectively clicking ‘save’ on those new files
The two most feared diseases throughout developed nations are dementia and cancer. Both are related to inadequate sleep. In Saturday’s Mail, I explained how a lack of sleep is connected to cancer. But it is also becoming recognised as a key lifestyle factor determining whether or not you will develop Alzheimer’s disease.
Sleep quality — especially that of deep, NREM or non-rapid eye movement sleep, which is the sleep we have in the first part of the night — naturally deteriorates as we age, which is linked to a decline in memory.
However, if you assess a patient with Alzheimer’s disease, the disruption of deep sleep is far more exaggerated. More telling, perhaps, is the fact that sleep disturbance precedes the onset of Alzheimer’s by several years, suggesting that it may be an early warning sign of the condition, or even a contributor to it.
Alzheimer’s disease is associated with the build-up of a toxic form of protein called beta-amyloid, which aggregates in sticky clumps, or plaques, in the brain. The amyloid plaques kill brain cells. But the amyloid plaques only affect some parts of the brain and not others, for reasons which remain unclear.
What struck me about this unexplained pattern was the location in the brain where amyloid accumulates during the early stages of Alzheimer’s and most severely in the later stages. It is the middle of the frontal lobe — which is essential for the generation of deep, non-rapid eye movement sleep.
Liverpool-born Professor Matthew Walker explains why sleep really is the best medicine (file photo)
I joined forces with my colleague Dr William Jagust, a leading authority on Alzheimer’s disease at the University of California, Berkeley. We discovered that the more amyloid deposits there were in the middle regions of the frontal lobe, the more impaired the deep sleep quality.
We are now examining whether this particular ‘dent’ in sleeping brainwave activity represents an early identifier of those who are at greatest risk of developing Alzheimer’s disease, years in advance.
Further studies in mice show that a lack of deep sleep also affects what can be called a night-time power cleanse, where cerebrospinal fluid bathes the brain to flush out metabolic waste.
Without sufficient sleep, this does not happen, creating a vicious cycle where amyloid plaques prevent deep sleep, and in turn a lack of deep sleep prevents brain cleansing, leading to more build-up of plaques.
From this comes a prediction: getting too little sleep across the adult life span will significantly raise your risk of developing Alzheimer’s disease.
By the way (and strictly non-scientifically) I have always found it interesting that Margaret Thatcher and Ronald Reagan — two heads of state who were very vocal, if not proud, about sleeping four to five hours a night — both went on to develop the disease.
Donald Trump, the current occupant of the White House and also a vociferous proclaimer of sleeping just a few hours each night, may want to take note.
The brain’s ability to learn new things and recall them years later depends on the quality and quantity of our sleep (file photo)
By the way (and strictly non-scientifically) I have always found it interesting that Margaret Thatcher and Ronald Reagan – two heads of state who were very vocal, if not proud, about sleeping four to five hours a night – both went on to develop the disease
Have you ever wondered how your memory works? How is it possible, for example, that you can keep on learning new things, day after day, and still remember them weeks, months or years later? That’s exactly what my team and I set out to discover some years ago.
We found that sleep is absolutely crucial to the process, both before learning (to prepare your brain for making new memories) and after learning (to cement those memories and prevent forgetting).
We began by asking how the brain, which is constantly acquiring information when awake, manages to retain it.
It is already known that for fact-based information, such as memorising someone’s name or a new phone number, the hippocampus — a long, finger-shaped structure tucked deep on either side of your brain — offers a short-term reservoir, or temporary information store, for accumulating new memories.
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Unfortunately, the hippocampus has a limited storage capacity, almost like a roll of camera film. How, then, does the brain deal with this limited storage — and is sleep part of the process?
To find out, my research team began by dividing participants into two groups and each group was set a rigorous learning task: they were given 100 face-name pairs to remember.
The results for each group were comparable. Then one group was allowed a 90-minute nap; the other stayed awake, playing board games or browsing the internet. Afterwards, they were given a different set of 100 face-name pairs to remember.
The group who’d had the 90-minute siesta did markedly better, and actually improved their earlier score, while the group who’d stayed awake became progressively worse at learning.
The difference between the two groups at 6pm was not small: a 20 per cent learning advantage for those who slept.
Sleep disturbance precedes the onset of Alzheimer’s by several years, suggesting that it may be an early warning sign of the condition, or even a contributor to it (file photo)
Next, we tried to discover exactly what it was about sleep that provided the benefit.
12-point plan to help you nod off
Analysing the electrical brainwaves of those in the nap group brought our answer.
The memory refreshment happened during lighter, stage 2 NREM sleep (nonrapid eye movement), and specifically short, powerful bursts of electrical activity called sleep spindles. The more spindles during the nap, the greater the restoration of learning.
As we analysed the sleep-spindle bursts of activity, we observed a strikingly reliable loop of electrical current pulsing throughout the brain that repeated every 100 to 200 milliseconds. The pulses kept weaving a path back and forth between the hippocampus, with its short-term, limited storage space, and the larger, long-term storage site of the cortex.
In that moment, we had just become privy to an electrical transaction occurring in the quiet secrecy of sleep.
That is, a shifting of fact-based memories from the temporary storage depot (the hippocampus) to a long-term secure vault (the cortex). Sleep had cleared out the hippocampus, replenishing this short-term information repository with plentiful free space so that the learning of new facts could begin again.
We and other research groups have since repeated this study across a full night of sleep and replicated the same finding: the more sleep spindles an individual has at night, the greater the restoration of learning ability come the next morning.
The second benefit of sleep for memory is that it effectively clicks the ‘save’ button on those newly created files.
Countless experiments in the past 100 years have shown that sleep provides a memory retention benefit of between 20 and 40 per cent, compared with the same amount of time awake — not a trivial amount when you consider studying for an exam, or, in an evolutionary context, being able to remember the locations of food, water and predators.
We obtain most of our deep NREM (non-rapid eye movement) sleep early in the night.
In contrast, we get most of our rapid eye movement (REM) sleep — the stage in which we dream — and lighter NREM sleep late in the night. The different sorts of sleep were discovered in the Fifties, and experiments in which participants were allowed to sleep only for the first or second half of the night were clear: for fact-based memory, it was early-night sleep, rich in deep non-rapid eye movement, that provided better memory retention.
Investigations in the early 2000s arrived at a similar conclusion. Using MRI scans, we have since looked deep into the brains of participants to see where memories are being retrieved from before sleep, and how that compares with from where they are retrieved after sleep.
Those information packets were being recalled from very different geographical locations within the brain at the two different times.
Before having slept, participants were fetching memories from the short-term storage site of the hippocampus — that temporary warehouse. But things looked very different by the next morning. The memories had moved.
After the full night of sleep, participants were retrieving that same information from the neocortex — a region at the top of the brain that serves as the long-term storage site for fact-based memories — where they can live safely, perhaps in perpetuity.
We had observed a transaction that takes place each night when we sleep. The slow brainwaves of deep NREM had served as a courier service, shifting memory packets from a temporary storage hold (hippocampus) to a more secure, permanent home (the cortex).
An important point to note here is that this process only works if you get a good night’s sleep the same day that you’ve learned something. If you miss out on that sleep, the memory will not be kept in the same way, even if you try to catch up on subsequent nights. In terms of memory, sleep is not like the bank. If you accumulate a debt, you cannot pay it off later.
One benefit of sleep for memory is that it effectively clicks the save button on those newly created memories (file photo)
Recent studies show that sleep also helps you regain access to memories that you could not retrieve before you went to sleep.
Like a computer hard drive where some files have become corrupted and inaccessible, sleep offers a recovery service at night, so that you awake the next morning able to locate and retrieve those once unavailable memory files with ease and precision.
That’s the, ‘Ah yes, now I remember’ sensation that you may have experienced after a good night of sleep.
All the studies I’ve described so far deal with one type of memory — factual, which we associate with textbooks or remembering someone’s name. There are, however, many other types of memory, including that for skills.
Take riding a bike, for example. There’s no point in reading about how to do it; you can only learn how to ride a bike by doing, which is to say by practising.
The same is true for all motor skills, whether you are learning a musical instrument, an athletic sport, a surgical procedure, or how to fly a plane.
The term ‘muscle memory’ is a misnomer. Muscles themselves have no such memory: a muscle that is not connected to a brain cannot perform any skilled actions, nor does a muscle store skilled routines.
Muscle memory is, in fact, brain memory. Training and strengthening muscles can help you better execute a memorised routine. But the routine itself — the memory programme — resides firmly and exclusively within the brain.
My studies have shown that practise does not make perfect. It is practise, followed by a night of sleep, that leads to perfection.
In what spanned almost a decade of research, I finally identified the type of sleep responsible for overnight motor-skills improvement.
They are directly related to the amount of lighter non rapid eye movement sleep, which happens especially in the last two hours of an eight-hour night of sleep (eg, from 5am to 7am, should you have fallen asleep at 11pm). Those last two hours of sleep are precisely the window that many of us decide to abandon in order to get ahead with the day.
As a result, we miss out on the benefits of this last stage of sleep.
Adapted from Why We Sleep: The New Science Of Sleep And Dreams by Matthew Walker, published by Penguin Books at £9.99. © Matthew Walker 2018. To buy a copy for £7.99 (20 per cent discount), call 0844 571 0640 or go to mailshop.co.uk/books. P&P is free on orders over £15. Offer valid until August 11, 2018.
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