Matt Walker – Sleep Scientist
Thank you very much.
Well, I would like to start with testicles.
Men who sleep five hours a night have significantly smaller testicles than those who sleep seven hours or more. In addition, men who routinely sleep just four to five hours a night will have a level of testosterone which is that of someone 10 years their senior.
So a lack of sleep will age a man by a decade in terms of that critical aspect of wellness. And we see equivalent impairments in female reproductive health caused by a lack of sleep. This is the best news that I have for you today.
From this point, it may only get worse. Not only will I tell you about the wonderfully good things that happen when you get sleep, but the alarmingly bad things that happen when you don’t get enough, both for your brain and for your body.
Let me start with the brain and the functions of learning and memory, because what we’ve discovered over the past 10 or so years is that you need sleep after learning to essentially hit the save button on those new memories so that you don’t forget.
But recently, we discovered that you also need sleep before learning to actually prepare your brain, almost like a dry sponge ready to initially soak up new information.
And without sleep, the memory circuits of the brain essentially become waterlogged, as it were, and you can’t absorb new memories. So let me show you the data.
Here in this study, we decided to test the hypothesis that pulling the all-nighter was a good idea. So we took a group of individuals and we assigned them to one of two experimental groups: a sleep group and a sleep deprivation group.
Now the sleep group, they’re going to get a full eight hours of slumber, but the deprivation group, we’re going to keep them awake in the laboratory, under full supervision. There’s no naps or caffeine, by the way, so it’s miserable for everyone involved.
And then the next day, we’re going to place those participants inside an MRI scanner and we’re going to have them try and learn a whole list of new facts as we’re taking snapshots of brain activity.
And then we’re going to test them to see how effective that learning has been. And that’s what you’re looking at here on the vertical axis. And when you put those two groups head to head, what you find is a quite significant, 40% deficit in the ability of the brain to make new memories without sleep.
I think this should be concerning, considering what we know is happening to sleep in our education populations right now. In fact, to put that in context, it would be the difference in a child acing an exam versus failing it miserably – 40%.
And we’ve gone on to discover what goes wrong within your brain to produce these types of learning disabilities. And there’s a structure that sits on the left and the right side of your brain, called the hippocampus.
And you can think of the hippocampus almost like the informational inbox of your brain. It’s very good at receiving new memory files and then holding on to them. And when you look at this structure in those people who’d had a full night of sleep, we saw lots of healthy learning-related activity.
Yet in those people who were sleep-deprived, we actually couldn’t find any significant signal whatsoever. So it’s almost as though sleep deprivation had shut down your memory inbox, and any new incoming files — they were just being bounced. You couldn’t effectively commit new experiences to memory.
So that’s the bad that can happen if I were to take sleep away from you, but let me just come back to that control group for a second.
Do you remember those folks that got a full eight hours of sleep? Well, we can ask a very different question: What is it about the physiological quality of your sleep when you do get it that restores and enhances your memory and learning ability each and every day?
And by placing electrodes all over the head, what we’ve discovered is that there are big, powerful brainwaves that happen during the very deepest stages of sleep that have riding on top of them these spectacular bursts of electrical activity that we call sleep spindles.
And it’s the combined quality of these deep-sleep brainwaves that acts like a file-transfer mechanism at night, shifting memories from a short-term vulnerable reservoir to a more permanent long-term storage site within the brain, and therefore protecting them, making them safe.
And it is important that we understand what during sleep actually transacts these memory benefits, because there are real medical and societal implications. And let me just tell you about one area that we’ve moved this work out into, clinically, which is the context of aging and dementia.
Because it’s of course no secret that, as we get older, our learning and memory abilities begin to fade and decline. But what we’ve also discovered is that a physiological signature of aging is that your sleep gets worse, especially that deep quality of sleep that I was just discussing.
And only last year, we finally published evidence that these two things, they’re not simply co-occurring, they are significantly interrelated. And it suggests that the disruption of deep sleep is an underappreciated factor that is contributing to cognitive decline or memory decline in aging, and most recently we’ve discovered, in Alzheimer’s disease as well.