Professor Matthew Walker, Director of UC Berkeley’s Sleep and Neuroimaging Lab discusses the latest discoveries about sleep and how it impacts our life, wellness, and lifespan.
JOSH: Right. And thank you all for coming. This is a great crowd. And I want to welcome Dr. Matthew Walker. He is professor of neuroscience and psychology at the University of California, Berkeley. And he’s the founder and director of the Center for Human Sleep Science, and he’s here today to talk about his new book, “Why We Sleep.”
So without further ado.
MATTHEW WALKER: Thank you very much, Josh. Thank you.
Well, it’s a delight and privilege to be here. And I would like to start with testicles.
Men who sleep five hours a night have significantly smaller testicles than those who sleep eight hours or more. In addition, men who routinely sleep five to six hours a night will have a level of testosterone which is that of someone 10 years their senior. So a lack of sleep ages you by a decade in terms of that aspect, that critical aspect of wellness and virility.
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 forward, it’s only going to get worse. Rather than tell you about the wonderfully good things that happen when you get sleep, I’m going to tell you about the alarmingly bad things that happen when you don’t get enough, both for the brain and for the body.
BRAIN: LEARNING & MEMORY
Let me start with the brain and the functions of learning and memory.
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. So sleep essentially future-proofs those facts within the brain.
But recently, we’ve discovered that you not only need sleep after learning, you also need sleep before learning. But now 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 effectively become waterlogged, as it were, and you can’t absorb new information.
So here in this study, we decided to test the hypothesis that pulling the all-nighter was a good idea. How do you do that? Well, we took a group of healthy adults and we assigned them to one of two experimental conditions — a sleep group and a sleep deprivation group.
Now, the sleep group, they’re going to get a full eight hours of shuteye. But the deprivation group, we’re going to keep them awake in the laboratory under full supervision. There’s no naps, there’s no caffeine. It’s miserable for everyone included, us as well.
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, the amount of learning. So the higher up you are, the more that you learn.
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. And I think this should be frightening considering what we know is happening to sleep in our education populations right now.
Just to frame this in context, it would be the difference between acing an exam and failing it miserably. And we’ve gone on to discover what goes wrong within your brain to produce these types of learning disabilities.
There is a structure on the left and the right side of your brain called the hippocampus. And you can see it here in these sort of orange-yellow colors. Think of the hippocampus like the informational inbox of your brain. It’s very good at receiving new memory files and holding on to them.
And when we looked at this structure in those people who’d had a full night of sleep here in green, 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. It’s almost as though sleep deprivation had shut down the memory inbox and any new incoming files, they were just being bounced. You couldn’t effectively commit new experiences to memory.
And parenthetically, I should note if you would like to know what life is like without a functioning hippocampus, just watch the movie “Memento.” I suspect many of you have seen this. But this gentleman suffers brain damage. And from that point forward, he can no longer make any new memories. He’s what we call densely amnesic.
The part of his brain that was damaged was the hippocampus, and it is the very same structure that sleep deprivation will attack and block your brain’s capacity for new learning. So that’s the bad that happens when you take sleep away.
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 here.
What is it about the physiological quality of sleep, when you do get it, that actually enhances and restores your learning and memory ability each and every day?
And by recording sleep with electrodes placed all over their head, we’ve discovered that there are big, powerful brain waves that happen during the very deepest stages of sleep that have, riding on top of them, these spectacular bursts of electrical activity called sleep spindles.
And it’s the combined quality of these deep sleep brainwaves at night that acts like a file transfer mechanism. It takes memories from a short-term, vulnerable reservoir and shifts them to a more permanent, long-term storage site within the brain called the cortex, this big, wrinkled, massive tissue that sits atop of your brain.
And it means that when you wake up the next morning, there are two benefits.
First, having shifted memories of yesterday to that long-term, safe storage haven in the brain, they are protected so that you will remember rather than forget.
The second benefit, however, is that having shifted those files from that short-term reservoir, almost like moving files from a USB stick, you’ve cleared out all of that memory-encoding capacity, so that when you wake up the next day, you can start acquiring new files all over again. You can start learning anew.
So it’s this elegant, beautiful, symbiotic system of memory that happens each and every night. And it’s 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 two areas that we’ve moved this work out into. I’ll begin clinically and specifically the context of aging and dementia. Because I think many of us have a sense or even know that as we get older, our learning and memory abilities start to fade. They begin to decline.
But what we’ve also known for many decades is that a physiological signature of aging is that your sleep gets worse. And not just any type of sleep — especially that deep quality of sleep that I was just describing.
And only last year, we finally published evidence that these two factors are not simply co-occurring. They are significantly interrelated. And it suggests that the disruption of deep sleep is perhaps an underappreciated factor that is contributing to what we call cognitive decline, or memory decline, in aging, and most recently, we’ve discovered, in Alzheimer’s disease as well.