#59 - Sleep & Motor Memory

Hi there, it's Matt here and welcome back to the podcast. Today we're going to take a deep dive into sleep and motor memory, or specifically motor skill memory. But before we get there, let me do a quick primer on what human memory actually is. Whilst it's overly simplistic, we commonly think in brain science of two broad classes or two broad types of memory. On the one hand, we have fact-based memory, which concerns the recall of things like names or historical dates, or when you're sitting in an exam and you can't bring back things to mind, that's what we call fact-based memory. One of the other categories of memory, or the other second category of memory, is something that we call procedural memories, and more specifically skill memories. So here a good example would be, how do you remember how to ride a bike or play a musical instrument? Now it's essential to understand that motor skill memories are not stored in our muscles. Now some of you may think that that's not true. There is another term that people use called muscle memory, and that might suggest that the memories are stored in your muscles. That's not what we're talking about. Instead, motor skill memories reside principally within your brain. And my story in terms of research with motor memories goes back all the way to my initial time at the Queens Medical Center in Nottingham in England. And there I was able to observe patients who were recovering from strokes in the brain. And as a result of those strokes, they had often lost muscle control. And for example, it prevented them from enunciating speech, or even paralyzing an entire arm or an entire leg. What I also observed though is that during their rehabilitation, and it happens gradually and slowly, but day by day, they seem to gradually start to regain some of that function. But I wondered, is it really day by day that they're doing that? Or is it night by night? Caused by sleep. At the time, as a young student, I didn't have the chance, I didn't have a laboratory, I didn't have the ability to test my hypothesis. And it wasn't until another profound experience, almost eight years later, when I was a young professor, that I began to research that question with gusto. At the time, I'd been asked to give a public lecture on the topic of sleep. And it was at a large celebratory event in the UK for the decade of the brain. And at the time, we still knew relatively little about the effects of sleep on memory. And I did mention some of the embryonic findings that were available at the time, suggesting that sleep could influence memory. And then after my lecture had finished a very distinguished looking gentleman with beautifully, kindly eyes. And he was sort of an elderly gentleman dressed in this tweed suit jacket with, gosh, I remember it, had this wondrous, subtle yellow green hue to it. He approached me. And that conversation was brief, but it was one of the most scientifically important of my entire life. He introduced himself after thanking me for my presentation. And he told me that he was a pianist. And he said he was intrigued by my description of sleep and how active of a brain state it actually is, that we may even be reviewing or strengthening things we had previously learned. And then came a comment that would leave me reeling. And it triggered a major focus of my research, gosh, for the next 16 years. Because in a very sincere tone, he said to me, as a pianist, I have an experience that seems to be far too frequent just to be chance. And he went on to say that he will practice a particularly difficult piece of music, perhaps even practicing late into the evening, and he just couldn't seem to master it. And he said that I often make the same mistake at the same place in this particular movement, time and time again. And then I go to bed, frustrated. But when I wake up the next morning and I sit back down at the piano, I can just play perfectly. And those words, I can just play, they reverberated in my mind as I tried to desperately compose a coherent response. And I told the gentleman that it was a fascinating idea and that it was certainly possible that sleep could boost musicianship and lead to almost error-free performance. But that in truth I knew of no scientific evidence to support the claim. And he smiled in his kindly eyes, crinkled some more, and he was unfazed by the absence of my empirical affirmation. And he thanked me again for my lecture, and he walked towards the reception hall, which is where I should have been answering questions with the public. But instead, I stood there on the spot, and I remained in the auditorium. Because I realised that this gentleman had just told me something that violated the most repeated and entrusted teaching edict. "Practice makes perfect." Not so, it seemed. What he had just intamated was this. It is practice with a night of sleep that makes perfect. A sponsor of today's show is Inside Tracker, which is a service that comes out to your home, and they will analyse your blood and DNA to know precisely what is going on inside of you. Hence the name Inside Tracker. They look at your blood to your metabolic signals, your hormonal health metrics, and then they give you a personalised, actionable set of lifestyle changes in response to that readout. And the goal there is to improve your health. I was looking in, informed, they have some new cardiovascular and new hormonal biomarkers that I'm particularly interested in. One that I'm focused on is something called "ApoB", which is an absolutely critical heart health measure. And I get it done now with them somewhere between 4-6 times a year. Why? Well, my family unfortunately has a strong history of cardiovascular disease, so I am checking that pretty ruthlessly. And by the way, I do buy the product myself out of pocket. I don't want to fall prey to any of those trappings and undue incentives. Although with full admission, I still use my own discount code that you can use to get some money off. And that code for you is inside tracker.com/matwalker. So just go over to insidetracker.com/matwalker. And again, if you want to get that discount, it is insidetracker.com/matwalker. Thanks very much. After three years of subsequent research, I published a paper with that very same title. And in the studies that followed, I and my team, we were able to gather evidence that ultimately confirmed all of the pianists' wonderful intuitions about sleep. And the findings also shed light on how the brain, after injury or damage, for example, by stroke, gradually regains some ability to guide motor movements day by day. I should say night by night. Now by that time, I had taken a position as a young professor of psychiatry at Harvard Medical School. And there I set about trying to determine if and how the brain continues to learn in the absence of any further practice. Time. It was all about time. I knew what I needed to do was to dissect time. And here, I mean that time was clearly doing something to me. motor skill memories after we've learned them. But scientifically, I could see that I needed to discriminate between three distinct possibilities, three different hypothesis predictions. Was that benefit simply about time, or was it about time awake? Was it about time in sleep that was incubating that type of motor memory perfection? So I took a large group of individuals, and I had them learn to type a number sequence on a keyboard with their left non-dominant hand. For example, 41324. And I asked them to learn how to repeat that sequence with their hand as quickly and accurately as possible. And it's not quite right with the number existing, but it's a little bit like learning to play a piano skill. And subjects practiced this motor skill over and over again for a total of 12 minutes, and they took short breaks in between. So over and over again, they were learning to type 41324, 41324, 41324. Unsurprisingly, the participants improved their performance across the training session. After all, practice we had been told makes perfect. And then I tested those individuals 12 hours later. Half of those participants had learned the sequence in the morning, and then they were tested 12 hours later that evening after remaining perfectly awake during the day. And this was the wake group. The other half of the participants, they learned the sequence in the evening. And then we retested them the next morning after the very same amount of time, 12 hours. But that 12 hours had contained a full eight-hour night of sleep. And this was the sleep group. What did we find? Well, those who remained awake across the day showed no evidence of significant performance improvements. They had not become any worse, but equally they had not become any better. They were basically just the same. However, those who were tested after the very same time interval of 12 hours. But that spanned an eight-hour night of sleep showed a striking 20% offline boost in their performance speed, and a near 35% improvement in their motor memory accuracy. And what was also important and interesting, by the way, is that those participants who had learned the motor skill in the morning and showed no improvement 12 hours later that evening, they did go on to show that offline memory boost and bump in performance when they were retested yet again a further 12 hours the next morning. But once again, following a night of sleep. In other words, after learning, your brain will continue to improve these motor memories in the absence of any further practice. It's really quite magical. Yet that delayed offline learning occurs exclusively across periods of sleep and not across equivalent time periods while you're awake, regardless of whether the time awake or the time asleep comes first. Practice, therefore, does not make perfect. Instead, it is practice followed by a night of sleep that leads to perfection. And we went on to show that these memory boosting benefits occur no matter whether you learn a short or even a very long complex sequence, such as 4234231431414. Instead of 41324. And yes, that actually was one of the long complex sequences that we taught people. And yes, they could learn it. Which, by the way, isn't so remarkable when you think of the complexity of a piano concerto. Well, I should also, I remember to tell you, we changed the complexity in a different way in terms of the body. And we had individuals learning these sequences using just one hand. In other words, performing unimanual motor memory learning. Or we increased the difficulty using coordinated, two handed or bimanual skill learning, which is very similar to a pianist. When I was then analyzing the individual elements of the motor sequence, such as 41324, it allowed me to discover something even more striking. What we discovered was precisely how it was that sleep was perfecting these motor memories. When you looked at their performance even after a long period of initial training after a long period of practice, participants would consistently struggle with particular transitions in the sequence. And we called these problem points. And when you look at each person's individual data, they stick out like a sore thumb. There would be a far longer pause or a consistent error at a very specific transition, rather than seamlessly typing 41324, 41324 over and over again, seamlessly in smooth pans. A participant would instead type 41324, 41324. And what they were doing was chunking the motor routine into individual pieces. As if they were attempting the sequence not all in one go, like a very large meal, but trying to break it down into learning-related bite-sized digestible chunks. Why? Because it was just too difficult. And different people had different problem points at different moments in the motor sequence routine. But what was common is that almost all individuals had at least one or two of these difficulties. It's so interesting, by the way, to-- because I assessed so many participants. And sometimes I would be outside in the control room and we would have two-way communication so I could be hearing what they're doing. I could just listen to what they were typing. And I could almost pick out the unique problem point just from their initial learning based on the tapping on the keyboard. And then, when we would bring the participants back the next day after a night of sleep, my ears would hear something very different. And I knew what was happening even before I analyzed the data. What I was hearing was mastery, sleep, inspired mastery. The typing after a night of sleep was now fluid. It was unbroken. And gone was the staccato performance that they had the day before. Sleep had replaced it with seamless automaticity. And if you ask any athlete or musician or dancer, that is ultimately the goal of motor learning. So instead of hearing 413-24, 413-24, now I could hear and subsequently see statistically in the data the following, 413-24, 413-24, 413-24. It was rapid and it was near perfect. Sleep had systematically identified where the difficult transitions or the problem points were in the motor memory routine and then smooth them out. And this finding rekindled the words of the pianist that I had met all of those years ago. But when I wake up the next morning and sit back down at the piano, I can just play perfectly. And so we didn't stop there. We went on to test participants inside a brain scanner after they had slept. And we could see how these delightful skill benefits had been achieved. Sleep had modified and in fact changed the location of those motor memories. Sleep had moved those motor memories to brain circuits that operate below the level of consciousness, in other words, that helped you perform things automatically. As a result, sleep had made those memories in stintual habits. They just flowed out of the bodies of these participants with ease, rather than feeling consciously effortful and deliberate, which is to say that sleep helped the brain automate the movement routine. Sleep had made those memories second nature. They were effortless. And that's precisely the goal of many an Olympic coach when perfecting the skills of their athletes. The other supporter of this podcast is the electrolyte drink company called Element. Now it's actually four letters LM. I am a bit of an exercise fanatic and I started buying their products some years ago already because of two key facts. First is the lack of sugar content. Element has no sugar. It also has no colourings, no artificial ingredients, which is unlike many of the other mixes out there that I was shopping. The second is because of the founders who have some serious years of biochemistry experience under their belts and they know what they're doing. So if you want to give it a try, just go to drinklmt.com/matwalker and you will get 8 free sample packs on any order that you place. Once again, that is drinklmt.com/matwalker. My final discovery in brushwat span to almost probably a decade of research identified the type of sleep that was responsible for these overnight motor skill memory enhancements and it carried with it societal and medical ramifications. When we examined the sleep of these individuals because we've been recording their sleep physiologically in the sleep laboratory, we found that the greater the amount of stage 2 non-ramp sleep which is a lighter form of non-ramp sleep, particularly in the last 2-3 hours of the night predicted how much improvement in those motor memories would occur the following day. And it wasn't just this light stage 2 non-ramp sleep. It was a very specific set of electrical bursting activity that are the hallmark of stage 2 non-ramp sleep that were the best predictors. And these are what we call sleep spindles. And the more of these sleep spindles these individuals had, particularly in those last few hours of the night, the greater the degree of motor memory enhancement the following morning. And what was stunning by the way, we found that it was even these bursting spindles right over the particular side of the brain and the specific motor cortex area of the brain that controlled the hand that they were using to learn the memory. That's what was associated with better performance. So perhaps an analogy here would be it's like getting a really good massage for that problematic muscle group in a very specific part of your body. And these sleep spindles were disproportionately working away on those parts of the brain that had been worked hardest during the day where the motor skill memory had been learned. And it's what we call local brain plasticity. And these sleep spindles seem to be almost an electrical fertilizer over that specific part of the brain to boost the plasticity and enhance those memories. And thankfully lots of other research groups around the world have now seen the same thing and they've done even better studies than any of my original experiments and the effects as seem to hold. But perhaps more relevant to you and I and the modern world brings me back to the finding I told you regarding the time of night effect. And so you'll remember that I said that it was that type of sleep, light stage two non-rem sleep and the bursting spindle activity that occurs there. And the last two hours of the night that most accurately predicted how much of a memory boost you would get the next day. Why is that important? Well it is precisely those last two hours of sleep that many of us feel is okay to cut short to get a jump start on the day. Perhaps where the type of individual and I have to resist being one of these two who wants to cut sleep short and get a jump start on the day and so I can get to the gym early. Or alternatively perhaps it's society forcing us to do this through our job demands or early school start times for kids that forces you to always skip those last few hours. And as a result we miss out on these late morning sleep spindles and we short change our brain of some additional memory benefits. And it again brought back to my mind the prototypical, or maybe I should say even maniacal Olympic coach who stoically has her athlete practicing late into the evening only then to request and always demand them to wake up in the early hours of the morning and return back to the practice field at 6 or 7 am the next day. Which I so understand by the way and I empathise with it's a very natural thought to have. However in doing so coaches may be innocently but very effectively denying an important phase of motor memory development within the brain. One that fine tunes those athletic skill performance abilities. And when you consider that it's very small performance differences that often separate winning a gold medal from perhaps coming in the middle of the pack or even finishing last in professional athletics. You can imagine that any competitive advantage that you gain such as that naturally offered by sleep can help determine whether or not you will hear your national anthem echoing around the stadium or someone else's. So what is the simple take home message here when it comes to motor memories? Perhaps without putting too finer point on it and saying it in a rather crash and in elegant fashion it is this if you don't snooze you lose when it comes to motor memories. So that's it folks, a quick tour of sleep and motor memory. Practice it seems does not quite make perfect. Add some lavish sleep into the equation and the next day you will just sit back down and you'll be able to play perfectly. Take care and bye for now. [Music]