Tools to Enhance Working Memory & Attention
Date: 2024-01-29 | Duration: 01:31:12
Transcript
0:00 Welcome to the Huberman Lab podcast where we discuss science and science-based tools for everyday life. I’m Andrew Huberman, and I’m a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today we are discussing working memory. Working memory is a special category of memory in which we are able to hold small amounts of information in our mind for short periods of time. Working memory is also very closely related to attention. So for any of you
0:30 that are interested in how to develop better focus and attention, understanding what working memory is and some of the things that you can do to improve your working memory can be very beneficial. Today I’m going to talk about what working memory is, including some of the underlying biology, although I promise irrespective of whether or not you know any biology or you are an expert in biology, I’ll make the conversation accessible to you. In addition, I will talk about tools to improve working memory, and I’ll also compare working memory to other forms of memory,
1:00 like long-term memory and short-term memory, and through that understanding, I’m confident that you’ll be able to develop better focus as well as be able to commit certain forms of information to your short- and long-term memory stores. Before we begin, I’d like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero-cost-to-consumer information about science and science-related tools to the general public. In keeping with that theme, I’d like to thank the sponsors of today’s podcast. Our first sponsor is Matina.
1:30 Matina makes loose-leaf and ready-to-drink yerba mate. I often discuss yerba mate’s benefits, such as regulating blood sugar, its high antioxidant content, the ways that it can improve digestion, and possible neuroprotective effects. I also drink yerba mate because I love the taste. While there are a lot of different choices of yerba mate drinks out there, I love Matina because they have the no-sugar variety as well as the fact that both their loose-leaf and their canned varieties are of the absolute
2:00 best quality, so much so that I decided to become a partial owner in the company. Although I must say, even if they hadn’t allowed me to do that, I would be drinking Matina. It is the cleanest-tasting and best yerba mate you can find. I love the taste of brewed loose-leaf Matina yerba mate, and I particularly love the taste of Matina’s new canned cold brew zero-sugar yerba mate, which I personally helped them develop. If you’d like to try Matina, go to drinkmatina.com/huberman.
2:30 Right now, Matina is offering a free one-pound bag of loose-leaf yerba mate tea and free shipping with the purchase of two cases of their cold brew yerba mate. Again, that’s drinkmatina.com/huberman to get the free bag of yerba mate loose-leaf tea and free shipping. Today’s episode is also brought to us by BetterHelp. BetterHelp offers professional therapy with a licensed therapist carried out online. Now, I’ve been going to therapy for well over 30 years. Initially, I didn’t have a choice; it was a condition of being allowed to stay in school, but pretty
3:00 soon I realized that therapy is extremely valuable. In fact, I consider doing regular therapy just as important as getting regular exercise, including cardiovascular exercise and resistance training, which of course I also do every week. The reason I know therapy is so valuable is that if you can find a therapist with whom you can develop a really good rapport, you not only get terrific support for some of the challenges in your life, but you also can derive tremendous insights from that therapy—insights that can allow you to better not just your emotional life and
3:30 your relationship life, but of course also the relationship to yourself and to your professional life, to all sorts of career goals. In fact, I see therapy as one of the key components for meshing together all aspects of one’s life and being able to really direct one’s focus and attention toward what really matters. If you’d like to try BetterHelp, go to betterhelp.com/huberman to get 10% off your first month. Again, that’s betterhelp.com/huberman. Today’s episode is also brought to us by Helix Sleep. Helix Sleep
4:00 makes mattresses and pillows that are of the absolute highest quality. I’ve spoken many times before on this and other podcasts about the fact that sleep is the foundation of mental health, physical health, and performance. One of the key things to getting a great night’s sleep is to make sure that your mattress matches your sleep requirements. The Helix website has a brief two-minute quiz that, if you go to it, will ask you questions such as: Do you sleep on your back, your side, or your stomach? Do you tend to run hot or cold during the middle of the night? As well as some other questions that allow you to determine the optimal mattress for you.
4:30 When I took the quiz, I personally matched to their Dusk mattress, which has allowed me to significantly improve my sleep. So if you’re interested in significantly improving your sleep, go to helixsleep.com/huberman, take their brief two-minute quiz, and they’ll match you to a customized mattress, and you’ll get up to 350 off and two free pillows. Okay, let’s talk about
5:00 working memory, and let’s start off this discussion by comparing working memory to other forms of memory that most people are more familiar with—or at least, when most people hear the word memory, they typically are thinking about long-term memory, like one’s ability to remember the capitals of states or countries, the different continents, directions from one location to another, even one’s name. All of those things are examples of long-term memory. Now, I want to emphasize that long-term memory really has two components. There are what
5:30 we call declarative long-term memories. So these are the things that we can declare, things like facts about ourselves or the world or others. And then there are procedural long-term memories. Procedural long-term memories, as the name suggests, are aspects of our memory that allow us to perform certain procedures. They are literally action steps that we take to, for instance, ride a bicycle or drive a car, which, by the way, we might not be conscious of ourselves doing after we learn—that is, after we pass information into our
6:00 procedural long-term memory. But even once those things become reflexive, they are stored in our long-term memory. Now, a discussion of long-term memory is not the focus today, but me being a neuroscientist—and I like to think you all generally being interested in the underlying biology—I’ll just mention that there’s a key structure within the brain that is part of a larger neural network, that is a collection of structures, which is absolutely essential for the formation and storage of long-term memories, and that’s the
6:30 hippocampus, which in Latin means seahorse, and it does look a little bit like a seahorse, but you actually have one on each side of your brain, so we say hippocampi, plural. And so what we know is that if people have damage to their hippocampus of any kind, people have trouble accessing or forming long-term memory, sometimes both. And there’s a lot more that we could say about long-term memory; indeed, I did an entire episode of the Huberman Lab podcast about the formation and storage of long-term memories, including some tools to improve long-term memories. We’ll touch on a few
7:00 of those tools later today, but you can access that episode if you go to hubermanlab.com and just put “memory” into the search function, and you’ll find it there. In the meantime, if we want to understand working memory, we not only have to understand how it’s different from long-term memory but also how it’s different from short-term memory. Short-term memory is a capacity that we all have that, as the name suggests, represents a short-term memory bank for information that may or may not get passed into long-term memory. So for instance, if you’ve learned anything—and
7:30 of course you have; if you can understand what I’m saying, you’ve learned the English language; if you can write, you’ve learned how to write, etc.—well, in order to learn those things and to commit them to long-term memory, the information required to do those things and to have that knowledge needed to be held in short-term memory. Short-term memories are the sorts of memories that we maintain for somewhere between a few minutes and potentially a few hours, maybe a little bit longer, but only a certain percentage of that is passed into our long-term memory. So for
8:00 instance, if you listen to this podcast or you go to a course lecture, whether or not that lecture is about cognitive material or whether or not it’s about learning a new physical skill, regardless of what you learn, you’re only going to learn a certain amount of that information. But were we to examine how much of the information you just heard, or that you’re hearing now, you remember immediately after this podcast episode as compared to, say, a week later, we know based on millions of scientific
8:30 papers and studies that you are going to have more information in your short-term memory stores shortly after being exposed to new information than you will later. In other words, only a small percentage of what we perceive—what we see, what we hear, etc.—gets passed into short-term memory, and then only a fraction of that gets passed into long-term memory. Now, the neural circuits for short-term memory and the passage of short-term memories into long-term memory involve a lot of different brain structures, but here again we can implicate the hippocampus because the
9:00 actual passage of short-term memories into long-term memories occurs in part within the hippocampus. And then—a lot of people don’t know this—some of the memories that we think of as long-term memories are actually distributed into the neocortex, which is the outer portion of the brain. Now, the point here is less to fill your mind with different names of things and nomenclature, but rather to get you thinking about what’s involved in creating short- and long-term memories, and equally important, that even though the hippocampus is critically involved
9:30 in the formation of short- and long-term memories, the formation of short- and long-term memories is really a network phenomenon. In fact, among the more important themes that comes up again and again on this podcast, anytime that we’re talking about neuroscience or actually biology in any case, is that rarely, if ever, is there one location in the brain where something happens. Typically, it’s a network phenomenon, meaning it’s the collaboration of a bunch of different brain areas passing information from one location to the next and storing it in a kind of distributed way. Now, another
10:00 key thing to understand about working memory and how it is different from short- and long-term memory is that the formation of short- and long-term memories almost always involves neuroplasticity. Neuroplasticity is the nervous system’s ability to change in response to experience. Now, there are different types of neuroplasticity. So often when we hear about neuroplasticity in the popular sphere, people don’t emphasize that there are different types of neuroplasticity, and it’s worth paying a little bit of attention to what those different types are. There is, for instance,
10:30 what we call long-term potentiation. Long-term potentiation, or LTP as the acronym goes, is the strengthening of connections between neurons as a consequence of their repeated firing very closely together in time. Okay, there’s a lot more to it, but if you’ve ever heard the phrase “fire together, wire together,” sometimes that is misattributed to Donald Hebb, who did talk about neuroplasticity. By the way, Donald Hebb was a psychologist up in Canada who talked about neuroplasticity in the
11:00 context of lots of different forms of learning, but that “fire together, wire together” phrase was not actually stated by Donald Hebb; it was stated by Carla Shatz, my colleague at Stanford, and she was referring to LTP, but other forms of neuroplasticity that occur mainly in development when neurons fire very closely in time and thereby strengthen those connections, which can include LTP. Okay, so for now, think of LTP as anytime that some small group of neurons—could be two neurons, could be 2,000 neurons—are very active
11:30 closely together in time and they have access to one another physically, and the consequence is often—not always, but it’s often—LTP, that is, the strengthening of those connections such that after that barrage of activity subsides, those neurons can speak to each other. They can communicate through electrical activity and chemical activity much more easily; their communication is more robust. It’s like removing a wall between a conversation such that the conversation
12:00 can take place more fluidly. Now, there are other forms of neuroplasticity, including LTD, long-term depression, which unfortunately the name often calls to mind ideas about depression as a psychiatric or a psychological symptom, but has nothing to do with that. Long-term depression is simply the inverse of LTP; it’s actually the weakening or the removal of connections that we call synapses between neurons. I want to emphasize that both LTP and LTD are both critically involved in lots of
12:30 different kinds of learning, and both of them tend to be involved in the formation of both short-term memories and long-term memories. And this is very important in the removal of short-term memories and long-term memories—literally forgetting of certain things—because as we all know, there are many things that we will never forget, and there are also things that we almost always forget. Now, there’s a third form of neuroplasticity that’s involved in the formation of short- and long-term memories that’s important for us to discuss just briefly, but I do want to emphasize that there are not just three
13:00 forms of neuroplasticity; there are many other forms, dozens if not more, things like spike-timing-dependent plasticity, paired-pulse facilitation, and on and on. But the third type of neuroplasticity that I’d like to mention now is neurogenesis. Neurogenesis is the formation of new neurons. Now, neurogenesis is robust in the developing nervous system; we know this. It’s robust in the developing nervous system of animals and humans. However, neurogenesis—the literal formation of new neurons in
13:30 the brain—is a very exciting idea, and it does occur. It’s very exciting in a way that has motivated lots of popular press outlets to talk about or to discuss papers that have discovered neurogenesis in the adult brain because, let’s be honest, what’s more exciting than the idea that your brain can add new brain cells later in life? And indeed, that has been shown even in people well into their 80s and 90s. However, it’s very important to know that the total amount of neurogenesis that occurs in the adult
14:00 human brain is infinitesimally small as a mechanism for neuroplasticity and learning as compared to the other forms of neuroplasticity that we discussed, such as long-term potentiation and long-term depression. So I don’t want to throw cold water on the topic of neurogenesis; it’s an incredibly interesting and important topic, but all too often they tend to eclipse the much more common mechanism for the formation of short- and long-term memories, which are those other forms we just talked about—LTP, LTD, etc. So the point here is
14:30 that yes, indeed, there are new neurons that can be added in the adult brain, maybe even in the adult human brain, and there is some evidence that some of those new neurons are added to the hippocampus—in fact, a particular region of the hippocampus called the dentate gyrus of the hippocampus. And there’s been a lot of controversy about how much neurogenesis occurs or doesn’t occur, and whether or not it occurs after puberty or not; there’s a whole field of people battling over this now for several decades. But one thing is very clear:
15:00 neurogenesis, while it’s very exciting and intriguing, is not the main mechanism by which the formation of short- and long-term memories occurs. When you learn new information, as you are right now, the storage of that information in your short-term memory networks, which is then passed on to your long-term memory networks and that can be recalled, that allows you to state certain facts about, for instance, the existence of this thing called a hippocampus—hopefully you will remember that going forward—or your ability to perform any kind of motor movement that you learned now or way
15:30 back in childhood, most of that is the consequence of the strengthening of particular connections and the weakening of other types of connections. Those are the two major forms of neuroplasticity. Okay, so I don’t want you to get the impression that there’s something wrong with my memory and that I forgot that this episode is not about short- or long-term memory, but it’s about working memory. And indeed, I have not forgotten. So now is where I tell you why I’ve been talking about short- and long-term memory and the mechanisms of those, because I want them to provide a stark contrast
16:00 for what we call working memory. Working memory, as far as we know, does not involve neuroplasticity—or at least, if it does, it’s not a particularly robust aspect of working memory. Rather, working memory is the reflection of a particular neural circuit running an algorithm over and over and over for different types of information, but the information isn’t stored; it is actually intentionally discarded. Now, what sorts of daily
16:30 activities and life activities would require working memory? The answer to that is basically everything that you need to do but that you don’t want to remember. Now, what types of things would those be? Well, let’s think about it. Most all of us learned at some point in our life to tie our own shoes. Presumably you know how to tie your own shoes; if you don’t, perhaps you should learn or wear Velcro or slippers, I don’t know. But assuming you can tie your own shoes, that’s something that you know how to do, and you can do it as a procedural long-term memory. You can do that action;
17:00 you don’t have to think about it too much. Working memory would come into play when, say, you wake up in the morning and you know that you need to head out for a jog, but you also need to make a cup of coffee first, and you need to remember where the coffee is, where your shoes are, and perhaps you’re making a phone call or you’re having a conversation while you need to tie your shoes, and so on and so forth. Working memory is basically the taking in of information that’s critical for you to sequence your actions over a short period of time and then forget
17:30 that sequence. For instance, I’m willing to bet that you put your shoes on to go running before you go running, and if you’re like me, you drink your water, your coffee, your yerba mate before you go running. The point here is that if you wake up in the morning and you like caffeine before you go for a run, there are certain series of action steps that you need to carry out to hydrate, make that cup of coffee or tea, drink it, put on your shoes, head out the door. You need to sequence things properly, but you don’t want to commit your long-term or even your short-term
18:00 memory stores to carrying out that sequence. You simply want to be able to carry out that sequence and then discard that information about the sequence and focus your attention on, for instance, what trajectory you’re going to run through the park or around your neighborhood. Then you want to discard that information and you want to lean into the next portion of your day, and so on and so on. In fact, working memory is involved in essentially every activity, both cognitive and motor, from the point you wake up in the morning until the time you go to sleep at night for every
18:30 single day of your life. And we know this because there are indeed people who have diminished working memory or even lack working memory entirely, although the latter is somewhat rare. It has happened, and as you can imagine, they have a complete failure of ability to sequence activities, and their lives are extremely difficult. They need a ton of assistance from other people, even more assistance than do people who have minimal or no long-term memory. Okay, so this is really highlighting just how important working
19:00 memory is. Working memory is basically the way that you navigate any immediate environment, and as I mentioned earlier, it’s very closely tied to attention because in order to know what to do now and then what to do subsequently, and then subsequent to that, you need to be able to hold your attention to the things you need to do. So working memory and attention collaborate literally at a neural circuit level and at a neurochemical level in order to allow you to move through your day in an adaptive, functional way. And people who have challenges with attention or focus
19:30 or working memory—and sometimes it can be hard to dissociate which one they’re having challenges with—really have a hard time moving through life as compared to people whose attention and working memory is more robust. Now, the good news is today we’re going to talk about working memory, some of the neural circuits involved, and some of the neurochemicals involved that can augment or improve working memory. And we’re also going to talk about what one can do to directly increase the amount of neurotransmission of those particular chemicals within the circuits that
20:00 control working memory—in other words, to improve your working memory. Now, I can talk about working memory and the mechanisms, etc., all day long, but as is often the case, sometimes it’s better to not just learn about concepts but actually to experience them in real time. So what we’re going to do now is I’m actually going to give you a working memory test. This is the sort of working memory test that you would take if you were to go into a psychology laboratory or a neuroscience laboratory and they were studying working memory in humans.
20:30 Now, there’s another advantage to us doing this in real time right here as you’re listening, or as you’re listening and watching, and that’s because you’re going to get data. You’re going to get information about what your baseline working memory capacity is, and you’re going to want to keep those data in your short-term memory stores—maybe even your long-term memory stores, but certainly your short-term memory stores—because shortly later in this episode, I’m going to talk about different ways to improve your working memory depending on where your baseline working memory starts,
21:00 which, by the way, turns out to be a pretty good proxy for the levels of a neuromodulator called dopamine within the neural circuits that control working memory. So right now, let’s take a working memory task. We’re going to do this purely through audio form because I realize some people are watching and listening to this on YouTube and others are just listening to this episode, so there are not going to be any visual cues or slides that I present. And that’s perhaps what distinguishes what we’re about to do most from what would happen in a
21:30 laboratory. Typically in a laboratory, there would be some visual presentation of what I’m about to say, but here, because of the format that most of you are consuming this information by, we’re going to do this purely by audio. So the first test of your working memory is very simple. I’m going to read off a series of letters, and your task is to remember as many of those letters as you can. The first string of letters is J, K, Z, P,
22:00 I. Okay, just to make this really easy, I’m going to say it twice, although typically in a working memory task it would just be said once, but I’m going to make this extra easy: J, K, Z, P, I. Okay, now you in your own head can try and recite back those letters if you like. Okay, second string of letters: R, O, M, K, L,
22:30 E. I’m going to make this extra simple and do it again—not typical for a working memory task, but there are some working memory tasks where that happens: R, O, M, K, L, E. Okay, now a third string of letters. This one’s going to be a little bit longer, so queue up that working memory and attention: W, A, C, Q, V, D,
23:00 N. I’ll repeat that again: W, A, C, Q, V, D, N. How many of the letters I just read can you remember? Okay, so depending on how many letters you can remember, perhaps you have a low, moderate, or high degree of working memory. Keep in mind that some of you are perhaps doing other things; you’re attending to driving or other tasks within your home or your office, and so perhaps you weren’t able to pay full attention, so there’ll be some variation
23:30 there, but nonetheless, after reading each of those strings of letters, you were asked to recall those letters in your mind. And if you wrote them down and you’re rereading them, yes, that’s cheating. But how about this: What if I were to ask you now about the simplest first string of letters, the one that consisted of only five letters? How many of you can remember any of those five letters now? Okay, I can’t hear you if you’re shouting them out; I can’t see you if you’re raising your hand, but chances are
24:00 most of you have forgotten the first series of letters, even though it was quite short and you could remember it early on. That ability to remember that string of letters when you first heard them—and indeed I read them twice, so I’d be very surprised if any of you couldn’t remember that string of letters after hearing them twice—but I also read you some other letters in the interim. Okay, so that now, just a couple minutes later, I’m asking you to remember that first string of five letters, and assuming that you didn’t write it down—you’re not cheating—chances are you remember
24:30 anywhere from two to zero of those letters in that first word, which is a perfect example of your working memory. Nothing got committed to short-term, much less long-term memory; rather, your working memory was able to work with that information, hold it in mind for just as long as you thought you needed to know that information, but then, thank goodness, that information was discarded. You didn’t know that I was going to ask you for that first string of letters again after reading you the longer string of letters, but I did that deliberately to show you how your
25:00 working memory works. So in some sense, the working memory task is a bit unusual in that it’s a test of, yes, memory in the very, very short term, but also a test of your ability to forget, to discard information that’s not critical. And that gets us back to the original definition of working memory, which is our ability to attend to specific small batches of information, remember it for just as long as we think we need to, and then to discard that information. And by the way, if you want to know what those first five letters were, they were J, K, Z, P, I.
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27:00 huberman. So now is where we talk a little bit about the neural circuitry and the neurochemistry of working memory. Now, it’s important that we do this because in a few minutes, you’re also going to learn that people generally fall into two broad bins of having a high or low baseline of a certain neurochemical in the brain that affords them either high or low working memory capacity. Now, in reality, it’s a distribution; in fact, it’s what we call a normal distribution, so it really isn’t
27:30 two bins, but during today’s discussion, and in fact in a lot of laboratory studies, we can actually bin people into these two groups. The neural circuitry underlying working memory involves a lot of different brain locations, that is, a lot of different neural networks collaborating to create this thing we call working memory. However, there are a couple of key hubs, that is, locations within the brain that are especially important for working memory. The ones that I’d like to focus on today involve the prefrontal cortex. So this is
28:00 neural real estate that resides just behind the forehead, and the neurons in the brainstem—so further back in the brain—that manufacture dopamine and that send their little wires that we call axons up to the prefrontal cortex to release dopamine. Dopamine is a neuromodulator. Many people are familiar with dopamine and familiar with it in the context of motivation and drive. Sometimes people mistakenly think it’s only involved in pleasure, but dopamine is involved in motivation and drive. When
28:30 dopamine systems go awry—that is, if their levels get too high—that can create manic states, it can create addictive states. When dopamine levels are too low, you can get movement challenges such as in Parkinson’s, which is a deficit or a literal destruction of the neurons that manufacture dopamine. There are a bunch of different areas of the brain that those dopamine neurons in the brainstem project to, but for right now, we’re going to focus almost entirely on the dopamine projections from the brainstem to the prefrontal cortex, which is called the
29:00 mesocortical circuitry. I’m not going to get into the origins or the meaning of the mesocortical versus other dopamine projection systems; I did that in a couple of episodes about ADHD and attention and dopamine in particular, and you can find those at hubermanlab.com. Just put “dopamine” and “circuits” into the search function, and it will take you to those particular timestamps where I describe that. But since we want to keep things fairly top-contour at the level of neural circuit here, just know that there are a bunch of neurons that manufacture dopamine back in the brain
29:30 stem that send their axons—those little wires—up to the prefrontal cortex, and that the amount of dopamine released per unit time—so in a certain amount of time—strongly dictates the extent to which working memory capacity is going to be high, medium, or low. Now, I want to be very clear, because I’m going to come back to this a little bit later again and again: It is the case that when dopamine levels are lower—that is, either there
30:00 are fewer neurons that have the potential to release dopamine in the frontal cortex, or for whatever reason less is being released in the frontal cortex, that working memory performance tends to be lower as compared to conditions where dopamine release or the availability of dopamine is higher. However, it is not the case that more dopamine is always going to equate to improved working memory. This is so important that I’m going to say it again: It is not always the case that increasing the amount of dopamine transmission in the frontal cortex leads to improvements in working memory. There
30:30 is a specific criteria that allows us to predict whether or not it will improve or maintain or actually degrade working memory performance. So before you head to the end of the podcast to try and figure out ways to increase dopamine to improve working memory, please keep that fact in mind. Don’t just commit it to your working memory; commit it to your short- and long-term memory, because that’s very important if your goal is to improve your working memory. With that said, I do want to describe just a little bit of research showing the relationship between having a low working memory span,
31:00 as it’s called—the ability to only remember a few letters or numbers or short batches of information—as compared to a high working memory span, meaning longer strings of letters, longer strings of numbers, which of course in the real world translates to being able to carry out shorter versus longer action sequences, as described earlier in the scenario where you’re getting up in the morning and you’re making coffee and you’re heading out for a run, etc., etc. People do differ in terms of their working memory capacity, and there’s a
31:30 classic study done by Cools and D’Esposito and colleagues—this was published in 2008—where they had a way to label the amount of dopamine that is available for release in the frontal cortex in human subjects. They did this by the injection of a specific dye. That dye gets taken up specifically by the neurons in the brain that manufacture dopamine. Then they were able to image the brains of those people while those people were wide awake using something called positron emission tomography. Again, the specific tool isn’t necessarily important, but since
32:00 some of you like to know, and what they found is that for people that had a high working memory span—that is, could remember long strings of numbers or letters or other information—they tended to be the people that had more dopamine available for release in the frontal cortex, either because they had more of the dopamine neurons themselves or a similar number of neurons, but those neurons had more dopamine to release. Okay, and they also found the converse: Individuals that had a low working memory span and ability had less
32:30 dopamine available for release. So that establishes a correlation, but it’s not causal. A different study, which is also a classic, was carried out by Brozoski, Brown, Rosvold, and Goldman, and this is a really important study because in this study they were able to introduce small amounts of dopamine directly into the cortex and evaluate working memory capacity. Now, anytime a working memory test is done, the same pattern always emerges:
33:00 This is regardless of any dopamine being infused into the brain, which is: People, and animals for that matter, are very good at remembering short spans of numbers, letters, or other types of information. So if you tell them one thing, like the letter A, and then you ask them, “Do you remember the letter?” almost everybody remembers that. But if you give them a string of 10 letters, they remember fewer of those 10 letters. That’s obvious, but it’s an important point to emphasize nonetheless. And so there’s a kind of dropping-off curve of performance as one progresses
33:30 from a fewer to a greater number of items to be remembered. In this study, when dopamine was introduced to the frontal cortex, the number of things that individuals could remember simply increased. It was a very straightforward result: More dopamine introduced allowed longer letter, number, and information strings to be remembered—and of course forgotten, because that’s what working memory involves: remembering and then discarding of information shortly thereafter. Now, the findings I just described complement what I said before,
34:00 which is the naturally occurring experiment: Bring people into the lab, measure their working memory span, look at how much dopamine they make. Higher dopamine, better working memory; lower dopamine, lower working memory. The experiment I just described was one in which dopamine is introduced, showing that dopamine is very likely the rate-limiting or the capacity-limiting—it’s probably the better way to put it—the capacity-limiting neuromodulator for improving working memory. That’s a fancy nerd-speaker way of saying more dopamine allows for better working memory. But a critical feature of this
34:30 experiment is that they did a number of experiments where they didn’t introduce dopamine, but instead they introduced other neuromodulators to the prefrontal cortex, such as norepinephrine or serotonin. And the interesting finding is that the addition of norepinephrine or serotonin—which of course are other neuromodulators that can change the firing patterns of neurons in the prefrontal cortex, but elsewhere as well; it’s just that in this case they were added to the prefrontal
35:00 cortex—had no effect on working memory. It neither improved nor degraded working memory when those neuromodulators were introduced. In other words, dopamine, and perhaps only dopamine, seems to be the dominant neuromodulator for regulating the degree—that is, whether or not you have small, medium, or large amounts of working memory capacity—in the prefrontal cortex. And of course, there have been a bunch of other experiments that are worth mentioning briefly in this context, such as taking people that
35:30 have a high working memory capacity and indeed have their brains imaged, and one sees that they have high levels of baseline dopamine, especially the dopamine projecting to the prefrontal cortex, and then they’re given a drug that depletes dopamine within the prefrontal cortex and their performance drops. And so what’s so nice about the literature around working memory is that while I’m not covering all of that literature exhaustively, it all tends to jive; it all points in a direction whereby the levels of dopamine being released in the prefrontal cortex during
36:00 working memory tasks correlates very strongly with capacity to perform working memory tasks. Lower dopamine, lower working memory span, as it’s called; higher dopamine, higher working memory span. Okay, so next we’re going to do another working memory task, different than the one we did earlier, and we’re going to do that with a specific purpose in mind, which is for you to be able to determine what your working memory capacity is and, by extension, your baseline levels of dopamine, or at least
36:30 the levels of dopamine that are likely being released into your prefrontal cortex while you do these working memory tasks. In other words, we’re going to try and figure out whether or not you are of the low, medium, or high working memory capacity. And of course, we’re doing that in part to try and establish whether or not you likely have low, medium, or high amounts of dopamine available for release in the prefrontal cortex. Of course, we’re not putting you into a positron emission tomography scanning device—we aren’t able to do that for obvious reasons—but keep in mind that
37:00 what we are about to do is very similar and in some cases identical to laboratory studies where the researchers were trying to determine what people’s levels of dopamine within these particular neural networks we’ve been discussing—the mesocortical pathway—are likely to be. In other words, performance on the working memory task that we are about to do is a decent indication of what the dopamine levels that are available for release in your prefrontal cortex perhaps might be. Now, I say “perhaps might be” because I don’t want to cause any unnecessary alarm if, for instance, you
37:30 fall into the low working memory span group. In fact, if you fall into the low working memory span group, there are actually some terrific tools that you can use to improve dopamine transmission in those pathways and improve your working memory. I also don’t want people to get the impression that somehow performance on this working memory task is reflective of some larger dopamine issue in the brain, and certainly it is not. I repeat: It is not diagnostic of Parkinson’s or any kind of neurodegenerative condition, although I will say that deficits in working memory are
38:00 common in patients with Parkinson’s for obvious reasons; those patients have deficits in dopamine neurons—not only production, but the number of dopamine neurons. It’s one of the hallmark features of Parkinson’s, but also in things like traumatic brain injury, etc. But the working memory task that you’re about to take, when given to a general population or a group of undergraduates or so-called normals or typical control subjects—which all of you are—okay, so unless you’re dealing with a traumatic brain injury or you have Parkinson’s, we know that the data
38:30 that you’re going to get back right now is very similar to the data that people get back when they do these sorts of studies in a laboratory. That is, it’s typical for some people to have a short working memory span, some people to have a medium working memory span, and some people that have a high working memory span. And today we’re actually just going to divide into two bins: short working memory span and high working memory span. And we can have some degree of confidence that correlates with the amount of dopamine available for release in the frontal cortex. But—and this is a very important point as we progress
39:00 along this discussion of working memory, the neural circuits, dopamine, etc.—I want to make clear something that I said earlier, which is that it is not the case that increasing the amount of dopamine that’s available always increases working memory span. In fact, there’s a common circumstance whereby people with a relatively high degree of working memory capacity increase their dopamine levels even further using pharmacology or other methods that we’ll discuss, and their performance actually can degrade. Okay, so if any of that is confusing now, we’ll make it all very
39:30 simple going forward, so that if you decide to implement any of the protocols discussed in this episode, you are aware of what you can expect and whether or not you are in the category of people that should or perhaps should not incorporate those protocols. Okay, let’s test your working memory again. This time, the working memory task is going to be a little bit different than the one you did previously. This working memory task involves me reading six different sentences to you, and your job is to pay attention to these six sentences because you’re going to be asked some
40:00 information about these sentences in a few moments. The first sentence is: Real estate costs are going up. The second sentence is: The Atlantic Ocean is warm in summer. The third sentence is: There’s a lot of interest now in electric cars. The fourth sentence is: Some reptiles eat only once a year. The fifth sentence is: Kids nowadays
40:30 look at screens more than 60% of their waking life. And the sixth and final sentence is: Football can mean different sports depending on the country. Okay, so I read you six sentences. They were moderately long, I confess. Your job for the working memory task is now to recall as many of the final words of each of those sentences as you can. I’ll give you a few moments to do that now.
41:00 Before I tell you what the final word of each of those sentences actually is, I want to remind everybody that working memory capacity follows a normal distribution. So some of you will be able to remember the final word of perhaps five or even six of those sentences, although I must say that is exceedingly rare. Some of you are going to be able to remember three to four of the final words of those sentences, and that’s more typical; that actually represents the average, or the mean, as we call it. And
41:30 fewer people, although still many of you, will only be able to remember one or two of the final words of those sentences. Okay, so now I’m assuming that most of you have tried to call to memory the final word of as many of those six sentences as you can, and maybe you’ve written them down or you’ve typed them into your phone or you have some record of what you recall those six final words of those sentences are. Now I’m going to tell you the actual final word of each of those sentences. The final word of the
42:00 first sentence was “up,” because as you may recall, the sentence was: Real estate costs are going up. The final word of the second sentence was “summer,” because the sentence was: The Atlantic Ocean is warm in summer. The final word of the third sentence was “cars,” because the sentence was: There is a lot of interest in electric cars. The final word of the fourth sentence was “year,” because the sentence was: Some reptiles eat only once a year. The final word of the fifth
42:30 sentence was “life,” because the sentence was: Kids nowadays look at screens more than 60% of their waking life. And the final word of the sixth sentence was “country,” because the sentence was: Depending on the country. Okay, so be honest with yourself and tell yourself—and you don’t have to tell anyone else if you don’t want to—how many of the final words of those six sentences you could remember correctly. It’s important that you remember them correctly. Again,
43:00 the number of words that you can recall—that is, your working memory span—is going to vary from person to person, but we can take the normal distribution of those