Andrew Huberman interviews neuroscientist Dr. Wendy Suzuki on memory, brain function, and the science of exercise
Andrew Huberman speaks with NYU neuroscientist Dr. Wendy Suzuki in this Huberman Lab Essentials episode.
Summary
Andrew Huberman speaks with Dr. Wendy Suzuki, a neuroscientist and professor at NYU, about the science of memory, attention, and brain health. Suzuki explains the four pillars of memorable experience — novelty, repetition, association, and emotional resonance — and how the hippocampus functions as the brain's central structure for forming long-term memories and enabling imagination. She recounts how her own weight gain and return to exercise during the tenure process at NYU led her to discover the profound effects of aerobic exercise on prefrontal cortex function and hippocampal memory. She presents research showing that regular cardio exercise stimulates the release of BDNF (brain-derived neurotrophic factor), which promotes the growth of new neurons in the hippocampus, and that even low-fit individuals exercising just two to three times per week for three months show measurable cognitive improvements. The episode concludes with Suzuki's top three tools for improving attention and memory: exercise, meditation, and sleep.
Key Takeaways
FULL TRANSCRIPT
What Makes Things Memorable: The Four Pillars
Dr. Wendy Suzuki: I like to say there are four things that make things memorable. Number one is novelty. If it's something new — the very first time we've seen something or experienced something — our brains are drawn to that. Our attentional systems draw us to that. And when you are paying attention to something, that's part of what makes things memorable. Second is repetition. Third is association. So if you meet somebody new who knows lots of people that you know — you and I share many people that we both know — it's easier to remember. Association. And then the fourth one is emotional resonance. We remember the happiest and the saddest moments of our lives, and that also includes funny and surprising things.
That is the interaction between two key brain structures. The amygdala, which is important for processing emotional, particularly threatening kinds of situations — those threatening, surprising kinds of situations. The amygdala takes that information and makes another key structure called the hippocampus work better to put new long-term memories into your brain. That is the key structure for long-term memory: the hippocampus.
The Hippocampus: Memory, Identity, and Imagination
Andrew Huberman: Step us through what this structure is, what it looks like.
Dr. Wendy Suzuki: The word hippocampus means seahorse. It is visually and anatomically beautiful, with these kinds of intertwining sub-regions within it. Functionally, it's easiest to understand what it does when you look at what happens when you no longer have one. We know this from the most famous neurological patient of all time. His initials were H.M. — every psychology and neuroscience student knows him. He was operated on in 1954 and the paper was published in 1957. They removed both his hippocampi because he had very severe epilepsy. They knew that the hippocampus was the genesis of his epilepsy, and this was experimental — his epilepsy was so bad that they decided to remove not just one hippocampus but both. What happened was an immediate loss of all ability to form new memories for facts and events.
So the hippocampus does something with all of these perceptions that are coming at us every single day, every minute. Not for all of them, but for some of them that have these features we just talked about — maybe they're novel, maybe they have associations, maybe they're emotionally relevant, maybe they've been repeated — some of those things in the realm of facts or events get encoded into long-term memory. The hippocampus and what it does really defines our own personal histories. It defines who we are. Because if we can't remember what we've done, the information we've learned, and the events of our lives, it changes us.
But what people have started to realize is that it's not just memory. It's not just putting together associations for the what, where, and when of events that happened in our past — it's also putting together information that is in our long-term memory banks in interesting new ways. I'm talking about imagination. Without the hippocampus, yes, you can't remember things, but you're also not able to imagine events or situations you've never experienced before. So the hippocampus is important for memory is too simple a way to think about it. What the hippocampus is truly important for is associating things together writ large. Anytime you need to associate something — for your past, your present, or your future — you are using your hippocampus. It takes on a much more important role in our cognitive lives when we think about it that way. That's the new hippocampus that neuroscientists are studying today.
One-Trial Learning and Emotional Memory
Andrew Huberman: There are some memories that can be formed very quickly — so-called one-trial learning. What is it about emotionally salient events that allows memories to get stamped in so powerfully?
Dr. Wendy Suzuki: There is this protective function of our brains that has evolved over the last 2.5 million years — you need to pay attention to and remember certain things for your survival. If something terrible or very scary happens, you remember it. I have one example: when I lived in Washington D.C., I went to work at NIH on a Sunday afternoon and came back to find that my apartment door had been crowbarred open. Somebody had broken in and stolen the nicest things I owned. Ever since then, whenever I rounded that corner coming home, I still had that memory. It was terrible because it put me in a terrible state just returning home. And that's a survival mechanism — do you want to be alert to possible danger? Absolutely. So part of those one-trial memories is taking advantage of this evolutionarily developed system to stamp in things that could be potentially dangerous into your memory. You will forever remember that particular corner or hallway because that is where something really bad happened to you.
How Personal Experience Led to the Exercise-Brain Connection
Andrew Huberman: For people trying to learn information that they're not that excited about — is there something we can do to leverage knowledge of how the memory system works naturally to make that a more straightforward process? Maybe we could talk about your story and how you came to where you are now, because I think it provides a number of tools that people could implement themselves.
Dr. Wendy Suzuki: As I was working to get tenure at NYU — and as you know, it's a stress-filled process. They give you six years to show your stuff and you are judged in front of all your colleagues, and either they say you can join the club or they say sorry. My strategy was: I'm just going to do nothing but work, as hard as I can, for six years. What happens when you work and you don't have any sort of life outside of work? You gain 25 pounds, which is exactly what I did. And you get really, really stressed.
So I decided to go on vacation — an adventure river rafting trip in Peru, by myself. I met other interesting people, and I was the weakest person on the whole trip. It was embarrassing. I came back and said, "I cannot be the weakest person. I'm in my late 30s. I have to do something." So I went to the gym. Fast forward a year and a half: I've lost the 25 pounds. So proud of myself. So much happier.
And I'm sitting in my office doing what you and I do a lot — writing an NIH grant — and this thought goes through my mind that had never gone through it before during those six frantic years of grant writing: grant writing went well today, that felt good. But when I thought about it more, I realized it wasn't just today. My grant writing had been getting smoother. I was able to focus longer. The sessions felt better. And the only thing I had changed in my life — and it was a huge thing — was that I had become a gym rat rather than a workaholic.
That's when my neuroscientist's spidey sense kicked in and I asked: what do we know about the effects of exercise on your brain? What was better about my writing was that I could focus longer and deeper — very important. And I could remember those little details that you try to pull together for a million-dollar NIH grant from 30 different articles open on your screen at the same time. That's hippocampal memory. I was studying hippocampal memory. I was writing grants on hippocampal memory. That's when I got really interested in the effects of exercise on both prefrontal focus and attention function and hippocampal function.
The thing that really sealed it for me was that right around that time, I got a phone call from my mom, who said my dad wasn't feeling well — that he had gotten lost driving back from the 7-Eleven, which was literally seven blocks from the house I grew up in. I knew that was hippocampal function. I suspected dementia. I suspected Alzheimer's dementia, which he did have. My dad was an engineer, not very active — he loved to sit and read books all day. My mom was the athlete. She played team tennis into her 80s, and it started to show.
I noticed that all the things that were improving in my brain were suddenly going away in my dad's brain. I started thinking: this isn't just something to help somebody who wants to get tenure — this is something that could help millions of people, most importantly our aging population.
BDNF, Neurogenesis, and the "Bubble Bath" of Neurochemicals
Dr. Wendy Suzuki: The thing that makes me wake up in the morning is the realization that every single time you move your body, you are releasing a whole bunch of neurochemicals. Some of them — dopamine, serotonin, and noradrenaline — give you that good mood. But what also gets released, particularly with aerobic exercise, is a growth factor called brain-derived neurotrophic factor, or BDNF. That is so important because it goes directly to your hippocampus and helps brand-new brain cells grow there. We all have that capacity. Even if you're a couch potato, you can get new brain cells in your hippocampus to grow. But it's like giving your hippocampus a boost with regular BDNF if you are exercising, which means we all have the capacity to grow a bigger, fatter, fluffier hippocampus.
What I like to give people is this image: every single time you move your body, it's like giving your brain a wonderful bubble bath of neurochemicals. With regular bubble baths, you are growing a big fat fluffy hippocampus. I'm not going to cure my father's Alzheimer's dementia. But if I go into my 70s with a big fat fluffy hippocampus, even if that disease is in my genes and starts to kick in, it's going to take longer for it to affect my ability to form and retain new long-term memories — and that is my motivation for getting up and doing my 30 to 45 minutes of aerobic exercise every day.
Andrew Huberman: Tell us your routine.
Dr. Wendy Suzuki: The data suggests that as long as your heart rate is getting up, you get these long-term effects on your hippocampus and prefrontal cortex — including improved ability to shift and focus attention. For that you need cardiovascular work. What I use is a video workout — 30 minutes, and I sometimes add on a 10 to 15 minute stretch at the beginning or end. I love the variety. Sometimes I do it with weights, sometimes without. I love kickboxing, so I choose a lot of kickboxing workouts. It just fits my routine, and it's always there — I don't have to get all dressed up to go to the gym.
How Exercise Triggers BDNF: Two Pathways
Andrew Huberman: So you do your cardiovascular exercise, you're pumping more blood — that's the definition of a higher heart rate. Blood flow to the brain is increasing. Do we know how that gets translated to a signal to release more BDNF?
Dr. Wendy Suzuki: Before I go into the aerobic side of things, I always like to start with the least amount of exercise to get something really useful — because I don't want people to say, "I hate sweating, I don't want to listen anymore." Studies have shown that just 10 minutes of walking outside can shift your mood. That is part of the neurochemical bubble bath — dopamine, serotonin, noradrenaline. Ten minutes. Anybody can walk for 10 minutes. That is the minimum amount of movement to get mood effects. But the big fat fluffy hippocampus? The better-performing prefrontal cortex? That's where you need the cardio workout.
There haven't been enough studies directly comparing and contrasting kickboxing with running with other forms of cardio. But my interpretation of the literature is that whatever way you get your heart rate up — including a power walk — is beneficial.
There are two pathways that have been studied connecting movement to more BDNF. The first is through a protein called myokine, which is released by skeletal muscles. Studies done in rats on running wheels showed that running rats had more myokine release; the myokine passed the blood-brain barrier and stimulated the release of BDNF in the brain. That's pathway number one.
Pathway number two comes through the liver. Exercise is a general physiological stress — cortisol is released when we exercise because we need blood sugar. And a ketone called beta-hydroxybutyrate, which we have known for a long time is released by the liver during exercise, also passes the blood-brain barrier and is another stimulant for BDNF. So the final common pathway seems to be BDNF stimulation in the hippocampus. It probably isn't the only pathway, but it is the one that has been studied most clearly. It comes from all of our physiological systems — our muscles working, our liver responding to the stress of exercise — and what it does is give more BDNF precursors entry into the brain, causing that upspike of BDNF that's part of your bubble bath every time you move.
Neurogenesis in the Adult Human Brain
Andrew Huberman: The issue of new neurons — neurogenesis — comes up a lot. The rodent literature is very clear that running on a wheel can trigger the literal birth and addition of new neurons to the hippocampus. In humans, it's been somewhat controversial. I do recall one study I don't think is contested — the work of Fred "Rusty" Gage at the Salk Institute, where they injected a marker into the brains of terminally ill humans who graciously offered to have their brains examined after death, and in some cases in very old individuals they did see evidence for new neurons being born in the hippocampus. Can I trust that idea still?
Dr. Wendy Suzuki: After that study, which was quite a while ago, there are more recent studies — still somewhat debated, but using even newer and better techniques than that original groundbreaking Rusty Gage study — that suggest and I believe show that new neurons are born in adult human brains into the ninth decade of life. Not only do you have neurogenesis in your 60s, as those original patients demonstrated, but these newer studies suggest that yes, you do, and we all do, even into old age.
Acute and Long-Term Cognitive Effects of Exercise
Andrew Huberman: If you would, could you tell us about some of the more specific effects of exercise on memory?
Dr. Wendy Suzuki: Let me start with the acute effects — what does a single exercise session do for your brain? There are three major effects that have been reproduced consistently. This is usually an aerobic session, 30 to 45 minutes. First, you get that mood boost — very consistent. Second, you get improved prefrontal function, typically tested with a Stroop task, which asks you to shift and focus your attention in specific ways. It's a challenging task largely dependent on the prefrontal cortex, and significant improvements in reaction time are reliably seen. Third, your speed of responding — often a cognitive-motor response — improves.
In one unpublished study I conducted, I looked at the effects of a 30-minute age-appropriate workout in subjects ranging in age from their 20s all the way up to their 90s. The most consistent finding, regardless of age, was decreased anxiety, depression, and hostility scores. Energy — the feeling of energy — went up. And in the older population even more than in the younger population, we saw improved performance on both the Stroop task and the Eriksen flanker task, another task dependent on focusing attention on specific stimuli.
How long do these effects last? One study I published from my lab showed that the immediate effects of exercise lasted up to two hours — and they were still present at that two-hour mark. That is a pretty big bang for your buck from one 30-minute session.
Andrew Huberman: What this tells me is that exercising early in the day may have a special effect.
Dr. Wendy Suzuki: I know there are moms and dads out there who say, "I have a kid — the kid's more important than my exercise." You will get benefits whenever you do it. But what all the neuroscience data suggests is that the best time to exercise is right before you need to use your brain in the most important way for that day. That is why the morning works best for most of us. That's why I do it in the morning.
Long-Term Exercise and Protecting Against Cognitive Decline
Andrew Huberman: I also want to touch on memory loss in general. My understanding is that somewhere in our 50s or 60s we start noticing little hiccups in memory. I imagine that doing exercise throughout one's entire life is going to help offset some of this, simply because of BDNF and other downstream effects.
Dr. Wendy Suzuki: I want to share one of my favorite studies — a longitudinal study done in Swedish women, published in 2018. Back in the 1960s, researchers found 300 Swedish women in their 40s and characterized them as low fit, mid-fit, or high fit. Then 40 years later, they came back and found these same women — now in their 80s — and asked what had happened to them cognitively as a function of their fitness level. What they found was that relative to the low-fit or mid-fit women, the women who had been high fit in their 40s gained nine more years of good cognition later in life. This is not a randomized controlled study — it's a correlational study — but does it agree with everything we've been talking about today? Yes. Does it agree with the idea that the high-fit women were giving their brains this bubble bath very regularly for 40 years and built up their big, fat, beautiful hippocampi? Yes, it does. It's one of my favorite studies.
Exercise Studies in Younger, Low-Fit Adults
Dr. Wendy Suzuki: When I entered the exercise research space, everybody was studying people 65 or older because that's when cognitive decline begins. But I wanted to know what happens in people in their 40s and 50s, maybe even their 30s and 20s — because that's when we as humans are willing and able to increase our exercise and get ourselves set up to build our brains as we go into our 60s.
The first study I did looked at low-fit participants from their 30s to mid-50s. Low-fit meant specifically that they were exercising less than 30 minutes per week in the three months prior to the experiment. We wanted to ask: how much exercise do you really need to start seeing benefits? So we assigned them to three months of two to three times per week of cardio — a spin class. The comparison group did two to three times per week of competitive video Scrabble: no heart rate change, but they came into the lab as a group, just like the spin class participants did.
What we found was that two to three times per week of cardio produced: an increase in baseline positive mood states relative to the Scrabble group; more positive body image; and, really importantly, their motivation to exercise went up significantly. The more you exercise, the more motivated you are to exercise.
What about cognition? We got improved performance on the Stroop task. And then, headed toward my favorite structure — the hippocampus — we found improved performance on both a recognition memory task assessing encoding and discrimination of similar items, and a spatial episodic memory task in which participants navigated a virtual city in a Doom-like game. Their performance on that spatial task improved significantly, which is very classically hippocampus-dependent. So I can now say: in 30 to 50-year-olds who are low fit, two to three times per week of cardio for three months produces measurable cognitive benefits. This is not about becoming a marathon runner. This is about starting to move your body on a regular basis.
Andrew Huberman: How long are those sessions again?
Dr. Wendy Suzuki: 45 minutes — with a 5-minute warm-up and a 5-minute cool-down, so it's really 35 minutes of hard work.
The second study was part two of that work, this time with mid-fit people — those already exercising two to three times per week. We collaborated with a spin studio and invited mid-fit participants to exercise as much as they wanted, anywhere from their baseline of two to three times per week up to seven times per week, for three months. The control group was asked not to change their exercise habits. What we ended up with was a range of exercise frequency, and the bottom line was: every drop of sweat counted. The more participants increased their workout — up to seven times per week — the better their mood was, with lower depression and anxiety, higher positive affect, and the better their hippocampal memory was. This was over three months. I love that result because it gives power to those of us who are already regularly exercising and wondering whether doing more will really help. The answer is yes. Our bodies are responsive, and you can get better hippocampal function and better overall baseline mood with a higher exercise load.
Affirmations, Exercise, and the intenSati Method
Andrew Huberman: What, if any, is the value of positive affirmations — telling yourself something positive about yourself — on mood, self-image, memory, and brain function?
Dr. Wendy Suzuki: I looked into this because I am also a certified exercise instructor. The form of exercise I teach is called intenSati — it was developed by an amazing fitness instructor named Patricia Moreno, who combined physical movements from kickboxing, dance, yoga, and martial arts with positive spoken affirmations. So each move, if you're punching back and forth as in a kickboxing class, you don't just punch — you say something like, "I am strong now," where each punch is associated with a word. You can create your own series of affirmations connected to the movements.
There is something about the declaration — using your own voice to say things you don't often say to yourself — like "I'm strong," "I'm inspired," "I believe I will succeed." I started to look into what was known about affirmations, and there is a clear literature showing that positive affirmations, whether said aloud or read, can change mood. It gets you into a habit of saying good things about yourself, and then you start to realize how mean you are to yourself — how many negative thoughts are running through your head. So what you get in intenSati is the mood boost from the positive spoken affirmations combined with all the other brain benefits we've been discussing from the exercise itself, since it is a sweaty workout.
Meditation: Ten Minutes a Day
Andrew Huberman: I'd like to touch on meditation. It sounds like you've found something close to a minimum threshold of meditation that can really benefit us. Tell us about that study.
Dr. Wendy Suzuki: Very practical. Just 10 minutes — not 30 minutes, not an hour; 10 minutes of guided meditation. It was actually a 12-minute body scan meditation, very basic and easy to follow. Eight weeks of daily 12-minute practice. What we found was significant decreases in stress response — we used the Trier Social Stress Test to measure response to an unexpected stressful situation, and the meditators did much better. Their mood was better and their cognitive performance was also better.
Andrew Huberman: How do you think it's working?
Dr. Wendy Suzuki: I think the most important thing that gets exercised when we do a simple 10 to 12-minute body scan meditation regularly is the habit-building and practice of focusing on the present moment. That is very hard for modern humans to do. If you know how to do that, it gives you a powerful tool for the rest of your day. You're not locked into fearful future thinking that so many of us have, or just reliving the terrible past. You can actually enjoy the present moment.
The Top Three Tools for Attention and Memory
Andrew Huberman: Are there any other things besides exercise and meditation that you would recommend for people trying to increase their powers of attention?
Dr. Wendy Suzuki: The top three tools that everybody can start using right this minute to increase their capacity to attend: first, exercise, for all the reasons we've talked about — it has a direct effect on the functioning of the prefrontal cortex. Second, meditation, which improves the ability to focus, and particularly to focus on the present moment. Third, and it has to be third, is sleep. It is so important for all core cognitive functions — including attention, creativity, and just basic brain function. Exercise, meditation, and sleep can help you learn, retain, and perform better than you would without these three things in your life.
Andrew Huberman: Wendy, thank you so much for your leadership in the university system, for your leadership in public education, and for the decades of important work on memory and neural circuitry that we've been able to learn about today. Thank you ever so much.
Dr. Wendy Suzuki: Thank you, Andrew. Fun conversation.