Growing A Bigger Brain Is A Walk In The Park

A new study in the Proceedings of the National Academy of Sciences shows that adults who walked for 40 minutes three times a week for a year had brain growth in the hippocampus — an area of the brain associated with spatial memory. Study author Arthur Kramer and psychologist Margaret Gatz discuss their research.

IRA FLATOW, host:

You're listening to SCIENCE FRIDAY. I'm Ira Flatow.

Want to make your brain bigger? It's a walk around the park, literally. A new study found that adults who walk for 40 minutes three times a week for a year had a region of the brain called the hippocampus - had that region grow bigger.

The control group who did stretching and toning, well, their brains actually shrunk. The walkers also performed better on some memory tests.

Why would exercise bulk up your brain? And is a bigger brain a healthier brain? These are some of the things we'll be talking about this hour, along with what else we can do to keep our brains health as we age. One of those things may not be doing crossword puzzle.

We'll talk about. Let me introduce my guests. Margaret Gatz is the director of Education Core at the USC Alzheimer Disease Research Center, professor of psychology, gerontology and preventive medicine at the University of Southern California in Los Angeles. She joins us from KUSC. Welcome to SCIENCE FRIDAY.

Prof. MARGARET GATZ (Director, Education Core, USC Alzheimer Disease Research Center; Professor of Psychology, Gerontology and Preventive Medicine, University of Southern California): Thanks for inviting me.

FLATOW: You're welcome. Arthur Kramer is the director of the Beckman Institute and a professor of neuroscience at the University of Illinois in Champaign-Urbana and author of the new study. Welcome to SCIENCE FRIDAY.

Prof. ARTHUR KRAMER (Director, Beckman Institute, Professor of Neuroscience, University of Illinois): Thank you very much.

FLATOW: Dr. Kramer, let me ask you first. Why would walking around a track make your brain bigger?

Prof. KRAMER: Well, the research we've done with humans is based upon a number of years, over a decade's work of research with animals, mostly rodents. And we know from the animal research that if you give an animal access to running wheel, and it uses it, that there are a number of changes in the brain, and the area that's been examined, probably most intensely, is the hippocampus.

The reason for that is twofold, or maybe threefold. The hippocampus is one of the few areas of the brain that produces new neurons from adult stem cells, supergenitor cells. So neural genesis, or the birth of new neurons that become functionally integrated with old neurons, occurs in the hippocampus.

Another reason is we know that the hippocampus supports an important aspect of memory called episodic or relational memory. An example would be meeting somebody at a party and trying to remember their name, their face, what you talked about and so forth, the hippocampus plays an important role in that.

And finally, hippocampal function declines during the case of normal aging and even pathological aging, such as with Alzheimer's. So there's a number of reasons that animal researchers have examined the hippocampus and its response to exercise and other factors.

And they have found improvements in neural genesis, or increases in neural genesis, the birth of new neurons, as a function of exercise and that those new neurons seem to be related to improvements in memory.

Hence, it looked like a good place for us to examine with regard to human hippocampal function, or in this case hippocampal structure, exercise and memory.

FLATOW: Do you have a reason, a speculation of why this, in nature, would be beneficial to us? Is it because we're a mobile sort of animal, and we need to move around a lot, and might that help us, you know, live longer?

Prof. KRAMER: Well, certainly, if we think of us in an evolutionary sense, moving was very important, moving quickly, remembering where we were, remembering routes and so forth. And the hippocampus plays an important role there.

So I guess it's not surprising from an evolutionary perspective that hippocampal structure and hippocampal function might be related to action or activity or exercise in support of better memory of spatial locations, where the food source is, where the predators are and so forth.

FLATOW: Dr. Gatz, does this research finding square with your research, looking at brain disease in Swedish twins?

Prof. GATZ: It does. There's a number of different designs one can use to look at the effect of different protective factors in relation to brain health. And one of those designs is exactly what Professor Kramer has done, setting up a group who had an intervention and comparing that group to those who did not.

Those kinds of studies don't let one go back a long, long time in the lifespan. And so another kind of study looks at people's reported or recorded history of exposure to different kinds of risks and protective factors throughout their whole lifespan and asks what are the different consequences when the person becomes old.

A variant of that design is comparing twins, in particular identical twins, where one twin has better brain health than the other twin or where one twin develops dementia or Alzheimer's disease, and the other twin does not.

So in our twin studies, we have found that the twin who has moderate exposure to exercise in midlife is at less risk of becoming demented in old age.

FLATOW: 1-800-989-8255 is our number. Sorry to drop in on you there. Also, you can tweet us @scifri, @-S-C-I-F-R-I.

But wouldn't the take-home on this be that if you get enough exercise and the right kind of exercise, and you're saying in your study, Dr. Kramer, it's 40 minutes three times a week, doesn't that make your whole body better?

Prof. KRAMER: It certainly does. I mean, we've known for many years that exercise, especially cardio-respiratory exercise, and there are other forms and all of which are important for different reasons, but exercise can reduce the risk for hypertension and heart disease, stroke, osteoporosis, a number of forms of cancer, diabetes and so forth.

So it's quite clear that exercise improves body and brain function in the long term. The kind of work we did was to look at even a shorter term, not a lifetime of exercise.

And I think it's important to point out that the participants in our study weren't lifetime exercisers. They were quite sedentary and hadn't done any formal exercise in at least five years.

And in fact, looking at their cardio-respiratory function, which we do with a test call VO2 Max - it's a treadmill test, it gets steeper, it goes faster, you breathe into an oxygen mask, and we measure heart rate. These older participants, the 120 people in our study, were very de-conditioned.

So I think what the data suggests from our study, which allows us to establish causality in a way that correlational studies that Professor Gatz talked about have a much tougher time doing, is that even individuals with very low levels of fitness and individuals in their 60s to 80s, can still show benefits in terms of brain health and cognitive health.

FLATOW: Yeah because, you know, a lot of times, people say, well, I've been a coach potato my whole life. What can I do now? Right? And you're saying you can do something now.

Prof. KRAMER: Well, the participants in our study could all say I've been a coach potato for quite some time, I'm very de-conditioned. In fact, when we start the study, we don't start out at 40 minutes a day. We start out at about 15 minutes a day because most of the participants in our study need to take a break after a few minutes because they don't walk.

I think, in the United States, we increasingly do little exercise, and I think that's often evidenced by parking lots in a mall, where people wait inordinate amounts of time to park a little closer rather than walk an extra block.

FLATOW: Dr. Gatz, is there a critical age for keeping your brain healthy later in life?

Prof. GATZ: I think there's not one critical age, but the suggestion that the brain develops over the whole lifespan is important to bear in mind. So our research and other people's research do point very strongly to the importance of good health in midlife.

So we find, for example, again in the twin study, that twins who are overweight or more obese in midlife have a steeper trajectory of cognitive decline when they're old and are at greater risk of becoming demented.

Diabetes in midlife or early old age is also a risk factor for Alzheimer's disease and for dementia. So it's important not just to think of what can I do now that I'm an older adult to protect my brain, but to think of it as a lifespan picture.

Nonetheless, I think Professor Kramer's results are really important in pointing out that no age is a bad age.

FLATOW: We've heard studies say that doing brain exercises like crossword puzzles - do a crossword puzzle, exercise your brain, your memory will get better. Does that hold up?

Prof. GATZ: In our work, we find small but statistically significant effects for greater exposure to intellectual and cultural stimulation in midlife being related to lower risk of dementia in older adults. In our studies, this was a particularly strong finding for women.

Across different studies, if one reviews the literature, the usual take-home message is that if one wants to do the most important things to improve brain health, focusing on reducing cardiovascular risk factors, protecting the brain from physical injury - like wear that bicycle helmet - and doing physical exercise are statistically stronger protective factors compared to cognitive exercise.

FLATOW: That's a long answer for what I would squeeze out to mean no. Crossword puzzles make you better at crossword puzzles, but may not make your memory any better. Would that be correct?

Prof. GATZ: Let me add one more caveat.

(Soundbite of laughter)

Prof. GATZ: No professor can say yes or no.

FLATOW: Okay.

Prof. GATZ: It's - there's also a distinction to be made between improving brain health and staving off dementia...

FLATOW: Oh.

Prof. GATZ: ...because the causes of dementia in old age also include strong input from genetic risk factors. So the conclusion that I am most cautious about making is giving the idea that somehow working crossword puzzles is going to stave off Alzheimer's disease.

FLATOW: Mm-hmm. Art, do you agree?

Prof. KRAMER: Yeah. As professor Gatz was saying, the epidemiological studies where you look at what people do in one period of time and then look later and see how they fared, certainly, suggest that intellectually challenging activities - and it's, usually, a variety of activities in the self-reported questioners. It could be reading, it could be playing board games. It could be learning to play an instrument or learning a language - seem to be protective of lower rates of cognitive decline in Alzheimer's.

But when you look at the shorter-term studies, it's pretty interesting. That is the cognitive training studies in which half the people are put into one cognitive training group and maybe another half into the control group. Cognitive training tends to have quite specific effects that is if you train somebody to improve their memory, you can do that, at least on the tasks that you're training them on and sometimes more broadly, but you don't improve their reasoning or their attention or decision-making and so forth.

So we've known for over a hundred years since Edward Thorndike proposed his theory that cognitive training tends to have very specific effects. There tend to be some really interesting exceptions, which is worth exploring if you'd like, but physical training is pretty interesting. In that by walking, you're not training any specific cognitive ability, be it perception or attention or decision-making or memory, and yet, you get these relatively broad effects.

Why that is, is still up in the air, but we know a little bit and quite a little bit these days about the molecular and cellular biology that underlies exercise. And I guess, the way I think about it based upon what we know today is that exercise changes the molecular and cellular building blocks which supports learning and various aspects of cognition, whereas cognitive training strengthens specific connections -we know from a fellow by the name of Hebb many years ago - and will improve specific abilities, but it's pretty tough to get general improvements. Again, there's some really interesting exceptions.

FLATOW: Mm-hmm. Do you - when you say the brain gets bigger and the hippocampus gets a little bigger, do you know what is growing there?

Prof. KRAMER: Well, we can't. I wish our humans would agree - our human subjects would agree to histological examination, but nobody ever does.

FLATOW: Yeah. You (Unintelligible) say to when you slice my brain up.

Prof. KRAMER: Yeah. I know. Everybody does.

(Soundbite of laughter)

Prof. KRAMER: The only way to really know that is with a non-human -often rodent studies, and there, you can do the stains and look at what's changing.

And as a function of exercise, lots of interesting changes happen. New neurons get born. New connections between neurons are made, which allows you to encode or develop new learning and memory and so forth and even new vascular structure. That is new capillary beds exist and are produced and lots of other neurochemical changes.

With humans, we're somewhat limited. We do this - use this technique called high-resolution MRI, which, by the way, isn't very high resolution compared to histology that we can do with animals. But we do find increases in volume, and we went a step further in this study that just came out, and we looked at the changes as a function of where in the hippocampus, in the front or anterior, and the posterior.

And the reason we did that was to try to tie our results to the animal research. We know that an area of the anterior hippocampus is the dentate gyrus, and that's where the new neurons are born in the animal studies. We can do the histology and the stains and so forth.

So we ask the question of whether the effect that we saw in humans with our limited ability to look into the brain was consistent with, in terms of the region that new neurons are born, the animal research. And that's exactly what we found. We found that the increases in volume were in the anterior portion and not in the posterior portion as a function of exercise.

FLATOW: All right. Let me just remind everybody that I'm Ira Flatow, and this is SCIENCE FRIDAY from NPR.

And that was surprising to you?

Prof. KRAMER: Well, it was a very good surprise.

FLATOW: Yeah.

Prof. KRAMER: It is consistent with the animal research. It doesn't mean that all of the changes are due to these - birth of the new neurons. My bet is that's certainly one of a number of changes that takes place as well as the others and more that I mentioned.

FLATOW: Could you have such a - I mean, this happened so quickly, I mean, in terms of lifetime.

Prof. KRAMER: Yeah.

FLATOW: Is it because maybe you had more circulation going to the brain, because you're, you know, getting more exercise?

Prof. KRAMER: Well, it - certainly, blood flow is important. Then the new vascular structure supports increase blood flow, and that happens as a function of exercise. But there's also a number of these proteins or molecules called neurotrophins, and some of them are produced in the brain, such as the brain- derived neurotrophin factor or BDNF, and some of them are produced in the periphery, such as IGF1 or insulin-like growth factor 1 produced in the muscles and other regions of the periphery.

And IGF1 can cross the blood-brain barrier, go into the brain, and it seems to be an early point in this molecular cascade or pathway which stimulates the next neurotrophin, BDNF, which stimulates in turn neurogenesis and new connections and so forth.

So really, it seems to be a constellation of effects that occur and produce the outcome, and the outcome, in our case, was increased brain size specific to the hippocampus where we looked, and at least in the aerobic group, a relationship between increased brain size or hippocampal size and memory.

FLATOW: Mm-hmm. Just about one minute left, Dr. Gatz. Could it be that we have tapped more of our cognitive reserve, you know, we say we only use a certain amount of our brain, maybe we're using more of that in this case?

Prof. GATZ: The idea of cognitive reserve very - it would be very similar to the idea of physical reserve. And if someone has less good physical health, it takes much less to knock you off your game, and the same idea is proposed in relation to cognition.

And so one of the things that may be - that well may be happening with the kinds of intervention studies described here is that people who already have differences in cognitive reserve based on a lifetime of good and less good practices with relation to brain health, through these interventions are tapping more of what that reserve capacity may be.

FLATOW: All right...

Prof. GATZ: I think it is important to look at both the short-term and the longer-term view of brain health and the kinds of ways that even maternal nutrition is important in early brain development, which sets the pathway, because good and bad health tends to be accumulative over the lifespan.

FLATOW: All right. Thank you. We've run out of time. I thank both of you.

Margaret Gatz of the University of Southern California, Los Angeles, and Professor Arthur Kramer was at the Beckman Institute and professor at the University of Illinois, Urbana-Champaign.

We're going to take a break. When we come back, we're going to talk about aquaria. Mm-hmm. Something we don't talk about often. So stay with us. We'll be right back after this break.

I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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