Transcript

Aging: It's Not What You Think | Thad Polk | TEDxUofM

[Applause] Have you heard the one about the two older couples who go out to dinner together? The two men are talking and one of them says, "You know, last week I went to this great memory seminar and they taught me all kinds of tricks and techniques that I can use to help keep my memory sharp as I get old." And his friend says, "Man, that sounds good. What was the name of that seminar? First guy thinks, um, oh yeah, what's the name of that red flower with the thorns that smells good? A rose. That's it. Then he turns to his wife. Hey Rose, what was the name of that memory seminar that I went to? Now, that joke actually reflects a pretty common belief, namely that aging is inevitably associated with significant mental deterioration or what's sometimes called sility. In fact, that belief is even reflected in the etmology of the word sility, which comes from a Latin word meaning old man. And the belief that senility is just a normal part of aging persists to this day. but it's wrong. So, I'm a psychologist and a neuroscientist and I study aging and the brain. And my goal in this talk is to convince you that maybe aging isn't what you thought it was and to give you a more accurate understanding about how aging really is likely to affect your mind and your brain. Now obviously age- related diseases like Alzheimer's disease can lead to very significant mental deterioration but in the absence of disease it turns out that the mental effects of aging are actually restricted to a few specific cognitive processes and many other aspects of mental life remain stable and some even improve. In particular, it's important to distinguish between what psychologists call fluid processing and what they call crystallized processing. So fluid processing refers to cognitive processes that don't depend on what you know. So just can you think logically? Can you recognize patterns? Can you solve novel problems that aren't related to any previous knowledge? A good example might be the card game concentration or memory where players take turns turning over pairs of cards and they're trying to find pairs that match. If they find a matching pair, they take it and if it doesn't match, they turn them back over. Well, that game doesn't depend on what you know, right? It just depends on your ability to remember the cards that have been turned over and exactly where they are on the table. So that would be a good example of a fluid processing task. On the other hand, crystallized processing tasks are tasks that do depend critically on your knowledge, on your experience, on your acquired skills. So think about solving crossword puzzles, for example. That depends a lot on your knowledge of the world. And so that would be a good example of crystallized processing. Now, it turns out that aging has dramatically different effects on fluid processing and on crystallized processing. So, here's some data that was collected by my colleague Denise Park. And she recruited about 350 people ranging in age from 20 to 80. And she gave them all a battery of cognitive tests including some tests of fluid processing ability. So for example, line span here that refers to how many random line drawings you can remember. Reading span, how many random words can you remember? Computation span, how many random numbers can you remember. So the horizontal axis here, how old you are. The vertical axis is your zcore. That is how well you did relative to everybody else being tested. So a a zcore of zero means your performance is average. A positive zcore means you're doing better than average and a negative zcore means you're doing worse than average. And as you can see, with each passing decade, fluid processing on these tasks declines a little bit. And I suspect that when you think about the effects of aging on cognition, this is what you might expect to see. Although my bet is that you may not have expected the decline to start at age 20. Sorry about that. Here's the same kind of graph though looking at crystallized processing ability. Okay, so here's some tasks that do depend on knowledge in particular in this case vocabulary. And what you can see is that if anything the older people are doing better than the younger people. Okay. So although fluid processing may decline as we get older, crystallized processing doesn't. And it's not just crystallized processing that's preserved. For example, your memory for skills and habits like how to play an instrument, how to read, how to ride a bike, how to speak a language, how to cook, how to tie your shoe. These are what psychologists call procedural memory. So, they're memory for wellpracticed procedures that you know how to execute. And a number of studies have found that procedural memory also remains intact as we get older. It's not just procedural memory either. Emotional processing actually seems to improve as we age. For example, 65 year olds, they actually typically report greater life satisfaction than people in their 20s. They also typically report fewer negative emotions and they're better at resolving interpersonal conflict. So, the take-home message so far is that although fluid processing may decline a little as we get older, many other aspects of our mental life don't decline and some actually improve. So, why is that? I mean, what is going on in the brain that might explain why fluid processing tends to decline but other things don't? Well, I got interested in that question and I decided to investigate it using a technique called functional magnetic resonance imaging. Now, many of you are probably familiar with traditional magnetic resonance imaging. And as its name suggests, MRI works by detecting magnetic differences in different tissues in your body. So bone has different magnetic properties than muscle and muscle has different magnetic properties than skin and so on. And by detecting those differences, MRI can create detailed three-dimensional images of the interior of your body. And you can with a few tweaks, you can use the same technique to take pictures of brain activity. Here's how. So it turns out that blood that's carrying oxygen also has different magnetic properties than blood that isn't carrying oxygen. And so that means you can use this technique to take pictures of where oxygen is in your blood. And since blood tends since oxygen tends to get sent to parts of the brain that are active, this means you can actually take a snapshot of brain activity at any point in time. And if you take snapshots every couple of seconds and you string them together, you can actually make a movie of brain activity while people are engaged in some cognitive task. That's functional MRI and it has absolutely revolutionized the study of human brain function and it has also revolutionized the study of the aging brain. Now I started doing functional MRI in the 1990s and at the time I was interested in how reading is implemented in your brain. I mean how does your brain recognize letters and words? So what I did was I recruited a bunch of college age students put them in an MRI scanner and I asked them to read letters and words and to read digits and numbers. And I found something kind of surprising. You use different parts of your brain to recognize letters and numbers. And it turns out other researchers have reported similar findings. You also use a different part of your brain to recognize faces. You use a different part of your brain to recognize body parts. You use a different part of your brain to recognize buildings. So each of these different stimulus categories actually evokes quite distinctive neural activation patterns. At least that's true in young adults. But what happens as we get older? Well, to answer that question, we scanned a bunch of college age people as well as older people averaging around age 70. And we asked them to process pictures of faces and pictures of houses. And then we looked at the patterns of neural activation that were evoked and we asked how distinctive are they? Okay, are they really different? Is it easy to tell them apart or are they kind of confusable and it's difficult to tell them apart? Here's what we found. So each dot here represents one of the subjects in our experiment with the young subjects on the left, the old subjects on the right. And the vertical axis here is how distinctive those two neural activation patterns were. How distinctive is the face pattern from the house pattern? Now, if you look at the young adults, you'll see that in every single one of them, they evoked very distinctive activation patterns in response to faces and buildings. But if you look at the older adults, you'll see that neural distinctiveness tends to decline a little bit as we age. But here's a critical point. It's not true for everybody, right? About half the subjects actually looked a lot like the young subjects, right? They were still evoking very distinctive neural activation patterns, but about half of the older people were showing less neural distinctiveness. And here's the cool thing. The very people who show reduced neural distinctiveness, those are the people who show declines in fluid processing. Okay, so check it out. Each dot here is one of the older subjects in our experiment. And on the horizontal axis is how distinctive those two neural activation patterns were. On the vertical axis is a a measure of a bunch of fluid processing tasks. So how well did these people do on a battery of fluid processing tasks? And what you can see is the people with less distinctive activation patterns, those are the ones who do poorly on fluid processing. And remember, fluid processing is the thing that declines as we get older. Crystallized processing doesn't. Here's the same kind of graph looking at the relationship between neural distinctiveness and crystallized processing. And as you can see now, it doesn't relate. So, what we have here then is a neural measure that actually relates specifically to the types of processes that tend to decline as we get older. And that's exciting because it it means we might be able to investigate the potential causes what's leading to neural distinctiveness declining and maybe we could e actually intervene and change it in the future. Okay. So I've told you one piece of very good news which is that many aspects of your mental life probably won't decline too much as you get older. But there's another good piece of news that I'd like to share and that's this. Your brains do not take aging lying down. They will actually reorganize themselves in order to try to process information more effectively. So if I took the college age kids in the room, stuck them in a scanner and asked you to perform some task like retrieve some information from memory, what I would typically find is that you would activate one of your two brain hemispheres. But suppose I now recruit your grandparents. I put them in the scanner and I ask them to do the exact same memory retrieval task. What I would typically find is that they use both hemispheres. Okay? So as you get older, you start recruiting new brain regions to perform the same task that you did um with fewer brain regions when you were young. Now here's a critical question. Is that a good thing? Does that actually help you perform the task better or does that reflect some kind of decline? Well, to address that question, uh, a researcher named Roberto Cabza at Duke University recruited three different groups of subjects. First, he got some high-erforming young people, college age students, who were doing well on a battery of fluid processing tasks. And then he recruited two different groups of older people. one group who were struggling with fluid processing and weren't performing as well and one group that was still doing very well. And then he put them in the scanner and he gave them a relatively difficult memory task. And he looked at brain activity. And here's what he found. In the high-erforming young subjects, he found that they tended to just activate one hemisphere of their brain. In the low performing old subjects, those who were struggling with fluid processing tasks, they also only activated one hemisphere of their brain. But check this out. In the high-erforming older subjects, the ones who were doing well on fluid processing, they were the ones who activated both hemispheres. So it suggests that this recruitment of the other brain hemisphere is actually helpful. It's actually compensatory and it's helping them perform the task better and age a little more gracefully. Okay. Well, I hope I've convinced you that aging isn't just about mental and neural deterioration. In fact, many aspects of your mental life will likely be preserved and many may even get better. And furthermore, you may start using parts of your brain that you didn't use before to help you age a little more gracefully. So, I want to suggest that it might be more accurate to think about aging as a kind of transformation rather than as deterioration. Now, your golf scores may go up, your bowling scores may go down, your hair might turn a different color, but I think there's a lot more to look forward to than you may have thought. Thank you.