Transcript
Speaker: Hello ! And welcome to Neuroblast, where we change brain myths that have shaped the way think about thinking, learning, life, all the above.
Speaker: I'm - Athena Stevens, actor, writer, neurology user. And I'm Tracy Tokuhama- Espinosa. I teach a course at Harvard University called The Neuroscience of Learning, an Introduction to Mind, Brain, Health, and Education.
Speaker: And I'm an international educational consultant. And today we are diving into the idea of - critical periods for learning. Are there times in our lives - where we must learn certain things or else we never learn them at all?
Speaker: Or is this just another myth? Now, Tracy, this particular myth holds I don't want to say it holds a bacon plate in my heart. That sounds awful. Um...
Speaker: But it holds a big place in my history, I guess. Because always thought, oh, you needed to learn to walk by age 7 or age 10. It kept moving.
Speaker: Otherwise, you will never learn it at all. So I heard this a lot. What's going on? What is a critical period? Why do we care?
Speaker: And this is a really fascinating idea, a concept in general, because it sets up this idea that there are key milestones in life that people should meet. And so when you look at developmental psychology, developmental science, if you're looking for physical development and mental development in people, all of these stages of development tend to hinge on this concept of milestones. Most people or Everybody who you know fits within a certain norm will reach you know this particular milestone at this particular age.
Speaker: And what is so fascinating is to see that this is sort of borne out in a lot of other animal studies, not just in human studies. And so we would extrapolate information we'd get from you know sewing kittens' eyes shut and then saying, okay, if we leave them sewn shut for one or two days, nothing's going to happen. But if we leave them shut longer, you know they're not going to ever be able to see. That was a critical moment in the development of being able to see well. And if they didn't have it, they would never have it.
Speaker: um This got spread -- into human activity when we started looking at um foreign languages, for example. We would say that if you don't learn a foreign language by the time you're seven, this was Lennonberg's idea,
Speaker: Well, you'll never learn a foreign language, right? And then it sort of got bumped up slightly higher, higher, higher until today when we actually have a fascinating, fascinating idea.
Speaker: Nothing you could ever learn in school has a critical period. It's a matter of the order of introduction of ideas. And so that sort of ah changes this idea of critical periods to really spreading out into a different kind of ah you know metaphorical thinking of windows of opportunity. So the windows of opportunity are much broader than we thought, and they provide a bigger, um I guess, scope of time within which you can learn different concepts.
Speaker: I like the idea of windows of opportunity being big and broad and perhaps depending on a solid foundation, having done some DIY work at home right now, um yeah, foundations.
Speaker: And all because we thought we knew what was happening because we sewed kittens' eyes shut. That was a grand experiment to see that, - is there a critical period of time of development, which was um you can't do any of these things ethically on humans, right? um So we have very, very few studies that help us understand this, whether or not there's critical periods in human development. So you have people studying human fetuses and you can see that, you know, phew,
Speaker: If the under, you know, 24 weeks of gestation, there's just nothing really viable there. But if you, you know, when is the critical period that that you would have some um an individual could be living on its own?
Speaker: Well, we had a handful of studies beyond prenatal development that had to do with language and physical abilities. And these were very rare studies. So in feral children, children who um get lost in a forest or whatever, or they are in the jungle and raised by Mowgli or monkeys or things like that, we realized that there were different ages um that made different impacts on how long it took for that kid to lose language or to be able to recuperate it later on. And so
Speaker: You'd have kids who might have learned language, you know, until they're three years old, and then they get lost in a forest and then are returned later on. And actually, they're pretty good at recuperating language.
Speaker: But if you have ah newborn thrown out to live with the dogs in the backyard, even for a shorter period of time, by the time they're rescued, they can't learn language. So this led people to think of there must be a critical period for actually gaining your first language.
Speaker: The real problem there is there's only about, I think it's 249 studies on feral children to actually you know think about this. And it's not ethical to test it, right? We can't say, hi, give me your newborn child and let me isolate them from the world for a while. Let's see if they get language.
Speaker: So we can't do that ethically. The second big study had to do with the Romanian orphans. If you recall, i don't know if you remember during Ceaușescu's time, they discovered that all of these orphans had been tied, really, they were stuck in their cribs, maybe not tied down, but they were in their cribs where they sat, stood, played, ate, defecated, all in the same little space, and they really didn't grow any kind of gross motor skills.
Speaker: So you get some of these kids and they're, say they're rescued at, you know, five years old and adopted by a really nice family and given a big yard and told to play. they still never gained 100% of their abilities back.
Speaker: And so we thought maybe there's a critical period for physical motor skill development as well. So for first language, physical motor skill, we have these kind of, we have these examples, but you can't really do an experiment to prove it. So we really don't know for sure if these are real critical periods in human development. We presume so presume so, something in prenatal stage, something with first language and something with motor skills.
Speaker: But aside from that, nothing that you learn in school, for example, math or reading, it has a critical period. It's a matter of order of introduction of concepts that's important. And just to reiterate, because I've done little bit of work studying feral children, not only is it not ethical knowingly to do this your child, but you have to have the problem of first, you have to have a child who this horrible life experience of abandonment has happened too, and then you have to find them.
Speaker: It's a small population, a small population, essentially, because they are doubly on the outlying spectrum. Is that right?
Speaker: That's absolutely right. and And it's terrible because in feral children, the the main thing you want to do is to have insights about all of humanity. But, you know, how humane is it to actually do experiments or, you know, with ah somebody who's already gone through so much trauma? So you're absolutely right. It's it's very, very hard to gather, um you know, inferences from these small number of cases. But, um It is, it you know, we can point to a lot of these things in the animal kingdom, which is why we use all these animal studies to try to see if there's critical periods and things like that. And so that was a very popular concept up until, I would have to say, it's really shifted only in about the past 12, 15 years where we stopped, we have given way to using windows of opportunity as opposed to critical periods. That's almost never used anymore, which is a pretty interesting evolution in the way that we discuss um this development .
Speaker: ah Okay, so what about lifelong changes? We talk about you can't teach an old dog new tricks. I teach my cat new tricks all the time.
Speaker: And I feel like teaching a cat is far harder than teaching any old dog. - What's going on across the lifespan? Well, since we know that all new learning passes through the filter of prior experience, right? Because your brain is really efficient. So it's always trying to compare and contrast.
Speaker: the outside world and new stimuli to to what it already knows. And that will save it energy in continuing to learn. So since all new learning passes to the filter of prior experience, the older we get,
Speaker: the more prior experiences there there are to pass through, right? And so eventually we might be even more efficient than a younger learner um when we go through all things, but it may appear that we're slower.
Speaker: But I want to give you one concrete, a beautiful example of um how neuroplasticity exists throughout the lifespan and the critical periods that we think might exist are sometimes self-imposed.
Speaker: I had a student in my class, she was 70 years old when she took the class and she, we got to the chapter on memory and she said, you know, forget that. I've always had a bad memory. My entire life I've had a bad memory.
Speaker: And I said, Marie, yeah that's not true. You know, your brain is neuroplastic. You can become better. You just have to work at it. And it takes a lot of energy to create new memories, but you, you can do this.
Speaker: And she took that to heart. She actually hired a trainer, a memory trainer. She became Florida State's memory champion. And then she was invited to MIT to give a talk on this, you know, and she's now writing a book on super aging, but her whole attitude shifted.
Speaker: She had just presumed she would be bad at memory because she was not good throughout her whole life. When she realized with a little bit of rehearsal, with some kind of practice, she got better and better and better. She saw the plasticity in her own brain. So just little incremental wins helped her see her human potential of being able to do this, something she'd always presumed she couldn't do.
Speaker: So a lot of this has to do with this attitude shift and embracing the idea that neuroplasticity exists throughout the lifespan and that you can and do learn until you die. And, just to reiterate to our listeners out there: A, Tracy has classes running.
Speaker: There's one running this podcast airs, but there'll be another one this summer at Harvard? That's right, yes. Um, so you can learn with Tracy. And if you are a student, we don't do things half.
Speaker: I was going um but I'll play another plug about that another time. Let's talk about pruning.
Speaker: so Okay. - Pruning is a very natural state of the brain. There's something called apoptosis, which is actually the natural cell death, right? But there are synaptopruning. What's that called?
Speaker: Aptosis. Aptosis. Not apoptosis. Apoptosis. - You and I, we always go back and forth of how many p's are in this word.
Speaker: ah In this natural cell death, it's a little bit different from what we're talking about synaptic pruning. So synaptic pruning are when the dendrites are actually pruned away and and the neural connections that were once made are gone.
Speaker: Whereas cell death is actually the entire cell body dies. So it's slightly different. But the natural state of the brain is to be efficient. And so it's constantly losing. It's gaining neural connections, but it's also losing certain connections. This is why we say use it or lose it. If you're not using those connections, they weaken and they they die off. And so this might be why, and who knows if this is true for you, Athena, if you studied French in the earlier years of your life, but you haven't used it for 30 years, you know, use it or lose it. If you haven't gone back to it, it's really hard to find it. It's a little bit of an effort there, right?
Speaker: However, if you dig hard enough or if you could go to, you know, Paris for a week, all of a sudden, you know, things come back to you and you're able to re-exercise connections that were already made. It's much easier than starting the foreign language all over again or a whole new language, right?
Speaker: Because you didn't really lose it completely. It's there somewhere, but you just don't haven't used those connections enough so that it's easy to retrieve them. So pruning is what your brain does to become efficient.
Speaker: Your brain says, hey, if I'm not going to use this, you know, what's the point of having this here and wasting energy on these things? And you lose the natural pruning that occurs is with lack of use of those connections.
Speaker: So pruning many ways somehow got confused with critical periods. To a certain extent. Um , critical periods was looking more at the timeframe, like a chronological age that you'd say, you know, you need to do X by this time, or you would never be able to do Y, which was pretty interesting. Like we were mentioning before, Lundberg said, okay, there's a critical period for learning foreign languages.
Speaker: If you don't learn a foreign language by X point in your life of of age, then you would never be able to to learn that. And it's you know i can see the parallel there of saying, okay, so pruning, if you had learned something, then things would prune away. so it's But it's not that you prune away your potential to learn.
Speaker: it's you prune away at what was already structured. So they re different concepts. And I think this is a lot of where the harm comes in. Is that we all have different seasons of life.
Speaker: And we all have seasons that we're learning a lot. And seasons where we are, you know, taking care of loved ones who need care wintering, as I call it, maybe.
Speaker: Depression is part of your seasons of life that comes and goes. And simply because learning has slowed down for period of life doesn't mean gone and doesn't mean it can't pick a back up again.
Speaker: Absolutely. And, and, you know, take that further. You know, if you you know metaphorical thinking of pruning is what you do in your garden. if you've If you've ever had roses, right, there's a point where you have to prune them back. You know, they might be growing beautifully and they're doing fine.
Speaker: Um, so maybe, you know, there is a period of of strong growth and you just need to prune them back anyways. Once you prune them back, though, they grow back twice as lush and full. And so having that period of pruning is actually really beneficial for the efficiency of the brain.
Speaker: Um, we also know that um it allows, you know, just sort of a ah refocusing , of really where how to strengthen the those base core elements of knowledge and then building off of them. So pruning, that's really fun how the words ah come from from the same roots.
Speaker: Dendrites also means you know from the branches of trees and things like that. So that's what also is occurring in your brain as well. So the pruning idea, dendritic formation, things that have to do with thinking about nature and growth and trees and bushes and things like that and how you have to prune them away to make them stronger um and to make them more efficient is a real natural process in the brain.
Speaker: And is this how we go from critical periods to sensitive periods? Yes. So these sensitive periods or these windows of opportunity actually show that they're really are developmentally, maybe this is the the best time, for example, if you're learning a foreign language, there are really good moments when you can pick up an accent, like you know zero to five, it's really great. If you've been exposed to a foreign language,
Speaker: the likelihood of pronouncing well and having no accent is really high. But if you go beyond that, here's where Lindenburg was saying, oh, look, you have a terrible accent. Well, that's just one of hundreds of sub-elements of language, right? But it's the most obvious one. It's one you that's very visible to people. So that's why they would say that this would be a a critical period, but we do know it's just a sensitive period. And we do know that if people want to perfect accents in foreign languages, they can definitely do it. But a lot of people just wonder if it's worth the effort.
Speaker: So long as I'm communicating well, does it really matter what kind of an accent I have? And so that makes those elements take a back seat. So we know that adults are better and faster, for example, in foreign language in terms of learning anything, grammar, vocabulary, all kinds of other things.
Speaker: um but they might be weaker in the foreign light in the accent because that accent has a sensitive period where your ear is more tuned to picking up sounds that it is not normally exposed to on a daily basis.
Speaker: So um yeah, sensitive periods and and windows of opportunity versus critical periods. Critical means you just shut the door completely and you'll never be able to open again, which we now see is pretty much not the case in most situations.
Speaker: The brain's adaptability is one of its greatest strengths. And the more I talk to you and the more learn about it, the more I'm going, what isn't possible?
Speaker: How do we make today's lesson actionable? I think a real key here um is almost in an attitude shift on our own parts to realize just how beautifully optimistic we should all be when you know about the neuroplasticity of the brain and how anything is really possible. you know It's possible to think about you know learning to have a better memory when you're 70 years old. I mean, it's possible. All of these things are possible.
Speaker: um And it does take a little bit of work and it does take a little bit of effort because learning you know uses a lot of energy in your brain. But it's really worth it. um Use it or lose it. It gives us this big protective factor for longevity, um for good mental and physical health and well-being. There's a lot of positives in here. So I'm really optimistic about um helping people just understand so and that neuroplasticity really is this big green light for us to just try things that we maybe have not tried before, didn't try before, or presumed or made an excuse about before because, oh, I'm too old for this.
Speaker: It's just not true. Try it and, you know, if you like it, great. If you don't like it, Try something new. Yes. Move on find something else.
Speaker: Lifelong learning. This is why Harvard now promotes what's called a 60-year curriculum. They do not believe that humans finish learning, you know, after college or after high school or whatever it is, that you should continue to grow and learn throughout your life because it is ah protective factor into cognitive aging. I mean, it's a protective factor to be able to continue to study and think and learn.
Speaker: But it's also something that just... um It just gives you quality of life to be able to know that you can actually take on new things and learn new things. And and yes, old dogs can learn new tricks.
Speaker: And so it might seem a little more effortful, but definitely um it's beneficial. And being a lifelong learner is not just a slogan in, in good schools. It really should be what we're looking for, for good mental and physical health and well-being.
Speaker: Absolutely. Well, thank you, Tracey, for this edition of Neuroblast, and thank you our listeners for joining us again.
Speaker: Remember, your brain is a lifelong learner, so by default, you are a lifelong learner. Keep growing, keep exploring, keep listening to us, and we'll see you next time.
Speaker: Thank you very much.
Speaker: Bye.
