01/13/2017

Why You Should Be Patient With Your Indecisive Teen

9:00 minutes

Salk scientists have found that, in the roundworm, neurological changes mark a transition from ambivalent adolescent to capable adult. Credit: Salk Institute
Salk scientists have found that, in the roundworm, neurological changes mark a transition from ambivalent adolescent to capable adult. Credit: Salk Institute

To many adults, teenagers can be a frustrating, inscrutable lot. They’re slow, indecisive, and picky. They’re moody and unreliable. But according to researchers from the Salk Institute for Biological Studies, this bad teenage behavior is actually an asset to a growing brain. Researcher Laura Hale joins us to explain how the behavior of the adolescent roundworm may help explain why teenage indecision might be an important evolutionary adaptation.

Segment Guests

Laura Hale

Laura Hale is a research associate at the Salk Institute for Biological Studies in La Jolla, California.

Segment Transcript

JOHN DANKOSKY: Teenage indecision, it sometimes feels like they’re doing it just to torture you. My next guest though, says that when we consider bad teenage behavior, well, it might actually be an asset for the adolescent brain even though it might not be doing us adults any favors. Joining me to discuss what might be going on inside the teenage brain is Laura Hale. She’s a collaborative researcher at the Salk Institute for Biological Studies and co-author of a paper out this week in the journal eNeuro. We’re going to find out what we can learn about this from roundworms. Laura, welcome to Science Friday.

LAURA HALE: Hi. Thanks for having me.

JOHN DANKOSKY: So first of all, how are we going to connect the teenage human brain to an experiment with roundworms?

LAURA HALE: So to back up a little bit, we are looking at the worm because it’s a simpler nervous system. And we are interested in understanding the nervous system. And if you think about humans brains, there’s about 100 billion neurons and then worms only have 300 neurons. And so, we want to take these general principles about how the nervous system develops in a younger worm and then try to apply these to people.

JOHN DANKOSKY: So we’re using roundworms here. And maybe you can describe the experiment first. The thing that struck me is that buttered popcorn is somehow involved in this.

LAURA HALE: Yeah. So the buttered popcorn flavor. So worms are really good at moving through the world through their sense of smell. And so they navigate based on odors in their environment. And so it turns out that the buttered popcorn smell diacetyl is a metabolic byproduct of bacteria. And this is a food source for E. coli, or excuse me, for C. elegans, these little round, soil-dwelling nematodes.

JOHN DANKOSKY: OK. So what did you do? So you’ve got this buttered popcorn smell, which by the way, is making me find buttered popcorn less and less appetizing all the time as I read about this. But anyway, so what do you do now? You’ve got mature roundworms and you’ve got adolescent roundworms and you’ve got this buttered popcorn smell. What happens next?

LAURA HALE: So basically we probe how well these worms respond, different stage worms, respond to the odor. So adults are very, very good at responding to this buttered popcorn smell and the younger worms are not very good at it. They kind of wander all over a plate.

And we have we basically have these small plates, about a cup. And you put an order on one side, you put the worms in the middle, and you see where they go across the plate. And the young worms, they just don’t go directly to the odor, they kind of wander around.

JOHN DANKOSKY: So the young worms wander around, the adults go right to it. So why is this? What do you think? Is it that the adults know that that’s a good food source? What’s happening here?

LAURA HALE: So that’s what we’re expecting is happening is that we speculate that the adults are going directly to the odor because they’ve had a lot of experience with bacteria that produce this diacetyl sense. So they can reliably depend on this bacteria being, this food source being in their environment. Whereas the younger worms haven’t yet had a lot of experience with this particular food source that might contain diacetyl. And so, they’re wandering all over the plate because they want to get a sense of what is happening in their environment, and they don’t want to become dependent on a food source that might not be available later. So the adults have had, we guess, a lot of experience with this diacetyl odor. And then, as they– so they learn to migrate to that odor really reliably whereas the younger worms, they’re testing their environment out and trying to sample different things.

JOHN DANKOSKY: And what’s happening in the brains of these worms as they’re doing this?

LAURA HALE: So the really cool finding is that we found that adults have additional neurons, multiple neurons that are active during and responding to this diacetyl odor. Whereas the younger worms have a smaller population of neurons that are responding to the odor. And so we think having more neurons, in the case of the adult that are responding, allows the adult worm to encode more features of their environment around them.

JOHN DANKOSKY: So if you have a different sort of stimulus, what happens? If you’ve got this yummy popcorn smell adults go for it, the adolescents sort of swim around a little bit. What happens when a negative stimulus is in there?

LAURA HALE: So interestingly, both stage worms, both the teenage and adult worms really respond similarly to a negative odor. If the situation is going to be harmful to them they both run away from the odor.

JOHN DANKOSKY: OK. So they both run away from the negative odor. So what does that tell us about how adolescent worms are learning about their environments?

LAURA HALE: So basically, it seems like they’re hardwired to respond to anything that might harm them but they haven’t yet learned what kind of sort of positive food sources are in their environment. So this gives them the flexibility to find additional positive sources because the chance of becoming dependent on a single food source can be detrimental in the long run if that food source isn’t available later. But the negative food source is always going to be a problem for both the adults and the younger world. So it’s important to learn to avoid those negative things in the environment and then learn to adapt to potentially multiple food sources that one might not be as good as another, but if it’s going to allow you to survive by providing you some nutrient substance then you will continue to explore your environment.

JOHN DANKOSKY: I’m John Dankosky and this is Science Friday from PRI, Public Radio International. We’re talking with Laura Hale. She’s a collaborative researcher at the Salk Institute for Biological Studies and co-author of a paper out this week in the journal eNeuro. And we’re talking about what roundworms can tell us about potentially the teenage brain. So what do we know about how this might be happening in humans too? is it safe to guess that the teenage human brain might be working somewhat in this way as well?

LAURA HALE: So what we’re thinking is that there’s these different stages of development, and that there’s this stage during transition to adulthood that is really important to have some flexibility in how you accommodate sensory information in the world. And so, this is just a different kind of normal stage along the process of becoming an adult. And that you have in the teenage brain, this kind of flexible plasticity to your brain to learn new things. And then, this allows you to perform certain tasks as an adult much, much more efficiently.

JOHN DANKOSKY: But does that also tell us something about– As we get older we’re always told it’s harder to learn when you’re an adult and it’s much easier to soak in information when you’re a kid. Is that part of what we’re seeing at work too, that the teenage brain is just more plastic, more able to soak in all this various stimuli so it can figure out what the world around them looks like?

LAURA HALE: So that’s kind of the next thing that we would like to try, is actually test whether your experiences matter. So this studies suggests that your experiences during adolescence affect your adult experiences. And so we would really want to probe whether your experiences during the adolescent stage affect the adult. And then also similarly, whether you can change as an adult, have different experiences, and that also alters your performance. So I think we can learn new things both as an adult and the young mind, and we shouldn’t restrict ourselves to thinking that this time period has passed and we’re no longer flexible.

JOHN DANKOSKY: Are there any other takeaways that you have about what we can learn about the adolescent brain from studying these roundworms?

LAURA HALE: Yeah. It’s a really great system for understanding how behavior originates all the way from individual cells. So we were able to look at individual neurons and then also go look at molecules within those. And just go from individual cells to behavior to the organism. So this is a really cool feature of studying worms that isn’t possible in humans.

JOHN DANKOSKY: And so, what’s the next thing there? I mean, if you’re able to get it down to the cellular level, what else is that telling you? Where do you go next with this research?

LAURA HALE: So one of the things we can look at is perhaps what is different in these neurons. Why are they able to– So why are different sets acting in the adults versus the younger ones? And then, what’s going on at the molecular level inside of those neurons to make them respond to the odor better?

JOHN DANKOSKY: Well, Laura Hale, a collaborative researcher at the Salk Institute for Biological Studies and co-author of a paper out this week in eNeuro, thanks so much for your time. I really appreciate it.

LAURA HALE: Thanks, I enjoyed this. This is exciting.

JOHN DANKOSKY: It was exciting to have you.

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