Adolescent Slowdown

Introduction

Puberty is a notoriously difficult time for kids. It's a time when the world feels like it's speeding up. According to new research, part of that feeling may come from the fact that adolescents' brains are actually slowing down. You'll hear about it in this Science Update

Podcast

Adolescent Slowdown

Transcript

Explaining the terrible teens. I'm Bob Hirshon and this is Science Update.

Scientists have discovered one more reason puberty can be such a drag: in addition to acne and voice changes, it seems the kids' brains may slow down.

That's according to Bob McGivern, a psychologist at San Diego State University. In a recent study, he and his colleagues tested the ability of young kids, preteens, and young adults to process emotional information.

McGivern:
What we told the kids was, we're going to show you a picture on the computer screen of a person's face. The expression's going to be happy, it's going to be angry, sad, or just a neutral expression. We want you to make a decision about whether the face is happy as quickly as you can.

Most of them answered the questions correctly. But those just entering puberty took ten to twenty percent longer to decide on an answer. McGivern believes the surge of hormones this age-group experiences can interfere with the decision-making areas of their brains.

McGivern:
What that really means, don't know for sure, but it does suggest that we perhaps ought to be a little more sensitive to teenage behavior, and perhaps give them a break from the fact that their brain may actually be undergoing a little bit of reorganization that's not under their control.

For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Listening to this report, you might have thought the adolescents were really in a fog (how hard can it be to decide whether or not a face is happy)? But keep in mind that during the experiment, the pictures of faces were flashed on a screen for only a tenth of a second, and the researchers recorded the speed of each subject's response down to the millisecond (one one-thousandth of a second). The difference between the slowest adolescents and the quickest kids and young adults was only about three-tenths of a second. So the pre-teens weren't exactly hopeless.

But they were consistently slower—slow enough that the difference is very unlikely to be the result of chance alone. (Scientists call that statistically significant.) What's more, girls tended to be slowest at around 11 years old, while boys were slowest around 12. And those ages match up with the typical start of puberty in each gender. So something about adolescence does seem to get in the way of a kid's thinking.

Based on previous research, McGivern thinks two main areas of the brain might be affected. The first is the limbic system, the part of our brain that handles basic emotions. Studies from animals show that the hormones that surge during puberty (mainly estrogen and testosterone) directly affect the limbic system, and its connections to other parts of the brain.

The second part of the brain that seems to be involved is the prefrontal cortex, the area that deals with higher thinking, reasoning, and decision-making. The prefrontal cortex also governs our social behavior. Previous research suggests that the prefrontal cortex undergoes some "re-modeling" during adolescence: the brain cells (called neurons) are re-wired to prepare the brain for more efficient and sophisticated kinds of thinking. But just like re-modeling a house or improving a street makes things messy for a while, the re-organization of the brain during puberty seems to create some snags and delays.

The exercise performed by the kids in this experiment relies on both the limbic system and the prefrontal cortex, since it involves making decisions about emotions. So it makes sense that kids who were in the thick of puberty ran into problems with it. In the future, McGivern and his colleagues hope to find out if adolescence also gets in the way of other kinds of thinking.

Other scientists who participated in this study include Julie Andersen, Desiree Byrd, Kandis Mutter, and Judy Reilly.

Now try and answer these questions:

1. Describe the experiment designed by McGivern and his colleagues. Why do you think they designed the experiment in this way?
2. If you just sat down and watched the experiment, you probably wouldn't notice any difference between the adolescents and the other subjects. But the results show a "statistically significant" difference. How can this be? What does this say about the way scientists have to conduct their experiments?
3. Suppose there was no difference between boys and girls in the study (for example, if both were slowest at age 12). How might that change the scientists' interpretation of the results?
4. How might these findings apply to the "real world"? Could they shed light on the emotional and behavioral changes seen in adolescents? How might delays or obstacles in the parts of the brain devoted to thinking and emotions cause more noticeable effects? Could you design a study to test that idea?

Going Further

The PBS online documentary Inside the Teenage Brain has a section devoted to the changes in the brain that occur during adolescence.

Teen Brains are Different is a lesson plan from CNN's "FYI" project, with links to information about adolescent brain development and questions for discussion.