The still-developing teen brain shapes the way they learn

James St. John,, CC BY 2.0
James St. John,, CC BY 2.0

We’ve been a little harsh on the teenage brain. From past studies we’ve determined that young, developing adolescents often display poor impulse control, suboptimal decision-making, and high sensitivity to reward. This has a lot to do with their brains, which are still developing. “Different parts of the brain grow over the course of adolescence at different rates,” says Juliet Davidow, a postdoctoral fellow in the Department of Psychology at Harvard University, “so at times there are parts of the brain that are more mature than other parts.”

For example, the area of the brain responsible for dampening our emotional responses and controlling some of our reactive behaviors, an area known as the prefrontal cortex, matures later in life than other parts. This imbalance throughout the growing teen brain is often what contributes to the behaviors we have come to expect from adolescents.

But some work has suggested that this imbalance is actually a good thing during these teen years. The area of the brain that responds to reward is kept in check at least in part by the prefrontal cortex in adults, helping to reign in impulsive behavior and poor decision-making. But since the prefrontal cortex isn’t developed fully in teens, their reward center has a bit more freedom.

This does contribute to their high sensitivity to reward, but as more recent research has shown that this area also contributes to learning, this imbalance of brain power actually helps promote exploration and learning in adolescents. “Everyday kinds of learning also use the same brain systems that respond to rewards,” says Davidow.

This led Davidow and her colleagues at Columbia University to look at a particular type of learning and compare it between the teenaged and adult brain. They were interested in reinforcement learning, a type of learning that takes place over time with successive trials and results. Say you try something out and you aren’t sure of what the outcome might be. You do it and see what happens. If you’re in this same situation again, you’ll now have previous experience to draw from that can inform you of what may happen.

If you proceed this way many times, you come to have a better idea of what the outcome will be with each new experience. Sometimes the outcome will reinforce your expectation and sometimes it won’t. During those times that it doesn’t, you then have to determine whether your expectation needs to change or if that outcome was a rare event.

Reinforcement learning in adults and teens

To study this, the researchers showed adults and teens pictures of four different butterflies and told them they had to figure out which of two flowers each butterfly would feed from. The participants would choose a flower and would then be told if they were right or wrong. Both teens and adults learned pretty quickly which flowers each butterfly preferred. But the researchers designed the task so that each butterfly chose its preferred flower most of the time, but not all of the time. If the participants chose the butterfly’s preferred flower during every trial, they would be wrong 20 percent of the time.

“This keeps the learning going,” says Davidow, “and makes learning harder.” And it was during this part of the task that the teens outperformed the adults. Overtime, the teens began choosing the preferred flower not every time but closer to the actual rate of the butterfly’s choice. “The adolescents were learning closer to the truth of what was programmed into our task,” says Davidow.

“These findings suggest that teens are learning things differently than adults and using different parts of the brain to do so.”

A part of the brain that has typically been associated with type of learning is an area called the striatum. During this task the participants had their brains imaged in an fMRI and the researchers expected to see heightened activity in the striatum, particularly when the butterfly chose the non-preferred flower, going against built-up expectations. But there wasn’t any difference observed between the striatal activity of teens and adults during these events.

However, there was a difference in another area, the hippocampus, which was a bit surprising. “The hippocampus hasn’t classically been a part of this story,” says Davidow. But here, when participants were surprised by a flower choice that went against their expectation, teens showed greater increases in activity in the hippocampus than adults.

How memory may play a role

The hippocampus is known to be important in forming and retrieving memories, so the fMRI findings may help inform the learning differences observed between teens and adults in this study.

To test if memory might be contributing to the observed effects, after each butterfly trial, the researchers showed each participant a random object. After all of the butterfly trials were completed, the participants were then shown objects and asked if they were any of the objects shown during the butterfly trial. Overall, the adults and teens performed this task similarly well. But when it came to the objects shown just after a butterfly’s flower choice had surprised the participant, the teens remembered those items better than the adults. “The things they saw when they were most surprised by positive reinforcement were the things that they were more likely to remember later,” says Davidow, “and the adults did not show that relationship.”

“This should lead parents and teachers to adjust how they frame learning experiences.”

These findings suggest that teens are learning things differently than adults and using different parts of the brain to do so. “The adolescents are paying attention to things not in an explicit, overt way but in a subtle way that is different than how adults are tracking information in their environment,” says Davidow. And this should maybe lead parents and teachers to adjust how they frame learning experiences. This work was published in the journal Neuron.

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