An Upside to the Adolescent Brain
Driven by reward, teenagers get a boost in learning and memory.
Posted August 27, 2018
It’s back-to-school time. The teenagers in my house are struggling to put away the temptations of vacation—Fortnite, anyone?—and finish the last of their summer assignments. I am struggling to stay out of it and encourage independent responsibility. Learning, for better or for worse, is on all of our minds. So, I called neuroscientist Daphna Shohamy of Columbia University’s Zuckerman Institute whose lab studies learning and memory and has been comparing the brains of adolescents and adults. Good news! The teenage penchant for reward-driven behavior has clear benefits when it comes to learning through reinforcement.
Multiple Forms of Learning and Memory
“There’s more than one way to learn and remember,” Shohamy says and these multiple forms of memory have different underpinnings in the brain. Episodic memory, which depends on the hippocampus, is our recall of facts and events that happen once, like that time last month when you met a friend at a coffee shop and talked about how you were spending the summer.
Another kind of memory, called procedural or implicit memory, underlies habits and is more action-oriented. It kicks in when you do something repeatedly and get better without really thinking about it. “Your brain is learning in the background to create associations based on repeated experiences,” Shohamy explains. An example would be going to that same coffee shop every morning and placing the same order each time. You know how you like your coffee and you order it out of habit. This form of memory uses a different part of the brain, the striatum.
Our New Understanding of the Teenage Brain
The striatum has been central to studies of adolescent brains because it has to do with reward, and therefore, with the teenage tendency toward risk-taking and their seeming inability to stop playing, ahem, Fortnite. Dopamine neurons project to the striatum and signal when something happens that’s better than expected. “It’s that dopamine squirt into the striatum that helps that learning system constantly update in a way that increases the ability to seek out rewards,” Shohamy says.
In the last fifteen years, a major new understanding of the teenage brain has emerged that is known as the imbalance model. It recognizes that there is a gap in the rate of development of different parts of the adolescent brain. The striatum and other reward-sensitive areas are heavily active, even overactive in the teen years, while the pre-frontal cortex that controls reason and judgment, the area that “puts the brakes on,” according to Shohamy, is slower to develop.
A Possible Upside for Memory and Learning
Together with her then-graduate student Juliet Davidow, who is now a post-doctoral fellow at Harvard University, Shohamy wondered if there might be an upside to this set-up in the brains of teenagers. “If there is this drive for reward that’s out of balance, then maybe there’s a reason, maybe there’s another side to this story,” says Shohamy. “Alongside increased risk-taking and impulsivity, is that system in adolescence actually better at learning?”
They investigated and found that yes, it was. In a 2016 study published in Neuron, Davidow, Shohamy and colleagues had both teenagers and adults play a computer-based guessing game. Participants had to figure out which card or object went with a better outcome. “Everybody starts out by guessing and everybody gets better,” Shohamy says. “But the teenagers were learning more quickly. They were more efficient at updating the right responses based on their experiences.” That is the essence of reinforcement learning.
The game also included objects that showed up onscreen but had no consequence for the outcome. Afterwards, the researchers sprung a memory test on everyone asking how well they remembered the inconsequential distractors, which were the equivalent of remembering where you were and who was next to you when you won the lottery. “You have these extra memories for things that were associated with that positive outcome,” Shohamy says. The teenagers were better than the adults at remembering these objects in the background.
When the researchers looked at what was happening in the brain, they found that the parts of the brain that handle different kinds of memories–the hippocampus and the striatum–were wired differently in adults and adolescents. In teenagers, “there was more activity in these parts of the brain and crucially, more communication between these separate memory systems. In the teenage brain, these different forms of learning are both working hard and working together,” Shohamy says.
The Teenage Brain in the World
The obvious question is why. “What this study and other similar studies show are fundamental differences in the teenage brain that are happening all the time,” Shohamy says. “It suggests the teenage brain is set up to learn about many different things as effectively as possible.”
That might be adaptive, she suggests. It could be that teen brains are designed this way because their owners are on the verge of independence and need not only to explore and try new things but to be learning from those experiences.
If that looks frustrating to parents and teachers, we might try viewing it more holistically, says Shohamy. “If your teenager seems to be learning less in the classroom, maybe there’s a tradeoff there and they’re learning more about the social structure, more about the world. We shouldn’t be thinking of the facts or dates they’re learning in the classroom as being the real learning as opposed to the rest of it, but that it is all important for helping them to become independent adults.”
Copyright: Lydia Denworth, 2018.