Teens, it is known, have brains “wired for risk.” They’re way more sensitive than adults to rewards, the research says — no wonder they do so much dumb stuff. But, reasoned neuroscientist Daphna Shohamy, idiocy can’t be what adolescence is for. Perhaps, she and her colleagues thought, the reward-sensitivity has something to do with how they learn. Specifically, she discovered, teens are great at learning because of the nifty way their brains thread together memory-formation processes that are separate once you get out of your teen years.
In a study published today in Neuron, Shohamy, a cognitive neuroscientist at Columbia University’s Zuckerman Institute, and her colleagues recruited 41 teens (aged 13 to 17) and 31 adults (aged 20 to 30) to play a picture-based learning game whilst in the cozy confines of an fMRI brain scanner. Players were presented with butterflies of different colors, and they had to figure out which flower the butterflies liked and predict their behavior. The researchers made it so that the butterflies wouldn’t go to the same flower every time, so that expectations would be violated, and players would have to slowly adapt. If players got it right, they got a message saying so, with an unrelated picture in the background. With every trial, the researchers calculated the prediction error for each person, whether they were right or wrong, and how surprised they were likely to be given what they predicted.
The youths’ and adults’ brains displayed surprisingly different activity while trying to figure out the butterfly behavior. The adults were mainly using the the striatum, an area of the brain associated with reinforcement learning — or how you learn by trial and error, tinkering with a situation so that the next time you encounter it, you “know how” to tackle it, like the deft swipe of a card required to make it through a New York subway turnstile. The teens used the striatum in combination with the hippocampus, which is associated with episodic memory, or what we’re usually talking about when we talked about “memories” — scenes you can reconstruct in your mind’s eye with sensory recall. Correspondingly, those impressionable youths were way better than the olds at recalling which images were displayed with the “you got it right!” screen, and they did better at predicting which butterfly would alight upon which flower.
That’s because, Shohamy says, the two brain systems are, in teens, working in concert. Because of that, she says, the reinforcement learning — or revising their expectations based on outcomes — and episodic memory — or the recall of scenes — are working together, whereas the two processes are differentiated for the grown-ups. “It’s hard to know how general this finding is, and what exactly it means,” she says. “Our interpretation is that, when you stop and think about it, this is a phase in life when a person or animal is transitioning from dependence to independence. You have to learn from your environment when you’re a teenager.”
This is just one study, she warns; it’ll need to be replicated, and she’d like to zoom in on when exactly the shift from the adolescent to the adult processing style happens, and how it’s different for different people, and how all that might relate to depression, addiction, and other risks that teens are especially vulnerable to. The million-dollar question about how reward-sensitivity couples with learning also remains. But what’s clear is that teens aren’t just given to doing ridiculous things; they’re primed to learn from them, too.