Teenagers are often portrayed as seeking immediate gratification, but new work suggests that their sensitivity to reward could be part of an evolutionary adaptation to learn from their environment. In a Neuron study published today, adolescents performed better than adults in a picture-based game that required learning from positive and negative reinforcement cues. The hippocampus and striatum were associated with this learning circuit in the teen brain.
“The adolescent brain is adapted, not broken,” says Juliet Davidow, a psychology postdoc at Harvard University and first author on the study. “The imbalances in the maturing teenage brain that make it more sensitive to reward have a purpose–they enable adolescents to be better at learning from their experiences.”
Davidow and her colleagues, including lead author Daphna Shohamy, at Columbia University’s Zuckerman Institute, and Adriana Galván, at the University of California, Los Angeles, set out to test whether teens’ sensitivity to reward could also make them better at learning from good or bad outcomes. The researchers recruited 41 teens (ages 13-17) and 31 adults (ages 20-30) to play a picture-based learning game. A subset of the adults and teens played the game while being scanned via fMRI.
The subjects were presented with an image of a butterfly and then a pair of flower pictures and asked to guess which flower the butterfly would land on. Through trial and error, participants could discern the pattern for which butterflies went to which flowers. If participants selected the right flower, the word “correct” would flash on their screen, and if they guessed wrong, the word “incorrect” would come up instead.
With every answer, an unrelated image (a watermelon or a pencil, for example) would also be displayed when the “correct” or “incorrect” label appeared. These images were later used in a memory test to examine how well the subjects remembered their environment during the learning process and what variables might affect their retention.
The teens in the study, learning from the accumulated evidence during the experiment, selected the right flower more often overall than the adults did. On the memory test, the teens also remembered the unrelated images better than the adults when the image had been displayed along with a surprising answer, suggesting that the teens have a better memory for retaining detail about unexpected outcomes.
When Davidow and her colleagues looked at the fMRI results, they saw that the adolescents’ brains were doing something different: the teen brains showed activity in both the striatum and the hippocampus during the learning task, whereas the adults were mainly using their striatum. The level of brain activity correlated with how well the teens remembered images associated with their correct answers. “This additional system in the brain is contributing to learning more in the adolescents,” says Shohamy. “The contribution of the hippocampus to reinforcement or reward learning during adolescence hasn’t really been recognized before.”
The team is working to determine what changes occur in the brain between adolescence and adulthood when it comes to reinforcement learning, as well as what other situations activate the hippocampus-striatum learning system in teens. The study results could also point to new approaches for teaching teens. “If you frame something positively, it could be the case that adolescents will remember things about the learning experience better,” says Davidow. “In everyday life, they’re paying attention to their environment in a way that is different from adults.”
For adolescents especially, getting ready to leave the nest may call for some ramped-up mental processes. “As a teenager, you’re navigating an environment that soon you will have to navigate on your own–and that’s a really good time to be particularly good at learning from experience,” says Shohamy.
This work was supported by the National Science Foundation.
Neuron, Davidow et al.: “An upside to reward sensitivity: The hippocampus supports enhanced reinforcement learning in adolescence” https://www.cell.com/neuron/fulltext/S0896-6273(16)30524-4