Researchers say that the reward center in an adolescent’s brain isn’t as fully developed or responsive as an adult’s, which could explain why teens tend to engage in risky behaviors such as consuming alcohol, using drugs, or having unsafe sex. 

Using magnetic resonance imaging (MRI), researchers scanned the brains of 12 teens aged 12 to 17 and 12 young adults aged 22 to 28. During the scan, participants played a game that involved monetary risk and reward. 

In comparing the scans, the researchers found that the ventral stratium, the section of the brain known as the reward center, showed increased activity as the reward increased for both groups. However, the right ventral stratium, which is responsible for motivation, showed more activation in adult participants than in the teens. 

“That region of the brain controls how much an organism is willing to work to get a reward,” Bjork said. “The data show that adolescents are just as happy and excited at the prospect of winning as adults, but they differed in the expenditure of effort for that reward.” 

The researchers concluded that adolescents are more likely to engage in risky behaviors, such as alcohol and other drug use, because they involve little effort but provide a greater reward in return. 

The research also may explain why teens sometimes seem unmotivated to adults. “Adults have readily active motivation in the brain,” said study co-author James Bjork, a research fellow in the Laboratory of Clinical Studies at the National Institute on Alcohol Abuse and Alcoholism. “But it may take exceptionally strong incentives to get kids jazzed up.”