This 2013 human study found that adolescents placed more value on rewards than did adults. Adolescents were also more sensitive to punishments than were adults.
Cerebral areas increased activity when the expected value of the reward increased. Limbic system areas increased activity when the expected value of the reward decreased.
The left ventral striatum was the brain area that had the most increase in activity in adolescents compared with adults when the expected value of the reward increased. This brain area is usually not fully developed until people are in their mid 20s.
As the researchers noted as a limitation of the study:
“Without including preadolescents it is not possible to say with certainty whether the observed difference is a uniquely adolescent sensitivity to expected value or part of an ongoing developmental trajectory.”
Another limitation of the study was that it studied only 22 teens aged 13 to 17. Nineteen adults were studied with an average age of 28.
http://www.pnas.org/content/111/4/1646.full “Neural representation of expected value in the adolescent brain”