Frontostriatal circuits undergo considerable elaboration during adolescence 50–53 that are particularly dramatic in the dopamine system. Peaks in the density of dopamine receptors, D1 and D2 in the striatum occur early in adolescence, followed by a loss of these receptors by young adulthood 54–56. In contrast, the prefrontal cortex does not show peaks in D1 and D2 receptor density until late adolescence and young adulthood 57, 58. Similar developmental changes have been shown in other reward related systems including cannabinoid receptors 59. It remains unclear how changes in the dopamine systems may relate to motivated behavior as controversy remains as to whether reward sensitivity is modulated by dopamine systems (e.g., 60, 61) and whether it is a result of less active or hypersensitive dopamine systems (e.g., 62, 63). However, given the dramatic changes in dopamine rich circuitry during adolescence, it is likely to be related to changes in sensitivity to rewards distinct from childhood or adulthood 50, 64. Beyond the significant changes in dopamine receptors, there are also dramatic hormonal changes which occur during adolescence that lead to sexual maturity,
