Fractionating impulsivity and reward-related phenotypes in adolescent mice

Adolescence is a developmental period characterized by changes in the brain and behavior, including heightened reward seeking, increased impulsivity, and elevated risk-taking behavior. It is also a sensitive period for the development of a number of behavioral and psychiatric disorders associated with pathological phenotypes of reward processing and impulsivity. Landmark human studies are charting the development of impulsivity and other reward-related phenotypes to identify the facets and timecourse of the adolescent phenotype. Collecting similar data from mice is important to enable molecular, cellular, and circuit-level interrogation of adolescent maturation of reward, motivation, and impulsive behavior. These complex phenotypes have traditionally been difficult to assay in adolescent mice. Here, using a combination of approaches including homecage testing, we tested a number of facets of reward seeking, impulsivity, motivation, and incentive salience attribution during adolescent development. We found that adolescent mice show increased reward seeking, impulsive action, and motivation. Interestingly, we found no effect of adolescence on impulsive choice, sign-tracking, reward-learning, or conditioned reinforcement. Overall, our studies set the stage for approaches to study multi-faceted phenotypes related to impulsivity and other reward-related behaviors in adolescent mice to examine the developmental trajectories of brain and behavior.