Adults titrate the degree of physical effort they are willing to expend according to the magnitude of reward they expect to obtain, a process guided by incentive motivation. However, it remains unclear whether adolescents, who are undergoing normative developmental changes in cognitive and reward processing, translate incentive motivation into action in a way that is similarly tuned to reward value and economical in effort utilization. The present study adapted a classic physical effort paradigm to quantify age-related changes in motivation-based and strategic markers of effort exertion for monetary rewards from adolescence to early adulthood. One hundred and three participants aged 12-23 years completed a task that involved exerting low or high amounts of physical effort, in the form of a hand grip, to earn low or high amounts of money. Adolescents and young adults exhibited highly similar incentive-modulated effort for reward according to measures of peak grip force and speed, suggesting that motivation for monetary reward is consistent across age. However, young adults expended energy more economically and strategically: whereas adolescents were prone to exert excess physical effort beyond what was required to earn reward, young adults were more likely to strategically prepare before each grip phase and conserve energy by opting out of low reward trials. This work extends theoretical models of development of incentive-driven behavior by demonstrating that layered on similarity in motivational value for monetary reward, there are important differences in the way behavior is flexibly adjusted in the presence of reward from adolescence to young adulthood.
Amphetamine Sensitization Alters Reward Processing in the Human Striatum and Amygdala