Reward sensitivity in impulsivity.
Impulsive individuals choose immediate small over delayed larger rewards, suggesting reward hypersensitivity. Single-unit studies have shown increased ventral tegmental activity to rewards and reward predictors and decreased activity when predicted rewards are withheld. The orbitofrontal ventral tegmental cortical target also responds to reward and expectation in single-unit and neuroimaging studies. The anterior P2a event-related potential component is a proposed index of reward-related orbitofrontal activity. In this reward prediction study in high and low impulsive subjects, the P2a localized to orbitofrontal cortex and was largest to non-predicted rewards and smallest in the absence of predicted rewards in subjects higher on self-reported impulsiveness, consistent with a P2a index of orbitofrontal reward processing and with reward hypersensitivity in impulsivity.