Reward-seeking behavior is under the control of brain systems that set a value for the outcome being sought. It is almost universally true that the value of rewards decrease (are “discounted”) as a function of the delay to their delivery, but the rate of this discounting of value as a function of delay varies across individuals and species.174 Organisms with rapid discounting rates tend to select actions and responses that lead to immediate outcomes and may therefore engage in a type of impulsive behavior marked by an abnormal preference for immediate gratification, even when it comes at the expense of overall reward receipt. This section deals with the phenomena of delay discounting – which has been conceived of as an independent form of impulsive decision-making, as well as its underlying neurobiology.
