Dissociable elements of human foresight: a role for the ventromedial frontal lobes in framing the future, but not in discounting future rewards.

Impaired future thinking may be a core aspect of impulsive decision making. Recent efforts to understand the brain processes that underlie impulsivity have suggested a role for the frontal lobes. However, future thinking is unlikely to be a unitary process, and the frontal lobes are not a homogeneous entity. The present study contrasted the effects of dorsolateral and ventromedial frontal lobe damage on two distinct aspects of future thinking in humans. Temporal discounting, the subjective devaluation of reward as a function of delay, is not affected by frontal lobe injury. In contrast, a normal future time perspective (a measure of the length of an individual's self-defined future) depends on the ventromedial, but not dorsolateral, frontal lobes. Furthermore, investigation of the relationship of these two measures with classical symptoms of frontal lobe damage indicates that future time perspective correlates with apathy, not impulsivity. Apathy may deserve more attention in understanding both impaired future thinking and the impaired decision making that may result.