Individual differences in self-control in a time discounting task: An fMRI study.

Abstract

The tendency to devalue rewards when offered later in time is known as time discounting and, although universal, shows interindividual differences that are proposed to be dependent on an individual's self-control abilities. In the current study we investigate how the neural correlates of delaying gratification during a time discounting task are associated with individual differences in self-control ability. We assess individual differences on the basis of a self-reported Effortful Control (Adult Temperament Questionnaire) and actual behavior during the task, while controlling for age. Using event-related fMRI, in a population of 41 healthy 18-24-year-old males, choosing for the delayed option activated a network including the inferior frontal gyrus, lateral and ventrolateral prefrontal cortices, and the lateral orbitofrontal cortex. Decisions of individuals who delay more often during the task are associated with more activity in the dorsolateral prefrontal cortex. They furthermore show correlated activity between the inferior frontal gyrus, dorsolateral prefrontal cortex and medial prefrontal regions during decision making compared with individuals who behave more impulsively. Choosing for the earlier reward was not associated with any increases in brain activation compared to choosing for the delayed reward. However, individuals who behave more impulsively show more activation in the medial prefrontal cortex (anterior cingulate cortex, medial frontal gyrus), and no correlated activity with the inferior frontal gyrus. These findings could not be replicated when groups were based on self-report data. We conclude that individual differences in self-control during time discounting may partly result from differential activation of the dorsolateral prefrontal cortex.