Individual Differences in Intertemporal Choice

Abstract

Intertemporal choice involves deciding between smaller, sooner and larger, later rewards. People tend to prefer smaller rewards that are available earlier to larger rewards available later, a phenomenon referred to as temporal or delay discounting. Despite its ubiquity in human and non-human animals, temporal discounting is subject to considerable individual differences. Here, we provide a critical narrative review of this literature and make suggestions for future work. We conclude that temporal discounting is associated with key socio-economic and health-related variables. Regarding personality, large-scale studies have found steeper temporal discounting to be associated with higher levels of self-reported impulsivity and extraversion; however, effect sizes are small. Temporal discounting correlates negatively with future-oriented cognitive styles and inhibitory control, again with small effect sizes. There are consistent associations between steeper temporal discounting and lower intelligence, with effect sizes exceeding those of personality or cognitive variables, although socio-demographic moderator variables may play a role. Neuroimaging evidence of brain structural and functional correlates is not yet consistent, neither with regard to areas nor directions of effects. Finally, following early candidate gene studies, recent Genome Wide Association Study (GWAS) approaches have revealed the molecular genetic architecture of temporal discounting to be more complex than initially thought. Overall, the study of individual differences in temporal discounting is a maturing field that has produced some replicable findings. Effect sizes are small-to-medium, necessitating future hypothesis-driven work that prioritizes large samples with adequate power calculations. More research is also needed regarding the neural origins of individual differences in temporal discounting as well as the mediating neural mechanisms of associations of temporal discounting with personality and cognitive variables.

Keywords: cognition; decision making; molecular genetics; neuroimaging; personality.

Figure 1

Individual differences in discount functions. (A) Future value of $1 received today with exponential discount function at different discount rates r, that is, the value of an amount received after a given delay that is equivalent to $1 received today. This is the amount at which a decision-maker with a given discount function is indifferent between receiving this amount at a given delay, and $1 received today. (B) Discounted value of $1 received at a given delay, assuming an exponential discount function with discount rate r, that is, the value to the decision-maker today of $1 received at a given delay. (C) Discounted value of $1 received at a given delay, assuming different discount functions (exponential function with discount rate r = 0.2, hyperbolic discount function with discount rate k = 0.25, quasi-hyperbolic discount function with parameters β = 0.8, δ = 0.9).

Figure 2

Summary of the associations between temporal discounting and socio-demographic, psychological, neuroimaging, and molecular genetic variables. The figure in a simplified way summarizes how the different variables relate to (steep) temporal discounting. However, the relation of these variables to temporal discounting is far from being so simple and isolated (as it may appear in the figure) as these variables often interact with each other. Low effect sizes are considered d (or r) < 0.15; moderate effect sizes are considered 0.15 ≤ d (or r) ≤ 0.35; high effect sizes are considered d (or r) > 0.35. vmPFC, ventromedial prefrontal cortex; vS, ventral striatum; OFC, orbitofrontal cortex; dlPFC, dorsolateral prefrontal cortex; PFC, prefrontal cortex; FP, frontal pole; DA, dopamine.