TABLE 1.

Core concepts

Subjective value: the worth of a reward after accounting for relevant internal factors. e.g. a chocolate bar has a higher subjective value for a person when hungry compared to full. This flexible representation of value is a hallmark of goal‐directed behavior and relies particularly on the ventromedial prefrontal cortex and ventral striatum. The interested reader is referred to Levy and Glimcher 30 for an in‐depth discussion of value.

Costs: (to obtain a reward): involve effort and/or temporal elements. Effort costs are directly associated with the behaviour leading to reward, and can be physical or cognitive. Time costs include delay until the rewarding outcome, but also the opportunity cost ‐ the value of alternatives foregone by the current behavioural goal.

Discounting: the decrease in value of a reward as costs increase. An immediately available reward has a higher value than the same reward available at a future time point, a phenomenon known as temporal or delay discounting. Similarly, rewards are devalued by poor odds (probability discounting) or increased effort requirements (effort discounting) to attain them.

Sensitivity: a measure of the separate weightings given to costs and rewards as they are integrated. Sensitivity can be quantified in computational models based on the change in behavior as rewards and costs vary, and thus estimated for individuals and groups.

Computational models: mathematical and algorithmic means of expressing these decision processes and variables. Whilst a discussion of computational models is beyond the scope of this review, the interested reader is referred to Pessiglione et al, 31 Rangel and Hare, 32 Teufel and Fletcher, 33 and Nair et al. 34