Inter-individual differences in human dopamine systems predict individual differences in decision-making

Dopamine has been identified in a large number of studies as a neurotransmitter that plays a central role in decision-making. In animal studies, for example, when healthy rats are to choose between freely available less desirable food and exerting effort to obtain more desirable food, they tend to choose the latter; and blocking the dopamine system decreases, and enhancing the dopaminergic system further increases, preference to exert effort to obtain the better-tasting food. What has been less clear is whether inter-individual differences in dopamine function in humans can predict variability in decision-making.

Treadway et al. (2012) recently studied the role of dopamine in effort-based decision-making is healthy humans. In their study, healthy volunteers were scanned with positron emission tomography (using [18F]fallypride and d-amphetamine) to quantify inter-individual differences in dopaminergic function. The same subjects also underwent a so-called effort expenditure for rewards task. In this task, subjects can choose between high-effort and low-effort trials that require different amounts of speeded button presses. If successful, the participants earn a lower monetary reward in the low-effort condition, and a higher reward in the high-effort condition; however, each successfully completed trial is not rewarded, as there are no-win trials. Before making their choice between the low and high effort conditions, the subjects are indicated the probability of winning (if successful) that varies between “high” (88% of successful trials rewarded), “medium” (50%), and “low” (12%).

The positron emission tomography data showed that there were inter-individual differences in dopamine function in multiple brain structures that correlated with the results of the behavioral task. Inter-individual variation in dopamine function in the left striatum and bilateral ventromedial prefrontal cortex correlated positively with the willingness to exert greater effort to obtain larger rewards in cases where the probability of reward receipt was lower. Insula, in contrast, showed a negative correlation between dopamine function and decision-making. This latter finding is in line with findings in previous studies suggesting that insula plays a central role in processing of response costs. Taken together, these highly interesting findings show that inter-individual differences in dopamine function explain individual differences in cost-benefit decision-making in human volunteers.

Reference: Treadway MT, Buckholtz JW, Cowan RL, Woodward ND, Li R, Ansari MS, Baldwin RM, Schwartzman AN, Kessler RM, Zald DH. Dopaminergic mechanisms of individual differences in human effort-based decision-making. J Neurosci (2012) 32: 6170-6176. http://dx.doi.org/10.1523/JNEUROSCI.6459-11.2012

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