Neural representation of expected value in the adolescent brain

Abstract

Previous work shows that the adolescent reward system is hyperactive, but this finding may be confounded by differences in how teens value money. To address this, we examined the neural ontogeny of objective value representation. Adolescent and adult participants performed a monetary gambling task in which they chose to accept or reject gambles of varying expected value. Increasing expected value had a stronger influence over gambling choices in adolescents relative to adults, an effect that was paralleled by greater activation in the ventral striatum in adolescents. This unique adolescent ventral striatum response remained even after matching groups on acceptance behavior. These behavioral and neural data suggest that the value of available options has a greater influence in adolescent versus adult choices, even when objective value and subjective choice are held constant. This research provides further evidence that hyperactivation of reward circuitry in adolescence may be a normative ontogenetic shift that is due to greater valuation in the adolescent brain.A dolescence is characterized by heightened sensitivity to rewards (1). This phenotype is subserved by exaggerated neural response in ventral striatum (VS) to the anticipation (2) and receipt of expected (3-5) and unexpected reward (6) in adolescents versus other age groups. The question remains, however, whether this effect is mediated by ontogenetic differences or simply a methodological consequence of using money as the rewarding stimulus. In other words, does the adolescent brain attribute greater value to available rewards, or is the effect driven by adolescents valuing money to a greater extent than adults because they typically have less access to and experience with it? The goal of this study was to disentangle these possibilities by examining subjective valuation (indexed by behavior) of objectively valued choices.Subjective value (SV) is defined as the value that an individual places on a stimulus (7). To make a choice, an organism determines the SV of each alternative and then selects the one with the greatest SV (8, 9). A recent metaanalysis of 206 studies of SV in adults identified the ventromedial prefrontal cortex (VMPFC) and VS as a "valuation system" (8). These regions represent SV during choice for monetary stimuli (10-14), charitable donations (15), consumer goods (16), and food (17)(18)(19). Despite the wealth of knowledge on the neural correlates of SV in adults, no previous studies have examined the neurobiological development of SV, which precludes ruling out the possibility that previous findings in support of a hyperactive adolescent reward system were confounded by differences in participant valuation.One approach to understanding the neural computation of SV is through measurement of expected value (EV), the sum of all of the possible outcomes of a particular choice multiplied by their probabilities (20). In adults, increasing EV yields parametric activation increases in bilateral VS, midbrain, medial prefrontal cortex (MPFC), an...

Normative development of ventral striatal resting state connectivity in humans

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“…Together, these measures lead to the inference that the longer time and effort adolescents are putting into information processing reflects their greater sensitivity to outcome values and probabilities. In fact, recent evidence shows that adolescents are more sensitive to EVs than adults as shown by both behavior and also in neural responses (Barkley-Levenson, & Galvan, 2014). …”

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