Decomposing the neural pathways in a simple, value-based choice.

Understanding the neural implementation of value-based choice has been an important focus of neuroscience for several decades. Although a consensus has emerged regarding the brain regions involved, including ventromedial prefrontal cortex (vmPFC), posterior parietal cortex (PPC), and the ventral striatum (vSTR), the multifaceted nature of decision processes is one cause of persistent debate regarding organization of the value-based choice network. In the current study, we isolate neural activity related to valuation and choice selection using a gambling task where expected gains and losses are dissociated from choice outcomes. We apply multilevel mediation analysis to formally test whether brain regions identified as part of the value-based choice network mediate between perceptions of expected value and choice to accept or decline a gamble. Our approach additionally makes predictions regarding interregional relationships to elucidate the chain of processing events within the value-based decision network. Finally, we use dynamic causal modelling (DCM) to compare plausible models of interregional relationships in value-based choice. We observe that activity in vmPFC does not predict take/pass choices, but rather is highly associated with outcome evaluation. By contrast, both PPC and bilateral vSTR (bilaterally) mediate the relationship between expected value and choice. Interregional mediation analyses reveal that vSTR fully mediates between PPC and choice, and this is supported by DCM. Together these results suggest that vSTR, and not vmPFC nor PPC, functions as an important driver of choice.