From optimality to reality: decision-making in basal ganglia output

Value-based decision-making requires translating abstract representations of alternative values into concrete decisions. Although this process is widespread, the neural mechanisms underlying this transformation remain unclear. Here, we address this question by examining neural dynamics in the substantia nigra pars reticulata (SNpr) of two monkeys performing a decision-making task. We found a dynamic shift in SNpr activity during the decision process. Before choice, SNpr activity encoded the optimal selection regardless of the eventual action taken, representing the action and value of the optimal choice even when the non-optimal target was ultimately selected. During choice, the SNpr shifted to code the actual selection made by the monkey. This pattern was reinforced by trials with suboptimal choices, revealing a clear transition in SNpr coding from representing the abstract value of the optimal selection to encoding the chosen action, thus suggesting a neural mechanism that transforms value representations into concrete decisions.