LETTER Communicated by Joshua Gold The Basal Ganglia and Cortex Implement Optimal Decision Making Between Alternative Actions

Neurophysiological studies have identified a number of brain regions critically involved in solving the problem of action selection or deci-sion making. In the case of highly practiced tasks, these regions include cortical areas hypothesized to integrate evidence supporting alternative actions and the basal ganglia, hypothesized to act as a central switch in gating behavioral requests. However, despite our relatively detailed knowledge of basal ganglia biology and its connectivity with the cor-tex and numerical simulation studies demonstrating selective function, no formal theoretical framework exists that supplies an algorithmic de-scription of these circuits. This article shows how many aspects of the anatomy and physiology of the circuit involving the cortex and basal ganglia are exactly those required to implement the computation defined by an asymptotically optimal statistical test for decision making: the multihypothesis sequential probability ratio test (MSPRT). The result-ing model of basal ganglia provides a new framework for understanding the computation in the basal ganglia during decision making in highly practiced tasks. The predictions of the theory concerning the properties of particular neuronal populations are validated in existing experimental data. Further,we show that this neurobiologically grounded implementa-tion ofMSPRT outperforms other candidates for neural decisionmaking, that it is structurally and parametrically robust, and that it can accommo-date cortical mechanisms for decisionmaking in away that complements those in basal ganglia.