The brain implements optimal decision making between multiple alternatives

Neurophysiological studies have identified a number of brain regions critically involved in solving the problem of ‘action selection ’ or ‘decision making ’ which has been extensively studied in cognitive psychology. In the case of highly practiced tasks, these regions include cortical areas hypothesized to integrate evidence supporting alternative actions, and the basal ganglia, hypothesised to act as a central ‘switch ’ in gating behavioural requests. However, despite our relatively detailed knowledge of basal ganglia biology and its connectivity with the cortex, and numerical simulation studies demonstrating selective function, no formal theoretical framework exists that supplies an algorithmic description of these circuits, and that can fully explain why they are organized in the specific way they are. This paper addresses this question by showing 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 Multiple Sequential Probability Ratio Test (MSPRT). The resulting model of basal ganglia provides a rationale for their inter-nucleus connectivity and the idiosyncratic properties of particular neuronal populations. The model is consistent with data regarding the reaction times in choice tasks, and provides a mechanistic explanation of how they are generated in neural circuits