Inhibitory midbrain neurons mediate decision making

Decision making is critical for survival but its neural basis is unclear. Here we examine how functional neural circuitry in the output layers of the midbrain superior colliculus (SC) mediates spatial choice, an SC-dependent tractable form of decision making. We focus on the role of inhibitory SC neurons, using optogenetics to record and manipulate their activity in behaving mice. Based on data from SC slice experiments and on a canonical role of inhibitory neurons in cortical microcircuits, we hypothesized that inhibitory SC neurons locally inhibit premotor output neurons that represent contralateral targets. However, our experimental results refuted this hypothesis. An attractor model revealed that our results were instead consistent with inhibitory neurons providing long-range inhibition between the two SCs, and terminal activation experiments supported this architecture. Our study provides mechanistic evidence for competitive inhibition between populations representing discrete choices, a common motif in theoretical models of decision making.