Neural correlates of combinatorial reasoning in prefrontal cortex

Complex economic decisions are often combinatorial: they require individuals to select from many alternatives under strict constraints on time, resources, and energy. Combinatorial reasoning is the cognitive process that enables decision makers to construct and evaluate multiple potential solutions in the face of these challenges, but its underlying neural mechanisms are not known. Using a combinatorial optimization paradigm, we show that rhesus macaques adopt distinct reasoning strategies and track the combinatorial upper bound--the best achievable outcome given the options examined so far. We recorded single units from the dorsolateral prefrontal cortex (DLPFC) - a structure central to higher cognition and complex behaviors - while the animals deliberated. Single DLPFC neurons encoded and updated the upper bound in real time, and the neuronal activity scaled with computational requirements. These findings uncover a neural correlate for combinatorial reasoning and reveal how the brain supports complex economic decisions.