CONJUNCTIVE REPRESENTATION OF VALUE AND SPACE IN THE GRANULAR RETROSPLENIAL CORTEX

The granular retrosplenial cortex (gRSC), a hippocampus-connected subdivision of the retrosplenial cortex (RSC), has been implicated in spatial navigation, episodic memory, and value-based decision making. To investigate the neural mechanisms underlying these functions, we examined the effects of gRSC inactivation and neural activity in mice performing a dynamic foraging task on a figure-eight maze. Bilateral inactivation of the gRSC with muscimol markedly impaired choice behavior. Reinforcement learning analyses indicated that gRSC inactivation increased choice bias while reducing learning rate. Consistent with this, optogenetic inhibition of the gRSC reduced the probability of rewarded trials. Calcium imaging revealed that gRSC neurons encoded multiple task-relevant signals, including robust representations of decision value before choice and chosen value after choice, in addition to spatial information. Notably, neurons significantly tuned to decision value exhibited a positive relationship between value-related signals and spatial tuning. Furthermore, pyramidal neuron activity in the gRSC was modulated by optogenetic inhibition of hippocampal axons during task performance, suggesting that hippocampal inputs convey task-related information to the gRSC. Together, these findings support a role for the gRSC in integrating value and spatial signals under hippocampal influence to guide flexible decision making.