Manakov, M.; Proskurin, M.; Wang, H.; Kuleshova, E.; Lustig, A.; Behnam, R.; Druckmann, S.; Tervo, D. G. R.; Karpova, A.

Mental maps of environmental structure enable the flexibility that defines intelligent behavior. We describe a striking internal representation in rat prefrontal cortex that exhibits hallmarks of a workspace for constructing goal-specific, cognitive graphs for sequences of abstract states that animals must traverse through their actions. As rats uncover - unguided - complex sequential patterns, neural ensemble activity in rostral Anterior Cingulate Cortex develops a highly structured yet compact, scalable representation anchored in states at the start and end of self-organized sequences. Graphs are organized to reflect relational similarities across contexts, and individually, permit flexible refinement of component states. The representation\'s crystalline organization permits instantaneous inference of the animal\'s current state within self-generated sequences, offering insights into the algorithmic and representational principles underlying unguided parsing of open-ended problems.