Learning to infer transitively on a mental line in premotor cortex.

Dorsal premotor cortex (PMd) carries a neural correlate of the mental line used for transitive inference, as monkeys learned ranked item relationships for motor decisions. PMd multiunit activity organized along a theoretically predicted direction, supporting a geometrical model that explained behavior, and the mental line rotated over learning to align with motor planning. This grounds a classic model of deductive reasoning in premotor cortex.