Learning to infer transitively on a mental line in premotor cortex

Transitive inference (TI) is a form of deductive reasoning that enables the derivation of unknown relationships among premises. It is hypothesized that this cognitive process relies on mapping stimuli onto a "mental line," a linear workspace organized by arbitrarily assigned ranks. However, its neural basis remains unclear: Does this mental line have a neural correlate and how is it learned? This study investigates the role of dorsal premotor cortex (PMd) in encoding the hypothesized mental line as monkeys acquire item relationships for motor decisions. Findings reveal that PMd multiunit activity organizes along a theoretically predicted direction, supporting a geometrical model that explains behavior. Moreover, a learning process is observed, where the mental line rotates to align with motor planning.