Neural dynamics of an extended frontal lobe network in goal-subgoal problem solving

In goal-directed behavior, cognitive control calls for representation of current state, goal state, and current move, often with hierarchical organization into a series of steps or subgoals. In the human brain, a network of multiple-demand or MD regions underpins cognitive control, and core task features are likely encoded and integrated across this distributed network. Here we recorded from four putative homologs to human MD regions in the frontal cortex -- ventrolateral (vlPFC), dorsomedial (dmPFC), dorsal premotor (dPM) and anterior insula/orbitofrontal (I/O) cortex -- as two male monkeys solved a multi-step, on-screen spatial maze. Across regions there was substantial overlap but also wide quantitative variation in encoding task variables. Sensory input and current state were strongly coded in vlPFC, goal most stably in dmPFC, and move most rapidly in vlPFC and dPM. I/O responded during revision of a prepared route. In all regions, an abstract code of problem structure marked progress from problem start to end, with hierarchical separation of progress within and between successive steps. Partial specialisations, we suggest, arise from distinct connectivity, while broad co-recruitment reflects strong information exchange. Our results show how core components of goal-directed behavior are encoded across a distributed network of partial frontal lobe specialists, putatively homologous to frontal components of the human MD system.