Achieving one’s goals requires knowing what to do and when. Tasks are typically hierarchical, with smaller steps nested within overarching goals. For effective, flexible behaviour, the brain must represent both levels. This study uses functional magnetic resonance imaging (fMRI) to contrast response time-courses and information content of two major cortical systems – the multiple-demand (MD) and default mode networks (DMN) – during multi-step task episodes. Both networks are found to be sensitive to step-level and episode-level information, but with dissociable profiles. Intra-episode progress is tracked by tonically increasing global responses, plus MD-specific increasing phasic step responses. Inter-episode boundaries evoke widespread responses at episode onset, plus DMN-specific offset responses. Both networks represent the content and sequential position of individual steps; however, the DMN and MD networks favour task identity and step-level information respectively. The results suggest collaboration of multiple brain regions in control of multi-step behaviour, with MD regions particularly involved in processing the detail of individual steps, and DMN adding representation of broad task context.
The full article can be read here: Hierarchical representation of multi-step tasks in multiple-demand and default mode networks