The default mode subnetworks’ involvement in diverse cognitive transitions suggests a role in external update of internal models

The Default Mode Network (DMN), traditionally associated with internally oriented cognition, has been increasingly implicated in processing external stimuli that signal the need to update an internal mental model, defined as neural representations that simulate and predict relationships between elements that make up events. This review synthesizes recent findings on the DMN’s role in diverse cognitive transitions, including feature changes and event boundaries during movie watching, and externally cued task switches during complex behavioural paradigms. Studies using naturalistic stimuli reveal the functional specialization of DMN subnetworks: the medial temporal lobe subnetwork responds to location and temporal transitions, the dorsomedial prefrontal cortex subnetwork prefers social transitions, and the Core DMN exhibits generalised responses across all these transition types. Meanwhile, in task-based paradigms, the Core DMN is also activated during external task switches, compared to task repeats, both representing and dependent upon a hierarchical task structure, further underscoring DMN involvement in maintaining and updating mental models. We propose that the Core DMN binds information across DMN subnetworks into a hierarchically chunked internal model, where elements are organized into nested levels of abstraction, to provide context for evolving naturalistic experiences and a substrate to guide behaviour. This unifying framework highlights the DMN's integral role in context-dependent cognitive transitions, dynamically integrating internal and external representations during both active and passive states. • The DMN is increasingly linked to shifts in understanding an evolving narrative. • Transition types distinguish DMN subnetworks, but Core DMN responds to them all. • Core DMN also responds at transitions between multiple tasks, versus task repeats. • This response is sensitive to hierarchical task structure held in memory. • Both findings may reflect a role in external updates to an internal mental model.