The default mode network (DMN) typically deactivates during external tasks but supports semantic cognition. Analysis of four human fMRI datasets shows that its subsystems respond differently: the frontotemporal subsystem activates across domains and modalities, especially during abstract verbal tasks, and shows more tuned states with higher semantic retrieval demands. The medial temporal subsystem activates for both perceptually coupled scenes and decoupled autobiographical memory, with stronger responses to picture associations, supporting scene construction. The core DMN consistently deactivates, particularly for externally oriented tasks. These distinct responses relate to each subsystem's location on intrinsic connectivity gradients, revealing complementary roles in semantic cognition.
The brain's default mode network (DMN) contains spatially distinct subregions that support different cognitive processes: some DMN areas are more active during perceptual decisions about faces, while others are more active during memory-guided decisions based on previously seen images. These subregions differ in their connectivity profiles—perception-related areas have receiver-like, afferent-biased connections across the heteromodal cortex, whereas memory-related areas have sender-like, efferent-biased connections with perceptual-motor and attentional systems beyond the DMN. This double dissociation, found across three fMRI datasets, suggests that DMN architecture is organized to flexibly support both external perception and internal memory-guided thought.