The default mode network (DMN) and semantic network (SN) are thought to overlap in brain regions like the anterior temporal lobe (ATL) and angular gyrus (AG), but their relationship is rarely tested directly. Using fMRI data from 69 participants performing semantic and nonsemantic tasks, the authors found that both networks split into subparts depending on task demands, stimulus type, and difficulty. The left ATL was active for semantic tasks and deactivated for nonsemantic ones, while the left AG was deactivated for all tasks, with deactivation linked to difficulty. Thus, ATL and AG do not share a common role in semantic processing; instead, both are inactive during nonsemantic tasks. These findings challenge the idea that both regions are semantic hubs and have implications for understanding DMN variability and resting-state fMRI.
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.