Distinctive and Complementary Roles of Default Mode Network Subsystems in Semantic Cognition

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neuroimaging

Background:

• The default mode network (DMN) typically deactivates during external tasks but supports semantic cognition.
• Its functional organization across subsystems (medial temporal [MT], core, frontotemporal [FT]) remains unclear regarding factors like perceptual coupling, input modality, information type, and control demands.

Purpose of the Study:

• To investigate how perceptual coupling, input modality, information type, and control demands influence the activation and deactivation of DMN subsystems during semantic cognition.
• To map these responses within the whole-brain state space defined by intrinsic connectivity gradients.

Main Methods:

• Analysis of four task-based human functional magnetic resonance imaging (fMRI) datasets.
• Examination of DMN subsystem responses (activation/deactivation) to semantic cognition tasks.
• Localization of responses in whole-brain state space based on intrinsic connectivity gradients.

Main Results:

• The FT subsystem showed consistent activation across domains, tasks, and modalities, particularly for abstract, verbal tasks, and exhibited "tuned" states with increased activation/deactivation under higher retrieval demands.
• The MT subsystem activated for both perceptually coupled (scenes) and decoupled (autobiographical memory) tasks, with stronger responses to picture associations, suggesting a role in scene construction.
• The core DMN consistently deactivated, especially during externally oriented tasks, with its activation distant from visual cortex and cognitive control areas.

Conclusions:

• Distinct DMN subsystems (MT and FT) support different memory-based representations accessed internally and externally.
• Deactivation in the core DMN is associated with demanding, external semantic tasks.
• The functional organization of DMN subsystems is related to their position on intrinsic connectivity gradients, with activated regions closer to sensory-motor cortex than deactivated regions.