Elucidating directed neural dynamics of scene construction across memory and imagination

Autobiographical memory (AM) and imagination both rely on the brains ability to construct vivid, coherent mental representations of past or imagined experiences. A central cognitive process underlying these functions is scene construction--the mental generation of spatially organized, imagery-rich representations of environments. Using ultra-high field 7T fMRI combined with Dynamic Causal Modeling (DCM), we examined directed effective connectivity among key nodes of the default mode network: the ventromedial prefrontal cortex (vmPFC), hippocampus, and precuneus during object imagery, single-scene construction, and AM retrieval. Our results revealed distinct patterns of network dynamics depending on task demands. During AM retrieval, effective connectivity was characterized by vmPFC-driven top-down modulation primarily targeting the precuneus, supporting the temporal and self-relevant structuring of episodic memory. In contrast, extended scenario imagination engaged hippocampal bidirectional influences with both vmPFC and precuneus, reflecting the dynamic simulation and integration of unfolding events. Single Scene construction shifted network leadership to the precuneus, which exerted modulatory effects on both vmPFC and hippocampus, consistent with its pivotal role in spatial integration and the generation of coherent mental scenes. Object imagery showed minimal stable connectivity within this network, suggesting limited engagement of the hippocampal-default mode circuit during simpler visual representations. Together, our findings highlight a flexible, task-dependent reorganization of effective connectivity within the vmPFC- hippocampus-precuneus network during the construction of rich mental experiences. Scene construction emerges as a unifying mechanism linking memory and imagination, with the direction and strength of neural interactions adapting according to whether temporal or spatial demands predominate. HighlightsO_LIAutobiographical memory is reflected by vmPFC-driven effective connectivity C_LIO_LIEffective connectivity varies flexibly amongst vmPFC, hippocampus and precuneus C_LIO_LIScene construction emerges as a core process across memory and imagination C_LI