Elucidating directed neural dynamics of scene construction across memory and imagination

Autobiographical memory (AM) and imagination both rely on the brain's 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 and Dynamic Causal Modeling (DCM), we examined directed effective connectivity among the ventromedial prefrontal cortex (vmPFC), hippocampus, and precuneus during object imagery, single-scene construction, scenario construction and AM retrieval across two independent datasets. Our results revealed distinct patterns of network dynamics across the investigated conditions. During AM retrieval, effective connectivity was characterized by vmPFC-driven top-down modulation primarily targeting the precuneus, consistent with a role in the temporal and self-relevant structuring of episodic memory. In contrast, extended scenario imagination showed hippocampal influences with both vmPFC and precuneus, consistent with a contribution of hippocampal output to the construction of unfolding imagined events. Single Scene construction shifted network leadership to the precuneus, which positively modulated the vmPFC, consistent with its pivotal role in spatial integration and the generation of coherent mental scenes. Object imagery showed no supported modulatory effects within this network. Exploratory cross-dataset PEB comparisons were broadly consistent with these patterns, although the observed differences cannot be attributed to task alone. Together, our findings highlight flexible variation in effective connectivity within the vmPFC-hippocampus-precuneus network during the construction of rich mental experiences. The findings are consistent with scene construction as a shared mechanism linking memory and imagination, with neural interactions varying according to the temporal and spatial characteristics of constructive cognition.