Effective connectivity during autobiographical memory search

Abstract

Autobiographical memory (AM) retrieval is known to recruit a widely distributed network of brain regions but much less is known regarding how these regions interact during the various phases that presumably take place during episodic memory retrieval in general and AM retrieval in particular. Here, we used dynamic causal modeling (DCM) to examine effective connectivity during cued AM search in a sub-network consisting of six major regions within this large network. Functional MRI data was acquired while participants were visually presented verbal cues describing common life events and requested to search for a personal memory that could be associated with each cue. We examined directed couplings between the ventromedial (vmPFC), dorsomedial (dmPFC) and dorsolateral prefrontal cortices (dlPFC), hippocampus, angular gyrus and a region in the posterior midline cortex (RSC/PCC/Prec), all located in the left hemisphere. Results indicated that during AM search, the vmPFC, dlPFC and RSC/PCC/Prec acted as primary drivers of activity in the rest of the network. Moreover, when AM search was completed successfully (Hits), an up-modulation of the effective connectivity of the hippocampus in the vmPFC and angular gyrus was observed. In the same way, there was an increase in the influence of the RSC/PCC/Prec in the activity of the dlPFC and dmPFC. Furthermore, during Hits the angular gyrus showed to have an inhibitory effect in all other nodes of the network. These results are consistent with the notion that midline cortical regions are crucial in supporting the retrieval of AMs, and highlight the interplay between the vmPFC and the RSC/PCC/Prec and the dlPFC during AM search.