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Abstract: Both the hippocampus and ventromedial prefrontal cortex (vmPFC) appear to be critical for episodic future simulation. Damage to either structure affects one's ability to remember the past and imagine the future, and both structures are commonly activated as part of a wider core network during future simulation. However, the precise role played by each of these structures and, indeed, the direction of information flow between them during episodic simulation, is still not well understood. In this study, we scanned participants using functional magnetic resonance imaging while they imagined future events in response to object cues. We then used dynamic causal modeling to examine effective connectivity between the left anterior hippocampus and vmPFC during the initial mental construction of the events. Our results show that while there is strong bidirectional intrinsic connectivity between these regions (i.e., irrespective of task conditions), only the hippocampus to vmPFC connection increases during the construction of episodic future events, suggesting that the hippocampus initiates event simulation in response to retrieval cues, driving activation in the vmPFC where episodic details may be further integrated. [ABSTRACT FROM AUTHOR]