Dissociating patterns of anterior and posterior hippocampal activity and connectivity during distinct forms of category fluency

Abstract

Recent work has suggested that there are functionally distinct contributions from hippocampal subregions to episodic memory retrieval. One view of this dissociation is that the anterior and posterior hippocampus support gist-based/conceptual and fine-grained/spatial memory representations, respectively. It is not clear if such distinctions hold for other cognitive domains. To test this possibility, we examined anterior and posterior hippocampal contributions to a standard semantic retrieval task, category fluency. During fMRI scanning, participants generated exemplars to categories that were based on conceptual (autobiographical categories - 'movies that you have seen') or spatio-perceptual (spatial categories - 'items in a kitchen') information. Our main finding was that the autobiographical categories preferentially recruited the anterior hippocampus whereas the spatial categories preferentially recruited the posterior hippocampus. Differences were also evident when we examined the patterns of task-based hippocampal connectivity associated with these two forms of fluency. Our findings provide evidence for a functional organization along the long axis of the hippocampus that is based on conceptual and perceptual relational retrieval and indicate that this manner of organization is apparent outside the domain of episodic memory.