Making Head or Tail of the Hippocampus A Long-Axis Account of Episodic and Spatial Memory

Persson, J. 2015. Making Head or Tail of the Hippocampus. A Long-Axis Account of Episodic and Spatial Memory. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Social Sciences 114. 81 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9328-8. While episodic and spatial memory both depend on the hippocampus, opposite gender differences in these functions suggest they are partly separate, with different neural underpinnings. The anterior and posterior hippocampus differ in structure and whole-brain connectivity, and studies point to the posterior hippocampus being more involved in spatial memory while the anterior hippocampus’ role in episodic memory is less clear. This thesis aims to explore the role of the anterior and posterior hippocampus, and associated brain regions, in episodic and spatial memory. Paper I studied gender differences in hippocampal activation underlying differences in spatial memory performance. Better performance in men was accompanied by greater right-lateralization of hippocampal activation compared to women. Paper II investigated regions of gray matter that covaried in volume with the anterior and posterior hippocampus, and whether these covariance patterns depended on gender and were related to behavior. The anterior and posterior hippocampus showed different patterns of covariance, with the anterior hippocampus covariance pattern observed in women and the posterior hippocampus covariance pattern primarily in men. Paper III considered whether the location of hippocampal recruitment in episodic memory depends on memory content. Verbal stimuli were associated with more anterior, and left-lateralized, encoding activations than pictorial stimuli, which in turn were associated with more posterior and bilateral encoding activations. This was not observed during retrieval. Paper IV investigated whether restingstate connectivity associated with the anterior and posterior hippocampus predicts episodic and spatial memory performance, respectively. Resting-state connectivity associated with the anterior, not posterior, hippocampus predicted episodic memory performance, while restingstate connectivity associated with the posterior, not anterior, hippocampus predicted spatial memory performance. This thesis lends further support to differences in function and structure between the anterior and posterior hippocampus suggesting that these two sub–segments play different roles in episodic and spatial memory. Further, it suggests that gender differences in anterior and posterior hippocampus function underlies gender differences in episodic and spatial memory, respectively. Considering the anterior and posterior hippocampus, as well as men and women, separately, is hence important when studying the effect of age and pathology on the hippocampus and associated memory functions.