Association Between Anterior Hippocampal Gyrification and Episodic Memory Performance in Neurotypical Young Adults.

The hippocampus is critical for episodic memory. The relationship between its structural variability and individual differences in episodic memory performance among neurotypical young adults, however, remains unclear. Previous studies have not consistently found associations between hippocampal volume and episodic memory or other aspects of hippocampally dependent performance in this population. Here, we moved beyond volumetric approaches and tested whether more fine-grained morphometric features, particularly gyrification, are related to behavioral performance. To obtain these measures, we used HippUnfold, a deep learning-based segmentation tool that models the hippocampus as a folded cortical ribbon and uniquely quantifies local variability in folding patterns, including in the hippocampal head. We focused on an open-access dataset with high-resolution MRI scans and multiple behavioral measures on hippocampal-dependent tasks, including episodic and semantic components of the Autobiographical Interview. To improve segmentation quality for the high-resolution images in this dataset, we trained an nnU-Net segmentation model for HippUnfold that was optimized for high-resolution T2w images. Volumetric and surface-based measures were computed for 186 participants (97 female). We found no reliable associations between hippocampal volumetric measures, including subfield volumes, and behavioral performance. In contrast, surface-based analysis of hippocampal gyrification revealed significant bilateral clusters in the anterior hippocampus, both of which were associated with measures of episodic but not semantic autobiographical memory. The right hemisphere cluster was located in the subiculum and CA1, whereas the left hemisphere cluster was primarily situated in the subiculum. These findings demonstrate the utility of surface-based hippocampal morphometry for linking hippocampal structure to behavioral performance. They suggest that even in neurotypical young adults individual differences in episodic memory are tied to structural hippocampal variation.