Hippocampal subfields' volumes are more relevant to fluid intelligence than verbal working memory

- Right CA1 size relates to Raven's Advanced Progressive Matrices (RAPM) performance
- RAPM has higher correlations with hippocampal subfields' volumes than verbal n-back
- RAPM and visual n-back has similar correlations with hippocampal subfields' volumes
- Sex moderates the correlation between left hippocampal fissure volume and n-back

The hippocampus plays an important role in learning and memory. Poor segmentation tools of hippocampal subfields, however, have hindered our understanding of their specific roles. Using FreeSurfer 6.0, which provides more accurate segmentation than previous versions (especially for Cornu Ammonis [CA] subfields), the current study examined the 12 hippocampal subfields' contributions to fluid intelligence (measured with Raven's Advanced Progressive Matrices, RAPM) and working memory (measured with n-back visual and verbal working memory tasks) in a sample of 417 healthy young adults. Results showed that RAPM and visual n-back working memory had similar correlations with hippocampal subfields' volumes, but RAPM was more highly correlated with the volumes of the right hippocampus as well as three of its subfields (CA1, molecular layer of the hippocampus, and hippocampal tail) than was verbal n-back working memory (after correcting for multiple comparisons). In addition, sex moderated the correlation between left hippocampal fissure volume and n-back working memory. These results suggest both shared and distinct neural substrates for fluid intelligence and visual and verbal working memory, and highlight the role of CA1 in visuospatial cognition.