Hippocampal Subfield Volumetry and Navigation in Congenital Blindness

The hippocampus is essential for efficient navigation. Although lack of visual experience from birth induces volumetric and structural modifications to the hippocampus, tactile and auditory navigation remain partially preserved in congenitally blind (CB) individuals. Structural studies in this population have relied on global volume or tail-body-head segmentations, leaving the contributions of individual hippocampal subfields to navigation unresolved. We investigated hippocampal subfield volumes and their association with navigational learning in CB adults compared to sighted controls. Structural MRI data were analyzed using probabilistic cytoarchitectonic ROIs to quantify volumes of Cornu Ammonis (CA), Fascia Dentata (FD), Subiculum (SUB), and the Hippocampal-Amygdaloid Transition Area (HATA). Participants performed obstacle detection and avoidance tasks with a tactile sensory substitution device in a real-world obstacle course. CB participants showed significant volume reductions in left CA and FD compared to sighted controls after total brain volume correction. Obstacle detection learning was associated with bilateral CA and SUB volumes in sighted controls, whereas in CB participants it was selectively associated with right CA and right HATA volumes. Obstacle avoidance learning showed no robust hippocampal associations in either group. Our results indicate that hippocampal subfield-navigation associations are selective and component-dependent in the absence of vision, rather than reflecting uniform hippocampal involvement.