Analysis of human hippocampal volumetry in relation to pattern separation ability in healthy young subjects.

INTRODUCTION:Hippocampal dentate gyrus related to pattern separation has attracted attention as an area for neurogenesis. However, the associations between the pattern separation and the volumes of hippocampal subfields in humans remain unknown. METHODS:58 young adults were examined the memory task (pattern separation, pattern completion) and the hippocampal volumes. Subjects were asked to determine whether the visual image is a new stimulus, or a similar but different stimulus (pattern separation), or the same stimulus (pattern completion), compared to preceding stimuli, and response time and correct response were measured. The volumes of the whole brain, hippocampus 6 subfields and perihippocampus 5 subfields, were measured using FreeSurfer 6.0. RESULTS:Negative associations between the pattern separation task and the volumes of whole brain areas were found in bilateral cerebellar cortex, fourth ventricle, left hippocampus, left thalamus, left ventral diencephalon, and brainstem. Simple linear regression analysis revealed a significant association with the left hippocampal-amygdaloid transition area only, while no significant associations were found in any of the subfield volumes when adjusted with covariates. CONCLUSIONS:The principle "bigger is better"-an idea that the larger the volume the better the function-could not be applied to the relation between the pattern separation ability and the dentate gyrus.