Greater hippocampal gray matter volume in subjective hyperosmia: a voxel-based morphometry study

Subjective hyperosmia refers to a self-reported olfactory ability that is superior to a normal, intact sense of smell (normosmia), and is associated with olfactory emotional experience. The current study used voxel-based morphometry to investigate the gray matter volume (GMV) in people with self-rated hyperosmia (subjective hyperosmia, SH, N=18) in comparison to people with self-rated normal olfaction (subjective normosmia, SN, N=14). Participants' olfactory function were assessed by the extensive olfactory test battery, the "Sniffin' Sticks" test. Within the predicted brain regions (regions-of-interest analyses), the SH participants showed larger GMV of the left hippocampus as compared to SN participants (FWE corrected p<0.05). Further, the whole-brain search indicated that SH had larger GMV of the bilateral hippocampus, the right hypothalamus, the left precuneus, and the left superior frontal gyrus as compared to the SN group. ROI analyses showed positive correlations between the left hippocampal GMV and odor threshold or discrimination scores across all participants. In addition, the whole-brain analysis suggested that the self-rated olfactory ability was positively associated with GMV in the cerebellum, superior frontal gyrus and the precentral gyrus among SH participants. In conclusion, the current results suggest that SH was associated with increased GMV in several brain regions that were previously shown to be involved in the processing of cognitive aspects of odors.