Investigating morphological changes in the brain in relation to etiology and duration of olfactory dysfunction with voxel-based morphometry

E M Postma,W M Boek,S Boesveldt,P A M Smeets

doi:10.1038/s41598-021-92224-w

Abstract

Olfactory loss (OL) affects up to 20% of the general population and is related to changes in olfaction-related brain regions. This study investigated the effect of etiology and duration of OL on gray matter volume (GMV) of these regions in 257 patients. Voxel-based morphometry was applied to measure GMV in brain regions of interest to test the effects of etiology and duration on regional GMV and the relation between olfactory function and regional GMV. Etiology of OL had a significant effect on GMV in clusters representing the gyrus rectus and orbitofrontal cortex (OFC), bilaterally. Patients with congenital anosmia had reduced GMV in the gyrus rectus and an increased OFC volume compared to patients with acquired OL. There was a significant association between volume of the left OFC and olfactory function. This implies that changes in GMV in patients with acquired OL are mainly reflected in the OFC and depend on olfactory function. Morphology of olfactory areas in the brain therefore seems to relate to olfactory function and the subsequent degree of exposure to olfactory input in patients with acquired OL. Differences in GMV in congenital anosmia are most likely due to the fact that patients were never able to smell.

Highlights

Olfactory loss (OL) affects up to 20% of the general population and is related to changes in olfactionrelated brain regions
Etiology of olfactory loss significantly affected the gray matter volume of clusters in the gyrus rectus and the orbitofrontal cortex, while there was no effect of duration of olfactory loss
Patients with congenital anosmia had increased gray matter volume in parts of the medial and superior orbitofrontal cortex (OFC), while gray matter volume of the gyrus rectus was decreased compared to the other patient groups

Summary

Introduction

Olfactory loss (OL) affects up to 20% of the general population and is related to changes in olfactionrelated brain regions. Training of the olfactory system can lead to changes in morphology of olfaction-related regions, as has been shown in for example wine tasters or p erfumers[15] These experts train their sense of smell in a professional way, which can lead to increased volume of the right insula and entorhinal cortex[16]. While these experts have an improved sense of smell due to their training, patients with olfactory loss are subject to decreased olfactory input. This might, induce morphological changes in olfaction-related regions of the brain. Previous studies demonstrated a decreased volume of the piriform cortex in patients with olfactory

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