Functional but Not Structural Brain Changes After Olfactory Training in Women With COVID-19-Associated Olfactory Dysfunction.

BACKGROUND: Olfactory training (OT) is a recommended treatment for olfactory loss and has proven effective in clinical contexts, yet its effects on the central-nervous system remain unclear. This study aimed to investigate the functional and structural brain changes in patients with post-viral olfactory loss undergoing OT. METHODS: Twenty patients with post-viral olfactory loss and 19 healthy controls underwent OT for 3 months. All participants were assessed using the Sniffin' Sticks test and magnetic resonance imaging (MRI). Voxel-based morphometry and olfactory bulb volumetry were performed on structural images. Presenting an unpleasant odor, n-butanol, in a canonical block design, functional MRI was performed using whole-brain and region of interest analyses. RESULTS: Patients with post-viral olfactory loss showed significant improvement following OT. Enhanced functional activations were observed in the orbitofrontal cortex and parahippocampus, while OT had little or no effects on brain structures. CONCLUSION: The present findings suggest that OT provides early perceptual and functional benefits, with structural changes potentially emerging later with extended training duration.