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I. Torvik Heian - A-S. Helvik - T.Å. Myklebust - E.M. Berntsen - T. Hummel - S. Nordgård - M. Bratt - W. Moe Thorstensen

DOI: 10.4193/Rhin25.424

BACKGROUND: Olfactory training (OT) has been linked to changes in olfactory function and structural modifications in the olfactory bulb (OB); however, the neuroplastic potential in the OB remains unclear. In this pilot study, we investigate how OT with different exposure lengths influences olfactory bulb volume (OBV) and olfactory function in individuals with normosmia. METHODOLOGY: Seventy-seven normosmic individuals were assigned to either standard OT, extended OT, or a control group. The intervention groups performed OT for three months, sniffing four odours - eucalyptus, lavender, mint and lemon – for 10 seconds per bottle, twice daily, totalling either 40 seconds (standard OT) or 4 minutes (extended OT), while the control group did not perform any OT. OBV (manual segmentation of 3-Tesla magnetic resonance images) and olfactory function (Sniffin' Sticks test) were assessed at baseline, post-intervention and at one-year follow-up. RESULTS: OBV increased significantly in both the standard and extended OT groups after the intervention and at follow-up, compared to controls. There were no differences between the training methods and no significant changes in olfactory function. CONCLUSIONS: In normosmic individuals, OBV increased after both standard and extended OT, with no differences between training methods. The volume increase was evident at three-month assessment and persisted at one-year follow-up, indicating that neuroplastic changes induced by OT occur rapidly and may extend beyond the duration of the training itself, an effect not previously reported. However, the OBV changes were not accompanied by improve-ments in olfactory function.

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