Olfactory training selectively modifies cortical responses to odors in healthy adults

Olfactory training (OT) is an effective method for rehabilitating smell dysfunctions through regular stimulation of the olfactory system. However, the exact mechanism through which OT improves olfaction remains elusive, especially regarding cortical processing of odors. This study aimed to examine the effects of OT on cortical responses to odors in young healthy individuals. Ninety-four participants (Mage = 25.3, SD = 4.5 years; 71 women) were asked to either (1) conduct bi-daily OT with the odors of rose (phenyl ethyl alcohol, PEA), cloves (eugenol), lemon (citronellal), eucalyptus (eucalyptol), or (2) participate in a placebo OT with odorless propylene glycol. At baseline and after 12 weeks of OT, we measured participants' olfactory detection threshold and odor identification, and recorded electroencephalogram-derived chemosensory event-related potentials (CSERP) for PEA, hydrogen sulfide (H2S), and carbon dioxide (CO2). Seventy-five participants (Mage = 25.1, SD = 4.3 years; 55 women) completed pre- and post-OT appointments. Participants in the OT group exhibited shorter latencies at P1, N1, and P2 CSERP components in response to PEA but not to H2S or CO2. Participants in the placebo group did not show any changes in latencies in response to any of the stimuli. Our results suggest that in healthy adults, OT leads to odor-specific changes in cortical responses to odors.