Olfactory training changes electrophysiological responses at the level of the olfactory epithelium

Background: Olfactory training (OT) has been shown to increase olfactory performance in healthy subjects and patients with post-traumatic or post-infectious olfactory loss. Morphological correlates such as olfactory bulb volume increase and gray matter changes suggest central changes in olfactory brain areas following olfactory exposure. Some evidence from animal studies indicates peripheral changes upon OT whereas no such data exist in humans. This study explores the question whether changes in olfaction following OT are associated with alterations of the electro-olfactogram (EOG) derived from the olfactory epithelium. Methodology: We compared electrophysiological EOG responses to a pleasant, rose-like odor (phenylethyl alcohol, PEA) and to an unpleasant odor (rotten eggs, H2S) in patients and controls. EOG were recorded in smell impaired patients before and after OT for a period of 4-6 months. Results: EOG recordings following PEA and H2S stimulation were significantly more often obtained in controls than in patients. OT was associated with a significantly higher number of EOG recordings. Conclusions: OT is associated with an increase in EOG responses implicating stimulus-induced plasticity to start at the level of the olfactory epithelium.