A new non-invasive method for recording the electro-olfactogram using external electrodes

Objective The aim of this investigation was to explore the possibility of recording the electro-olfactogram (EOG) using external electrodes placed on the root of the nose on either side of the bridge and at the medial termination of the eyebrows. The EOG is considered to be the summated generator potential of olfactory receptor cells and therefore represents peripheral olfactory events. Recording of human EOG is technically difficult due to poor access to the olfactory mucosa and the nasal irritation is tolerated by few subjects. Methods The evoked potentials at these sites in response to two odourants, n-amyl acetate and benzaldehyde, were recorded simultaneously with the EOG, recorded conventionally with an intranasal electrode, and the olfactory event-related potential (OERP) recorded using scalp electrodes. Results The extranasal potential recorded at the root of the nose, 0.5–1 cm below the nasion, 1 cm from the ridge and ipsilateral with the stimulus, had the highest degree of correlation with the intranasal EOG. We refer to this site as N1 (left side) and N2 (right side). Further analysis demonstrated that the latency, the time constant of the rising phase and the amplitude of the evoked potential recorded at N1 also had a higher correlation coefficient with the EOG than did those potentials recorded at other sites. Statistical analysis indicated that the latency and time constant of the response recorded externally at N1 were the same as those of the EOG recorded intranasally. Conclusions We conclude that an olfactory evoked potential, with many of the characteristics of the EOG recorded from the olfactory mucosa, can be recorded externally at a site close to the bridge of the nose. Significance This non-invasive method of recording the EOG will have benefits for the objective assessment of olfactory function.