gms | German Medical Science

Objective: After chemical stimulation of the human olfactory epithelium it is possible to record a negative response (electro-olfactogram, EOG) which is interpreted as the summated generator potential of olfactory neurons. The aim of this investigation was to test whether the EOG is present when olfactory stimuli are not perceived by the subject.

Methods: Twelve healthy volunteers participated in the experiments (6 female, 6 male; age from 25-34 years). Stimulation was performed with vanillin and eugenol at concentrations around threshold (stimulus duration 500 ms, interval ~60 s). The stimuli were chosen on the basis of differences in transduction pathways (vanillin: IP3; eugenol: cAMP). EOG was recorded by means of tubular electrodes (cutaneous reference contralateral bridge of the nose; impedance < 8 kΩ; bandpass DC to 30 Hz, sampling rate 125 Hz). Eye blinks were monitored via the Fp2 lead (referenced against A1). The electrode was positioned under endoscopical control; recording sites were marked in a map of the human nasal cavity.

Results: EOG could be recorded in 4 out of 12 subjects. Two subjects were unable to compensate the sneezing reflex; responses of 3 other subjects had to be discarded due to an excessive number of artifacts. For both stimulants EOGs could be obtained even when the stimuli were not perceived. All recording sites were localized superior to the insertion of the middle turbinate. In 3 out of 4 cases EOGs to both stimulants were obtained at the same position.

Conclusion: This indicates at an electrophysiological level that olfactory information is present even when stimuli are not subjectively perceived; this may provide the basis of subconscious behavioural modifications induced by odorants.