A device for controlling odorant stimulation and olfactory evoked responses in humans

We developed a device for odorous stimuli control to record olfactory evoked responses from the human scalp. The characteristics of the apparatus are as follows. Translating the subject's respiration into electric signals with a sensor attached to the nose. The period and timing of odorous stimuli could be adjusted, so that stimuli could be synchronous with respiration. The interstimulus interval could be arbitrarily selected once every 1 to 9 respiration(s) so that adaptation could be prevented. We obtained evoked responses to odorous stimuli using this apparatus from the human scalp, whose positive peak latencies were approximately 350 and 700 msec. Such responses were not recorded if oxygen stimuli were used instead of odorous stimuli or with click sounds produced by the switching electromagnetic valve. Three types of odorant evoked scalp potentials were obtained in normal human subjects. The first type consisted mainly of two positive peaks with a peak latency of about 350 msec (P350) and about 700 msec (P700). The second type and the third type consisted of only one positive peak with a peak latency of about 350 msec and 700 msec, respectively. Such a P350 or P700 peak as that observed in the normal subjects was not detected in anosmic patients.