Differences in human evoked potentials related to olfactory or trigeminal chemosensory activation.

The aim of the present study was to determine, whether there are differences in the topographical distribution of chemosensory evoked potentials (CSEPs) due to stimulation with different odorous substances. The odorants used in the study which mainly excited the olfactory nerve were vanillin and acetaldehyde; those which additionally excited the trigeminal nerve were sulphur dioxide and ammonia. Twelve subjects participated in the study. The subjects separately estimated the intensity of the odorous and of the painful/pricking sensation caused by the stimuli, and described the odorous qualities in their own words. CSEPs were recorded from 7 positions. After stimulation with "olfactory" substances maximum CSEP amplitudes were recorded at parieto-central sites, and after stimulation with "trigeminal" substances maximum amplitudes were obtained at the vertex. Following stimulation with ammonia and sulphur dioxide amplitudes were largest contralateral to the stimulated nostril. In contrast, little difference in CSEP amplitudes was observed between hemispheres after stimulation with vanillin or acetaldehyde. Thus, the topographical distribution of CSEP amplitudes may provide information with regard to the sensory system (olfactory or trigeminal) activated by the presentation of an odorous stimulus.