Chemosensory event-related potentials in the investigation of interactions between the olfactory and the somatosensory (trigeminal) systems.

The aim of the study was to investigate the interaction of the olfactory and somatosensory systems in the perception of chemical stimuli. Stimuli were chosen so as to selectively activate the olfactory (hydrogen sulphide, H2S) and trigeminal (carbon dioxide, CO2) nerves. In addition, carvone was included as a stimulus with mixed properties. Thirty healthy volunteers participated in the experiments. Subjects rated the intensity of each of the stimulants when presented alone and as a component of binary mixtures. Chemosensory event-related potentials (CSERPs) were obtained from 5 recording positions. Analysis of the intensity ratings indicated that there was no difference between the 3 stimulants when used as single components. In binary mixtures intensity estimates of H2S were suppressed by CO2 and carvone. In addition, while estimates of CO2 were suppressed by carvone estimates of the latter were enhanced in the same mixture. CSERP data confirmed earlier findings with regard to the topographic distribution of amplitudes, i.e., if the olfactory system had been activated largest amplitudes were observed at position Pz, whereas activation of the trigeminal nerve produced largest amplitudes at Cz. Moreover, the suppression of CO2 estimates by carvone was reflected in a corresponding suppression of the CSERP amplitudes. In addition, when CO2 was mixed with H2S or carvone there was a decrease in the CSERP latency indicating interactions of both sensory systems in the time domain.