Psychophysiological basis of smells

There has been an increase in the use of psychophysiological techniques, especially event-related potentials (ERPs) to evaluate the effects of odor on the central nervous system. In the study of ERPs related to odor, there are two main methods of the odor presentation: (1) to investigate the olfactory ERP (OERP) or chemosensory ERP (CSERP), that is to calculate electrophysiological responses to odor stimulation as a trigger; (2) to compare ERP of mental functioning during the odor exposed condition with that of no odor exposure. The amplitude of contingent negative variation (CNV) varies with the odorant being present, when the odor is presented as a trigger and when it is administrated during a task. It is suggested that CNV changes depend on not only the odorant but the anticipation, expectation and emotion of the subject. The latency of the N1 component becomes shorter with increasing concentrations of odors. The N1 amplitude does not depend on the odor concentration while the amplitude of the auditory N1 strongly depends on the stimulus intensity. There is only one report that the olfactory mismatch negativity (MMN) is present in the CSERP. On the other hand, auditory MMN is not affected by odor administration. In relation to the P3 component, rare odors evoked a larger amplitude in contrast to frequent odors, as well as P3 evoked by other modalities. These ERP studies with odors are expected to be applied to such clinical settings as the differentiation between the anosmic patients and normosmic persons, the functional evaluation of patients with brain tumors, the earlier detection of dementia, and the objective evaluation of aromatherapy.