Olfaction: From Percept to Molecule

Abstract

Despite major progress in elucidating the anatomical and molecular foundations of olfaction, the rules underlying the link between the olfactory stimulus and the olfactory percept remain unknown. We argue that this lack is a reflection of visual primacy in human perception and thinking, primacy that has prevented the development of a perception-based approach to studying olfactory coding. With this in mind, in this chapter, we first provide a tutorial on the organization of the mammalian olfactory system and then describe our recent efforts to generate a perception-based olfactory metric. The primary olfactory perceptual axis revealed by this effort was odorant pleasantness. We found that pleasantness is a perceptual representation of the physical axis that best explains the variance in molecular odorant structure. That the most important dimension in olfactory perception should be the best correlate of the most discriminating physicochemical measures suggests that, as with other senses, the olfactory system has evolved to exploit a fundamental regularity in the physical world. In this respect, olfactory pleasantness can be likened to visual color and auditory pitch. Finally, we review our use of this olfactory metric in predicting odor perception in humans and odorant-induced neural activity in the olfactory system of nonhuman animals.