Orthonasal and Retronasal Olfaction

Olfaction is phylogenetically considered the oldest sense, yet remains the least well understood. Olfaction comprises the chemosensory modality dedicated to detecting low concentrations of airborne, volatile chemical substances. Orthonasal olfaction occurs when odor molecules are sampled via nasal inhalation or sniff; odors are delivered with inhaled air to the olfactory receptors through the nose. The key issue for the investigation of retronasal olfaction is the delivery of odorous stimuli to the back of the throat. Orthonasal and retronasal olfaction differ in terms of odor threshold, odor intensity, ability to localize an odor, and the neuronal processing. A number of studies have reported psychophysical differences between ortho- and retronasal olfaction. For food odors, orthonasal perception represents information from the food sources in the environment, while retronasal stimulation signals information from odor sources in the oral cavity. The orthonasal olfaction may function as a detection system for nutrients content within natural food sources.