Swallowing is differentially influenced by retronasal compared with orthonasal stimulation in combination with gustatory stimuli

Identical stimuli are processed differently when presented ortho- or retronasally. In contrast to orthonasal olfaction, retronasal odorant perception is strongly associated with flavor and food intake, which is usually followed by swallowing. Along with other stimuli, gustatory stimuli are known to influence the swallowing reflex. It was therefore the aim of present study to examine whether retronasal olfaction, in combination with simultaneous gustatory stimuli, influences swallowing in a manner different from that of orthonasal olfaction. Fifty normosmic and normogeusic subjects took part in the study. A sweet taste (glucose, delivered via an intraoral taste dispenser) was presented simultaneously with vanillin, a food-like odor, either ortho- or retronasally at random using a computer-controlled olfactometer. Ultrasound imaging of the mouth floor was recorded on videotape to continuously monitor swallowing activity. After retronasal stimulation, swallowing occurred significantly faster (7.49 vs. 9.42 s; P > 0.001) and also took place more frequently compared with swallowing after orthonasal stimulation (1.38 times vs. 1.14 times; P > 0.001). These results show that a food-like odorant presented retronasally in combination with a congruent taste stimulus can influence swallowing. Whether these results can be assigned to other, unfamiliar, unpleasant nonfood-like odors has yet to be determined.