Capsaicin cross-desensitization on the tongue: psychophysical evidence that oral chemical irritation is mediated by more than one sensory pathway

Abstract

Psychophysical measurements were made of the perceived intensity and quality of sensations of chemical irritation before and after the tip of the tongue had been desensitized to capsaicin (10 ppm). The results of the first experiment showed that capsaicin desensitization tended to reduce the perceived intensity of irritation produced by approximately equipotent concentrations of capsaicin (3 ppm), ethanol (30%), cinnamic aldehyde (2.5%) and NaCl (5M) applied to the tongue on filter paper disks; however, the reduction in irritation was less for the latter three compounds than for capsaicin and failed to reach statistical significance for ethanol. Ratings of sensation quality suggested that the four irritants produced different quality ‘profiles’, and that ethanol and cinnamic aldehyde were characterized by sensations of numbness as well as by sensations of burning and stinging/pricking. Follow-up experiments in which subjects rated the perceived intensity of individual sensation qualities showed that desensitization dramatically reduced the burning and stinging/pricking components of irritation, but left the sensations of numbness and chemogenic warmth unchanged. It is concluded that lingual chemesthetic sensations are multidimensional, and mediated by both capsaicinsensitive and capsaicin-insensitive sensory pathways.