Background: Since antiquity human taste has been divided into 4-5 taste qualities. However, responses in taste fibers of other animal species have only partly clustered according to human qualities. We realized taste qualities vary according to phylogeny, where species closer to humans show higher fidelity to human taste qualities.
Methods/Results: We compared psychophysical data and taste nerve recording from humans to behavioral tests and single taste fiber recordings in chimpanzee, rhesus and marmoset. Our data show how, with phylogenetic closeness to humans, taste fibers responded more exclusively to taste stimuli within each human taste quality. We then used the human sweet taste modifiers, miraculin and gymnemic acid. In human, miraculin adds sweet to sour taste and doubles nerve responses to acids. After miraculin nonhuman primates also doubled acid intake while both acid-specific and sweet-specific single taste fibers responded to acids. In human gymnemic acid eliminates sweet quality. In chimpanzee gymnemic acid abolished taste fiber responses to sweet without affecting responses to other tastes.
Analytical and statistical tools: Clusters of taste fibers in both CT and NG were identified with hierarchical cluster analysis. Responses to all stimuli were taken into consideration and the analysis considers each stimulus as an independent variable and a Pearson correlation coefficient is calculated between the responses. The results of hierarchical cluster analysis were presented as a Dendrogram. Multidimensional Scaling presented the single fiber results in a multidimensional space for further analyses.
The animal research was conducted in accordance with the principle and guidelines established by the Association for the Assessment and Accreditation of Laboratory Animal Care International (AAALAC) and procedures were approved by the local Institutional Animal Care and Use Committee (IACUC) from the University of Wisconsin-Madison, WI, USA (marmoset and rhesus monkey) and Laboratory for Experimental Medicine and Surgery in Primates, New York Medical Center, NY, USA. (chimpanzee).
Conclusions: Information from each type of taste receptor cell reaches a specific cortical taste area where it gives rise to taste qualities; taste is created in the cortical region where taste fibers deliver action potentials, thus satisfying the criteria of labeled-line coding which follows Mueller’s law of specific nerve energy for pain, touch, and temperature where sensation is created in the cortex after conveyance by sensory fibers. In humans these cortical areas give rise to the taste qualities, sweet, sour, bitter, salt and umami. It is likely that this principle applies to other mammals, but their taste qualities differ due to species differences in taste receptor structure.