Evidence for neural inhibition in bittersweet taste mixtures.

Abstract

Lines (3) of evidence from psychophysical experiments implied that mutual suppression of bitter and sweet tastes is due to neural inhibition rather than chemical interactions in solution or competition of molecules for common receptors sites. Removal of sweetness from bittersweet mixtures caused the bitterness to increase. This was accomplished by adaptation to sucrose or by treatment with Gymnema sylvestre, neither of which affect the concentration of sucrose on the tongue. Increases in the bitterness of mixtures, independent of the concentration of the sweet masking substance, are difficult to reconcile with suppression by means of chemical interactions. Similar dependence of suppression on perceived intensity (and independence from concentration) was observed with mixtures of phenylthiocarbamide and sucrose. Tasters (human) of phenylthiocarbamide showed stronger suppression of sweetness than nontasters. This was inconsistent with molecular interactions causing suppression, which would have resulted in the same degree of suppression for the 2 groups. Findings support neural explanations of mixture suppression, e.g., antidromic inhibition or occlusion.