Taste responses of human chorda tympani nerve

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Abstract
Records from humans of summated action potential discharges of the chorda tympani nerve were examined. The magnitudes of neural and psychophysical responses were well related only when the comparison was made within a given taste quality. The response to a mixture of 0 02 M citric acid and 0.5 M sucrose was less than the sum of the separate responses to the mixture components. Citric acid failed to cross-adapt the response to sucrose, implying the receptor sites for sucrose are independent of citric acid. The human chorda tympani nerve shows vigorous responses to mechanical stimulation and cooling of the tongue that are maintained after treatment of the tongue with a water extract of the herb Gymnema sylvestre . Gymnema extract selectively suppressed the response to all sweeteners tested (sucrose, fructose, saccharin and cyclamate) and also suppressed by – 50% the water-after-citric-acid response which has a predominantly sweet taste. Gymnema suppressed by 0 – 10% the water-rinse response following NaCl. fructose and sucrose that have a predominantly bitter-sour taste. Water-rinse responses were present even when mechanical and thermal stimulation of the tongue were minimized. The human chorda tympani nerve appears to have positive water-rinse taste responses. These are solute-specific off-responses that are probably mediated by receptor sites independent of those responsible for the on-response to the given solute.