GENETIC AND PATHOLOGICAL TASTE VARIATION - WHAT CAN WE LEARN FROM ANIMAL-MODELS AND HUMAN-DISEASE

The study of patients with taste disorders (i.e. 'experiments of nature') suggests that the old tongue maps (e.g. sweet on the tip, bitter on the back) that often appear in textbooks are wrong. If they were correct, severing the taste nerves that innervate the front of the tongue would result in a loss of the ability to taste sweet, etc. This does not occur. Severing these nerves has little effect on everyday taste experience because taste nerves inhibit one another. Damaging one nerve abolishes its ability to inhibit others and the release-of-inhibition compensates for the damage. There is sometimes a clinical cost for this redundancy; release-of-inhibition can produce taste phantoms. Genetic variation in taste ability occurs across and within species. For example, about 25% of humans are relatively unresponsive to a variety of sweet and bitter compounds (non-tasters) while another 25% are unusually responsive (supertasters). Supertasters have about four times as many taste buds as non-tasters and have smaller and more densely packed fungiform papillae. Since there are pain fibres associated with taste buds, supertasters are unusually responsive to the oral burn of spices.