Thermal stimulation of taste

The first electrophysiological recordings from animal(1) and human(2) taste nerves gave clear evidence of thermal sensitivity, and studies have shown that as many as half of the neurons in mammalian taste pathways respond to temperature(3-6). Because temperature has never been shown to induce sensations of taste, it has been assumed that thermal stimulation in the gustatory system is somehow nulled(6). Here we show that heating or cooling small areas of the tongue can in fact cause sensations of taste: warming the anterior edge of the tongue (chorda tympani nerve) from a cold temperature can evoke sweetness, whereas cooling can evoke sourness and/or saltiness. Thermal taste also occurs on the rear of the tongue (glossopharyngeal nerve), but the relationship between temperature and taste is different there than on the front of the tongue. These observations indicate the human gustatory system contains several different types of thermally sensitive neurons that normally contribute to the sensory code for taste.