The effect of anesthesia of the chorda tympani nerve on taste perception in humans

Four experiments were conducted to clarify a long-standing puzzle in the history of taste research: people with extensive damage to the tongue or to the nerves supplying taste to the tongue often fail to experience any subjective change in real-world taste experience. It was hypothesized that the taste nerves form a network of excitation and inhibition such that when one nerve is damaged, release of its inhibition of other taste nerves compensates for the lost nerve function. In addition, it was hypothesized that because taste localization is poor, the brain employs other senses to localize taste sensations to areas devoid of functional taste receptors.;Experiments 1-3 were designed to determine whether unilaterally blocking the chorda tympani nerve would result in intensification of taste perception at areas supplied by the taste nerves still functioning. A total of thirty-eight subjects received either a lingual nerve block or an auditory canal block to anesthetize the chorda tympani nerve. Blocking the chorda tympani resulted in an overall increase in whole-mouth and contralateral circumvallate papillae taste ratings. Intensification of perceived taste intensity at the circumvallate papillae may offset the loss at the anterior portion of the tongue and thereby provide for the constancy demonstrated in whole-mouth perceived intensities.;Experiment 4 was designed to address the question of why individuals fail to notice when an area in the mouth is devoid of taste sensation. An "illusion of taste" in areas devoid of taste receptors has been described previously, and it has been hypothesized that individuals use the sense of touch to localize taste sensations throughout the mouth. This hypothesis was tested using twenty-five subjects from Experiments 2 and 3. A modified taste illusion protocol was used to compare taste ratings under two forms of anesthesia, one that preserves touch and one that blocks it. A striking difference was found between the experiences of a taste illusion with and without the sense of touch intact. With the chorda tympani nerve anesthetized, but touch intact (auditory canal block), the illusion was similar to that with no anesthetic. However, with touch absent (lingual nerve block) the magnitude of the illusion was diminished significantly.