Effects of anesthesia of the facial nerve on taste

Two cranial nerves, the facial (7th) and the glossopharyngeal (9th), play important roles in taste perception, yet patients with damage to the 7th nerve often fail to experience reduced taste intensities. In an effort to explain this, branches of the 7th (the chorda tympani which innervates the anterior two-thirds of the tongue and the greater superficial petrosal which innervates the posterior palate near the junction of the hard and soft palates) were temporarily anesthetized in healthy volunteers. Even bilateral anesthesia of both branches of the 7th nerve produced only small taste decrements (the largest from NaCl). When smaller portions of the 7th nerve were anesthetized, some tastes actually became more intense. This suggests that the 7th nerve normally inhibits the 9th nerve. When the 7th nerve is anesthetized, that inhibition is released and more intense taste sensations are evoked from the 9th nerve.