The degree of taste function in the various areas of the tongue and oral cavity can be assessed using the Taste-Quadrant (Spatial) Test. As the gustatory system is multiply innervated, damage to 1 of the 3 major nerves (ie, chorda tympani, glossopharyngeal, greater superficial petrosal) or their ganglia may cause a disturbance of taste that can only be evaluated by testing the anatomic areas supplied by those nerves. This test can ascertain whether a localized deficit is present due to the pathology of the chorda tympani, glossopharyngeal, or greater superficial petrosal nerves or their sensory ganglia or central connections. Damage to these nerves can result in a partial loss of taste that is not revealed in whole-mouth tests.
In this test, the four quadrants of the tongue (right and left front and right and left rear sides of the tongue and the two sides of the soft palate) are tested with strong concentrations of the four tastes, These six areas all represent innervation by a separate nerve. The patient identifies the taste (salt, sugar, acid or quinine) and assigns a number proportional to its intensity. Loss of sensitivity in one of the six quadrants can reveal dysfunction of the right or left chorda tympani nerve (front tongue) or glossopharyngeal nerve (rear tongue) or greater superficial petrosal nerves (palate). Loss of sensitivity to a particular taste quality can indicate a receptor dysfunction. The four stimuli are presented to each area for at least once minimum of 24 trials. The test takes about 45 minutes to conduct.