Effect of imagining and actually tasting a sour taste on one side of the tongue.

To determine whether images can stimulate brainstem reflexes directly, parotid salivation was measured bilaterally in 24 subjects when they imagined, and actually tasted, a sour taste on one side of the tongue. Salivation increased in both cheeks during unilateral gustatory stimulation; furthermore, the response was greater on the stimulated side than contralaterally, indicating that the gustatory reflex has a unilateral component. Subjects imagined the sour taste more clearly after actually experiencing it. However, salivation did not increase significantly during imagery trials, either before or after exposure to the sour taste; in fact, salivation to imagery decreased below baseline after exposure. These findings suggest that extraneous factors (e.g. the emotional connotations of images, anxiety, discomfort, repetitive measurement or fatigue) might sometimes inhibit specific reflex activity induced by images.