Effect of taste stimulation of tongue on swallowing reflex in humans

Abstract

We have shown that distilled water (DW) applied to the pharyngolaryngeal region is effective for elicitation of swallowing reflex, but NaCl solutions reduced the effect of DW. However, little is known about role of taste in swallowing reflex in humans. In the present study, we examined how taste stimulation of the tongue is involved in swallowing reflex in humans. Each subject was instructed to repeat swallowing as fast as possible. In dry swallowing without a supply of fluid, the time between the first and 6th swallowing (the dry swallowing test time) was measured. Then, taste solutions were delivered to the anterior tongue through a fine tube at a slow rate (0.2 ml/min). In taste stimulation, the intervals between two consecutive swallowings in a test (swallowing intervals) were measured. The effect of Na salts taste stimulation on swallowing reflex appeared only in subjects who showed long dry swallowing test time (>60 sec). That is, swallowing intervals induced by 0.15 M NaCl and 0.15 M Na acetate were much shorter than those by DW, 0.15 M KCl and olive oil. While, the effect of Na salts taste stimulation on swallowing reflex did not appear in subjects who showed short dry swallowing test time (<55 sec). The present study suggests that salty taste is effective for swallowing initiated voluntarily. Since the effect of Na salts appeared only when swallowing intervals are long, it is also suggested that excitation of sodium-taste receptors affects swallowing center in brain stem slowly. [J Physiol Sci. 2006;56 Suppl:S182]