Effect of tongue temperature on oral tactile sensitivity and viscosity discrimination

© 2019 Elsevier Ltd An Individual's oral capability in perceiving food texture influences greatly food appreciation and preference. While there is no doubt that one's ability of texture discrimination depends on various oral physiological characteristics of the individual, it is not yet clear how tongue surface temperature affects the sensitivity of texture discrimination. This study was designed to test the effects of tongue surface temperature on oral tactile sensitivity and viscosity discrimination. A total of twenty healthy subjects (ten females and ten males; mean age: 25 ± 1 yrs, mean body mass index: 20.5 ± 2.9 kg/m2) participated in this study. Water at different temperatures (0, 20, 37, and 45 °C) and capsaicin solutions (5,10, and 20 ppm) were used as physical and chemical stimulations to alter tongue temperature, respectively. Semmes-Weinstein monofilaments, Bio-Thesiometer, and Touch-Test®Two-point discriminator were respectively applied to assess the tongue's sensitivity of light touch, vibratory perception and two-point discrimination before and after treatment with both physical and chemical stimuli. Maltodextrin solutions were used for oral viscosity discrimination. Tongue's vibratory perception thresholds varied significantly (P < 0.01), indicating an increase of 0.6 × 10−6cm in vibratory perception threshold when tongue surface temperature decreased from 33 °C to 20 °C, while light touch and two-point discrimination thresholds remained unchanged. The application of capsaicin (5, 10, and 20 ppm) produced an increase in tongue surface temperature but did not affect oral tactile sensitivity. Viscosity discrimination increased both after rinsing the mouth with warm water and capsaicin application (20 ppm). Capsaicin (20 ppm) increased tongue temperature by 1.3 °C and lead to a decrease in viscosity discrimination threshold from 34.7% to 20.2%. After stimulation with water at 37 °C and 45 °C, the tongue temperature increased by 3 °C (from 34.2 °C to 37.2 °C), while threshold of viscosity discrimination decreased from 28.1% to 23.1%. When water was used to change tongue surface temperature, a positive correlation was found between vibratory perception sensitivity and viscosity discrimination ability, suggesting the capacity of discriminating viscosity might depend on vibratory perception sensitivity