Expectation, expectoration and disgust: information manipulation alters spitting efficiency, a proxy for salivary flow

Saliva is becoming an increasingly useful research material across multiple fields of inquiry, including biomedical, dental, psychological, nutritional, and food choice research. However, both the flow rate and protein composition of stimulated saliva differ as a function of the collection method. We hypothesized that the context in which a salivary stimulus is presented to participants may alter salivation via behavioral (i.e., spitting efficiency) or top down cognitive effects. We presented participants with a constant stimulus (commercially available green tea) in two distinct contexts, once where the tea was described as a food item (“tea”) and once where it was described as a disgusting non-food item (“rabbit hair extract”). Saliva and the expectorated stimulus were collected following 15 seconds of oral exposure in a crossover design with the identical stimulus presented under both contextual conditions; saliva was also collected for 5 minutes after stimulation while chewing a piece of wax. Participants also completed several validated personality instruments to measure food involvement, sensation seeking, sensitivity to reward, and sensitivity to punishment. Our data indicate participants spat out more sample when told they received the ‘non-food’ stimulus compared to the ‘food’ stimulus, particularly when they were given the non-food stimulus first. Further, individuals who were more sensation seeking spat out more sample during the ‘food’ condition compared to individuals with lower sensation seeking scores, but this difference was not observed during the ‘non-food’ condition. We interpret these data as showing either a greater motivation to spit for the ‘non-food’ stimulus, or a top down cognitive effect on salivary flow: that is, the context in which a salivary stimulus is presented alters how much sample/saliva is expectorated, and this effect may interact with personality factors