A Causal Role for Gastric Rhythm in Human Disgust Avoidance

Rotten food, maggots, bodily waste—all elicit disgust in humans. Disgust promotes survival by encouraging avoidance of disease vectors(1) but is also implicated in prejudice toward minority groups; avoidance of environmentally beneficial foods, such as insect protein; and maladaptive avoidance behavior in neuropsychiatric conditions.2, 3, 4, 5 Unlike fear, pathological disgust is not improved substantially by exposure therapy clinically,(6) nor in experimental work does behavioral avoidance of disgusting images habituate following prolonged exposure.(7)(,)(8) Under normal physiological conditions, perception of disgusting stimuli disrupts myoelectrical rhythms in the stomach,9, 10, 11, 12, 13 inducing gastric dysrhythmias that correlate with neural signatures of disgust.(11) However, the causal role of gastric rhythm in disgust avoidance is unknown. We manipulated gastric rhythm using domperidone, a peripheral dopamine D2/D3 antagonist and common anti-emetic, at a dose (10 mg) that acts to convert gastric dysrhythmias to normal rhythms.(9) In a preregistered, randomized, double-blind, placebo-controlled crossover design in 25 healthy volunteers (aged 18–25), we measured the effects of domperidone on core disgust avoidance, using eye tracking to measure implicit (oculomotor) avoidance of disgusting images (feces) before and after an “exposure” intervention (monetary reinforcement for looking at disgusting images).(7)(,)(8) We find that domperidone significantly reduces oculomotor disgust avoidance following incentivized exposure. This suggests that domperidone may weaken the “immunity” of disgust to habituation, putatively by reducing gastric dysrhythmias during incentivized engagement with disgusting stimuli. This indicates a causal role for disgust-related visceral changes in disgust avoidance, supporting the hypothesis that physiological homeostasis contributes to emotional experience.