Pavlovian conditioning of nausea and vomiting.

Cancer patients undergoing cytotoxic drug treatment often experience side-effects, the most distressing being nausea and vomiting. Despite antiemetic drugs, 25-30% of the chemotherapy patients report these side-effects when being re-exposed to the stimuli that usually signal the chemotherapy session and its drug infusion. These symptoms are called anticipatory nausea and anticipatory vomiting. The present paper summarizes the evidence that anticipatory vomiting is acquired by Pavlovian conditioning, and, consequently, may be alleviated by conditioning techniques. To explore the mechanisms that induce and alleviate conditioned nausea and vomiting further, a conditioned nausea model was established in healthy humans using body rotation as the nausea-inducing treatment. The validity of this motion sickness model to examine conditioning mechanisms in the acquisition and alleviation of conditioned nausea was demonstrated. Cortisol and tumor-necrosis factor-alpha were elevated as endocrine and immunological correlates of nausea. Data in the rotation-induced motion sickness model indicated that gender is an important moderator variable to be considered in further studies. The paper concludes with a review of applications of the demonstrated conditioning principles as interventions to ameliorate distressing anticipatory nausea or anticipatory vomiting in cancer patients undergoing chemotherapy.