Effects of overshadowing on conditioned and unconditioned nausea in a rotation paradigm with humans
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We examine whether overshadowing by salient stimuli is effective in reducing the ability of a certain environment (the putative conditioned stimulus) to evoke conditioned nausea in healthy humans that experience nausea-evoking rotation (as the unconditioned stimulus, US) in that environment. Twenty-four rotation-susceptible subjects (12 males, 12 females) were randomly assigned to receive either overshadowing by salient tasting beverages (OS+), or a control treatment (a familiar beverage, water; OS−) prior to rotation on three consecutive days (acquisition). To control for taste experiences, the alternative beverage was consumed 12 h later in the home environment (OS+: water, OS−: salient beverage). At Day 4 (test), all subjects drank the familiar beverage (water) prior to rotation (US). Rotation was standardized as 2 × 1-min rotation/day. Nausea was determined by a 7-item symptom scale measuring symptom number (SN) prior to (anticipatory), immediately after, and 15 and 30 min after rotation and by the Nausea Profile (NP) questionnaire immediately after rotation. Cortisol and tumour necrosis factor (TNF)-α in saliva were sampled at the same time-points. SN and cortisol were also measured at home. Overshadowing reduced anticipatory (conditioned) SN. Post-rotation nausea (i.e. the unconditioned response) measured by the NP decreased within the OS+ group only. Anticipatory cortisol and TNF-α were not affected by overshadowing. Treatment × gender interactions manifested for post-rotation cortisol and TNF-α. Groups did not differ in SN and cortisol at home. Overshadowing is effective in reducing symptoms of anticipatory nausea and rotation-induced unconditioned nausea; its effect on endocrine and immunological parameters is gender specific. Its application in alleviation of anticipatory nausea in cancer patients is considered.