Pre-exposure to an environment in which a nausea-inducing body rotation will subsequently be given constitutes a latent inhibition procedure that might act to reduce anticipatory and postrotation nausea.
This was tested in 24 healthy subjects randomly assigned to receive no pre-exposure (group 0), a single pre-exposure (group 1), or three pre-exposures (group 3). Rotation was standardized as 5 × 1 minute rotation, but the subjects could terminate it on request. Nausea was determined on a 7-item symptom rating scale before, during, and after rotation on days 3 and 4, whereas anticipatory nausea was measured before presumed rotation on day 5. Saliva cortisol and tumor necrosis factor α (TNF-α) levels were determined at baseline before, directly, and 15 and 30 minutes after rotation every day, and before presumed rotation on day 5.
Pre-exposure significantly reduced the degree of anticipatory nausea on day 5. Cortisol levels increased with rotation and were higher at baseline on days 4 and 5, but subjects habituated from day 3 to day 4; levels were lower in women than in men. In contrast, TNF-α decreased with rotation but showed no habituation. For both cortisol and TNF-α, no effects on postrotational nausea were found.
It is concluded that repetitive pre-exposure (latent inhibition) reduces anticipatory but not postrotation nausea; behavioral measures (rotation time) and measures of acute stress (cortisol, TNF-α) do not respond to latent inhibition. Thus, Pavlovian conditioning rules are effective in healthy humans with anticipatory nausea but not with postrotation nausea. Hormonal responses—TNF-α decrease with stress, compensatory cortisol increase—and gender-related effects on learning and habituation are discussed with regard to psychophysiological and psychoimmunological processes.
AN = anticipatory nausea;
CS = conditioned stimulus;
US = unconditioned stimulus;
CR = conditioned response;
PN = posttreatment nausea;
UR = unconditioned response;
TNF-α = tumor necrosis factor α;
RT = rotation tolerance;
MSSQ = motion sickness susceptibility questionnaire;
SR = symptom rating;
ANOVA = analysis of variance.