Latent inhibition of rotation chair-induced nausea in healthy male and female volunteers.

OBJECTIVES 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. METHODS 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 x 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 alpha (TNF-alpha) levels were determined at baseline before, directly, and 15 and 30 minutes after rotation every day, and before presumed rotation on day 5. RESULTS 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-alpha decreased with rotation but showed no habituation. For both cortisol and TNF-alpha, no effects on postrotational nausea were found. CONCLUSION 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-alpha) 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-alpha decrease with stress, compensatory cortisol increase--and gender-related effects on learning and habituation are discussed with regard to psychophysiological and psychoimmunological processes.