Gender and the nocebo response following conditioning and expectancy.

OBJECTIVE: To investigate the role of Pavlovian conditioning and expectancy and of gender on the nocebo effects. METHODS: Conditioning experiment: Forty-eight healthy male and female volunteers were investigated for 3 days using a standard rotation procedure. Subjects in the experimental group received a salient oral stimulus prior to rotation; subjects in the control group received the stimulus 12 h after rotations on Days 1 and 2; on Day 3, all subjects received the stimulus prior to rotation. Expectancy experiment: Another 48 healthy subjects were rotated 5 x 1 min once only. All subjects received the same oral stimulus immediately prior to rotation; subjects in the experimental group were told that the symptoms might worsen with the stimulus; controls did not receive additional information. In both experiments, symptom rating (SR) and rotation tolerance (RT) were determined. RESULTS: Conditioning significantly reduced RT (P=.015) and increased SR (P=.024). For both RT and SR, a significant "day x group x gender" effect was found (P=.044; SR: P=.011) indicating that conditioning was more effective in women. Expectancies lowered RT (P=.085) without affecting SR. There was a significant "rotation x gender" interaction on RT (P=.005) indicating that the expectancy was more effective in men. CONCLUSION: Women responded stronger to conditioning while men responded to expectancies, but to a lesser degree. It needs to be determined whether this is restricted to nausea-specific conditions or can be generalized across clinical and experimental conditions.

Nausea induced by vection drum: contributions of body position, visual pattern, and gender.

INTRODUCTION: The purpose of this work was to investigate intrinsic (gender) and extrinsic factors (body position, visual pattern) and their relative contribution to the development of motion sickness during pseudo-rotation. METHODS: A series of 3 experiments with 24, 12, and 48 subjects respectively, balanced for gender, was completed: Experiment 1 investigated the effect of body position (upright, supine) and gender; Experiment 2 investigated the additional influence of the visual pattern (dots, stripes), but only for the supine position; and Experiment 3 investigated the complex interaction of gender, body position, and visual pattern on symptom rating (SR), rotation tolerance (RT), and time to first perception of vection (VT). A novel vection drum that allowed varied body positions and visual patterns was used to create pseudo-rotation. RESULTS: Experiment 1: there was a significant effect of rotation on SR, and a significant rotation x position interaction such that the rotation-induced symptom increase was significantly higher in the supine compared to the upright position. In addition, there was a significant effect of gender, with women showing lower SR in both positions. RT was lower while supine compared to upright; this effect was significantly more pronounced in male subjects. Experiment 2: a significant effect of rotation on SR was found, but no effect of the visual stimulus pattern or gender on SR, RT, or VT. Women exhibited significantly lower VT than men. Experiment 3: rotation induced a significant increase in SR independent of gender, body position, and visual pattern. Supine position induced significantly higher SR and RT than upright, and a significant interaction between gender, body position, and visual pattern. CONCLUSION: The complex interaction of intrinsic and extrinsic factors may partially explain the mixed findings in the literature regarding the relationship of gender to motion sickness.

Gender and race as determinants of nausea induced by circular vection.

BACKGROUND: Within- and between-subject variability of susceptibility for motion sickness is well established, but which factors determine susceptibility is less well known. OBJECTIVE: We investigated whether and to what degree sex, race, and head movements contribute to the development of nausea and vomiting (N&V) during pseudorotation in a vection drum in healthy participants. METHODS: Male and female, Chinese and white subjects were exposed to 5x1 minute of circular vection in a conventional rotation drum, with half of the participants performing nausea-enforcing head movements. The symptom ratings (SR) at baseline and after stimulation, the time to perception of illusory self-motion (vection), and the total rotation tolerance (RT) were noted and compared between groups using a 2x2x2 analysis of variance. RESULTS: A total of 48 healthy young adults (24 Chinese, 24 white; 12 males, 12 females in each group) screened for susceptibility to develop motion sickness participated in this study. SR at baseline and after rotation were significantly lower in Chinese compared with white subjects (for baseline SR: F=20.04, P<0.001; for maximal SR: F=7.09, P=0.011). Vection was equal between both groups, with no effects of gender or head movements. Rotation tolerance was significantly shortened for Chinese compared with white participants (mean [SEM], 216.5 [15.4] sec vs 262.6 [11.3] sec, respectively; F=7.21, P=0.011), with independent influence of head movements (F=8.84, P=0.005) but not of gender. CONCLUSIONS: In this study, the strongest intrinsic factor that contributed to N&V during circular vection was racial origin, whereas sex played a minor role in the degree of N&V under the conditions studied. Head movement-induced vestibular stimulation was a further contributing factor.

Effects of ethnicity and gender on motion sickness susceptibility.

INTRODUCTION: Susceptibility to motion sickness (MS) is known to be affected by gender and ethnic origin, but whether gender and ethnicity are interacting is unknown. METHODS: We investigated MS development in healthy Caucasian subjects (n = 227), and in subjects of Chinese origin (n = 82). All subjects were exposed to nausea-inducing body rotations in a rotation chair, and rotated around the yaw axis for 5 x 1 min, while they were instructed to move their heads. Prior to rotation, subjects had to fill out a motion-sickness susceptibility questionnaire (MSSQ). Total rotation tolerance time (RT) was noted. Symptom ratings (SR) were performed at the beginning, and immediately after the end of each rotation, and 15 and 30 min later. RESULTS: The average RT was significantly higher in Caucasian (163 +/- 6 s) than in Chinese subjects (111 +/- 7 s) (F = 24.84, p < 0.0001). The adult MSSQ score was significantly lower in Caucasians (17.8 +/- 1.1) than in Chinese volunteers (24.2 +/- 2.1) (F = 6.05, p = 0.014). Maximal SR post rotation was similar in Chinese and Caucasian subjects. RT was highly predictable from the MSSQ scores, but separate for both genders. CONCLUSION: Susceptibility to MS is affected by both ethnic origin and by gender in a rather complex fashion. The most reliable prediction of RT can be based on the individual's history as assessed by the MSSQ.

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.