Gender and the nocebo response following conditioning and expectancy

To investigate the role of Pavlovian conditioning and expectancy and of gender on the nocebo effects.

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.

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.

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.