Nocebo Induction: Nocebo Conditioning in Part 1
pain
All participants were given open-label instructions about nocebo effects and how they can be induced by the principles of classic conditioning. They were informed that a sham nerve stimulator, called DNS, would be used for conditioning them to expect pain increase. This would be achieved by administering a moderately painful pressure stimulus to the thumb nail during the sham activation of the DNS device, but in fact, the DNS device would not send any electrical signals. The electrodes would remain attached to the arm to mimic the administration of electrical signals, similar to the act of swallowing a placebo pill even when knowing it does not contain any active components. During the 20 trials of the learning phase, participants were conditioned to expect a pain increase in half of the trials, hereafter referred to as experimental trials. For this, the text “DNS on” appeared on the screen 1 second before receiving a moderately painful pressure stimulus, and the experimenter pressed a button on the DNS to evoke a beep sound to indicate its sham activation. In the other half of the trials, that is, the control trials, “DNS off” appeared on the screen, and a slightly painful pressure stimulus was administered. Directly after the learning phase trials, the testing phase followed. During the testing phase, 3 trials were associated with “DNS on” and 3 trials with “DNS off”, where this time, both DNS conditions were paired with only slightly painful pressure stimuli. Participants were not informed during the open-label instructions that they would be receiving only slightly painful pressure stimuli during the testing phase.