Chapter 4 – Experimental learning 117 Nocebo treatment A commercial Transcutaneous Electrical Nerve Stimulation (TENS) device (Beurer EM 80) was used to serve as the nocebo treatment in the procedure. Negative suggestions were used to create expectations regarding the pain enhancing effects of the device (Appendix 1). Two TENS electrodes were placed in a diagonal line on the ball of the hand and the inner elbow. Prior to the start of the induction phase, participants underwent a short mock calibration procedure during which they felt a light electrical pulse of the TENS. This pulse was delivered in order to increase the believability of the nocebo verbal suggestion. Participants were told that the device was called “ENS”, to avoid that participants would recognize or associate any prior experience with this device. The device was not actually activated during the conditioning procedure, but messages displayed on a computer screen via E-Prime 2.0 (Psychology Software Tools, Pittsburgh, PA, USA) signaled the sham activation and deactivation of the TENS device during nocebo and control trials, respectively. As part of the nocebo suggestions, participants read an information sheet (see Appendix 1), displayed on a tablet, containing (sham) information regarding the supposed effects of the TENS treatment. During nocebo induction, negative suggestions indicated to all participants that when the messages “ENS on” (in purple font; nocebo cue) and “ENS off” (in yellow font; control cue) were displayed, their pain would be aggravated or not altered, respectively. Sham TENS activation was paired to surreptitiously increased pain stimulation during nocebo trials, while moderate pain was delivered during control trials during the induction phase. For the partial reinforcement groups, the activation of the TENS device was paired with high pain stimuli in only 70% of nocebo trials (un-paired trials were
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