Chapter 5 – Experimental fear 155 procedure during which they felt a light electrical pulse. This pulse was delivered in order to increase the credibility of the nocebo manipulation. The device was not actually activated during conditioning, but messages displayed on a computer screen via E-Prime 2.0 (Psychology Software Tools, Pittsburgh, PA, USA) signaled the sham activation (conditioned stimulus) of the electrical stimulation during nocebo trials. Negative suggestions indicated to all participants that when the messages “on” (in purple font; nocebo conditioned stimulus) and “off” (in yellow font; control stimulus) were displayed, their pain would be aggravated or not altered, respectively. In the acquisition phase, the activation of sham electrical stimulation was repeatedly paired with increased pain stimulation during the 12 nocebo trials, while the 12 control trials were paired with lower pain stimulation. This is in line with previous nocebo studies 5,27 implementing classical conditioning for the experimental induction of nocebo hyperalgesia. In the extinction phase, both nocebo and control cues were paired with the same lower intensity pain stimulation. Extinction was also in line with previous studies and served to attenuate induced nocebo responses. Fear inductions While all groups received nocebo suggestions, the High-pain and Highthreat groups were exposed to additional fear-inducing manipulations. Pain intensity manipulation The High-pain group received higher pain during nocebo acquisition and extinction (2-3 points higher on the NRS), which was intended to increase participants’ pain-related fear, especially on nocebo trials.
RkJQdWJsaXNoZXIy MTk4NDMw