Pain intensity ratings and placebo and nocebo effects during calibration and test sessions.

(A) Mean pain intensity ratings in the placebo, nocebo and control condition during calibration, and during the test sessions at day 1 and day 8. (B) Placebo effect (control condition vs placebo condition) and nocebo effect (nocebo condition vs control condition) on day 1 and day 8. Error bars indicate the standard error of the mean, circles indicate mean ratings of individual participants. ***: p< .001, **: p< .01, n.s.: non-significant.

Mean and trial-by-trial pain intensity ratings, placebo and nocebo effects during conditioning.

(A) Mean pain intensity ratings of the placebo, nocebo and control condition during conditioning. (B) Placebo effect (control condition vs. placebo condition) and nocebo effect (nocebo condition vs control condition) during conditioning. (C) Trial-by-trial pain intensity ratings (with confidence intervals) during conditioning. Error bars indicate the standard error of the mean, circles indicate mean ratings of individual participants. ***: p< .001.

Expectancy ratings obtained before conditioning and before the test sessions on day 1 and day 8.

Expectations were assessed using the Generic Rating Scale for Previous Treatment Experiences, Treatment Expectations, and Treatment Effects (GEEE, Rief et al., 2021). The expected pain relief was derived from the item asking how much improvement the participant expected from the treatment on a 10-point Likert-scale from 0 (= no improvement) to 10 (= greatest improvement imaginable). Analogously, the expected pain increase (nocebo effect) was taken from the item asking how much worsening of pain they expected from the treatment from 0 (= no worsening) to 10 (= greatest worsening imaginable). Black diamond shapes indicate the mean and circles the individual scores. ***: p< .001, **: p< .01, * p< .05, n.s.: non-significant

Study and trial design.

(A) Study design: On day 1, participants underwent a conditioning procedure in which a noxious heat was applied directly after a (sham) TENS stimulation in three conditions. In the placebo condition (PLC), the thermal stimulation was lowered to VAS 40, in the nocebo condition (NOC), it was increased to VAS 80 and in the control condition (CTR) it remained unchanged (VAS 60). During the two tests on day 1 and day 8, the same moderate stimulation intensity of VAS 60 was applied in all three conditions. (B) Position of the electrode on the inner lower left arm for (sham) TENS stimulation (approximately 2.5 cm above the wrist) and the thermode at three possible locations (approximately, 3.5 cm above the electrode with a distance of 0.5 cm between each of the three locations. (C) Trial design: Following the presentation of a visual cue to indicate the condition (e.g., green cross for the placebo condition), first the sham TENS stimulation and then the heat stimulus were applied before participants rated the pain intensity on a visual analogue scale.