Figure 1

Study protocol. (A,B) Noxious thermal stimulation (44.5 °C, 15 s, 5 times) was applied to participants in practice. Following those practice phase, noxious thermal stimulation (44.5 °C, 15 s) in the control condition was repeated ten times during fMRI scanning. (C) The thermode temperature in the conditioning session of the placebo condition was surreptitiously reduced from 44.5 to 43.7 °C for weak placebo conditioning (negative experience group) and to 40.0 °C for strong placebo conditioning (positive experience group). Following the weak and strong placebo conditioning sessions, participants in the negative and positive experience groups again received noxious stimulation in the placebo condition during fMRI scanning. After the pain perception experiment in the control and placebo conditions, participants received noxious thermal stimulation in the cold-pack condition during fMRI scanning. Therefore, participants in the positive and negative experience groups received noxious stimulation under three conditions: (1) control, (2) placebo, and (3) cold-pack. The total intensity and duration of noxious stimuli during fMRI scanning were identical in each of the three conditions.