Figure 2.

Psychophysical data of painful (A) and warm (B) trials. Illustrated are the temperature courses in blue, averaged across trials and participants, and the VAS ratings, equally averaged across trials and participants, in red. For better illustration, we downsampled the displayed data (interval length = 250 ms) and do not display the temperature rise in the beginning of the trial; that is, illustrated are the 20 s after reaching the target temperature. Gray ribbons represent the SEM. Because increasing ratings at the beginning of the uncontrollable trials do not reflect sensitization (the subjects needed time to adjust their rating after the thermode had reached the target temperature), the first 4 s of the uncontrollable trials were excluded. The red bars indicate the time segment that was included in the comparison of intensity ratings between end and beginning of the trial, as well as as pain-rating regressors in the fMRI analysis of the uncontrollable trials (see Materials and Methods). The red dotted line depicts the “just painful” anchor of the VAS. The blue dotted line marks habituation (values >0) and sensitization behavior (values <0) for the controllable trials. The initial variations in temperature were due to fluctuations of the thermode.