Fig. 2.

Mean and standard deviation of pain ratings (0–10 pain scale) during the placebo and control sessions. The same laser energy was applied in the pre-conditioning and post-conditioning blocks in both sessions, set at each individual’s moderately painful level. Mean rating during the placebo session: pre-conditioning 4.82 (0.77), conditioning 2.09 (0.69), post-conditioning 3.77 (1.29), and during the control session: preconditioning 4.68 (0.76), conditioning 2.19 (0.70), post-conditioning 4.26 (1.03).