Fig. 2

Time course of pain perception evoked by repetitive painful stimuli of the hand before (1st to 15th), during (16th to 30th), and after (31st to 45th) application of non-painful (in yellow) or painful (in green) conditioning thermal stimulation on the contralateral foot in (A) control subjects and (B) burning mouth syndrome patients. To assess CPM, blocks of 4 thermal test stimuli (Nd:YAP laser stimulator) were delivered at 0.2 Hz on the back of the non-dominant hand, repeated every 40 s for 30 min, at an intensity producing a pain intensity between 3–6 on 0–10 VAS. Between the 10th and 20th min (16th to 30th), the contralateral foot was immersed into a water bath at non-painful (30 °C) or painful cold (8 °C) temperature. A linear mixed model was used to explore the effects of CPM. P values indicate the differences between the non-painful and painful conditioning thermal stimulation