Fig. 3. The three upper plots display the average change of the heat pain threshold from baseline (± SEM) versus time at the lumbar (L4), thoracic (T10), and trigeminal (V2) dermatome after epidural administration of morphine and saline placebo, respectively. The three lower plots display corresponding results for the heat pain tolerance. The area under the curve (pain threshold/tolerance vs. time) was significantly different between morphine and saline placebo treatments at L4 and T10 when measuring the heat pain threshold. The area under the curve was significantly different at all three dermatomes when measuring the heat pain tolerance (P < 0.017, paired t test or Wilcoxon signed rank test with Bonferroni correction). Times at which morphine and saline placebo treatments were significantly different are marked with an asterisk (P < 0.0,125, paired t test or Wilcoxon signed rank test with Bonferroni correction).