Figure 1.

Schematic drawings of the rectal distension protocols. (a) In Cohort 1, an AML protocol was used with phasic distensions of 30-second durations, separated by 30-second rest intervals with the balloon at the OP. At each distension step, the participants rated their perceived rectal sensation and indicated their painful sensations on a body map (indicated on both front and back of the body, with only the frontal image shown here). Arrows indicate sensory thresholds. (b) In Cohort 2, an AML protocol with step-wise successive increase in distension level was completed to assess sensory thresholds. After a resting period at OP, random phasic distensions at 12, 24, 36 and 48 mmHg above OP were performed during which participants scored intensity ratings for pain on a visual analog scale. AML: ascending method of limits; OP: operating pressure.