Fig. 1. Experimental procedure. Ant = anticipation; 45 = 45-mm Hg rectal balloon distension; sigmoid stimulation = repeated 30-second, 60-mm Hg inflations of sigmoid balloon. Horizontal axis and width of bars are drawn to represent relative times involved (eg, 1-minute rectal stimuli followed by 10 minutes of rest before next trial). Balloon insertion and 30-minute rest period before first scan is not shown.

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