Role of abnormal central processing of pain
Abnormal central processing, such as down-regulation of incoming visceral sensations, has also been found in patients with IBS. In IBS patients, rectal distention fails to activate the perigenual anterior cingulated cortex (ACC), the area containing large amounts of B-endorphin activity, which may serve to down-regulate pain, but instead shows increased activation of the rostral ACC, an area associated with unpleasantness and attention. Also, patients with IBS and a history of abuse reported greater activation of the middle and posterior dorsal cingulate regions, and reduced activity of the supragenual anterior cingulate, and are implicated in pain inhibition and arousal. Therefore IBS patients may have an alteration of the pain modulatory system, as well as up-regulation of afferent signals at the primary splanchnic afferent or its spinal connections.