Anticipatory brain activity in irritable bowel syndrome.

Editor's Note: These short reviews of a recent paper in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to mimic the journal clubs that exist in your own departments or institutions. For more information on the format and purpose of the Journal Club, please see Review of Berman et al. Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders. It is considered a chronic functional disorder because of the lack of an identifiable structural or biochemical basis. However , functional brain imaging studies have identified abnormal brain responses to visceral stimuli (such as rectal disten-tion) in IBS patients (for review, see Ohman and Simren, 2007), suggesting that IBS involves a dysregulation of the communication between the central and enteric nervous systems. Furthermore, patients suffering from functional pain disorders often show symptom-related anxiety, and this may affect their ability to anticipate and cope with impending pain stimuli. Therefore, expectation-related brain responses to potentially painful stimuli may contribute to IBS symptoms. A recent study by Berman et al. (2008) suggests that IBS patients have a deficit in corticolimbic inhibition, and this may be associated with symptom-related anxiety and hypervigilance. The authors propose a mechanism through which deficient coping mechanisms lead to dysfunctional homeostatic and motivational–affective processing of expected and actual visceral sensations. Normally, a homeostatic af-ferent processing network is downregu-lated during anticipation, and an antino-ciceptive network is activated during stimulus delivery, which leads to a higher pain threshold. The former network includes areas such as insula, anterior cingu-late, amygdala, and dorsal brainstem, whereas the latter network involves the right lateral orbital frontal cortex and su-pragenual anterior cingulate cortex (ACC). Using a cued rectal distention stimulus paradigm, brain activity was examined under six conditions: rest, cue, mild/mod-erate/sham rectal distention, and rating. Compared with controls, IBS patients showed less anticipatory inactivation of the homeostatic afferent processing network , and more extensive increases in dorsal ACC and brainstem activity during distention [Berman et al. showed that less anticipatory inactivation of specific brainstem areas, the locus cer-uleus complex and parabrachial nucleus, correlated with lower discomfort thresholds , higher negative affect, and greater activation of bilateral rostral ACC and right lateral orbital frontal cortex during rectal distention. The authors concluded that higher anxiety in IBS patients leads to overactivity in the arousal circuit and thereby failure to trigger coping mechanisms during anticipation of pain via cor-ticolimbic inhibition. Although the interpretation …