Neural Substrates of Decision Making in Irritable Bowel Syndrome

Aim: Patients with irritable bowel syndrome (IBS) show exaggerated sensorimotor function of the gastrointestinal tract against stress. However, emotion-cognition sequence of IBS is largely unknown. The emotional experience begins from the unconscious level and “gut feelings” may be used as somatic marker that guides decision making (Bechara, A, et al Science 1997). We hypothesized that brain processing in individuals with IBS, during decision making, is different from that of healthy controls, due to increased activity of the insula and ventromedial prefrontal cortex (vmPFC) and altered connectivity among brain regions. Methods: Subjects were individuals with IBS (n=30, 15 men and 15 women, aged 21.5 ± 2.2) diagnosed with Rome III criteria. IBS subtypes were 8 constipation, 14 diarrhea, and 8mixed. Age-, sex-, and education-matched controls (n = 30) were compared. All subjects scored Wechsler Adult Intelligence Scale-III (WAIS-III). Using PHILIPS 3.0T Scanner, eventrelated functional magnetic resonance imaging (fMRI) was performed to determine the specific location and pattern of activation in the brain during the IOWA Gambling Task (IGT). Subjects must select 100 cards, one at a time, from 4 identical-looking decks, labelled A, B, C, and D. We obtained behavioural data, which entailed the number of selections from ‘advantageous’ (card C and D) vs. ‘disadvantageous’ (card A and B) decks during the IGT. We counted the total number of card selections from the advantageous minus disadvantageous ((C + D)-(A +B)) decks for each block of 20 cards. This is net score. Decision-making reaction times were also examined. Each time a card was selected, the participant received a monetary reward. During the control task, subjects were presented with 4 decks of cards labeled E, F, G and H, and were instructed to pick a card from a specific deck. Brain image was analyzed with statistical parametric mapping 8. We compared BOLD activity of the two groups during card selection in the decision-making and control task. Results: IBS subjects showed no difference in WAIS-III, reaction time and net scores. IBS subjects had significantly more one of advantageous card selections (p < 0.05) and gaining money (p < 0.05). Brain imaging data revealed that IBS subjects showed significantly less activity in the left anterior insula (p < 0.005) and significantly more activity in the right vmPFC (p < 0.005) during decision making conditions than controls. Conclusion: Conversely to visceral stimulation-induced insular activation, insula in IBS subjects is likely to be inactivated during decision making task. These findings suggest that individuals with IBS show advantageous decision making due to more activity of vmPFC.