FYIIRRITABLE BOWEL SYNDROME: ALTEREDNEUROLOGICAL ACTIVITY Irritable bowel syndrome (IBS) is a common disorder ofthe intestines that leads to pain, intestinal gas, bloating,and changes in bowel habits. People with IBS mayhave constipation or diarrhea and some people experienceboth. Other symptoms include the urge to movethe bowels but an inability to do so. The cause of IBS isnot known, and as yet there is no cure. IBS is classified asa functional disorder because there is no sign of diseasewhen the colon is examined. Although it does not causepermanent harm to the intestines and does not lead tointestinal bleeding of the bowel or to a serious diseasesuch as cancer, IBS patients suffer a great deal of discomfortand distress.The underlying physiologic cause of IBS is unknown.Ordinary events such as eating and distention from gas orother material in the colon can cause the colon to overreactin a person with IBS. Individuals with IBS seem tohave a colon that is more reactive and sensitive thanusual, so it responds strongly to stimuli that would notbother most people. Researchers have found that thecolon muscle of a person with IBS begins to spasm afteronly mild stimulation. Stress may also be a factor in themanifestation of disease symptoms.Patients with IBS also seem to have an enhanced awarenessof and sensitivity to normal gastrointestinal events,such as muscle contractions and the filling of the viscerafollowing a meal. This has led some researchers to speculatethat when the brains of persons with IBS receiveinformation from the visceral nerves in the intestines,they may process the information differently than personswithout IBS.To examine the possible role of information processingby the brain in causing IBS, researchers studied brainactivity in affected patients. In the experiment, the scientistsrecruited twelve people with IBS, as well as twelvehealthy volunteers, and inserted a catheter through therectum and into the volunteersï¿½ colons. Each cathetercontained two small balloons along its length that couldbe inflated to a precise pressure by the researchers.Inflation of balloons of this size is designed to producemild discomfort, but no serious pain or tissue damage.After the catheters were inserted and the patients had abrief recovery period, the researchers initiated a PositronEmission Tomography (PET) scan of the patientsï¿½ brains.This scan permitted researchers to see relative rates ofmetabolism based on energy usage and blood flow within specific regions of the brain. The researchers theninitiated a three-part experimental phase, in which theytold patients that the balloons would or would not beinflated, but did not consistently inflate the balloons inthe manner stated. This experimental design allowed theresearchers to see responses to no inflation phase 1, anexpected and delivered inflation phase 2, and anexpected but undelivered inflation phase 3. During thisprocedure brain activity was monitored by PET scans.When the scientists analyzed the data generated by thePET scans, they found significant similarities between thenormal and IBS patients, but also noted important differences.Brain regions activated by actual and simulatedballoon inflations were similar in both groups; however,differences in three important areas of the brain could bedetected. First, patients with IBS exhibited enhanced activationof right prefrontal cortex in response to actual orexpected balloon inflation, whereas in normal patients,both sides of the brain reacted to a similar extent. Thisregion of the brain is thought to be very important forhigher cognitive functions, including concentration andjudgment. Second, within the anterior cingulate an areadeep within the brain thought to be involved in emotionssuch as sadness an enhanced reaction was seen in IBSpatients in a sub-region associated with the perception ofpain and unpleasantness. Third, the IBS patients demon-stratedan overall decreased activation of circuits in thebrain believed to activate fear and defense responses.All three of these observations indicate that IBSpatients show altered brain responses to rectal stimuli,regardless of whether these stimuli are actually deliveredor simply anticipated. This study provides solid evidenceof altered brain activity in patients suffering with this syndrome that is of unknown origin. To help fostermore research into the causes of IBS and its possibletreatmentsthe NIDDK is working with members of theIBS community to develop a conference on the topic offecal and urinary incontinence that is relevant to many ofthe quality of life issues that have an impact on peoplewith IBS.Naliboff BD, Derbyshire SWG, Munakata J, Berman S,Mandelkern M, Chang L, Mayer EA. Cerebral activation inpatients with irritable bowel syndrome and control subjectsduring rectosigmoid stimulation. Psychosomatic Med 63 3:365-375, 2001.