Inclusion Criteria:  18 to 55 years of age, inclusive. Diagnosis or symptoms of Irritable Bowel Syndrome (IBS) meeting ROME IV diagnostic criteria for IBS (all sub-types). Must be absent of red flags including unexplained weight loss, fevers, anemia or blood in stools. Females must be premenopausal menstruating females. If female and of childbearing potential must be not pregnant, post-partum or breast feeding for at least 6 months. Must have a negative urine test for pregnancy. Must be willing to avoid pregnancy and practice a non-hormonal birth control method such as abstinence, non-hormonal IUD's, or barrier method with spermicide, during the time of study enrollment. Subjects who are on hormonal based birth control (e.g OCP's or implants) will be allowed in the study as long as they still get a monthly menses so menstrual phase can be identified using ovulation kits. Ambulatory outpatient (not depending exclusively on a wheelchair for mobility) Ability to speak the English language fluently due to the standardized assessments involved.  Exclusion Criteria:  Evidence of structural abnormality of the gastrointestinal tract. Exclusionary GI conditions include but are not limited to gastrointestinal surgery (exceptions: appendectomy, benign polypectomy, cholecystectomy). Presence of a significant and ongoing medical problem that would interfere with participation in the study or testing the study hypotheses (e.g., major heart disease, neurological disorders, inflammatory diseases such as IBD; esophagitis, celiac disease, gastrointestinal malignancy or obstruction, peptic, duodenal or gastric ulcer disease, etc.). Malignancy (other than localized skin cancer that has been resected) within the previous 5 years. Presence of a major psychiatric diagnosis such as schizophrenia, Bipolar disorder, current ADD diagnosis, Post-traumatic Stress Disorder, Obsessive Compulsive disorder or current history of tobacco or alcohol abuse. Subjects with a history of DSMIV diagnosis of Anxiety or Depression in whom symptoms are not active, will be allowed but noted for post-hoc analysis. Use of investigational drugs, products or devices within 28 days prior to screen and through study participation. Subjects with current regular use of narcotics and or opioids. Use of centrally acting medications that will interfere with the neuroimaging testing (such as systemic steroids, opiate analgesics). Medications which alter GI motility and gastric pH will need to be stopped at least 72 hours prior to any physiologic test visit and during the baseline and treatment intervention. For this we will ask the subject to get approval from their own PCP to stop prior to any intervention. However, rescue medication of bisacodyl and loperamide will be allowed for prolonged constipation and diarrhea, respectively, during intervention periods but not during baseline or within 3 days of follow up MRI. For rescue medication, such as laxatives or antidiarrheal, we will ask to hold off use up to 3 days prior to collecting stool sample. Obesity (BMI >35) Subjects with claustrophobia, metal implants, dental braces, large tattoos (e.g. full arm or back); making MRI safety not possible. History of heavy use of tobacco products or current use of more than 1/3 ppd. Plans to undergo a major medical intervention such a surgery within 6 months of enrollment or during the study, or had major surgery in last 6 months. Current or past history of chronic pain syndrome other than IBS in the IBS group (pain >6 months at any location). Use of antibiotics or probiotics within 3 months of the study enrollment or regular use of probiotics within 4 weeks of enrollment. (enrollment may be deferred) Subjects who currently actively practice CBT or have completed a CBT therapy within 2 years prior to enrolling. Must must have a score of ≥175 (at least moderate severity IBS) on the IB-SSS symptom severity scale completed at screening. Have an average abdominal pain of at least 3 on a 0-10 point scale where 0=no pain and 10=worst imaginable pain.  Any other condition that the investigator believes would jeopardize the safety or rights of the subject or would render the subject unable to comply with the study protocol or make use of acquired data non-analyzable.  -