Inclusion Criteria:

IBS patients:

• One hundred fifty male and female IBS patients (Rome III criteria), aged 18 to 70 years, recruited from primary and secondary care via advertisements and referral networks.
• Minimum IBS symptom rating of 75 in IBS severity scoring system (IBS-SSS) in last two weeks.
• IBS discomfort or pain must have been patient's most prominent symptom.
• A minimum of 40 patients each IBS-constipated (IBS-C) and IBS-diarrhoeic (IBS-D) (Rome III) to be included.
• Patients must have been off all IBS and analgesic medication and any drugs potentially influencing sensory function for at least two weeks before study start.

Healthy controls:

• Fifteen healthy controls aged 18 to 70 years without any gastrointestinal pathology or history of significant abdominal pain, bowel disorders, bloating or discomfort during the last 3 months.

Exclusion Criteria:

Exclusion criteria for both IBS patients and healthy controls:

• Organic gastrointestinal or other significant systemic disease, including cardiovascular, psychiatric, neurological and endocrine diseases, as judged by investigator
• Chronic or acute pain, except related to other functional syndromes (functional dyspepsia, chronic pelvic pain, fibromyalgia, migrane)
• Bowel resections (except appendectomy)
• Multiple abdominal operations, excluding hysterectomy
• History of brain disease or brain surgery
• Ongoing treatment with any anticoagulants, antidiabetics, antimigraine drugs, antispasmodics, analgesics, psychoactive agents including antidepressants, Zelmac®, TCM or acupuncture for IBS and any drugs affecting nociception as judged by investigator within last 14 days
• Treatment with any investigational drug during the preceding 30 days
• Pregnancy or lactation.
• Claustrophobia
• Metal implants in body (fMRI exclusion criterion)
• No written informed consent obtained from subject