Abdominal pain is a central symptom of Inflammatory Bowel Disease (IBD) and Irritable Bowel Syndrome (IBS). IBD is an autoimmune disease characterized by inflammation of the gastrointestinal tract. IBS does not have clear biomarkers and is diagnosed based on symptom reports. The aim of this study is to explore biopsychosocial factors which may perpetuate and/or increase the severity of pain in these conditions. The main focus will be on the role of top-down brain processes in the experience of abdominal pain.

It remains unclear why a large proportion of people with inflammatory bowel disease (IBD) report ongoing abdominal pain during remission or why people with irritable bowel syndrome (IBS) develop abdominal pain. One theory is that people with chronic pain have somehow grown more sensitive.

It is assumed that such heightened sensitivity depends both on bottom-up processing and top-down processing. Bottom-up processing refers to information that is relayed to the brain along so-called afferent fibres. Top-down processing refers to feedback provided by the brain to lower areas along efferent fibres.

The investigators will (1) measure the capacity of people to inhibit pain through top-down processing, (2) test if the human pain experience is enhanced due to sustained activation of certain afferents, and (3) assess to what extent people are impacted by psychosocial inhibition and activation factors. Results of people with IBS in remission will be compared with the results of two groups of people with IBD (those with pain and those without) and the investigators will explore if their measurements differentiate between groups.

It is hypothesized that (1) IBS patients and IBD patients with abdominal pain will be less able to inhibit their pain compared to IBD patients without abdominal pain (2) IBS patients and IBD patients with abdominal pain will score higher on psychosocial inhibition factors and lower on psychosocial activation factors when compared to IBD patients without abdominal pain. (3) In the total cohort, laboratory measures of pain inhibition will correlate with self-reported psychosocial inhibition and activation factors. (4) IBS patients and IBD patients with abdominal pain will show more temporal summation compared to IBD patients without abdominal pain.

General inclusion criteria:

• Aged 18 and over
• Sufficient command of written and spoken English

IBD in remission inclusion criteria:

• Proof of diagnosis of IBD (Crohn's disease or ulcerative colitis) for more than 6 months - - Clear indicators of remission: on faecal calprotectin (≤200 µg/g) or measurements of C-reactive protein (CRP; ≤10 mg/dl) within the last 3 months or as part of recruitment
• No previous episodes of acute or sub-acute obstruction

IBS inclusion criteria:

• Current diagnosis of IBS measured with Rome IV criteria
• No serious other bowel diseases

Exclusion criteria:

• Major abdominal surgery in the last 6 months, or 3 or more previous major abdominal surgeries
• Pregnancy or childbirth in the last 6 months
• Any other diagnosed medical condition that may explain abdominal pain, including but not limited to known gynaecological conditions such as endometriosis and known post-surgical adhesions
• Any diagnosed co-morbid medical conditions associated with known neuropathy, such as diabetic neuropathy, renal neuropathy, multiple sclerosis
• Use of opioids in the last week
• Use of anti-depressants used as pain medication in the last month

Patients with quiescent Inflammatory Bowel Disease or Irritable Bowel Syndrome