UCLA researchers found that women with IBS cannot effectively turn-off a pain modulation mechanism in the brain, which causes them to be more sensitive to abdominal pain, compared to women without IBS.
The findings, appearing in the January 9 issue of the Journal of Neuroscience, may lead to a greater understanding of irritable bowel syndrome and new treatment approaches.
Irritable bowel syndrome affects 10 to 15 percent of the U.S. population and causes discomfort in the abdomen, along with diarrhea and/or constipation. Currently there is no cure and treatments only lessen symptoms.
“A large number of patients with irritable bowel disease suffer major decrements in their quality of life,” said Dr. Emeran Mayer, study author and professor of medicine, digestive diseases and physiology, David Geffen School of Medicine at UCLA.. “Our research team studies the brain activity underlying the pain experience in patients with chronic pain disorders like IBS.”
Previous research in the field has shown that the brain can prepare for pain in ways that either inhibit or amplify the sensory experience. When expected pain is predictable, tolerable, inescapable and will result in a reward -- like a doctor's injection to improve your health -- most people tell their brain to inhibit the intensity of the pain experience. One way they do this is by turning down the gain within brain circuits that process the pain signal --- similar to turning down the volume on a stereo amplifier -- in order to make the body's perception of pain less acute.
When anticipated pain is perceived as escapable and potentially dangerous – such as burning your hand on a hot stove – most people tell their brain to amplify the pain response, which is like increasing the volume on a stereo amplifier, in order to react faster and minimize possible tissue damage.
The current study showed that IBS patients cannot turn down the amplifier of the pain response, even when expected pain is not dangerous, which makes them more sensitive to even mild discomfort.
UCLA researchers used functional magnetic resonance imaging (fMRI) to record brain activity of 14 women with IBS and 12 healthy women during cued anticipation and mild abdominal pain stimulus.
During anticipation of pain, subjects without IBS decreased activity within brain areas involved with pain and emotional arousal, including the insula, amygdala and brainstem. IBS patients could not deactivate these circuits effectively, although they also knew the pain was not dangerous.
“The abdominal hypersensitivity that is a hallmark of IBS may represent an inability to downregulate pain and emotional arousal circuits, said Steven Berman, lead study author and a senior research scientist at UCLA. “IBS patients may have an inability to inhibit the competing tendency to upregulate emotional arousal in order to escape pain faster.”
As expected, IBS patients reported lower pain thresholds and more anxiety than healthy women. Anxiety correlated with more brain activity during anticipation, but not receipt of pain.
“Negative emotions like anxiety and anger may interfere with the brain's ability to strategically downregulate pain arousal pathways, in situations where such an increased sensitivity is maladaptive,” said Berman.