Patients with irritable bowel syndrome have altered brain responses to the anticipation of pain and to pain itself, which might make them more sensitive to painful stimuli, reported Dr. Steven M. Berman and his colleagues from the Center for the Neurobiology of Stress at the University of California, Los Angeles.
During expectation of pain, irritable bowel syndrome patients generate higher levels of tonic noradrenergic activity, producing a bias toward interpretation of network activity as pain, and are inefficient at reducing such activity when discrimination of nonpainful stimulation should be maximized, they said (J. Neurosci. 2008;28:349–59).
Functional magnetic resonance imaging (fMRI) was used to measure the blood oxygen level-dependent response to anticipated and delivered rectal distention in 14 female IBS patients and 12 healthy controls (mean age 36 years). When controls were anticipating a painful stimulus, brain activity decreased in several regions, but there was less of this anticipatory deactivation in the IBS patients.
Visceral distention of the rectum was then performed using a computer-driven pump and rectal balloon. Four to six sessions of 16 inflations were performed. Each inflation was preceded by an anticipatory cue. During rectal distention, increases in activity in the insula, dorsal anterior cingulate cortex, and dorsal brainstem were more extensive in IBS patients than in controls.
The results show that during expectation of experimental abdominal/pelvic discomfort, female IBS patients are more anxious and less able than healthy controls to downregulate activity within the CNS network activated by potentially aversive stimuli, the authors noted.