Insula Activity to Visceral Stimulation and Endocrine Stress Responses as Associated With Alexithymia in Patients With Irritable Bowel Syndrome

Objective Few studies have investigated associations between alexithymia and physiological mechanisms in psychosomatic diseases. We examined associations between alexithymia and 1) perception and brain processing of visceral stimulation and 2) the endocrine responses to corticotrophin-releasing hormone (CRH) in healthy individuals and patients with irritable bowel syndrome (IBS). Methods The study included 29 patients with IBS and 35 age- and sex-matched healthy controls (HCs). Alexithymia was measured using the 20-item Toronto Alexithymia Scale (TAS-20). Brain responses to rectal distention and its anticipation were measured by functional magnetic resonance imaging and analyzed at a voxel-level threshold of p(uncorrected) < .001 combined with a cluster-level threshold of p(FWE-corrected) < .05. On a different day, plasma adrenocorticotropic hormone and cortisol responses after intravenous CRH administration were measured. Results TAS-20 scores did not differ significantly between patients with IBS and HCs (p = .18). TAS-20 scores correlated positively with the individual rectal discomfort thresholds (beta(robust) = 0.49, p = .03) and negatively with the rating of fear before rectal distention (beta(robust) = -1.63, p = .04) in patients with IBS but not in HCs. Brain responses to rectal distention in the right insula and other brain regions were positively associated with TAS-20 scores to a greater extent in patients with IBS than in HCs. Individuals with higher TAS-20 scores (both patients with IBS and HCs) demonstrated stronger adrenocorticotropic hormone responses to CRH administration (F(4,224) = 3.54, p = .008). Conclusion Higher alexithymia scores are associated with stronger physiological responses, but lower anticipatory fear ratings and higher discomfort thresholds, particularly in patients with IBS.