Similarities and Differences in Resting-State Brain Activity Changes of Distinct Chronic Pain Types

To explore neural similarities and differences between visceral and somatic pain by comparing spontaneous brain activity in patients with chronic temporomandibular disorder (TMD) and irritable bowel syndrome (IBS).

Twenty eight IBS patients, 21 TMD patients, and 28 healthy controls (HC) underwent resting-state fMRI and behavioral assessments. The correlations between fMRI metrics such as the amplitude of low-frequency fluctuations (ALFF), regional homogeneity (ReHo), functional connectivity (FC), and clinical manifestations were further analyzed.

Compared with HC, both patient groups demonstrated increased ALFF in right parahippocampal gyrus (PHG), insula, medial superior frontal gyrus (SFGmed), precentral gyrus (PreCG), and increased ReHo in right SFGmed and left supplementary motor area (SMA). Compared with IBS patients, TMD patients exhibited reduced ALFF in right SFGmed and insula, increased ALFF in right PHG and PreCG, decreased ReHo in right SFGmed and left lingual gyrus, and increased ReHo in left SMA. Both patient groups exhibited enhanced right PHG-related FC in left precuneus and right cingulate gyrus, and right insula-related FC in left superior temporal gyrus and right paracentral lobule. Specifically, IBS patients showed higher FC between right PHG and orbitofrontal cortex than TMD patients, which was negatively correlated with mood and gastrointestinal symptoms. Mediation analysis revealed that pain in TMD and gastrointestinal symptoms in IBS mediated these relationships.

Visceral and somatic pain share abnormal activity in multiple brain networks. Abnormalities in affective region present potential neuroimaging markers for pain disorders, with depression in somatic pain linked to pain intensity and in visceral pain to gastrointestinal symptoms.