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Background: Although pain is inevitable in nonsuicidal self-injury (NSSI), the understanding of pain during self-injury from neurobiological perspectives is still insufficient. This study aimed to investigate gray matter volume changes in regions responsible for pain processing in individuals currently engaging in NSSI. Methods: Unmedicated adults who reported five or more NSSI episodes in the past year (n = 63) and age-, sex-, and handedness- matched controls (n = 63) were included in this study. Anatomical T1-weighted MRI data were obtained for all participants at 3T, and voxel-based morphometry was performed to explore gray matter volume alterations in regions of interest (ROIs). Their associations with the frequency, the number of methods used for NSSI, duration, functions, and pain intensity of self-injury were identified using partial correlation analyses. Results: As a result, we found regional gray matter volume reductions in the right insula, bilateral secondary somatosensory cortex (S2), and left opercular part of the inferior frontal gyrus (IFG). The reduced right insula and bilateral S2 volumes were correlated with the affect-regulation function of NSSI. Also, the decreased volume of the right S2 was correlated with both the sensation-seeking function of NSSI and the pain intensity of self-injury. Limitations: Due to the cross-sectional design employed in this study, the directionality between NSSI and gray matter volumes needs further investigation. Conclusions: Our results provide the first neural evidence that structural brain abnormalities in the pain processing regions may be a pathophysiological phenotype of NSSI.

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