Frequency of bullying modulates amygdala response during social exclusion in participants with non-suicidal self-injury

Non-suicidal self-injury (NSSI) is a phenomenon of high worldwide prevalence. Social exclusion as a major form of bullying has been reported to be an important risk factor for NSSI. We investigated how different frequencies of previous bullying experiences affect the neural processing of social exclusion in groups of female adolescents and young adults engaging in NSSI (n = 57), and matched healthy controls (n = 58). The Cyberball paradigm was used to experimentally contrast the neural effects of social exclusion relative to social inclusion. MR-based perfusion imaging measuring changes in regional cerebral blood flow (rCBF) was served as a marker of functional brain activation. Without considering previous bullying experiences, group comparisons revealed that individuals engaging in NSSI showed greater differential activation of lateral temporal brain regions, anterior hippocampus, and amygdala during social exclusion compared to healthy controls. The frequency of past bullying experiences modulated this activation pattern. Increased differential activation was particularly driven by NSSI individuals with occasional bullying experiences (around 0.5–1 time per month) while NSSI individuals with a higher frequency showed the lowest magnitude of the “exclusion > inclusion” effect. The blunted amygdala activation of NSSI individuals with a higher frequency of bullying experiences could be interpreted as a sign of emotional numbing. Following this putative interpretation, the results suggest that emotional numbing should be given the same attention as increased sensitisation to social exclusion during the treatment of NSSI to promote functional emotion regulation.