Altered EEG microstate dynamics in adolescents with non-suicidal self-injury at rest and following acute social exclusion.

Background: Non-suicidal self-injury (NSSI) is highly prevalent in adolescence, yet the fast dynamics of large-scale brain networks remain poorly understood. We aimed to characterize resting-state EEG microstate dynamics in a clinically recruited adolescent NSSI sample and to examine state-dependent changes following acute social exclusion. Methods: Resting-state EEG was recorded in hospitalized, medicated adolescents with NSSI and in healthy controls (HCs). An NSSI subgroup then completed EEG assessments before and after either Cyberball-induced social exclusion or a non-stress control condition. Microstate parameters and transition probabilities were analyzed. Results: After multiple-comparison correction, the core baseline finding was robustly reduced microstate A duration in the NSSI group relative to HCs. In uncorrected exploratory analyses, additional differences included shorter durations of microstates B and F, higher occurrence of microstate D, and increased F→D transition probability. A multivariate pattern analysis suggested group-related information but must be interpreted cautiously given the modest sample size. Within the NSSI group, the exclusion group showed reduced microstate A expression and increased microstate D expression relative to the non-stress subgroup, with a broader transition shift toward microstate D. Several interaction effects survived correction. Conclusions: In this medicated inpatient sample, resting-state microstate dynamics differed from HCs, most robustly in reduced microstate A duration, and reorganized after social exclusion. Specificity to NSSI remains uncertain given the absence of an MDD-only clinical-control group and healthy Cyberball comparison. These preliminary findings require replication in larger studies including medication-naive MDD-only, MDD+NSSI, and HC groups.