Normative modeling reveals functional connectivity heterogeneity in internet gaming disorder

BACKGROUND: Internet gaming disorder (IGD) is associated with abnormal functional connectivity (FC) in brain networks. However, findings from resting-state functional magnetic resonance imaging studies are highly inconsistent, likely due to individual heterogeneity in IGD-related neural alterations-a feature commonly observed in other psychiatric disorders but understudied in IGD. METHODS: We applied normative modeling to nucleus accumbens (NAcc) seed-to-voxel resting-state FC to derive individualized deviation (Z) maps for 173 IGD participants relative to age- and sex-adjusted normative ranges from 232 healthy controls. We then performed exploratory unsupervised clustering of network-level deviation features across three sample data, three atlas templates, and two clustering algorithms, selecting the optimal number of clusters using the silhouette criterion. RESULTS: IGD showed marked heterogeneity in FC deviations: voxel-level deviations were largely idiosyncratic in both spatial distribution and direction. When deviations were summarized at the network level, clustering consistently selected a two-cluster solution across data, atlases, and algorithms, separating a majority "low-deviation" stratum from a smaller "high-deviation" stratum. CONCLUSIONS: IGD is characterized by pronounced individual variability in FC deviations. Network-level deviations yield a robust higher- vs. lower-deviation stratification, although the present findings do not support interpreting this pattern as evidence for discrete subtypes. The present study highlights the utility of individualized deviation mapping beyond conventional case-control analyses for characterizing heterogeneity in IGD.