Autistic Trait Dimensions and Resting-State Neural Markers: A Multimodal EEG/fNIRS Study in Non-Clinical Adults

Autistic traits are continuously distributed in the general population, but whether this variation is reflected in resting-state brain activity remains unclear. We recorded simultaneous EEG and fNIRS during alternating eyes-open and eyes-closed rest in 51 non-diagnosed young adults, 44 of whom had complete EEG and questionnaire data. Total and subscale scores on the Abridged Autism-Spectrum Quotient (AQ-28) were related to electrophysiological, hemodynamic, and multimodal measures, with adjustment for age and sex, FDR correction within each analytic family, and sensitivity analyses across EEG preprocessing choices. No association survived correction in any family: global and dynamic connectivity, regional spectral power, microstates, fNIRS amplitude measures, or the multimodal canonical correlation. The only regularity was directional: greater self-reported social difficulty was associated with lower theta power across regions, but this pattern was neither significant after correction nor specific to theta. In a secondary analysis, the change in right frontal beta power between eyes-closed and eyes-open conditions varied with the AQ total; this interaction depended on channel handling and remains provisional. The results do not support a stable resting-state neural marker of autistic traits in this sample. Larger, preregistered studies are needed to establish whether these patterns replicate.