Reduced Backward Alpha Propagation at Rest Marks the Autism Continuum

Autism spectrum disorder and subclinical variation along the autism continuum are characterized by in sensory processing and cognitive integration, phenomena increasingly linked to atypical large-scale communication across cortical hierarchies. While structural and functional connectivity differences have been extensively documented, whether autistic traits are associated with a reorganization of the directional properties of ongoing cortical activity remains less understood. Here, we recorded resting-state EEG from 201 young adults selected from the lower and upper terciles of the Autism Quotient distribution and analyzed traveling-wave dynamics over parieto-frontal lines. Individuals with higher autistic traits showed a selective shift in left-hemisphere alpha-band traveling-wave directionality, driven primarily by reduced backward-dominant propagation and accompanied by a reciprocal shift toward forward dominance. This effect was anatomically specific, absent in an occipito-central control line set, and not accompanied by a matching pattern of group differences in oscillatory power, aperiodic spectral parameters, or peak alpha frequency. These findings identify resting-state alpha traveling waves as a candidate physiological signature of altered directional organization across the autism continuum, with potential relevance as a trait-sensitive neural marker.