Disrupted Top-Down Modulation as a Mechanism of Impaired Multisensory Processing in Autistic Children

Atypical sensory processing is commonly observed in autism, particularly when integration across sensory modalities is required. The neural mechanisms underlying multisensory differences remain unclear. We recorded EEG while autistic children aged 8-13 (AU;n = 40), siblings of autistic children (SIB;n = 26), and non-autistic controls (NA;n = 36) performed a simple reaction-time task to auditory (A), visual (V), and audiovisual (AV) stimuli. Analyses targeted event-related potentials (ERPs), alpha-band event-related desynchronization (α-ERD), and long-range theta-band functional connectivity. Groups did not differ across unisensory measures, indicating comparable unisensory processing. By contrast, multisensory integration (MSI;AV-(A+V)) differed across groups: NA children showed significant ERP MSI over parieto-central sites that was absent in AU and SIB; and α-ERD MSI was significantly reduced in AU, with SIB showing an intermediate profile. Connectivity analyses revealed reduced AV fronto-parieto-occipital coupling in autistic children relative to non-autistic children, suggesting weaker large-scale coordination during multisensory processing. These results point to a multisensory-specific deficit spanning early sensory encoding, posterior α-ERD, and fronto-posterior coupling and support disrupted multisensory influences on sensory processing due to reduced multisensory attentional orienting. SIB profiles suggest inherited liability for these neural phenotypes. These results help explain well-documented behavioral MSI differences in autism by linking impaired early enhancement with attenuated top-down control of sensory cortex.