Change in aperiodic activity over first year of life is associated with later autism diagnosis and 18-month language development in infants with family history of autism.

Delays in language often co-occur among toddlers diagnosed with autism. Despite the high prevalence of language delays, the neurobiology underlying such language challenges remains unclear. Prior research has shown reduced EEG power across multiple frequency bands in 3-to-6-month-old infants with an autistic sibling, followed by accelerated increases in power with age. Here we apply new methods to decompose the power spectra into aperiodic (broad band neural firing) and periodic (oscillations) activity to explore possible links between aperiodic changes in the first year of life and later language outcomes. Combining EEG data across two longitudinal studies of infants with and without autistic siblings, we assessed whether infants with an elevated familial likelihood (EFL) exhibit altered changes in both periodic and aperiodic EEG activity at 3 and 12 months of age, compared to those with a low likelihood (LL), and whether developmental change in activity is associated with language development. At 3-months of age, we observed that EFL infants have significantly lower aperiodic activity from 6.7-55Hz (p<0.05). However, change in aperiodic activity from 3 to 12 months was significantly increased in infants with a later diagnosis of autism, compared to EFL infants without an autism diagnosis. In addition, greater increases in aperiodic offset and slope from 3-to12-months were associated with worse language development measured at 18 months. Findings suggest that early age-dependent changes in EEG aperiodic power may serve as potential indicators of autism and language development in infants with family history of autism.