Altered early cortical EEG maturation and its relationship to language development in Down syndrome

Down syndrome (DS) is the most common genetic cause of intellectual disability, yet age-related cortical maturation patterns that contribute to developmental delays remain poorly understood. We analyzed longitudinal resting-state EEG and developmental data from 86 children with DS and 154 typically developing (TD) children between 12 and 81 months of age. Linear mixed-effect models tested age-related trajectories of aperiodic and periodic spectral features, and manifold learning was used to characterize multivariate EEG profiles associated with age and developmental ability. Children with DS showed altered maturation across multiple EEG features. Aperiodic exponent decreased with age in DS, but not TD children, indicating possible altered maturation of cortical excitability. While TD children showed expected age-related increases in theta-alpha peak frequency and amplitude, children with DS exhibited limited alpha maturation and greater persistence of theta-only and theta+alpha peak profiles. We next asked whether multivariate EEG organization reflected chronological maturation or individual differences in developmental ability. A spectral dimension associated with chronological age in TD children was not similarly age-associated in DS. Instead, a second spectral dimension was associated with verbal developmental quotient in children with DS, independent of chronological age and nonverbal developmental ability. This language-associated profile included features considered atypical relative to TD maturation, including increased aperiodic activity and continued presence of theta activity. These findings suggest that in DS there is an altered relationship between cortical spectral organization, chronological age, and language development, extending beyond a uniform delay in typical maturation.