Relating ADHD to the aperiodic component of the EEG signal in both males and females across development.

The aperiodic EEG signal has been shown to differ in those with versus without Attention-Deficit Hyperactivity Disorder (ADHD). However, the underrepresentation of females and relatively narrow age-ranges investigated, made it difficult to characterise the interaction of age, sex and ADHD on aperiodic activity. This is important, because the aperiodic exponent has been put forward as a promising biomarker of ADHD, despite generalizability limitations. This registered report draws upon the Healthy Brains Biobank to analyze resting EEG data of children ages 5-18 years. We compared the aperiodic exponent of boys with ADHD (n = 863), girls with ADHD (n = 320), boys without ADHD (n = 136) and girls without ADHD (n = 107) as a function of age, biological sex and ADHD, while controlling for important covariates (social economic status, IQ, medication). We found that neither aperiodic EEG activity, nor its development, reliably differs between individuals with and without ADHD. Instead, the aperiodic exponent shows a linear decrease from ages 5-18 across all participants, regardless of ADHD status. This decline is steeper in females than males in some conditions. Given rising ADHD diagnoses worldwide, especially among females, neurodevelopmental studies should prioritize balanced male-female representation.