A fundamental assumption about how ADHD affects brain development may need revision. For years, researchers have proposed that delayed cortical thinning—the natural process where brain tissue becomes thinner as children mature—could serve as a reliable biomarker for attention disorders. This concept has influenced both diagnostic approaches and our understanding of ADHD neurobiology.
Using brain scans from over 11,000 children in the Adolescent Brain Cognitive Development Study, investigators found that when sex differences were properly accounted for, the previously reported association between attention problems and altered cortical development completely disappeared. Initial analyses appeared to confirm earlier findings, showing children with attention difficulties had reduced rates of cortical thinning. However, when researchers included sex-specific developmental patterns in their statistical models, these associations vanished across all brain regions examined. Neither boys nor girls showed the expected relationship between attention problems and cortical maturation patterns.
This finding represents more than a statistical correction—it challenges a decade of research that may have overlooked critical sex-specific neurodevelopmental trajectories. The failure to replicate this biomarker in such a large, well-powered study suggests that previous smaller studies may have been detecting statistical artifacts rather than true biological relationships. For parents and clinicians, this underscores that ADHD diagnosis should continue relying on behavioral assessments rather than brain imaging. The research highlights a broader issue in neuroscience: the critical importance of accounting for sex differences in brain development studies, as male and female brains mature along distinctly different timelines that can confound apparent disease-related changes.