Cortical development in typically developing children with symptoms of hyperactivity and impulsivity: support for a dimensional view of attention deficit hyperactivity disorder.

Objective: There is considerable epidemiological and neuropsychological evidence that attention deficit hyperactivity disorder (ADHD) is best considered dimensionally, lying at the extreme end of a continuous distribution of symptoms and underlying cognitive impairments. The authors investigated whether cortical brain development in typically developing children with symptoms of hyperactivity and impulsivity resembles that found in the syndrome of ADHD. Specifically, they examined whether a slower rate of cortical thinning during late childhood and adolescence, which they previously found in ADHD, is also linked to the severity of symptoms of hyperactivity and impulsivity in typically developing children.

Anatomic magnetic resonance imaging of the developing child and adolescent brain and effects of genetic variation.

Magnetic resonance imaging studies have begun to map effects of genetic variation on trajectories of brain development. Longitudinal studies of children and adolescents demonstrate a general pattern of childhood peaks of gray matter followed by adolescent declines, functional and structural increases in connectivity and integrative processing, and a changing balance between limbic/subcortical and frontal lobe functions, which extends well into young adulthood. Twin studies have demonstrated that genetic factors are responsible for a significant amount of variation in pediatric brain morphometry.