Development of Cortical Asymmetry in Typically Developing Children and Its Disruption in Attention-Deficit/Hyperactivity Disorder

Abstract

Just as typical development of anatomical asymmetries in the human brain has been linked with the normal lateralization of motor and cognitive functions,^1,2 disruption of asymmetry has been implicated in the pathogenesis of several neurodevelopmental disorders, such as autism, schizophrenia, and attention-deficit/hyperactivity disorder (ADHD).^3-5 The most consistently reported structural asymmetry in typically developing adults is a relative increase in the dimensions of the right frontal and left occipital lobes.^6-10 Such adult structural asymmetries are classically thought to result from the action of torque, a rotational force, on the brain.¹¹ This concept implies that adult asymmetries are the result of a dynamic developmental process, which is supported by demonstrations of different patterns of structural asymmetry in healthy children and infants. For example, one volumetric study⁴ of 46 children reported complete reversal of adult asymmetries (it found larger childhood left anteroinferior frontal cortical and right temporo-occiptal volumes), and others^12-15 reported only a partial, but not yet complete, pattern of adult asymmetry. If asymmetry is, indeed, an evolving property of the childhood brain, such a dynamic phenomenon could be further understood using longitudinal neuroanatomical data. To date, to our knowledge, all studies have been cross sectional.