Abstract
There is abundant evidence that attention-deficit/hyperactivity disorder (ADHD) is a neurobiologic disorder. Yet, some of the most common methods for directly assessing neurobiologic substrates have not been used in 3- to 5-year-old preschoolers. Therefore, we must use other means to infer the neurobiology of ADHD in this young age group. In this review, we provide the following: (1) a brief review of neuropsychologic studies of preschoolers with ADHD; (2) a brief summary of structural and functional neuroimaging studies of ADHD in older children as they might relate to findings in preschoolers; (3) an empirically based theory of the neurologic substrate of ADHD, in particular, the cerebellar-prefrontal-striatal network; (4) an overview of the evidence for the etiology of ADHD; and (5) support for the idea that the neurobiology of ADHD is largely stable over time, such that we can infer abnormalities in preschoolers on the basis of data from older children with ADHD. We hope that this information can be used to guide our thinking and treatment approaches in these young children with ADHD.