Definitional issues and neurobiological foundations of selected severe neurodevelopmental disorders

This article reviews current definitional issues, selected neuropsychological findings, and presumed neurobiological underpinnings of two of the more commonly identified severe neurodevelopmental disorders: mental retardation and autistic disorder. Although these disorders represent two of the more common severe neurodevelopmental disorders encountered by child neuropsychologists practicing in clinical and research settings, they have not received the amount of attention from the field of neuropsychology as other kinds of neurodevelopmental disorders. Although there are few definitional controversies surrounding these disorders, findings accrued to date reveal solid evidence for neurological processes underlying each of these disorders. In addition, each of these diagnoses likely represents a heterogeneous group of disorders, suggesting that a syndrome analysis approach would prove beneficial for increasing our understanding of each disorder. Conclusions are drawn for the clinician and researcher, particularly with respect to using a neuropsychological perspective and assessment strategies with children with more severe disorders.