. Over recent years, it has become clear that the functional plasticity of the brain following damage sustained in infancy varies according to the functions being assessed and the anatomic areas affected by the damage. Although out understanding of the effect of early damage on language and visuospatial functions has increased greatly, studies of the executive functions normally associated with the frontal lobes, such as planning, problem solving, working memory and inhibition, have not been done with children who sustained early focal brain injury. Such research has the potential to provide information regarding the degree of functional plasticity of prefrontal cortex. By specifically looking for dissociations among aspects of informational processing hypothesized to underlie more complex frontal behaviors, this study also proposes to examine the separability of these functions in development and whether they are specifically related to distinct areas of the frontal lobes as has been seen in adults. A further goal of the study is to investigate whether damage to frontal areas is associated with greater developmental disabilities in adaptive and social functions than damage to posterior areas. These goals will be accomplished by comparing a group of children with unilateral, focal brain lesions sustained prior to 6 months of age with normally developing controls on a battery of executive functioning measures. Dissociations on specific measures of working memory and inhibitory functioning will be examined within the focal lesion group as well as within normally developing controls. Finally, the relationship of performance on these measures to social and adaptive functioning will be examined.