Language Development in Children with Unilateral Brain Injury

Abstract

Aphasia (defined as the loss or impairment of language abilities following acquired brain injury) is strongly associated with damage to the left hemisphere in adults. This well-known finding has led to the hypothesis that the left hemisphere is innately specialized for language, and may be the site of a specific “language organ.” However, we have known for more than a century that young children with left-hemisphere damage (LHD) do not suffer from aphasia, and in most studies do not differ significantly from children with right-hemisphere damage (RHD). This result provides strong evidence for plasticity—brain reorganization in response to experience—and constitutes a serious challenge to the language organ hypothesis. This chapter reviews the history of research on language outcomes in children versus adults with unilateral brain injury. In that review we address some of the discrepancies in the literature to date, including the methodological confounds that may be responsible for those discrepancies. We also review recent prospective studies of children with unilateral injury as they pass through the first stages of language development. Prospective studies have demonstrated specific correlations between lesion site and profiles of language delay, but they look quite different from lesion–symptom correlations in adults, and gradually disappear across the course of language development. The classic pattern of brain organization for language observed in normal adults may be the product rather than the cause of language learning, emerging out of regional biases in information processing that are relevant for language, but only indirectly related to language itself. If those regions are damaged early in life, other parts of the brain can emerge to solve the language-learning problem.