Neurobiological aspects of language in children.

This article discusses the relevance of the study of the neurobiology of cognitive development, both for an understanding of the neural bases of cognition and of the nature of cognition itself. A key issue is the age at which hemisphere specialization first appears and whether it changes over time. The neuropsychological literature concerning language in both normal and brain-damaged children is reviewed. The usefulness of studying cognition in other clinical disorders and variation in normal cognition is indicated. The various methods used in the research are described and the methodological and interpretational difficulties arising from the diversity of groups studied and the methods used are discussed. The model is advanced that hemisphere specialization exists from birth onward and does not undergo further change in either its nature or degree. The apparent increase in the extent of hemisphere specialization during childhood is interpreted as an epiphenomenon of the increasing cognitive and behavioral repertoire of the child. Neural plasticity, assumed to underlie recovery of function, is seen as being coexistent with, but independent of, hemisphere specialization.