Plasticity, Localization, and Language Development

Abstract

Abstract The term aphasia refers to acute or chronic impairment of language, an acquired condition that is most often associated with damage to the left side of the brain, usually due to trauma or stroke. We have known about the link between left hemi sphere damage (LHD) and language loss for more than a century (Goodglass, 1993). For almost as long, we have also known that the lesion-symptom correlations observed in adults do not appear to hold for very young children (Basser, 1962; Lenneberg, 1967). In fact, in the absence of other complications, infants with congenital damage to one side of the brain (left or right) usually go on to acquire language abilities that are well within the normal range (Eisele and Aram, 1995; Feldman et al., 1992; Vargha-Khadem et al., 1994). To be sure, children with a his tory of early brain injury typically perform below neurologically intact age matched controls on a host of language and nonlanguage measures, including an average full-scale IQ difference somewhere between 4 and 8 points from one study to another (especially in children with persistent seizures; Vargha-Khadem et al., 1994). Brain damage is not a good thing to have, and some price must be paid for wholesale reorganization of the brain to compensate for early injuries. But the critical point for present purposes is that these children are not aphasic, despite early damage of a sort that often leads to irreversible aphasia when it occurs in an adult. In addition to the reviews by other authors cited above, my colleagues and I have also published several detailed reviews, from various points of view, of language, cognition, and communicative development in children with focal brain in jury (e.g., Bates et al., 1997, 1998; Elman et al., 1996; Reilly et al., 1998; Stiles, 1995; Stiles et al., 1998; Stiles and Thal, 1993; Thal et al., 1991). As these reviews attest, a consensus has emerged that stands midway between the historical ex tremes of equipotentiality (Lenneberg, 1967) and innate predetennination of the adult pattern of brain organization for language (e.g., Curtiss, 1988; Stromswold, 1995).