Specialization of the Cerebral Hemispheres

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Abstract
Cerebral hemisphere specialization and its relation to learning disabilities are examined in the light of concepts and findings from contemporary neuropsychology. Attention is focused upon four constructs—cognitive ability, laterality, functional brain asymmetry, and structural brain asymmetry—and the associations among them. It is emphasized that these constructs represent different levels of analysis and consequently are not readily related to each other. In particular, it is argued that laterality, which is a behavioral phenomenon, does not provide direct information about physiological or anatomical characteristics of the brain. Although the available evidence is inconclusive in many respects, it points to certain conclusions about hemispheric specialization and cognitive development: (1) Differential specialization of the left and right halves of the brain occurs very early in life; (2) anomalous hemispheric specialization in an otherwise normal brain is not associated with cognitive deficit; (3) left-and right-hemisphere cognitive styles are metaphors without neurological substance; and (4) abnormal cognitive development may stem either from damage to the cerebrum or from a combination of cerebral damage and a maladaptive pattern of activation by a subcortical activating system.