objects is presented to only one hemisphere or the other (Hellige, 1993; Springer and Deutsch, 1993).

Brain imaging studies reveal extraordinary degrees of hemispheric specialization (Thompson, 2000). Spatial navigation involves the right hippocampus; attention shift involves the right parietal lobe; attention processes also involve the right anterior cingulate gyrus and right anterior medial frontal lobe; and visual attention processes also activate areas in the left cerebellum. Verbal short-term memory involves the left parietal and frontal areas; spatial short-term memory involves the right parietal, occipital, and frontal areas and the superior frontal sulcus bilaterally; and face working memory predominantly involves the left precentral sulcus, the left middle frontal gyrus, and the left inferior frontal gyrus. The left prefrontal cortex is more involved in retrieval of information from semantic memory, whereas the right prefrontal cortex is more involved in episodic memory retrieval.

In short, hemispheric specialization is the norm for cognitive processes. But from an educational standpoint, this is of little consequence. While there may be some educational implications, those claimed most often (e.g., that a teacher should address the left and right hemispheres separately) are ill founded. In normal humans, the two hemispheres communicate seamlessly. Information projected to one hemisphere is immediately transferred to the other as needed. During most cognitive operations, both hemispheres are activated.

Enriched Environments and Brain Development: Realities and Myths

Another strand of neuroscientific research has examined the effects of enriched environments on the development of the brain and behavior (Greenough, 1976). Various studies have concluded that rats raised together in a complex environment (“rich” rats) have a significantly thicker cerebral cortex and many more dendritic spines (synapses) on their cortical neurons than rats raised alone in plain cages. Similar results have been found with monkeys. Enhanced cortical development can occur in adult rats, but in rich rats it regresses if the animals are placed in poor environments. Rich rats also perform better than poor rats on learning tasks, but we do not yet know whether the cortical changes relate to learning experiences per se or to other processes, such as arousal.

There is a major problem, however, in the way this literature has been interpreted and applied to humans, such that parents believe they should expose their infants to super-rich environments filled with bells, whistles, and moving objects. A particular example of this phenomenon is the attention given to “the Mozart effect” (see Annex Box 3–1). In fact, the animal literature suggests that the effects of a rich environment on brain develop-



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement