[Aging and hemispheric cerebral lateralization].

Cerebral hemispheric lateralization is an old concept, particularly concerning language. In children, numerous arguments favour a left hemispheric predisposition for language, but do not exclude its strengthening during childhood. In the elderly, changes in the lateralization have been described. Two models were proposed to explain these changes. The right hemi-aging model is supported by behavioral studies and the age-related asymmetry reduction model is documented by brain imaging studies. We review the data supporting the two models. The significance of this age-related asymmetry reduction is questionable. The dedifferentiation view suggests that bilateral activation in older adults reflects difficulty in recruiting specialized neural mechanisms. Age-related asymmetry reduction may also be evidence of compensatory mechanisms and plasticity of the aging brain. It is useful for understanding physiopathology of cognitive decline and rehabilitation potential of the aging brain.