Aging and hemispheric cerebral lateralization

Centre Mémoire Ressource Recherche (CMRR) de la Région Centre et Médecine Interne Gériatrique, Hôpital Bretonneau et Université Rabelais, Tours, France.
Psychologie & neuropsychiatrie du vieillissement (Impact Factor: 0.89). 04/2008; 6(1):49-56. DOI: 10.1684/pnv.2008.0114
Source: PubMed


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.

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    • "In a cross-sectional study Goldstein and Shelly (1981) tested the neuropsychological functioning of 1247 participants, divided into six age groups (20s to 70s). The older as compared to younger age groups yielded a stronger decline in task performances, but this decline was more pronounced for tasks targeting the right than left hemisphere (see also Hommet et al., 2008). Cherry et al. (2005), comparable to the study by Reuter-Lorenz et al. (1999), performed letter-matching tasks, i.e., a physical and a name identity task. "
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    ABSTRACT: The population of industrialised societies has increased tremendously over the last century, raising the question of how an enhanced age affects cognition. The relevance of two models of healthy ageing are contrasted in the present study that both target the functioning of the two cerebral hemispheres. The right hemi-ageing model (RHAM) assumes that functions of the right hemisphere decline before those of the left hemisphere. The Hemispheric Asymmetry Reduction in Older Adults (HAROLD) model suggests that the contralateral hemisphere supports the normally superior hemisphere in a given task resulting in a reduced hemispheric asymmetry overall. In a mixed design 20 younger and 20 older adults performed both a task assessing a left (lateralised lexical decisions) and a right (sex decisions on chimeric faces) hemisphere advantage. Results indicated that lateralised performance in both tasks was attenuated in older as compared to younger adults, in particular in men. These observations support the HAROLD model. Future studies should investigate whether this reduced functional hemispheric asymmetry in older age results from compensatory processes or from a process of de-differentiation.
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    • "On the other hand, neural task-related changes present in older adults, and absent in young adults, that correlate with good task performance in seniors are considered compensatory (see Grady, 2008, for a review). With these criteria, some dedifferentiation can be considered compensatory (Hommet et al., 2008; Li et al., 2001; Rajah & McIntosh, 2008). Dennis and Cabeza (2010) proposed that normal aging causes a decrease in brain function which leads to a loss of competition between different systems or processes. "
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