Aging and hemispheric cerebral lateralization
ABSTRACT 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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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.Laterality 10/2012; DOI:10.1080/1357650X.2012.724072 · 1.13 Impact Factor
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ABSTRACT: We used fMRI to assess the neural correlates of autobiographical, semantic, and episodic memory retrieval in healthy young and older adults. Participants were tested with an event-related paradigm in which retrieval demand was the only factor varying between trials. A spatio-temporal partial least square analysis was conducted to identify the main patterns of activity characterizing the groups across conditions. We identified brain regions activated by all three memory conditions relative to a control condition. This pattern was expressed equally in both age groups and replicated previous findings obtained in a separate group of younger adults. We also identified regions whose activity differentiated among the different memory conditions. These patterns of differentiation were expressed less strongly in the older adults than in the young adults, a finding that was further confirmed by a barycentric discriminant analysis. This analysis showed an age-related dedifferentiation in autobiographical and episodic memory tasks but not in the semantic memory task or the control condition. These findings suggest that the activation of a common memory retrieval network is maintained with age, whereas the specific aspects of brain activity that differ with memory content are more vulnerable and less selectively engaged in older adults. Our results provide a potential neural mechanism for the well-known age differences in episodic/autobiographical memory, and preserved semantic memory, observed when older adults are compared with younger adults.Journal of Cognitive Neuroscience 06/2011; 23(12):4150-63. DOI:10.1162/jocn_a_00079 · 4.69 Impact Factor