Increased inter-hemispheric efficiency accounts for preserved attentional performance in elderly individuals

Description

Several studies in Functional Magnetic Resonance Imaging done among elderly people have revealed a bilateral activation, which correlated with higher performance among elderly adults. Cabeza posited the HAROLD model (i.e., Hemispheric Asymmetry Reduc- tion in Older Adults, HAROLD) to account for this effect: compared to younger adults, brain activity among elderly people tends to be less lateralized. The aim of this work is to focus on the nature of the inter-hemispheric mechanisms among elderly adults by studying the sharing of processing efficiency between the two hemispheres. It is assumed that the age-related hemispheric asymmetry reductions result from the emergence of an inter-hemispheric compensa- tion mechanism that expresses a modification of the distribution of the exchanges between the two hemi- spheres. Thus, the elderly appear to take advantage of a bi-hemispheric processing even for the most simple tasks. Twenty participants (10 young and 10 elderly adults) were submitted to a letter-matching task under a divided visual field tachistoscopic presentation. The main results show an early shift in efficiency from within- to across-hemisphere processing with aging. Young adults showed an across-hemisphere advantage only for the most complex task. In contrast, older adults showed an across-hemisphere advantage at all levels of task complexity for accuracy and latency data. The benefits associated with greater computational power outweigh the costs of integrating process- ing between the hemispheres in elderly adults. In conclusion, inter-hemispheric interactions may consti- tute a flexible mechanism that can improve the brain's ability and thus may compensate for neural decline that accompanies normal aging.

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