Abstract
In recent years, several theories have been proposed in attempts to identify the neural mechanisms underlying successful cognitive aging. Old subjects show increased neural activity during the performance of tasks, mainly in prefrontal areas, which is interpreted as a compensatory mechanism linked to functional brain efficiency. Moreover, resting-state studies have concluded that elders show disconnection or disruption of large-scale functional networks. We used functional MRI during resting-state and a verbal n-back task with different levels of memory load in a cohort of young and old healthy adults to identify patterns of networks associated with working memory and brain default mode. We found that the disruption of resting-state networks in the elderly coexists with task-related overactivations of certain brain areas and with reorganizations within these functional networks. Moreover, elders who were able to activate additional areas and to recruit a more bilateral frontal pattern within the task-related network achieved successful performance on the task. We concluded that the balanced and plastic reorganization of brain networks underlies successful cognitive aging. This observation allows the integration of several theories that have been proposed to date regarding the aging brain.
Highlights
Cognitive aging affects a wide range of functions including working memory, processing speed, and inhibitory function (Park et al, 2002; Reuter-Lorenz and Park, 2010)
Low-healthy elders (HE) and high-HE groups differed in task-performance, but there were no significant differences in the performance of the 3back task between young adults (YA) and high-HE subjects
Using independent component analysis (ICA) we identified intrinsic functional connectivity networks that are in operation during resting-state functional MRI (fMRI) and during task fMRI, supporting the idea that brain connectivity has a network-based functional substrate that is not limited to the fact that the brain is functionally active (Smith et al, 2009)
Summary
Cognitive aging affects a wide range of functions including working memory, processing speed, and inhibitory function (Park et al, 2002; Reuter-Lorenz and Park, 2010). Age-related functional reorganizations have been described as changes in brain responsivity in several brain regions when subjects are scanned during the performance of cognitively demanding tasks (see Spreng et al, 2010; Turner and Spreng, 2012 for recent meta-analyses). Both reductions and increases in activity have been described in different brain regions. Reductions in activity are commonly located in the left prefrontal cortex (PFC) and temporo-occipital areas and are normally associated with less efficient processing in aging (Cabeza et al, 1997), but the interpretation of increases is less straightforward. When associated with better or preserved performance they have been commonly interpreted as evidence of functional compensatory mechanisms (Grady, 2000; Cabeza et al, 2002b; Grady et al, 2006; Mattay et al, 2006; Berlingeri et al, 2010)
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