Compensatory Activity in the Aging Brain

Abstract

Event Abstract Back to Event Compensatory Activity in the Aging Brain Roberto Cabeza1* 1 Duke University, Center for Cognitive Neuroscience, United States Although aging is associated with a significant decline in brain anatomy and function, functional neuroimaging evidence suggests that the aging brain can partially counteract this decline by reorganizing its functions. The talk makes three main points. First, two patterns of brain activity have been consistently observed in multiple cognitive domains and they have been both associated with functional compensation. In the pattern known as Posterior-Anterior Shift with Aging (PASA), older adults show weaker occipital activity but stronger frontal activity than younger adults (Davis, Dennis, Daselaar, Fleck, & Cabeza, 2008). In the pattern known as Hemispheric Asymmetry Reduction in Older adults (HAROLD), older adults display a more bilateral pattern of frontal activity than younger adults (Cabeza, 2002). Three types of evidence link these patterns to functional compensation: (i) a positive association between increased frontal activity and cognitive performance (both PASA and HAROLD), (ii) a negative correlation between increased frontal activity and reduced occipital activity (PASA), and (iii) greater sensitivity of older adults to the disruption of contralateral frontal function (HAROLD). Second, older adults tend display stronger functional connectivity between frontal and posterior regions (c.f. PASA) and between contralateral frontal regions (c.f. HAROLD). These effects have been linked to enhanced cognitive performance and may occur even when frontal activity is weaker in older adults than younger adults. Thus, functional compensation in older may be mediated not only by a local increase in frontal activity but also by an increase in frontal interactions with other brain regions. Third, preliminary evidence suggests that age-related increases in frontal connectivity are modulated by white matter integrity (as measured with diffusion tensor imaging) in specific fiber tracts. For example, connectivity between frontal and medial temporal regions in older adults is modulated by the integrity of the uncinate fasciculus, and connectivity between left and right frontal regions, by the integrity of the genu of the corpus callosum. These findings suggest boundaries to functional compensation in older adults and highlight the importance of linking the effects of aging on brain activity to its effects on brain structure. From an applied perspective, understanding the mechanisms of compensatory activity in the aging brain and the factors that modulate them is critical for the use of functional neuroimaging as an aid in the diagnosis of Alzheimer's disease and in the development and evaluation of cognitive rehabilitation approaches.