Specifying the link between brain integrity, cognitive, and affective functioning in aging individuals.

T hIS special issue presents methodologically innovative work that advances our understanding of the relationship between cognitive performance and affect, in particular highlighting the contribution of brain to behavior. Studies investigating the effects of aging on brain anatomy and physiology suggest targeted areas which are most affected by aging, and are characterized by cerebral atrophy, synaptic loss, changes in receptor numbers and function, among other anatomical changes. These changes are likely responsible for most of the observed age-related changes in cognitive function reported in many studies of aging. Identifying precisely how these brain changes affect cognition is a formidable challenge, though new testing methodologies, along with advances in neuroimaging analysis techniques, have led to testable hypotheses and models of the link between brain and behavior. A key question in the field of cognitive aging is whether we can identify factors that can account for the considerable variability that exists in cognitive decline across normal aging individuals. For example, research shows that extensive brain atrophy and synaptic density reduction can result in demen-tia symptoms in some individuals, while surprisingly, others are much more resilient and asymptomatic, despite having equivalent neural degradation (Katzman et al., 1988). Such protection from dementia symptoms has been linked to elevated " cognitive reserve, " defined as one's efficiency at using existing neural circuits, and/or one's flexibility in using compensatory mechanisms to accomplish cognitive tasks. Propensity for physical activity, among other factors (Stern, 2012), appears to elevate cognitive reserve. It is possible that such a stimulating environment fosters plasticity, and neurogenesis, through the production of growth factors within the brain (hötting & Röder, 2013), and these in turn could produce redundancy or duplication in the brain's circuitry , making the brain more resilient to damage. The studies featured in this issue all aim to uncover more sensitive measures of brain integrity in the hopes of better specifying the relationship between biological changes in aging, and cognitive changes associated with aging. Vaughan and colleagues examined whether engagement in cognitive activities would be associated with improved cog-nitive task performance, as well as brain volume. Because cognitive training studies have been shown to lead to macro-structural brain changes, they left open the possibility that differences in everyday level of cognitive activity could increase gray matter, allowing more of a cognitive reserve which would protect the individual from the usual age-related decline in cognitive performance. Similarly, the stability and robustness of …