Three consecutive chapters considered three cognitive functions. In each instance, abilities were paired with the underlying neurobiological evidence of decline. From our separate treatment of attention, memory, and processing, the unified nature of this decline is not obvious. For the sake of illustration and in the face of complexity, we have thus far followed the modularity thesis, a common approach to viewing the brain as a conglomeration of compartmentalized regions with distinctly identifiable functions. However, even where individual abilities are directly supported by discrete brain regions, disaggregation is difficult. Any complex brain function is reliant on modules being networked through white matter pathways. Beyond this, complex reasoning, executive functioning, and working memory more fully defy modularity, arising from emergent properties of integrated networks. Supporting these networked modules and emergent abilities is an extraordinarily elaborate complexity of circulatory architecture, neuroendocrine chemicals, and axonal projections. To better appreciate this more unified understanding of cognitive decline, we present literature on general intelligence, first showing its psychometric unity and next showing its global decline. By the chapter’s end, one can move from seeing the brain as comprised of compartmentalized islands of ability to seeing a tight integration among brain regions as giving rise to a more unified general intelligence, which then declines along with its supporting neurobiological networks.