What metaphor for the aging brain?

Abstract
In this issue, Wilson and colleagues1 report that people who habitually engage in high levels of cognitive activity showed less cognitive decline—and less often had Alzheimer disease (AD)—than did people with less cognitively activating routines. The Rush Memory and Aging Project is a prospective clinicopathologic study, whose 931 participants have agreed to annual examinations and brain autopsy. Its high retention rate (93.5% of people enrolled for more than 1 year average were followed 3.5 times on average) and detailed evaluations provide insights into the …