The idea of reserve against brain damage stems from the repeated observation that there does not appear to be a direct relationship between the degree of brain pathology or brain damage and the clinical manifestation of that damage. The literature suggests that both brain reserve and cognitive reserve are not entirely determined at birth but are influenced by experiences and environmental factors throughout the lifespan. Recently, investigators have been looking at the possibility of imparting reserve via lifestyle enrichment, cognitive training, (...) exercise, and other interventions. This article reviews the concept of CR and then discusses the potential ethical implications connected with this concept. The key conceptual point is that there is a disconnection between the underlying Alzheimer's disease pathology and the clinical expression of that pathology. This provides an effective research setting for exploring the severity of brain insult that is required before cognitive networks change. (shrink)