There are numerous high-level hypotheses that seek to explain why different people suffer neurodegeneration to different levels. Some people remain sharp in old age, whilst others descend into dementia. At the fine-grained level of measuring different types of mental capacity, there are also large variations across an aging population: "Episodic memory and working memory decline with advancing age. Nevertheless, large-scale population-based studies document well-preserved memory functioning in some older individuals. The influential 'reserve' notion holds that individual differences in brain characteristics or in the manner people process tasks allow some individuals to cope better than others with brain pathology and hence show preserved memory performance. Here, we discuss a complementary concept, that of brain maintenance (or relative lack of brain pathology), and argue that it constitutes the primary determinant of successful memory aging. We discuss evidence for brain maintenance at different levels: cellular, neurochemical, gray- and white-matter integrity, and systems-level activation patterns. Various genetic and lifestyle factors support brain maintenance in aging and interventions may be designed to promote maintenance of brain structure and function in late life." It makes more sense for neurodegeneration to be more greatly affected by the impact of regular exercise on long-term tissue health than by the genetics of having a cognitive research.
Link: http://www.ncbi.nlm.nih.gov/pubmed/22542563
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