Aging of the nervous system

The aging nervous system encompasses two related research areas. One is the effect of aging itself on nervous system function, also referred to as normal aging. A second area of consideration is that of neurodegenerative diseases with aging-Associated onset, which are not representative of normal nervous system aging. This chapter examines both aspects of the aging nervous system, with emphasis on comparative studies that have revealed important insights in these areas. Both normal and pathological nervous system aging involve elevated oxidative stress, perturbed energy metabolism and the accumulation of protein aggregates. Changes in pathways for cell replacement, regeneration and repair are also important factors that are altered in the aging nervous system. The major neurodegenerative diseases associated with aging are Alzheimer's disease, Parkinson's disease, Huntington's disease and ALS Clinical, cellular and molecular features of each disease are described. For many of these diseases, underlying genetic and environmental causes have been identified. Environmental factors capable of modifying nervous system aging and neurodegenerative disease susceptibility are also examined. Overall, many factors impact the nervous system during aging in humans as well as other species. Recent studies have shown that some are protective (exercise, dietary energy restriction and cognitive stimulation) while others (diabetes, depression and dietary factors) enhance nervous system decline at the end of life. Comparative approaches have identified those changes that represent evolutionarily conserved aspects of nervous system aging.