This chapter reviews several biological functions that in the past have been most directly linked to changes in motivation during aging. For heuristic purposes, it discusses the changes on the organismic or physiological rather than the cellular level, though it is assumed that, ultimately, the cellular mechanisms lead to the organismic changes. The biologist Cristofalo (1996), in his review of recent theories of aging, observed that aging refers to several phenomena. There is no singular biological change that can be used as a criterion of aging. He also recommended that we dissect (his term) the various aspects of aging.
KeywordsFatigue Manifold Estrogen Dementia Serotonin
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