Cognitive and motor alterations in old age

Major brain-related effects of age have been shown in regard to cognition, motor functions and sensory systems. Studies of age-related alterations of cognition must distinguish between changes in cognitive activity itself and those secondary to deterioration in peripheral sensory mechanisms. The definition of "normal" aging is difficult with regard to the human nervous system since loss of function may be due to illness or environmental factors rather than aging itself. The question remains whether neurological and psychiatric disorders such as Alzheimer's disease and Parkinson's disease represent an exaggeration of normal aging or whether they are diseases caused by factors not normally active during the course of aging. More brain systems and functions appear to be preserved in old age than may be predicted from the hypothesis that aging is associated with a continuous decline until death, Neurobiological studies have focussed on the assessment of neuronal loss in the brain. The lack of neuronal loss in a given brain region does not necessarily signify the absence of age-related alterations. It is therefore essential not only to determine the number of neurons but also to assess their functional integrity. Neuronal attrition may not be synonymous with cognitive decline. The loss of neurons and synapses at certain stages of an individual's development could represent a process of gradual fine-tuning establishing more effective patterns of information processing and behavior. Despite neural cell loss during senescence, the functional capacity of neuronal circuits in the brain may be better preserved than would be predicted from cell loss alone. The brain appears to retain plasticity during aging since reactive synaptogenesis has been reported in the injured aged brain. Compensatory mechanisms of remodeling and growth may be able to maintain and adapt brain function during senescence.