Aging

Neuroanatomical Correlates of Aging

It comes as no surprise that our brain ages in a manner much similar to other bodily organs. These changes are evident using techniques that range from the molecular to the psychological, and everything between. Age-related changes in function are associated[Page 60] with structural brain changes that can have profound psychological consequences. For example, visual impairment is one of the first symptoms of aging, with the average 85-year-old demonstrating about 80% less visual acuity than that of a 40-year-old. Fortunately, from an aging brain perspective, retinal degeneration appears to be the major cause of this change because the brain areas involved in visual processing appear to remain generally unaffected. Although this observation may not be cause for celebration, it does suggest that brain circuitry remains relatively intact with advanced age, dispelling a common misconception about how the brain ages: the idea that age-related neuron loss is ubiquitous. Technological advances have been instrumental in debunking this belief, with evidence accumulating that the brain does not atrophy in a nonspecific, passive manner akin to that of a muscle with misuse. In contrast, brain atrophy appears to be limited in extent, selective in regional expression, and subject to considerable individual variability. For example, early research suggested that widespread, senescence-associated cell loss occurred throughout the hippocampus, an area of the brain heavily implicated in the formation of many types of new memories. Consistent with this notion are the observations that the types of memories processed by the hippocampus are frequently compromised in older adults. Yet, recent studies using improved microscopic techniques indicate that hippocampal cell loss is relatively minimal and restricted to specific hippocampal subfields. These regional and discrete observations parallel those of memory decline seen in old age; not all aspects of memory function are impaired; rather, only specific modes are influenced by the aging process. In particular, hippocampal function is strongly correlated with the ability to form durable memory traces, with older adults showing greater declines in memory for newly acquired information dependent on this ability, relative to well-established, long-standing memories that are more readily retrieved by older adults. Other areas of the brain yield similar observations. Consider, for example, the cerebellum—a brain region that plays a major role in orchestrating directed movement. Impaired motor coordination and balance are common complaints in old age, which could suggest impaired cerebellar function. In part, this is true because there is significant age-associated neuron loss in the anterior lobe of this structure, yet the entire cerebellum is not equally affected.

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