The Impact of Age on Cognition

Abstract

This article reviews the cognitive changes that occur with normal aging, the structural and functional correlates of these cognitive changes, and the prevalence and cognitive effects of age-associated diseases. Understanding these age-related changes in cognition is important given our growing elderly population and the importance of cognition in maintaining functional independence and effective communication with others. The most important changes in cognition with normal aging are declines in performance on cognitive tasks that require one to quickly process or transform information to make a decision, including measures of speed of processing, working memory, and executive cognitive function. Cumulative knowledge and experiential skills are well maintained into advanced age. Structural and function changes in the brain correlate with these age-related cognitive changes, including alterations in neuronal structure without neuronal death, loss of synapses, and dysfunction of neuronal networks. Age-related diseases accelerate the rate of neuronal dysfunction, neuronal loss, and cognitive decline, with many persons developing cognitive impairments severe enough to impair their everyday functional abilities. There is emerging evidence that healthy lifestyles may decrease the rate of cognitive decline seen with aging and help delay the onset of cognitive symptoms in the setting of age-associated diseases.

Keywords: Cognition; aging; neurodegeneration.

Figure 1

Change in “crystalized” cognitive abilities, represented here as vocabulary, and “fluid” cognitive abilities, represented here as processing speed, with age in normal subjects. Graph is based upon data presented by T.A. Salthouse and colleagues. Zero line represents the mean or average performance on these measures, while values above zero represent better than average performance and below the line worse than average performance.

Figure 2

Change in synaptic density with advancing age in four groups. When synaptic density declines to 60% of maximal density, symptoms of dementia would be expected (i.e., dementia threshold line). Someone with normal reserve and normal rate of synaptic loss with age (i.e., normal aging) would cross the dementia threshold line around age 130. An intervention that slowed the rate of synaptic loss with age (slower aging) would keep the synaptic density above the dementia threshold beyond age 150. However, someone that started with 30% less synaptic density than normal at age 25 would cross the threshold line much earlier even with normal aging (age 62), as would someone with normal density who developed a degenerative disease such as Alzheimer's that increased the rate of synapse loss with age (i.e., age 72). Graph and concepts based upon data and hypothesis presented by R.D. Terry and R. Katzman.