Elsevier

Neurobiology of Aging

Volume 23, Issue 5, September–October 2002, Pages 941-955
Neurobiology of Aging

Exercise, experience and the aging brain

https://doi.org/10.1016/S0197-4580(02)00028-3Get rights and content

Abstract

While limited research is available, evidence indicates that physical and mental activity influence the aging process. Human data show that executive functions of the type associated with frontal lobe and hippocampal regions of the brain may be selectively maintained or enhanced in humans with higher levels of fitness. Similarly enhanced performance is observed in aged animals exposed to elevated physical and mental demand and it appears that the vascular component of the brain response may be driven by physical activity whereas the neuronal component may reflect learning. Recent results have implicated neurogenesis, at least in the hippocampus, as a component of the brain response to exercise, with learning enhancing survival of these neurons. Non-neuronal tissues also respond to experience in the mature brain, indicating that the brain reflects both its recent and its longer history of experience. Preliminary measures of brain function hold promise of increased interaction between human and animal researchers and a better understanding of the substrates of experience effects on behavioral performance in aging.

Introduction

For the most part, investigations of aging on plasticity of brain and cognition have been functionally dichotomized. Brain plasticity typically has been examined using animal models while studies of cognitive plasticity have been performed predominantly in humans. Recent advances in neuroimaging techniques and a convergence of behavioral intervention strategies have begun to narrow the gulf between animal brain plasticity and human cognitive studies of aging. In the following discussion, we will review the unique contributions of animal and human studies to our understanding of plasticity during aging, highlight those areas of overlap, and speculate on promising avenues for further research.

Section snippets

Human cognitive decline: fitness and aging

Much of the current research on human cognition and aging has focused on characterizing the qualitative and quantitative changes that take place in human cognition from young adulthood to old age. Indeed, the great majority of this research suggests that both general as well as process specific declines occur in a variety of perceptual, cognitive and action-related processes during the course of normal aging. Older adults typically perform more poorly than young adults in terms of both response

Behavioral effects of exercise in aging animals

There is a small but consistent body of literature on the effects of exercise on behavioral learning tasks in animals. One aspect of this work that parallels observations from human studies involves hippocampal-dependent tasks that parallel those requiring executive function in humans. For example, it has been demonstrated that physical activity enhanced performance on a spatial learning task in rodents [65], [67]. In addition to increasing performance, exercise has also been shown to increase

Brain plasticity in aging animals

The responsiveness of human cognition to interventions such as exercise is paralleled by animal studies of brain responsiveness to experience. Origins of this work date to Hebb [88], [89], who was among the first to show that the conditions under which animals were housed affected their behavioral abilities. Subsequently, Rosenzweig et al. [144] demonstrated that the volume of the cerebral cortex could be altered by rearing animals in what they termed “enriched” versus “impoverished”

Synaptogenesis

Early studies of brain morphology indicated that regions of cerebral cortex were heavier and thicker in rats exposed to a complex environment [20]. These observations could be accounted for by one of two primary neural mechanisms: (1) that neurogenesis was occurring at a rate that greatly exceeded that of apoptotic cell death; or (2) that existing cells were expanding the number of contacts made with surrounding neurons. The former explanation was not met with overwhelming enthusiasm as mitosis

Neurogenesis

In addition to maintaining the ability to modify specific neuronal properties outlined above, it has become clear that at least some regions of the adult brain can also respond to environmental stimuli by adding new neurons. Though this form of brain plasticity still evokes some controversy, postnatal neurogenesis is now gaining general acceptance. The first report of adult neurogenesis dates back to 1962 in a study assessing the response of the brain to injury. Using 6H-thymidine incorporation

Glial plasticity

Less well known than these effects of neuron addition and plasticity of established neurons are the extensive effects of experience upon non-neuronal elements of the brain. For example, astrocyte process surface density is approximately 20% greater per neuron in the visual cortex of EC rats, compared to IC rats [157]. An issue of interest, already addressed above, is the specific relationship of these changes to the types of functional demands. Specifically, there are at least two aspects of

Vascular plasticity

As is evident above, investigations of pathological modifications of the brain associated with the aging process have focused almost exclusively on neuronal morphology; however, significant deterioration of the brain’s vasculature also occurs [50], [51], [61], [62]. This decline may include loss of vessels, changes in vessel wall characteristics, deposition of collagen and other material, and declines in blood flow, oxygen extraction and glucose transport [156]. The precise role that these

Brain imaging and humans

The rapidly developing field of human neuroimaging provides a means for establishing the relationship between fitness, cognition and brain function. Indeed, in recent years, there has been a growing body of literature examining age-related differences in patterns of brain activation, through the use of PET and fMRI, in a variety of cognitive operations including attention, multi-task processing and task switching, linguistic processing, and aspects of working and long-term memory. Although it

Summary and conclusions

The overall goal of this special section of Neurobiology of Aging is to ask whether there are interventions that can mitigate the brain aging process. As our review of some of the data regarding the effects of experience, and particularly of physical exercise, makes clear, studies of the aging brain and behavioral response to experience have revealed parallel patterns across animal and human research, despite the rather disparate measures that have been applied to the issues. In the human

Acknowledgements

Supported in part by grants NIA/AG10154 (WTG), NIA/AG14966 (AFK), MH35321 (WTG), Institute for the Study of Aging (AFK).

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    The first three authors contributed equally to this publication.

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