Faculty Bibliography

Cardiovascular fitness is thought to offset declines in cognitive performance, but little is known about the cortical mechanisms that underlie these changes in humans. Research using animal models shows that aerobic training increases cortical capillary supplies, the number of synaptic connections, and the development of new neurons. The end result is a brain that is more efficient, plastic, and adaptive, which translates into better performance in aging animals. Here, in two separate experiments, we demonstrate for the first time to our knowledge, in humans that increases in cardiovascular fitness results in increased functioning of key aspects of the attentional network of the brain during a cognitively challenging task. Specifically, highly fit (Study 1) or aerobically trained (Study 2) persons show greater task-related activity in regions of the prefrontal and parietal cortices that are involved in spatial selection and inhibitory functioning, when compared with low-fit (Study 1) or nonaerobic control (Study 2) participants. Additionally, in both studies there exist groupwise differences in activation of the anterior cingulate cortex, which is thought to monitor for conflict in the attentional system, and signal the need for adaptation in the attentional network. These data suggest that increased cardiovascular fitness can affect improvements in the plasticity of the aging human brain, and may serve to reduce both biological and cognitive senescence in humans.

We investigated the relationship between behavioral measures of conflict and the degree of activity in the anterior cingulate cortex (ACC). We reanalyzed an existing data set that employed the Stroop task using functional magnetic resonance imaging [Milham et al., Brain Cogn 2002;49:277-296]. Although we found no changes in the behavioral measures of conflict from the first to the second half of task performance, we found a reliable reduction in the activity of the anterior cingulate cortex. This result suggests the lack of a strong relationship between behavioral measurements of conflict and anterior cingulate activity. A concomitant increase in dorsolateral prefrontal cortex activity was also found, which may reflect a tradeoff in the neural substrates involved in supporting conflict resolution, detection, or monitoring processes. A second analysis of the data revealed that the duration of an experiment can dramatically affect interpretations of the results, including the roles in which particular regions are thought to play in cognition. These results are discussed in relation to current conceptions of ACC's role in attentional control. In addition, we discuss the implication of our results with current conceptions of conflict and of its instantiation in the brain. Hum. Brain Mapping 21:96-105, 2004

In the first century, ce, the Roman satirist Juneval famously observed Orandum est, ut sit mens sana in corpore sano, or "A sound mind in a sound body is something to be prayed for." This implicit link between mental and physical health, also paralleled by Eastern philosophies and practices such as tai chi, has survived the millennia since Juneval and his contemporaries. More recently, controlled examinations of the effects of physical fitness on cognitive performance have shown that improving cardiovascular fitness (CVF) can help to reduce the deleterious effects of age on cognition and brain structure. Thus, as we age, it may well be the case that a sound mind is a natural concomitant of a sound body. Numerous cross-sectional and longitudinal studies have examined the effects of aerobic exercise on cognitive performance in aging humans since earlier studies, which found that physically fit older adults performed better on simple cognitive tasks than their less-fit counterparts. This base of knowledge recently has been furthered through examinations of cortical structure (Colcombe et al., 2003) and neurocognitive function in aging humans via functional and structural magnetic resonance imaging techniques. In this manuscript, we will briefly review some of our recent research on the effects of CVF on brain function, structure, and behavior in older adults. We will then outline some of our current and future directions in this area.

The present experiment examined the degree to which experience with different stimulus characteristics affects attentional capture, particularly as related to aging. Participants were presented with onset target/color singleton distractor or color singleton target/onset distractor pairs across three experimental sessions. The target/distractor pairs were reversed in the second session such that the target in the first session became the distractor in the second and third sessions. For both young and old adults previous experience with color as a target defining feature influenced oculomotor capture with task-irrelevant color distractors. Experience with sudden onsets had the same effect for younger and older adults, although capture effects were substantially larger for onset than for color distractors. Experience-based capture effects diminished relatively rapidly after target and distractor-defining properties were reversed. The results are discussed in terms of top-down and stimulus-driven effects on age-related differences in attentional control.

A meta-analytic study was conducted to examine the hypothesis that aerobic fitness training enhances the cognitive vitality of healthy but sedentary older adults. Eighteen intervention studies published between 1966 and 2001 were entered into the analysis. Several theoretically and practically important results were obtained. Most important fitness training was found to have robust but selective benefits for cognition, with the largest fitness-induced benefits occurring for executive-control processes. The magnitude of fitness effects on cognition was also moderated by a number of programmatic and methodological factors, including the length of the fitness-training intervention, the type of the intervention, the duration of training sessions, and the gender of the study participants. The results are discussed in terms of recent neuroscientific and psychological data that indicate cognitive and neural plasticity is maintained throughout the life span.

BACKGROUND:The human brain gradually loses tissue from the third decade of life onward, with concomitant declines in cognitive performance. Given the projected rapid growth in aged populations, and the staggering costs associated with geriatric care, identifying mechanisms that may reduce or reverse cerebral deterioration is rapidly emerging as an important public health goal. Previous research has demonstrated that aerobic fitness training improves cognitive function in older adults and can improve brain health in aging laboratory animals, suggesting that aerobic fitness may provide a mechanism to improve cerebral health in aging humans. We examined the relationship between aerobic fitness and in vivo brain tissue density in an older adult population, using voxel-based morphometric techniques. METHODS:We acquired high-resolution magnetic resonance imaging scans from 55 older adults. These images were segmented into gray and white matter maps, registered into stereotaxic space, and examined for systematic variation in tissue density as a function of age, aerobic fitness, and a number of other health markers. RESULTS:Consistent with previous studies of aging and brain volume, we found robust declines in tissue densities as a function of age in the frontal, parietal, and temporal cortices. More importantly, we found that losses in these areas were substantially reduced as a function of cardiovascular fitness, even when we statistically controlled for other moderator variables. CONCLUSIONS:These findings extend the scope of beneficial effects of aerobic exercise beyond cardiovascular health, and they suggest a strong solid biological basis for the benefits of exercise on the brain health of older adults.

Five studies were conducted to examine the nature of life satisfaction judgments. When the category of "excitement" was made accessible experimentally, individuals based their life satisfaction judgments more heavily on the frequency of excitement, in comparison to a "peaceful" condition in Study 1 and to both "neutral priming" and "no-priming" conditions in Study 2. A 7-day diary study (Study 3) showed that as "excitement" became naturally more accessible on weekends, the correlations between excitement and daily satisfaction also increased significantly. Study 3 thus illustrated a systematic contextual shift in the bases of life satisfaction judgments. Study 4 showed that high sensation seekers, for whom "excitement" should be chronically accessible, based their life satisfaction judgments more heavily on the frequency of excitement than did low sensation seekers. Finally, Study 5 demonstrated that the chronic accessibility of "excitement" measured at Time 1 predicted the degree to which individuals based their life satisfaction judgments on the frequency of excitement at Time 2. Altogether, these five studies highlight the contextually sensitive, yet systematic nature of life satisfaction judgments. © 2003 Elsevier Science (USA). All rights reserved.

This study investigated the hypothesis that age differences in memory performance may be influenced by stereotype threat associated with negative cultural beliefs about the impact of aging on memory. Recall was examined in 48 young and 48 older adults under conditions varying in the degree of induced threat. Conditions that maximize threat resulted in lower performance in older adults relative to both younger adults and to older adults who did not experience threat. The degree to which threat affected older adults' performance increased along with the value that these individuals placed on their memory ability. Older adults' memory performance across experimental conditions was observed to covary with degree of activation of the negative aging stereotype, providing support for the hypothesized relationship between stereotype activation and performance. Finally, stereotype threat also influenced mnemonic strategy use, which in turn partially mediated the impact of threat on recall. These results emphasize the important role played by contextual factors in determining age differences in memory performance.

The present article provides a brief review of the human and animal literature that has investigated the relationship between fitness training and brain and cognitive function. The animal research clearly suggests that improvements in fitness can lead to both morphological and functional changes in the brains of older animals. Results of a recent meta-analysis suggest that fitness training can also have beneficial effects on human cognition, particularly on tasks requiring executive control processing. These effects are also moderated by a number of factors, including the proportion of men and women in the intervention studies, the length of training sessions, the age of the participants, and the combination of fitness training regimes. The article also discusses preliminary results that link, for the first time, fitness training and differences in human brain structure and function. Finally, we discuss the important issue of participant adherence to fitness training programs and the factors that influence fitness participation.