Effects of cardiorespiratory fitness and cerebral blood flow on cognitive outcomes in older women

Age-related decline in controlled retrieval: the role of the PFC and sleep

Age-related cognitive impairments often include difficulty retrieving memories, particularly those that rely on executive control. In this paper we discuss the influence of the prefrontal cortex on memory retrieval, and the specific memory processes associated with the prefrontal cortex that decline in late adulthood. We conclude that preretrieval processes associated with preparation to make a memory judgment are impaired, leading to greater reliance on postretrieval processes. This is consistent with the view that impairments in executive control significantly contribute to deficits in controlled retrieval. Finally, we discuss age-related changes in sleep as a potential mechanism that contributes to deficiencies in executive control that are important for efficient retrieval. The sleep literature points to the importance of slow-wave sleep in restoration of prefrontal cortex function. Given that slow-wave sleep significantly declines with age, we hypothesize that age-related changes in slow-wave sleep could mediate age-related decline in executive control, manifesting a robust deficit in controlled memory retrieval processes. Interventions, like physical activity, that improve sleep could be effective methods to enhance controlled memory processes in late life.

Reversal of glial and neurovascular markers of unhealthy brain aging by exercise in middle-aged female mice

Healthy brain aging and cognitive function are promoted by exercise. The benefits of exercise are attributed to several mechanisms, many which highlight its neuroprotective role via actions that enhance neurogenesis, neuronal morphology and/or neurotrophin release. However, the brain is also composed of glial and vascular elements, and comparatively less is known regarding the effects of exercise on these components in the aging brain. Here, we show that aerobic exercise at mid-age decreased markers of unhealthy brain aging including astrocyte hypertrophy, a hallmark of brain aging. Middle-aged female mice were assigned to a sedentary group or provided a running wheel for six weeks. Exercise decreased hippocampal astrocyte and myelin markers of aging but increased VEGF, a marker of angiogenesis. Brain vascular casts revealed exercise-induced structural modifications associated with improved endothelial function in the periphery. Our results suggest that age-related astrocyte hypertrophy/reactivity and myelin dysregulation are aggravated by a sedentary lifestyle and accompanying reductions in vascular function. However, these effects appear reversible with exercise initiated at mid-age. As this period of the lifespan coincides with the appearance of multiple markers of brain aging, including initial signs of cognitive decline, it may represent a window of opportunity for intervention as the brain appears to still possess significant vascular plasticity. These results may also have particular implications for aging females who are more susceptible than males to certain risk factors which contribute to vascular aging.

Association between white matter microstructure, executive functions, and processing speed in older adults: the impact of vascular health

Cerebral white matter damage is not only a commonly reported consequence of healthy aging, but is also associated with cognitive decline and dementia. The aetiology of this damage is unclear; however, individuals with hypertension have a greater burden of white matter signal abnormalities (WMSA) on MR imaging than those without hypertension. It is therefore possible that elevated blood pressure (BP) impacts white matter tissue structure which in turn has a negative impact on cognition. However, little information exists about whether vascular health indexed by BP mediates the relationship between cognition and white matter tissue structure. We used diffusion tensor imaging to examine the impact of vascular health on regional associations between white matter integrity and cognition in healthy older adults spanning the normotensive to moderate-severe hypertensive BP range (43-87 years; N = 128). We examined how white matter structure was associated with performance on tests of two cognitive domains, executive functioning (EF) and processing speed (PS), and how patterns of regional associations were modified by BP and WMSA. Multiple linear regression and structural equation models demonstrated associations between tissue structure, EF and PS in frontal, temporal, parietal, and occipital white matter regions. Radial diffusivity was more prominently associated with performance than axial diffusivity. BP only minimally influenced the relationship between white matter integrity, EF and PS. However, WMSA volume had a major impact on neurocognitive associations. This suggests that, although BP and WMSA are causally related, these differential metrics of vascular health may act via independent pathways to influence brain structure, EF and PS.

Improving cognition by adherence to physical or mental exercise: a moderated mediation analysis

BACKGROUND

The role of adherence to an intervention is examined to further understand the relationship between performing new challenging activities (either mental or physical ones) and their putative cognitive benefits.

METHOD

Healthy older women (N = 229, age range: 70-93 years) took part in a six-month randomised controlled trial, covering either a physical or mental activity (three × weekly). They completed five tests, measuring episodic and working memory pre- and post-intervention. A moderated mediation model was specified to test the strength of the indirect effect of the activity mode (i.e. physical vs. mental) through adherence (i.e. time spent on course attendance) on levels of baseline cognitive performance.

RESULTS

Both physical and mental activity groups performed better over time than the control group (p < 0.001). Adherence predicted cognitive performance (p = 0.011). The indirect effect of the activity mode on cognitive performance through adherence was especially seen when levels of baseline composite scores were low (p = 0.023).

CONCLUSION

Older healthy women can improve episodic and working memory through spending time on a challenging physical or mental activity. Results are most promising for cognitively less fit women. Time spent on course attendance can be interpreted as an adherence indicator that makes a difference for various cognitive outcomes of the intervention.

Contribution of physical fitness, cerebrovascular reserve and cognitive stimulation to cognitive function in post-menopausal women

Studies of the effects of physical fitness on cognition suggest that exercise can improve cognitive abilities in healthy older adults, as well as delay the onset of age-related cognitive decline. The mechanisms for the positive benefit of exercise and how these effects interact with other variables known to influence cognitive function (e.g., involvement in cognitive activities) are less well understood. The current study examined the associations between the physical fitness, cerebrovascular blood flow regulation and involvement in cognitive activities with neuropsychological function in healthy post-menopausal women.

METHODS

Forty-two healthy women between the ages of 55 and 90 were recruited. Physical fitness (V˙O2 max), cerebrovascular reserve (cerebral blood flow during rest and response to an increase in end-tidal (i.e., arterial) PCO2), and cognitive activity (self-reported number and hours of involvement in cognitive activities) were assessed. The association of these variables with neuropsychological performance was examined through linear regression.

RESULTS

Physical fitness, cerebrovascular reserve and total number of cognitive activities (but not total hours) were independent predictors of cognitive function, particularly measures of overall cognitive performance, attention and executive function. In addition, prediction of neuropsychological performance was better with multiple variables than each alone.

CONCLUSIONS

Cognitive function in older adults is associated with multiple factors, including physical fitness, cerebrovascular health and cognitive stimulation. Interestingly, cognitive stimulation effects appear related more to the diversity of activities, rather than the duration of activity. Further examination of these relationships is ongoing in a prospective cohort study.

Variation in blood pressure is associated with white matter microstructure but not cognition in African Americans

Although hypertension is a major risk factor for cerebrovascular disease (CVD) and is highly prevalent in African Americans, little is known about how blood pressure (BP) affects brain-behavior relationships in this population. In predominantly Caucasian populations, high BP is associated with alterations in frontal-subcortical white matter and in executive functioning aspects of cognition. We investigated associations among BP, brain structure, and neuropsychological functioning in 52 middle-older-age African Americans without diagnosed history of CVD. All participants underwent diffusion tensor imaging for examination of white matter integrity, indexed by fractional anisotropy (FA). Three regions of interest were derived in the anterior (genu) and posterior (splenium) corpus callosum and across the whole brain. A brief neuropsychological battery was administered from which composite scores of executive function and memory were derived. Blood pressure was characterized by mean arterial blood pressure (MABP). When controlling for age, higher MABP was associated with lower FA in the genu, and there was a trend for this same relationship with regard to whole-brain FA. When the sample was broken into groups on the basis of treatment for BP regulation (medicated vs. nonmedicated), MABP was related to genu and whole-brain FA only in the nonmedicated group. Neither MABP nor FA was significantly related to either neuropsychological composite score regardless of medication use. These data provide important evidence that variation in BP may contribute to significant alterations in specific neural regions of white matter in nonmedicated individuals without symptoms of overt CVD.

Aerobic exercise and neurocognitive performance: a meta-analytic review of randomized controlled trials

OBJECTIVES

To assess the effects of aerobic exercise training on neurocognitive performance. Although the effects of exercise on neurocognition have been the subject of several previous reviews and meta-analyses, they have been hampered by methodological shortcomings and are now outdated as a result of the recent publication of several large-scale, randomized, controlled trials (RCTs).

METHODS

We conducted a systematic literature review of RCTs examining the association between aerobic exercise training on neurocognitive performance between January 1966 and July 2009. Suitable studies were selected for inclusion according to the following criteria: randomized treatment allocation; mean age > or =18 years of age; duration of treatment >1 month; incorporated aerobic exercise components; supervised exercise training; the presence of a nonaerobic-exercise control group; and sufficient information to derive effect size data.

RESULTS

Twenty-nine studies met inclusion criteria and were included in our analyses, representing data from 2049 participants and 234 effect sizes. Individuals randomly assigned to receive aerobic exercise training demonstrated modest improvements in attention and processing speed (g = 0.158; 95% confidence interval [CI]; 0.055-0.260; p = .003), executive function (g = 0.123; 95% CI, 0.021-0.225; p = .018), and memory (g = 0.128; 95% CI, 0.015-0.241; p = .026).

CONCLUSIONS

Aerobic exercise training is associated with modest improvements in attention and processing speed, executive function, and memory, although the effects of exercise on working memory are less consistent. Rigorous RCTs are needed with larger samples, appropriate controls, and longer follow-up periods.

Increased heart rate variability and executive performance after aerobic training in the elderly

This study examined the effects of two short physical training programs on various parameters of heart rate variability (HRV) and on executive performance in older people. Twenty-four sedentary men and women aged 65-78 years were randomly assigned to an aerobic exercise program or a stretching program three times a week for 12 weeks. Resting HRV was measured in time and frequency domains in each participant before and after the 12-week programs. Executive performance was measured with the Wisconsin card sorting test (WCST). Significant group-session interactions emerged for the standard deviation of normal beat-to-beat (R-R) intervals, the root-mean-square of successive R-R, and high frequency power. Only the aerobic training group increased vagal-mediated HRV parameters. Moreover, only the participants in the aerobic training group improved their performance on the WCST. These results highlight the role of aerobic exercise as an important cardiac and brain protective factor, and suggest a direct link between exercise, HRV, and cognition in the aged population.