Associations Between Cardiorespiratory Fitness, Adiposity, and White Matter Integrity

White matter (WM) is essential for transmitting neural signal between brain regions, and supporting healthy brain aging and cognitive function. Risk for WM deterioration is heightened in overweight and obesity, whereas increasing cardiorespiratory fitness may promote WM integrity. However, there is a lack of research comparing adiposity and cardiorespiratory fitness with WM. Further, it is not clear whether increasing cardiorespiratory fitness may outweigh the influence of excess adiposity on WM integrity in middle adulthood. In a sample of adults with overweight and obesity, we examined whether cardiorespiratory fitness and adiposity associate with WM integrity, both independently and jointly. We assessed WM pathways sensitive to cardiorespiratory fitness, adiposity, or both, and tested potential interactions. Baseline data from 125 middle-aged participants (Mage = 44.33 ± 8.60), with overweight or obesity (MBMI = 32.45 ± 4.19), were included in the study. Fitness was assessed via a submaximal graded exercise test. To quantify adiposity, whole body estimates of body fat % were calculated using dual-energy X-ray absorptiometry. Diffusion weighted images were acquired during an MRI protocol. We conducted whole-brain voxelwise analyses using the FMRIB’s Software Library randomise function to examine main effects of adiposity and fitness, as well as the interaction term, on WM integrity. After controlling for age, gender, and years of education, there were no significant main effects of adiposity or cardiorespiratory fitness on FA (all p > .05). There was a significant interaction (p = .03) such that with higher fitness levels, greater adiposity was associated with higher WM integrity, whereas with lower fitness levels greater adiposity was negatively associated with WM integrity. This pattern of findings was unexpected, and may be a function of the unique nature of the sample or related to the confounding effects of WM lesions or local inflammation. Future work may focus on accounting for the influence of WM lesions, and extending the analysis to older adults and patient populations

Examining the relationship between fitness, cortical excitability, and neurochemistry of the brain (GABA, glutamate, and NAA)

L'exercice aérobique (AE) est associé à de nombreuses modifications fonctionnelles et anatomiques dans le cerveau humain. Par exemple, il a été démontré que l'EA modulait l'excitabilité corticale et la neurochimie immédiatement après l'exercice. Les effets d'une activité physique répétée et soutenue sur les fonctions cérébrales restent toutefois mal compris. En effet, peu de données sont disponibles permettant de déterminer si les personnes ayant une bonne condition physique présentent des modifications persistantes de l'excitabilité corticale et du métabolisme cérébral malgré les changements rapportés dans la matière grise et la matière blanche. Dans la présente étude, 20 personnes sédentaires en bonne santé ( 6 heures/semaine d'activité physique) sur la base de mesures de l'excitabilité corticale (rMT, courbe I/O, SICI, ICF) et de la concentration de métabolites (GABA, Glx, NAA) dans la représentation corticale de la main droite. L'épaisseur corticale de la représentation du cortex moteur primaire de la main droite et la densité apparente des fibres de la voie corticospinale (CST) ont également été évaluées. L'aptitude cardiorespiratoire (VO2max) était significativement plus élevée chez les athlètes que chez les sédentaires, ce qui n'était pas le cas de l'indice de masse corporelle. Aucune différence entre les groupes n'a été constatée en ce qui concerne les mesures du rMT, du SICI et de l'ICF. Les valeurs de la courbe I/O étaient significativement plus élevées et la courbe I/O était plus prononcée chez les individus actifs. Aucune différence significative n'a été observée pour l'épaisseur corticale, la concentration de métabolites et les valeurs de diffusion de la CST. La pente de la courbe I/O était positivement corrélée à la VO2max. Les présentes données suggèrent que des niveaux élevés de capacité aérobique sont associés à une excitabilité corticale accrue dans la représentation de la main du cortex moteur primaire.Aerobic exercise is associated with widespread functional and anatomical modifications in the human brain. For example, AE has been shown to modulate cortical excitability and neurochemistry immediately after exercise. The effects of repeated and sustained physical activity on brain function, however, remain poorly understood. Indeed, little is known about whether individuals with high levels of fitness display persistent modifications in cortical excitability and brain metabolism despite reported changes in grey and white matter. In the present study, 20 healthy sedentary individuals ( 6 hours/week AE) on measures of cortical excitability (rMT, I/O curve, SICI, ICF) and metabolite concentration (GABA, Glx, NAA) in the cortical representation of the right hand. Cortical thickness of the primary motor cortex representation of the right hand and corticospinal tract (CST) apparent fiber density (AFD) were also assessed. Cardiorespiratory fitness (VO2max) was significantly higher in athletes compared to sedentary individuals whereas body mass index was not. No group differences were found on measures of rMT, SICI and ICF. I/O curve values were significantly higher, and the I/O curve was steeper in active individuals. No significant differences were observed between the groups for cortical thickness, metabolite concentration and CST diffusion values. I/O curve slope was positively correlated with VO2max. The present data suggest that high levels of aerobic fitness are associated with increased cortical excitability in the hand representation of the primary motor cortex

ASSOCIATIONS BETWEEN CARDIORESPIRATORY FITNESS AND WORKING MEMORY FMRI BRAIN ACTIVITY

Working memory (WM) and associated brain areas show deficits with increasing age. However, higher cardiorespiratory fitness (CRF) has been associated with better WM across the lifespan. The mechanisms by which CRF impacts WM are poorly understood. One possible mechanism is that CRF influences the integrity and function of brain regions that are involved in supporting WM function, and that this, in turn, influences accuracy rates on tasks that measure WM. Very few studies have tested whether the association between CRF and WM is statistically mediated by measures of brain function. This study addressed this gap in knowledge by examining the relationship between CRF, brain activation, and WM. We tested whether brain activation during a WM task statistically mediated the relationship between CRF and WM. Baseline data of 125 adults (M=44.34 ± 8.60 years) were included in this study. CRF was assessed via a submaximal graded exercise test. Magnetic resonance images were collected during the n-back task to examine neural responses to WM. FMRIB’s Software Library was used for fMRI data preprocessing and analysis. Regions-of-interest were defined by conducting a conjunction analysis to identify brain regions sensitive to both CRF and performance on the n-back task. Linear regression models examined the association of CRF with WM and brain activation in the left anterior cingulate cortex, left insula, and right insula. After controlling for age, gender, race, and years of education, CRF was not significantly related to accuracy on the WM task (all p>.15). However, consistent with our hypotheses, higher CRF was significantly related to greater brain activation in the left insula (p<.028) during the 2-back WM condition. Heightened brain activation in the left insula was not associated with WM accuracy (p=.12) after correction for variation due to age, gender, race, and education. Thus, statistical mediation could not be tested. Although higher CRF was associated with greater brain activation in the left insula, neither CRF nor heightened left insula activation were associated with variations in WM performance after adjusting for several confounding variables. These results suggest that there are other mediators that explain the relationship between CRF and WM performance in midlife

The Effects of Exercise on Working Memory in Adults

Background: Working memory (WM) is a crucial element of cognitive function. A reduction in WM capacity may adversely impact the quality of life and elevate the risk of developing neurodegenerative diseases in the future. Presently, no established medication can effectively prevent cognitive decline. Objective: Over the past decade, numerous research articles have investigated the consequences of exercise on cognitive function, mainly focusing on WM in adults.Methods: Critical reading of several pieces of literature discussing exercise's effect on WM. A search for scientific articles was conducted using online databases such as PubMed and Google Scholar.Results: Exercise improves WM through neuroplasticity. Post-exercise improvement in WM can be seen in every age studied. Exercise can reduce the risk of neurodegenerative diseases by maintaining the integrity of the substantia alba.Conclusion: Exercise emerges as a cost-effective strategy accessible to many individuals. It can potentially prevent declines in cognitive function, positively impacting both present and future quality of life

Physical Activity Predicts Population-Level Age-Related Differences in Frontal White Matter.

Physical activity has positive effects on brain health and cognitive function throughout the life span. Thus far, few studies have examined the effects of physical activity on white matter microstructure and psychomotor speed within the same, population-based sample (critical if conclusions are to extend to the wider population). Here, using diffusion tensor imaging and a simple reaction time task within a relatively large population-derived sample (N = 399; 18-87 years) from the Cambridge Centre for Ageing and Neuroscience (Cam-CAN), we demonstrate that physical activity mediates the effect of age on white matter integrity, measured with fractional anisotropy. Higher self-reported daily physical activity was associated with greater preservation of white matter in several frontal tracts, including the genu of corpus callosum, uncinate fasciculus, external capsule, and anterior limb of the internal capsule. We also show that the age-related slowing is mediated by white matter integrity in the genu. Our findings contribute to a growing body of work, suggesting that a physically active lifestyle may protect against age-related structural disconnection and slowing

Physical Activity and Hippocampal Sub-Region Structure in Older Adults with Memory Complaints.

BackgroundPhysical activity (PA) plays a major role in maintaining cognition in older adults. PA has been shown to be correlated with total hippocampal volume, a memory-critical region within the medial temporal lobe (MTL). However, research on associations between PA and MTL sub-region integrity is limited.ObjectiveTo examine the relationship between PA, MTL thickness, and its sub-regions, and cognitive function in non-demented older adults with memory complaints.MethodsTwenty-nine subjects aged ≥60 years, with memory complaints were recruited for this cross-sectional study. PA was tracked for 7 days using accelerometers, and average number of steps/day determined. Subjects were categorized into two groups: those who walked ≤4000 steps/day (lower PA) and those with &gt;4000 steps/day (higher PA). Subjects received neuropsychological testing and 3T MRI scans. Nonparametric ANCOVAs controlling for age examined differences between the two groups.ResultsTwenty-six subjects aged 72.7(8.1) years completed the study. The higher PA group (n = 13) had thicker fusiform gyrus (median difference = 0.11 mm, effect size (ES) = 1.43, p = 0.001) and parahippocampal cortex (median difference = 0.12 mm, ES = 0.93, p = 0.04) compared to the lower PA group. The higher PA group also exhibited superior performance in attention and information-processing speed (median difference = 0.90, ES = 1.61, p = 0.003) and executive functioning (median difference = 0.97, ES = 1.24, p = 0.05). Memory recall was not significantly different between the two groups.ConclusionOlder non-demented individuals complaining of memory loss who walked &gt;4000 steps each day had thicker MTL sub-regions and better cognitive functioning than those who walked ≤4000 steps. Future studies should include longitudinal analyses and explore mechanisms mediating hippocampal related atrophy

Cardiorespiratory Fitness Diminishes the Effects of Age on White Matter Hyperintensity Volume

White matter hyperintensities (WMHs) are among the most commonly observed marker of cerebrovascular disease. Age is a key risk factor for WMH development. Cardiorespiratory fitness (CRF) is associated with increased vessel compliance, but it remains unknown if high CRF affects WMH volume. This study explored the effects of CRF on WMH volume in community-dwelling older adults. We further tested the possibility of an interaction between CRF and age on WMH volume. Participants were 76 adults between the ages of 59 and 77 (mean age = 65.36 years, SD = 3.92) who underwent a maximal graded exercise test and structural brain imaging. Results indicated that age was a predictor of WMH volume (beta = .32, p = .015). However, an age-by-CRF interaction was observed such that higher CRF was associated with lower WMH volume in older participants (beta = -.25, p = .040). Our findings suggest that higher levels of aerobic fitness may protect cerebrovascular health in older adults

Neuroprotective Effects of Cardiorespiratory Fitness on White Matter Integrity and Cognition Across the Adult Lifespan

Objective: Cardiorespiratory fitness (CRF) is associated with decreased risk for cognitive decline. Accumulating evidence has linked CRF to more conserved white matter (WM) integrity and better cognitive performance in older adults. Additional research is needed to determine: (1) which WM tracts are most strongly related to CRF, (2) whether CRF-related benefits on WM translate to enhanced executive functioning (EF), and (3) if the neuroprotective effects of CRF are age-dependent. This study aimed to evaluate CRF as an intervention for modulating decreased WM integrity and EF in aging. Method: Participants were community-dwelling adults (N = 499; ages 20-85) from the open-access Nathan Kline Institute – Rockland Sample (NKIRS) with CRF (bike test), self-report of physical activity, diffusion tensor imaging (DTI), and EF data. Mixed-effect modeling tested the interaction between CRF and age on WM integrity (global and local microstructure). Significant WM tracts were retained for structural equation modeling to determine whether enhanced microstructure mediated a positive relationship between CRF and EF. Results: Among older participants (age 60), CRF was significantly related to stronger whole-brain (z-score slope = 0.11) and local WM integrity within five tracts (z-score slope range = 0.14 – 0.20). In support of the age-dependent hypothesis, the CRF–WM relationship was comparably weaker (z-score slopes 0.11) and more limited (one WM tract) in younger adults. CRF was more consistently related to WM than self-report of physical activity. Although CRF was linked to enhanced WM integrity, its potential benefits on EF were not directly observed. Conclusion: The findings highlight the importance of positive lifestyle factors, such as physical activity, in maintaining brain health in senescence. CRF may selectively preserve a collection of anterior and posterior WM connections related to visuomotor function

The relationships between cardiorespiratory fitness, white matter integrity, and cognitive function in older adulthood

White matter in the brain supports higher-order cognitive processes by facilitating signal transmission between diverse cortical regions. White matter integrity declines with advancing age, leading to impairments in memory and executive processes in older adulthood. Recent research suggests that higher-fit older adults may be less susceptible to white matter degeneration, although evidence for this relationship is limited. Here we examine whether cardiorespiratory fitness correlates with white matter integrity and whether this relationship further predicts cognitive performance in a large, older adult sample. Diffusion tensor imaging was used to determine microstructural white matter integrity in a group of 113 (mean age = 66.61) neurologically healthy adults. Measures of cardiorespiratory fitness (VO2), working memory, and executive function were also collected. Using a whole-brain voxelwise analysis, we found that higher fitness levels predicted greater white matter integrity in multiple fiber pathways. We explored this relationship further using a region of interest approach, and found that higher fitness was associated with greater microstructural integrity in the anterior internal capsule and corona radiata, which contain fibers that project from subcortical to prefrontal structures. Further, statistical mediation analysis revealed that white matter integrity within the anterior internal capsule and corona radiata mediated the relationship between fitness and spatial working memory performance. Results suggest that higher levels of aerobic fitness may protect against age-related declines in white matter integrity, which may, in turn, preserve memory performance in older adulthood

A life-long approach to physical activity for brain health

It is well established that engaging in lifelong Physical activity (PA) can help delay the onset of many chronic lifestyle related and non-communicable diseases such as cardiovascular disease, type two diabetes, cancer and chronic respiratory diseases. Additionally, growing evidence also documents the importance of PA for brain health, with numerous studies indicating regular engagement in physical activities may be protective against cognitive decline and dementia in late life. Indeed, the link between PA and brain health may be different at each stage of life from childhood, mid-life and late life. Building on this emerging body of multidisciplinary research, this review aims to summarize the current body of evidence linking regular PA and brain health across the lifespan. Specifically, we will focus on the relationship between PA and brain health at three distinct stages of life: childhood and adolescence, mid-life, late life in cognitively healthy adults and later life in adults living with age-related neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease (AD).Helen Macpherson, Wei-P. Teo, Luke A. Schneider and Ashleigh E. Smit