Increased neural differentiation after a single session of aerobic exercise in older adults.

Aging is associated with decreased cognitive function. One theory posits that this decline is in part due to multiple neural systems becoming dedifferentiated in older adults. Exercise is known to improve cognition in older adults, even after only a single session. We hypothesized that one mechanism of improvement is a redifferentiation of neural systems. We used a within-participant, cross-over design involving 2 sessions: either 30 minutes of aerobic exercise or 30 minutes of seated rest (n = 32; ages 55-81 years). Both functional Magnetic Resonance Imaging (fMRI) and Stroop performance were acquired soon after exercise and rest. We quantified neural differentiation via general heterogeneity regression. There were 3 prominent findings following the exercise. First, participants were better at reducing Stroop interference. Second, while there was greater neural differentiation within the hippocampal formation and cerebellum, there was lower neural differentiation within frontal cortices. Third, this greater neural differentiation in the cerebellum and temporal lobe was more pronounced in the older ages. These data suggest that exercise can induce greater neural differentiation in healthy aging.

Blood pressure-related differences in brain health between young African Americans and Caucasian Americans.

BACKGROUND: Although there are moderating effects of race on blood pressure (BP) and brain health in older adults, it is currently unknown if these race-related differences in cardiovascular and associated brain function are also present in younger adults. The purpose of this study was to investigate the interaction between race and BP on brain health in younger African (AA) and Caucasian Americans (CA). METHODS: We studied 971 younger adults (29.1 ± 3.5 years; 180 AAs and 791 CAs) who volunteered to participate in the Human Connectome Project. Cognitive composite scores, brain volume, and cortical thickness using MRI were cross-sectionally assessed. ANCOVA was used to examine interactions between race and mean arterial pressure (MAP) on cognitive test scores and brain structure. RESULTS: After controlling for age, sex, education, and BMI, there were significant Race × MAP interaction effects on cognitive composite scores and cortical thickness. Among AAs but not CAs, as MAP increased, both global cognitive performance and entorhinal cortex (ERC) thickness decreased. CONCLUSIONS: MAP was an important moderator of racial differences in cognitive performance and ERC thickness. Our findings suggest that young AAs may carry a greater hypertension-associated risk for cognitive brain health deficit. Interventions that address early signs of hypertension in AAs are needed to determine if the racial disparities in BP-related brain health in late adulthood can be reduced.

Greater Semantic Memory Activation After Exercise Training Cessation in Older Endurance-Trained Athletes.

PURPOSE: To examine the effects of a 10-day exercise-training cessation on semantic memory functional activation in older distance runners. METHODS: Ten master runners (62.6 ± 7.0 years) with a long-term endurance-training history (29.0 ± 6.0 years) underwent a 10-day training cessation. Before and immediately after the training cessation, semantic memory activation was measured during the famous name recognition task, using functional magnetic resonance imaging. RESULTS: The 10-day training cessation resulted in greater semantic memory activation in three brain regions, including the left inferior frontal gyrus, parahippocampal gyrus, and inferior semilunar lobule. The 10-day training cessation did not significantly alter famous name recognition task performance. CONCLUSIONS: The findings demonstrate that even a relatively short period without exercise training alters the functional activation patterns of semantic memory-related neural networks. Increased semantic memory activation after training cessation may indicate reduced neural efficiency during successful memory retrieval.

Episodic Memory and Hippocampal Volume Predict 5-Year Mild Cognitive Impairment Conversion in Healthy Apolipoprotein ε4 Carriers.

OBJECTIVE: The Apolipoprotein (APOE) ε4 allele increases the risk for mild cognitive impairment (MCI) and dementia, but not all carriers develop MCI/dementia. The purpose of this exploratory study was to determine if early and subtle preclinical signs of cognitive dysfunction and medial temporal lobe atrophy are observed in cognitively intact ε4 carriers who subsequently develop MCI. METHODS: Twenty-nine healthy, cognitively intact ε4 carriers (ε3/ε4 heterozygotes; ages 65-85) underwent neuropsychological testing and MRI-based measurements of medial temporal volumes over a 5-year follow-up interval; data were converted to z-scores based on a non-carrier group consisting of 17 ε3/ε3 homozygotes. RESULTS: At follow-up, 11 ε4 carriers (38%) converted to a diagnosis of MCI. At study entry, the MCI converters had significantly lower scores on the Mini-Mental State Examination, Rey Auditory Verbal Learning Test (RAVLT) Trials 1-5, and RAVLT Immediate Recall compared to non-converters. MCI converters also had smaller MRI volumes in the left subiculum than non-converters. Follow-up logistic regressions revealed that left subiculum volumes and RAVLT Trials 1-5 scores were significant predictors of MCI conversion. CONCLUSIONS: Results from this exploratory study suggest that ε4 carriers who convert to MCI exhibit subtle cognitive and volumetric differences years prior to diagnosis.

Caudate Volume Mediates the Interaction between Total Sleep Time and Executive Function after Acute Exercise in Healthy Older Adults.

Although both exercise and sleep are significant lifestyle factors in cognitive aging, the interaction of these two factors with respect to cognition remains to be determined. Also, little is known regarding the role of the basal ganglia (BG) in cognitive aging despite its involvement in both sleep and executive function. The primary objective of this study was to investigate the interaction between sleep and acute exercise on executive function performance, and secondarily, to assess if BG volume mediates this interaction. Thirty healthy older adults (65.8±7.3 years) completed 30 minutes of seated rest or moderate-intensity cycling exercise on different days. Structural MRI was used to assess the volumes of BG components including caudate, putamen, and globus pallidus shortly after the experimental conditions. Approximately 90 minutes after each condition, the Stroop task was administered to measure executive function. To examine sleep, participants wore a wrist actigraph for 8.0±3.6 days prior to the first experimental session. Results revealed that while longer total sleep time (TST) was associated with shorter Stroop response time (RT), shorter TST was associated with longer RT after exercise, compared to rest, for both congruent (p = 0.029) and incongruent (p = 0.022) trials. Longer TST was correlated with greater caudate volume, and greater caudate volume was associated with exercise-related improvement in Stroop incongruent RT. Ultimately, we found that the association between longer sleep duration and faster processing speed after acute exercise was mediated by greater caudate volume. These findings suggest that TST is an important factor for acute exercise-induced cognitive improvements in older adults, and that our study is a first step in understanding the interactive effects of these important lifestyle factors in cognitive aging that might simultaneously be addressed to promote healthy cognitive aging. Future studies should examine the interactive effects of sleep and chronic exercise on cognitive function, and whether BG volume might also mediate this interaction.

Comparison of semantic and episodic memory BOLD fMRI activation in predicting cognitive decline in older adults.

Previous studies suggest that task-activated functional magnetic resonance imaging (fMRI) can predict future cognitive decline among healthy older adults. The present fMRI study examined the relative sensitivity of semantic memory (SM) versus episodic memory (EM) activation tasks for predicting cognitive decline. Seventy-eight cognitively intact elders underwent neuropsychological testing at entry and after an 18-month interval, with participants classified as cognitively "Stable" or "Declining" based on ≥ 1.0 SD decline in performance. Baseline fMRI scanning involved SM (famous name discrimination) and EM (name recognition) tasks. SM and EM fMRI activation, along with Apolipoprotein E (APOE) ε4 status, served as predictors of cognitive outcome using a logistic regression analysis. Twenty-seven (34.6%) participants were classified as Declining and 51 (65.4%) as Stable. APOE ε4 status alone significantly predicted cognitive decline (R(2) = .106; C index = .642). Addition of SM activation significantly improved prediction accuracy (R(2) = .285; C index = .787), whereas the addition of EM did not (R(2) = .212; C index = .711). In combination with APOE status, SM task activation predicts future cognitive decline better than EM activation. These results have implications for use of fMRI in prevention clinical trials involving the identification of persons at-risk for age-associated memory loss and Alzheimer's disease.