Representativeness of samples enrolled in Alzheimer's disease research centers.

To generalize findings on the mechanisms and prognosis in Alzheimer's disease and related dementias (ADRD), it is critical for ADRD research to be representative of the population. Sociodemographic and health characteristics across ethnoracial groups included in the National Alzheimer's Coordinating Center sample (NACC) were compared to the nationally representative Health and Retirement Study (HRS).Baseline NACC data (n = 36,639) and the weighted 2010 HRS wave (N = 52,071,840) were included. We assessed covariate balance by calculating standardized mean differences across harmonized covariates (i.e., sociodemographic, health).NACC participants were older, more educated, with worse subjective memory and hearing, but endorsed fewer depressive symptoms compared to HRS participants. While all racial and ethnic groups in NACC differed from HRS participants in the same way overall, these differences were further amplified between racial and ethnic groups.NACC participants do not represent the U.S. population in key demographic and health factors, which differed by race and ethnicity. HIGHLIGHTS: We examined selection factors included in NACC studies compared to a nationally representative sample.Selection factors included demographic and health factors and self-reported memory concerns.Results suggest that NACC participants are not representative of the U.S. population.Importantly, selection factors differed across racial and ethnic groups.Findings are suggestive of selection bias within NACC studies.

Impact of cardiovascular risk factors on the relationships of physical activity with mood and cognitive function in a diverse sample.

Physical activity has well-known benefits for older adults' mood and cognitive functioning; however, it is not clear whether risk factors for cardiovascular disease (CVD) affect the relationships of physical activity with these health outcomes among diverse older adults. This study investigated the impact of CVD risk burden on the relationships among self-reported physical activity, mood, and cognitive functioning in a diverse sample of 62 adults age 45 and older. We found that higher physical activity was associated with better attention and verbal working memory at lower CVD risk, but with worse attention and verbal working memory at higher CVD risk levels. Thus, higher CVD risk might limit the effectiveness of exercise interventions for mood and cognitive functioning. Future studies are needed to further clarify individual differences that impact the relationships among physical activity, CVD risk, and cognitive outcomes.

Subthreshold depressive symptoms relate to cuneus structure: Thickness asymmetry and sex differences.

Despite the prominence of frontolimbic regions in depression research, recent studies also implicate posterior brain regions, including the cuneus. The current study examined the relationship between depressive symptoms and asymmetry in cuneal cortical thickness in healthy adults between the ages of 18 and 81 with primarily subthreshold levels of depressive symptoms. An asymmetry index was calculated for cortical thickness in the cuneus [(left - right) × 100/(left + right)], and regression analyses were conducted with total scores on the Center for Epidemiologic Studies Depression Scale predicting this asymmetry index, controlling for age and sex. Higher depressive symptoms were associated with a left > right asymmetry in cuneal cortical thickness, reflecting greater cortical thickness in the left hemisphere compared to right hemisphere. Follow-up analyses examining CES-D subscales showed significant effects for somatic symptoms of depression, but not negative affect or anhedonia. Analyses stratified by sex yielded significant effects in men but not in women. Results of this preliminary study further support the cuneus' role in depression and highlight the importance of examining symptom dimensions and sex differences in the neurobiology of depression.

Be Fit, Be Sharp, Be Well: The Case for Exercise as a Treatment for Cognitive Impairment in Late-life Depression.

OBJECTIVE: To lay out the argument that exercise impacts neurobiological targets common to both mood and cognitive functioning, and thus more research should be conducted on its use as an alternative or adjunctive treatment for cognitive impairment in late-life depression (LLD). METHOD: This narrative review summarizes the literature on cognitive impairment in LLD, describes the structural and functional brain changes and neurochemical changes that are linked to both cognitive impairment and mood disruption, and explains how exercise targets these same neurobiological changes and can thus provide an alternative or adjunctive treatment for cognitive impairment in LLD. RESULTS: Cognitive impairment is common in LLD and predicts recurrence of depression, poor response to antidepressant treatment, and overall disability. Traditional depression treatment with medication, psychotherapy, or both, is not effective in fully reversing cognitive impairment for most depressed older adults. Physical exercise is an ideal treatment candidate based on evidence that it 1) is an effective treatment for depression, 2) enhances cognitive functioning in normal aging and in other patient populations, and 3) targets many of the neurobiological mechanisms that underlie mood and cognitive functioning. Results of the limited existing clinical trials of exercise for cognitive impairment in depression are mixed but overall support this contention. CONCLUSIONS: Although limited, existing evidence suggests exercise may be a viable alternative or adjunctive treatment to address cognitive impairment in LLD, and thus more research in this area is warranted. Moving forward, additional research is needed in large, diverse samples to translate the growing research findings into clinical practice.

Orbitofrontal and Cingulate Thickness Asymmetry Associated with Depressive Symptom Dimensions.

Both clinical depression and subthreshold depressive symptoms have been associated with alterations in cortical thickness. Studies have yielded conflicting results regarding whether cortical thinning or cortical thickening best characterize the depressive state. Also unclear is whether cortical thickness differences are lateralized. This study examined the relationship between depressive symptom dimensions and cortical thickness asymmetry in cingulate and orbitofrontal regions. Fifty-four community-dwelling adults between the ages of 18 and 81 years received a 3-Tesla magnetic resonance imaging scan and completed the Center for Epidemiologic Studies Depression Scale (CES-D). Cortical thickness values were extracted for the rostral anterior cingulate, caudal anterior cingulate, posterior cingulate, isthmus cingulate, and orbitofrontal cortex. An asymmetry index was calculated for each region. Data were analyzed using separate general linear models for each region, in which the CES-D somatic symptoms, negative affect, and anhedonia subscale scores predicted the asymmetry indices, controlling for age and sex. Higher scores on the anhedonia subscale were associated with right-sided asymmetry in orbitofrontal thickness, whereas higher somatic symptom subscale scores predicted greater left-sided asymmetry in posterior cingulate thickness. Follow-up analyses showed the orbitofrontal effect was specific to the medial, not the lateral, orbitofrontal cortex. These results suggest asymmetries in cortical thickness are apparent at even subthreshold levels of depressive symptoms, as all but five participants were below the CES-D cutoff for clinical depression, and that the relationship varies for different symptom dimensions of depression. Understanding brain asymmetries across the range of depressive symptom severity is important for informing targeted depression treatment.