Variation in the fitted filtration efficiency of disposable face masks by sex.

BACKGROUND & OBJECTIVE: Disposable face masks are a primary protective measure against the adverse health effects of exposure to infectious and toxic aerosols such as airborne viruses and particulate air pollutants. While the fit of high efficiency respirators is regulated in occupational settings, relatively little is known about the fitted filtration efficiencies of ear loop style face masks worn by the public. METHODS: We measured the variation in fitted filtration efficiency (FFE) of four commonly worn disposable face masks, in a cohort of healthy adult participants (N = 100, 50% female, 50% male, average age = 32.3 ± 9.2 years, average BMI = 25.5 ± 3.4) using the U.S. Occupational Safety and Health Administration Quantitative Fit Test, for an N95 (respirator), KN95, surgical, and KF94 masks. The latter three ear loop style masks were additionally tested in a clip-modified condition, tightened using a plastic clip to centrally fasten loops in the back of the head. RESULTS: The findings show that sex is a major determinant of the FFE of KN95, surgical, and KF94 masks. On average, males had an 11% higher FFE relative to females, at baseline testing. We show that a simple modification using an ear loop clip, results in improvements in the average FFE for females but provides comparatively minor changes for males. On average, females had a 20% increased FFE when a clip was worn behind the head, relative to a 6% increase for males. IMPACT: The efficacy of a disposable face mask as protection against air contaminants depends on the efficiency of the mask materials and how well it fits the wearer. We report that the sex of the wearer is a major determinant of the baseline fitted filtration efficiency (FFE) of commonly available ear loop style face masks. In addition, we show that a simple fit modifier, an ear loop clip fastened behind the head, substantially improves baseline FFE for females but produces only minor changes for males. These findings have significant public health implications for the use of face masks as a protective intervention against inhalational exposure to airborne contaminants.

Association of Redlining and Natural Environment with Depressive Symptoms in Women in the Sister Study.

BACKGROUND: Improving mental health is recognized as an important factor for achieving global development goals. Despite strong evidence that neighborhood greenery promotes better mental health, there are environmental justice concerns over the distribution of neighborhood greenery. Underlying these concerns are present-day consequences of historical discriminatory financial investment practices, such as redlining which was established by the U.S. Federal Home Owners' Loan Corporation (HOLC) in the 1930s. The impacts of redlining on environmental and health disparities have been researched extensively. However, the influences of redlining on the associations between neighborhood environment and health outcomes have not been fully assessed. OBJECTIVES: The aim of this study was to examine whether associations between residential tree cover and depressive symptoms vary across areas subject to HOLC practices. METHODS: Depressive symptoms were defined by the 10-item Center for Epidemiologic Studies Depression Scale collected during the period 2008-2012 for 3,555 women in the Sister Study cohort residing in cities subject to HOLC practices across the United States. HOLC rating maps were obtained from the Mapping Inequality Project, University of Richmond, with neighborhoods graded as A (best for financial investment, green), B (still desirable, blue), C (declining, yellow), and D (hazardous, red-known as redlined). Tree cover within 500m and 2,000m from residences was estimated using 2011 U.S. Forest Service Percent Tree Canopy Cover. Mixed model using climate zone as the random effect was applied to evaluate the associations with adjustments for potential covariates. Analyses were stratified by HOLC grade. RESULTS: Tree cover was significantly higher in neighborhoods with better HOLC grades. A 10% increase in tree cover was associated with reduced odds of depressive symptoms for the full study population, with adjusted odds ratios (AORs) of 0.93 [95% confidence interval (CI): 0.88, 0.99], and 0.91 (0.85, 0.97) for 500-m and 2,000-m buffer, respectively. Across HOLC grades, the strongest associations were observed in redlined neighborhoods, with respective AORs of 0.72 (95% CI: 0.52, 0.99) and 0.63 (95% CI: 0.45, 0.90) for 500-m and 2,000-m buffer. DISCUSSION: Findings support a remediation strategy focused on neighborhood greenery that would address multiple public health priorities, including mental health and environmental justice. https://doi.org/10.1289/EHP12212.

A novel method for the quantitative assessment of the fitted containment efficiency of face coverings.

BACKGROUND: Face masks reduce disease transmission by protecting the wearer from inhaled pathogens and reducing the emission of infectious aerosols. Although methods quantifying efficiency for wearer protection are established, current methods for assessing face mask containment efficiency rely on measurement of a low concentration of aerosols emitted from an infected or noninfected individual. METHODS: A small port enabled the introduction of 0.05 µm sodium chloride particles at a constant rate behind the mask worn by a study participant. A condensation particle counter monitored ambient particle numbers 60 cm in front of the participant over 3-minute periods of rest, speaking, and coughing. The containment efficiency (%) for each mask and procedure was calculated as follows: 100 × (1 - average ambient concentration with face covering worn/average ambient concentration with a sham face covering in place). The protection efficiency (%) was also measured using previously published methods. The probability of transmission (%) from infected to uninfected (a function of both the containment efficiency and the protection efficiency) was calculated as follows: {1 - (containment efficiency/100)}×{1 - (protection efficiency/100)}×100. RESULTS: The average containment efficiencies for each mask over all procedures and repeated measures were 94.6%, 60.9%, 38.8%, and 43.2%, respectively, for the N95 mask, the KN95 mask, the procedure face mask, and the gaiter. The corresponding protection efficiencies for each mask were 99.0%, 63.7%, 45.3%, and 24.2%, respectively. For example, the transmission probability for 1 infected and 1 uninfected individual in close proximity was ∼14.2% for KN95 masks, compared to 36%-39% when only 1 individual wore a KN95 mask. CONCLUSION: Overall, we detected a good correlation between the protection and containment that a face covering afforded to a wearer.

Improvement in Fitted Filtration Efficiency of N95 Respirators With Escalating Instruction of the Wearer.

Introduction: Fitted filtration performance of an N95 respirator may benefit from differing levels of instructions. Methods: Using a modified Occupational Safety and Health Administration fit test protocol, we measured fitted filtration efficiency for an N95 respirator in 21 screened, healthy participants given 4 levels of escalating instruction: (1) uninstructed (baseline), (2) written/pictorial manufacturer instructions, (3) step-by-step video demonstration, and (4) staff instruction (visual inspection of respirator fit and verbal suggestions to adjust when applicable). Results: Baseline fitted filtration efficiency was not significantly different between participants with or without previous experience of N95 use. Clear improvements in fitted filtration efficiency were observed progressing from baseline (average=86.1%) to manufacturer paper instructions (93.3%), video instructions (97.5%), and post staff intervention (98.3%). Baseline fitted filtration efficiency values were significantly lower than those after video instruction (p<0.037) and staff intervention (p<0.033) sessions. Conclusions: Beyond uninstructed wear or provision of manufacturer instructions, efforts to train and instruct users in proper respirator fit principles with visual feedback are likely to yield benefits to public health outcomes in reducing respiratory exposure during air quality emergencies such as airborne viral outbreaks and wildland fires.

Can disposable masks be worn more than once?

Disposable facemasks are a primary tool to prevent the transmission of SARS-COV-2 during the COVID-19 pandemic. However, plastic waste generated from their disposal represents a significant environmental problem that can be reduced by maximizing the service life of disposable masks. We evaluated the effect of repeated wearing on the fitted filtration efficiency (FFE) of N95, KF94, KN95, and procedure/surgical masks. The FFEs of masks were compared following extended wearing with and without washing. Results reveal that most disposable facemasks can retain a high level of their baseline FFE after extended wearing, even after 40 h of wearing. Laundering disposable masks degraded FFE in some instances. We conclude that the durability of disposable facemask performance is considerably longer than their intended single use indication, suggesting that reusing disposable masks is a safe means of reducing plastic waste in the environment.

Trends in Fire Danger and Population Exposure along the Wildland-Urban Interface.

The increased risk of wildfires and associated smoke exposure in the United States is a growing public health problem, particularly along the Wildland-Urban Interface (WUI). Using the measure of fire danger, the Energy Release Component, we define fire danger as the onset and duration of fire season, in the continental US, between 1979 and 2016. We then combine the measure of fire danger with census data to quantify changes in population fire exposure across the WUI. We determined that the largest increases in fire danger were observed in the Southwest, Intermountain, and Pacific Southwest regions. The increased fire danger, specifically during peak fire season, accounted for 6.1 more fires each year and 78,000 more acres burned each year, underscoring the link between fire danger and the risks of large fire occurrence and burn acreage. Finally, we observed significant population growth (121.2% between 1990 and 2010) within high-danger WUI areas, further implying significant increases in potential fire exposure.

Types and spatial contexts of neighborhood greenery matter in associations with weight status in women across 28 U.S. communities.

Excess body weight is a risk factor for many chronic diseases. Studies have identified neighborhood greenery as supportive of healthy weight. However, few have considered plausible effect pathways for ecosystem services (e.g., heat mitigation, landscape aesthetics, and venues for physical activities) or potential variations by climate. This study examined associations between weight status and neighborhood greenery that capture ecosystem services most relevant to weight status across 28 U.S. communities. Weight status was defined by body mass index (BMI) reported for 6591 women from the U.S. Sister Study cohort. Measures of greenery within street and circular areas at 500 m and 2000 m buffer distances from homes were derived for each participant using 1 m land cover data. Street area was defined as a 25 m-wide zone on both sides of street centerlines multiplied by the buffer distances, and circular area was the area of the circle centered on a home within each of the buffer distances. Measures of street greenery characterized the pedestrian environment to capture physically and visually accessible greenery for shade and aesthetics. Circular greenery was generated for comparison. Greenery types of tree and herbaceous cover were quantified separately, and a combined measure of tree and herbaceous cover (i.e., aggregate greenery) was also included. Mixed models accounting for the clustering at the community level were applied to evaluate the associations between neighborhood greenery and the odds of being overweight or obese (BMI > 25) with adjustment for covariates selected using gradient boosted regression trees. Analyses were stratified by climate zone (arid, continental, and temperate). Tree cover was consistently associated with decreased odds of being overweight or obese. For example, the adjusted odds ratio [AOR] was 0.92, 95% Confidence Interval [CI]: 0.88-0.96, given a 10% increase in street tree cover at the 2000 m buffer across the 28 U.S. communities. These associations held across climate zones, with the lowest AOR in the arid climate (AOR: 0.74, 95% CI: 0.54-1.01). In contrast, associations with herbaceous cover varied by climate zone. For the arid climate, a 10% increase in street herbaceous cover at the 2000 m buffer was associated with lower odds of being overweight or obese (AOR: 0.75, 95% CI: 0.55-1.03), whereas the association was reversed for the temperate climate, the odds increased (AOR: 1.19, 95% CI: 1.05-1.35). Associations between greenery and overweight/obesity varied by type and spatial context of greenery, and climate. Our findings add to a growing body of evidence that greenery design in urban planning can support public health. These findings also justify further defining the mechanism that underlies the observed associations.

Assessing the effect of beard hair lengths on face masks used as personal protective equipment during the COVID-19 pandemic.

BACKGROUND: Globally, a large percentage of men keep a beard at least occasionally. Workplace regulations prohibit beards with N95 respirators, but there is little information on the effect of beards with face masks worn by the public for protection against SARS-CoV-2. METHODS AND FINDINGS: We examined the fitted filtration efficiency (FFE) of five commonly worn protective face masks as a function of beard length following the US Occupational Safety and Health Administration Quantitative Fit Test: N95 (respirator), KF94 and KN95, surgical/procedure, and cloth masks. A comparison using N95 respirators was carried out in shaven and bearded men. A detailed examination was conducted for beard lengths between 0 and 10 mm (0.5 mm increments). The effect of an exercise band covering the beard on FFE was also tested. Although N95 respirators showed considerable variability among bearded men, they had the highest FFE for beard lengths up to 10 mm. KF94 and KN95 masks lost up to 40% of their FFE. Procedure and cotton masks had poor performance even on bare skin (10-30% FFE) that did not change appreciably with beard length. Marked performance improvements were observed with an exercise band worn over the beard. CONCLUSIONS: Though variable, N95 respirators offer the best respiratory protection for bearded men. While KF94 and KN95 FFE is compromised considerably by increasing beard length, they proved better options than procedure and cotton face masks. A simple exercise band improves FFE for face masks commonly used by bearded men during the COVID-19 pandemic.

Knowing Your Audience: A Typology of Smoke Sense Participants to Inform Wildfire Smoke Health Risk Communication.

Central to public health risk communication is understanding the perspectives and shared values among individuals who need the information. Using the responses from a Smoke Sense citizen science project, we examined perspectives on the issue of wildfire smoke as a health risk in relation to an individual's preparedness to adopt recommended health behaviors. The Smoke Sense smartphone application provides wildfire-related health risk resources and invites participants to record their perspectives on the issue of wildfire smoke. Within the app, participants can explore current and forecasted daily air quality, maps of fire locations, satellite images of smoke plumes, and learn about health consequences of wildfire smoke. We used cluster analysis to identify perspective trait-clusters based on health status, experience with fire smoke, risk perception, self-efficacy, access to exposure-reducing resources, health information needs, and openness to health risk messaging. Differences between traits were examined based on demographics, health status, activity level and engagement with the app. We mapped these traits to the Precaution Adoption Process Model (PAPM) to indicate where each trait lies in adopting recommended health behaviors. Finally, we suggest messaging strategies that may be suitable for each trait. We determined five distinct perspective traits which included individuals who were Protectors and have decided to engage on the issue by adopting new behaviors to protect their health; Cautious, Proactive, and Susceptible individuals who were at a Deciding stage but differed based on risk perceptions and information needs; and the Unengaged who did not perceive smoke as a health issue and were unlikely to change behavior in response to messaging. Across all five traits, the level of engagement and information needs differed substantially, but were not defined by demographics. Individuals in the Susceptible trait had the highest level of engagement and the highest information needs. Messaging that emphasizes self-efficacy and benefits of reducing exposure may be effective in motivating individuals from the deciding stage to taking health protective action. Shared perspectives define an individual's propensity for acting on recommended health behaviors, therefore, health risk message content should be tailored based on these perspectives.

How do natural features in the residential environment influence women's self-reported general health? Results from cross-sectional analyses of a U.S. national cohort.

BACKGROUND: The relationship between health and human interaction with nature is complex. Here we conduct analyses to provide insights into potential health benefits related to residential proximity to nature. OBJECTIVES: We aimed to examine associations between measures of residential nature and self-reported general health (SRGH), and to explore mediation roles of behavioral, social, and air quality factors, and variations in these relationships by urbanicity and regional climate. METHODS: Using residential addresses for 41,127 women from the Sister Study, a U.S.-based national cohort, we derived two nature exposure metrics, canopy and non-gray cover, using Percent Tree Canopy and Percent Developed Imperviousness from the National Land Cover Database. Residential circular buffers of 250 m and 1250 m were considered. Gradient boosted regression trees were used to model the effects of nature exposure on the odds of reporting better SRGH (Excellent/Very Good versus the referent, Good/Fair/Poor). Analyses stratified by urbanicity and regional climate (arid, continental, temperate) and mediation by physical activity, social support, and air quality were conducted. RESULTS: A 10% increase in canopy and non-gray cover within 1250 m buffer was associated with 1.02 (95% CI: 1.00-1.03) and 1.03 (95% CI: 1.01-1.04) times the odds of reporting better SRGH, respectively. Stronger associations were observed for the urban group and for continental climate relative to other strata. Social support and physical activity played a more significant mediation role than air quality for the full study population. DISCUSSION: Findings from this study identified a small but important beneficial association between residential nature and general health. These findings could inform community planning and investments in neighborhood nature for targeted health improvements and potential societal and environmental co-benefits.

Past Actions as Self-Signals: How Acting in a Self-Interested Way Influences Environmental Decision Making.

In the last few decades, awareness of environmental issues has increased significantly. Little has changed, however, in human activities contributing to environmental damage. Why is it so difficult for us to change our behavior in a domain that is clearly so important to the future of humanity? Here we propose and test the possibility that self-signaling, the way we view ourselves based on our past behaviors, is one of the factors contributing to the difficulty of taking environmental action. In three experiments, we show that previous self-interested thoughts or behaviors serve as important signals that hinder the likelihood of acting in line with an individual's reported concern for the environment. This study not only helps explain the gap between environmental awareness and action, but also suggests alternative strategies for policymakers and environmental agencies to promote proenvironmental behavior.

Fear-relevant outcomes modulate the neural correlates of probabilistic classification learning.

Although much work has implicated the contributions of frontostriatal and medial temporal lobe (MTL) systems during probabilistic classification learning, the impact of emotion on these learning circuits is unknown. We used a modified version of the weather prediction task in which two participant groups were scanned with identical neutral cue cards probabilistically linked to either emotional (snake/spider) or neutral (mushroom/flower) outcomes. Owing to the differences in visual information shown as outcomes, analyses were restricted to the cue phase of the trials. Learning rates did not differ between the two groups, although the Emotional group was more likely to use complex strategies and to respond more slowly during initial learning. The Emotional group had reduced frontostriatal and MTL activation relative to the Neutral group, especially for participants who scored higher on snake/spider phobia questionnaires. Accurate performance was more tied to medial prefrontal activity in the Emotional group early in training, and to MTL activity in the Neutral group later in training. Trial-by-trial fluctuations in functional connectivity between the caudate and MTL were also reduced in the Emotional group compared to the Neutral group. Across groups, reaction time indexed a switch in learning systems, with faster trials mediated by the caudate and slower trials mediated by the MTL and frontal lobe. The extent to which the caudate was activated early in training predicted later performance improvements. These results reveal insights into how emotional outcomes modulate procedural learning systems, and the dynamics of MTL-striatal engagement across training trials.

Neurobehavioral mechanisms of human fear generalization.

While much research has elucidated the neurobiology of fear learning, the neural systems supporting the generalization of learned fear are unknown. Using functional magnetic resonance imaging (fMRI), we show that regions involved in the acquisition of fear support the generalization of fear to stimuli that are similar to a learned threat, but vary in fear intensity value. Behaviorally, subjects retrospectively misidentified a learned threat as a more intense stimulus and expressed greater skin conductance responses (SCR) to generalized stimuli of high intensity. Brain activity related to intensity-based fear generalization was observed in the striatum, insula, thalamus/periacqueductal gray, and subgenual cingulate cortex. The psychophysiological expression of generalized fear correlated with amygdala activity, and connectivity between the amygdala and extrastriate visual cortex was correlated with individual differences in trait anxiety. These findings reveal the brain regions and functional networks involved in flexibly responding to stimuli that resemble a learned threat. These regions may comprise an intensity-based fear generalization circuit that underlies retrospective biases in threat value estimation and overgeneralization of fear in anxiety disorders.

Posterior midline and ventral parietal activity is associated with retrieval success and encoding failure.

The ventral part of lateral posterior parietal cortex (VPC) and the posterior midline region (PMR), including the posterior cingulate cortex and precuneus, tend to show deactivation during demanding cognitive tasks, and have been associated with the default mode of the brain. Interestingly, PMR and VPC activity has been associated with successful episodic retrieval but also with unsuccessful episodic encoding. However, the differential contributions of PMR and VPC to retrieval vs. encoding has never been demonstrated within-subjects and within the same experiment. Here, we directly tested the prediction that PMR and VPC activity should be associated with retrieval success but with encoding failure. Consistent with this prediction, we found across five different fMRI experiments that, during retrieval, activity in these regions is greater for hits than misses, whereas during encoding, it is greater for subsequent misses than hits. We also found that these regions overlap with the ones that show deactivations during conscious rest. Our findings further aid in clarifying the role of the default mode regions in learning and memory.

Encoding and retrieving faces and places: distinguishing process- and stimulus-specific differences in brain activity.

Among the most fundamental issues in cognitive neuroscience is how the brain may be organized into process-specific and stimulus-specific regions. In the episodic memory domain, most functional neuroimaging studies have focused on the former dimension, typically investigating the neural correlates of various memory processes. Thus, there is little information about what role stimulus-specific brain regions play in successful memory processes. To address this issue, the present event-related fMRI study used a factorial design to focus on the role of stimulus-specific brain regions, such as the fusiform face area (FFA) and parahippocampal place area (PPA) in successful encoding and retrieval processes. Searching within regions sensitive to faces or places, we identified areas similarly involved in encoding and retrieval, as well as areas differentially involved in encoding or retrieval. Finally, we isolated regions associated with successful memory, regardless of stimulus and process type. There were three main findings. Within face sensitive regions, anterior medial PFC and right FFA displayed equivalent encoding and retrieval success processes whereas left FFA was associated with successful encoding rather than retrieval. Within place sensitive regions, left PPA displayed equivalent encoding and retrieval success processes whereas right PPA was associated with successful encoding rather than retrieval. Finally, medial temporal and prefrontal regions were associated with general memory success, regardless of stimulus or process type. Taken together, our results clarify the contribution of different brain regions to stimulus- and process-specific episodic memory mechanisms.

Modulation of a human memory circuit by subsyndromal depression in late life: a functional magnetic resonance imaging study.

OBJECTIVE: Functional deactivation of the posteromedial cortex (PMC) seems to be a physiologic process underlying normal memory. The authors examined whether older subjects with subsyndromal depressive symptoms show impaired PMC deactivation. DESIGN: Subjects underwent 4T functional magnetic resonance imaging scan while performing a novel and familiar face-name associative encoding task. The Beck-II Depression Inventory (BDI) was used to self-rate depression symptoms. A novel-minus-familiar encoding contrast was built into a simple regression model showing brain activation magnitudes that covaried with BDI score. A region-of-interest mask was applied to isolate the PMC and other midline structures of the default-mode network. SETTING: The study was conducted at a university-based medical center. PARTICIPANTS: Participants included 62 nondemented subjects aged 55-85, with and without mild memory deficits. BDI scores ranged from 0 to 17. RESULTS: Analysis revealed a distinct PMC cluster confined to the dorsal posterior cingulate cortex (BA 31) whose activity correlated significantly with BDI score. A multiple regression model further showed that BDI score, as well as a history of depression and current use of antidepressants, had a significant effect on cluster variance, while age, education, gender, and mini-mental state exam scores did not. CONCLUSIONS: Our findings raise the hypothesis that subsyndromal depressive symptoms in late life may impair physiological PMC deactivation in the dorsal posterior cingulate cortex. A prospective study of a full spectrum of depressed patients may be warranted.

Effects of aging on the neural correlates of successful item and source memory encoding.

To investigate the neural basis of age-related source memory (SM) deficits, young and older adults were scanned with fMRI while encoding faces, scenes, and face-scene pairs. Successful encoding activity was identified by comparing encoding activity for subsequently remembered versus forgotten items or pairs. Age deficits in successful encoding activity in hippocampal and prefrontal regions were more pronounced for SM (pairs) as compared with item memory (faces and scenes). Age-related reductions were also found in regions specialized in processing faces (fusiform face area) and scenes (parahippocampal place area), but these reductions were similar for item and SM. Functional connectivity between the hippocampus and the rest of the brain was also affected by aging; whereas connections with posterior cortices were weaker in older adults, connections with anterior cortices, including prefrontal regions, were stronger in older adults. Taken together, the results provide a link between SM deficits in older adults and reduced recruitment of hippocampal and prefrontal regions during encoding. The functional connectivity findings are consistent with a posterior-anterior shift with aging previously reported in several cognitive domains and linked to functional compensation.

Prognostic value of posteromedial cortex deactivation in mild cognitive impairment.

BACKGROUND: Normal subjects deactivate specific brain regions, notably the posteromedial cortex (PMC), during many tasks. Recent cross-sectional functional magnetic resonance imaging (fMRI) data suggests that deactivation during memory tasks is impaired in Alzheimer's disease (AD). The goal of this study was to prospectively determine the prognostic significance of PMC deactivation in mild cognitive impairment (MCI). METHODOLOGY/PRINCIPAL FINDINGS: 75 subjects (34 MCI, 13 AD subjects and 28 controls) underwent baseline fMRI scanning during encoding of novel and familiar face-name pairs. MCI subjects were followed longitudinally to determine conversion to AD. Regression and analysis of covariance models were used to assess the effect of PMC activation/deactivation on conversion to dementia as well as in the longitudinal change in dementia measures. At longitudinal follow up of up to 3.5 years (mean 2.5+/-0.79 years), 11 MCI subjects converted to AD. The proportion of deactivators was significantly different across all groups: controls (79%), MCI-Nonconverters (73%), MCI-converters (45%), and AD (23%) (p<0.05). Mean PMC activation magnitude parameter estimates, at baseline, were negative in the control (-0.57+/-0.12) and MCI-Nonconverter (-0.33+/-0.14) groups, and positive in the MCI-Converter (0.37+/-0.40) and AD (0.92+/-0.30) groups. The effect of diagnosis on PMC deactivation remained significant after adjusting for age, education and baseline Mini-Mental State Exam (p<0.05). Baseline PMC activation magnitude was correlated with change in dementia ratings from baseline. CONCLUSION: Loss of physiological functional deactivation in the PMC may have prognostic value in preclinical AD, and could aid in profiling subgroups of MCI subjects at greatest risk for progressive cognitive decline.