White Matter Hyperintensities and Cognition: Testing the Reserve Hypothesis

OBJECTIVE: White matter hyperintensities (WMH), visualized on T2-weighted MRI, are thought to reflect small-vessel vascular disease. Much like other markers of brain disease, the association between WMH and cognition is imperfect. The concept of reserve may account for this imperfect relationship. The purpose of this study was to test the reserve hypothesis in the association between WMH severity and cognition. We hypothesized that individuals with higher amounts of reserve would be able to tolerate greater amounts of pathology than those with lower reserve. METHODS: Neurologically healthy older adults (n=717) from a community-based study received structural MRI, neuropsychological assessment, and evaluation of reserve. WMH volume was quantified algorithmically. We derived latent constructs representing four neuropsychological domains, a measure of cognitive reserve, and a measure of brain reserve. Measures of cognitive and brain reserve consisted of psychosocial (e.g., education) and anthropometric (e.g., craniometry) variables, respectively. RESULTS: Increased WMH volume was associated with poorer cognition and higher cognitive and brain reserve were associated with better cognition. Controlling for speed/executive function or for language function, those with higher estimates of cognitive reserve had significantly greater degrees of WMH volume, particularly among women. Controlling for cognitive functioning across all domains, individuals with higher estimates of brain reserve had significantly greater WMH volume. CONCLUSIONS: For any given level of cognitive function, those with higher reserve had more pathology in the form of WMH, suggesting that they are better able to cope with pathology than those with lower reserve. Both brain reserve and cognitive reserve appear to mitigate the impact of pathology on cognition

Reduction in Cerebral Blood Flow in Areas Appearing as White Matter Hyperintensities on Magnetic Resonance Imaging

The purpose of this study was to examine cerebral blood flow (CBF) as measured by arterial spin labeling (ASL) in tissue classified as white matter hyperintensities (WMH), normal appearing white matter, and grey matter. Seventeen healthy older adults received structural and ASL MRI. Cerebral blood flow was derived for three tissue types: WMH, normal appearing white matter, and grey matter. Cerebral blood flow was lower in WMH areas relative to normal appearing white matter, which in turn, was lower than grey matter. Regions with consistently lower CBF across individuals were more likely to appear as WMH. Results are consistent with an emerging literature linking diminished regional perfusion with the risk of developing WMH

Regional white matter hyperintensity volume, not hippocampal atrophy, predicts incident Alzheimer disease in the community

Background: New-onset Alzheimer disease (AD) is often attributed to degenerative changes in the hippocampus. However, the contribution of regionally distributed small vessel cerebrovascular disease, visualized as white matter hyperintensities (WMHs) on magnetic resonance imaging, remains unclear. Objective: To determine whether regional WMHs and hippocampal volume predict incident AD in an epidemiological study. Design: A longitudinal community-based epidemiological study of older adults from northern Manhattan, New York. Setting: The Washington Heights/Inwood Columbia Aging Project. Participants: Between 2005 and 2007, 717 participants without dementia received magnetic resonance imaging scans. A mean (SD) of 40.28 (9.77) months later, 503 returned for follow-up clinical examination and 46 met criteria for incident dementia (45 with AD). Regional WMHs and relative hippocampal volumes were derived. Three Cox proportional hazards models were run to predict incident dementia, controlling for relevant variables. The first included all WMH measurements; the second included relative hippocampal volume; and the third combined the 2 measurements. Main Outcome: Measure Incident AD. Results: White matter hyperintensity volume in the parietal lobe predicted time to incident dementia (hazard ratio [HR] = 1.194; P = .03). Relative hippocampal volume did not predict incident dementia when considered alone (HR = 0.419; P = .77) or with the WMH measures included in the model (HR = 0.302; P = .70). Including hippocampal volume in the model did not notably alter the predictive utility of parietal lobe WMHs (HR = 1.197; P = .049). Conclusions: The findings highlight the regional specificity of the association of WMHs with AD. It is not clear whether parietal WMHs solely represent a marker for cerebrovascular burden or point to distinct injury compared with other regions. Future work should elucidate pathogenic mechanisms linking WMHs and AD pathology

Reduction in Cerebral Blood Flow in Areas Appearing as White Matter Hyperintensities on Magnetic Resonance Imaging

The purpose of this study was to examine cerebral blood flow (CBF) as measured by arterial spin labeling (ASL) in tissue classified as white matter hyperintensities (WMH), normal appearing white matter, and grey matter. Seventeen healthy older adults received structural and ASL MRI. Cerebral blood flow was derived for three tissue types: WMH, normal appearing white matter, and grey matter. Cerebral blood flow was lower in WMH areas relative to normal appearing white matter, which in turn, was lower than grey matter. Regions with consistently lower CBF across individuals were more likely to appear as WMH. Results are consistent with an emerging literature linking diminished regional perfusion with the risk of developing WMH

Simultaneous EEG-fMRI Reveals Temporal Evolution of Coupling between Supramodal Cortical Attention Networks and the Brainstem

Cortical and subcortical networks have been identified that are commonly associated with attention and task engagement, along with theories regarding their functional interaction. However, a link between these systems has not yet been demonstrated in healthy humans, primarily because of data acquisition and analysis limitations. We recorded simultaneous EEG–fMRI while subjects performed auditory and visual oddball tasks and used these data to investigate the BOLD correlates of single-trial EEG variability at latencies spanning the trial. We focused on variability along task-relevant dimensions in the EEG for identical stimuli and then combined auditory and visual data at the subject level to spatially and temporally localize brain regions involved in endogenous attentional modulations. Specifically, we found that anterior cingulate cortex (ACC) correlates strongly with both early and late EEG components, whereas brainstem, right middle frontal gyrus (rMFG), and right orbitofrontal cortex (rOFC) correlate significantly only with late components. By orthogonalizing with respect to event-related activity, we found that variability in insula and temporoparietal junction is reflected in reaction time variability, rOFC and brainstem correlate with residual EEG variability, and ACC and rMFG are significantly correlated with both. To investigate interactions between these correlates of temporally specific EEG variability, we performed dynamic causal modeling (DCM) on the fMRI data. We found strong evidence for reciprocal effective connections between the brainstem and cortical regions. Our results support the adaptive gain theory of locus ceruleus–norepinephrine (LC–NE) function and the proposed functional relationship between the LC–NE system, right-hemisphere ventral attention network, and P300 EEG response

Do existing research summaries on health systems match immunisation managers' needs in middle- and low-income countries? Analysis of GAVI health systems strengthening support

<p>Abstract</p> <p>Background</p> <p>The GAVI Alliance was created in 2000 to increase access to vaccines. More recently, GAVI has supported evidence-based health systems strengthening to overcome barriers to vaccination. Our objectives were: to explore countries' priorities for health systems strengthening; to describe published research summaries for each priority area in relation to their number, quality and relevance; and to describe the use of national data from surveys in identifying barriers to immunisation.</p> <p>Methods</p> <p>From 44 health systems strengthening proposals submitted to GAVI in 2007 and 2008, we analysed the topics identified, the coverage of these topics by existing systematic reviews and the use of nation-wide surveys with vaccination data to justify the needs identified in the proposals.</p> <p>Results</p> <p>Thirty topics were identified and grouped into three thematic areas: health workforce (10 topics); organisation and management (14); and supply, distribution and maintenance (6). We found 51 potentially relevant systematic reviews, although for the topic that appeared most frequently in the proposals ('Health information systems') no review was identified. Thematic and geographic relevance were generally categorised as "high" in 33 (65%) and 25 (49%) reviews, respectively, but few reviews were categorised as "highly relevant for policy" (7 reviews, 14%). With regard to methodological quality, 14 reviews (27%) were categorised as "high".</p> <p>The number of topics that were addressed by at least one high quality systematic review was: seven of the 10 topics in the 'health workforce' thematic area; six of the 14 topics in the area of 'organisation and management'; and none of the topics in the thematic area of 'supply, distribution and maintenance'. Only twelve of the 39 countries with available national surveys referred to them in their proposals.</p> <p>Conclusion</p> <p>Relevant, high quality research summaries were found for few of the topics identified by managers. Few proposals used national surveys evidence to identify barriers to vaccination. Researchers generating or adapting evidence about health systems need to be more responsive to managers' needs. Use of available evidence from local or national surveys should be strongly encouraged.</p