White matter lesions in the elderly: Pathophysiological hypothesis on the effect on brain plasticity and reserve

Cognitive resilience/reserve: Myth or reality? A review of definitions and measurement methods

INTRODUCTION

This review examines the concept of cognitive reserve (CR) in relation to brain aging, particularly in the context of dementia and its early stages. CR refers to an individual's ability to maintain or regain cognitive function despite brain aging, damage, or disease. Various factors, including education, occupation complexity, leisure activities, and genetics are believed to influence CR.

METHODS

We revised the literature in the context of CR. A total of 842 articles were identified, then we rigorously assessed the relevance of articles based on titles and abstracts, employing a systematic approach to eliminate studies that did not align with our research objectives.

RESULTS

We evaluate-also in a critical way-the methods commonly used to define and measure CR, including sociobehavioral proxies, neuroimaging, and electrophysiological and genetic measures. The challenges and limitations of these measures are discussed, emphasizing the need for more targeted research to improve the understanding, definition, and measurement of CR.

CONCLUSIONS

The review underscores the significance of comprehending CR in the context of both normal and pathological brain aging and emphasizes the importance of further research to identify and enhance this protective factor for cognitive preservation in both healthy and neurologically impaired older individuals.

HIGHLIGHTS

This review examines the concept of cognitive reserve in brain aging, in the context of dementia and its early stages. We have evaluated the methods commonly used to define and measure cognitive reserve. Sociobehavioral proxies, neuroimaging, and electrophysiological and genetic measures are discussed. The review emphasizes the importance of further research to identify and enhance this protective factor for cognitive preservation.

Mediation of Age and Thrombectomy Outcome by Neuroimaging Markers of Frailty in Patients With Stroke

Importance

Age is a leading predictor of poor outcomes after brain injuries like stroke. The extent to which age is associated with preexisting burdens of brain changes, visible on neuroimaging but rarely considered in acute decision-making or trials, is unknown.

Objectives

To explore the mediation of age on functional outcome by neuroimaging markers of frailty (hereinafter neuroimaging frailty) in patients with acute ischemic stroke receiving endovascular thrombectomy (EVT).

Design, Setting, and Participants

This cohort study was a post hoc analysis of the Safety and Efficacy of Nerinetide (NA-1) in Subjects Undergoing Endovascular Thrombectomy for Stroke (ESCAPE-NA1) randomized clinical trial, which investigated intravenous (IV) nerinetide in patients who underwent EVT within a 12-hour treatment window. Patients from 48 acute care hospitals in 8 countries (Canada, US, Germany, Korea, Australia, Ireland, UK, and Sweden) were enrolled between March 1, 2017, and August 12, 2019. Markers of brain frailty (brain atrophy [subcortical or cortical], white matter disease [periventricular or deep], and the number of lacunes and chronic infarctions) were retrospectively assessed while reviewers were blinded to other imaging (eg, computed tomography angiography, computed tomography perfusion) or outcome variables. All analyses were done between December 1, 2022, and January 31, 2023.

Exposures

All patients received EVT and were randomized to IV nerinetide (2.6 mg/kg of body weight) and alteplase (if indicated) treatment vs best medical management.

Main Outcome and Measures

The primary outcome was the proportion of the total effect of age on 90-day outcome, mediated by neuroimaging frailty. A combined mediation was also examined by clinical features associated with frailty and neuroimaging markers (total frailty). Structural equation modeling was used to create latent variables as potential mediators, adjusting for baseline, early ischemic changes; stroke severity; onset-to-puncture time; nerinetide treatment; and alteplase treatment.

Results

Among a total of 1105 patients enrolled in the study, 1102 (median age, 71 years [IQR, 61-80 years]; 554 [50.3%] male) had interpretable imaging at baseline. Of these participants, 549 (49.8%) were treated with IV nerinetide. The indirect effect of age on 90-day outcome, mediated by neuroimaging frailty, was associated with 85.1% of the total effect (β coefficient, 0.04 per year [95% CI, 0.02-0.06 per year]; P < .001). When including both frailty constructs, the indirect pathway was associated with essentially 100% of the total effect (β coefficient, 0.07 per year [95% CI, 0.03-0.10 per year]; P = .001).

Conclusions and Relevance

In this cohort study, a secondary analysis of the ESCAPE-NA1 trial, most of the association between age and 90-day outcome was mediated by neuroimaging frailty, underscoring the importance of features like brain atrophy and small vessel disease, as opposed to chronological age alone, in predicting poststroke outcomes. Future trials could include such frailty features to stratify randomization or improve adjustment in outcome analyses.

White matter lesion load determines exercise-induced dopaminergic plasticity and working memory gains in aging

Age-related dopamine reductions have been suggested to contribute to maladaptive working memory (WM) function in older ages. One promising intervention approach is to increase physical activity, as this has been associated with plasticity of the striatal dopamine system and WM improvements, however with individual differences in efficacy. The present work focused on the impact of individual differences in white-matter lesion burden upon dopamine D2-like receptor (DRD2) availability and WM changes in response to a 6 months physical activity intervention. While the intervention altered striatal DRD2 availability and WM performance in individuals with no or only mild lesions (p < 0.05), no such effects were found in individuals with moderate-to-severe lesion severity (p > 0.05). Follow-up analyses revealed a similar pattern for processing speed, but not for episodic memory performance. Linear analyses further revealed that lesion volume (ml) at baseline was associated with reduced DRD2 availability (r = -0.41, p < 0.05), and level of DRD2 change (r = 0.40, p < 0.05). Taken together, this study underlines the necessity to consider cerebrovascular health in interventions with neurocognitive targets. Future work should assess whether these findings extend beyond measures of DRD2 availability and WM.

White matter hyperintensities in Burning Mouth Syndrome assessed according to the Age-Related White Matter Changes scale

Background

White matter hyperintensities (WMHs) of the brain are observed in normal aging, in various subtypes of dementia and in chronic pain, playing a crucial role in pain processing. The aim of the study has been to assess the WMHs in Burning Mouth Syndrome (BMS) patients by means of the Age-Related White Matter Changes scale (ARWMCs) and to analyze their predictors.

Methods

One hundred BMS patients were prospectively recruited and underwent magnetic resonance imaging (MRI) of the brain. Their ARWMCs scores were compared with those of an equal number of healthy subjects matched for age and sex. Intensity and quality of pain, psychological profile, and blood biomarkers of BMS patients were further investigated to find potential predictors of WMHs. Specifically, the Numeric Rating Scale (NRS), Short-Form McGill Pain Questionnaire (SF-MPQ), Hamilton rating scale for Depression and Anxiety (HAM-D and HAM-A), Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS) were administered.

Results

The BMS patients presented statistically significant higher scores on the ARWMCs compared to the controls, especially in the right frontal, left frontal, right parietal-occipital, left parietal-occipital, right temporal and left temporal lobes (p-values: <0.001, <0.001, 0.005, 0.002, 0.009, 0.002, and <0.001, respectively). Age, a lower educational level, unemployment, essential hypertension, and hypercholesterolemia were correlated to a higher total score on the ARWMCs (p-values: <0.001, 0.016, 0.014, 0.001, and 0.039, respectively). No correlation was found with the blood biomarkers, NRS, SF-MPQ, HAM-A, HAM-D, PSQI, and ESS.

Conclusion

Patients with BMS showed a higher frequency of WMHs of the brain as suggested by the higher ARWCs scores compared with the normal aging of the healthy subjects. These findings could have a role in the pathophysiology of the disease and potentially affect and enhance pain perception.

Cortical Short-Range Fiber Connectivity and Its Association With Deep Brain White Matter Hyperintensities in Older Diabetic People With Low Serum Vitamin B12

Although previous studies have indicated that older people with diabetes mellitus (DM) had an approximately two times larger white matter hyperintensity (WMH) load than those without DM, the influence of WMHs on cognition is uncertain and inconsistent in the literature. It is unclear whether the short-range fibers in the juxtacortical region, traditionally considered to be spared from WMH pathology, are enhanced as an adaptive response to deep WM degeneration in older diabetic people with normal cognition. Moreover, the specific effect of vitamin B₁₂ deficiency, commonly accompanied by DM, remains to be investigated. This study implemented a specialized analysis of the superficial cortical short-range fiber connectivity density (SFiCD) based on a data-driven framework in 70 older individuals with DM and low serum vitamin B₁₂. Moreover, the effects of time and vitamin B₁₂ supplementation were assessed based on a randomized placebo-controlled trial in 59 individuals. The results demonstrated a higher SFiCD in diabetic individuals with a higher deep WMH load. Additionally, a significant interaction between DWMH load and homocysteine on SFiCD was found. During the 27-month follow-up period, a longitudinal increase in the SFiCD was observed in the bilateral frontal cortices. However, the observed longitudinal SFiCD change was not dependent on vitamin B₁₂ supplementation; thus, the specific reason for the longitudinal cortical short fiber densification may need further study. Overall, these findings may help us better understand the neurobiology of brain plasticity in older patients with DM, as well as the interplay among DM, WMH, and vitamin B₁₂ deficiency.

A Multivariate Assessment of Age-Related Cognitive Impairment in Octodon degus

Aging is a progressive functional decline characterized by a gradual deterioration in physiological function and behavior. The most important age-related change in cognitive function is decline in cognitive performance (i.e., the processing or transformation of information to make decisions that includes speed of processing, working memory, and learning). The purpose of this study is to outline the changes in age-related cognitive performance (i.e., short-term recognition memory and long-term learning and memory) in long-lived Octodon degus. The strong similarity between degus and humans in social, metabolic, biochemical, and cognitive aspects makes it a unique animal model for exploring the mechanisms underlying the behavioral and cognitive deficits related to natural aging. In this study, we examined young adult female degus (12- and 24-months-old) and aged female degus (38-, 56-, and 75-months-old) that were exposed to a battery of cognitive-behavioral tests. Multivariate analyses of data from the Social Interaction test or Novel Object/Local Recognition (to measure short-term recognition memory), and the Barnes maze test (to measure long-term learning and memory) revealed a consistent pattern. Young animals formed a separate group of aged degus for both short- and long-term memories. The association between the first component of the principal component analysis (PCA) from short-term memory with the first component of the PCA from long-term memory showed a significant negative correlation. This suggests age-dependent differences in both memories, with the aged degus having higher values of long-term memory ability but poor short-term recognition memory, whereas in the young degus an opposite pattern was found. Approximately 5% of the young and 80% of the aged degus showed an impaired short-term recognition memory; whereas for long-term memory about 32% of the young degus and 57% of the aged degus showed decreased performance on the Barnes maze test. Throughout this study, we outlined age-dependent cognitive performance decline during natural aging in degus. Moreover, we also demonstrated that the use of a multivariate approach let us explore and visualize complex behavioral variables, and identified specific behavioral patterns that allowed us to make powerful conclusions that will facilitate further the study on the biology of aging. In addition, this study could help predict the onset of the aging process based on behavioral performance.

Assessing the Effect of Training on the Cognition and Brain of Older Adults: Protocol for a Three-Arm Randomized Double-Blind Controlled Trial (ACTOP)

BACKGROUND

To prevent age-related cognitive impairment, many intervention programs offer exercises targeting different central cognitive processes. However, the effects of different process-based training programs are rarely compared within equivalent experimental designs.

OBJECTIVE

Using a randomized double-blind controlled trial, this project aims to examine and compare the impact of 2 process-based interventions, inhibition and updating, on the cognition and brain of older adults.

METHODS

A total of 90 healthy older adults were randomly assigned to 1 of 3 training conditions: (1) inhibition (Stroop-like exercises), (2) updating (N-back-type exercises), and (3) control active (quiz game exercise). Training was provided in 12 half-hour sessions over 4 weeks. First, the performance gain observed will be measured on the trained tasks. We will then determine the extent of transfer of gain on (1) untrained tasks that rely on the same cognitive process, (2) complex working memory (WM) measurements hypothesized to involve 1 of the 2 trained processes, and (3) virtual reality tasks that were designed to mimic real-life situations that require WM. We will assess whether training increases cortical volume given that the volume of the cortex is determined by cortical area and thickness in regions known to be involved in WM or changes task-related brain activation patterns measured with functional magnetic resonance imaging. Dose effects will be examined by measuring outcomes at different time points during training. We will also determine whether individual characteristics moderate the effect of training on cognitive and cerebral outcomes. Finally, we will evaluate whether training reduces the age-related deficit on transfer and brain outcomes, by comparing study participants to a group of 30 younger adults.

RESULTS

The project was funded in January 2017; enrollment began in October 2017 and data collection was completed in April 2019. Data analysis has begun in June 2020 and the first results should be published by the end of 2020 or early 2021.

CONCLUSIONS

The results of this study will help understand the relative efficacy of 2 attentional control interventions on the cognition and the brain of older adults, as well as the moderating role of individual characteristics on training efficiency and transfer.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03532113; https://clinicaltrials.gov/ct2/show/NCT03532113.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/20430.

BOLD signal within and around white matter lesions distinguishes multiple sclerosis and non-specific white matter disease: a three-dimensional approach

Multiple sclerosis (MS) diagnostic criteria are based upon clinical presentation and presence of white matter hyperintensities on two-dimensional magnetic resonance imaging (MRI) views. Such criteria, however, are prone to false-positive interpretations due to the presence of similar MRI findings in non-specific white matter disease (NSWMD) states such as migraine and microvascular disease. The coexistence of age-related changes has also been recognized in MS patients, and this comorbidity further poses a diagnostic challenge. In this study, we investigated the physiologic profiles within and around MS and NSWMD lesions and their ability to distinguish the two disease states. MS and NSWMD lesions were identified using three-dimensional (3D) T₂-FLAIR images and segmented using geodesic active contouring. A dual-echo functional MRI sequence permitted near-simultaneous measurement of blood-oxygen-level-dependent signal (BOLD) and cerebral blood flow (CBF). BOLD and CBF were calculated within lesions and in 3D concentric layers surrounding each lesion. BOLD slope, an indicator of lesion metabolic capacity, was calculated as the change in BOLD from a lesion through its surrounding perimeters. We observed sequential BOLD signal reductions from the lesion towards the perimeters for MS, while no such decreases were observed for NSWMD lesions. BOLD slope was significantly lower in MS compared to NSWM lesions, suggesting decreased metabolic activity in MS lesions. Furthermore, BOLD signal within and around lesions significantly distinguished MS and NSWMD lesions. These results suggest that this technique shows promise for clinical utility in distinguishing NSWMD or MS disease states and identifying NSWMD lesions occurring in MS patients.

Relationship of White Matter Lesions with Intracerebral Hemorrhage Expansion and Functional Outcome: MISTIE II and CLEAR III

BACKGROUND/OBJECTIVE

Intracerebral hemorrhage (ICH) patients commonly have concomitant white matter lesions (WML) which may be associated with poor outcome. We studied if WML affects hematoma expansion (HE) and post-stroke functional outcome in a post hoc analysis of patients from randomized controlled trials.

METHODS

In ICH patients from the clinical trials MISTIE II and CLEAR III, WML grade on diagnostic computed tomography (dCT) scan (dCT, < 24 h after ictus) was assessed using the van Swieten scale (vSS, range 0-4). The primary outcome for HE was > 33% or > 6 mL ICH volume increase from dCT to the last pre-randomization CT (< 72 h of dCT). Secondary HE outcomes were: absolute ICH expansion, > 10.4 mL total clot volume increase, and a subgroup analysis including patients with dCT < 6 h after ictus using the primary HE definition of > 33% or > 6 mL ICH volume increase. Poor functional outcome was assessed at 180 days and defined as modified Rankin Scale (mRS) ≥ 4, with ordinal mRS as a secondary endpoint.

RESULTS

Of 635 patients, 55% had WML grade 1-4 at dCT (median 2.2 h from ictus) and 13% had subsequent HE. WML at dCT did not increase the odds for primary or secondary HE endpoints (P ≥ 0.05) after adjustment for ICH volume, intraventricular hemorrhage volume, warfarin/INR > 1.5, ictus to dCT time in hours, age, diabetes mellitus, and thalamic ICH location. WML increased the odds for having poor functional outcome (mRS ≥ 4) in univariate analyses (vSS 4; OR 4.16; 95% CI 2.54-6.83; P < 0.001) which persisted in multivariable analyses after adjustment for HE and other outcome risk factors.

CONCLUSIONS

Concomitant WML does not increase the odds for HE in patients with ICH but increases the odds for poor functional outcome.

CLINICAL TRIAL REGISTRATION

http://www.clinicaltrials.gov trial-identifiers: NCT00224770 and NCT00784134.

MRI-based evaluation of structural degeneration in the ageing brain: Pathophysiology and assessment

Advances in MRI technology have significantly contributed to our ability to understand the process of brain ageing, allowing us to track and assess changes that occur during normal ageing and neurological conditions. This paper focuses on reviewing structural changes of the ageing brain that are commonly seen using MRI, summarizing the pathophysiology, prevalence, and neuroanatomical distribution of changes including atrophy, lacunes, white matter lesions, and dilated perivascular spaces. We also review the clinically accessible methodology for assessing these MRI-based changes, covering visual rating scales, as well computer-aided and fully automated methods. Subsequently, we consider novel assessment methods designed to evaluate changes across the whole brain, and finally discuss new directions in this field of research.

Mental speed is associated with the shape irregularity of white matter MRI hyperintensity load

Brain MRI white matter hyperintensities (WMHs) are common in elderly subjects. Their impact on cognition, however, appears highly variable. Complementing conventional scoring of WMH load (volume and location) by quantitative characterization of the shape irregularity of WMHs might improve the understanding of the relationship between WMH load and cognitive performance. Here we propose the "confluency sum score" (COSU) as a marker of the total shape irregularity of WMHs in the brain. The study included two independent patient samples: 87 cognitively impaired geriatric inpatients from a prospective neuroimaging study (iDSS) and 198 subjects from the National Alzheimer's Coordinating Center (NACC) database (132 with, 66 w/o cognitive impairment). After automatic segmentation and clustering of the WMHs on FLAIR (LST toolbox, SPM8), the confluency of the i-th contiguous WMH cluster was computed as confluency_i = [1/(36π)∙surface_i³/volume_i²]^1/3-1. The COSU was obtained by summing the confluency over all WMH clusters. COSU was tested for correlation with CERAD-plus subscores. Correlation analysis was restricted to subjects with at least moderate WMH load (≥ 13.5 ml; iDSS / NACC: n = 52 / 80). In the iDSS sample, among the 12 CERAD-plus subtests the trail making test A (TMT-A) was most strongly correlated with the COSU (Spearman rho = -0.345, p = 0.027). TMT-A performance was not associated with total WMH volume (rho = 0.147, p = 0.358). This finding was confirmed in the NACC sample (rho = -0.261, p = 0.023 versus rho = -0.040, p = 0.732). Cognitive performance in specific domains including mental speed and fluid abilities seems to be more strongly associated with the shape irregularity of white matter MRI hyperintensities than with their volume.

White matter hyperintensities associated with small vessel disease impair social cognition beside attention and memory

Age-related white matter hyperintensities (WMH) are a manifestation of white matter damage seen on magnetic resonance imaging (MRI). They are related to vascular risk factors and cognitive impairment. This study investigated the cognitive profile at different stages of WMH in a large community-dwelling sample; 849 subjects aged 21 to 79 years were classified on the 4-stage Fazekas scale according to hyperintense lesions seen on individual T2-weighted fluid-attenuated inversion recovery MRI scans. The evaluation of cognitive functioning included seven domains of cognitive performance and five domains of subjective impairment, as proposed by the DSM-5. For the first time, the impact of age-related WMH on Theory of Mind was investigated. Differences between Fazekas groups were analyzed non-parametrically and effect sizes were computed. Effect sizes revealed a slight overall cognitive decline in Fazekas groups 1 and 2 relative to healthy subjects. Fazekas group 3 presented substantial decline in social cognition, attention and memory, although characterized by a high inter-individual variability. WMH groups reported subjective cognitive decline. We demonstrate that extensive WMH are associated with specific impairment in attention, memory, social cognition, and subjective cognitive performance. The detailed neuropsychological characterization of WMH offers new therapeutic possibilities for those affected by vascular cognitive decline.

Supplementary motor area-primary motor cortex facilitation in younger but not older adults

Growing evidence implicates a decline in white matter integrity in the age-related decline in motor control. Functional neuroimaging studies show significant associations between functional connectivity in the cortical motor network, including the supplementary motor area (SMA), and motor performance. Dual-coil transcranial magnetic stimulation studies show facilitatory connections between SMA and the primary motor cortex (M1) in younger adults. Here, we investigated whether SMA-M1 facilitation is affected by age and whether the strength of SMA-M1 facilitation is associated with bilateral motor control. Dual-coil transcranial magnetic stimulation was used to measure SMA-M1 connectivity in younger (N = 20) and older adults (N = 18), and bilateral motor control was measured with the assembly subtest of the Purdue Pegboard and clinical measures of dynamic balance. SMA-M1 facilitation was seen in younger but not older adults, and a significant positive association was found between SMA-M1 facilitation and bimanual performance. These results show that SMA-M1 facilitation is reduced in older adults compared to younger adults and provide evidence of the functional importance of SMA-M1 facilitation.

The Spatial Associations of Cerebral Blood Flow and Spontaneous Brain Activities with White Matter Hyperintensities-An Exploratory Study Using Multimodal Magnetic Resonance Imaging

White matter hyperintensities (WMHs) have been reported to be correlated with functional brain changes, but the association of the specific WMHs distribution pattern with regional functional changes remains uncertain. The aim of this study is to explore the possible spatial correlation of WMH with changes in cerebral blood flow (CBF) and spontaneous brain activities in elderly using a novel approach. The WMHs, CBF, and spontaneous brain activities measured by intrinsic connectivity contrast (ICC), were quantified using multimodal magnetic resonance imaging for 69 elderly subjects. Such approach enables us to expand our search for newly identified correlated areas by drawing strengths of different modes and provides a means for triangulation as well as complementary insights. The results showed significant positive correlations between WMH volumes in the right superior corona radiata and CBF in the left supplementary motor area, as well as between WMH volumes in left anterior limb internal capsule and CBF in the right putamen. Significant correlations of regional WMH volumes and ICC were also detected between the right anterior corona radiata and the left cuneus, and the right superior occipital cortex, as well as between the right superior corona radiata and the left superior occipital cortex. These findings may suggest a regional compensatory functional enhancement accounting for the maintenance of cognitively normal status, which can be supported by the widely observed phenomenon that mild to moderate WMH load could have little effect on global cognitive performance.

Structural MR Imaging in the Diagnosis of Alzheimer's Disease and Other Neurodegenerative Dementia: Current Imaging Approach and Future Perspectives

With the rise of aging population, clinical concern and research attention has shifted towards neuroimaging of dementia. The advent of 3T, magnetic resonance imaging (MRI) has permitted the anatomical imaging of neurodegenerative disease, specifically dementia, with improved resolution. Furthermore, more powerful techniques such as diffusion tensor imaging, quantitative susceptibility mapping, and magnetic transfer imaging have successfully emerged for the detection of micro-structural abnormalities. In the present review article, we provide a brief overview of Alzheimer's disease and explore recent neuroimaging developments in the field of dementia with an emphasis on structural MR imaging in order to propose a simple and easily applicable systematic approach to the imaging diagnosis of dementia.

Brain atrophy in Alzheimer's Disease and aging

Thanks to its safety and accessibility, magnetic resonance imaging (MRI) is extensively used in clinical routine and research field, largely contributing to our understanding of the pathophysiology of neurodegenerative disorders such as Alzheimer's disease (AD). This review aims to provide a comprehensive overview of the main findings in AD and normal aging over the past twenty years, focusing on the patterns of gray and white matter changes assessed in vivo using MRI. Major progresses in the field concern the segmentation of the hippocampus with novel manual and automatic segmentation approaches, which might soon enable to assess also hippocampal subfields. Advancements in quantification of hippocampal volumetry might pave the way to its broader use as outcome marker in AD clinical trials. Patterns of cortical atrophy have been shown to accurately track disease progression and seem promising in distinguishing among AD subtypes. Disease progression has also been associated with changes in white matter tracts. Recent studies have investigated two areas often overlooked in AD, such as the striatum and basal forebrain, reporting significant atrophy, although the impact of these changes on cognition is still unclear. Future integration of different MRI modalities may further advance the field by providing more powerful biomarkers of disease onset and progression.

Neuroplasticity: Insights from Patients Harboring Gliomas

Neuroplasticity is the ability of the brain to reorganize itself during normal development and in response to illness. Recent advances in neuroimaging and direct cortical stimulation in human subjects have given neuroscientists a window into the timing and functional anatomy of brain networks underlying this dynamic process. This review will discuss the current knowledge about the mechanisms underlying neuroplasticity, with a particular emphasis on reorganization following CNS pathology. First, traditional mechanisms of neuroplasticity, most relevant to learning and memory, will be addressed, followed by a review of adaptive mechanisms in response to pathology, particularly the recruitment of perilesional cortical regions and unmasking of latent connections. Next, we discuss the utility and limitations of various investigative techniques, such as direct electrocortical stimulation (DES), functional magnetic resonance imaging (fMRI), corticocortical evoked potential (CCEP), and diffusion tensor imaging (DTI). Finally, the clinical utility of these results will be highlighted as well as possible future studies aimed at better understanding of the plastic potential of the brain with the ultimate goal of improving quality of life for patients with neurologic injury.

Gray matter volume and white matter lesions in chronic kidney disease: exploring the association with depressive symptoms

OBJECTIVE

Chronic kidney disease (CKD) is associated with structural brain damage and with a high prevalence of depression. We therefore investigated structural brain alterations in both gray and white matter in CKD patients, focusing on depression-related (frontal-subcortical) regions.

METHOD

This cross-sectional MRI study in 24 CKD patients and 24 age- and sex-matched controls first tested whether CKD was associated with regionally lower gray matter (GM) volumes and more severe white matter lesions (WMLs). In exploratory subanalyses, we examined whether differences were more pronounced in CKD patients with depressive symptoms.

RESULTS

CKD patients showed lower global GM volume (P=.04) and more severe WMLs (P=.04) compared to controls. In addition, we found substantial clusters of lower GM in the bilateral orbitofrontal-cortex for CKD patients, which were however nonsignificant after proper multiple-comparison correction. In exploratory analyses for depressed CKD patients, reduced GM clusters were mainly detected within the frontal lobe. WML severity was unrelated to depression.

CONCLUSION

CKD was characterized by differences in brain structure. Although subthreshold, lower GM volumes were observed in depression-related brain areas and were more pronounced for depressed patients. There is a need for replication in larger and longitudinal studies to investigate whether WMLs and regional GM reductions may render CKD patients more susceptible for depression.

Physical activity, motor function, and white matter hyperintensity burden in healthy older adults

OBJECTIVE

To test the hypothesis that physical activity modifies the association between white matter hyperintensity (WMH) burden and motor function in healthy older persons without dementia.

METHODS

Total daily activity (exercise and nonexercise physical activity) was measured for up to 11 days with actigraphy (Actical; Philips Respironics, Bend, OR) in 167 older adults without dementia participating in the Rush Memory and Aging Project. Eleven motor performances were summarized into a previously described global motor score. WMH volume was expressed as percent of intracranial volume. Linear regression models, adjusted for age, education, and sex, were performed with total WMH volume as the predictor and global motor score as the outcome. Terms for total daily physical activity and its interaction with WMH volume were then added to the model.

RESULTS

Higher WMH burden was associated with lower motor function (p = 0.006), and total daily activity was positively associated with motor function (p = 0.002). Total daily activity modified the association between WMH and motor function (p = 0.007). WMH burden was not associated with motor function in persons with high activity (90th percentile). By contrast, higher WMH burden remained associated with lower motor function in persons with average (50th percentile; estimate = -0.304, slope = -0.133) and low (10th percentile; estimate = -1.793, slope = -0.241) activity.

CONCLUSIONS

Higher levels of physical activity may reduce the effect of WMH burden on motor function in healthy older adults.

Associations between age and gray matter volume in anatomical brain networks in middle-aged to older adults

Aging is associated with cognitive decline, diminished brain function, regional brain atrophy, and disrupted structural and functional brain connectivity. Understanding brain networks in aging is essential, as brain function depends on large-scale distributed networks. Little is known of structural covariance networks to study inter-regional gray matter anatomical associations in aging. Here, we investigate anatomical brain networks based on structural covariance of gray matter volume among 370 middle-aged to older adults of 45-85 years. For each of 370 subjects, we acquired a T1-weighted anatomical MRI scan. After segmentation of structural MRI scans, nine anatomical networks were defined based on structural covariance of gray matter volume among subjects. We analyzed associations between age and gray matter volume in anatomical networks using linear regression analyses. Age was negatively associated with gray matter volume in four anatomical networks (P < 0.001, corrected): a subcortical network, sensorimotor network, posterior cingulate network, and an anterior cingulate network. Age was not significantly associated with gray matter volume in five networks: temporal network, auditory network, and three cerebellar networks. These results were independent of gender and white matter hyperintensities. Gray matter volume decreases with age in networks containing subcortical structures, sensorimotor structures, posterior, and anterior cingulate cortices. Gray matter volume in temporal, auditory, and cerebellar networks remains relatively unaffected with advancing age.

White matter hyperintensities and hypobaric exposure

OBJECTIVE

Demonstrate that occupational exposure to nonhypoxic hypobaria is associated with subcortical white matter hyperintensities (WMHs) on fluid-attenuated inversion recovery magnetic resonance imaging (MRI).

METHODS

Eighty-three altitude chamber personnel (PHY), 105 U-2 pilots (U2P), and 148 age- controlled and health-matched doctorate degree controls (DOC) underwent high-resolution MRI. Subcortical WMH burden was quantified as count and volume of subcortical WMH lesions after transformation of images to the Talairach atlas-based stereotactic frame.

RESULTS

Subcortical WMHs were more prevalent in PHY (volume p = 0.011/count p = 0.019) and U2P (volume p < 0.001/count p < 0.001) when compared to DOC, whereas PHY were not significantly different than U2P.

INTERPRETATION

This study provides strong evidence that nonhypoxic hypobaric exposure may induce subcortical WMHs in a young, healthy population lacking other risk factors for WMHs and adds this occupational exposure to other environmentally related potential causes of WMHs. Ann Neurol 2014;76:719-726.

Multimodal white matter imaging to investigate reduced fractional anisotropy and its age-related decline in schizophrenia

We hypothesized that reduced fractional anisotropy (FA) of water diffusion and its elevated aging-related decline in schizophrenia patients may be caused by elevated hyperintensive white matter (HWM) lesions, by reduced permeability-diffusivity index (PDI), or both. We tested this hypothesis in 40/30 control/patient participants. FA values for the corpus callosum were calculated from high angular resolution diffusion tensor imaging (DTI). Whole-brain volume of HWM lesions was quantified by 3D-T2w-fluid-attenuated inversion recovery (FLAIR) imaging. PDI for corpus callosum was ascertained using multi b-value diffusion imaging (15 b-shells with 30 directions per shell). Patients had significantly lower corpus callosum FA values, and there was a significant age-by-diagnosis interaction. Patients also had significantly reduced PDI but no difference in HWM volume. PDI and HWM volume were significant predictors of FA and captured the diagnosis-related variance. Separately, PDI robustly explained FA variance in schizophrenia patients, but not in controls. Conversely, HWM volume made equally significant contributions to variability in FA in both groups. The diagnosis-by-age effect of FA was explained by a PDI-by-diagnosis interaction. Post hoc testing showed a similar trend for PDI of gray mater. Our study demonstrated that reduced FA and its accelerated decline with age in schizophrenia were explained by pathophysiology indexed by PDI, rather than HWM volume.

Lower neurocognitive function in U-2 pilots: Relationship to white matter hyperintensities

OBJECTIVE

Determine whether United States Air Force (USAF) U-2 pilots (U2Ps) with occupational exposure to repeated hypobaria had lower neurocognitive performance compared to pilots without repeated hypobaric exposure and whether U2P neurocognitive performance correlated with white matter hyperintensity (WMH) burden.

METHODS

We collected Multidimensional Aptitude Battery-II (MAB-II) and MicroCog: Assessment of Cognitive Functioning (MicroCog) neurocognitive data on USAF U2Ps with a history of repeated occupational exposure to hypobaria and compared these with control data collected from USAF pilots (AFPs) without repeated hypobaric exposure (U2Ps/AFPs MAB-II 87/83; MicroCog 93/80). Additional comparisons were performed between U2Ps with high vs low WMH burden.

RESULTS

U2Ps with repeated hypobaric exposure had significantly lower scores than control pilots on reasoning/calculation (U2Ps/AFPs 99.4/106.5), memory (105.5/110.9), information processing accuracy (102.1/105.8), and general cognitive functioning (103.5/108.5). In addition, U2Ps with high whole-brain WMH count showed significantly lower scores on reasoning/calculation (high/low 96.8/104.1), memory (102.9/110.2), general cognitive functioning (101.5/107.2), and general cognitive proficiency (103.6/108.8) than U2Ps with low WMH burden (high/low WMH mean volume 0.213/0.003 cm(3) and mean count 14.2/0.4).

CONCLUSION

In these otherwise healthy, highly functioning individuals, pilots with occupational exposure to repeated hypobaria demonstrated lower neurocognitive performance, albeit demonstrable on only some tests, than pilots without repeated exposure. Furthermore, within the U2P population, higher WMH burden was associated with lower neurocognitive test performance. Hypobaric exposure may be a risk factor for subtle changes in neurocognition.

Pathways linking regional hyperintensities in the brain and slower gait

IMPORTANCE

Cerebral white matter hyperintensities (WMHs) are involved in the evolution of impaired mobility and executive functions. Executive functions and mobility are also associated. Thus, WMHs may impair mobility directly, by disrupting mobility-related circuits, or indirectly, by disrupting circuits responsible for executive functions. Understanding the mechanisms underlying impaired mobility in late life will increase our capacity to develop effective interventions.

OBJECTIVE

To identify regional WMHs most related to slower gait and to examine whether these regional WMHs directly impact mobility, or indirectly by executive functions.

DESIGN

Cross-sectional study. Twenty-one WMH variables (i.e., total WMH volume and WMHs in 20 tracts), gait speed, global cognition (Modified Mini-Mental State Examination; 3MS), and executive functions and processing speed (Digit-Symbol Substitution Test; DSST) were assessed. An L1-L2 regularized regression (i.e., Elastic Net model) identified the WMH variables most related to slower gait. Multivariable linear regression models quantified the association between these WMH variables and gait speed. Formal tests of mediation were also conducted.

SETTING

Community-based sample.

PARTICIPANTS

Two hundred fifty-three adults (mean age: 83years, 58% women, 41% black).

MAIN OUTCOME MEASURE

Gait speed.

RESULTS

In older adults with an average gait speed of 0.91m/sec, total WMH volume, WMHs located in the right anterior thalamic radiation (ATRR) and frontal corpuscallosum (CCF) were most associated with slower gait. There was a >10% slower gait for each standard deviation of WMH in CCF, ATRR or total brain (standardized beta in m/sec [p value]: -0.11 [p=0.046], -0.15 [p=0.007] and -0.14 [p=0.010], respectively). These associations were substantially and significantly attenuated after adjustment for DSST. This effect was stronger for WMH in CCF than for ATRR or total WMH (standardized beta in m/sec [p value]: -0.07 [p=0.190], -0.12 [p=0.024] and -0.10 [p=0.049], respectively). Adjustment for 3MS did not change these associations. The mediation analyses also found that DSST significantly mediated the associations between WMHs and gait speed. Our models were adjusted for age, sex, BMI, quadriceps strength, years of education, standing height, and prevalent hypertension.

CONCLUSION

The impact, direct or indirect, of WMHs on gait speed depended on their location and was mediated by executive function. Thus, multi-faceted interventions targeting executive control functions as well as motor functions, such as balance and strength training, are candidates to the maintenance of mobility across the lifespan.

A pattern approach to focal white matter hyperintensities on magnetic resonance imaging

Evaluation of focal white matter hyperintensities on magnetic resonance imaging in any age group is always challenging because the cause of these hyperintensities varies extensively. Understanding the clinical presentation, pathophysiology, and associated imaging findings can allow the radiologist to limit the differential diagnosis. A specific imaging approach including age, pattern of distribution, signal characteristics on various sequences, enhancement pattern, and other ancillary findings helps to identify a correct cause for these hyperintensities. This article provides a pattern approach to differentiate various common and a few uncommon diseases presenting as focal white matter hyperintensities.

White matter hyperintensities on MRI in high-altitude U-2 pilots

OBJECTIVE

To demonstrate that U-2 pilot occupational exposure to hypobaria leads to increased incidence of white matter hyperintensities (WMH) with a more uniform distribution throughout the brain irrespective of clinical neurologic decompression sickness history.

METHODS

We evaluated imaging findings in 102 U-2 pilots and 91 controls matched for age, health, and education levels. Three-dimensional, T2-weighted, high-resolution (1-mm isotropic) imaging data were collected using fluid-attenuated inversion recovery sequence on a 3-tesla MRI scanner. Whole-brain and regional WMH volume and number were compared between groups using a 2-tailed Wilcoxon rank sum test.

RESULTS

U-2 pilots demonstrated an increase in volume (394%; p = 0.004) and number (295%; p < 0.001) of WMH. Analysis of regional distribution demonstrated WMH more uniformly distributed throughout the brain in U-2 pilots compared with mainly frontal distribution in controls.

CONCLUSION

Pilots with occupational exposure to hypobaria showed a significant increase in WMH lesion volume and number. Unlike the healthy controls with predominantly WMH in the frontal white matter, WMH in pilots were more uniformly distributed throughout the brain. This is consistent with our hypothesized pattern of damage produced by interaction between microemboli and cerebral tissue, leading to thrombosis, coagulation, inflammation, and/or activation of innate immune response, although further studies will be necessary to clarify the pathologic mechanisms responsible.

Anodal transcranial direct current stimulation temporarily reverses age-associated cognitive decline and functional brain activity changes

The rising proportion of elderly people worldwide will yield an increased incidence of age-associated cognitive impairments, imposing major burdens on societies. Consequently, growing interest emerged to evaluate new strategies to delay or counteract cognitive decline in aging. Here, we assessed immediate effects of anodal transcranial direct current stimulation (atDCS) on cognition and previously described detrimental changes in brain activity attributable to aging. Twenty healthy elderly adults were assessed in a crossover sham-controlled design using functional magnetic resonance imaging (fMRI) and concurrent transcranial DCS administered to the left inferior frontal gyrus. Effects on performance and task-related brain activity were evaluated during overt semantic word generation, a task that is negatively affected by advanced age. Task-absent resting-state fMRI (RS-fMRI) assessed atDCS-induced changes at the network level independent of performance. Twenty matched younger adults served as controls. During sham stimulation, task-related fMRI demonstrated that enhanced bilateral prefrontal activity in older adults was associated with reduced performance. RS-fMRI revealed enhanced anterior and reduced posterior functional brain connectivity. atDCS significantly improved performance in older adults up to the level of younger controls; significantly reduced task-related hyperactivity in bilateral prefrontal cortices, the anterior cingulate gyrus, and the precuneus; and induced a more "youth-like" connectivity pattern during RS-fMRI. Our results provide converging evidence from behavioral analysis and two independent functional imaging paradigms that a single session of atDCS can temporarily reverse nonbeneficial effects of aging on cognition and brain activity and connectivity. These findings may translate into novel treatments to ameliorate cognitive decline in normal aging in the future.

Functional language shift to the right hemisphere in patients with language-eloquent brain tumors

Objectives

Language function is mainly located within the left hemisphere of the brain, especially in right-handed subjects. However, functional MRI (fMRI) has demonstrated changes of language organization in patients with left-sided perisylvian lesions to the right hemisphere. Because intracerebral lesions can impair fMRI, this study was designed to investigate human language plasticity with a virtual lesion model using repetitive navigated transcranial magnetic stimulation (rTMS).

Experimental design

Fifteen patients with lesions of left-sided language-eloquent brain areas and 50 healthy and purely right-handed participants underwent bilateral rTMS language mapping via an object-naming task. All patients were proven to have left-sided language function during awake surgery. The rTMS-induced language errors were categorized into 6 different error types. The error ratio (induced errors/number of stimulations) was determined for each brain region on both hemispheres. A hemispheric dominance ratio was then defined for each region as the quotient of the error ratio (left/right) of the corresponding area of both hemispheres (ratio >1  =  left dominant; ratio <1  =  right dominant).

Results

Patients with language-eloquent lesions showed a statistically significantly lower ratio than healthy participants concerning “all errors” and “all errors without hesitations”, which indicates a higher participation of the right hemisphere in language function. Yet, there was no cortical region with pronounced difference in language dominance compared to the whole hemisphere.

Conclusions

This is the first study that shows by means of an anatomically accurate virtual lesion model that a shift of language function to the non-dominant hemisphere can occur.

Hyperintense white matter lesions in 50 high-altitude pilots with neurologic decompression sickness

INTRODUCTION

Neurologic decompression sickness (NDCS) can affect high-altitude pilots, causing variable central nervous system symptoms. Five recent severe episodes prompted further investigation.

METHODS

We report the hyperintense white matter (HWM) lesion imaging findings in 50 U-2 pilot volunteers, and compare 12 U-2 pilots who experienced clinical NDCS to 38 U-2 pilots who did not. The imaging data were collected using a 3T magnetic resonance imaging scanner and high-resolution (1-mm isotropic) three-dimensional fluid-attenuated inversion recovery sequence. Whole-brain and regional lesion volume and number were compared between groups.

RESULTS

The NDCS group had significantly increased whole brain and insular volumes of HWM lesions. The intergroup difference in lesion numbers was not significant.

CONCLUSION

A clinical episode of NDCS was associated with a significant increase in HWM lesion volume, especially in the insula. We postulate this to be due to hypobaric exposure rather than hypoxia since all pilots were maintained on 100% oxygen throughout the flight. Further studies will be necessary to better understand the pathophysiology underlying these lesions.

Associations between T1 white matter lesion volume and regional white matter microstructure in aging

White matter lesions, typically manifesting as regions of signal intensity abnormality (WMSA) on MRI, increase in frequency with age. However, the role of this damage in cognitive decline and disease is still not clear, as lesion volume has only loosely been associated with clinical status. Diffusion tensor imaging (DTI) has been used to examine the quantitative microstructural integrity of white matter, and has applications in the examination of subtle changes to tissue that appear visually normal on conventional imaging. The primary goal of this study was to determine whether major macrostructural white matter damage, (total WMSA volume), is associated with microstructural integrity of normal appearing white matter, and if these macrostructural changes fully account for microstructural changes. Imaging was performed in 126 nondemented individuals, ages 43-85 years, with no history of cerebrovascular disease. Controlling for age, greater WMSA volume was associated with decreased fractional anisotropy (FA) in widespread brain regions. Patterns were similar for FA and radial diffusivity but in contrast, WMSA was associated with axial diffusivity in fewer areas. Age was associated with FA in several regions, and many of these effects remained even when controlling for WMSA volume, suggesting the etiology of WMSAs does not fully account for all age-associated white matter deterioration. These results provide evidence that WMSA volume is associated with the integrity of normal-appearing white matter. In addition, our results suggest that overt lesions may not account for the association of increasing age with decreased white matter tissue integrity.

The association between cognitive function and white matter lesion location in older adults: a systematic review

Background

Maintaining cognitive function is essential for healthy aging and to function autonomously within society. White matter lesions (WMLs) are associated with reduced cognitive function in older adults. However, whether their anatomical location moderates these associations is not well-established. This review systematically evaluates peer-reviewed evidence on the role of anatomical location in the association between WMLs and cognitive function.

Methods

In accordance with the preferred reporting items for systematic reviews and meta-analysis (PRISMA) statement, databases of EMBASE, PUBMED, MEDLINE, and CINAHL, and reference lists of selected papers were searched. We limited our search results to adults aged 60 years and older, and studies published in the English language from 2000 to 2011. Studies that investigated the association between cognitive function and WML location were included. Two independent reviewers extracted: 1) study characteristics including sample size, sample characteristic, and study design; 2) WML outcomes including WML location, WML quantification method (scoring or volume measurement), strength of the MRI magnet in Tesla, and MRI sequence used for WML detection; and 3) cognitive function outcomes including cognitive tests for two cognitive domains of memory and executive function/processing speed.

Results

Of the 14 studies included, seven compared the association of subcortical versus periventricular WMLs with cognitive function. Seven other studies investigated the association between WMLs in specific brain regions (e.g., frontal, parietal lobes) and cognitive function. Overall, the results show that a greater number of studies have found an association between periventricular WMLs and executive function/processing speed, than subcortical WMLs. However, whether WMLs in different brain regions have a differential effect on cognitive function remains unclear.

Conclusions

Evidence suggests that periventricular WMLs may have a significant negative impact on cognitive abilities of older adults. This finding may be influenced by study heterogeneity in: 1) MRI sequences, WML quantification methods, and neuropsychological batteries; 2) modifying effect of cardiovascular risk factors; and 3) quality of studies and lack of sample size calculation.

Correlations between Stroop task performance and white matter lesion measures in late-onset major depression

Cerebral white matter lesions (WMLs) are believed to play an important role in a subset of patients with late-onset depression by affecting the white matter connectivity in circuitries essential for mood and cognition. In this study we used diffusion tensor imaging-based (DTI-based) tractography to assess white matter fiber tracts affected by deep WMLs (DWMLs) in patients with late-onset major depression and age- and gender-matched controls. Tractography outcome, illustrated as pathways affected by DWMLs, was analyzed for associations with cognitive performance on the Stroop Test (ST). The patients (n=17) performed significantly worse on the ST than the controls (n=22). Poor performance on the ST correlated with higher lesion load. Regression analysis showed a significant correlation between poor performance on the ST and tracts affected by DWMLs in multiple brain areas in the control group, but very sparse correlation in the patient group. Our results suggest that DWMLs play an important role in the cognitive performance of controls,whereas their influence in depressed patients is overruled by additional, state-dependent factors. Future focus on the tract-specific localization of WMLs using DTI tractography may reveal important associations between neuroconnectivity and clinical measures.

Enhanced motor cortex facilitation in patients with vascular cognitive impairment-no dementia

Data on Transcranial Magnetic Stimulation (TMS) derived measures of cortical excitability and intracortical circuits in age-related white matter changes are scarce. We aimed to assess early changes of motor cortex excitability in nondemented elderly patients with subcortical ischemic vascular disease (SVD). Ten SVD elderly and ten age-matched controls underwent paired-pulse TMS for the analysis of intracortical inhibition (ICI) and facilitation (ICF). All subjects performed neuropsychological assessment and brain magnetic resonance imaging. SVD patients showed abnormal executive control function. No statistically significant differences were found for resting motor threshold, cortical silent period between SVD patients and controls or between the two hemispheres, in patients. A significant enhancement of mean ICF was observed in SVD patients. This study provides the first evidence of functional changes in intracortical excitatory neuronal circuits in patients with SVD and clinical features of vascular cognitive impairment-no dementia. Further studies are required to evaluate whether the observed change of ICF might predict cognitive and/or motor impairment in a population at risk for subcortical vascular dementia.

The nature of episodic memory deficits in MCI with and without vascular burden

This study measured episodic memory deficits in individuals with mild cognitive impairment (MCI) as a function of their vascular burden. Vascular burden was determined clinically by computing the number of vascular risk factors and diseases and neuroradiologically by assessing the presence and severity of white matter lesions (WML). Strategic memory processes were measured with free recall and temporal contextual memory tasks requiring self-initiated retrieval. Nonstrategic memory retrieval processes were appraised with a five-choice recognition procedure. Results showed that MCI participants with high vascular burden displayed impairment of strategic memory processes, whereas MCI participants with no vascular burden showed impairment of both strategic and nonstrategic memory processes. A similar pattern was found whether vascular burden was measured using a clinical index of vascular risk profile or whether it was measured neuroradiologically by assessing the extent and severity of subcortical WML. However, the effect of WML on memory differed as function of level of education, used here as a proxy for cognitive reserve. Among participants with MCI, those who had higher education and no WML were the least memory impaired. The study also examined memory as a function of whether patients later progressed to dementia after a three-year follow-up. When examining progressors' performance, strategic and nonstrategic processes were both impaired in progressors with no concomitant vascular conditions, whereas progressors with a high vascular burden showed less impairment of nonstrategic than strategic processes. Overall, results indicate that the presence of vascular burden in MCI is associated with selective impairment of strategic memory processes.

Association between white matter hyperintensities and executive decline in mild cognitive impairment is network dependent

White matter hyperintensities (WMH) in Mild Cognitive Impairment (MCI) have been associated with impaired executive functioning, although contradictory findings have been reported. The aim of this study was to examine whether WMH location influenced the relation between WMH and executive functioning in MCI participants (55-90 years) in the European multicenter memory-clinic-based DESCRIPA study, who underwent MRI scanning at baseline (N = 337). Linear mixed model analysis was performed to test the association between WMH damage in three networks (frontal-parietal, frontal-subcortical and frontal-parietal-subcortical network) and change in executive functioning over a 3-year period. WMH in the frontal-parietal and in the frontal-parietal-subcortical network were associated with decline in executive functioning. However, the frontal-subcortical network was not associated with change in executive functioning. Our results suggest that parietal WMH are a significant contributor to executive decline in MCI and that investigation of WMH in the cerebral networks supporting cognitive functions provide a new way to differentiate stable from cognitive declining MCI individuals.

Whole brain and regional hyperintense white matter volume and blood pressure: overlap of genetic loci produced by bivariate, whole-genome linkage analyses

BACKGROUND AND PURPOSE

The volume of T2-hyperintense white matter (HWM) is an important neuroimaging marker of cerebral integrity with a demonstrated high heritability. Pathophysiology studies have shown that the regional, ependymal, and subcortical HWM lesions are associated with elevated arterial pulse pressure and arterial blood pressure (BP), respectively. We performed bivariate, whole-genome linkage analyses for HWM volumes and BP measurements to identify chromosomal regions that contribute jointly to both traits in a population of healthy Mexican Americans. Our aims were to localize novel quantitative trait loci acting pleiotropically on these phenotypes and to replicate previous genetic findings on whole brain HWM volume and BP measurements.

METHODS

BP measurements and volumes of whole-brain (WB), subcortical, and ependymal HWM lesions, measured from high-resolution (1 mm(3)) 3-dimensional fluid-attenuated inversion recovery images, served as focal quantitative phenotypes. Data were collected from 357 (218 females; mean age=47.9±13.2 years) members of large extended families who participated in the San Antonio Family Heart Study.

RESULTS

Bivariate genomewide linkage analyses localized a significant quantitative trait locus influencing WB and regional (ependymal) HWM volumes and pulse pressure and systolic BP to chromosomal location 1q24 between markers D1S196 and D1S1619. Several other chromosomal regions (1q42, 10q24-q26, and 15q26) exhibited suggestive linkages. The results of the post hoc analyses that excluded 55 subjects taking antihypertensive medication showed no substantive differences from the results obtained in the full cohort.

CONCLUSIONS

This study confirms several previously observed quantitative trait loci influencing BP and cerebral integrity and identifies a novel significant quantitative trait locus at chromosome 1q24. The genetic results strongly support a role for pleiotropically acting genes jointly influencing BP and cerebral white matter integrity.

White matter hyperintensities alter functional organization of the motor system

Severe white matter hyperintensities (WMH) represent cerebral small vessel disease and predict functional decline in the elderly. We used fMRI to test if severe WMH impact on functional brain network organization even before clinical dysfunction. Thirty healthy right-handed/footed subjects (mean age, 67.8 ± 7.5 years) underwent clinical testing, structural MRI and fMRI at 3.0T involving repetitive right ankle and finger movements. Data were compared between individuals with absent or punctuate (n = 17) and early confluent or confluent (n = 13) WMH. Both groups did not differ in mobility or cognition data. On fMRI, subjects with severe WMH demonstrated excess activation in the pre-supplementary motor area (SMA), frontal, and occipital regions. Activation differences were noted with ankle movements only. Pre-SMA activation correlated with frontal WMH load for ankle but not finger movements. With simple ankle movements and no behavioral deficits, elderly subjects with severe WMH demonstrated pre-SMA activation, usually noted with complex tasks, as a function of frontal WMH load. This suggests compensatory activation related to disturbance of frontosubcortical circuits.

Brain aging and gait

Aging is associated with a reduction in several functions including gait. The preservation of gait is important in order to prevent falls and consequent injury as one gets older. Poorer gait may also be an important marker for health status and a determinant of quality of life in later life. It is now recognized that specific regions of the brain such as the frontal motor, prefrontal and parietal cortices, the basal ganglia and cerebellum play an important role in the initiation, planning, execution and maintenance of gait, in tandem with other neuromuscular factors. Aging and age-related disease may affect areas of the brain that are involved in the regulation of gait. Recent technological advances in brain imaging have enabled the identification of age-related changes occurring in the brain, such as cortical atrophy, brain infarctions or cerebral white matter lesions. There is a small, but growing, amount of research examining the association between these changes and gait. The objective of this review is to summarize the current state of knowledge on the impact of the aging brain on gait, and to identify directions for future research. Such research may lead to the development of interventions aimed at preventing or reducing the effect of brain aging on gait.

Quantitative evaluation of Alzheimer's disease

Alzheimer's disease (AD) can be definitively diagnosed only by histopathologic examination of brain tissue; the identification and differential diagnosis of AD is especially challenging in its early stages. Neuroimaging is playing an increasingly relevant role in the identification and quantification of AD in vivo, especially in the preclinical stages, when therapeutic intervention could be more effective. Neuroimaging enables quantification of brain volume loss (structural imaging), detection of early cerebral dysfunction (functional imaging), probing into the finest cerebral structures (microstructural imaging), and investigation of amyloid plaque and neurofibrillary tangle build-up (amyloid imaging). Throughout the years, several imaging tools have been developed, ranging from simple visual rating scales to sophisticated computerized algorithms. As recently revised criteria for AD require quantitative evaluation of biomarkers mostly based on imaging, this paper provides an overview of the main neuroimaging tools which might be used presently or in the future in routine clinical practice for AD diagnosis.

Age-related brain pathology in Octodon degu: blood vessel, white matter and Alzheimer-like pathology

Recently it has been shown that over 3-year-old wild-type South American rodents, Octodon degus, the "common degu" or degu, of their own accord develop Alzheimer's disease neuropathological hallmarks: amyloid-β-peptide depositions and accumulation of tau-protein. Here we analyzed brains of 1-, 3- and 6-year-old degu's, bred in standard animal facilities. Significant amounts of Aβ and tau deposits are present in the hippocampal formation of 6-year-old O. degus, primarily in the white matter, but these hippocampal Aβ and tau deposits are not present in younger ones. In contrast, significant Aβ deposits in blood vessel walls are already found in 3-year-old animals. The tau deposits in the hippocampal formation coincide with a significant decrease in staining for myelin in the same areas, indicating hippocampal disconnection and, likely, dysfunction. Our findings indicate that (1) cerebral amyloid angiopathy precedes brain parenchyma pathology in aged degu's and (2) the onset of disease seems to be delayed in the laboratory vs. wild-type degu's.

Analysis of genetic variability and whole genome linkage of whole-brain, subcortical, and ependymal hyperintense white matter volume

BACKGROUND AND PURPOSE

The cerebral volume of T2-hyperintense white matter (HWM) is an important neuroimaging marker of cerebral integrity. Pathophysiology studies identified that subcortical and ependymal HWM are produced by 2 different mechanisms but shared a common risk factor: high arterial pulse pressure. Recent studies have demonstrated high heritability of the whole-brain HMW volume and reported significant and suggestive evidence of genetic linkage. We performed heritability and whole-genome linkage analysis to replicate previous reported findings and to study shared genetic variance, and possible overlap for specific loci, between subcortical and ependymal HWM volumes in a population of healthy Mexican Americans.

METHODS

The volumes of subcortical and ependymal HWM regions were measured from high-resolution (1 mm(3)), 3-dimensional fluid-attenuated inversion recovery images acquired for 459 (283 females, 176 males) active participants in the San Antonio Family Heart Study. Subjects ranged in age from 19 to 85 years of age (47.9+/-13.5 years) and were part of 49 families (9.4+/-8.5 individuals per family).

RESULTS

The volumes of whole-brain, subcortical, and ependymal HWM were highly heritable (h(2)=0.72, 0.66, and 0.73, respectively). The subcortical and ependymal HWM volumes shared 21% of genetic variability indicating significant pleiotropy. Genomewide linkage analysis showed only a suggestive bivariate linkage for subcortical and ependymal HWM volumes (log of odds=2.12) on chromosome 1 at 288 cM.

CONCLUSIONS

We replicated previous findings of high heritability for the whole-brain HWM volume. We also showed that subcortical and ependymal volume shared a significant portion of genetic variability and the bivarate linkage analysis produced a suggestive linkage near the locus previously identified in a study of whole-brain HWM volume and arterial pulse pressure.