Mobility decline in the elderly relates to lesion accrual in the splenium of the corpus callosum

Cognitive impairment mediates the white matter injury load and gait disorders in subcortical ischemic vascular disease

Gait disorders are common in patients with subcortical ischemic vascular disease (SIVD). We aim to explore the impact of white matter (WM) damage on gait disorders in SIVD. 21 SIVD patients and 20 normal controls (NC) were included in the study. Montreal Cognitive Assessment (MoCA) was used to evaluate general cognition, while Speed-Accuracy Trade-Off (SAT) was used to assess executive function. Gait velocity, cadence, and stride length were measured. Diffusion Tensor Imaging (DTI) data were analyzed using Tract-Based Spatial Statistics (TBSS) and Peak Width of Skeletonized Mean Diffusivity (PSMD). The relationships among WM damage, gait disorders, and cognitive function were examined through mediation analysis. SIVD scored lower than NC in MoCA and SAT tests (P < 0.001). Gait velocity and stride length were decreased in SIVD. SIVD had lower PSMD (P < 0.001). PSMD correlated with gait parameters, which were totally mediated by MoCA and partially mediated by SAT. The fractional anisotropy (FA) and mean diffusivity (MD) of the genu of the corpus callosum (GCC) and body of CC (BCC) were correlated with gait parameters. The FA of the bilateral anterior corona radiata (ACR) was positively correlated with gait parameters, while the MD of the bilateral superior corona radiata (SCR), bilateral superior longitudinal fasciculus (SLF), and left external capsule (EC) were negatively correlated with them (P < 0.05). Gait impairments in SIVD were associated with cognitive deficits. Cognitive impairment mediated the WM damage and gait disorders. The microstructural alterations of CC, SLF, EC, and CR may be related to changes in gait.

Lower Myelin Content Is Associated With Lower Gait Speed in Cognitively Unimpaired Adults

Mounting evidence indicates that abnormal gait speed predicts the progression of neurodegenerative diseases, including Alzheimer's disease. Understanding the relationship between white matter integrity, especially myelination, and motor function is crucial to the diagnosis and treatment of neurodegenerative diseases. We recruited 118 cognitively unimpaired adults across an extended age range of 22-94 years to examine associations between rapid or usual gait speeds and cerebral myelin content. Using our advanced multicomponent magnetic resonance relaxometry method, we measured myelin water fraction (MWF), a direct measure of myelin content, as well as longitudinal and transverse relaxation rates (R1 and R2), sensitive but nonspecific magnetic resonance imaging measures of myelin content. After adjusting for covariates and excluding 22 data sets due to cognitive impairments or artifacts, our results indicate that participants with higher rapid gait speed exhibited higher MWF, R1, and R2 values, that is, higher myelin content. These associations were statistically significant within several white matter brain regions, particularly the frontal and parietal lobes, splenium, anterior corona radiata, and superior fronto-occipital and longitudinal fasciculus. In contrast, we did not find any significant associations between usual gait speed and MWF, R1, or R2, which suggests that rapid gait speed may be a more sensitive marker of demyelination than usual gait speed. These findings advance our understanding on the implication of myelination in gait impairment among cognitively unimpaired adults, providing further evidence of the interconnection between white matter integrity and motor function.

Hormonal factors moderate the associations between vascular risk factors and white matter hyperintensities

To examine the moderation effects of hormonal factors on the associations between vascular risk factors and white matter hyperintensities in men and women, separately. White matter hyperintensities were automatically segmented and quantified in the UK Biobank dataset (N = 18,294). Generalised linear models were applied to examine (1) the main effects of vascular and hormonal factors on white matter hyperintensities, and (2) the moderation effects of hormonal factors on the relationship between vascular risk factors and white matter hyperintensities volumes. In men with testosterone levels one standard deviation higher than the mean value, smoking was associated with 27.8% higher white matter hyperintensities volumes in the whole brain. In women with a shorter post-menopause duration (one standard deviation below the mean), diabetes and higher pulse wave velocity were associated with 28.8% and 2.0% more deep white matter hyperintensities, respectively. These findings highlighted the importance of considering hormonal risk factors in the prevention and management of white matter hyperintensities.

Longitudinal Changes of White Matter Hyperintensities in Sporadic Small Vessel Disease: A Systematic Review and Meta-analysis

BACKGROUND AND OBJECTIVES

White matter hyperintensities (WMHs) are frequent imaging features of small vessel disease (SVD) and related to poor clinical outcomes. WMH progression over time is well described, but regression was also noted recently, although the frequency and associated factors are unknown. This systematic review and meta-analysis aims to assess longitudinal intraindividual WMH volume changes in sporadic SVD.

METHODS

We searched EMBASE and MEDLINE for articles up to 28 January 2022 on WMH volume changes using MRI on ≥2 time points in adults with sporadic SVD. We classified populations (healthy/community-dwelling, stroke, cognitive, other vascular risk factors, and depression) based on study characteristics. We performed random-effects meta-analyses with Knapp-Hartung adjustment to determine mean WMH volume change (change in milliliters, percentage of intracranial volume [%ICV], or milliliters per year), 95% CI, and prediction intervals (PIs, limits of increase and decrease) using unadjusted data. Risk of bias assessment tool for nonrandomized studies was used to assess risk of bias. We followed Preferred Reporting in Systematic Review and Meta-Analysis guidelines.

RESULTS

Forty-one articles, 12,284 participants, met the inclusion criteria. Thirteen articles had low risk of bias across all domains. Mean WMH volume increased over time by 1.74 mL (95% CI 1.23-2.26; PI -1.24 to 4.73 mL; 27 articles, N = 7,411, mean time interval 2.7 years, SD = 1.65); 0.25 %ICV (95% CI 0.14-0.36; PI -0.06 to 0.56; 6 articles, N = 1,071, mean time interval 3.5 years, SD = 1.54); or 0.58 mL/y (95% CI 0.35-0.81; PI -0.26 to 1.41; 8 articles, N = 3,802). In addition, 13 articles specifically mentioned and/or provided data on WMH regression, which occurred in asymptomatic, stroke, and cognitive disorders related to SVD.

DISCUSSION

Net mean WMH volume increases over time mask wide-ranging change (e.g., mean increase of 1.75 mL ranging from 1.25 mL decrease to 4.75 mL increase), with regression documented explicitly in up to one-third of participants. More knowledge on underlying mechanisms, associated factors, and clinical correlates is needed, as WMH regression could be an important intervention target.

Identification of Deep Brain Stimulation Targets for Neuropathic Pain After Spinal Cord Injury Using Localized Increases in White Matter Fiber Cross Section

OBJECTIVES

The spinal cord injury (SCI) patient population is overwhelmingly affected by neuropathic pain (NP), a secondary condition for which therapeutic options are limited and have a low degree of efficacy. The objective of this study was to identify novel deep brain stimulation (DBS) targets that may theoretically benefit those with NP in the SCI patient population. We hypothesize that localized changes in white matter identified in SCI subjects with NP compared to those without NP could be used to develop an evidence-based approach to DBS target identification.

MATERIALS AND METHODS

To classify localized neurostructural changes associated with NP in the SCI population, we compared white matter fiber density (FD) and cross section (FC) between SCI subjects with NP (n = 17) and SCI subjects without NP (n = 15) using diffusion-weighted magnetic resonance imaging (MRI). We then identified theoretical target locations for DBS using fiber bundles connected to significantly altered regions of white matter. Finally, we used computational models of DBS to determine if our theoretical target locations could be used to feasibly activate our fiber bundles of interest.

RESULTS

We identified significant increases in FC in the splenium of the corpus callosum in pain subjects when compared to controls. We then isolated five fiber bundles that were directly connected to the affected region of white matter. Our models were able to predict that our fiber bundles of interest can be feasibly activated with DBS at reasonable stimulation amplitudes and with clinically relevant implantation approaches.

CONCLUSIONS

Altogether, we identified neuroarchitectural changes associated with NP in the SCI cohort and implemented a novel evidence-driven target selection approach for DBS to guide future research in neuromodulation treatment of NP after SCI.

Grip strength from midlife as an indicator of later-life brain health and cognition: evidence from a British birth cohort

BACKGROUND

Grip strength is an indicator of physical function with potential predictive value for health in ageing populations. We assessed whether trends in grip strength from midlife predicted later-life brain health and cognition.

METHODS

446 participants in an ongoing British birth cohort study, the National Survey of Health and Development (NSHD), had their maximum grip strength measured at ages 53, 60-64, and 69, and subsequently underwent neuroimaging as part of a neuroscience sub-study, referred to as "Insight 46", at age 69-71. A group-based trajectory model identified latent groups of individuals in the whole NSHD cohort with below- or above-average grip strength over time, plus a reference group. Group assignment, plus standardised grip strength levels and change from midlife were each related to measures of whole-brain volume (WBV) and white matter hyperintensity volume (WMHV), plus several cognitive tests. Models were adjusted for sex, body size, head size (where appropriate), sociodemographics, and behavioural and vascular risk factors.

RESULTS

Lower grip strength from midlife was associated with smaller WBV and lower matrix reasoning scores at age 69-71, with findings consistent between analysis of individual time points and analysis of trajectory groups. There was little evidence of an association between grip strength and other cognitive test scores. Although greater declines in grip strength showed a weak association with higher WMHV at age 69-71, trends in the opposite direction were seen at individual time points with higher grip strength at ages 60-64, and 69 associated with higher WMHV.

CONCLUSIONS

This study provides preliminary evidence that maximum grip strength may have value in predicting brain health. Future work should assess to what extent age-related declines in grip strength from midlife reflect concurrent changes in brain structure.

Sarcopenia and Neuroscience: Learning to Communicate

In the 1990s and early 2000s, the common definition for sarcopenia was age-related loss of skeletal muscle, and low levels of muscle mass were central to sarcopenia diagnosis. In more recent consensus definitions, however, low muscle strength displaces low muscle mass as a defining feature of sarcopenia. The change stems from growing evidence that muscle weakness is a better predictor of adverse health outcomes (e.g., mobility limitations) than muscle mass. This evidence accompanies an emerging recognition that central neural mechanisms are critical determinants of age-related changes in strength and mobility that can occur independently of variations in muscle mass. However, strikingly little practical attention is typically given to the potential role of the central nervous system in the aetiology or remediation of sarcopenia (i.e., low muscle function). In this article, we provide an overview of some mechanisms that mediate neural regulation of muscle contraction and control, and highlight the specific contributions of neural hypoexcitability, dopaminergic dysfunction, and degradation of functional and structural brain connectivity in relation to sarcopenia. We aim to enhance the lines of communication between the domains of sarcopenia and neuroscience. We believe that appreciation of the neural regulation of muscle contraction and control is fundamental to understanding sarcopenia and to developing targeted therapeutic strategies for its treatment.

Heterogeneity of cellular inflammatory responses in ageing white matter and relationship to Alzheimer's and small vessel disease pathologies

White matter lesions (WML) are common in the ageing brain, often arising in a field effect of diffuse white matter abnormality. Although WML are associated with cerebral small vessel disease (SVD) and Alzheimer’s disease (AD), their cause and pathogenesis remain unclear. The current study tested the hypothesis that different patterns of neuroinflammation are associated with SVD compared to AD neuropathology by assessing the immunoreactive profile of the microglial (CD68, IBA1 and MHC‐II) and astrocyte (GFAP) markers in ageing parietal white matter (PARWM) obtained from the Cognitive Function and Ageing Study (CFAS), an ageing population‐representative neuropathology cohort. Glial responses varied extensively across the PARWM with microglial markers significantly higher in the subventricular region compared to either the middle‐zone (CD68 p = 0.028, IBA1 p < 0.001, MHC‐II p < 0.001) or subcortical region (CD68 p = 0.002, IBA1 p < 0.001, MHC‐II p < 0.001). Clasmatodendritic (CD) GFAP⁺ astrocytes significantly increased from the subcortical to the subventricular region (p < 0.001), whilst GFAP⁺ stellate astrocytes significantly decreased (p < 0.001). Cellular reactions could be grouped into two distinct patterns: an immune response associated with MHC‐II/IBA1 expression and CD astrocytes; and a more innate response characterised by CD68 expression associated with WML. White matter neuroinflammation showed weak relationships to the measures of SVD, but not to the measures of AD neuropathology. In conclusion, glial responses vary extensively across the PARWM with diverse patterns of white matter neuroinflammation. Although these findings support a role for vascular factors in the pathogenesis of age‐related white matter neuroinflammation, additional factors other than SVD and AD pathology may drive this. Understanding the heterogeneity in white matter neuroinflammation will be important for the therapeutic targeting of age‐associated white matter damage.

Predictors of gait speed and its change over three years in community-dwelling older people

We aimed to assess whether and how changes in brain volume and increases in white matter hyperintensity (WMH) volume over three years predict gait speed and its change independently of demographics, vascular risk factors and physical status. We analyzed 443 individuals from the Lothian Birth Cohort 1936, at mean age 73 and 76 years. Gait speed at age 76 was predicted by age, grip strength and body mass index at mean age 73, three-year brain volume decrease and WMH volume increase, explaining 26.1% of variance. Decline in gait speed to age 76 was predicted by the same five variables explaining 40.9% of variance. In both analyses, grip strength and body mass index explained the most variance. A clinically significant decline in gait speed (≥ 0.1 m/s per year) occurred in 24.4%. These individuals had more structural brain changes. Brain volume and WMH changes were independent predictors of gait dysfunction and its three-year change, but the impact of malleable physical factors such as grip strength or body mass index was greater.

Brain White Matter: A Substrate for Resilience and a Substance for Subcortical Small Vessel Disease

Age-related brain white matter disease is a form of small vessel disease (SVD) that may be associated with lacunar and other small subcortical infarcts, cerebral microbleeds, and perivascular spaces. This common form of cerebrovascular disease may manifest clinically as cognitive impairment of varying degrees and difficulty with mobility. Whereas some persons show cognitive decline and mobility failure when there are brain white matter hyperintensities (WMH) and acute stroke, others recover, and not everyone with brain white matter disease is disabled. Thus, repair or compensation of brain white matter may be possible, and furthermore, certain vascular risks, such as raised blood pressure, are targets for prevention of white matter disease or are administered to reduce the burden of such disease. Vascular risk modification may be useful, but alone may not be sufficient to prevent white matter disease progression. In this chapter, we specifically focus on WMH of vascular origin and explore white matter development, plasticity, and enduring processes of myelination across the health span in the context of experimental and human data, and compare and contrast resilient brain white matter propensity to a diseased white matter state. We conclude with thoughts on novel ways one might study white matter resilience, and predict future healthy cognitive and functional outcomes.

Association between structural changes in brain with muscle function in sarcopenic older women: the women's healthy ageing project (WHAP)

OBJECTIVES

The involvement of changes in brain structure in the pathophysiology of muscle loss (sarcopenia) with aging remains unclear. In this study, we investigated the associations between brain structure and muscle strength in a group of older women. We hypothesized that structural changes in brain could correlate with functional changes observed in sarcopenic older women.

METHODS

In 150 women (median age of 70 years) of the Women's Healthy Ageing Project (WHAP) Study, brain grey (total and cortex) volumes were calculated using magnetic resonance imaging (MRI) analyses. Grip strength and timed up and go (TUG) were measured. The brain volumes were compared between sarcopenic vs. non-sarcopenic subjects and women with previous falls vs. those without.

RESULTS

Based on handgrip strength and TUG results respectively, 27% and 15% of women were classified as sarcopenic; and only 5% were sarcopenic based on both criteria. At least one fall was experienced by 15% of participants. There was no difference in brain volumetric data between those with vs. without sarcopenia (p>0.24) or between women with falls (as a symptom of weakness or imbalance) vs. those without history of falls (p>0.25).

CONCLUSIONS

Brain structure was not associated with functional changes or falls in this population of older women.

The neural correlates of discrete gait characteristics in ageing: A structured review

Gait is complex, described by diverse characteristics underpinned by widespread central nervous system networks including motor and cognitive functions. Despite this, neural substrates of discrete gait characteristics are poorly understood, limiting understanding of gait impairment in ageing and disease. This structured review aims to map gait characteristics, defined from a pre-specified model reflecting independent gait domains, to brain imaging parameters in older adults. Fifty-two studies of 38,029 yielded were reviewed. Studies showed inconsistent approaches when mapping gait assessment to neural substrates, limiting conclusions. Gait impairments typically associated with brain deterioration, specifically grey matter atrophy and white matter integrity loss. Gait velocity, a global measure of gait control, was most frequently associated with these imaging markers within frontal and basal ganglia regions, and its decline predicted from white matter volume and integrity measurements. Fewer studies assessed additional gait measures or functional imaging parameters. Future studies mapping regional neuroanatomical and functional correlates of gait are needed, including those which take a multi-process network perspective to better understand mobility in health and disease.

Deep white matter hyperintensities, microstructural integrity and dual task walking in older people

To examine neural, physiological and cognitive influences on gait speed under single and dual-task conditions. Sixty-two community-dwelling older people (aged 80.0 ± 4.2 years) participated in our study. Gait speed was assessed with a timed 20-meter walk under single and dual-task (reciting alternate letters of the alphabet) conditions. Participants also underwent tests to estimate physiological fall risk based on five measures of sensorimotor function, cognitive function across five domains, brain white matter (WM) hyperintensities and WM microstructural integrity by measuring fractional anisotropy (FA). Univariate linear regression analyses showed that global physiological and cognitive measures were associated with single (β = 0.594 and β=-0.297, respectively) and dual-task gait speed (β = 0.306 and β=-0.362, respectively). Deep WMHs were associated with dual-task gait speed only (β = 0.257). Multivariate mediational analyses showed that global and executive cognition reduced the strength of the association between deep WMHs and dual-task gait speed by 27% (β = 0.188) and 44% (β = 0.145) respectively. There was a significant linear association between single-task gait speed and mean FA values of the genu (β=-0.295) and splenium (β=-0.326) of the corpus callosum, and between dual-task gait speed and mean FA values of Superior Cerebellar Peduncle (β=-0.284), splenium of the Corpus Callosum (β=-0.286) and Cingulum (β=-0.351). Greater deep WMH volumes are associated with slower walking speed under dual-task conditions, and this relationship is mediated in part by global cognition and executive abilities specifically. Furthermore, both cerebellum and cingulum are related to dual-task walking due to their role in motor skill performance and attention, respectively.

Relationships among clinic, home, and ambulatory blood pressures with small vessel disease of the brain and functional status in older people with hypertension

BACKGROUND

Subcortical small vessel disease, represented as white matter hyperintensity (WMH) on magnetic resonance images (MRI) is associated with functional decline in older people with hypertension. We evaluated the relationships of clinic and out-of-office blood pressures (BP) with WMH and functional status in older persons.

METHODS

Using cross-sectional data from 199 older study participants enrolled in the INFINITY trial, we analyzed the clinic, 24-hour ambulatory, and home BPs and their relationships with WMH burden and mobility and cognitive outcomes.

RESULTS

Volume of WMH was associated with clinic and 24-hour ambulatory systolic BP but not home systolic BP. The mobility measure, supine-to-sit time, had a significant association with 24-hour systolic BP and pulse pressure but not with diastolic BP or values obtained by home BP. Cognitive measures of processing speed (Trails Making Test Part A and the Stroop Word Test) were significantly associated with 24-hour systolic BP, but not clinic and home BPs.

CONCLUSION

These data demonstrate that ambulatory BP measurements in older people are more strongly associated with WMH and certain measures of functional status compared to home BP measurements. Hence, home BP may not be a useful substitute for ambulatory BP for assessing subcortical small vessel disease and its consequences. Further longitudinal analyses comparing clinic and various types of out-of-office BP measures with small vessel brain disease are needed. Clinicaltrials.gov identifier: NCT01650402.

Longitudinal microstructural changes of cerebral white matter and their association with mobility performance in older persons

Mobility impairment in older persons is associated with brain white matter hyperintensities (WMH), a common finding in magnetic resonance images and one established imaging biomarker of small vessel disease. The contribution of possible microstructural abnormalities within normal-appearing white matter (NAWM) to mobility, however, remains unclear. We used diffusion tensor imaging (DTI) measures, i.e. fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), to assess microstructural changes within supratentorial NAWM and WMH sub-compartments, and to investigate their association with changes in mobility performance, i.e. Tinetti assessment and the 2.5-meters walk time test. We analyzed baseline (N = 86, age ≥75 years) and 4-year (N = 41) follow-up data. Results from cross-sectional analysis on baseline data showed significant correlation between WMH volume and NAWM-FA (r = -0.33, p = 0.002), NAWM-AD (r = 0.32, p = 0.003) and NAWM-RD (r = 0.39, p = 0.0002). Our longitudinal analysis showed that after 4-years, FA and AD decreased and RD increased within NAWM. In regional tract-based analysis decrease in NAWM-FA and increase in NAWM-RD within the genu of the corpus callosum correlated with slower walk time independent of age, gender and WMH burden. In conclusion, global DTI indices of microstructural integrity indicate that significant changes occur in the supratentorial NAWM over four years. The observed changes likely reflect white matter deterioration resulting from aging as well as accrual of cerebrovascular injury associated with small vessel disease. The observed association between mobility scores and regional measures of NAWM microstructural integrity within the corpus callosum suggests that subtle changes within this structure may contribute to mobility impairment.

Prospective associations between white matter hyperintensities and lower extremity function

Objective

To evaluate the relationship of white matter hyperintensities (WMH) with decline in lower extremity function (LEF) over approximately 3 years in dementia-free older adults with memory complaints.

Methods

We obtained brain MRI data from 458 community-dwelling adults, aged 70 years or over, at baseline, and from 358 adults over an average follow-up of 963 days. We evaluated LEF using the Short Physical Performance Battery (SPPB). We related baseline WMH volumes and progression to SPPB scores over time, using mixed-effect linear regressions. For the secondary analyses, we categorized baseline WMH volume into quartiles, and dichotomized the WMH progression to compare fast and slow progression.

Results

Baseline WMH volume (β = −0.017, 95% confidence interval [CI] −0.025 to −0.009), as well as WMH progression (β = −0.002, 95% CI −0.003 to −0.001), significantly associated with a decline in SPPB performance in adjusted analyses. Compared with the lowest quartile of baseline WMH volume, the highest quartile associated with a decline in SPPB performance (β = −0.301, 95% CI −0.558 to −0.044). Fast progression also associated with a decline in SPPB performance. We found clinically meaningful differences in the SPPB, with higher scores in participants with slow progression of WMH, at both 24 and 36 months.

Conclusions

Baseline level and WMH progression associated with longitudinal decline in SPPB performance among older adults. We detected clinically meaningful differences in SPPB performance on comparing fast with slow progression of WMH, suggesting that speed of WMH progression is an important determinant of LEF during aging.

White matter changes and gait decline in cerebral small vessel disease

The relation between progression of cerebral small vessel disease (SVD) and gait decline is uncertain, and diffusion tensor imaging (DTI) studies on gait decline are lacking. We therefore investigated the longitudinal associations between (micro) structural brain changes and gait decline in SVD using DTI. 275 participants were included from the Radboud University Nijmegen Diffusion tensor and Magnetic resonance imaging Cohort (RUN DMC), a prospective cohort of participants with cerebral small vessel disease aged 50-85 years. Gait (using GAITRite) and magnetic resonance imaging measures were assessed during baseline (2006-2007) and follow-up (2011 - 2012). Linear regression analysis was used to investigate the association between changes in conventional magnetic resonance and diffusion tensor imaging measures and gait decline. Tract-based spatial statistics analysis was used to investigate region-specific associations between changes in white matter integrity and gait decline. 56.2% were male, mean age was 62.9 years (SD8.2), mean follow-up duration was 5.4 years (SD0.2) and mean gait speed decline was 0.2 m/s (SD0.2). Stride length decline was associated with white matter atrophy (β = 0.16, p = 0.007), and increase in mean white matter radial diffusivity and mean diffusivity, and decrease in mean fractional anisotropy (respectively, β = - 0.14, p = 0.009; β = - 0.12, p = 0.018; β = 0.10, p = 0.049), independent of age, sex, height, follow-up duration and baseline stride length. Tract-based spatial statistics analysis showed significant associations between stride length decline and fractional anisotropy decrease and mean diffusivity increase (primarily explained by radial diffusivity increase) in multiple white matter tracts, with the strongest associations found in the corpus callosum and corona radiata, independent of traditional small vessel disease markers. White matter atrophy and loss of white matter integrity are associated with gait decline in older adults with small vessel disease after 5 years of follow-up. These findings suggest that progression of SVD might play an important role in gait decline.

Mental steps: Differential activation of internal pacemakers in motor imagery and in mental imitation of gait

Gait imagery and gait observation can boost the recovery of locomotion dysfunctions; yet, a neurologically justified rationale for their clinical application is lacking as much as a direct comparison of their neural correlates. Using functional magnetic resonance imaging, we measured the neural correlates of explicit motor imagery of gait during observation of in-motion videos shot in a park with a steady cam (Virtual Walking task). In a 2 × 2 factorial design, we assessed the modulatory effect of gait observation and of foot movement execution on the neural correlates of the Virtual Walking task: in half of the trials, the participants were asked to mentally imitate a human model shown while walking along the same route (mental imitation condition); moreover, for half of all the trials, the participants also performed rhythmic ankle dorsiflexion as a proxy for stepping movements. We found that, beyond the areas associated with the execution of lower limb movements (the paracentral lobule, the supplementary motor area, and the cerebellum), gait imagery also recruited dorsal premotor and posterior parietal areas known to contribute to the adaptation of walking patterns to environmental cues. When compared with mental imitation, motor imagery recruited a more extensive network, including a brainstem area compatible with the human mesencephalic locomotor region (MLR). Reduced activation of the MLR in mental imitation indicates that this more visually guided task poses less demand on subcortical structures crucial for internally generated gait patterns. This finding may explain why patients with subcortical degeneration benefit from rehabilitation protocols based on gait observation. Hum Brain Mapp 38:5195-5216, 2017. © 2017 Wiley Periodicals, Inc.

The Corpus Callosum Splenium Sign in Fragile X-Associated Tremor Ataxia Syndrome

Background

Hyperintensities in the splenium of the corpus callosum (CCS) have been proposed as a radiographic diagnostic criterion for fragile X-associated tremor ataxia syndrome (FXTAS).

Methods

Magnetic resonance images from patients with FXTAS and from nonpremutation carriers with movement disorders were viewed by a radiologist who was blinded to gene status, and radiographic criteria for FXTAS were scored. Phenotypic data used for diagnosis of FXTAS also were collected.

Results

Twenty-two patients with FXTAS and 23 controls were included. Hyperintensity in the CCS (the CCS sign) was more common in men with FXTAS versus controls (87% vs. 40%) but not in women with FXTAS (100% vs. 50% in controls). The CCS sign had higher sensitivity compared with the middle cerebellar peduncle sign (white matter lesions in middle cerebellar peduncle) in both men (0.87 vs. 0.67) and women (1 vs. 0.29) with FXTAS, but it had lower specificity in both men (0.6 vs. 0.8) and women (0.5 vs. 1).

Conclusions

The CCS sign is common in patients with FXTAS, but it is not significantly more prevalent in women with FXTAS compared with controls. This may be due to small sample sizes in the current study. Other signs, such as brainstem white matter disease, were more common in women with FXTAS and differed from those in men with FXTAS. This finding suggests that additional studies evaluating the diagnostic criteria for FXTAS need to be conducted, ideally with neuropathological confirmation of the disease.

Cardiovascular risk factors and small vessel disease of the brain: Blood pressure, white matter lesions, and functional decline in older persons

Several potential vascular risk factors exist for the development and accumulation of subcortical white matter disease in older people. We have reported that in older people followed for up to 4 years white matter hyperintensity (WMH) lesions on magnetic resonance imaging nearly doubled in volume and were associated with alterations in mobility and cognitive function. Herein we review the genetic, metabolic, and vascular risk factors that have been evaluated in association with the development and pathogenesis of WMH in older persons. Our research efforts have focused on systemic hypertension, particularly in the out-of-office setting as 24-hour ambulatory blood pressure (BP) has proven to be a stronger indicator of the progression of WMH in older people and the associated functional decline than doctor’s office BP. Based on relations between 24-hour systolic BP levels, the accrual of WMH, and functional decline, we have designed the INFINITY trial, the first interventional study to use ambulatory BP to guide antihypertensive therapy to address this problem in the geriatric population.

Successful aging: Advancing the science of physical independence in older adults

The concept of 'successful aging' has long intrigued the scientific community. Despite this long-standing interest, a consensus definition has proven to be a difficult task, due to the inherent challenge involved in defining such a complex, multi-dimensional phenomenon. The lack of a clear set of defining characteristics for the construct of successful aging has made comparison of findings across studies difficult and has limited advances in aging research. A consensus on markers of successful aging is furthest developed is the domain of physical functioning. For example, walking speed appears to be an excellent surrogate marker of overall health and predicts the maintenance of physical independence, a cornerstone of successful aging. The purpose of the present article is to provide an overview and discussion of specific health conditions, behavioral factors, and biological mechanisms that mark declining mobility and physical function and promising interventions to counter these effects. With life expectancy continuing to increase in the United States and developed countries throughout the world, there is an increasing public health focus on the maintenance of physical independence among all older adults.

A diffusion-tensor-based white matter atlas for rhesus macaques

Atlases of key white matter (WM) structures in humans are widely available, and are very useful for region of interest (ROI)-based analyses of WM properties. There are histology-based atlases of cortical areas in the rhesus macaque, but none currently of specific WM structures. Since ROI-based analysis of WM pathways is also useful in studies using rhesus diffusion tensor imaging (DTI) data, we have here created an atlas based on a publicly available DTI-based template of young rhesus macaques. The atlas was constructed to mimic the structure of an existing human atlas that is widely used, making results translatable between species. Parcellations were carefully hand-drawn on a principle-direction color-coded fractional anisotropy image of the population template. The resulting atlas can be used as a reference to which registration of individual rhesus data can be performed for the purpose of white-matter parcellation. Alternatively, specific ROIs from the atlas may be warped into individual space to be used in ROI-based group analyses. This atlas will be made publicly available so that it may be used as a resource for DTI studies of rhesus macaques.

Utilization of central nervous system resources for preparation and performance of complex walking tasks in older adults

Introduction: Walking in the home and community often involves performance of complex walking tasks. Understanding the control of such tasks is crucial to preserving independence and quality of life in older adults. However, very little research has been conducted in this area. Here, we assess the extent to which two measures of central nervous system (CNS) activity are responsive to the challenges posed by preparation and performance of complex walking tasks. Prefrontal cortical activity was measured by functional near-infrared spectroscopy (fNIRS) and sympathetic nervous system arousal was measured by skin conductance level (SCL).

Materials and methods: Sixteen older men and women (age: 77.2 ± 5.6 years) with mild mobility deficits participated in this study. Participants walked at their preferred speed without distractions along an unobstructed, well-lit course (control task) and also walked on the same course under five separate challenging conditions: performing a cognitive verbal fluency task (verbal task), dim lighting (dim task), carrying a tray (carry task), negotiating obstacles (obstacles task) and wearing a weighted vest (vest task). Mean prefrontal activation and SCL were calculated during the preparation and performance phases of each task. Gait spatiotemporal measurements were acquired by an instrumented gait mat.

Results: Prefrontal cortical activity and SCL were elevated during the preparation phase of complex walking tasks relative to the control task. During the performance phase, prefrontal activity remained elevated to a similar level as during task preparation. In contrast, SCL continued to increase beyond the level observed during task preparation. A larger increase in prefrontal activity was found to be linked to preserved quality of gait during complex walking tasks.

Discussion: These findings indicate that availability and utilization of CNS resources are important for optimizing performance of complex walking tasks in older adults.

Altered visual-spatial attention to task-irrelevant information is associated with falls risk in older adults

Executive cognitive functions play a critical role in falls risk—a pressing health care issue in seniors. In particular, intact attentional processing is integral for safe mobility and navigation. However, the specific contribution of impaired visual–spatial attention in falls remains unclear. In this study, we examined the association between visual–spatial attention to task-irrelevant stimuli and falls risk in community-dwelling older adults. Participants completed a visual target discrimination task at fixation while task-irrelevant probes were presented in both visual fields. We assessed attention to left and right peripheral probes using event-related potentials (ERPs). Falls risk was determined using the valid and reliable Physiological Profile Assessment (PPA). We found a significantly positive association between reduced attentional facilitation, as measured by the N1 ERP component, and falls risk. This relationship was specific to probes presented in the left visual field and measured at ipsilateral electrode sites. Our results suggest that fallers exhibit reduced attention to the left side of visual space and provide evidence that impaired right hemispheric function and/or structure may contribute to falls.

A systematic review of the evidence that brain structure is related to muscle structure and their relationship to brain and muscle function in humans over the lifecourse

BACKGROUND

An association between cognition and physical function has been shown to exist but the roles of muscle and brain structure in this relationship are not fully understood. A greater understanding of these relationships may lead to identification of the underlying mechanisms in this important area of research. This systematic review examines the evidence for whether: a) brain structure is related to muscle structure; b) brain structure is related to muscle function; and c) brain function is related to muscle structure in healthy children and adults.

METHODS

Medline, Embase, CINAHL and PsycINFO were searched on March 6th 2014. A grey literature search was performed using Google and Google Scholar. Hand searching through citations and references of relevant articles was also undertaken.

RESULTS

53 articles were included in the review; mean age of the subjects ranged from 8.8 to 85.5 years old. There is evidence of a positive association between both whole brain volume and white matter (WM) volume and muscle size. Total grey matter (GM) volume was not associated with muscle size but some areas of regional GM volume were associated with muscle size (right temporal pole and bilateral ventromedial prefrontal cortex). No evidence was found of a relationship between grip strength and whole brain volume however there was some evidence of a positive association with WM volume. Conversely, there is evidence that gait speed is positively associated with whole brain volume; this relationship may be driven by total WM volume or regional GM volumes, specifically the hippocampus. Markers of brain ageing, that is brain atrophy and greater accumulation of white matter hyperintensities (WMH), were associated with grip strength and gait speed. The location of WMH is important for gait speed; periventricular hyperintensities and brainstem WMH are associated with gait speed but subcortical WMH play less of a role. Cognitive function does not appear to be associated with muscle size.

CONCLUSION

There is evidence that brain structure is associated with muscle structure and function. Future studies need to follow these interactions longitudinally to understand potential causal relationships.

Higher-level gait disorders: an open frontier

The term higher-level gait disorders (HLGD) defines a category of balance and gait disorders that are not explained by deficits in strength, tone, sensation, or coordination. HLGD are characterized by various combinations of disequilibrium and impaired locomotion. A plethora of new imaging techniques are beginning to determine the neural circuits that are the basis of these disorders. Although a variety of neurodegenerative and other pathologies can produce HLGD, the most common cause appears to be microvascular disease that causes white-matter lesions and thereby disrupts balance/locomotor circuits.

Neuroimaging of mobility in aging: a targeted review

BACKGROUND

The relationship between mobility and cognition in aging is well established, but the relationship between mobility and the structure and function of the aging brain is relatively unknown. This, in part, is attributed to the technological limitations of most neuroimaging procedures, which require the individual to be immobile or in a supine position. Herein, we provide a targeted review of neuroimaging studies of mobility in aging to promote (i) a better understanding of this relationship, (ii) future research in this area, and (iii) development of applications for improving mobility.

METHODS

A systematic search of peer-reviewed studies was performed using PubMed. Search terms included (i) aging, older adults, or elderly; (ii) gait, walking, balance, or mobility; and (iii) magnetic resonance imaging, voxel-based morphometry, fluid-attenuated inversion recovery, diffusion tensor imaging, positron emission tomography, functional magnetic resonance imaging, electroencephalography, event-related potential, and functional near-infrared spectroscopy.

RESULTS

Poor mobility outcomes were reliably associated with reduced gray and white matter volume. Fewer studies examined the relationship between changes in task-related brain activation and mobility performance. Extant findings, however, showed that activation patterns in the cerebellum, basal ganglia, parietal and frontal cortices were related to mobility. Increased involvement of the prefrontal cortex was evident in both imagined walking conditions and conditions where the cognitive demands of locomotion were increased.

CONCLUSIONS

Cortical control of gait in aging is bilateral, widespread, and dependent on the integrity of both gray and white matter.

Brain structural change and gait decline: a longitudinal population-based study

OBJECTIVES

To investigate longitudinal associations between changes in brain structure and gait decline.

DESIGN

Longitudinal.

SETTING

Population-based Tasmanian Study of Cognition and Gait.

PARTICIPANTS

Two hundred twenty-five individuals aged 60 to 86 (mean age 71.4 ± 6.8) randomly selected from the electoral roll with baseline and follow-up data.

MEASUREMENTS

Volumes of gray matter, white matter, hippocampi, and white matter lesions (WML) were estimated using automated segmentation from magnetic resonance imaging (MRI). Gait variables were measured using a computerized walkway. Linear regression was used to estimate the association between change in brain MRI measures and change in gait. Time between measurements, age, sex, BMI, education level, total intracranial volume, baseline infarcts, and medical history were used as baseline covariates.

RESULTS

Mean follow-up was 30.6 months. White matter atrophy was associated with a decline in gait speed (P = .001), step length (P = .005), and cadence (P = .001). WML progression was associated with a decline in gait speed (P = .04), and its association with decline in step length was stronger with greater baseline age (P for interaction = .04). Hippocampal atrophy was associated with a decline in gait speed (P = .006) and step length (P = .001). Total gray matter atrophy was associated with decline in cadence in those with cerebral infarcts (P for interaction = .02).

CONCLUSION

These are the first longitudinal data demonstrating the relative contributions of brain atrophy and WML progression to gait decline in older people. Effect modification according to age and infarcts suggests a contribution of reduced physiological and brain reserve. Interventions targeting brain health may be important in preventing mobility decline in older people.

Rapid buildup of brain white matter hyperintensities over 4 years linked to ambulatory blood pressure, mobility, cognition, and depression in old persons

BACKGROUND

Brain white matter hyperintensities (WMH) are associated with functional decline in older people. We performed a 4-year cohort study examining progression of WMH, its effects on mobility, cognition, and depression with the role of clinic and 24-hour ambulatory systolic blood pressure as a predisposing factor.

METHODS

Ninety-nine subjects, 75-89 years were stratified by age and mobility, with the 67 completing 4-years comprising the cohort. Mobility, cognition, depressive symptoms, and ambulatory blood pressure were assessed, and WMH volumes were determined by quantitative analysis of magnetic resonance images.

RESULTS

WMH increased from 0.99±0.98% of intracranial cavity volume at baseline to 1.47±1.2% at 2 years and 1.74±1.30% after 4 years. Baseline WMH was associated with 4-year WMH (p < .0001), explaining 83% of variability. Small, but consistent mobility decrements and some evidence of cognitive decline were noted over 4 years. Regression analyses using baseline and 4-year WMHs were associated with three of five mobility measures, two of four cognitive measures and the depression scale, all performed at 4 years. Increases in ambulatory systolic blood pressure but not clinic systolic blood pressure during the initial 2 years were associated with greater WMH accrual during those years, while ambulatory systolic blood pressure was related to WMH at 4 years.

CONCLUSION

Declines in mobility, cognition, and depressive symptoms were related to WMH accrual over 4 years, and WMH was related to out-of-office blood pressure. This suggests that prevention of microvascular disease, even in asymptomatic older persons, is fundamental for preserving function. There may be value in tighter 24-hour blood pressure control in older persons although this requires further investigation.

INtensive versus standard ambulatory blood pressure lowering to prevent functional DeclINe in the ElderlY (INFINITY)

Reductions in mobility and cognitive function linked to accrual of brain microvascular disease related white matter hyperintensities (WMHs) on magnetic resonance imaging can occur in older hypertensive patients in as little as 2 years. We have designed a trial evaluating 2 levels of ambulatory blood pressure (ABP) control in individuals with normal or mildly impaired mobility and cognition who have detectable cerebrovascular disease (>0.5% WMH fraction of intracranial volume) on functional outcomes. The study is a prospective randomized, open-label trial with blinded end points, in patients ages ≥75 years with elevated 24-hour systolic blood pressure (BP) (145 mm Hg in the untreated state) who do not have unstable cardiovascular disease, heart failure, or stroke. The primary and key secondary outcomes in the trial are change from baseline in mobility and cognitive function and damage to brain white matter as demonstrated by accrual of WMH volume and changes in diffusion tensor imaging. Approximately 300 patients will be enrolled, and 200 randomized to 1 of 2 levels of ABP control (intensive to achieve a goal 24-hour systolic BP of ≤130 mm Hg or standard to achieve a goal 24-hour systolic BP of ≤145 mm Hg) for a total of 36 months using similar antihypertensive regimens. The analytical approach provides 85% power to show a clinically meaningful effect in differences in mobility accompanied by quantitative differences in WMH between treatment groups. The INFINITY trial is the first to guide antihypertensive therapy using ABP monitoring rather than clinic BP to reduce cerebrovascular disease.