Corpus callosum atrophy is associated with mental slowing and executive deficits in subjects with age-related white matter hyperintensities: the LADIS Study

Ideational Slippage in Middle-Aged and Older Adults: A Preliminary Study

Ideational slippage-characterized by incorrect word usage and strained logic during dialogue-is common in aging and, at greater frequency, is an indicator of pre-clinical cognitive decline. Performance-based assessment of ideational slippage may be useful in the study of cognitive aging and Alzheimer's-disease-related pathology. In this preliminary study, we examine the association between corpus callosum volume and a performance-based assessment of ideational slippage in middle-aged and older adults (age 61-79 years). Ideational slippage was indexed from cognitive special scores using the Rorschach Inkblot Method (RIM), which are validated indices of deviant verbalization and logical inaccuracy (Sum6, WSum6). Among middle-aged and older adults, smaller splenium volume was associated with greater ideational slippage (ηp2 = 0.48), independent of processing speed and fluid intelligence. The observed negative associations are consistent with visuospatial perception and cognitive functions of the splenium. The effect was strongest with the splenium, and volumes of the genu and total white matter had small effects that were not statistically significant. Conclusions: Results are discussed with future application of RIM special scores for the assessment of pre-clinical cognitive decline and, based on observed effect sizes, power analyses are reported to inform future study planning.

Structural MRI analysis of age-related changes and sex differences in marmoset brain volume

The field of aging biology, which aims to extend healthy lifespans and prevent age-related diseases, has turned its focus to the Callithrix jacchus (common marmoset) to understand the aging process better. This study utilized magnetic resonance imaging (MRI) to non-invasively analyze the brains of 216 marmosets, investigating age-related changes in brain structure; the relationship between body weight and brain volume; and potential differences between males and females. The key findings revealed that, similar to humans, Callithrix jacchus experiences a reduction in total intracranial volume, cortex, subcortex, thalamus, and cingulate volumes as they age, highlighting site-dependent changes in brain tissue. Notably, the study also uncovered sex differences in cerebellar volume. These insights into the structural connectivity and volumetric changes in the marmoset brain throughout aging contribute to accumulating valuable knowledge in the field, promising to inform future aging research and interventions for enhancing healthspan.

Diffusion in the corpus callosum predicts persistence of clinical symptoms after mild traumatic brain injury, a multi-scanner study

Background

Mild traumatic brain injuries (mTBIs) comprise 80% of all TBI, but conventional MRI techniques are often insensitive to the subtle changes and injuries produced in a concussion. Diffusion tensor imaging (DTI) is one of the most sensitive MRI techniques for mTBI studies with outcome and symptom associations described. The corpus callosum (CC) is one of the most studied fiber tracts in TBI and mTBI, but the comprehensive post-mTBI symptom relationship has not fully been explored.

Methods

This is a retrospective observational study of how quantitative DTI data of the CC and its sub-regions may relate to clinical presentation of symptoms and timing of resolution of symptoms in patients diagnosed with uncomplicated mTBI. DTI and clinical data were obtained retrospectively from 446 (mean age 42 years, range 13-82) civilian patients. From patient medical charts, presentation of the following common post-concussive symptoms was noted: headache, balance issues, cognitive deficits, fatigue, anxiety, depression, and emotional lability. Also recorded was the time between injury and a visit to the physician when improvement or resolution of a particular symptom was reported. FA values from the total CC and 3 subregions of the CC (genu or anterior, mid body, and splenium or posterior) were obtained from hand tracing on the Olea Sphere v3.0 SP12 free-standing workstation. DTI data was obtained from 8 different 3T MRI scanners and harmonized via ComBat harmonization. The statistical models used to explore the association between regional Fractional Anisotropy (FA) values and symptom presentation and time to symptom resolution were logistic regression and interval-censored semi-parametric Cox proportional hazard models, respectively. Subgroups related to age and timing of first scan were also analyzed.

Results

Patients with the highest FA in the total CC (p = 0.01), anterior CC (p < 0.01), and mid-body CC (p = 0.03), but not the posterior CC (p = 0.91) recovered faster from post-concussive cognitive deficits. Patients with the highest FA in the posterior CC recovered faster from depression (p = 0.04) and emotional lability (p = 0.01). There was no evidence that FA in the CC or any of its sub-regions was associated with symptom presentation or with time to resolution of headache, balance issues, fatigue, or anxiety. Patients with mTBI under 40 had higher FA in the CC and the anterior and mid-body subregions (but not the posterior subregion: p = 1.00) compared to patients 40 or over (p ≤ 0.01). There was no evidence for differences in symptom presentation based on loss of consciousness (LOC) or sex (p ≥ 0.18).

Conclusion

This study suggests that FA of the CC has diagnostic and prognostic value for clinical assessment of mTBI in a large diverse civilian population, particularly in patients with cognitive symptoms.

The shared white matter developmental trajectory anomalies of attention-deficit/hyperactivity disorder and autism spectrum disorders: A meta-analysis of diffusion tensor imaging studies

Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) show common brain area abnormalities, which may contribute to the high shared co-occurrence symptoms and comorbidity of the two disorders. However, neuroanatomic anomalies in neurodevelopmental disorders may change over the course of development, and the developmental variation of these two disorders is unclear. Our study conducted a systematic literature search of PubMed, Web of Science, and EMBASE databases to identify disorder-shared abnormalities of white matter (WM) from childhood to adulthood in ADHD and ASD. 28 ADHD and 23 ASD datasets were included in this meta-analysis and were analysed by AES-SDM to detect differences in fractional anisotropy in patients compared to typically developing individuals. Our main findings reveal the variable WM developmental trajectories in ADHD and ASD respectively, and the two disorders showed overlapping corpus callosum tract abnormalities in their development from children to adults. Furthermore, the overlapping abnormalities of the corpus callosum tract increased with age, which may be related to their gradually increasing shared symptoms and comorbidity in these two disorders.

More extensive white matter disruptions present in untreated obstructive sleep apnea than we thought: A large sample diffusion imaging study

Obstructive sleep apnea (OSA) may lead to white mater (WM) disruptions and cognitive deficits. However, no studies have investigated the full extent of the brain WM, and its associations with cognitive deficits in OSA remain unclear. We thus applied diffusion tensor imaging (DTI) tractography with multi-fiber models and used atlas-based bundle-specific approach to investigate the WM abnormalities for various tracts of the cerebral cortex, thalamus, brainstem, and cerebellum in patients with untreated OSA. We enrolled 100 OSA patients and 63 healthy controls. Fractional anisotropy (FA) and mean diffusivity (MD) values mapped on 33 regions of interest including WM tracts of cortex, thalamus, brainstem, and cerebellum were obtained from tractography-based reconstructions. We compared FA/MD values between groups and correlated FA/MD with clinical data in the OSA group after controlling for age and body mass index. OSA patients showed significantly lower FA values in multiple WM fibers including corpus callosum, inferior fronto-occipital fasciculus, middle/superior longitudinal fasciculi, thalamic radiations, and uncinate (FDR <0.05). Higher FA values were found in medial lemniscus of patients compared to controls (FDR <0.05). Lower FA values of rostrum of corpus callosum correlated with lower visual memory performance in OSA group (p < .005). Our quantitative DTI analysis demonstrated that untreated OSA could negatively impact the integrity of pathways more broadly, including brainstem structures such as medial lemniscus, in comparison to previous findings. Fiber tract abnormalities of the rostral corpus callosum were associated with impaired visual memory in untreated OSA may provide insights into the related pathomechanism.

Myelin and Physical Activity in Older Adults With Cerebral Small Vessel Disease and Mild Cognitive Impairment

BACKGROUND

Myelin loss is a feature of cerebral small vessel disease (cSVD). Although physical activity levels may exert protective effects over cSVD pathology, its specific relationship with myelin content in people living with the cSVD is unknown. Thus, we investigated whether physical activity levels are associated with myelin in community-dwelling older adults with cSVD and mild cognitive impairment.

METHODS

Cross-sectional data from 102 individuals with cSVD and mild cognitive impairment were analyzed (mean age [SD] = 74.7 years [5.5], 63.7% female). Myelin was measured using a magnetic resonance gradient and spin echo sequence. Physical activity was estimated using the Physical Activity Scale for the Elderly. Hierarchical regression models adjusting for total intracranial volume, age, sex, body mass index, and education were conducted to determine the associations between myelin content and physical activity. Significant models were further adjusted for white matter hyperintensity volume.

RESULTS

In adjusted models, greater physical activity was linked to higher myelin content in the whole-brain white matter (R2change = .04, p = .048). Greater physical activity was also associated with myelin content in the sagittal stratum (R2change = .08, p = .004), anterior corona radiata (R2change = .04, p = .049), and genu of the corpus callosum (R2change = .05, p = .018). Adjusting for white matter hyperintensity volume did not change any of these associations.

CONCLUSIONS

Physical activity may be a strategy to maintain myelin in older adults with cSVD and mild cognitive impairment. Future randomized controlled trials of exercise are needed to determine whether exercise increases myelin content.

Optogenetic Stimulation of mPFC Alleviates White Matter Injury-Related Cognitive Decline after Chronic Ischemia through Adaptive Myelination

White matter injury (WMI), which reflects myelin loss, contributes to cognitive decline or dementia caused by cerebral vascular diseases. However, because pharmacological agents specifically for WMI are lacking, novel therapeutic strategies need to be explored. It is recently found that adaptive myelination is required for homeostatic control of brain functions. In this study, adaptive myelination-related strategies are applied to explore the treatment for ischemic WMI-related cognitive dysfunction. Here, bilateral carotid artery stenosis (BCAS) is used to model ischemic WMI-related cognitive impairment and uncover that optogenetic and chemogenetic activation of glutamatergic neurons in the medial prefrontal cortex (mPFC) promote the differentiation of oligodendrocyte precursor cells (OPCs) in the corpus callosum, leading to improvements in myelin repair and working memory. Mechanistically, these neuromodulatory techniques exert a therapeutic effect by inducing the secretion of Wnt2 from activated neuronal axons, which acts on oligodendrocyte precursor cells and drives oligodendrogenesis and myelination. Thus, this study suggests that neuromodulation is a promising strategy for directing myelin repair and cognitive recovery through adaptive myelination in the context of ischemic WMI.

Mapping lesion, structural disconnection, and functional disconnection to symptoms in semantic aphasia

Patients with semantic aphasia have impaired control of semantic retrieval, often accompanied by executive dysfunction following left hemisphere stroke. Many but not all of these patients have damage to the left inferior frontal gyrus, important for semantic and cognitive control. Yet semantic and cognitive control networks are highly distributed, including posterior as well as anterior components. Accordingly, semantic aphasia might not only reflect local damage but also white matter structural and functional disconnection. Here, we characterise the lesions and predicted patterns of structural and functional disconnection in individuals with semantic aphasia and relate these effects to semantic and executive impairment. Impaired semantic cognition was associated with infarction in distributed left-hemisphere regions, including in the left anterior inferior frontal and posterior temporal cortex. Lesions were associated with executive dysfunction within a set of adjacent but distinct left frontoparietal clusters. Performance on executive tasks was also associated with interhemispheric structural disconnection across the corpus callosum. In contrast, poor semantic cognition was associated with small left-lateralized structurally disconnected clusters, including in the left posterior temporal cortex. Little insight was gained from functional disconnection symptom mapping. These results demonstrate that while left-lateralized semantic and executive control regions are often damaged together in stroke aphasia, these deficits are associated with distinct patterns of structural disconnection, consistent with the bilateral nature of executive control and the left-lateralized yet distributed semantic control network.

An Antioxidant and Anti-ER Stress Combo Therapy Decreases Inflammation, Secondary Brain Damage and Promotes Neurological Recovery following Traumatic Brain Injury in Mice

The complex pathophysiology of post-traumatic brain damage might need a polypharmacological strategy with a combination of drugs that target multiple, synergistic mechanisms. We currently tested a combination of apocynin (curtails formation of reactive oxygen species), tert-butylhydroquinone (promotes disposal of reactive oxygen species), and salubrinal (prevents endoplasmic reticulum stress) following a moderate traumatic brain injury (TBI) induced by controlled cortical impact in adult mice. Adult mice of both sexes treated with the above tri-combo showed alleviated motor and cognitive deficits, attenuated secondary lesion volume, and decreased oxidative DNA damage. Concomitantly, tri-combo treatment regulated post-TBI inflammatory response by decreasing the infiltration of T cells and neutrophils and activation of microglia in both sexes. Interestingly, sexual dimorphism was seen in the case of TBI-induced microgliosis and infiltration of macrophages in the tri-combo-treated mice. Moreover, the tri-combo treatment prevented TBI-induced white matter volume loss in both sexes. The beneficial effects of tri-combo treatment were long-lasting and were also seen in aged mice. Thus, the present study supports the tri-combo treatment to curtail oxidative stress and endoplasmic reticulum stress concomitantly as a therapeutic strategy to improve TBI outcomes.SIGNIFICANCE STATEMENT Of the several mechanisms that contribute to TBI pathophysiology, oxidative stress, endoplasmic reticulum stress, and inflammation play a major role. The present study shows the therapeutic potential of a combination of apocynin, tert-butylhydroquinone, and salubrinal to prevent oxidative stress and endoplasmic reticulum stress and the interrelated inflammatory response in mice subjected to TBI. The beneficial effects of the tri-combo include alleviation of TBI-induced motor and cognitive deficits and lesion volume. The neuroprotective effects of the tri-combo are also linked to its ability to prevent TBI-induced white matter damage. Importantly, neuroprotection by the tri-combo treatment was observed to be not dependent on sex or age. Our data demonstrate that a polypharmacological strategy is efficacious after TBI.

Does essential tremor increase risk of cognitive impairment and dementia? Yes

Essential Tremor (ET), by definition, is a disorder of movement. Yet over the years, epidemiologic, clinical, pathologic, and neuroimaging studies have converged to reveal a cognitive side of ET. The cognitive symptoms in ET are heterogeneous and are likely to reflect heterogeneous underlying mechanisms. In this chapter, we review and synthesize a diverse set of studies from both population-based settings to cohorts with more detailed investigations into cognition to consider the various mechanisms by which cognitive symptoms may emerge in a subset of individuals with ET. As part of our analysis, we consider questions surrounding ET diagnosis and the possibility of comorbid disease as potential factors that, upon closer examination, appear to strengthen the argument in favor of ET as a risk factor for dementia. Importantly, we also consider the clinical relevance of cognitive impairment in ET. While ET is not universally characterized by significant cognitive deficits, the data from epidemiological, cognitive, neuroimaging, and postmortem neuropathologic studies converge to reveal an increased risk for cognitive impairment and dementia among individuals with ET. We conclude by offering directions for future research, and a neurocognitive framework with which to consider existing findings and to use in the design of novel studies dedicated to clarifying the basis, nature, and course of cognitive impairments in ET.

White matter damage due to vascular, tau, and TDP-43 pathologies and its relevance to cognition

Multi-compartment modelling of white matter microstructure using Neurite Orientation Dispersion and Density Imaging (NODDI) can provide information on white matter health through neurite density index and free water measures. We hypothesized that cerebrovascular disease, Alzheimer's disease, and TDP-43 proteinopathy would be associated with distinct NODDI readouts of white matter damage which would be informative for identifying the substrate for cognitive impairment. We identified two independent cohorts with multi-shell diffusion MRI, amyloid and tau PET, and cognitive assessments: specifically, a population-based cohort of 347 elderly randomly sampled from the Olmsted county, Minnesota, population and a clinical research-based cohort of 61 amyloid positive Alzheimer's dementia participants. We observed an increase in free water and decrease in neurite density using NODDI measures in the genu of the corpus callosum associated with vascular risk factors, which we refer to as the vascular white matter component. Tau PET signal reflective of 3R/4R tau deposition was associated with worsening neurite density index in the temporal white matter where we measured parahippocampal cingulum and inferior temporal white matter bundles. Worsening temporal white matter neurite density was associated with (antemortem confirmed) FDG TDP-43 signature. Post-mortem neuropathologic data on a small subset of this sample lend support to our findings. In the community-dwelling cohort where vascular disease was more prevalent, the NODDI vascular white matter component explained variability in global cognition (partial R2 of free water and neurite density = 8.3%) and MMSE performance (8.2%) which was comparable to amyloid PET (7.4% for global cognition and 6.6% for memory). In the AD dementia cohort, tau deposition was the greatest contributor to cognitive performance (9.6%), but there was also a non-trivial contribution of the temporal white matter component (8.5%) to cognitive performance. The differences observed between the two cohorts were reflective of their distinct clinical composition. White matter microstructural damage assessed using advanced diffusion models may add significant value for distinguishing the underlying substrate (whether cerebrovascular disease versus neurodegenerative disease caused by tau deposition or TDP-43 pathology) for cognitive impairment in older adults.

Symptom-Related Differential Neuroimaging Biomarkers in Children with Corpus Callosum Abnormalities

We aimed to identify symptom-related neuroimaging biomarkers for patients with dysgenesis of the corpus callosum (dCC) by summarizing neurological symptoms reported in clinical evaluations and correlating them with retrospectively collected structural/diffusion brain magnetic resonance imaging (MRI) measures from 39 patients/controls (mean age 8.08 ± 3.98). Most symptoms/disorders studied were associated with CC abnormalities. Total brain (TB) volume was related to language, cognition, muscle tone, and metabolic/endocrine abnormalities. Although white matter (WM) volume was not related to symptoms studied, gray matter (GM) volume was related to cognitive, behavioral, and metabolic/endocrine disorders. Right hemisphere (RH) cortical thickness (CT) was linked to language abnormalities, while left hemisphere (LH) CT was linked to epilepsy. While RH gyrification index (GI) was not related to any symptoms studied, LH GI was uniquely related to cognitive disorders. Between patients and controls, GM volume and LH/RH CT were significantly greater in dCC patients, while WM volume and LH/RH GI were significantly greater in controls. TB volume and diffusion indices for tissue microstructures did not show differences between the groups. In summary, our brain MRI-based measures successfully revealed differential links to many symptoms. Specifically, LH GI abnormality can be a predictor for dCC patients, which is uniquely associated with the patients' symptom. In addition, patients with CC abnormalities had normal TB volume and overall tissue microstructures, with potentially deteriorated mechanisms to expand/fold the brain, indicated by GI.

Microstructural changes in normal-appearing white matter in male sleep apnea patients are reversible after treatment: A pilot study

Visually appreciable white matter (WM) changes have been described in obstructive sleep apnea (OSA). However, few data exist on the involvement of silent WM abnormalities. This prospective study investigated the microstructural integrity of normal-appearing white matter (NAWM) in male OSA patients before and after continuous positive airway pressure (CPAP) treatment, using a neuroimaging approach. Magnetic resonance imaging (MRI) was acquired from 32 participants (16 severe never-treated OSA and 16 controls). Diffusion tensor imaging (DTI) and Tract-Based Spatial Statistics (TBSS) were used to assess the microstructural NAWM changes in fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). In order to evaluate the efficacy of the therapy, OSA patients underwent MRI evaluations at baseline and after 3 months of treatment (follow-up). CPAP treatment significantly increased the FA in NAWM of the brain stem, corpus callosum and bilateral internal capsule of OSA patients at follow-up compared to baseline (p < 0.05, TFCE-corrected). OSA patients also showed increases in AD in the corpus callosum, superior corona radiata, and internal capsule of the right hemisphere (p < 0.05, TFCE-corrected) after CPAP treatment. A significant negative correlation was found between the FA of the corona radiata, corpus callosum, internal capsule, limbic structures, and neuropsychological scores at follow-up evaluation. No significant differences were found in MD and RD of NAWM in our patients after treatment. Our results demonstrate that FA and AD of NAWM in major tracts such as the corpus callosum and the internal capsule increased significantly after CPAP treatment, as a potential beneficial effect of ventilatory therapy. The recovery of NAWM alterations might also be related to the improvement in the neurocognitive profile, suggesting that nonclearly visible WM alterations may contribute to the physiopathology of OSA-related cognitive impairment.

Diffusion models reveal white matter microstructural changes with ageing, pathology and cognition

White matter microstructure undergoes progressive changes during the lifespan, but the neurobiological underpinnings related to ageing and disease remains unclear. We used an advanced diffusion MRI, Neurite Orientation Dispersion and Density Imaging, to investigate the microstructural alterations due to demographics, common age-related pathological processes (amyloid, tau and white matter hyperintensities) and cognition. We also compared Neurite Orientation Dispersion and Density Imaging findings to the older Diffusion Tensor Imaging model-based findings. Three hundred and twenty-eight participants (264 cognitively unimpaired, 57 mild cognitive impairment and 7 dementia with a mean age of 68.3 ± 13.1 years) from the Mayo Clinic Study of Aging with multi-shell diffusion imaging, fluid attenuated inversion recovery MRI as well as amyloid and tau PET scans were included in this study. White matter tract level diffusion measures were calculated from Diffusion Tensor Imaging and Neurite Orientation Dispersion and Density Imaging. Pearson correlation and multiple linear regression analyses were performed with diffusion measures as the outcome and age, sex, education/occupation, white matter hyperintensities, amyloid and tau as predictors. Analyses were also performed with each diffusion MRI measure as a predictor of cognitive outcomes. Age and white matter hyperintensities were the strongest predictors of all white matter diffusion measures with low associations with amyloid and tau. However, neurite density decrease from Neurite Orientation Dispersion and Density Imaging was observed with amyloidosis specifically in the temporal lobes. White matter integrity (mean diffusivity and free water) in the corpus callosum showed the greatest associations with cognitive measures. All diffusion measures provided information about white matter ageing and white matter changes due to age-related pathological processes and were associated with cognition. Neurite orientation dispersion and density imaging and diffusion tensor imaging are two different diffusion models that provide distinct information about variation in white matter microstructural integrity. Neurite Orientation Dispersion and Density Imaging provides additional information about synaptic density, organization and free water content which may aid in providing mechanistic insights into disease progression.

Distinct fiber-specific white matter reductions pattern in early- and late-onset Alzheimer's disease

Background: The underlying white matter impairment in patients with early and late-onset Alzheimer’s disease (EOAD and LOAD) is still unclear, and this might due to the complex AD pathology.

Methods: We included 31 EOAD, 45 LOAD, and 64 younger, 46 elder controls in our study to undergo MRI examinations. Fiber density (FD) and fiber bundle cross-section (FC) were measured using fixel-based analysis based on diffusion weighted images. On whole brain and tract-based level, we compared these parameters among different groups (p<0.05, FWE corrected). Moreover, we verified our results in another independent dataset using the same analyses.

Results: Compared to young healthy controls, EOAD had significantly lower FD in the splenium of corpus callosum, limbic tracts, cingulum bundles, and posterior thalamic radiation, and higher FC in the splenium of corpus callosum, dorsal cingulum and posterior thalamic radiation. On the other hand, LOAD had lower FD and FC as well. Importantly, a similar pattern was found in the independent validation dataset. Among all groups, both the FD and FC were associated with cognitive function. Furthermore, FD of fornix column and body, and FC of ventral cingulum were associated with composite amyloid and tau level (r=-0.34 and -0.53, p<0.001) respectively.

Conclusions: EOAD and LOAD were characterized by distinct white matter impairment patterns, which may be attributable to their different neuropathologies.

Multi-compartment analysis of the complex gradient-echo signal quantifies myelin breakdown in premanifest Huntington's disease

White matter (WM) alterations have been identified as a relevant pathological feature of Huntington's disease (HD). Increasing evidence suggests that WM changes in this disorder are due to alterations in myelin-associated biological processes. Multi-compartmental analysis of the complex gradient-echo MRI signal evolution in WM has been shown to quantify myelin in vivo, therefore pointing to the potential of this technique for the study of WM myelin changes in health and disease. This study first characterized the reproducibility of metrics derived from the complex multi-echo gradient-recalled echo (mGRE) signal across the corpus callosum in healthy participants, finding highest reproducibility in the posterior callosal segment. Subsequently, the same analysis pipeline was applied in this callosal region in a sample of premanifest HD patients (n = 19) and age, sex and education matched healthy controls (n = 21). In particular, we focused on two myelin-associated derivatives: i. the myelin water signal fraction (fm), a parameter dependent on myelin content; and ii. The difference in frequency between myelin and intra-axonal water pools (Δω), a parameter dependent on the ratio between the inner and the outer axonal radii. fm was found to be lower in HD patients (β = -0.13, p = 0.03), while Δω did not show a group effect. Performance in tests of working memory, executive function, social cognition and movement was also assessed, and a greater age-related decline in executive function was detected in HD patients (β = -0.06, p = 0.006), replicating previous evidence of executive dysfunction in HD. Finally, the correlation between fm, executive function, and proximity to disease onset was explored in patients, and a positive correlation between executive function and fm was detected (r = 0.542; p = 0.02). This study emphasises the potential of complex mGRE signal analysis for aiding understanding of HD pathogenesis and progression. Moreover, expanding on evidence from pathology and animal studies, it provides novel in vivo evidence supporting myelin breakdown as an early feature of HD.

Early Detection of Radiation-Induced Injury and Prediction of Cognitive Deficit by MRS Metabolites in Radiotherapy of Low-Grade Glioma

Purpose

To compare the sensitivity of MRS metabolites and MoCA and ACE-R cognitive tests in the detection of radiation-induced injury in low grade glioma (LGG) patients in early and early delayed postradiation stages.

Methods

MRS metabolite ratios of NAA/Cr and Cho/Cr, ACE-R and MoCA cognitive tests, and dosimetric parameters in corpus callosum were analyzed during RT and up to 6-month post-RT for ten LGG patients.

Results

Compared to pre RT baseline, a significant decline in both NAA/Cr and Cho/Cr in the corpus callosum was seen at the 4th week of RT, 1, 3, and 6-month post-RT. These declines were detected at least 3 months before the detection of declines in cognitive functions by ACE-R and MoCA tools. Moreover, NAA/Cr alterations at 4th week of RT and 1-month post-RT were significantly negatively correlated with the mean dose received by the corpus callosum, as well as the corpus callosum 40 Gy dose volume, i.e., the volume of the corpus callosum receiving a dose greater than 40 Gy.

Conclusion

MRS-based biomarkers may be more sensitive than the state-of-the-art cognitive tests in the prediction of postradiation cognitive impairments. They would be utilized in treatment planning and dose sparing protocols, with a specific focus on the corpus callosum in the radiation therapy of LGG patients.

Microstructural Injury to Corpus Callosum and Intrahemispheric White Matter Tracts Correlate With Attention and Processing Speed Decline After Brain Radiation

PURPOSE

The corpus callosum (CC) and intrahemispheric white matter tracts (IHWM) subserve critical aspects of attention and processing speed. We analyzed imaging biomarkers of microstructural injury within these regions and association with attention and processing speed performance before and after radiation therapy in primary brain tumor patients.

METHODS AND MATERIALS

In a prospective clinical trial, 44 primary brain tumor patients underwent cognitive testing and magnetic resonance imaging/diffusion-weighted imaging at baseline (pre-radiation therapy) and 3-, 6-, and 12-months post-radiation therapy. CC (subregions, total) and IHWM tracts (left/right without CC, total) were autosegmented; tumor, tumor bed, and edema were censored. Biomarkers included volume changes (cm³), mean diffusivity ([MD]; higher values indicate white matter injury), fractional anisotropy ([FA]; lower values indicate white matter injury). Reliable-change indices measured changes in attention (Weschler Adult Intelligence Scale [WAIS-IV] digits-forward; Delis-Kaplan Executive Function System Trail Making [D-KEFS-TM] visual-scanning), and processing speed (WAIS-IV coding; D-KEFS-TM number-sequencing, letter-sequencing), accounting for practice effects. Linear mixed-effects models evaluated associations between mean radiation dose and biomarkers (volume, MD, FA) and imaging biomarkers and neurocognitive performance. Statistics were corrected for multiple comparisons.

RESULTS

Processing speed declined at 6 months following radiation therapy (number sequencing, letter sequencing; P < .04). Seizures and antiepileptic drug therapy were associated with lower visual-scanning attention reliable-change indices at 6 months (P = .039). Higher radiation dose correlated with smaller midanterior CC volume (P = .023); lower FA in posterior CC, anterior CC, and total CC (all P < .03); and higher MD in anterior CC (P = .012). Smaller midanterior CC and left IHWM volume correlated with worse processing speed (coding, letter-sequencing, number-sequencing; all P < .03). Higher FA in right, left, and total IHWM correlated with better coding scores (all P < .01). Lower FA in total IHWM (P = .009) was associated with worse visual-scanning attention scores. Higher FA in midposterior CC (P = .029) correlated with better digits-forward attention scores.

CONCLUSIONS

The CC demonstrated radiation dose-dependent atrophy and WM injury. Microstructural injury within the CC and IHWM was associated with attention and processing speed decline after radiation therapy. These areas represent possible avoidance regions for preservation of attention and processing speed.

White matter pathways underlying Chinese semantic and phonological fluency in mild cognitive impairment

Neuroimaging evidence has suggested that Chinese-language processing differs from that of its alphabetic-language counterparts. However, the underlying white matter pathway correlations between semantic and phonological fluency in Chinese-language processing remain unknown. Thus, we investigated the differences between two verbal fluency tests on 50 participants with amnestic mild cognitive impairment (aMCI) and 36 healthy controls (HC) with respect to five groups (ventral and dorsal stream fibers, frontal-striatal fibers, hippocampal-related fibers, and the corpus callosum) of white matter microstructural integrity. Diffusion spectrum imaging was used. The results revealed a progressive reduction in advantage in semantic fluency relative to phonological fluency from HC to single-domain aMCI to multidomain aMCI. Common and dissociative white matter correlations between tests of the two types of fluency were identified. Both types of fluency relied on the corpus callosum and ventral stream fibers, semantic fluency relied on the hippocampal-related fibers, and phonological fluency relied on the dorsal stream and frontal-striatal fibers. The involvement of bilateral tracts of interest as well as the association with the corpus callosum indicate the uniqueness of Chinese-language fluency processing. Dynamic associations were noted between white matter tract involvement and performance on the two fluency tests in four time blocks. Overall, our findings suggest the clinical utility of verbal fluency tests in geriatric populations, and they elucidate both task-specific and language-specific brain-behavior associations.

Corpus callosum integrity loss predicts cognitive impairment in Leukoaraiosis

Objective

To investigate regional white matter fibers loss in Leukoaraiosis (LA) and its relationship with cognitive impairments.

Methods

Fifty‐six participants with LA and 38 healthy controls underwent clinical evaluations and MR scans. Participants with LA were classified as cognitively normal (LA‐NC, n = 18), vascular cognitive impairment of none dementia (LA‐VCIND, n = 24), and vascular dementia (LA‐VaD, n = 14) by Mini‐Mental State Examination and Clinical Dementia Rating. Cognitive domains including visual‐spatial, naming, attention, language, abstraction, memory, and orientation were assessed. With the use of Tract‐based spatial statistics, mean fractional anisotropy (FA) of major white matter fiber tracts were compared between LA and controls and among LA groups with varying levels of cognitive impairments. Regression analyses were performed to evaluate relationships between FA values and cognitive performance.

Results

Participants showed significant FA reduction in the corpus callosum (CC), bilateral corona radiata, anterior limb of the internal capsule, external capsule, posterior thalamic radiation, and superior longitudinal fasciculus compared to controls and across LA groups. The LA‐VaD group showed consistent damage in the body and genu of CC compared to the LA‐NC and LA‐VCIND groups. A positive correlation between visual‐spatial and FA reduction in right anterior corona radiates in LA‐VCIND and body of CC in LA‐ VaD.

Interpretation

We found regional fiber loss in the CC across the cognitive spectrum in patients with LA and correlations between FA and visuospatial impairment in the anterior corona radiata in patients with LA‐VCIND and in the body of CC in patients with LA‐VaD.

Normative Data for the Symbol Digit Modalities Test in Older White Australians and Americans, African-Americans, and Hispanic/Latinos

Background

Processing speed, which can be assessed using the Symbol Digit Modalities Test (SDMT), is central to many brain functions. Processing speed declines with advanced age but substantial impairments are indicative of brain injury or disease.

Objective

The purpose of this study was to provide SDMT normative data for older community-dwelling individuals in the U.S. and Australia.

Methods

The ASPREE trial recruited 19,114 relatively healthy older men and women in Australia and the U.S. from the general community. All participants were without a diagnosis of dementia and with a Modified Mini-Mental State examination score of 78 or more at enrolment. The SDMT was administered at baseline as part of a neuropsychological test battery.

Results

The median age of participants was 74 years (range 65-99), and 56% were women. The median years of education was 12. Ethno-racial differences in SDMT performance were observed and normative data were thus presented separately for 16,289 white Australians, 1,082 white Americans, 891 African-Americans, and 316 Hispanic/Latinos. There were consistent positive associations found between SDMT and education level, and negative associations between SDMT and age. Mean scores for women were consistently higher than men with the exception of Hispanic/Latinos aged ≥70 years.

Conclusion

This study provides comprehensive SDMT normative data for whites (Australian and U.S.), Hispanic/Latinos, and African-Americans, according to gender, age, and education level. These norms can be used clinically as reference standards to screen for cognitive impairments in older individuals.

Functional Disorganization of Small-World Brain Networks in Patients With Ischemic Leukoaraiosis

Cognitive impairment is a key clinical feature of ischemic leukoaraiosis (ILA); however, the underlying neurobiological mechanism is still unclear. ILA has been associated with widespread gray and white matter (WM) damage mainly located in cortical-cortical and cortico-subcortical pathways. A total of 36 patients with ILA (Fazekas rating score ≥2) and 31 healthy controls (HCs) underwent comprehensive neuropsychological assessments (covering four cognitive domains, i.e., information processing speed, episodic memory, executive and visuospatial function) and resting-state functional MRI scans. Graph theory-based analyses were employed to explore the topological organization of the brain connectome in ILA patients, and we further sought to explore the associations of connectome-based metrics and neuropsychological performances. An efficient small-world architecture in the functional brain connectome was observed in the ILA and control groups. Moreover, compared with the HCs, the ILA patients showed increased path length and decreased network efficiency (i.e., global and local efficiency) in their functional brain networks. Further network-based statistic (NBS) analysis revealed a functional-disconnected network in ILA, which is comprised of functional connections linking different brain modules (i.e., default mode, frontoparietal, ventral attention and limbic systems) and connections within single modules (i.e., ventral attention and limbic systems). Intriguingly, the abnormal network metrics correlated with cognitive deficits in ILA patients. Therefore, our findings provide further evidence to support the concept that ILA pathologies could disrupt brain connections, impairing network functioning, and cognition via a “disconnection syndrome.”

Childhood autism spectrum disorder: insights from a tertiary hospital cohort in Kenya

INTRODUCTION

Autism spectrum disorder (ASD) is characterized by impairments in behavior, social communication, and interaction. There is little data on ASD from sub-Saharan Africa (SSA) describing clinical characteristics in large cohorts of patients. Preliminary studies report a high male sex ratio, excess of nonverbal cases, possible infectious etiologies, and comorbidities e.g. epilepsy.

OBJECTIVE

To describe the clinical characteristics of children diagnosed with ASD in an African context.

METHODS

A retrospective medical chart review identified 116 children diagnosed with ASD according to DSM-5 criteria at a pediatric neurology clinic in Nairobi, Kenya.

RESULTS

The male to female ratio was 4.3:1. The median age at presentation was 3 years with speech delay as the most common reason for presentation. Expressive language delay was observed in 90% of the population. Sixty percent who obtained imaging had normal MRI brain findings. Only 44% and 34% of children had access to speech therapy and occupational therapy respectively. Epilepsy and ADHD were the most prevalent comorbidities.

CONCLUSION

An early median age at presentation and preponderance of male gender is observed. Access to speech therapy and other interventions was low. A prospective study would help determine outcomes for similar children following appropriate interventions.

Brain Morphometry and Longitudinal Relaxation Time of Spontaneously Hypertensive Rats (SHRs) in Early and Intermediate Stages of Hypertension Investigated by 3D VFA-SPGR MRI

Cerebral small vessel disease(s) (SVD) results from pathological changes of the small blood vessels in the brain and is common in older people. The diagnostic features by which SVD manifests in brain includes white matter hyperintensities, lacunes, dilated perivascular spaces, microbleeds, and atrophy. In the present study, we use in vivo magnetic resonance imaging (MRI) to characterize brain morphometry and longitudinal relaxation time (T1) of spontaneously hypertensive rats (SHRs) to study the contribution of chronic hypertension to SVD relevant pathology. Male SHR and Wistar-Kyoto (WKY) rats underwent 3D variable flip angle spoiled gradient echo brain MRI at 9.4 T at early (seven weeks old) and established (19 weeks old) stages of hypertension. The derived proton density weighted and T1 images were utilized for morphometry and to characterize T1 properties in gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF). Custom tissue probability maps were constructed for accurate computerized whole brain tissue segmentations and voxel-wise analyses. Characteristic morphological differences between the two strains included enlarged ventricles, smaller corpus callosum (CC) volumes and general 'thinning' of CC in SHR compared to WKY rats at both age groups. While we did not observe parenchymal T1 differences, the T1 of CSF was elevated in SHR compared to controls. Collectively these findings indicate that SHRs develop WM atrophy which is a clinically robust MRI biomarker associated with WM degeneration.

Compromised prefrontal structure and function are associated with slower walking in older adults

Our previous work demonstrates that reduced activation of the executive network is associated with slow walking speed in a cohort of older adults from the MOBILIZE Boston Study. However, the influence of underlying white matter integrity on the activation of this network and walking speed is unknown. Thus, we used diffusion-weighted imaging and fMRI during an n-back task to assess associations between executive network structure, function, and walking speed. Whole-brain tract-based spatial statistics (TBSS) were used to identify regions of white matter microstructural integrity that were associated with walking speed. The integrity of these regions was then entered into multiple regression models to predict task performance and executive network activation during the n-back task. Among the significant associations of FA with walking speed, we observed the anterior thalamic radiation and superior longitudinal fasciculus were further associated with both n-back response speed and executive network activation. These findings suggest that subtle damage to frontal white matter may contribute to altered executive network activation and slower walking in older adults.

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Older adult walking speed was not associated with white matter lesion burden.

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Walking speed was associated with microstructural white matter integrity.

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The integrity of prefrontal areas was associated with executive network activation.

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Low executive network activation also corresponded to slower walking.

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Interventions targeting the executive network may preserve older adult mobility.

Correlation of nerve fibers in corpus callosum and number of neurons in cerebral cortex: an innovative mathematical model

Purpose/aim: It is estimated that 10⁹ bits/s information are processed in the human brain. The transmission of this huge amount of information requires all connections in the brain to be highly accurate and have order. The current study attempted to present a new aspect of order and proportion in the ultra-structure of the human brain and to calculate the degree of neural interdependence between the two hemispheres.

MATERIALS AND METHODS

In this model, intensity of interdependence of the brain to hemispheres is estimated to be equal to the mathematical proportion of number of neurons in cerebral cortex divided by 2 (number of hemispheres), divided by number of nerve fibers in the human corpus callosum.

RESULTS

The calculated number is equal to 30-50 and it indicates that for every 30-50 neurons between the two hemispheres, there is a neural interconnecting bridge.

CONCLUSIONS

This connection indicates that the brain's function output follows a mathematical relation.

The crux of Cux genes in neuronal function and plasticity

Cux1 and Cux2 are the vertebrate members of a family of homeodomain transcription factors (TF) containing Cut repeat DNA-binding sequences. Perturbation of their expression has been implicated in a wide variety of diseases and disorders, ranging from cancer to autism spectrum disorder (ASD). Within the nervous system, both genes are expressed during neurogenesis and in specific neuronal subpopulations. Their role during development and circuit specification is discussed here, with a particular focus on the cortex where their restricted expression in pyramidal neurons of the upper layers appears to be responsible for many of the specialized functions of these cells, and where their functions have been extensively investigated. Finally, we discuss how Cux TF represent a promising avenue for manipulating neuronal function and for reprogramming.

Reduced inter-hemispheric interference in ageing: Evidence from a divided field Stroop paradigm

One of the most important structural changes that occur in the brain during the course of life relates to the corpus callosum, the largest neural pathway that connects the two cerebral hemispheres. It has been shown that the corpus callosum, and in particular its anterior sections, endures a process of degeneration in ageing. Hence, a primary question is whether such structural changes in the brain of older adults have functional consequences on inter-hemispheric communication. In particular, whether the atrophy of the corpus callosum in ageing may lead to a higher or lower level of inter-hemispheric interference is currently unknown. To investigate this question, we asked young and healthy older adults to perform modified versions of the classic Stroop paradigm in which the target and distracter were spatially separated. Across two experiments, we found that the Stroop effect was significantly reduced in older adults when the two stimuli were distributed in two different hemifields as opposed to the same single hemifield. This new finding suggests that age-related callosal thinning reduces inter-hemispheric interference by facilitating the two hemispheres to process information in parallel.

The effects of environmental enrichment on white matter pathology in a mouse model of chronic cerebral hypoperfusion

White matter (WM) disintegration is common in the older population and is associated with vascular cognitive impairment (VCI). This study explored the effects of environmental enrichment (EE) on pathological sequelae in a mouse model of chronic cerebral hypoperfusion induced by bilateral common carotid artery stenosis (BCAS). Male C57BL/6 J mice underwent BCAS or sham surgery. One-week after surgery, mice were exposed to three different degrees of EE; either standard housing conditions (std), limited 3 h exposure to EE per day (3 h) or full-time exposure to EE (full) for 12 weeks. At 13 weeks after surgery, cognitive testing was performed using a three-dimensional 9-arm radial maze. At 16 weeks after surgery, nesting ability was assessed in each mouse immediately before euthanasia. Brains retrieved after perfusion fixation were examined for WM pathology. BCAS caused WM changes, as demonstrated by corpus callosum atrophy and greater WM disintegrity. BCAS also caused impaired nesting ability and cognitive function. These pathological changes and working memory deficits were attenuated, more so by limited rather than full-time exposure to EE regime. Our results suggest that limited exposure to EE delays the onset of WM degeneration. Therefore, the implementation of even limited EE may be beneficial for patients diagnosed with VCI.

A panel of clinical and neuropathological features of cerebrovascular disease through the novel neuroimaging methods

The last decade has witnessed substantial progress in acquiring diagnostic biomarkers for the diagnostic workup of cerebrovascular disease (CVD). Advanced neuroimaging methods not only provide a strategic contribution for the differential diagnosis of vascular dementia (VaD) and vascular cognitive impairment (VCI), but also help elucidate the pathophysiological mechanisms ultimately leading to small vessel disease (SVD) throughout its course.

OBJECTIVE

In this review, the novel imaging methods, both structural and metabolic, were summarized and their impact on the diagnostic workup of age-related CVD was analysed. Methods: An electronic search between January 2010 and 2017 was carried out on PubMed/MEDLINE, Institute for Scientific Information Web of Knowledge and EMBASE.

RESULTS

The use of full functional multimodality in simultaneous Magnetic Resonance (MR)/Positron emission tomography (PET) may potentially improve the clinical characterization of VCI-VaD; for structural imaging, MRI at 3.0 T enables higher-resolution scanning with greater imaging matrices, thinner slices and more detail on the anatomical structure of vascular lesions.

CONCLUSION

Although the importance of most of these techniques in the clinical setting has yet to be recognized, there is great expectancy in achieving earlier and more refined therapeutic interventions for the effective management of VCI-VaD.

Reaction Time Is Negatively Associated with Corpus Callosum Area in the Early Stages of CADASIL

BACKGROUND AND PURPOSE

Reaction time was recently recognized as a marker of subtle cognitive and behavioral alterations in the early clinical stages of CADASIL, a monogenic cerebral small-vessel disease. In unselected patients with CADASIL, brain atrophy and lacunes are the main imaging correlates of disease severity, but MR imaging correlates of reaction time in mildly affected patients are unknown. We hypothesized that reaction time is independently associated with the corpus callosum area in the early clinical stages of CADASIL.

MATERIALS AND METHODS

Twenty-six patients with CADASIL without dementia (Mini-Mental State Examination score > 24 and no cognitive symptoms) and without disability (modified Rankin Scale score ≤ 1) were compared with 29 age- and sex-matched controls. Corpus callosum area was determined on 3D-T1 MR imaging sequences with validated methodology. Between-group comparisons were performed with t tests or χ² tests when appropriate. Relationships between reaction time and corpus callosum area were tested using linear regression modeling.

RESULTS

Reaction time was significantly related to corpus callosum area in patients (estimate = -7.4 × 10³, standard error = 3.3 × 10³, P = .03) even after adjustment for age, sex, level of education, and scores of depression and apathy (estimate = -12.2 × 10³, standard error = 3.8 × 10³, P = .005). No significant relationship was observed in controls.

CONCLUSIONS

Corpus callosum area, a simple and robust imaging parameter, appears to be an independent correlate of reaction time at the early clinical stages of CADASIL. Further studies will determine whether corpus callosum area can be used as an outcome in future clinical trials in CADASIL or in more prevalent small-vessel diseases.

Youthful Processing Speed in Older Adults: Genetic, Biological, and Behavioral Predictors of Cognitive Processing Speed Trajectories in Aging

Objective: To examine the impact of genetic, inflammatory, cardiovascular, lifestyle, and neuroanatomical factors on cognitive processing speed (CPS) change over time in functionally intact older adults.

Methods: This observational study conducted over two time points, included 120 community dwelling cognitively normal older adults between the ages of 60 and 80 from the University of California San Francisco Memory and Aging Center. Participants were followed with composite measures of CPS, calculated based on norms for 20–30 year-olds. Variables of interest were AD risk genes (APOE, CR1), markers of inflammation (interleukin 6) and cardiovascular health (BMI, LDL, HDL, mean arterial pressure, fasting insulin), self-reported physical activity, and corpus callosum (CC) volumes. The sample was divided into three groups: 17 “resilient-agers” with fast and stable processing speed; 56 “average-agers” with average and stable processing speed; and 47 “sub-agers” with average baseline speed who were slower at follow-up.

Results: Resilient-agers had larger baseline CC volumes than sub-agers (p < 0.05). Resilient-agers displayed lower levels of interleukin-6 (IL-6) and insulin (ps < 0.05) than sub-agers, and reported more physical activity than both average- and sub-agers (ps < 0.01). In a multinomial logistic regression, physical activity and IL-6 predicted average- and sub-ager groups. Resilient-agers displayed a higher frequency of APOE e4 and CR1 AA/AG alleles.

Conclusion: Robust and stable CPS is associated with larger baseline CC volumes, lower levels of inflammation and insulin, and greater self-reported physical activity. These findings highlight the relevance of neuroanatomical, biological, and lifestyle factors in the identification and prediction of heterogeneous cognitive aging change over time.

Corpus callosal atrophy and associations with cognitive impairment in Parkinson disease

OBJECTIVE

To investigate atrophy of the corpus callosum on MRI in Parkinson disease (PD) and its relationship to cognitive impairment.

METHODS

One hundred patients with PD and 24 healthy control participants underwent clinical and neuropsychological evaluations and structural MRI brain scans. Participants with PD were classified as cognitively normal (PD-NC; n = 28), having mild cognitive impairment (PD-MCI; n = 47), or having dementia (PDD; n = 25) by Movement Disorder Society criteria. Cognitive domain (attention/working memory, executive function, memory, language, visuospatial function) z scores were calculated. With the use of FreeSurfer image processing, volumes for total corpus callosum and its subsections (anterior, midanterior, central, midposterior, posterior) were computed and normalized by total intracranial volume. Callosal volumes were compared between participants with PD and controls and among PD cognitive groups, covarying for age, sex, and PD duration and with multiple comparison corrections. Regression analyses were performed to evaluate relationships between callosal volumes and performance in cognitive domains.

RESULTS

Participants with PD had reduced corpus callosum volumes in midanterior and central regions compared to healthy controls. Participants with PDD demonstrated decreased callosal volumes involving multiple subsections spanning anterior to posterior compared to participants with PD-MCI and PD-NC. Regional callosal atrophy predicted cognitive domain performance such that central volumes were associated with the attention/working memory domain; midposterior volumes with executive function, language, and memory domains; and posterior volumes with memory and visuospatial domains.

CONCLUSIONS

Notable volume loss occurs in the corpus callosum in PD, with specific neuroanatomic distributions in PDD and relationships of regional atrophy to different cognitive domains. Callosal volume loss may contribute to clinical manifestations of PD cognitive impairment.

Effects of citicoline therapy on the network connectivity of the corpus callosum in patients with leukoaraiosis

This study aimed to investigate the effects of citicoline therapy on the network connectivity of the corpus callosum in patients with leukoaraiosis (LA) by diffusion tension imaging (DTI).A total of 30 LA patients with Fazekas score of 2 to 3 were voluntarily assigned into citicoline group (n = 14) and control group (n = 16). In citicoline group, citicoline was administered at 0.6 g/d for 1 year. In control group, central nervous system drugs should not be used, except for sleeping pills and antidepressants. Interventions for pre-existing diseases should be conducted in both groups. During the periods of citicoline therapy and post-treatment follow-up, cranial magnetic resonance imaging and DTI were routinely performed in these patients, and the genu, body, and splenium of corpus callosum were selected as the regions of interest (ROIs). The fractional anisotropy (FA) and mean diffusivity (MD) of each ROI were determined with PANDA software.On recruitment, there were no significant differences in the general characteristics, blood biochemical results, cognition function, and the FA and MD of the corpus callosum between 2 groups (P > 0.05). After 1-year treatment, the FA of the corpus callosum reduced gradually, but the MD of the corpus callosum tended to increased in both group, although significant differences were not observed. However, the reductions in FA of genu and splenium of corpus callosum in citicoline group were significantly lower than in control group (P < 0.05); the reductions in MD of genu, body, and splenium of corpus callosum in citicoline group were significantly lower than in control group (P < 0.05).In LA patients, the disruption of the network connectivity of the corpus callosum deteriorates over time. Citicoline treatment may delay the reduction in FA of corpus callosum, which might be beneficial for the improvement of network connectivity of the corpus callosum.

Impact of cerebral white matter changes on functionality in older adults: An overview of the LADIS Study results and future directions

The evidence on the clinical significance of cerebral white matter changes (WMC) has mounted over the past few decades. WMC are recognized as one of the neuroimaging features of cerebral small vessel disease, and are associated with various disturbances and a poor prognosis. The Leukoaraiosis and Disability (LADIS) Study has contributed substantially to this body of knowledge. LADIS is a European multicenter collaboration aimed at assessing the role of WMC as an independent predictor of the transition to disability in initially non-disabled patients aged 65-84 years. Besides the demonstration that severe WMC cause a more than double risk of transition from an autonomous to a dependent status after 3 years of follow-up, the LADIS Study has also provided evidence on the role of WMC in relation to the decline of cognitive and motor performances, depressive symptoms associated with aging and cerebrovascular diseases, the presence of urinary disturbances, and various neurological abnormalities. The possible role of other lesions (lacunar infarcts, cerebral atrophy, corpus callosum morphology) and microstructural abnormalities (diffusion-weighted imaging changes in normal appearing brain tissue and in WMC) has also been investigated. In the present article, we review the main results of the LADIS Study and offer some considerations for future developments in the field, paying attention to the potential use of WMC progression as a surrogate marker in intervention trials in cerebral small vessel diseases. We also discuss some therapeutic perspectives regarding the beneficial impact of physical activity on the risk of vascular cognitive impairment in patients with WMC.

Tractography at 3T MRI of Corpus Callosum Tracts Crossing White Matter Hyperintensities

BACKGROUND AND PURPOSE

The impact of white matter hyperintensities on the diffusion characteristics of crossing tracts is unclear. This study used quantitative tractography at 3T MR imaging to compare, in the same individuals, the diffusion characteristics of corpus callosum tracts that crossed white matter hyperintensities with the diffusion characteristics of corpus callosum tracts that did not pass through white matter hyperintensities.

MATERIALS AND METHODS

Brain T2 fluid-attenuated inversion recovery-weighted and diffusion tensor 3T MR imaging scans were acquired in 24 individuals with white matter hyperintensities. Tractography data were generated by the Fiber Assignment by Continuous Tracking method. White matter hyperintensities and corpus callosum tracts were manually segmented. In the corpus callosum, the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts crossing white matter hyperintensities were compared with the fractional anisotropy, radial diffusivity, and mean diffusivity of tracts that did not cross white matter hyperintensities. The cingulum, long association fibers, corticospinal/bulbar tracts, and thalamic projection fibers were included for comparison.

RESULTS

Within the corpus callosum, tracts that crossed white matter hyperintensities had decreased fractional anisotropy compared with tracts that did not pass through white matter hyperintensities (P = .002). Within the cingulum, tracts that crossed white matter hyperintensities had increased radial diffusivity compared with tracts that did not pass through white matter hyperintensities (P = .001).

CONCLUSIONS

In the corpus callosum and cingulum, tracts had worse diffusion characteristics when they crossed white matter hyperintensities. These results support a role for white matter hyperintensities in the disruption of crossing tracts.

Neuroanatomical correlates of verbal fluency in early Alzheimer's disease and normal aging

Verbal fluency (VF) impairments occur early in Alzheimer's disease (AD) and to a lesser extent also in normal aging. However, the neural underpinnings of these impairments are not fully understood. The present study evaluated whether VF impairments in early AD and normal aging rely upon common or different neuroanatomical correlates. We examined the association between VF performance and brain structure in 18 mild AD patients and 24 healthy elderly. Linear regressions were performed between accuracy and time intervals in VF scores and structural measurements of cerebral gray matter (GM) and white matter (WM) using MRI. Results showed that semantic VF correlated exclusively with GM in cerebellum, left temporal fusiform cortex, and WM in uncinate fasciculus, inferior fronto-occipital fasciculus and corpus callosum. Phonemic VF showed unique associations between intervals and WM in left-hemisphere tracts. The association between GM in hippocampus, subcortical structures and semantic accuracy differentiated patients from controls. Results showed that VF impairments are primarily associated with same structural brain changes in AD as in healthy elderly but at exaggerated levels. However, specific VF deficiencies and their underlying neural correlates exist and these clearly differentiate the initial stages of AD.

Neurocognitive Deficits After Radiation Therapy for Brain Malignancies

Radiotherapy (RT) has proven to be an effective therapeutic tool in treatment of a wide variety of brain tumors; however, it has a negative impact on quality of life and neurocognitive function. Cognitive dysfunction associated with both the disease and adverse effects of RT is one of the most concerning complication among long-term survivors. The effects of RT to brain can be divided into acute, early delayed, and late delayed. It is, however, the late delayed effects of RT that lead to severe neurological consequences such as minor-to-severe cognitive deficits due to irreversible focal or diffuse necrosis of brain parenchyma. In this review, we discuss current and emerging data regarding the relationship between RT and neurocognitive outcomes, and therapeutic strategies to prevent/treat postradiation neurocognitive deficits.

White matter integrity in small vessel disease is related to cognition

Cerebral small vessel disease, including white matter hyperintensities (WMH) and lacunes of presumed vascular origin, is common in elderly people and is related to cognitive impairment and dementia. One possible mechanism could be the disruption of white matter tracts (both within WMH and normal-appearing white matter) that connect distributed brain regions involved in cognitive functions. Here, we investigated the relation between microstructural integrity of the white matter and cognitive functions in patients with small vessel disease. The Radboud University Nijmegen Diffusion tensor and Magnetic resonance Cohort study is a prospective cohort study among 444 independently living, non-demented elderly with cerebral small vessel disease, aged between 5500 and 85 years. All subjects underwent magnetic resonance imaging and diffusion tensor imaging scanning and an extensive neuropsychological assessment. We showed that loss of microstructural integrity of the white matter at specific locations was related to specific cognitive disturbances, which was mainly located in the normal-appearing white matter (p < 0.05, FWE-corrected for multiple comparisons). The microstructural integrity in the genu and splenium showed the highest significant relation with global cognitive function and executive functions, in the cingulum bundle with verbal memory performance. Associations between diffusion tensor imaging parameters and most cognitive domains remained present after adjustment for WMH and lacunes. In conclusion, cognitive disturbances in subjects with cerebral small vessel disease are related to microstructural integrity of multiple white matter fibers (within WMH and normal-appearing white matter) connecting different cortical and subcortical regions.

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White matter integrity in small vessel disease (SVD) was assessed with DTI.

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White matter integrity was related to cognition independent of SVD-markers.

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This relation was seen in multiple fibers within white matter hyperintensities.

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But also in normal-appearing white matter connecting different (sub)cortical regions

Quantitative measurement to evaluate morphological changes of the corpus callosum in patients with subcortical ischemic vascular dementia

BACKGROUND

Subcortical ischemic vascular dementia (SIVD) is a subtype of dementia associated with abnormalities in the subcortical white matter regions. Recent imaging techniques can be used to detect such abnormalities in vivo.

PURPOSE

To examine morphological changes of the corpus callosum in patients with SIVD by using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI).

MATERIAL AND METHODS

MRI was performed to explore changes of cerebral white matter, especially corpus callosum. Brain matter diffusivity was examined with DTI by measuring the fractional anisotropy (FA). Results of 30 patients diagnosed with SIVD and 30 healthy subjects were analyzed and compared.

RESULTS

The thicknesses of the genu, the anterior third, middle, and posterior third of the body, and the splenium of the corpus callosum were smaller in SIVD patients compared to healthy controls (0.54 ± 0.08 vs. 0.68 ± 0.09 cm, P = 0.0011; 0.27 ± 0.06 vs. 0.38 ± 0.07 cm, P = 0.002; 0.28 ± 0.05 vs. 0.38 ± 0.08 cm, P = 0.009; 0.18 ± 0.04 vs. 0.26 ± 0.06 cm, P = 0.013; 0.54 ± 0.07 vs. 0.72 ± 0.09 cm, P = 0.003, respectively). The FA values of the genu and splenium of the corpus callosum in patients with SIVD were decreased compared to healthy controls (0.664 ± 0.042 vs. 0.778 ± 0.041, P < 0.001; 0.691 ± 0.038 vs. 0.786 ± 0.039, P = 0.001, respectively).

CONCLUSION

Patients with SIVD exhibit corpus callosum atrophy and morphological changes, and these characteristics may be useful for diagnosis.