Jugular venous reflux and brain parenchyma volumes in elderly patients with mild cognitive impairment and Alzheimer's disease

Association of Age-Related Spontaneous Internal Jugular Vein Reflux with Cognitive Impairment and Incident Dementia

BACKGROUND

It remains unclear whether changes in the venous circulation contribute to cognitive decline.

OBJECTIVE

This study aimed to clarify whether the spontaneous jugular vein reflux (JVR) is associated with cognitive impairment and incident dementia.

METHODS

Patients with any evidence of cerebral vessel disease on magnetic resonance imaging (MRI) were consecutively enrolled between October 2015 to July 2019. We employed carotid duplex sonography to measure the internal jugular vein (IJV). The subjects were classified into two groups based on the degree of JVR on either side: none, mild (JVR(-) group) and moderate, severe (JVR (+) group) JVR. They underwent both the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment-Japanese (MoCA-J) global tests. Their cognitive status was prospectively assessed until March 2023.

RESULTS

302 patients with an MMSE score ≥24 underwent duplex sonography of the IJV. Among them, 91 had spontaneous JVR on either side. Both MMSE and MoCA-J were significantly lower in patients with JVR (+) group than in the JVR (-) group. After the adjustment for risk factors and MRI findings, intergroup differences in MoCA-J remained significant. Among the cognitive subdomains, median executive function and memory scores were significantly lower in the JVR (+) group than in the JVR (-) group. During the median 5.2-year follow-up, 11 patients with incident dementia were diagnosed. Patients with severe JVR were significantly more likely to be diagnosed with dementia (log-rank test, p = 0.031).

CONCLUSIONS

Spontaneous IJV reflux especially severe JVR, was associated with global cognitive function, and potentially with incident dementia.

Results of Numerical Modeling of Blood Flow in the Internal Jugular Vein Exhibiting Different Types of Strictures

The clinical relevance of nozzle-like strictures in upper parts of the internal jugular veins remains unclear. This study was aimed at understanding flow disturbances caused by such stenoses. Computational fluid dynamics software, COMSOL Multiphysics, was used. Two-dimensional computational domain involved stenosis at the beginning of modeled veins, and a flexible valve downstream. The material of the venous valve was considered to be hyperelastic. In the vein models with symmetric 2-leaflets valve without upstream stenosis or with minor 30% stenosis, the flow was undisturbed. In the case of major 60% and 75% upstream stenosis, centerline velocity was positioned asymmetrically, and areas of reverse flow and flow separation developed. In the 2-leaflet models with major stenosis, vortices evoking flow asymmetry were present for the entire course of the model, while the valve leaflets were distorted by asymmetric flow. Our computational fluid dynamics modeling suggests that an impaired outflow from the brain through the internal jugular veins is likely to be primarily caused by pathological strictures in their upper parts. In addition, the jugular valve pathology can be exacerbated by strictures located in the upper segments of these veins.

The aging venous system: from varicosities to vascular cognitive impairment

Aging-induced pathological alterations of the circulatory system play a critical role in morbidity and mortality of older adults. While the importance of cellular and molecular mechanisms of arterial aging for increased cardiovascular risk in older adults is increasingly appreciated, aging processes of veins are much less studied and understood than those of arteries. In this review, age-related cellular and morphological alterations in the venous system are presented. Similarities and dissimilarities between arterial and venous aging are highlighted, and shared molecular mechanisms of arterial and venous aging are considered. The pathogenesis of venous diseases affecting older adults, including varicose veins, chronic venous insufficiency, and deep vein thrombosis, is discussed, and the potential contribution of venous pathologies to the onset of vascular cognitive impairment and neurodegenerative diseases is emphasized. It is our hope that a greater appreciation of the cellular and molecular processes of vascular aging will stimulate further investigation into strategies aimed at preventing or retarding age-related venous pathologies.

Numerical modeling of blood flow in the internal jugular vein with the use of computational fluid mechanics software

OBJECTIVES

To determine the site and nature of altered hemodynamics in pathological internal jugular veins.

METHOD

With the use of computational fluid mechanics software we simulated blood flow in 3 D models of the internal jugular veins that exhibited different morphologies, including nozzle-like strictures in their upper parts and valves in the lower parts.

RESULTS

In a majority of models with nozzle-like strictures, especially those positioned asymmetrically, abnormal flow pattern was revealed, with significant flow separation and regions with reversed flow. Abnormal valves had no significant impact on flow in a case of already altered flow evoked by stricture in upper part of the vein.

CONCLUSIONS

In our jugular model, cranially-located stenoses, which in clinical practice are primarily caused by external compression, cause more significant outflow impact respect to endoluminal defects and pathological valves located more caudally.

Jugular Venous Reflux Can Mimic Posterior Fossa Dural Arteriovenous Fistulas on MRI-MRA

Dural arteriovenous fistulas (DAVFs) are high-flow acquired shunts that can carry high risk of intracranial hemorrhage. Because DAVFs can often be managed by endovascular means, early and accurate diagnosis can markedly improve patient morbidity. Time-of-flight and arterial spin-labeling MRA have increased the diagnostic utility of MRI for DAVF by showing hemodynamic rather than anatomic evidence of shunting. The purpose of this article is to describe the cases of seven patients who had co-localization of arterial spin-labeling signal intensity and time-of-flight flow-related enhancement in the left skull base, resulting in a misdiagnosis of DAVF and a recommendation for catheter angiography by the interpreting radiologist. Benign jugular venous reflux is identified as a common mechanism in each case, and the physiology behind this imaging pitfall is described. An algorithmic diagnostic approach to differentiating physiologic venous reflux from true posterior skull base DAVFs is presented.

Anatomical Morphology Analysis of Internal Jugular Veins and Factors Affecting Internal Jugular Vein Size

Background and objectives: There is a paucity of research on the shape of internal jugular vein (IJV) and their association with an individual's morphology and various chronic diseases. Therefore, this study aimed to analyze the anatomy of the IJV across various patients and to relate the differences in anatomy to basic patient characteristics. Materials and Methods: This retrospective study included a total of 313 patients who underwent contrast-enhanced neck computed tomography between January 2017 and December 2018. The circumferences of the right and left IJVs were measured at three locations (hyoid bone, cricoid cartilage, and first thoracic vertebra) and parameters affecting the size of the IJV were analyzed. Results: The right IJV was significantly larger than the left IJV at each position (p < 0.001), and the area of the lumen was the largest at the cricoid cartilage level (p < 0.001). After dividing the right IJV data into two groups (above and below the median area), multivariate logistic regression analysis showed that age (odds ratio (OR) 1.040; 95% confidence interval (CI) 1.022-1.058, p < 0.001) and body mass index (BMI, OR 1.080; 95% CI 1.011-1.154, p = 0.0.23) affected size. Conclusions: The right IJV is larger than the left and has a rhomboid morphology. Age and BMI are significant factors affecting the IJV size.

Role of age-related alterations of the cerebral venous circulation in the pathogenesis of vascular cognitive impairment

There has been an increasing appreciation of the role of vascular contributions to cognitive impairment and dementia (VCID) associated with old age. Strong preclinical and translational evidence links age-related dysfunction and structural alterations of the cerebral arteries, arterioles, and capillaries to the pathogenesis of many types of dementia in the elderly, including Alzheimer's disease. The low-pressure, low-velocity, and large-volume venous circulation of the brain also plays critical roles in the maintenance of homeostasis in the central nervous system. Despite its physiological importance, the role of age-related alterations of the brain venous circulation in the pathogenesis of vascular cognitive impairment and dementia is much less understood. This overview discusses the role of cerebral veins in the pathogenesis of VCID. Pathophysiological consequences of age-related dysregulation of the cerebral venous circulation are explored, including blood-brain barrier disruption, neuroinflammation, exacerbation of neurodegeneration, development of cerebral microhemorrhages of venous origin, altered production of cerebrospinal fluid, impaired function of the glymphatics system, dysregulation of cerebral blood flow, and ischemic neuronal dysfunction and damage. Understanding the age-related functional and phenotypic alterations of the cerebral venous circulation is critical for developing new preventive, diagnostic, and therapeutic approaches to preserve brain health in older individuals.

Safety and efficacy of venoplasty in MS: A randomized, double-blind, sham-controlled phase II trial

Objective

To determine the safety and efficacy of balloon vs sham venoplasty of narrowing of the extracranial jugular and azygos veins in multiple sclerosis (MS).

Methods

Patients with relapsing or progressive MS were screened using clinical and ultrasound criteria. After confirmation of >50% narrowing by venography, participants were randomized 1:1 to receive balloon or sham venoplasty of all stenoses and were followed for 48 weeks. Participants and research staff were blinded to intervention allocation. The primary safety outcome was the number of adverse events (AEs) during 48 weeks. The primary efficacy outcome was the change from baseline to week 48 in the patient-reported outcome MS Quality of Life–54 (MSQOL-54) questionnaire. Standardized clinical and MRI outcomes were also evaluated.

Results

One hundred four participants were randomized (55 sham; 49 venoplasty) and 103 completed 48 weeks of follow-up. Twenty-three sham and 21 venoplasty participants reported at least 1 AE; one sham (2%) and 5 (10%) venoplasty participants had a serious AE. The mean improvement in MSQOL-54 physical score was +1.3 (sham) and +1.4 (venoplasty) (p = 0.95); MSQOL-54 mental score was +1.2 (sham) and −0.8 (venoplasty) (p = 0.55).

Conclusions

Our data do not support the continued use of venoplasty of extracranial jugular and/or azygous venous narrowing to improve patient-reported outcomes, chronic MS symptoms, or the disease course of MS.

ClinicalTrials.gov identifier

NCT01864941.

Classification of evidence

This study provides Class I evidence that for patients with MS, balloon venoplasty of extracranial jugular and azygous veins is not beneficial in improving patient-reported, standardized clinical, or MRI outcomes.

Understanding jugular venous outflow disturbance

Extracranial venous abnormalities, especially jugular venous outflow disturbance, were originally viewed as nonpathological phenomena due to a lack of realization and exploration of their feature and clinical significance. The etiology and pathogenesis are still unclear, whereas a couple of causal factors have been conjectured. The clinical presentation of this condition is highly variable, ranging from insidious to symptomatic, such as headaches, dizziness, pulsatile tinnitus, visual impairment, sleep disturbance, and neck discomfort or pain. Standard diagnostic criteria are not available, and current diagnosis largely depends on a combinatory use of imaging modalities. Although few researches have been conducted to gain evidence-based therapeutic approach, several recent advances indicate that intravenous angioplasty in combination with stenting implantation may be a safe and efficient way to restore normal blood circulation, alleviate the discomfort symptoms, and enhance patients' quality of life. In addition, surgical removal of structures that constrain the internal jugular vein may serve as an alternative or adjunctive management when endovascular intervention is not feasible. Notably, discussion on every aspect of this newly recognized disease entity is in the infant stage and efforts with more rigorous designed, randomized controlled studies in attempt to identify the pathophysiology, diagnostic criteria, and effective approaches to its treatment will provide a profound insight into this issue.

Jugular Venous Reflux Is Associated with Perihematomal Edema after Intracerebral Hemorrhage

The purpose of this study was to determine whether jugular venous reflux (JVR) is associated with perihematomal edema (PHE) in individuals with intracerebral hemorrhage (ICH). Patients with spontaneous supratentorial ICH within 72 h of symptom onset were enrolled. Baseline brain computed tomography (CT) scan was performed, with a follow-up CT examination at 12 ± 3 days after onset. Jugular venous color Doppler ultrasound was performed at 12 ± 3 days after onset to examine the JVR status. A total of 65 patients with ICH were enrolled. In logistic regression analysis, absolute PHE volume was significantly associated with JVR (OR, 5.46; 95% CI, 1.04–28.63; p = 0.044) and baseline hematoma volume (OR, 1.14; 95% CI, 1.03–1.26; p = 0.009) within 72 h of onset. It was also correlated with JVR (OR, 15.32; 95% CI, 2.52–92.99; p = 0.003) and baseline hematoma volume (OR, 1.14; 95% CI, 1.04–1.24; p = 0.006) at 12 ± 3 days after onset. In a similar manner, relative PHE volume was significantly associated with JVR (OR, 14.85; 95% CI, 3.28–67.17; p < 0.001) within 72 h of onset and at 12 ± 3 days after onset (OR, 5.87; 95% CI, 1.94–17.77; p = 0.002). JVR is associated with both absolute and relative PHE volumes after ICH.

Age-related brain atrophy may be mitigated by internal jugular vein enlargement in male individuals without neurologic disease

Objectives To assess the relationship between cross-sectional area of internal jugular veins and brain volumes in healthy individuals without neurologic disease. Methods A total of 193 healthy individuals without neurologic disease (63 male and 130 female; age > 20 to < 70 years) received magnetic resonance venography and structural brain magnetic resonance imaging at 3T. The internal jugular vein cross-sectional area was assessed at C2-C3, C4, C5-C6, and C7-T1. Normalized whole brain volume was assessed. Partial correlation analyses were used to determine associations. Results There was an inverse relationship between normalized whole brain volume and total internal jugular vein cross-sectional area (C7-T1: males r = -0.346, p = 0.029; females r = -0.301, p = 0.002). After age adjustment, association of normalized whole brain volume and normalized gray matter volume with internal jugular vein cross-sectional area became positive in males (normalized whole brain volume and right internal jugular vein cross-sectional area (C2-C3) changed from r = -0.163 to r = 0.384, p = 0.002), but not in the females. Conclusion Sex differences exist in the relationship between brain volume and internal jugular vein cross-sectional area in healthy individuals without neurologic disease.

Intra- and Extracranial MR Venography: Technical Notes, Clinical Application, and Imaging Development

Scientific debate over chronic cerebrospinal venous insufficiency (CCSVI) has drawn attention to venous system involvement in a series of pathologic brain conditions. In the last few decades, the MRI venography (MRV) field has developed a number of valuable sequences to better investigate structural anatomy, vessel patency, and flow characteristics of venous drainage in the intra- and extracranial systems. A brief two-tier protocol is proposed to encompass the study of intra- and extracranial venous drainage with and without contrast administration, respectively. Contrast-enhanced protocol is based on time-resolved contrast-enhanced MRV of the whole region plus extracranial flow quantification through 2D Cine phase contrast (PC); non-contrast-enhanced protocol includes intracranial 3D PC, extracranial 2D time of flight (TOF), and 2D Cine PC flow quantification. Total scanning time is reasonable for clinical applications: approximately seven minutes is allocated for the contrast protocol (most of which is due to 2D Cine PC), while the noncontrast protocol accounts for around twenty minutes. We believe that a short though exhaustive MRI scan of the whole intra- and extracranial venous drainage system can be valuable for a variety of pathologic conditions, given the possible venous implication in several neurological conditions.

Identifying Talent in Youth Sport: A Novel Methodology Using Higher-Dimensional Analysis

Prediction of adult performance from early age talent identification in sport remains difficult. Talent identification research has generally been performed using univariate analysis, which ignores multivariate relationships. To address this issue, this study used a novel higher-dimensional model to orthogonalize multivariate anthropometric and fitness data from junior rugby league players, with the aim of differentiating future career attainment. Anthropometric and fitness data from 257 Under-15 rugby league players was collected. Players were grouped retrospectively according to their future career attainment (i.e., amateur, academy, professional). Players were blindly and randomly divided into an exploratory (n = 165) and validation dataset (n = 92). The exploratory dataset was used to develop and optimize a novel higher-dimensional model, which combined singular value decomposition (SVD) with receiver operating characteristic analysis. Once optimized, the model was tested using the validation dataset. SVD analysis revealed 60 m sprint and agility 505 performance were the most influential characteristics in distinguishing future professional players from amateur and academy players. The exploratory dataset model was able to distinguish between future amateur and professional players with a high degree of accuracy (sensitivity = 85.7%, specificity = 71.1%; p<0.001), although it could not distinguish between future professional and academy players. The validation dataset model was able to distinguish future professionals from the rest with reasonable accuracy (sensitivity = 83.3%, specificity = 63.8%; p = 0.003). Through the use of SVD analysis it was possible to objectively identify criteria to distinguish future career attainment with a sensitivity over 80% using anthropometric and fitness data alone. As such, this suggests that SVD analysis may be a useful analysis tool for research and practice within talent identification.

Internal Jugular Vein Cross-Sectional Area and Cerebrospinal Fluid Pulsatility in the Aqueduct of Sylvius: A Comparative Study between Healthy Subjects and Multiple Sclerosis Patients

Objectives

Constricted cerebral venous outflow has been linked with increased cerebrospinal fluid (CSF) pulsatility in the aqueduct of Sylvius in multiple sclerosis (MS) patients and healthy individuals. This study investigates the relationship between CSF pulsatility and internal jugular vein (IJV) cross-sectional area (CSA) in these two groups, something previously unknown.

Methods

65 relapsing-remitting MS patients (50.8% female; mean age = 43.8 years) and 74 healthy controls (HCs) (54.1% female; mean age = 43.9 years) were investigated. CSF flow quantification was performed on cine phase-contrast MRI, while IJV-CSA was calculated using magnetic resonance venography. Statistical analysis involved correlation, and partial least squares correlation analysis (PLSCA).

Results

PLSCA revealed a significant difference (p<0.001; effect size = 1.072) between MS patients and HCs in the positive relationship between CSF pulsatility and IJV-CSA at C5-T1, something not detected at C2-C4. Controlling for age and cardiovascular risk factors, statistical trends were identified in HCs between: increased net positive CSF flow (NPF) and increased IJV-CSA at C5-C6 (left: r = 0.374, p = 0.016; right: r = 0.364, p = 0.019) and C4 (left: r = 0.361, p = 0.020); and increased net negative CSF flow and increased left IJV-CSA at C5-C6 (r = -0.348, p = 0.026) and C4 (r = -0.324, p = 0.039), whereas in MS patients a trend was only identified between increased NPF and increased left IJV-CSA at C5-C6 (r = 0.351, p = 0.021). Overall, correlations were weaker in MS patients (p = 0.015).

Conclusions

In healthy adults, increased CSF pulsatility is associated with increased IJV-CSA in the lower cervix (independent of age and cardiovascular risk factors), suggesting a biomechanical link between the two. This relationship is altered in MS patients.

Internal Jugular Vein Cross-Sectional Area Enlargement Is Associated with Aging in Healthy Individuals

Background

Internal jugular vein (IJV) narrowing has been implicated in central nervous system pathologies, however normal physiological age- and gender-related IJV variance in healthy individuals (HIs) has not been adequately assessed.

Objectives

We assessed the relationship between IJV cross-sectional area (CSA) and aging.

Materials and Methods

This study involved 193 HIs (63 males and 130 females) who received 2-dimensional magnetic resonance venography at 3T. The minimum CSA of the IJVs at cervical levels C2/C3, C4, C5/C6, and C7/T1 was obtained using a semi-automated contouring-thresholding technique. Subjects were grouped by decade. Pearson and partial correlation (controlled for cardiovascular risk factors, including hypertension, heart disease, smoking and body mass index) and analysis of variance analyses were used, with paired t-tests comparing side differences.

Results

Mean right IJV CSA ranges were: in males, 41.6 mm² (C2/C3) to 82.0 mm² (C7/T1); in females, 38.0 mm² (C2/C3) to 62.3 mm² (C7/T1), while the equivalent left side ranges were: in males, 28.0 mm² (C2/C3) to 52.2 mm² (C7/T1); in females, 27.2 mm² (C2/C3) to 47.8 mm² (C7/T1). The CSA of the right IJVs was significantly larger (p<0.001) than the left at all cervical levels. Controlling for cardiovascular risk factors, the correlation between age and IJV CSA was more robust in males than in the females for all cervical levels.

Conclusions

In HIs age, gender, hand side and cervical location all affect IJV CSA. These findings suggest that any definition of IJV stenosis needs to account for these factors.

The Oscillating Component of the Internal Jugular Vein Flow: The Overlooked Element of Cerebral Circulation

The jugular venous pulse (JVP) provides valuable information about cardiac haemodynamics and filling pressures and is an indirect estimate of the central venous pressure (CVP). Recently it has been proven that JVP can be obtained by measuring the cross-sectional area (CSA) of the IJV on each sonogram of an ultrasound B-mode sonogram sequence. It has also been proven that during its pulsation the IJV is distended and hence that the pressure gradient drives the IJV haemodynamics. If this is true, then it will imply the following: (i) the blood velocity in the IJV is a periodic function of the time with period equal to the cardiac period and (ii) the instantaneous blood velocity is given by a time function that can be derived from a flow-dynamics theory that uses the instantaneous pressure gradient as a parameter. The aim of the present study is to confirm the hypothesis that JVP regulates the IJV blood flow and that pressure waves are transmitted from the heart toward the brain through the IJV wall.

An anatomy-based lumped parameter model of cerebrospinal venous circulation: can an extracranial anatomical change impact intracranial hemodynamics?

BACKGROUND

The relationship between extracranial venous system abnormalities and central nervous system disorders has been recently theorized. In this paper we delve into this hypothesis by modeling the venous drainage in brain and spinal column areas and simulating the intracranial flow changes due to extracranial morphological stenoses.

METHODS

A lumped parameter model of the cerebro-spinal venous drainage was created based on anatomical knowledge and vessels diameters and lengths taken from literature. Each vein was modeled as a hydraulic resistance, calculated through Poiseuille's law. The inputs of the model were arterial flow rates of the intracranial, vertebral and lumbar districts. The effects of the obstruction of the main venous outflows were simulated. A database comprising 112 Multiple Sclerosis patients (Male/Female = 42/70; median age ± standard deviation = 43.7 ± 10.5 years) was retrospectively analyzed.

RESULTS

The flow rate of the main veins estimated with the model was similar to the measures of 21 healthy controls (Male/Female = 10/11; mean age ± standard deviation = 31 ± 11 years), obtained with a 1.5 T Magnetic Resonance scanner. The intracranial reflux topography predicted with the model in cases of internal jugular vein diameter reduction was similar to those observed in the patients with internal jugular vein obstacles.

CONCLUSIONS

The proposed model can predict physiological and pathological behaviors with good fidelity. Despite the simplifications introduced in cerebrospinal venous circulation modeling, the key anatomical feature of the lumped parameter model allowed for a detailed analysis of the consequences of extracranial venous impairments on intracranial pressure and hemodynamics.

Head and Neck Veins of the Mouse. A Magnetic Resonance, Micro Computed Tomography and High Frequency Color Doppler Ultrasound Study

To characterize the anatomy of the venous outflow of the mouse brain using different imaging techniques. Ten C57/black male mice (age range: 7-8 weeks) were imaged with high-frequency Ultrasound, Magnetic Resonance Angiography and ex-vivo Microcomputed tomography of the head and neck. Under general anesthesia, Ultrasound of neck veins was performed with a 20MHz transducer; head and neck Magnetic Resonance Angiography data were collected on 9.4T or 7T scanners, and ex-vivo Microcomputed tomography angiography was obtained by filling the vessels with a radiopaque inert silicone rubber compound. All procedures were approved by the local ethical committee. The dorsal intracranial venous system is quite similar in mice and humans. Instead, the mouse Internal Jugular Veins are tiny vessels receiving the sigmoid sinuses and tributaries from cerebellum, occipital lobe and midbrain, while the majority of the cerebral blood, i.e. from the olfactory bulbs and fronto-parietal lobes, is apparently drained through skull base connections into the External Jugular Vein. Three main intra-extracranial anastomoses, absent in humans, are: 1) the petrosquamous sinus, draining into the posterior facial vein, 2) the veins of the olfactory bulb, draining into the superficial temporal vein through a foramen of the frontal bone 3) the cavernous sinus, draining in the External Jugular Vein through a foramen of the sphenoid bone. The anatomical structure of the mouse cranial venous outflow as depicted by Ultrasound, Microcomputed tomography and Magnetic Resonance Angiography is different from humans, with multiple connections between intra- and extra- cranial veins.

Is there a link between the extracranial venous system and central nervous system pathology?

The extracranial venous system is complex and variable between individuals. Until recently, these variations were acknowledged as developmental variants and were not considered pathological findings. However, in the last decade, the presence and severity of uni- or bi-lateral jugular venous reflux (JVR) was linked to several central nervous system (CNS) disorders such as transient global amnesia, transient monocular blindness, cough headache, primary exertional headache and, most recently, to Alzheimer's disease. The most recent introduction of a composite criteria-based vascular condition named chronic cerebrospinal venous insufficiency (CCSVI), which was originally linked to multiple sclerosis, increased the interest in better understanding the role of the extracranial venous system in the pathophysiology of CNS disorders. The ultimate cause-consequence relationship between these conditions and CNS disorders has not been firmly established and further research is needed. The purpose of this article collection in BMC Medicine and BMC Neurology is to synthesize current concepts and most recent findings concerning the evaluation, etiology, pathophysiology and clinical relevance of the potential involvement of the extracranial venous system in the pathology of multiple CNS disorders and in aging.