Hippocampal atrophy in early Alzheimer's disease: anatomic specificity and validation

Psychoplastogenic DYRK1A Inhibitors with Therapeutic Effects Relevant to Alzheimer's Disease

Tauopathy, neuronal atrophy, and psychological impairments are hallmarks of neurodegenerative diseases, such as Alzheimer's disease, that currently lack efficacious clinical treatments capable of rectifying these issues. To address these unmet needs, we used rational drug design to combine the pharmacophores of DYRK1A inhibitors and isoDMTs to develop psychoplastogenic DYRK1A inhibitors. Using this approach, we discovered a nonhallucinogenic compound capable of promoting cortical neuron growth and suppressing tau hyperphosphorylation while also having the potential to mitigate the biological and psychological symptoms of dementia. Together, our results suggest that hybridization of the DYRK1A and psychoplastogen pharmacophores represents a promising strategy for identifying compounds that might address the cognitive as well as the behavioral and psychological symptoms of dementia.

Identification of region-specific splicing QTLs in human hippocampal tissue and its distinctive role in brain disorders

Alternative splicing (AS) regulation has an essential role in complex diseases. However, the AS profiles in the hippocampal (HIPPO) region of human brain are underexplored. Here, we investigated cis-acting sQTLs of HIPPO region in 264 samples and identified thousands of significant sQTLs. By enrichment analysis and functional characterization of these sQTLs, we found that the HIPPO sQTLs were enriched among histone-marked regions, transcription factors binding sites, RNA binding proteins sites, and brain disorders-associated loci. Comparative analyses with the dorsolateral prefrontal cortex revealed the importance of AS regulation in HIPPO (rg = 0.87). Furthermore, we performed a transcriptome-wide association study of Alzheimer's disease and identified 16 significant genes whose genetically regulated splicing levels may have a causal role in Alzheimer. Overall, our study improves our knowledge of the transcriptome gene regulation in the HIPPO region and provides novel insights into elucidating the pathogenesis of potential genes associated with brain disorders.

Breakdown of the blood-brain barrier: A mediator of increased Alzheimer's risk in patients with metabolic disorders?

Metabolic disorders (MDs), including type 1 and 2 diabetes and chronic obesity, are among the faster growing diseases globally and are a primary risk factor for Alzheimer's disease (AD). The term "type-3 diabetes" has been proposed for AD due to the interrelated cellular, metabolic, and immune features shared by diabetes, insulin resistance (IR), and the cognitive impairment and neurodegeneration found in AD. Patients with MDs and/or AD commonly exhibit altered glucose homeostasis and IR; systemic chronic inflammation encompassing all of the periphery, blood-brain barrier (BBB), and central nervous system; pathological vascular remodeling; and increased BBB permeability that allows transfusion of neurotoxic molecules from the blood to the brain. This review summarizes the components of the BBB, mechanisms through which MDs alter BBB permeability via immune and metabolic pathways, the contribution of BBB dysfunction to the manifestation and progression of AD, and current avenues of therapeutic research that address BBB permeability. In addition, issues with the translational applicability of current animal models of AD regarding BBB dysfunction and proposals for future directions of research that address the relationship between MDs, BBB dysfunction, and AD are discussed.

Biomarkers of Alzheimer's Disease and Cerebrovascular Lesions and Clinical Progression in Patients with Subjective Cognitive Decline: A Systematic Review

BACKGROUND

Early identification of Alzheimer's disease (AD) may be extremely beneficial for delaying disease progression. Subjective cognitive decline (SCD) may be an early indicator of AD pathology. Not all individuals with SCD will eventually develop AD, making it critical to identify biomarkers during the SCD stage which indicate likely clinical progression.

OBJECTIVE

The present review aims to summarize available data on structural MRI and cerebrospinal fluid (CSF) biomarkers and their association with clinical progression to mild cognitive impairment (MCI) or AD in people with SCD.

METHODS

Database searches were conducted using Embase and PubMed until June 2020. Longitudinal studies assessing biomarkers in individuals with SCD and assessing clinical progression to MCI/AD were included. Two assessors performed data extraction and assessed the risk of bias in the included studies. Data were synthesized narratively.

RESULTS

An initial search identified 1,065 papers; after screening and review 14 studies were included. Sample size of the included studies ranged from 28-674, mean age was 60.0-68.6 years, and 10.2%-52%of participants converted to MCI/AD. Lower levels of CSF Aβ 42 were consistently associated with clinical progression. Combination measures identifying an AD-like profile of Aβ 42 and tau levels were strongly associated with clinical progression. Biomarkers identified with structural MRI were less conclusive, as some studies found significant associations while others did not.

CONCLUSION

Biomarkers may be able to predict clinical progression in those with cognitive complaints. Aβ 42, or combinations of Aβ 42 and tau may be useful biomarkers in identifying individuals with SCD who will progress to MCI/AD.

Epileptic Mechanisms Shared by Alzheimer's Disease: Viewed via the Unique Lens of Genetic Epilepsy

Our recent work on genetic epilepsy (GE) has identified common mechanisms between GE and neurodegenerative diseases including Alzheimer's disease (AD). Although both disorders are seemingly unrelated and occur at opposite ends of the age spectrum, it is likely there are shared mechanisms and studies on GE could provide unique insights into AD pathogenesis. Neurodegenerative diseases are typically late-onset disorders, but the underlying pathology may have already occurred long before the clinical symptoms emerge. Pathophysiology in the early phase of these diseases is understudied but critical for developing mechanism-based treatment. In AD, increased seizure susceptibility and silent epileptiform activity due to disrupted excitatory/inhibitory (E/I) balance has been identified much earlier than cognition deficit. Increased epileptiform activity is likely a main pathology in the early phase that directly contributes to impaired cognition. It is an enormous challenge to model the early phase of pathology with conventional AD mouse models due to the chronic disease course, let alone the complex interplay between subclinical nonconvulsive epileptiform activity, AD pathology, and cognition deficit. We have extensively studied GE, especially with gene mutations that affect the GABA pathway such as mutations in GABA_A receptors and GABA transporter 1. We believe that some mouse models developed for studying GE and insights gained from GE could provide unique opportunity to understand AD. These include the pathology in early phase of AD, endoplasmic reticulum (ER) stress, and E/I imbalance as well as the contribution to cognitive deficit. In this review, we will focus on the overlapping mechanisms between GE and AD, the insights from mutations affecting GABA_A receptors, and GABA transporter 1. We will detail mechanisms of E/I imbalance and the toxic epileptiform generation in AD, and the complex interplay between ER stress, impaired membrane protein trafficking, and synaptic physiology in both GE and AD.

Transfer learning for predicting conversion from mild cognitive impairment to dementia of Alzheimer's type based on a three-dimensional convolutional neural network

Dementia of Alzheimer's type (DAT) is associated with devastating and irreversible cognitive decline. Predicting which patients with mild cognitive impairment (MCI) will progress to DAT is an ongoing challenge in the field. We developed a deep learning model to predict conversion from MCI to DAT. Structural magnetic resonance imaging scans were used as input to a 3-dimensional convolutional neural network. The 3-dimensional convolutional neural network was trained using transfer learning; in the source task, normal control and DAT scans were used to pretrain the model. This pretrained model was then retrained on the target task of classifying which MCI patients converted to DAT. Our model resulted in 82.4% classification accuracy at the target task, outperforming current models in the field. Next, we visualized brain regions that significantly contribute to the prediction of MCI conversion using an occlusion map approach. Contributory regions included the pons, amygdala, and hippocampus. Finally, we showed that the model's prediction value is significantly correlated with rates of change in clinical assessment scores, indicating that the model is able to predict an individual patient's future cognitive decline. This information, in conjunction with the identified anatomical features, will aid in building a personalized therapeutic strategy for individuals with MCI.

Disorientation in Time and Place in Old Age: Longitudinal Evidence from Three Old Age Cohorts in Germany (AgeDifferent.de Platform)

BACKGROUND

Only little evidence is available on disorientation, one of the most challenging symptoms of Alzheimer's disease and related dementias.

OBJECTIVES

The aim of this study was to investigate the prevalence of disorientation in older age in association with the level of cognitive status, personal characteristics, and life events.

METHODS

Three longitudinal population-based cohort studies on cognitive health of elderly adults were harmonized (LEILA 75 + , AgeCoDe/AgeQualiDe, AgeMooDe). Participants who completed a baseline and at least one follow-up assessment of cognitive functioning and who did not have stroke, Parkinson's disease, atherosclerosis, kidney disease, and/or alcoholism were included in the analysis (n = 2135, 72.6% female, mean age 80.2 years). Data was collected in standardized interviews and questionnaires with the participant, a proxy informant, and the participant's general practitioner.

RESULTS

Making three errors in the MMSE other than in the questions on orientation (MMSEwo) came with a probability of 7.8% for disorientation, making ten errors with a probability of 88.9%. A lower MMSEwo score (HR 0.75, CI 95 0.71-0.79, p < 0.001), older age (HR 1.11, CI 95 1.08-1.14, p < 0.001), and living in a nursing home (HR 1.64, CI 95 1.02-2.64, p = 0.042) were associated with incident disorientation. Impairments in walking (OR 2.41, CI 95 1.16-4.99, p = 0.018) were associated with a greater probability for prevalent disorientation. None of the life events were significant.

CONCLUSION

Our findings suggest that disorientation is primarily associated with cognitive status. Regular walking activities might possibly reduce the risk for disorientation but further research is necessary.

Value of magnetic resonance spectroscopy in geriatric patients with cognitive impairment

Background

Mild cognitive impairment is a transitional stage prior to dementia, and it is reported in depressed patients. Early diagnosis could predict the reversible etiologies and prevent further deterioration. Proton magnetic resonance spectroscopy has been used for early diagnosis and differential diagnosis of cognitive impairment.

Objective

We aimed to study the difference of hippocampal and frontal white matter metabolites between patients with Alzheimer’s disease, mild cognitive impairment, and cognitive impairment associated with depression, and if those metabolites can differentiate between them.

Subjects and methods

Geriatric patients with cognitive impairment were recruited from neurology and psychiatry clinics. All subjects underwent comprehensive medical evaluations, neuropsychological testing, laboratory tests as well as brain MRI and 1H-MRS studies.

Results

The present study included 85 subjects. Patients with MCI and AD had lower hippocampal NAA and NAA/Cr ratio than patients with depression and normal controls, while, frontal NAA and NAA/Cr ratio were lower in all patient’s subgroups compared to normal control.

Conclusion

Hippocampal NAA and NAA/Cr ratio might help to differentiate between MCI and cognitive impairment associated with depression.

The effect of repetition on pronoun resolution in patients with memory impairment

Referring to things in the world - that woman, her idea, she - is a central component of language. Understanding reference requires the listener to keep track of the unfolding discourse history while integrating multiple sources of information to interpret the speech stream as it unfolds in time. Pronouns are a common way to establish reference. But due to their impoverished form, to understand them listeners must relate features of the pronoun (e.g., gender, animacy) with existing representations of potential discourse referents. Successful referential processing seems to place demands on memory. In a previous study, patients with hippocampal amnesia and healthy participants listened to short stories as their eye movements were monitored. When interpreting ambiguous pronouns, healthy participants demonstrated order-of-mention effects, whereby ambiguous pronouns are interpreted as referring to the first-mentioned referent in the story. By contrast, memory-impaired patients exhibited significant disruptions in their ability to use information about which character had been mentioned first to interpret pronouns. Repetition of the most salient information is a common clinical recommendation for improving pronoun resolution and communication in individuals with memory disorders (e.g., Alzheimer's disease) but this recommendation lacks an evidentiary basis. The present study seeks to determine whether the pronoun resolution performance of hippocampal patients can be improved, by repetition of the target referent, increasing its salience. Results indicate that patients with hippocampal damage demonstrate improved processing of pronouns following repetition of the target referent, but benefit from this repetition to a significantly smaller degree compared to healthy participants. These results provide further evidence for the role of the hippocampal-dependent memory system in language processing and point to the need for empirically tested communication interventions.

Modeling Alzheimer's disease with human iPS cells: advancements, lessons, and applications

One in three people will develop Alzheimer's disease (AD) or another dementia and, despite intense research efforts, treatment options remain inadequate. Understanding the mechanisms of AD pathogenesis remains our principal hurdle to developing effective therapeutics to tackle this looming medical crisis. In light of recent discoveries from whole-genome sequencing and technical advances in humanized models, studying disease risk genes with induced human neural cells presents unprecedented advantages. Here, we first review the current knowledge of the proposed mechanisms underlying AD and focus on modern genetic insights to inform future studies. To highlight the utility of human pluripotent stem cell-based innovations, we then present an update on efforts in recapitulating the pathophysiology by induced neuronal, non-neuronal and a collection of brain cell types, departing from the neuron-centric convention. Lastly, we examine the translational potentials of such approaches, and provide our perspectives on the promise they offer to deepen our understanding of AD pathogenesis and to accelerate the development of intervention strategies for patients and risk carriers.

Neuroimaging Biomarkers for Alzheimer's Disease

Currently, over five million Americans suffer with Alzheimer’s disease (AD). In the absence of a cure, this number could increase to 13.8 million by 2050. A critical goal of biomedical research is to establish indicators of AD during the preclinical stage (i.e. biomarkers) allowing for early diagnosis and intervention. Numerous advances have been made in developing biomarkers for AD using neuroimaging approaches. These approaches offer tremendous versatility in terms of targeting distinct age-related and pathophysiological mechanisms such as structural decline (e.g. volumetry, cortical thinning), functional decline (e.g. fMRI activity, network correlations), connectivity decline (e.g. diffusion anisotropy), and pathological aggregates (e.g. amyloid and tau PET). In this review, we survey the state of the literature on neuroimaging approaches to developing novel biomarkers for the amnestic form of AD, with an emphasis on combining approaches into multimodal biomarkers. We also discuss emerging methods including imaging epigenetics, neuroinflammation, and synaptic integrity using PET tracers. Finally, we review the complementary information that neuroimaging biomarkers provide, which highlights the potential utility of composite biomarkers as suitable outcome measures for proof-of-concept clinical trials with experimental therapeutics.

Coupled changes in hippocampal structure and cognitive ability in later life

Introduction

The hippocampus plays an important role in cognitive abilities which often decline with advancing age.

Methods

In a longitudinal study of community-dwelling adults, we investigated whether there were coupled changes in hippocampal structure and verbal memory, working memory, and processing speed between the ages of 73 (N = 655) and 76 years (N = 469). Hippocampal structure was indexed by hippocampal volume, hippocampal volume as a percentage of intracranial volume (H_ICV), fractional anisotropy (FA), mean diffusivity (MD), and longitudinal relaxation time (T1).

Results

Mean levels of hippocampal volume, H_ICV, FA, T1, and all three cognitive abilities domains decreased, whereas MD increased, from age 73 to 76. At baseline, higher hippocampal volume was associated with better working memory and verbal memory, but none of these correlations survived correction for multiple comparisons. Higher FA, lower MD, and lower T1 at baseline were associated with better cognitive abilities in all three domains; only the correlation between baseline hippocampal MD and T1, and change in the three cognitive domains, survived correction for multiple comparisons. Individuals with higher hippocampal MD at age 73 experienced a greater decline in all three cognitive abilities between ages 73 and 76. However, no significant associations with changes in cognitive abilities were found with hippocampal volume, FA, and T1 measures at baseline. Similarly, no significant associations were found between cognitive abilities at age 73 and changes in the hippocampal MRI biomarkers between ages 73 and 76.

Conclusion

Our results provide evidence to better understand how the hippocampus ages in healthy adults in relation to the cognitive domains in which it is involved, suggesting that better hippocampal MD at age 73 predicts less relative decline in three important cognitive domains across the next 3 years. It can potentially assist in diagnosing early stages of aging-related neuropathologies, because in some cases, accelerated decline could predict pathologies.

Texture analyses of quantitative susceptibility maps to differentiate Alzheimer's disease from cognitive normal and mild cognitive impairment

PURPOSE

Although a number of studies have focused on finding anatomical regions in which iron concentrations are high, no study has been conducted to examine the overall variations in susceptibility maps of Alzheimer's disease (AD). The objective of this study, therefore, was to differentiate AD from cognitive normal (CN) and mild cognitive impairment (MCI) using a texture analysis of quantitative susceptibility maps (QSMs).

METHODS

The study was approved by the local institutional review board, and informed consent was obtained from all subjects. In each participant group-CN, MCI, and AD-18 elderly subjects were enrolled. A fully first-order flow-compensated 3D gradient-echo sequence was run to obtain axial magnitudes and phase images and to produce QSM data. Sagittal structural 3D T1-weighted (3DT1W) images were also obtained with the magnetization-prepared rapid acquisition of gradient-echo sequence to obtain brain tissue images. The first- and second-order texture parameters of the QSMs and 3DT1W images were obtained to evaluate group differences using a one-way analysis of covariance.

RESULTS

For the first-order QSM analysis, mean, standard deviation, and covariance of signal intensity separated the subject groups (F = 5.191, p = 0.009). For the second-order analysis, angular second moment, contrast, and correlation separated the subject groups (F = 6.896, p = 0.002). Finally, a receiver operating characteristic curve analysis differentiated MCI from CN in white matter on the QSMs (z = 3.092, p = 0.0020).

CONCLUSIONS

This was the first study to evaluate the textures of QSM in AD, which overcame the limitations of voxel-based analyses. The QSM texture analysis successfully distinguished both AD and MCI from CN and outperformed the voxel-based analysis using 3DT1-weighed images in separating MCI from CN. The first-order textures were more efficient in differentiating MCI from CN than did the second-order.

Impact of regional white matter lesions on cognitive function in subcortical vascular cognitive impairment

OBJECTIVES

Exact characterization and localization of white matter lesions (WMLs) as they relate and contribute to vascular cognitive impairment is highly debated. The purpose of this study was to investigate the impact of WML on cognitive function by using a new anatomy-based classification method.

METHODS

We detected WML accurately by using a three-dimensional fluid-attenuated inversion recovery (3D FLAIR) imaging technique and subsequently segmented WMLs by using an anatomy-based method. Participants included 56 consecutive patients diagnosed with subcortical vascular cognitive impairment (SubVCI). The volume of WMLs in different anatomic regions was measured. The volume of the hippocampus, the corpus callosum (CC), any lacunar infarcts, total gray matter (GM), and total brain volumes were also calculated.

RESULTS

Hippocampal (P  =  0.005) as well as temporal WML volumes (P  =  0.039) were both independently associated with mini-mental state examination (MMSE) score. Only the parietal WML volume (P  =  0.000) was independently associated with Montreal Cognitive Assessment (MoCA) score. Frontal WMLs were independently correlated with executive function. Occipital WMLs were independently associated with visuospatial and recall function. Language impairment was independently correlated with both parietal GM and parietal WML volume. Functions related to orientation were independently associated with parietal WML volume.

DISCUSSION

The volume of WMLs in the temporal region as well as in the hippocampus were both independently associated with MMSE score. For the MoCA score, however, only parietal WML volumes were independently correlated. White matter lesions within different anatomic regions were separately correlated with different subdomains of cognitive function.

Neural substrates of verbal memory impairments in adults with type 2 diabetes mellitus

BACKGROUND

Verbal memory impairment is well documented in type 2 diabetes mellitus (T2DM) but, to date, the neural substrates remain unclear. The present study evaluated verbal memory and ascertained the degree of frontal and temporal lobe involvement in the anticipated verbal memory impairment among adults with T2DM.

METHOD

Forty-six late-middle-aged and elderly adults with T2DM and 50 age-, sex-, and education-matched adults without T2DM underwent medical evaluation, verbal memory assessment, and brain magnetic resonance imaging (MRI) evaluations.

RESULTS

As anticipated, participants with T2DM had clear verbal memory impairments. Consistent with prior reports, we found volume reductions restricted to the hippocampus. Our diffusion tensor imaging analysis revealed that participants with T2DM had extensive cerebral gray and white matter microstructural abnormalities predominantly in the left hemisphere, with a larger concentration present in the temporal lobe. In contrast, we uncovered mostly nonspecific microstructural abnormalities in the absence of tissue loss in the frontal lobe. Of great importance, we present the first evidence among participants with T2DM linking verbal memory impairment and compromised microstructural integrity of the left parahippocampal gyrus, a key memory-relevant structure.

CONCLUSIONS

Our results suggest that the hippocampus and parahippocampal gyrus may be particularly vulnerable to the deleterious effects of T2DM. The parahippocampal gyrus in particular may play a crucial role in the verbal memory impairments frequently reported in T2DM. Future studies should employ methods such as resting state functional magnetic resonance imaging and diffusion tensor imaging tractography to better characterize network connectivity, which may help further characterize the verbal memory impairment frequently reported in T2DM.

Insulin growth factor binding protein 7 is a novel target to treat dementia

Alzheimer's disease (AD) is the most common form of dementia in the elderly but effective therapeutic strategies to treat AD are not yet available. This is also due to the fact that the pathological mechanisms that drive the pathogenesis of sporadic AD are still not sufficiently understood and may differ on the individual level. Several risk factors such as altered insulin-like peptide (ILP) signaling have been linked to AD and modulating the ILP system has been discussed as a potential therapeutic avenue. Here we show that insulin-like growth factor binding protein 7 (IGFBP7), a protein that attenuates the function of ILPs, is up-regulated in the brains of AD patients and in a mouse model for AD via a process that involves altered DNA-methylation and coincides with decreased ILP signaling. Mimicking the AD-situation in wild type mice, by increasing hippocampal IGFBP7 levels leads to impaired memory consolidation. Consistently, inhibiting IGFBP7 function in mice that develop AD-like memory impairment reinstates associative learning behavior. These data suggest that IGFBP7 is a critical regulator of memory consolidation and might be used as a biomarker for AD. Targeting IGFBP7 could be a novel therapeutic avenue for the treatment of AD patients.

Dementia in Down's syndrome: an MRI comparison with Alzheimer's disease in the general population

BACKGROUND

Down's syndrome (DS) is the most common genetic cause of intellectual disability. People with DS are at an increased risk of Alzheimer's disease (AD) compared to the general population. Neuroimaging studies of AD have focused on medial temporal structures; however, to our knowledge, no in vivo case-control study exists comparing the anatomy of dementia in DS to people with AD in the general population. We therefore compared the in vivo brain anatomy of people with DS and dementia (DS+) to those with AD in the general population.

METHOD

Using MRI in 192 adults, we compared the volume of whole brain matter, lateral ventricles, temporal lobes and hippocampus in DS subjects with and without dementia (DS+, DS-), to each other and to three non-DS groups. These included one group of individuals with AD and two groups of controls (each age-matched for their respective DS and general population AD cohorts).

RESULTS

AD and DS+ subjects showed significant reductions in the volume of the whole brain, hippocampus and temporal lobes and a significant elevation in the volume of the lateral ventricle, compared to their non-demented counterparts. People with DS+ had a smaller reduction in temporal lobe volume compared to individuals with AD.

CONCLUSIONS

DS+ and AD subjects have a significant reduction in volume of the same brain regions. We found preliminary evidence that DS individuals may be more sensitive to tissue loss than others and have less 'cognitive reserve'.

Perturbations of neural circuitry in aging, mild cognitive impairment, and Alzheimer's disease

Alzheimer's disease (AD) is a global public health threat that continues to rise as the proportion of the population over the age of 60 rapidly increases. Aging and dementia are both associated with cognitive decline and share some features in terms of structural and functional alterations in neural circuitry. In this review, we attempt to highlight the network perturbations that occur in "typical" aging and emphasize how they may differ from those that manifest in dementia. We focus in particular on neuroimaging studies of the medial temporal lobe (MTL) network, which is involved in episodic memory and is known to change both with age and with AD pathology. We propose a temporal model of structural and functional alterations in the MTL along the aging-dementia continuum. The earliest changes are synaptic in nature and are detectable in particularly vulnerable white matter pathways such as the perforant path. These are followed by structural degradation in the transentorhinal region and subsequently neurodegeneration of the hippocampus as a result of accumulating pathology as well as deafferentation from entorhinal input. We believe that testing this model explicitly is an important direction for future research, particularly in the context of biomarker discovery and clinical trial design.

Decreased recall of primacy words predicts cognitive decline

One of the cognitive changes associated with Alzheimer's disease is a diminution of the primacy effect, i.e., the tendency toward better recall of items studied early on a list compared with the rest. We examined whether learning and recall of primacy words predicted subsequent cognitive decline in 204 elderly subjects who were non-demented and cognitively intact when first examined. Our results show that poorer primacy performance in the Rey Auditory Verbal Learning Test delayed recall trials, but not in immediate recall trials, is an effective predictor of subsequent decline in general cognitive function. This pattern of performance can be interpreted as evidence that failure to consolidate primacy items is a marker of cognitive decline.

Mild cognitive impairment: historical development and summary of research

This review article broadly traces the historical development, diagnostic criteria, clinical and neuropathological characteristics, and treatment strategies related to mild cognitive impairment (MCI), The concept of MCI is considered in the context of other terms that have been developed to characterize the elderly with varying degrees of cognitive impairment Criteria based on clinical global scale ratings, cognitive test performance, and performance on other domains of functioning are discussed. Approaches employing clinical, neuropsychological, neuroimaging, biological, and molecular genetic methodology used in the validation of MCI are considered, including results from cross-sectional, longitudinal, and postmortem investigations. Results of recent drug treatment studies of MCI and related methodological issues are also addressed.

Hippocampal atrophy in Alzheimer’s disease

SUMMARY New research criteria for Alzheimer’s disease (AD) and mild cognitive impairment (MCI) emphasize the use of imaging biomarkers in clinical diagnosis of these disorders. The volume loss of medial temporal lobe structures, especially hippocampal atrophy, is the best validated marker of AD. Manual tracing on MRI is the present gold standard for evaluating hippocampal volume; however, it is laborious and tracer-dependent. We categorized the most recent full- or semi-automated methods by the nature of the output of the method: size and shape of subcortical structures, cortical thickness, atrophy-rate and voxel- and region-based characteristics. The features of each method are introduced. The findings in structural MRI studies, especially in those studies utilizing the most recent methods, and the accuracies of those new methods in differentiating AD from healthy controls and stable MCI from progressive MCI are reviewed.

Cerebrospinal fluid cortisol concentrations in healthy elderly are affected by both APOE and TOMM40 variants

Abnormalities of the hypothalamic-pituitary-adrenal (HPA) axis have been reported in subjects with Alzheimer's disease (AD) and may include increased cerebrospinal fluid (CSF) cortisol concentrations. Moreover, presence of the APOE ɛ4 allele, which is an established risk factor for the development of AD, has been shown to associate with higher CSF cortisol levels, especially in AD sufferers. In this study, we examined whether TOMM40 variants, which have been reported to influence age of onset of AD, also had an effect on CSF cortisol levels, in healthy, cognitively intact individuals with or without APOE ɛ4. In our results, the increase in CSF cortisol associated with the presence of the APOE ɛ4 allele was only detected when a short TOMM40 poly-T variant, shown to associate with later age of onset of AD in ɛ4 carriers, was not present. These results are consistent with previous reports (e.g., Roses et al., 2009) suggesting that TOMM40 poly-T variants influence the effects of APOE alleles.

Quantization and analysis of hippocampal morphometric changes due to dementia of Alzheimer type using metric distances based on large deformation diffeomorphic metric mapping

The metric distance obtained from the large deformation diffeomorphic metric mapping (LDDMM) algorithm is used to quantize changes in morphometry of brain structures due to neuropsychiatric diseases. For illustrative purposes we consider changes in hippocampal morphometry (shape and size) due to very mild dementia of the Alzheimer type (DAT). LDDMM, which was previously used to calculate dense one-to-one correspondence vector fields between hippocampal shapes, measures the morphometric differences with respect to a template hippocampus by assigning metric distances on the space of anatomical images thereby allowing for direct comparison of morphometric differences. We characterize what information the metric distances provide in terms of size and shape given the hippocampal, brain and intracranial volumes. We demonstrate that metric distance is a measure of morphometry (i.e., shape and size) but mostly a measure of shape, while volume is mostly a measure of size. Moreover, we show how metric distances can be used in cross-sectional, longitudinal analysis, as well as left-right asymmetry comparisons, and provide how the metric distances can serve as a discriminative tool using logistic regression. Thus, we show that metric distances with respect to a template computed via LDDMM can be a powerful tool in detecting differences in shape.

Brain structure and cerebrovascular risk in cognitively impaired patients: Shanghai Community Brain Health Initiative-pilot phase

OBJECTIVE

To investigate the associations among brain morphologic changes as seen on magnetic resonance imaging (MRI), cerebrovascular risk (CVR), and clinical diagnosis and cognition in elderly patients with mild cognitive impairment and dementia living in urban Shanghai.

DESIGN

Cross-sectional study performed from May 1, 2007, to November 31, 2008.

SETTING

Memory Disorders Clinic of the Huashan Hospital and the Shanghai community.

PARTICIPANTS

Ninety-six older people: 32 with normal cognition (NC), 30 with amnestic mild cognitive impairment (aMCI), and 34 with dementia.

MAIN OUTCOME MEASURES

For each patient, we administered a neurologic and physical examination, neuropsychological evaluation, and brain MRI and genotyped the apolipoprotein E-ε4 (APOE-ε4) gene. The volumes determined by MRI were assessed using a semiautomatic method.

RESULTS

Brain volume was significantly smaller in the dementia patients compared with the NC (P < .001) and aMCI patients (P = .04). Hippocampal volume (HV) was lower and white matter hyperintensity (WMH) volume was higher in those with aMCI (HV: P = .03; WMH volume: P = .04) and dementia (HV: P < .001; WMH volume: P = .002) compared with NC participants. The presence of APOE-ε4 was significantly associated with reduced HV (P = .02). Systolic blood pressure was positively associated with CVR score (P = .04); diastolic blood pressure (P = .02) and CVR score (P = .04) were positively associated with WMH volume. The WMH volume (P = .03) and CVR score (P = .03) were higher among dementia patients compared with NC participants.

CONCLUSIONS

Brain structure changes seen on MRI were significantly associated with clinical diagnosis. In addition, blood pressure was highly associated with CVR score and WMH volume. These results suggest that MRI is a valuable measure of brain injury in a Chinese cohort and can serve to assess the effects of various degenerative and cerebrovascular diseases.

Hippocampal Asymmetry with Hippocampal Sulcus Remnants in a Patient with Mild Cognitive Impairment

A 65-year-old woman underwent MRI for a mild cognitive impairment (MCI) at Mini-Mental State Examination (MMSE). MRI showed hippocampal sulcus remnants bilaterally, although they were larger on the right, and left hippocampal atrophy with increased left fimbrio-subicular distance (right side: 1.2 mm; left side: 2.0 mm). The meaning of these findings in relation to clinical aspects is discussed and reviewed according to data from the literature.

Effect of tramiprosate in patients with mild-to-moderate Alzheimer's disease: exploratory analyses of the MRI sub-group of the Alphase study

OBJECTIVES

The efficacy, safety and disease-modification of tramiprosate (homotaurine)were investigated in a recently completed large-scale Phase III clinical study in patients with mild to moderate Alzheimer's disease (AD), the Alphase study. Disease-modification was assessed using longitudinal volumetric MRI (vMRI) measurements of the hippocampus in a subgroup of patients. The present study describes the vMRI, cognitive and clinical results obtained in this subgroup.

DESIGN

Multi-center, double-blind, randomized, placebo-controlled study in a subset of the 1052 patients of the Alphase study.

SETTING

51 vMRI investigative sites in the United States and Canada.

PARTICIPANTS

A total of 508 patients underwent vMRI scanning. Of these, 312 provided scan pairs for assessing hippocampus volume changes and were included in the analyses.

INTERVENTIONS

Patients were randomized to receive Placebo BID (n = 109), tramiprosate 100 mg BID (n = 103), or tramiprosate 150 mg BID (n = 100) for 78 weeks.

MEASUREMENTS

Alzheimer's Disease Assessment Scale-cognitive subscale (ADAS-cog) and Clinical Dementia Rating-Sum-of-boxes CDR-SB assessments were conducted at Baseline and at Weeks 13, 26, 39, 52, 65 and 78. Exploratory analyses were performed using similar First and Final mixed-effects repeated-measures models that were used for the analysis of the entire patient dataset.

RESULTS

Psychometric score results showed numerical trends in favour of tramiprosate that did not reach statistical significance. While there were no statistically significant group differences in hippocampus volume using the First modeling approach, a significant dose-response reduction in hippocampus volume change was found in the Final models. Moreover, there was a marginally significant overall treatment main effect and a significant slope difference in favour of tramiprosate according to the Final model analysis of the ADAS-cog scores. ADAS-cog scores analyzed according to this model also revealed differences in favor of the tramiprosate 150 mg group at weeks 26 and 52, with marginally significant differences at Weeks 13 and 39. Slope analyses of ADAS-cog score changes showed significant differences in favor of the 150 mg BID group, and when both active groups were combined, in comparison to the placebo group. No between-group differences with respect to changes to each visit in the CDR-SB were observed with either modeling approach. Although there was a similar dose-response relationship observed in the hippocampus volume and ADAS-cog Final model analyses, the overall changes in psychometric scores and hippocampus volume were not significantly correlated.

CONCLUSION

Exploratory analysis of the vMRI subgroup suggests that tramiprosate slows hippocampal atrophy, and reveals some evidence of a beneficial effect on cognition. The clinical validity of the vMRI biomarker is discussed.

Quantitative and qualitative measures of hippocampal atrophy are not correlated in healthy older men

BACKGROUND AND PURPOSE

In neuroimaging studies of dementia and mild cognitive impairment, hippocampal atrophy (HA) is commonly assessed by qualitative ratings of hippocampal appearance, or by measuring hippocampal volumes. These estimates of HA are considered to be equivalent. However, few studies have examined their relationship, especially in healthy older individuals. We therefore examined the relationship between hippocampal qualitative atrophy scores and quantitative volumetric measurements in healthy older men.

METHODS

Ninety-seven healthy community-dwelling 65-70-year-old men underwent magnetic resonance imaging scanning. Hippocampal volumes were measured and adjusted for intracranial size. A validated 4-point visual rating scale was used to assess hippocampal atrophy.

RESULTS

There was a wide range of unadjusted hippocampal volumes among subjects (right: 2,582 to 5,196 mm(3)[mean 3,626 mm(3); SD 465.5 mm(3)] and left: 2,111 to 4,580 mm(3)[mean 3,501 mm(3); SD 439.5 mm(3)]), which was maintained following adjustment for intracranial size. However, only 9% of subjects were rated as having moderate or severe HA. Qualitative and quantitative measures were not significantly correlated (left hippocampus: rho = .07, P= .52; right hippocampus: rho = .10, P= .34).

CONCLUSIONS

This study shows that qualitative and quantitative indices of hippocampal atrophy in healthy older men are not equivalent. Small hippocampal volumes do not necessarily equate to hippocampal atrophy.

Volumetric MRI and cognitive measures in Alzheimer disease : comparison of markers of progression

BACKGROUND

Both cognitive tests and MRI-based measures have been suggested as outcomes in trials assessing disease-modifying therapies in Alzheimer's disease (AD).

OBJECTIVE

To compare changes in longitudinal MRI measures with changes in performance on cognitive tests routinely used in AD clinical trials.

METHOD

Fifty-two subjects from the placebo-arm of a clinical trial in mild-to-moderate AD had volumetric T(1)-weighted scans and cognitive tests including the Mini-Mental State Examination (MMSE), AD Assessment Scale-Cognitive Subscale, Disability Assessment for Dementia, AD Cooperative Study-Clinical Global Impression of Change and Clinical Dementia Rating at baseline and one-year later. Rates of brain atrophy and ventricular enlargement were measured using the boundary shift integral. Hippocampal (Hc) atrophy was calculated from manual volume measurements. The relationships between MRI and cognitive measures were investigated.

RESULTS

Rates of brain atrophy and/or ventricular enlargement were correlated with declining performance on cognitive scales. The strongest association was between brain atrophy rate and MMSE decline (r = 0.59, p < 0.0001). Hc atrophy rate was not significantly correlated with any of the cognitive scales.

CONCLUSION

The lack of correlation between Hc atrophy and cognitive scales may reflect a combination of: the extensive functional damage to the Hc by the time AD is clinically established, the greater influence of ongoing cortical degeneration, and errors in Hc outlining. The strong correlations between brain atrophy and ventricular enlargement, and cognitive scales probably reflect the correspondence between these measures of overall cerebral loss and global cognitive measures in the moderate stages of AD.

Neuropathological quantification of dtg APP/PS1: neuroimaging, stereology, and biochemistry

Murine models that mimic the neuropathology of Alzheimer's disease (AD) have the potential to provide insight into the pathogenesis of the disease and lead to new strategies for the therapeutic management of afflicted patients. We used magnetic resonance imaging (MRI), design-based stereology, and high performance liquid chromatography (HPLC) to assess the age-related neuropathology in double transgenic mice that overexpress two AD-related proteins--amyloid precursor protein (APP) and presenilin 1 (PS1)--and age- and gender-matched wild-type (WT) controls. In mice ranging in age from 4-28 months, total volumes of the hippocampal formation (V (HF)) and whole brain (V (brain)) were quantified by the Cavalieri-point counting method on a systematic-random sample of coronal T2-weighted MRI images; the same stereological methods were used to quantify V (HF) and V (brain) after perfusion and histological processing. To assess changes in AD-type beta-amyloid (A beta) plaques, sections from the hippocampal formation and amylgdaloid complex of mice aged 5, 12, and 15 months were stained by Congo Red histochemistry. In aged mice with large numbers of amyloid plaques, systematic-random samples of sections were stained by GFAP immunocytochemistry to assess gender and genotype effects on total numbers of astrocytes. In addition, levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and 5-HT metabolites were assayed by HPLC in fresh-frozen samples from neocortex, striatum, hippocampus, and brainstem. We confirmed age-related increases in amyloid plaques, beginning with a few plaques at 5 months of age and increasing densities by 12 and 15 months. At 15 months of age, there were robust genotype effects, but no gender effects, on GFAP-immunopositive astrocytes in the amygdaloid complex and hippocampus. There were no effects on monoamine levels in all brain regions examined, and no volume changes in hippocampal formation or whole brain as quantified on either neuroimages or tissue sections. Strong correlations were present between volume estimates from MRI images and histological sections, with about 85% reduction in mean V (HF) or mean V (brain) between MRI and processed histological sections. In summary, these findings show that the double transgenic expression of AD-type mutations is associated with age-related increases in amyloid plaques and astrocytosis; however, this model does not recapitulate the cortical atrophy or neurochemical changes that are characteristic of AD.

Magnetic resonance approaches to brain aging and Alzheimer disease-associated neuropathology

The noninvasive, nonradioactive, quantitative nature of magnetic resonance techniques has propelled them to the forefront of neuroscience and neuropsychiatric research. In particular, recent advances have confirmed their enormous potential in patients with Alzheimer disease (AD). Structural and functional magnetic resonance (MR) imaging have demonstrated significant correlation with clinical outcomes and underlying pathology and are used increasingly in the AD clinic. This review will highlight the role of high-resolution structural MR imaging and functional magnetic resonance imaging in the identification of atrophic and hemodynamic changes in AD and their potential as diagnostic biomarkers and surrogates of therapeutic response. Advanced MR techniques based on diffusion, perfusion, and neurochemical abnormalities in the aging brain will be presented briefly. These newer techniques continue to expand our understanding of neuropathology in the aging brain and are likely to play an important clinical role in the future.

The role of quantitative structural imaging in the early diagnosis of Alzheimer's disease

The goal of this article is to review the role of structural neuroimaging in the diagnosis of Alzheimer's disease (AD). We present relevant neuroanatomy, highlight progress in the domain of AD imaging, and review the clinical characteristics of the prodromal phase of AD. We describe the history of the diagnostic issue by examining at cross-section and longitudinally the differences between patients who have AD and normal controls. We also present how subsequent works applied these characteristic traits to the early detection of the prodromal disease and to prediction of future decline. The article delineates the differences between subjects who have mild cognitive impairment and AD, which illustrate the spreading of the pathology with disease progression. The last section describes problems encountered in the differential diagnosis.

Development of a method for reconstructing three-dimensional data from axial, sagittal, and coronal MR images

Magnetic resonance (MR) imaging is useful for the diagnosis of brain atrophy and intracranial abnormalities. We have developed a method of automated volumetry to evaluate the degree of brain atrophy for the diagnosis of dementia. Whole-brain MR images with thin slices without gaps are required for segmentation and volumetry. However, obtaining such images requires that the patient remain at rest for a prolonged period, thereby reducing the throughput of MR imaging examinations. Therefore, a method is needed for the reconstruction of isotropic three-dimensional (3D) data using routine axial, sagittal, and coronal MR images with 30% gaps and measurement of brain volume. The method of reconstructing 3D data consists of four processes: 1) segmentation of the brain region on axial, sagittal, and coronal MR images using the region-growing technique; 2) setting data to a 3D domain; 3) registration by manual operation; and 4) interpolation between the data based on linear interpolation. In clinical MR images, the differences between this method and the conventional technique were less than 10%. These results demonstrate that this technique is able to construct 3D data from axial, sagittal, and coronal MR images.

Comparisons between Alzheimer disease, frontotemporal lobar degeneration, and normal aging with brain mapping

Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD) are both common degenerative dementias in the under 65 age group. Although clinical criteria have been defined for both diseases, there is considerable overlap in clinical features, and hence, diagnosis still can be very difficult particularly in the early stages of the disease. As a result, there has been increasing interest in using magnetic resonance imaging to better characterize these diseases and to aid in diagnosis. Voxel-based morphometry (VBM) is an automated technique that assesses patterns of regional gray matter atrophy on magnetic resonance imaging between 2 groups of subjects. It is unbiased in that it looks throughout the whole brain and does not require any a priori assumptions concerning which structures to assess, giving it a significant advantage over traditional region of interest-based methods. Voxel-based morphometry has been widely used to assess patterns of regional atrophy in subjects with AD and FTLD. These studies have demonstrated specific patterns of regional loss in both diseases, compared the 2 diseases to look for differences that could be diagnostically useful, and have correlated regions of gray matter loss to cognitive and behavioral deficits in these subjects. This article will review the findings of these studies and discuss the role of VBM in these neurodegenerative diseases.

Does Alzheimer's disease affect hippocampal asymmetry? Evidence from a cross-sectional and longitudinal volumetric MRI study

OBJECTIVE

To determine whether Alzheimer's disease (AD) is associated with preferential atrophy of either the left or right hippocampus.

METHODS

We examined right-left asymmetry in hippocampal volume and atrophy rates in 32 subjects with probable AD and 50 age-matched controls. Hippocampi were measured on two serial volumetric MRI scans using a technique that minimizes laterality bias.

RESULTS

We found a non-significant trend for right > left (R > L) asymmetry in controls at both time points (R > L: 1.7%; CI: -0.3-3.7%; p = 0.1). AD subjects showed a similar non-significant trend for R > L asymmetry at baseline (R > L: 1.8%; CI: -1.9-5.5%; p = 0.32), but not at repeat (p = 0.739). Change in R/L ratio between visits in AD patients was significant (p = 0.02). The AD group had significantly higher variance in these ratios than the controls at baseline (p = 0.02), but not repeat (p = 0.06). AD patients had higher atrophy rates than controls (p < 0.001). Mean (CI) annualized atrophy rates for left and right hippocampi were 1.2% (0.5-1.8%) and 1.1% (0.5-1.8%) for the controls, and 4.6% (3.3-6.0%) and 6.3% (4.9-7.8%) for AD subjects. There was no significant asymmetry in atrophy rates in controls (p = 0.9), but borderline significantly higher atrophy rates in the right hippocampus of the AD group (p = 0.05) compared to the left. Presence of an APOEepsilon4 allele had no significant effect on the size, asymmetry or atrophy rates in AD (p > 0.20).

CONCLUSIONS

We report minor R > L asymmetry in hippocampal volumes in controls and present some evidence to suggest that there is a change in the natural R > L asymmetry during the progression of AD.

MR-based in vivo hippocampal volumetrics: 2. Findings in neuropsychiatric disorders

Magnetic resonance imaging (MRI) has opened a new window to the brain. Measuring hippocampal volume with MRI has provided important information about several neuropsychiatric disorders. We reviewed the literature and selected all English-language, human subject, data-driven papers on hippocampal volumetry, yielding a database of 423 records. Smaller hippocampal volumes have been reported in epilepsy, Alzheimer's disease, dementia, mild cognitive impairment, the aged, traumatic brain injury, cardiac arrest, Parkinson's disease, Huntington's disease, Cushing's disease, herpes simplex encephalitis, Turner's syndrome, Down's syndrome, survivors of low birth weight, schizophrenia, major depression, posttraumatic stress disorder, chronic alcoholism, borderline personality disorder, obsessive-compulsive disorder, and antisocial personality disorder. Significantly larger hippocampal volumes have been correlated with autism and children with fragile X syndrome. Preservation of hippocampal volume has been reported in congenital hyperplasia, children with fetal alcohol syndrome, anorexia nervosa, attention-deficit and hyperactivity disorder, bipolar disorder, and panic disorder. Possible mechanisms of hippocampal volume loss in neuropsychiatric disorders are discussed.

Differentiating AD from aging using semiautomated measurement of hippocampal atrophy rates

Manual segmentation of the hippocampus is the gold standard in volumetric hippocampal magnetic resonance imaging (MRI) analysis; however, this is difficult to achieve reproducibly. This study explores whether application of local registration and calculation of the hippocampal boundary shift integral (HBSI) can reduce random variation compared with manual measures. Hippocampi were outlined on the baseline and registered-repeat MRIs of 32 clinically diagnosed Alzheimer's disease (AD) patients and 47 matched controls (37-86 years) with a wide range of scanning intervals (175-1173 days). The scans were globally registered using 9 degrees of freedom and subsequently locally registered using 6 degrees of freedom and HBSI was then calculated automatically. HBSI significantly reduced the mean rate (P < 0.01) and variation in controls (P < 0.001) and increased group separation between AD cases and controls. When comparing HBSI atrophy rates with manually derived atrophy rates at 90% sensitivity, specificities were 98% and 81%, respectively. From logistic regression models, a 1% increase in HBSI atrophy rates was associated with an 11-fold (CI 3, 36) increase in the odds of a diagnosis of AD. For manually derived atrophy rates, the equivalent odds ratio was 3 (CI 2,4). We conclude that HBSI-derived atrophy rates reduce operator time and error, and are at least as effective as the manual equivalent as a diagnostic marker and are a potential marker of progression in longitudinal studies and trials.

A unified approach for morphometric and functional data analysis in young, old, and demented adults using automated atlas-based head size normalization: reliability and validation against manual measurement of total intracranial volume

Atlas normalization, as commonly used by functional data analysis, provides an automated solution to the widely encountered problem of correcting for head size variation in regional and whole-brain morphometric analyses, so long as an age- and population-appropriate target atlas is used. In the present article, we develop and validate an atlas normalization procedure for head size correction using manual total intracranial volume (TIV) measurement as a reference. The target image used for atlas transformation consisted of a merged young and old-adult template specifically created for cross age-span normalization. Automated atlas transformation generated the Atlas Scaling Factor (ASF) defined as the volume-scaling factor required to match each individual to the atlas target. Because atlas normalization equates head size, the ASF should be proportional to TIV. A validation analysis was performed on 147 subjects to evaluate ASF as a proxy for manual TIV measurement. In addition, 19 subjects were imaged on multiple days to assess test-retest reliability. Results indicated that the ASF was (1) equivalent to manual TIV normalization (r = 0.93), (2) reliable across multiple imaging sessions (r = 1.00; mean absolute percentage of difference = 0.51%), (3) able to connect between-gender head size differences, and (4) minimally biased in demented older adults with marked atrophy. Hippocampal volume differences between nondemented (n = 49) and demented (n = 50) older adults (measured manually) were equivalent whether corrected using manual TIV or automated ASF (effect sizes of 1.29 and 1.46, respectively). To provide normative values, ASF was used to automatically derive estimated TIV (eTIV) in 335 subjects aged 15-96 including both clinically characterized nondemented (n = 77) and demented (n = 90) older adults. Differences in eTIV between nondemented and demented groups were negligible, thus failing to support the hypothesis that large premorbid brain size moderates Alzheimer's disease. Gender was the only robust factor that influenced eTIV. Men showed an approximately approximately 12% larger eTIV than women. These results demonstrate that atlas normalization using appropriate template images provides a robust, automated method for head size correction that is equivalent to manual TIV correction in studies of aging and dementia. Thus, atlas normalization provides a common framework for both morphometric and functional data analysis.

Frontal-Hippocampal Double Dissociation Between Normal Aging and Alzheimer's Disease

Controversy persists regarding whether Alzheimer's disease (AD) is a distinct entity or instead exists on a continuum with nondemented aging. To explore this issue, volumetric analyses of callosal and hippocampal regions were performed on 150 participants aged 18-93 years. Group-level analyses revealed that nondemented age-related differences were greater in anterior than posterior callosal regions and were not augmented by early-stage AD. In contrast, early-stage AD was associated with substantial reduction in hippocampal volume. Examination of the 100 older adults using regression analyses demonstrated age-associated differences in callosal volume that were similar in demented and nondemented individuals. Early-stage AD was again characterized by a marked reduction in hippocampal volume while age alone induced only mild differences in hippocampal volume. As a final analysis, the formal double dissociation was confirmed by comparing the effects of age directly against the effects of dementia. These results suggest a multiple-component model of aging. One process, associated with AD, manifests early and prominently in the medial temporal lobe. A separate process, ubiquitous in aging, affects brain white matter with an anterior-to-posterior gradient and may underlie the executive difficulties common in aging.

MRI and CSF studies in the early diagnosis of Alzheimer's disease

The main goal of our studies has been to use MRI, FDG-PET, and CSF biomarkers to identify in cognitively normal elderly (NL) subjects and in patients with mild cognitive impairment (MCI), the earliest clinically detectable evidence for brain changes due to Alzheimer's disease (AD). A second goal has been to describe the cross-sectional and longitudinal interrelationships amongst anatomical, CSF and cognition measures in these patient groups. It is now well known that MRI-determined hippocampal atrophy predicts the conversion from MCI to AD. In our summarized studies, we show that the conversion of NL subjects to MCI can also be predicted by reduced entorhinal cortex (EC) glucose metabolism, and by the rate of medial temporal lobe atrophy as determined by a semi-automated regional boundary shift analysis (BSA-R). However, whilst atrophy rates are predictive under research conditions, they are not specific for AD and cannot be used as primary evidence for AD. Consequently, we will also review our effort to improve the diagnostic specificity by evaluating the use of CSF biomarkers and to evaluate their performance in combination with neuroimaging. Neuropathology studies of normal ageing and MCI identify the hippocampal formation as an early locus of neuronal damage, tau protein pathology, elevated isoprostane levels, and deposition of amyloid beta 1-42 (Abeta42). Many CSF studies of MCI and AD report elevated T-tau levels (a marker of neuronal damage) and reduced Abeta42 levels (possibly due to increased plaque sequestration). However, CSF T-tau and Abeta42 level elevations may not be specific to AD. Elevated isoprostane levels are also reported in AD and MCI but these too are not specific for AD. Importantly, it has been recently observed that CSF levels of P-tau, tau hyperphosphorylated at threonine 231 (P-tau231) are uniquely elevated in AD and elevations found in MCI are useful in predicting the conversion to AD. In our current MCI studies, we are examining the hypothesis that elevations in P-tau231 are accurate and specific indicators of AD-related changes in brain and cognition. In cross-section and longitudinally, our results show that evaluations of the P-tau231 level are highly correlated with reductions in the MRI hippocampal volume and by using CSF and MRI measures together one improves the separation of NL and MCI. The data suggests that by combining MRI and CSF measures, an early (sensitive) and more specific diagnosis of AD is at hand. Numerous studies show that neither T-tau nor P-tauX (X refers to all hyper-phosphorylation site assays) levels are sensitive to the longitudinal progression of AD. The explanation for the failure to observe longitudinal changes is not known. One possibility is that brain-derived proteins are diluted in the CSF compartment. We recently used MRI to estimate ventricular CSF volume and demonstrated that an MRI-based adjustment for CSF volume dilution enables detection of a diagnostically useful longitudinal P-tau231 elevation. Curiously, our most recent data show that the CSF isoprostane level does show significant longitudinal elevations in MCI in the absence of dilution correction. In summary, we conclude that the combined use of MRI and CSF incrementally contributes to the early diagnosis of AD and to monitor the course of AD. The interim results also suggest that a panel of CSF biomarkers can provide measures both sensitive to longitudinal change as well as measures that lend specificity to the AD diagnosis.

Quantitative magnetic resonance techniques as surrogate markers of Alzheimer's disease

Recent advances in understanding the molecular biology of Alzheimer's disease (AD) offer the promise of useful therapeutic intervention in the foreseeable future. Hence, improved methods for early diagnosis and noninvasive surrogates of disease severity in AD have become more imperative. Various quantitative magnetic resonance (MR) techniques that measure the anatomic, biochemical, microstructural, functional, and blood-flow changes are being evaluated as possible surrogate measures of disease progression. Cross-sectional and longitudinal studies indicate that MR-based volume measurements are potential surrogates of disease progression in AD, starting from the preclinical stages. The validity of MR-based volumetry as a surrogate marker for therapeutic efficacy in AD remains to be tested in a positive disease-modifying drug trial. Recent development of amyloid imaging tracers for positron emission tomography has been a major breakthrough in the field of imaging markers for AD. Efforts to image plaques are also underway in MR imaging. As with indirect MR measures, these approaches of directly imaging the pathological substrate will need to undergo a validation process with longitudinal studies to prove their usefulness as surrogate markers in AD.

Changes in hippocampal volume and shape across time distinguish dementia of the Alzheimer type from healthy aging☆

Rates of hippocampal volume loss have been shown to distinguish subjects with dementia of the Alzheimer type (DAT) from nondemented controls. In this study, we obtained magnetic resonance scans in 18 subjects with very mild DAT (CDR 0.5) and 26 age-matched nondemented controls (CDR 0) 2 years apart. Large-deformation high-dimensional brain mapping was used to quantify and compare changes in hippocampal shape as well as volume in the two groups of subjects. Hippocampal volume loss over time was significantly greater in the CDR 0.5 subjects (left = 8.3%, right = 10.2%) than in the CDR 0 subjects (left = 4.0%, right = 5.5%) (ANOVA, F = 7.81, P = 0.0078). We used singular-value decomposition and logistic regression models to quantify hippocampal shape change across time within individuals, and this shape change in the CDR 0.5 and CDR 0 subjects was found to be significantly different (Wilks's lambda, P = 0.014). Further, at baseline, CDR 0.5 subjects, in comparison to CDR 0 subjects, showed inward deformation over 38% of the hippocampal surface; after 2 years this difference grew to 47%. Also, within the CDR 0 subjects, shape change between baseline and follow-up was largely confined to the head of the hippocampus and subiculum, while in the CDR 0.5 subjects, shape change involved the lateral body of the hippocampus as well as the head region and subiculum. These results suggest that different patterns of hippocampal shape change in time as well as different rates of hippocampal volume loss distinguish very mild DAT from healthy aging.

Dissociating hippocampal versus basal ganglia contributions to learning and transfer

Based on prior animal and computational models, we propose a double dissociation between the associative learning deficits observed in patients with medial temporal (hippocampal) damage versus patients with Parkinson's disease (basal ganglia dysfunction). Specifically, we expect that basal ganglia dysfunction may result in slowed learning, while individuals with hippocampal damage may learn at normal speed. However, when challenged with a transfer task where previously learned information is presented in novel recombinations, we expect that hippocampal damage will impair generalization but basal ganglia dysfunction will not. We tested this prediction in a group of healthy elderly with mild-to-moderate hippocampal atrophy, a group of patients with mild Parkinson's disease, and healthy controls, using an "acquired equivalence" associative learning task. As predicted, Parkinson's patients were slower on the initial learning but then transferred well, while the hippocampal atrophy group showed the opposite pattern: good initial learning with impaired transfer. To our knowledge, this is the first time that a single task has been used to demonstrate a double dissociation between the associative learning impairments caused by hippocampal versus basal ganglia damage/dysfunction. This finding has implications for understanding the distinct contributions of the medial temporal lobe and basal ganglia to learning and memory.

Hippocampal atrophy disrupts transfer generalization in nondemented elderly

Specific reductions in hippocampal volume in nondemented elderly individuals with mild cognitive impairment have been shown to correlate with future development of Alzheimer's disease (AD). Hippocampal atrophy (HA) is also correlated with cognitive impairments, leading to the promise of behavioral markers for early AD. Prior theoretical work has suggested that hippocampal dysfunction may selectively impair generalization involving novel recombinations of familiar stimuli. In this study, nondemented elderly individuals were trained on a series of concurrent visual discriminations and were then tested for transfer when stimulus features were recombined in new ways. Presence or absence of HA, revealed by neuroimaging, was not correlated with concurrent discrimination performance; however, individuals with mild HA showed significant decreases in transfer performance relative to nonatrophied participants. These preliminary results suggest that even very mild degrees of hippocampal atrophy may be associated with subtle behavioral impairments.

Early diagnosis of Alzheimer's disease: contribution of structural neuroimaging

To accurately predict the development of Alzheimer's disease (AD) at its predementia stage would be a major breakthrough from both therapeutic and research standpoints. In this review, our focus is on markers obtained with structural imaging--especially magnetic resonance imaging (MRI)--and on studies of subjects at risk of developing AD. Among the latter, amnestic mild cognitive impairment (MCI) is currently the most commonly accepted reference, and therefore is specially targeted in this review. MCI refers to patients with significant but isolated memory impairment relative to subjects of identical age. Consistent with established histopathological data, structural imaging studies comparing patients with early probable AD to healthy aged subjects have shown that the most specific and sensitive features of AD at this stage are hippocampal and entorhinal cortex atrophy, especially when combined with a reduced volume of the temporal neocortex. MCI patients have significant hippocampal atrophy when compared to aged normal controls. When comparing patients with probable AD to MCI subjects, hippocampal region atrophy significantly extends to the neighboring temporal association neocortex. However, only longitudinal studies of MCI subjects are suited to assess (in a retrospective way) the predictive value of initial atrophy measurements for progression to AD. Few such studies have been published so far and for the most they were based on small samples. Furthermore, the comparison among studies is clouded by differences in both populations studied and MRI methodology used. Nevertheless, comparing the initial MRI data of at-risk subjects who convert to AD at follow-up to those of nonconverters suggests that a reduced association temporal neocortex volume combined with hippocampal or anterior cingulate cortex atrophy may be the best predictor of progression to AD. These data, although still preliminary, are consistent with postmortem studies describing the hierarchical progression of tau lesions in normal aging and early stages of AD, such that damage to the medial temporal lobe and association cortex would account for the memory and nonmemory cognitive impairments, respectively, the combination of which is required to operationally define probable AD. Future research in this field should capitalize on thorough methodology for brain structure delineation, and combine atrophy measurements to cognitive and/or functional imaging data.

Volumetric MRI predicts rate of cognitive decline related to AD and cerebrovascular disease

OBJECTIVE

To examine volumetric MRI correlates of longitudinal cognitive decline in normal aging, AD, and subcortical cerebrovascular brain injury (SCVBI).

BACKGROUND

Previous cross-sectional studies examining the relationship between cognitive impairment and dementia have shown that hippocampal and cortical gray matter atrophy are the most important predictors of cognitive impairment, even in cases with SCVBI. The authors hypothesized that hippocampal and cortical gray matter volume also would best predict rate of cognitive decline in cases with and without SCVBI.

METHODS

Subjects were recruited for a multicenter study of contributions to dementia of AD and SCVBI. The sample (n = 120) included cognitively normal, cognitively impaired, and demented cases with and without lacunes identified by MRI. Cases with cortical strokes were excluded. Average length of follow-up was 3.0 years. Measures of hippocampal volume, volume of cortical gray matter, presence of subcortical lacunes, and volume of white matter hyperintensity were derived from MRI. Random effects modeling of longitudinal data was used to assess effects of baseline MRI variables on longitudinal change in a measure of global cognitive ability.

RESULTS

Cortical gray matter atrophy predicted cognitive decline regardless of whether lacunes were present. Hippocampal atrophy predicted decline only in those without lacunes. Neither lacunes nor white matter hyperintensity independently predicted decline.

CONCLUSIONS

Results suggest that cortical atrophy is an index of disease severity in both AD and subcortical cerebrovascular brain injury and consequently predicts faster progression. Hippocampal volume may index disease severity and predict progression in AD. The absence of this effect in cases with lacunes suggests that this group is etiologically heterogeneous and is not composed simply of cases of AD with incidental stroke.

Hippocampal atrophy in persons with age-associated memory impairment: volumetry within a common space

OBJECTIVE

The objective of this study is to demonstrate the assessment of hippocampal atrophy within a standard brain atlas for persons with age-associated memory impairment (AAMI) compared with cognitively intact elderly.

METHODS

High-resolution three-dimensional (3D) brain magnetic resonance imaging (MRI) was performed on 20 nondemented persons: 10 had AAMI and 10 were normal elderly. Scans were aligned to a common atlas template to control for errors due to variable brain size and orientation as well as facilitating communication of results across centers. Manual outlining every 1 mm with volumes determined for both the hippocampal head and body was accomplished after coronal resampling perpendicular to the long axis of the hippocampus.

RESULTS

Subject groups were similar in age, sex ratios, and educational achievement. The AAMI group had significantly lower volumes for the right hippocampus and hippocampal head (p =.02) compared with controls.

CONCLUSION

A growing body of work suggests the right hippocampal head as an early site of atrophy in early memory impairment. Subtle atrophic changes are detectable within a common atlas template allowing imaging assessment across centers.

MRI measures of entorhinal cortex vs hippocampus in preclinical AD

BACKGROUND

MRI measures of the entorhinal cortex and the hippocampus have been used to predict which nondemented individuals with memory problems will progress to meet criteria for AD on follow-up, but their relative accuracy remains controversial.

OBJECTIVES

To compare MRI measures of the entorhinal cortex and the hippocampus for predicting who will develop AD.

METHODS

MRI volumes of the entorhinal cortex and the hippocampus were obtained in 137 individuals comprising four groups: 1) individuals with normal cognition both at baseline and after 3 years of follow-up (n = 28), 2) subjects with memory difficulty but not dementia both at baseline and after 3 years of follow-up (n = 73), 3) subjects with memory difficulty at baseline who were diagnosed with probable AD within 3 years of follow-up (n = 21), and 4) patients with mild AD at baseline (n = 16).

RESULTS

Measures of both the entorhinal cortex and the hippocampus were different for each of the pairwise comparisons between the groups (p < 0.001) and were correlated with tests of memory (p < 0.01). However, the volume of the entorhinal cortex differentiated the subjects from those destined to develop dementia with considerable accuracy (84%), whereas the measure of the hippocampus did not.

CONCLUSION

These findings are consistent with neuropathologic data showing substantial involvement of the entorhinal cortex in the preclinical phase of AD and suggest that, as the disease spreads, atrophic change develops within the hippocampus, which is measurable on MRI.