Medial temporal atrophy and memory impairment in early stage of Alzheimer's disease: an MRI volumetric and memory assessment study

Amidst an amygdala renaissance in Alzheimer's disease

The amygdala was highlighted as an early site for neurofibrillary tau tangle pathology in Alzheimer's disease in the seminal 1991 article by Braak and Braak. This knowledge has, however, only received traction recently with advances in imaging and image analysis techniques. Here, we provide a cross-disciplinary overview of pathology and neuroimaging studies on the amygdala. These studies provide strong support for an early role of the amygdala in Alzheimer's disease and the utility of imaging biomarkers of the amygdala in detecting early changes and predicting decline in cognitive functions and neuropsychiatric symptoms in early stages. We summarize the animal literature on connectivity of the amygdala, demonstrating that amygdala nuclei that show the earliest and strongest accumulation of neurofibrillary tangle pathology are those that are connected to brain regions that also show early neurofibrillary tangle accumulation. Additionally, we propose an alternative pathway of neurofibrillary tangle spreading within the medial temporal lobe between the amygdala and the anterior hippocampus. The proposed existence of this pathway is strengthened by novel experimental data on human functional connectivity. Finally, we summarize the functional roles of the amygdala, highlighting the correspondence between neurofibrillary tangle accumulation and symptomatic profiles in Alzheimer's disease. In summary, these findings provide a new impetus for studying the amygdala in Alzheimer's disease and a unique perspective to guide further study on neurofibrillary tangle spreading and the occurrence of neuropsychiatric symptoms in Alzheimer's disease.

A review of neuroimaging-based data-driven approach for Alzheimer's disease heterogeneity analysis

Alzheimer's disease (AD) is a complex form of dementia and due to its high phenotypic variability, its diagnosis and monitoring can be quite challenging. Biomarkers play a crucial role in AD diagnosis and monitoring, but interpreting these biomarkers can be problematic due to their spatial and temporal heterogeneity. Therefore, researchers are increasingly turning to imaging-based biomarkers that employ data-driven computational approaches to examine the heterogeneity of AD. In this comprehensive review article, we aim to provide health professionals with a comprehensive view of past applications of data-driven computational approaches in studying AD heterogeneity and planning future research directions. We first define and offer basic insights into different categories of heterogeneity analysis, including spatial heterogeneity, temporal heterogeneity, and spatial-temporal heterogeneity. Then, we scrutinize 22 articles relating to spatial heterogeneity, 14 articles relating to temporal heterogeneity, and five articles relating to spatial-temporal heterogeneity, highlighting the strengths and limitations of these strategies. Furthermore, we discuss the importance of understanding spatial heterogeneity in AD subtypes and their clinical manifestations, biomarkers for abnormal orderings and AD stages, the recent advancements in spatial-temporal heterogeneity analysis for AD, and the emerging role of omics data integration in advancing personalized diagnosis and treatment for AD patients. By emphasizing the significance of understanding AD heterogeneity, we hope to stimulate further research in this field to facilitate the development of personalized interventions for AD patients.

Contributions of hippocampal subfields and subregions to episodic memory performance in healthy cognitive aging

In the present study we investigated whether hippocampal subfield (cornu ammonis 1-3, dentate gyrus, and subiculum) and anteroposterior hippocampal subregion (head,body, and tail) volumes can predict episodic memory function using high-field high resolution structural magnetic resonance imaging (MRI). We recruited 126 healthy participants (18-85 years). MRI datasets were collected on a 4.7 T system. Participants were administered the Wechsler Memory Scale (WMS-IV) to evaluate episodic memory function. Structural equation modeling was used to test the relationship between studied variables. We found that the volume of the dentate gyrus subfield and posterior hippocampus (body) showed a significant direct effect on visuospatial memory performance; additionally, an indirect effect of age on visuospatial memory mediated through these hippocampal subfield/subregion was significant. Logical and verbal memory were not significantly associated with hippocampal subfield or subregion volumes.

Profiling baseline performance on the Longitudinal Early-Onset Alzheimer's Disease Study (LEADS) cohort near the midpoint of data collection

OBJECTIVE

The Longitudinal Early-Onset Alzheimer's Disease Study (LEADS) seeks to provide comprehensive understanding of early-onset Alzheimer's disease (EOAD; onset <65 years), with the current study profiling baseline clinical, cognitive, biomarker, and genetic characteristics of the cohort nearing the data-collection mid-point.

METHODS

Data from 371 LEADS participants were compared based on diagnostic group classification (cognitively normal [n = 89], amyloid-positive EOAD [n = 212], and amyloid-negative early-onset non-Alzheimer's disease [EOnonAD; n = 70]).

RESULTS

Cognitive performance was worse for EOAD than other groups, and EOAD participants were apolipoprotein E (APOE) ε4 homozygotes at higher rates. An amnestic presentation was common among impaired participants (81%), with several clinical phenotypes present. LEADS participants generally consented at high rates to optional trial procedures.

CONCLUSIONS

We present the most comprehensive baseline characterization of sporadic EOAD in the United States to date. EOAD presents with widespread cognitive impairment within and across clinical phenotypes, with differences in APOE ε4 allele carrier status appearing to be relevant.

HIGHLIGHTS

Findings represent the most comprehensive baseline characterization of sporadic early-onset Alzheimer's disease (EOAD) to date. Cognitive impairment was widespread for EOAD participants and more severe than other groups. EOAD participants were homozygous apolipoprotein E (APOE) ε4 carriers at higher rates than the EOnonAD group. Amnestic presentation predominated in EOAD and EOnonAD participants, but other clinical phenotypes were present.

Amygdala activity and amygdala-hippocampus connectivity: Metabolic diseases, dementia, and neuropsychiatric issues

With rapid aging of the population worldwide, the number of people with dementia is dramatically increasing. Some studies have emphasized that metabolic syndrome, which includes obesity and diabetes, leads to increased risks of dementia and cognitive decline. Factors such as insulin resistance, hyperglycemia, high blood pressure, dyslipidemia, and central obesity in metabolic syndrome are associated with synaptic failure, neuroinflammation, and imbalanced neurotransmitter levels, leading to the progression of dementia. Due to the positive correlation between diabetes and dementia, some studies have called it "type 3 diabetes". Recently, the number of patients with cognitive decline due to metabolic imbalances has considerably increased. In addition, recent studies have reported that neuropsychiatric issues such as anxiety, depressive behavior, and impaired attention are common factors in patients with metabolic disease and those with dementia. In the central nervous system (CNS), the amygdala is a central region that regulates emotional memory, mood disorders, anxiety, attention, and cognitive function. The connectivity of the amygdala with other brain regions, such as the hippocampus, and the activity of the amygdala contribute to diverse neuropathological and neuropsychiatric issues. Thus, this review summarizes the significant consequences of the critical roles of amygdala connectivity in both metabolic syndromes and dementia. Further studies on amygdala function in metabolic imbalance-related dementia are needed to treat neuropsychiatric problems in patients with this type of dementia.

7T amygdala and hippocampus subfields in volumetry-based associations with memory: A 3-year follow-up study of early Alzheimer's disease

INTRODUCTION

The hippocampus is the most prominent single region of interest (ROI) for the diagnosis and prediction of Alzheimer's disease (AD). However, its suitability in the earliest stages of cognitive decline, i.e., subjective cognitive decline (SCD), remains uncertain which warrants the pursuit of alternative or complementary regions. The amygdala might be a promising candidate, given its implication in memory as well as other psychiatric disorders, e.g. depression and anxiety, which are prevalent in SCD. In this 7 tesla (T) magnetic resonance imaging (MRI) study, we aimed to compare the contribution of volumetric measurements of the hippocampus, the amygdala, and their respective subfields, for early diagnosis and prediction in an AD-related study population.

METHODS

Participants from a longitudinal study were grouped into SCD (n = 29), mild cognitive impairment (MCI, n = 23), AD (n = 22) and healthy control (HC, n = 31). All participants underwent 7T MRI at baseline and extensive neuropsychological testing at up to three visits (baseline n = 105, 1-year n = 78, 3-year n = 39). Analysis of covariance (ANCOVA) was used to assess group differences of baseline volumes of the amygdala and the hippocampus and their subfields. Linear mixed models were used to estimate the effects of baseline volumes on yearly changes of a z-scaled memory score. All models were adjusted to age, sex and education.

RESULTS

Compared to the HC group, individuals with SCD showed smaller amygdala ROI volumes (range across subfields -11% to -1%), but not hippocampus ROI volumes (-2% to 1%) except for the hippocampus-amygdala-transition-area (-7%). However, cross-sectional associations between baseline memory and volumes were smaller for amygdala ROIs (std. ß [95% CI] ranging between 0.16 [0.08; 0.25] and 0.46 [0.31; 0.60]) than hippocampus ROIs (between 0.32 [0.19; 0.44] and 0.53 [0.40; 0.67]). Further, the association of baseline volumes with yearly memory change in the HC and SCD groups was similarly weak for amygdala ROIs and hippocampus ROIs. In the MCI group, volumes of amygdala ROIs were associated with a relevant yearly memory decline [95% CI] ranging between -0.12 [-0.24; 0.00] and -0.26 [-0.42; -0.09] for individuals with 20% smaller volumes than the HC group. However, effects were stronger for hippocampus ROIs with a corresponding yearly memory decline ranging between -0.21 [-0.35; -0.07] and -0.31 [-0.50; -0.13].

CONCLUSION

Volumes of amygdala ROIs, as determined by 7T MRI, might contribute to objectively and non-invasively identify patients with SCD, and thus aid early diagnosis and treatment of individuals at risk to develop dementia due to AD, however associations with other psychiatric disorders should be evaluated in further studies. The amygdala's value in the prediction of longitudinal memory changes in the SCD group remains questionable. Primarily in patients with MCI, memory decline over 3 years appears to be more strongly associated with volumes of hippocampus ROIs than amygdala ROIs.

Neuroimaging and verbal memory assessment in healthy aging adults using a portable low-field MRI scanner and a web-based platform: results from a proof-of-concept population-based cross-section study

Consumer wearables and health monitors, internet-based health and cognitive assessments, and at-home biosample (e.g., saliva and capillary blood) collection kits are increasingly used by public health researchers for large population-based studies without requiring intensive in-person visits. Alongside reduced participant time burden, remote and virtual data collection allows the participation of individuals who live long distances from hospital or university research centers, or who lack access to transportation. Unfortunately, studies that include magnetic resonance neuroimaging are challenging to perform remotely given the infrastructure requirements of MRI scanners, and, as a result, they often omit socially, economically, and educationally disadvantaged individuals. Lower field strength systems (< 100 mT) offer the potential to perform neuroimaging at a participant's home, enabling more accessible and equitable research. Here we report the first use of a low-field MRI "scan van" with an online assessment of paired-associate learning (PAL) to examine associations between brain morphometry and verbal memory performance. In a sample of 67 individuals, 18-93 years of age, imaged at or near their home, we show expected white and gray matter volume trends with age and find significant (p < 0.05 FWE) associations between PAL performance and hippocampus, amygdala, caudate, and thalamic volumes. High-quality data were acquired in 93% of individuals, and at-home scanning was preferred by all individuals with prior MRI at a hospital or research setting. Results demonstrate the feasibility of remote neuroimaging and cognitive data collection, with important implications for engaging traditionally under-represented communities in neuroimaging research.

Consideration of different scoring approaches for a verbal incidental learning measure from the WAIS-IV using hippocampal volumes

Objective: While Spencer's verbal incidental learning (IL) task-from Vocabulary and Similarities subtests of the WAIS-has been validated relative to traditional memory measures and Alzheimer's disease (AD) pathology, the effectiveness of the particular scoring method used has not been assessed relative to alternative scoring weightings. The purpose of this study was to compare original and alternative scoring methods of this IL task by using an AD biomarker-benchmark to arrive at an optimal approach. Methods: Fifty-five memory-clinic patients aged 59-87 received neuropsychological assessment, measures of IL, and quantitative brain imaging. Partial correlation coefficients with total hippocampal volume-controlling for age, sex, and intracranial volume-were assessed across several IL scoring methods, and partial correlations with measures of memory were examined to evaluate convergent validity.Results: IL scoring methods maximizing the contribution of paired-associate-recall-performance were significantly correlated with both hippocampal volumes and traditional memory measures, whereas discrimination-emphasized scoring methods were not.Conclusions: IL scoring methods emphasizing memory paired-associate recall appeared to be preferable to those emphasizing memory discrimination. Administration of the IL- Similarities subtest alone, without IL- Vocabulary, may strike a balance between strength of relationships with both hippocampal volumes and standard memory measures, while also limiting administration time.

Relationship between a novel learning slope metric and Alzheimer's disease biomarkers

The Learning Ratio (LR) is a novel learning score examining the proportion of information learned over successive learning trials relative to information available to be learned. Validation is warranted to understand LR's sensitivity to Alzheimer's disease (AD) pathology. One-hundred twenty-three participants across the AD continuum underwent memory assessment, quantitative brain imaging, and genetic analysis. LR scores were calculated from the HVLT-R, BVMT-R, RBANS List Learning, and RBANS Story Memory, and compared to total hippocampal volumes,18F-Flutemetamol composite SUVR uptake, and APOE ε4 status. Lower LR scores were consistently associated with smaller total hippocampal volumes, greater cerebral β-amyloid deposition, and APOE ε4 positivity. This LR score outperformed a traditional learning slope calculation in all analyses. LR is sensitive to AD pathology along the AD continuum - more so than a traditional raw learning score - and reducing the competition between the first trial and subsequent trials can better depict learning capacity.

Emotional Valence Affects Word Retrieval During Verb Fluency Tasks in Alzheimer's Dementia

Individuals with amnestic Alzheimer's disease (AD) often demonstrate preserved emotional processing skills despite the neurodegenerative disease that affects their limbic system. Emotional valence encompasses the encoding and retrieval of memory and it also affects word retrieval in healthy populations, but it remains unclear whether these effects are preserved in individuals with amnestic AD. Previous studies used a variety of encoding procedures and different retrieval methods that resulted in mixed findings. Therefore, the purpose of the current study is to investigate whether emotional enhancement of memory effects is observed in an experimental condition where the memory encoding process is not required, namely verb (action) fluency tasks. Seventeen participants who were cognitively healthy older adults (CHOA) and 15 participants with amnestic AD were asked to complete verb fluency tasks, and the relative degree of emotional valence observed in their responses was compared between the two groups. A neuropsychological test battery was administered to determine the participants' cognitive and linguistic profiles, and correlational analyses were conducted to delineate relationships between emotional valence, verbal memory, and learning abilities. The results indicated that the participants with amnestic AD produced words with higher emotional valence (i.e., more pleasant words) compared to CHOA during action fluency testing. In addition, the degree of emotional valence in the words was negatively correlated with verbal memory and learning skills, showing that those with poorer memory skills tend to retrieve words with higher emotional valence. The findings are consistent with those previous studies that stressed that individuals with AD have preserved emotional enhancement of memory effects and may benefit from them for retrieval of information, which may offer some insight into the development of novel rehabilitative strategies for this population.

Preliminary Validation of the Learning Ratio for the HVLT-R and BVMT-R in Older Adults

BACKGROUND

The learning slope is typically represented as the raw difference between the final score and the score of the first learning trial. A new method for calculating the learning slope, the learning ratio (LR), was recently developed; it is typically represented as the number of items that are learned after the first trial divided by the number of items that are yet to be learned.

OBJECTIVE

To evaluate the convergent and criterion validity of the LR in order to understand its sensitivity to Alzheimer disease (AD) pathology.

METHOD

Fifty-six patients from a memory clinic underwent standard neuropsychological assessment and quantitative brain imaging. LR scores were calculated from the Hopkins Verbal Learning Test-Revised and the Brief Visuospatial Memory Test-Revised and were compared with both standard memory measures and total hippocampal volumes, as well as between individuals with AD and those with mild cognitive impairment.

RESULTS

Lower LR scores were consistently associated with poorer performances on standard memory measures and smaller total hippocampal volumes, generally more so than traditional learning slope scores. The LR scores of the AD group were smaller than those of the group with mild cognitive impairment. Furthermore, the aggregation of LR scores into a single metric was partially supported.

CONCLUSION

The LR is sensitive to AD pathology along the AD continuum. This result supports previous claims that the LR score can reflect learning capacity better than traditional learning calculations can by considering the amount of information that is learned at trial 1.

A Review of Brain Atrophy Subtypes Definition and Analysis for Alzheimer’s Disease Heterogeneity Studies

Alzheimer’s disease (AD) is a heterogeneous disease with different subtypes. Studying AD subtypes from brain structure, neuropathology, and cognition are of great importance for AD heterogeneity research. Starting from the study of constructing AD subtypes based on the features of T1-weighted structural magnetic resonance imaging, this paper introduces the major connections between the subtype definition and analysis strategies, including brain region-based subtype definition, and their demographic, neuropathological, and neuropsychological characteristics. The advantages and existing problems are analyzed, and reasonable improvement schemes are prospected. Overall, this review offers a more comprehensive view in the field of atrophy subtype in AD, along with their advantages, challenges, and future prospects, and provide a basis for improving individualized AD diagnosis.

Early Long-Term Memory Impairment and Changes in the Expression of Synaptic Plasticity-Associated Genes, in the McGill-R-Thy1-APP Rat Model of Alzheimer's-Like Brain Amyloidosis

Accruing evidence supports the hypothesis that memory deficits in early Alzheimer Disease (AD) might be due to synaptic failure caused by accumulation of intracellular amyloid beta (Aβ) oligomers, then secreted to the extracellular media. Transgenic mouse AD models provide valuable information on AD pathology. However, the failure to translate these findings to humans calls for models that better recapitulate the human pathology. McGill-R-Thy1-APP transgenic (Tg) rat expresses the human amyloid precursor protein (APP751) with the Swedish and Indiana mutations (of familial AD), leading to an AD-like slow-progressing brain amyloid pathology. Therefore, it offers a unique opportunity to investigate learning and memory abilities at early stages of AD, when Aβ accumulation is restricted to the intracellular compartment, prior to plaque deposition. Our goal was to further investigate early deficits in memory, particularly long-term memory in McGill-R-Thy1-APP heterozygous (Tg+/–) rats. Short-term- and long-term habituation to an open field were preserved in 3-, 4-, and 6-month-old (Tg+/–). However, long-term memory of inhibitory avoidance to a foot-shock, novel object-recognition and social approaching behavior were seriously impaired in 4-month-old (Tg+/–) male rats, suggesting that they are unable to either consolidate and/or evoke such associative and discriminative memories with aversive, emotional and spatial components. The long-term memory deficits were accompanied by increased transcript levels of genes relevant to synaptic plasticity, learning and memory processing in the hippocampus, such as Grin2b, Dlg4, Camk2b, and Syn1. Our findings indicate that in addition to the previously well-documented deficits in learning and memory, McGill-R-Thy1-APP rats display particular long-term-memory deficits and deep social behavior alterations at pre-plaque early stages of the pathology. This highlights the importance of Aβ oligomers and emphasizes the validity of the model to study AD-like early processes, with potentially predictive value.

Cognitive improvements and reduction in amyloid plaque deposition by saikosaponin D treatment in a murine model of Alzheimer's disease

Alzheimer's disease (AD), is a severe neurodegenerative disease that currently lacks an optimally effective therapeutic agent for its management. Saikosaponin D (SSD) is a component extracted from the herb Bupleurum falcatum that is commonly used in Chinese medicine. Although SSD has been reported to exert neuroprotective effects, its pharmacological role in AD has not been previously elucidated. Therefore, the aim of the present study was to investigate whether SSD treatment improves the cognitive function and pathological features of 3xTg mice, a triple-transgenic mouse model of AD that displays classical pathological features of AD. The effects of SSD treatment on the behavioral, histological and physiological features of the animal were quantified. Results from the behavioral experiments on the SSD-treated 3xTg mice identified a significant reduction in memory impairment. In addition, histological staining results indicated that SSD application could preserve the morphology of neurons, reduce apoptosis and significantly inhibit amyloid-β deposition in the hippocampus of 3xTg mice. SSD treatment also decelerated the activation of microglia and astrocytes in the hippocampus of 3xTg mice, possibly via the inhibition of the NF-κB signal transduction pathway. Therefore, the present study demonstrated the protective effects of SSD against progressive neurodegeneration and identified the potential underlying pharmacological mechanism. It was speculated that SSD may serve as a possible therapeutic agent in AD treatment in the future.

Examining the Relationship between a Verbal Incidental Learning Measure from the WAIS-IV and Neuroimaging Biomarkers for Alzheimer's Pathology

Convergent validation of a verbal incidental learning (IL) task from the WAIS-IV using neuroimaging biomarkers is warranted to understand its sensitivity to Alzheimer's disease (AD) pathology. Fifty-five memory clinic patients aged 59 to 87 years received neuropsychological assessment, and measures of IL and quantitative brain imaging. Worse IL-Total Score and IL-Similarities performances were significantly associated with smaller hemispheric hippocampal volumes. IL measures were not significantly correlated with cerebral β-amyloid burden, though a trend was present and effect sizes were mild. These hippocampal volume results suggest that this IL task may be sensitive to AD pathology along the AD continuum.

Evaluation of Cognitive Function in Relation to Progression of Parkinson Disease

OBJECTIVE

Cognitive impairments are among the nonmotor symptoms in patients with Parkinson disease. Understanding the cognitive impairments in patients with Parkinson disease may be critical for developing effective rehabilitation interventions. The aims of this study were to assess cognitive function in patients with Parkinson disease using the Wechsler Adult Intelligence Scale Third Edition, and the Wechsler Memory Scale Revised and to investigate how cognitive impairments relate to progression of disease in patients with Parkinson disease according to the Hoehn and Yahr stages.

DESIGN

Seventy-eight patients with Parkinson disease participated in the present study. Our study consisted of patients in the following Hoehn and Yahr groups: 1 (no disability, n = 11), 2 (mild, n = 34), 3 (moderate, n = 26), and 4 and 5 (severe, n = 7). Cognitive function was assessed using the Wechsler Adult Intelligence Scale Third Edition, and the Wechsler Memory Scale Revised.

RESULTS

The verbal memory was significantly higher in group 1 (106.4 ± 12.0) than in the other groups (2: 90.5 ± 14.0, 3: 89.9 ± 16.9, 4 and 5: 89.6 ± 11.4). Visual memory and delayed recall were similar to the results seen with verbal memory; however, the differences between groups were not statistically significant. The full-scale IQ was not significantly different (1: 107.3 ± 8.1, 2: 96.9 ± 18.2, 3: 96.7 ± 14.8, 4 and 5: 91.7 ± 9.5).

CONCLUSIONS

These results suggest that a comprehensive assessment focused on memory impairments is important for applying the appropriate interventions in patients with early-stage Parkinson disease.

Decomposed Temporal Complexity Analysis of Neural Oscillations and Machine Learning Applied to Alzheimer's Disease Diagnosis

Despite growing evidence of aberrant neuronal complexity in Alzheimer's disease (AD), it remains unclear how this variation arises. Neural oscillations reportedly comprise different functions depending on their own properties. Therefore, in this study, we investigated details of the complexity of neural oscillations by decomposing the oscillations into frequency, amplitude, and phase for AD patients. We applied resting-state magnetoencephalography (MEG) to 17 AD patients and 21 healthy control subjects. We first decomposed the source time series of the MEG signal into five intrinsic mode functions using ensemble empirical mode decomposition. We then analyzed the temporal complexities of these time series using multiscale entropy. Results demonstrated that AD patients had lower complexity on short time scales and higher complexity on long time scales in the alpha band in temporal regions of the brain. We evaluated the alpha band complexity further by decomposing it into amplitude and phase using Hilbert spectral analysis. Consequently, we found lower amplitude complexity and higher phase complexity in AD patients. Correlation analyses between spectral complexity and decomposed complexities revealed scale-dependency. Specifically, amplitude complexity was positively correlated with spectral complexity on short time scales, whereas phase complexity was positively correlated with spectral complexity on long time scales. Regarding the relevance of cognitive function to the complexity measures, the phase complexity on the long time scale was found to be correlated significantly with the Mini-Mental State Examination score. Additionally, we examined the diagnostic utility of the complexity characteristics using machine learning (ML) methods. We prepared a feature pool using multiple sparse autoencoders (SAEs), chose some discriminating features, and applied them to a support vector machine (SVM). Compared to the simple SVM and the SVM after feature selection (FS + SVM), the SVM with multiple SAEs (SAE + FS + SVM) had improved diagnostic accuracy. Through this study, we 1) advanced the understanding of neuronal complexity in AD patients using decomposed temporal complexity analysis and 2) demonstrated the effectiveness of combining ML methods with information about signal complexity for the diagnosis of AD.

The hippocampal-to-ventricle ratio (HVR): Presentation of a manual segmentation protocol and preliminary evidence

Disentangling age-related changes from developmental variations in hippocampal volume has proven challenging. This article presents a manual segmentation protocol for the hippocampal-to-ventricle ratio (HVR), a measure combining the assessment of hippocampal volume with surrounding ventricular volume. By providing in a single measure both a standard volumetric assessment of the hippocampus and an approximation of volume loss, based on ventricular enlargement, we believe the HVR provides a superior cross-sectional estimation of hippocampal structural integrity. In a first attempt to validate this measure, we contrasted the HVR and standard hippocampal volume in their associations with age and memory performance in two independent cohorts of healthy aging individuals. The first cohort consisted in 50 cognitively normal subjects (mean age: 66.8 years, SD: 4.96, range: 60-75 years), while the second cohort included 88 cognitively normal subjects (mean age: 65.06 years, SD: 6.42, range: 55-80 years). We showed that the manual segmentation protocol for the HVR can be implemented with high reliability. In both cohorts, the HVR showed stronger negative associations with age than standard hippocampal volume. Correlations with memory performance were also numerically superior with the HVR than standard hippocampal volume, across the two cohorts. These findings support an added benefit of using the HVR over standard hippocampal volume when examining relationships with age or memory function in aging individuals. Although further validation is required, we propose that the computation of the HVR is a promising method to improve the evaluation of hippocampal integrity from cross-sectional MR images.

In Vivo Pharmacological Comparison of TAK-071, a Positive Allosteric Modulator of Muscarinic M1 Receptor, and Xanomeline, an Agonist of Muscarinic M1/M4 Receptor, in Rodents

Activation of the M₁ muscarinic acetylcholine receptor (M₁R) may be an effective therapeutic approach for Alzheimer's disease (AD), dementia with Lewy bodies, and schizophrenia. Previously, the M₁R/M₄R agonist xanomeline was shown to improve cognitive function and exert antipsychotic effects in patients with AD and schizophrenia. However, its clinical development was discontinued because of its cholinomimetic side effects. We compared in vivo pharmacological profiles of a novel M₁R-selective positive allosteric modulator, TAK-071, and xanomeline in rodents. Xanomeline suppressed both methamphetamine- and MK-801-induced hyperlocomotion in mice, whereas TAK-071 suppressed only MK-801-induced hyperlocomotion. In a previous study, we showed that TAK-071 improved scopolamine-induced cognitive deficits in a rat novel object recognition task (NORT) with 33-fold margins versus cholinergic side effects (diarrhea). Xanomeline also improved scopolamine-induced cognitive impairments in a NORT; however, it had no margin versus cholinergic side effects (e.g., diarrhea, salivation, and hypoactivity) in rats. These side effects were observed even in M₁R knockout mice. Evaluation of c-Fos expression as a marker of neural activation revealed that xanomeline increased the number of c-Fos-positive cells in several cortical areas, the hippocampal formation, amygdala, and nucleus accumbens. Other than in the orbital cortex and claustrum, TAK-071 induced similar c-Fos expression patterns. When donepezil was co-administered to increase the levels of acetylcholine, the number of TAK-071-induced c-Fos-positive cells in these brain regions was increased. TAK-071, through induction of similar neural activation as that seen with xanomeline, may produce procognitive and antipsychotic effects with improved cholinergic side effects.

Additive effect of cerebral atrophy on cognition in dementia-free elderly with cerebrovascular disease

Objective

To explore the additive effect of neurodegenerative diseases, measured by atrophy, on neurocognitive function in Asian dementia-free elderly with cerebrovascular disease (CeVD).

Methods

The present study employed a cross-sectional design and was conducted between 2010 and 2015 among community-dwelling elderly participants recruited into the study. Eligible participants were evaluated with an extensive neuropsychological battery and neuroimaging. The weighted CeVD burden scale comprising markers of both small- and large-vessel diseases was applied, with a score of ≥2, indicating significant CeVD burden. Cortical atrophy (CA) and medial temporal atrophy (MTA) were graded using the global cortical atrophy scale and Schelten’s scale, respectively. Global and domain-specific (attention, executive function, language, visuomotor speed, visuoconstruction, visual memory, and verbal memory) neurocognitive performance was measured using a locally validated neuropsychological battery (Vascular Dementia Battery, VDB).

Results

A total of 819 dementia-free participants were included in the analysis. Among none-mild CeVD subjects, there was no significant difference in the global cognitive performance across atrophy groups (no atrophy, CA, and CA+MTA). However, in moderate-severe CeVD subjects, CA+MTA showed significantly worse global cognitive performance compared with those with CA alone (mean difference=−0.35, 95% CI −0.60 to −0.11, p=0.002) and those without atrophy (mean difference=−0.46, 95% CI −0.74 to −0.19, p<0.001, p<0.001). In domain-specific cognitive performance, subjects with CA+MTA performed worse than other groups in visual memory (p=0.005), executive function (p=0.001) and visuomotor speed (p<0.001) in moderate-severe CeVD but not in none-mild CeVD.

Conclusions and relevance

Atrophy and moderate-severe CeVD burden showed an additive effect on global and domain-specific cognitive performance. This study highlights the importance of investigating the mechanisms of clinico-pathological interactions between neurodegenerative processes and vascular damage, particularly in the pre-dementia stage.

White matter microstructural abnormalities and default network degeneration are associated with early memory deficit in Alzheimer's disease continuum

Instead of assuming a constant relationship between brain abnormalities and memory impairment, we aimed to examine the stage-dependent contributions of multimodal brain structural and functional deterioration to memory impairment in the Alzheimer’s disease (AD) continuum. We assessed grey matter volume, white matter (WM) microstructural measures (free-water (FW) and FW-corrected fractional anisotropy), and functional connectivity of the default mode network (DMN) in 54 amnestic mild cognitive impairment (aMCI) and 46 AD. We employed a novel sparse varying coefficient model to investigate how the associations between abnormal brain measures and memory impairment varied throughout disease continuum. We found lower functional connectivity in the DMN was related to worse memory across AD continuum. Higher widespread white matter FW and lower fractional anisotropy in the fornix showed a stronger association with memory impairment in the early aMCI stage; such WM-memory associations then decreased with increased dementia severity. Notably, the effect of the DMN atrophy occurred in early aMCI stage, while the effect of the medial temporal atrophy occurred in the AD stage. Our study provided evidence to support the hypothetical progression models underlying memory dysfunction in AD cascade and underscored the importance of FW increases and DMN degeneration in early stage of memory deficit.

p38 MAPK Inhibition Improves Synaptic Plasticity and Memory in Angiotensin II-dependent Hypertensive Mice

The pathogenesis of hypertension-related cognitive impairment has not been sufficiently clarified, new molecular targets are needed. p38 MAPK pathway plays an important role in hypertensive target organ damage. Activated p38 MAPK was seen in AD brain tissue. In this study, we found that long-term potentiation (LTP) of hippocampal CA1 was decreased, the density of the dendritic spines on the CA1 pyramidal cells was reduced, the p-p38 protein expression in hippocampus was elevated, and cognitive function was impaired in angiotensin II-dependent hypertensive C57BL/6 mice. In vivo, using a p38 heterozygous knockdown mice (p38(KI/+)) model, we showed that knockdown of p38 MAPK in hippocampus leads to the improvement of cognitive function and hippocampal synaptic plasticity in angiotensin II-dependent p38(KI/+) hypertensive mice. In vitro, LTP was improved in hippocampal slices from C57BL/6 hypertensive mice by treatment with p38MAPK inhibitor SKF86002. Our data demonstrated that p38 MAPK may be a potential therapeutic target for hypertension-related cognitive dysfunction.

BFLCRM: A BAYESIAN FUNCTIONAL LINEAR COX REGRESSION MODEL FOR PREDICTING TIME TO CONVERSION TO ALZHEIMER'S DISEASE

The aim of this paper is to develop a Bayesian functional linear Cox regression model (BFLCRM) with both functional and scalar covariates. This new development is motivated by establishing the likelihood of conversion to Alzheimer's disease (AD) in 346 patients with mild cognitive impairment (MCI) enrolled in the Alzheimer's Disease Neuroimaging Initiative 1 (ADNI-1) and the early markers of conversion. These 346 MCI patients were followed over 48 months, with 161 MCI participants progressing to AD at 48 months. The functional linear Cox regression model was used to establish that functional covariates including hippocampus surface morphology and scalar covariates including brain MRI volumes, cognitive performance (ADAS-Cog), and APOE status can accurately predict time to onset of AD. Posterior computation proceeds via an efficient Markov chain Monte Carlo algorithm. A simulation study is performed to evaluate the finite sample performance of BFLCRM.

Prevalence and cognitive impact of medial temporal atrophy in a hospital stroke service: retrospective cohort study

BACKGROUND

Cerebrovascular disease and neurodegeneration cause cognitive impairment and frequently coexist.

AIMS

Our objectives were to investigate the prevalence and cognitive impact of medial temporal lobe atrophy - a radiological marker often associated with Alzheimer's disease - in a hospital stroke service.

METHODS

Retrospective cohort study of patients from a hospital stroke service. Patients assessed for suspected ischemic stroke or transient ischemic attack, irrespective of final diagnosis, underwent neuropsychological testing and magnetic resonance imaging. medial temporal lobe atrophy, white matter hyperintensities, lacunes, and cerebral microbleeds were rated using established criteria and validated scales. The associations between medial temporal lobe atrophy and cognition were tested using multivariable logistic regression analyses, adjusted for age and imaging markers of cerebrovascular disease.

RESULTS

Three hundred and ninety-three patients were included, of whom 169 (43%; 95% confidence interval: 38·1-48·1%) had medial temporal lobe atrophy; in 38 patients (9·7%), medial temporal lobe atrophy was severe (mean score ≥2). In unadjusted logistic regression analyses in the whole cohort, mean medial temporal lobe atrophy score was associated with verbal memory, nominal and perceptual skills, executive function, and speed and attention. After adjustment for age, white matter hyperintensities, number of lacunes, presence of cerebral microbleeds, previous ischemic stroke or transient ischemic attack, and premorbid intelligence quotient, mean medial temporal lobe atrophy score remained associated with impairment in verbal memory (odds ratio: 1·64; 95% confidence interval 1·04-2·58) and nominal skills (odds ratio: 1·61; 95% confidence interval 1·04-2·48).

CONCLUSIONS

Medial temporal lobe atrophy is common and has an independent impact on cognitive function in a stroke service population, independent of confounding factors including age and magnetic resonance imaging markers of cerebrovascular disease. Medial temporal lobe atrophy is independently related to verbal memory and nominal skills, while small vessel pathology also contributes to speed and attention, and executive and perceptual functions.

Amyloid burden, cortical thickness, and cognitive function in the Wisconsin Registry for Alzheimer's Prevention

There is a growing interest in understanding how amyloid β (Aβ) accumulation in preclinical Alzheimer's disease relates to brain morphometric measures and cognition. Existing investigations in this area have been primarily conducted in older cognitively normal (CN) individuals. Therefore, not much is known about the associations between Aβ burden, cortical thickness, and cognition in midlife. We examined this question in 109, CN, late to middle-aged adults (mean age = 60.72 ± 5.65 years) from the Wisconsin Registry for Alzheimer's Prevention. They underwent Pittsburgh Compound B (PiB) and anatomical magnetic resonance (MR) imaging, and a comprehensive cognitive examination. Blinded visual rating of the PiB scans was used to classify the participants as Aβ+ or Aβ−. Cortical thickness measurements were derived from the MR images. The Aβ+ group exhibited significant thinning of the entorhinal cortex and accelerated age-associated thinning of the parahippocampal gyrus compared with the Aβ− group. The Aβ+ group also had numerically lower, but nonsignificant, test scores on all cognitive measures, and significantly faster age-associated cognitive decline on measures of Speed & Flexibility, Verbal Ability, and Visuospatial Ability. Our findings suggest that early Aβ aggregation is associated with deleterious changes in brain structure and cognitive function, even in midlife, and that the temporal lag between Aβ deposition and the inception of neurodegenerative/cognitive changes might be narrower than currently thought.

Magnetization transfer MRI in dementia disorders, Huntington's disease and parkinsonism

Magnetic resonance imaging is the most used technique of neuroimaging. Using recent advances in magnetic resonance application it is possible to investigate several changes in neurodegenerative disease. Among different techniques, magnetization-transfer imaging (MTI), a magnetic resonance acquisition protocol assessing the magnetization exchange between protons bound to water and those bound to macromolecules, is able to identify microstructural brain tissue changes peculiar of neurodegenerative diseases. This review provides a report on the MTI technique and its use in the dementia disorders, Huntington's disease and parkinsonisms, comprehensive of the predictive values of MTI in the identification of early-phase disease.

Running exercise delays neurodegeneration in amygdala and hippocampus of Alzheimer's disease (APP/PS1) transgenic mice

Alzheimer's disease (AD) is an age-related neurodegenerative disease. Post-mortem examination and brain imaging studies indicate that neurodegeneration is evident in the hippocampus and amygdala of very early stage AD patients. Exercise training is known to enhance hippocampus- and amygdala-associated neuronal function. Here, we investigated the effects of exercise (running) on the neuronal structure and function of the hippocampus and amygdala in APP/PS1 transgenic (Tg) mice. At 4-months-old, an age before amyloid deposition, the amygdala-associated, but not the hippocampus-associated, long-term memory was impaired in the Tg mice. The dendritic complexities of the amygdalar basolateral neurons, but not those in the hippocampal CA1 and CA3 neurons, were reduced. Furthermore, the levels of BDNF/TrkB signaling molecules (i.e. p-TrkB, p-Akt and p-PKC) were reduced in the amygdala, but not in the hippocampus of the 4-month-old Tg mice. The concentrations of Aβ40 and Aβ42 in the amygdala were higher than those in the hippocampus. Ten weeks of treadmill training (from 1.5- to 4-month-old) increased the hippocampus-associated memory and dendritic arbor of the CA1 and CA3 neurons, and also restored the amygdala-associated memory and the dendritic arbor of amygdalar basolateral neurons in the Tg mice. Similarly, exercise training also increased the levels of p-TrkB, p-AKT and p-PKC in the hippocampus and amygdala. Furthermore, exercise training reduced the levels of soluble Aβ in the amygdala and hippocampus. Exercise training did not change the levels of APP or RAGE, but significantly increased the levels of LRP-1 in both brain regions of the Tg mice. In conclusion, our results suggest that tests of amygdala function should be incorporated into subject selection for early prevention trials. Long-term exercise protects neurons in the amygdala and hippocampus against AD-related degeneration, probably via enhancements of BDNF signaling pathways and Aβ clearance. Physical exercise may serve as a means to delay the onset of AD.

Should losartan be administered following brain injury?

Brain injury is a major health concern and associated with delayed neurological complications, including post-injury epilepsy, cognitive and emotional disabilities. Currently, there is no strategy to prevent post-injury delayed complications. We recently showed that dysfunction of the blood-brain barrier, often reported in brain injuries, can lead to epilepsy and neurodegeneration via activation of inflammatory TGF-β signaling in astrocytes. We further showed that the FDA approved angiotensin II type 1 receptor antagonist, losartan, blocks brain TGF-β signaling and prevents epilepsy in the albumin or blood-brain barrier breakdown models of epileptogenesis. Here we discuss the potential of losartan as an anti-epileptogenic and a neuroprotective drug, the rationale of its use following brain injury and the challenges of designing clinical trials. We highlight the urgent need to develop reliable biomarkers for epileptogenesis (and other complications) after brain injury as a pre-requisite to challenge neuroprotective therapies.

Intracellular Aβ pathology and early cognitive impairments in a transgenic rat overexpressing human amyloid precursor protein: a multidimensional study

Numerous studies have implicated the abnormal accumulation of intraneuronal amyloid-β (Aβ) as an important contributor to Alzheimer's disease (AD) pathology, capable of triggering neuroinflammation, tau hyperphosphorylation and cognitive deficits. However, the occurrence and pathological relevance of intracellular Aβ remain a matter of controversial debate. In this study, we have used a multidimensional approach including high-magnification and super-resolution microscopy, cerebro-spinal fluid (CSF) mass spectrometry analysis and ELISA to investigate the Aβ pathology and its associated cognitive impairments, in a novel transgenic rat model overexpressing human APP. Our microscopy studies with quantitative co-localization analysis revealed the presence of intraneuronal Aβ in transgenic rats, with an immunological signal that was clearly distinguished from that of the amyloid precursor protein (APP) and its C-terminal fragments (CTFs). The early intraneuronal pathology was accompanied by a significant elevation of soluble Aβ42 peptides that paralleled the presence and progression of early cognitive deficits, several months prior to amyloid plaque deposition. Aβ38, Aβ39, Aβ40 and Aβ42 peptides were detected in the rat CSF by MALDI-MS analysis even at the plaque-free stages; suggesting that a combination of intracellular and soluble extracellular Aβ may be responsible for impairing cognition at early time points. Taken together, our results demonstrate that the intraneuronal development of AD-like amyloid pathology includes a mixture of molecular species (Aβ, APP and CTFs) of which a considerable component is Aβ; and that the early presence of these species within neurons has deleterious effects in the CNS, even before the development of full-blown AD-like pathology.

Bigger is better! Hippocampal volume and declarative memory performance in healthy young men

The importance of the hippocampus for declarative memory processes is firmly established. Nevertheless, the issue of a correlation between declarative memory performance and hippocampal volume in healthy subjects still remains controversial. The aim of the present study was to investigate this relationship in more detail. For this purpose, 50 healthy young male participants performed the California Verbal Learning Test. Hippocampal volume was assessed by manual segmentation of high-resolution 3D magnetic resonance images. We found a significant positive correlation between putatively hippocampus-dependent memory measures like short-delay retention, long-delay retention and discriminability and percent hippocampal volume. No significant correlation with measures related to executive processes was found. In addition, percent amygdala volume was not related to any of these measures. Our data advance previous findings reported in studies of brain-damaged individuals in a large and homogeneous young healthy sample and are important for theories on the neural basis of episodic memory.

Preserved and impaired emotional memory in Alzheimer's disease

Patients with early atrophy of both limbic structures involved in memory and emotion processing in Alzheimer's disease (AD) provide a unique clinical population for investigating how emotion is able to modulate retention processes. This review focuses on the emotional enhancement effect (EEE), defined as the improvement of memory for emotional events compared with neutral ones. The assessment of the EEE for different memory systems in AD suggests that the EEE could be preserved under specific retrieval instructions. The first part of this review examines these data in light of compelling evidence that the amygdala can modulate processes of hippocampus-dependent memory. We argue that the EEE could be a useful paradigm to reduce impairment in episodic memory tasks. In the second part, we discuss theoretical consequences of the findings in favor of an EEE, according to which a compensatory mechanism in patients with AD solicits greater amygdala functioning or additional networks, even when amygdala atrophy is present. These considerations emphasize the relevance of investigating patients with AD to understand the relationship between emotion and memory processes.

Staging neurodegenerative disorders: structural, regional, biomarker, and functional progressions

The notion of staging in the neurodegenerative disorders is modulated by the constant and progressive loss of several aspects of brain structural integrity, circuitry, and neuronal processes. These destructive processes eventually remove individuals' abilities to perform at sufficient and necessary functional capacity at several levels of disease severity. The classification of (a) patients on the basis of diagnosis, risk prognosis, and intervention outcome, forms the basis of clinical staging, and (b) laboratory animals on the basis of animal model of brain disorder, extent of insult, and dysfunctional expression, provides the components for the clinical staging and preclinical staging, respectively, expressing associated epidemiological, biological, and genetic characteristics. The major focus of clinical staging in the present account stems from the fundamental notions of Braak staging as they describe the course and eventual prognosis for Alzheimer's disease, Lewy Body dementia, and Parkinson's disease. Mild cognitive impairment, which expresses the decline in episodic and semantic memory performance below the age-adjusted normal range without marked loss of global cognition or activities of daily living, and the applications of longitudinal magnetic resonance imaging, major instruments for the monitoring of either disease progression in dementia, present important challenges for staging concepts. Although Braak notions present the essential basis for further developments, current staging conceptualizations seem inadequate to comply with the massive influx of information dealing with neurodegenerative processes in brain, advanced both under clinical realities, and discoveries in the laboratory setting. The contributions of various biomarkers of disease progression, e.g., amyloid precursor protein, and neurotransmitter system imbalances, e.g., dopamine receptor supersensitivity and interactive propensities, await their incorporation into the existing staging models thereby underlining the ongoing, dynamic feature of the staging of brain disorders.

Amygdala atrophy is prominent in early Alzheimer's disease and relates to symptom severity

Despite numerous studies on the role of medial temporal lobe structures in Alzheimer's disease (AD), the magnitude and clinical significance of amygdala atrophy have been relatively sparsely investigated. In this study, we used magnetic resonance imaging (MRI) to compare the level of amygdala atrophy to that of the hippocampus in very mild and mild AD subjects in two large samples (Sample 1 n=90; Sample 2 n=174). Using a series of linear regression analyses, we investigated whether amygdala atrophy is related to global cognitive functioning (Clinical Dementia Rating Sum of Boxes: CDR-SB; Mini Mental State Examination: MMSE) and neuropsychiatric status. Results indicated that amygdala atrophy was comparable to hippocampal atrophy in both samples. MMSE and CDR-SB were strongly related to amygdala atrophy, with amygdala atrophy predicting MMSE scores as well as hippocampal atrophy, but predicting CDR-SB scores less robustly. Amygdala atrophy was related to aberrant motor behavior, with potential relationships to anxiety and irritability. These results suggest that the magnitude of amygdala atrophy is comparable to that of the hippocampus in the earliest clinical stages of AD, and is related to global illness severity. There also appear to be specific relationships between the level of amygdala atrophy and neuropsychiatric symptoms that deserve further investigation.

The relationship between plasma amyloid-β peptides and the medial temporal lobe in the homebound elderly

BACKGROUND

The ratio of high amyloid-β peptide40 (Aβ40) and low Aβ42 in plasma predicts the risk of Alzheimer's disease (AD) and is associated with episodic recall in depression. We thus examined the relationship between plasma Aβ levels and brain volumes.

METHODS

Homebound elders (N = 352) who had undergone brain MRI were used. Plasma Aβ1-40 and Aβ1-42 were measured by ELISA. Volumes of medial temporal regions, including the amygdala and hippocampus, were manually measured.

RESULTS

Amygdala volume was associated with log(10) of plasma Aβ1-42 (β = +0.19, SE = 0.07, p = 0.005) after adjusting for AD, infarcts, white matter hyperintensities and demographics. In the absence of dementia, decreasing quartiles of plasma Aβ1-42 (Mean + SD ml: Q4 = 4.1 ± 0.8; Q3 = 3.9 ± 0.7; Q2 = 3.6 ± 0.8 and Q1 = 3.7 ± 0.8, p = 0.01) and increasing quartiles of plasma Aβ1-40/1-42 ratio were associated with smaller amygdala volume. Those depressed subjects with a high plasma Aβ1-40/1-42 ratio had smaller amygdala (Mean + SD ml: 3.3 ± 0.8 vs. 3.6 ± 0.8, p = 0.04) and total brain volume (Mean + SD liter: 0.95 ± 0.07 vs. 1.04 ± 0.12, p = 0.005), and had a higher rate of MCI (67 vs. 36%, p = 0.02) than those with a low plasma Aβ1-40/1-42 ratio.

CONCLUSIONS

The combination of low plasma Aβ1-42 concentration and atrophy of the medial temporal lobe structures, which regulates mood and cognition, may represent a biomarker for a prodromal stage of AD.

Sex differences in grey matter atrophy patterns among AD and aMCI patients: results from ADNI

We used longitudinal magnetic resonance imaging (MRI) data to determine whether there are any gender differences in grey matter atrophy patterns over time in 197 individuals with probable Alzheimer's disease (AD) and 266 with amnestic mild cognitive impairment (aMCI), compared with 224 healthy controls participating in the Alzheimer's Disease Neuroimaging Initiative (ADNI). While previous research has differentiated probable AD and aMCI groups from controls in brain atrophy, it is unclear whether and how sex plays a role in patterns of change over time. Using regional volumetric maps, we fit longitudinal models to the grey matter data collected at repeated occasions, seeking differences in patterns of volume change over time by sex and diagnostic group in a voxel-wise analysis. Additionally, using a region-of-interest approach, we fit longitudinal models to the global volumetric data of predetermined brain regions to determine whether this more conventional approach is sufficient for determining sex and group differences in atrophy. Our longitudinal analyses revealed that, of the various grey matter regions investigated, males and females in the AD group and the aMCI group showed different patterns of decline over time compared to controls in the bilateral precuneus, bilateral caudate nucleus, right entorhinal gyrus, bilateral thalamus, bilateral middle temporal gyrus, left insula, and right amygdala. As one of the first investigation to model more than two time points of structural MRI data over time, our findings add insight into how AD and aMCI males and females differ from controls and from each other over time.

Multicentre variability of MRI-based medial temporal lobe volumetry in Alzheimer's disease

Magnetic resonance imaging (MRI)-based volumetry of medial temporal lobe regions is among the best established biomarker candidates of Alzheimer's disease (AD) to date. This study assessed the effect of multicentre variability of MRI-based hippocampus and amygdala volumetry on the discrimination between patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI) and on the association of morphological changes with ApoE4 genotype and cognition. We studied 113 patients with clinically probable AD and 150 patients with amnestic MCI using high-resolution MRI scans obtained at 12 clinical sites. We determined effect sizes of group discrimination and random effects linear models, considering multicentre variability. Hippocampus and amygdala volumes were significantly reduced in AD compared with MCI patients using data pooled across centres. Multicentre variability did not significantly affect the power to detect a volume difference between AD and MCI patients. Among cognitive measures, delayed recall of verbal and non-verbal material was significantly correlated with hippocampus and amygdala volumes. Amygdala and hippocampus volumes were not associated with ApoE4 genotype in AD or MCI. Our data indicate that multicentre acquisition of MRI data using manual volumetry is reliable and feasible for cross-sectional diagnostic studies, and they replicate essential findings from smaller scale monocentre studies.

Medial temporal lobe correlates of memory screening measures in normal aging, MCI, and AD

This article aimed to study the correlations for both the Memory Impairment Screen (MIS) and the Free and Cued Selective Reminding Test (FCSRT) with regard to the volumetric measures of hippocampal formation and entorhinal cortex and to explore the effect size of these measures.

METHODS

A total of 34 healthy controls, 24 participants with mild cognitive impairment (MCI), and 20 mild-to-moderate-staged Alzheimer disease (AD) participants underwent neuropsychological testing and magnetic resonance imaging (MRI). Global volumetric measures were obtained and hippocampal and entorhinal volumes were calculated. Spearman correlations were calculated between memory scores and brain volumes and an effect size analysis was performed.

RESULTS

No significant correlations with global brain volumes were found. There were dissimilar correlations among groups regarding memory and hippocampal and entorhinal volumes. No significant relationships were observed in healthy controls. The MCI group reached the higher correlation indexes, up to r = .55. In AD, only one significant correlation was observed between the delayed score of the FCSRT and the left hippocampus. Effect size values were higher for memory tests than for MRI measures, reaching d = 4.3 for the delayed score of the FCSRT.

CONCLUSIONS

Although the MIS did not reach the strong results of the FCSRT, it demonstrated a similar pattern to the FCSRT in correlational analysis. These results support the validity and usefulness of the MIS despite its brevity of application. Memory testing showed better discrimination among healthy controls, MCI, and AD participants than MRI measures by means of effect size analysis.

Neuropsychological profile of prodromal Alzheimer's disease (Prd-AD) and their radiological correlates

This study describes the cognitive profile of Prd-AD, the neuropsychological tests that may predict progression to dementia, and to study their brain structural correlates. We enrolled 24 stable amnesics who did not develop dementia after two years follow-up; 27 patients were considered as Prd-AD, in the initial visit, since they fulfilled NINCDS-ADRDA criteria after two years; 31 Alzheimer's disease (AD) patients and 27 controls (CTR). Structural magnetic resonance imaging (MRI), as well as a neuropsychological battery was performed at the initial visit. The key findings were: Prd-AD patients were characterized by prominent episodic memory dysfunction and minimal semantic memory and executive dysfunction. Semantic fluency test (Sem-Flu), delayed text memory test (Del-text-mem) and memory alteration test (M@T) (including both episodic and semantic memory), together with trail making test A (TMT-A), resulted significant predictors for dementia development in this group of amnesic patients. This optimal predictive model obtained an estimated accuracy of 53% after two years follow-up. M@T and semantic Sem-Flu test performance presented high correlation with decreased gray matter density in the left lateral temporal lobe. We conclude that Prd-AD is characterized by prominent episodic memory dysfunction and minimal semantic memory and executive dysfunction which are related with left medial, inferior and lateral temporal density loss, predominantly in the left side.

Manual validation of FreeSurfer's automated hippocampal segmentation in normal aging, mild cognitive impairment, and Alzheimer Disease subjects

Hippocampal volume is reduced in Alzheimer Disease (AD) and has been proposed as a possible surrogate biomarker to aid early diagnosis. Whilst automated methods to segment the hippocampus from magnetic resonance images are available, manual segmentation, in spite of being time-consuming and unsuitable for large samples, is still the standard. In order to study the validity of FreeSurfer's automated method, we compared hippocampal automated measures with manual tracing in a sample composed of healthy elderly (N=41), Mild Cognitive Impairment (MCI) (N=23), and AD (N=25) subjects. Percent volume overlap, percent volume difference, correlations, and Bland-Altman plots were studied. Automated measures were slightly larger than hand tracing ones (mean difference 10%). Percent volume overlap showed good results, but was far from perfect (78%). Manual and automated volume correlations were approximately 0.84 and the Bland-Altman analysis showed acceptable interchangeability of methods. Within-group analysis demonstrated that patient samples obtained smaller values in validity indexes than controls. Globally, FreeSurfer's automated hippocampal volumetry showed adequate validity when compared to manual tracing, with a tendency to overestimation. Nevertheless, the greater difference between automated and manual segmentation in atrophic brains suggests that studies in AD based on this software could be more likely to produce false negatives.

Increased hippocampal head diffusivity predicts impaired episodic memory performance in early Alzheimer's disease

Recent neuroanatomical and functional neuroimaging studies indicate that the anterior part of the hippocampus, rather than the whole structure, may be specifically involved in episodic memory. In the present work, we examined whether anterior structural measurements are superior to other regional or global measurements in mapping functionally relevant degenerative alterations of the hippocampus in Alzheimer's disease (AD). Twenty patients with early AD (MMSE 25.7+/-1.7) and 18 healthy controls were studied using magnetic resonance and diffusion-tensor imaging. Using a regions-of-interest analysis, we obtained volumetric and diffusivity measures of the hippocampal head and body-tail-section as well as of the whole hippocampus. Detailed cognitive evaluation was based on the CERAD battery. All volumetric measures as well as diffusivity of the hippocampus head were significantly (p<0.01) altered in patients as compared to controls. In patients, increased left head diffusivity significantly (p<0.01) correlated with performance on free delayed verbal recall test (DVR) (r=-0.74, p=0.0002) and with the CERAD global score. Reduced volume of the left body-tail was also associated with performance on DVR (r=0.62, p=0.004). Stepwise regression analyses revealed that increased left head diffusivity was the only predictor for performance on DVR (R(2)=52%, p<0.0005). These findings suggest that anterior hippocampus diffusivity is more closely related to verbal episodic memory impairment than other regional or global structural measures. Our data support the hypothesis of functional differentiation in general and the specific role of the anterior hippocampus in episodic memory in particular. Diffusivity measurements might be highly sensitive to functionally relevant degenerative alterations of the hippocampus.

Memory with emotional content, brain amygdala and Alzheimer's disease

OBJECTIVES

A highly adaptive aspect of human memory is the enhancement of explicit, consciously accessible memory by emotional stimuli. We studied the performance of Alzheimer's disease (AD) patients and elderly controls using a memory battery with emotional content, and we correlated these results with the amygdala and hippocampus volume.

METHODS

Twenty controls and 20 early AD patients were subjected to the International Affective Picture System (IAPS) and to magnetic resonance imaging-based volumetric measurements of the medial temporal lobe structures.

RESULTS

The results show that excluding control group subjects with 5 or more years of schooling, both groups showed improvement with pleasant or unpleasant figures for the IAPS in an immediate free recall test. Likewise, in a delayed free recall test, both the controls and the AD group showed improvement for pleasant pictures, when education factor was not controlled. The AD group showed improvement in the immediate and delayed free recall test proportional to the medial temporal lobe structures, with no significant clinical correlation between affective valence and amygdala volume.

CONCLUSION

AD patients can correctly identify emotions, at least at this early stage, but this does not improve their memory performance.

Emotional valence and semantic relatedness differentially influence false recognition in mild cognitive impairment, Alzheimer's disease, and healthy elderly

This study examined whether patients with mild cognitive impairment (MCI) who are at higher risk for later Alzheimer disease (AD) display deficits comparable to patients with diagnosed dementia. We assessed 27 patients with MCI, 36 patients with AD, and 20 healthy older adults with an emotional variant of the Deese-Roediger-McDermott-paradigm. Participants studied four lists that were semantically related to a nonpresented critical theme word. These theme words were either depression-related (i.e., loneliness) or delusion-related (betrayal) or had a positive (holidays) or neutral (window) valence. Despite a normal overall emotional memory and a normal corrected overall false recognition, patients with MCI, as predicted, produced as many false memories as patients with AD. On closer examination, both patient groups showed enhanced false memories to unrelated stimuli and a significant bias to falsely remember stimuli with a positive valence. We conclude that although patients with MCI are not distinguishable from healthy older adults in terms of their overall emotional recognition, positively valenced memories and more specifically false positive memories may represent the signature of a breakdown of emotional memory along the continuum between normal aging and AD.

[Development of semi-automated segmentation of the brain and CSF Region on MR images]

MR imaging (MRI) is an important method for the diagnosis of abnormalities of the brain. In the present report, a semi-automated method is presented to segment the brain and CSF region on brain MR images. MR images were obtained from 6 subjects by SE sequence and 8 subjects by GRE sequence. The semi-automated method consisted of the following three steps: (1) segmentation of the intracranial region using the region-growing technique, (2) segmentation of the brain region using histogram analysis and mathematical morphology, and (3) segmentation of the CSF region using the top-hat transformation technique. The average ratio of a correctly recognized region (CRR) between the semi-automated method and manual method was 87.9%, 85.1% for the intracranial region (IRR), and 94.8% and 86.8% for the brain region in the SE and GRE sequences.

3D maps from multiple MRI illustrate changing atrophy patterns as subjects progress from mild cognitive impairment to Alzheimer's disease

Mild cognitive impairment (MCI), particularly the amnestic subtype (aMCI), is considered as a transitional stage between normal aging and a diagnosis of clinically probable Alzheimer's disease (AD). The aMCI construct is particularly useful as it provides an opportunity to assess a clinical stage which in most subjects represents prodromal AD. The aim of this study was to assess the progression of cerebral atrophy over multiple serial MRI during the period from aMCI to progression to AD. Thirty-three subjects were selected that fulfilled clinical criteria for aMCI and had three serial MRI scans: the first scan approximately 3 years before the diagnosis of AD, the second scan approximately 1 year before, and the third scan at the time of the diagnosis of AD. A group of 33 healthy controls were age and gender-matched to the study cohort. Voxel-based morphometry (VBM) was used to assess patterns of grey matter atrophy in the aMCI subjects at each time-point compared to the control group. Customized templates and prior probability maps were used to avoid normalization and segmentation bias. The pattern of grey matter loss in the aMCI subject scans that were 3 years before the diagnosis of AD was focused primarily on the medial temporal lobes, including the amygdala, anterior hippocampus and entorhinal cortex, with some additional involvement of the fusiform gyrus, compared to controls. The extent and magnitude of the cerebral atrophy further progressed by the time the subjects were 1 year before the diagnosis of AD. At this point atrophy in the temporal lobes spread to include the middle temporal gyrus, and extended into more posterior regions of the temporal lobe to include the entire extent of the hippocampus. The parietal lobe also started to become involved. By the time the subjects had progressed to a clinical diagnosis of AD the pattern of grey matter atrophy had become still more widespread with more severe involvement of the medial temporal lobes and the temporoparietal association cortices and, for the first time, substantial involvement of the frontal lobes. This pattern of progression fits well with the Braak and Braak neurofibrillary pathological staging scheme in AD. It suggests that the earliest changes occur in the anterior medial temporal lobe and fusiform gyrus, and that these changes occur at least 3 years before progression to the diagnosis of AD. These results also suggest that 3D patterns of grey matter atrophy may help to predict the time to the first diagnosis of AD in subjects with aMCI.

Does the Hippocampal Atrophy Correlate With the Cortical Theta Power in Elderly Subjects With a Range of Cognitive Impairment?

A previous study with a small sample (N = 39) showed a significant correlation between the cortical theta activity and the hippocampal volume in different stages of cognitive impairment in aged subjects. The recent study was aimed to replicate these results in a much bigger sample. The authors examined a sample of 121 right-handed subjects. The sample consisted of 37 healthy controls, 40 patients with questionable dementia, and 44 patients with mild dementia assessed by Clinical Dementia Rating. All subjects underwent EEG and brain MRI. Mean spectral power was calculated, and volume of hippocampal segments was measured. EEG theta power of the left and right hemisphere correlated significantly with the hippocampal volume on the left and right side in different stages of cognitive impairment. An increase of theta power was associated with decreased hippocampal volume. No other significant correlations were found for alpha or beta band power. No correlation was found between cortical theta and global brain volume. There seems to be a direct relationship between neuronal loss of the hippocampus and changed cortical theta activity for different stages of cognitive impairment in aged subjects.