Administration of the neurosteroid progesterone (PROG) has been shown to be beneficial in a number of brain injury models and in two recent clinical trials. Given widespread vitamin D deficiency and increasing traumatic brain injuries (TBIs) in the elderly, we investigated the interaction of vitamin D deficiency and PROG with cortical contusion injury in aged rats. Vitamin D deficient (VitD-deficient) animals showed elevated inflammatory proteins (TNFα, IL-1β, IL-6, NFκB p65) in the brain even without injury. VitD-deficient rats with TBI, whether given PROG or vehicle, showed increased inflammation and greater open-field behavioral deficits compared to VitD-normal animals. Although PROG was beneficial in injured VitD-normal animals, in VitD-deficient subjects neurosteroid treatment conferred no improvement over vehicle. A supplemental dose of 1,25-dihydroxyvitamin D3 (VDH) given with the first PROG treatment dramatically improved results in VitD-deficient rats, but treatment with VDH alone did not. Our results suggest that VitD-deficiency can increase baseline brain inflammation, exacerbate the effects of TBI, and attenuate the benefits of PROG treatment; these effects may be reversed if the deficiency is corrected.
Aging; Inflammation; Progesterone; 1,25-Dihydroxyvitamin D3; Traumatic brain injury; Vitamin D deficiency
The aged canine (dog) is an excellent model for investigating the neurobiological changes that underlie cognitive impairment and neurodegeneration in humans, as canines and humans undergo similar pathological and behavioural changes with aging. Recent evidence indicates that a combination of environmental enrichment and antioxidant-fortified diet can be used to reduce the rate of age-dependent neuropathology and cognitive decline in aged dogs, although the mechanisms underlying these changes have not been established. We examined the hypothesis that an increase in levels of brain-derived neurotrophic factor (BDNF) is one of the factors underlying improvements in learning and memory. Old, cognitively impaired animals that did not receive any treatment showed a significant decrease in BDNF mRNA in the temporal cortex when compared with the young group. Animals receiving either an antioxidant diet or environmental enrichment displayed intermediate levels of BDNF mRNA. However, dogs receiving both an antioxidant diet and environmental enrichment showed increased levels of BDNF mRNA when compared to untreated aged dogs, approaching levels measured in young animals. BDNF receptor TrkB mRNA levels did not differ between groups. BDNF mRNA levels were positively correlated with improved cognitive performance and inversely correlated with cortical Aβ(1–42) and Aβ(1–40) levels. These findings suggest that environmental enrichment and antioxidant diet interact to maintain brain levels of BDNF, which may lead to improved cognitive performance. This is the first demonstration in a higher animal that non-pharmacological changes in lifestyle in advanced age can up-regulate BDNF to levels approaching those in the young brain.
Alzheimer’s disease; neurotrophin; amyloid; diet; environmental enrichment; antioxidant; mRNA
It is well established that there are remarkable similarities between song learning in oscine birds and acquisition of speech in young children. Human speech shows marked changes with senescence, but few studies have evaluated how song changes with advanced age in songbirds. To investigate the effect of old age on song, we compared song of old Bengalese finches (Lonchura striata domestica) with that of middle-aged birds. The main observed difference was a decrease in the song tempo, largely due to an increased inter-syllable duration. Aging also affected the acoustic characteristics of the song, causing a decrease in pitch and in the range of frequency modulations. Gross morphological measurements of selected vocal muscles did not show detectable changes over this age range, suggesting that song deterioration may be due to neural deterioration. The age-induced temporal and acoustic changes in song parallel the acoustic changes that occur in human speech, suggesting songbirds as a suitable model for aging studies on learned vocal behavior.
Birdsong; speech; respiration; timing; sensorimotor integration
Alzheimer’s disease (AD) is a complex disorder with a clear genetic component. Three genes have been identified as the cause of early onset familial AD (EOAD). The most common form of the disease is, however, a sporadic one presenting itself in later stages of life (LOAD). The genetic component of this late onset form of AD has been the target of a large number of studies, since only one genetic risk factor (APOE4) has been consistently associated with the disease. However, technological advances allow new approaches in the study of complex disorders. In this review, we discuss the new results produced by genome wide association studies, in light of the current knowledge of the complexity of AD genetics.
Two recent large genome-wide association studies have reported significant associations in the CLU (APOJ), CR1 and PICALM genes. In order to replicate these findings, we examined 7 single nucleotide polymorphisms (SNPs) most significantly implicated by these studies in a large case-control sample comprising of 2,707 individuals. Principle components analysis revealed no population substructure in our sample. While no association was observed with CR1 SNPs (P=0.30–0.457), a trend of association was seen with the PICALM (P=0.071–0.086) and CLU (P=0.148–0.258) SNPs. A meta-analysis of three studies revealed significant associations with all three genes. Our data from an independent and large case-control sample suggest that these gene regions should be followed up by comprehensive resequencing to find functional variants.
Alzheimer's disease; Genetics; Association
Accumulating evidence indicates that white matter degeneration contributes to the neural disconnections that underlie Alzheimer’s disease pathophysiology. Although this white matter degeneration is partly attributable to axonopathy associated with neuronal degeneration, amyloid β (Aβ) protein-mediated damage to oligodendrocytes could be another mechanism. To test this hypothesis, we studied effects of soluble Aβ in oligomeric form on survival and differentiation of cells of the oligodendroglial lineage using highly purified oligodendroglial cultures from rats at different developmental stages. Aβ oligomer at 10 μM or higher reduced survival of mature oligodendrocytes, whereas oligodendroglial progenitor cells (OPCs) were relatively resistant to the Aβ oligomer-mediated cytotoxicity. Further study revealed that Aβ oligomer even at 1 μM accelerated 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) formazan exocytosis in mature oligodendrocytes, and, more significantly, inhibited myelin sheet formation after induction of in vitro differentiation of OPCs. These results imply a novel pathogenetic mechanism underlying Aβ oligomer-mediated white matter degeneration, which could impair myelin maintenance and remyelination by adult OPCs, resulting in accumulating damage to myelinating axons thereby contributing to neural disconnections.
Alzheimer’s disease; Amyloid β; Lipid; Myelin; Oligodendroglia; White matter degeneration
Normal aging is accompanied by global as well as regional structural changes. While these age-related changes in grey matter volume have been extensively studied, less has been done using newer morphological indices such as cortical thickness and surface area. To this end, we analyzed structural images of 216 healthy volunteers, ranging from 18 to 87 years of age, using a surface-based automated parcellation approach. Linear regressions of age revealed a concomitant global age-related reduction in cortical thickness, surface area and volume. Cortical thickness and volume collectively confirmed the vulnerability of the prefrontal cortex, whereas in other cortical regions such as in the parietal cortex, thickness was the only measure sensitive to the pronounced age-related atrophy. No cortical regions showed more surface area reduction than the global average. The distinction between these morphological measures may provide valuable information to dissect age-related structural changes of the brain, with each of these indices probably reflecting specific histological changes occurring during aging.
Aging; Magnetic resonance imaging; morphology; cortical thickness; cortical volume; cortical surface
Studies of recovery from stroke mainly utilize rodent models and focus primarily on young subjects despite the increased prevalence of stroke with age and the fact that recovery of function is more limited in the aged brain. In the present study, a nonhuman primate model of cortical ischemia was developed to allow the comparison of impairments in young and middle-aged monkeys. Animals were pretrained on a fine motor task of the hand and digits and then underwent a surgical procedure to map and lesion the hand-digit representation in the dominant motor cortex. Animals were retested until performance returned to preoperative levels. To assess the recovery of grasp patterns, performance was videotaped and rated using a scale adapted from human occupational therapy. Results demonstrated that the impaired hand recovers to baseline in young animals in 65–80 days and in middle-aged animals in 130–150 days. However, analysis of grasp patterns revealed that neither group recover preoperative finger thumb grasp patterns, rather they develop compensatory movements.
Stroke; Cortical ischemia; Rhesus monkey; Aging; Recovery of function; Motor function; Hand; Digits
The authors investigated whether cognitive function may be used as an endophenotype for longevity by assessing the cognitive performance of a family-based cohort consisting of one thousand three hundred and eighty individuals from 283 families recruited for exceptional survival in field centers in Boston, New York, Pittsburgh and Denmark. Cognitive performance was assessed in the combined offspring of the Long Life Family Study (LLFS) probands and their LLFS siblings as compared with their spouses’ cognitive performance. Our results indicate that the combined offspring of the LLFS probands and their siblings achieve significantly higher scores on both digit forward and backward tasks (p=5E-5 and p=8E-4 respectively) as well as on a verbal fluency task (p=0.008) when compared with their spouse controls. No differences between groups were found for the other cognitive tests assessed. We conclude that LLFS family members in the offspring generation demonstrate significantly better performance on multiple tasks requiring attention, working memory, and semantic processing when compared with individuals without a family history of exceptional survival, suggesting that cognitive performance may serve as an important endophenotype for longevity.
exceptional survival; cognitive performance; endophenotype
In Huntington's disease (HD), mutated huntingtin (mhtt) causes striatal neurodegeneration which is paralleled by elevated microglia cell numbers. In vitro cortico-striatal slice and primary neuronal culture models, in which neuronal expression of mhtt fragments drives HD-like neurotoxicity, were employed to examine wild type microglia during both the initiation and progression of neuronal pathology. As neuronal pathology progressed, microglia initially localized in the vicinity of neurons expressing mhtt fragments increased in number, demonstrated morphological evidence of activation, and expressed the proliferation marker, Ki67. These microglia were positioned along irregular neurites, but did not localize with mhtt inclusions nor exacerbate mhtt fragment-induced neurotoxicity. Prior to neuronal pathology, microglia upregulated Iba1, signaling a functional shift. With neurodegeneration, interleukin-6 and complement component 1q were increased. The results suggest a stimulatory, proliferative signal for microglia present at the onset of mhtt fragment-induced neurodegeneration. Thus, microglia effect a localized inflammatory response to neuronal mhtt expression that may serve to direct microglial removal of dysfunctional neurites or aberrant synapses, as is required for reparative actions in vivo.
Huntington's disease; microglia; huntingtin; htt; microgliosis; neuron-microglia interaction; complement; interleukin-6; neuroinflammation; protein aggregation; neurite; neurodegeneration; slice culture; neurotoxicity
Mitochondrial dysfunction is likely a significant contributing factor to Alzheimer disease pathogenesis, and both Aβ and pathological forms of tau may contribute to this impairment. Cleavage of tau at Asp421 occurs early in Alzheimer disease, and Asp421-cleaved tau likely negatively impacts neuronal function. Previously we showed that expression of caspase-cleaved tau in a neuronal cell model resulted in mitochondrial impairment. To extend these findings we expressed either full-length tau or Asp421-cleaved tau (truncated tau) in primary cortical neurons and measured different aspects of mitochondrial function with or without the addition of sub-lethal concentrations of Aβ. The expression of truncated tau alone induced significant mitochondrial fragmentation in neurons. When truncated tau expression was combined with Aβ at sub-lethal concentrations, increases in the stationary mitochondrial population and the levels of oxidative stress in cortical neurons were observed. Truncated tau expression also enhanced Aβ-induced mitochondrial potential loss in primary neurons. These new findings show that Asp421-cleaved tau and Aβ cooperate to impair mitochondria, which likely contributes to the neuronal dysfunction in Alzheimer disease.
tau; Alzheimer; mitochondria; caspase; Aβ; oxidative stress
Cognitively normal (NL) individuals with a maternal history of late-onset Alzheimer’s disease (MH) show reduced brain glucose metabolism on FDG-PET as compared to those with a paternal history (PH) and those with negative family history (NH) of Alzheimer’s disease (AD). This FDG-PET study investigates whether metabolic deficits in NL MH are associated with advancing maternal age at birth. Ninety-six NL individuals with FDG-PET were examined, including 36 MH, 24 PH, and 36 NH. Regional-to-whole brain gray matter standardized FDG uptake value ratios were examined for associations with parental age across groups using automated regions-of-interest and statistical parametric mapping. Groups were comparable for clinical and neuropsychological measures. Brain metabolism in AD-vulnerable regions was lower in MH compared to NH and PH, and negatively correlated with maternal age at birth only in MH. There were no associations between paternal age and metabolism in any group. Evidence for a maternally inherited, maternal age-related mechanism provides further insight on risk factors and genetic transmission in late-onset AD.
Alzheimer’s disease; family history; PET imaging; glucose metabolism; age at birth; early detection
Inheritance of the ε4 allele of ApoE is the only confirmed and consistently replicated risk factor for late onset AD. ApoE is also a key ligand for LRP, a major neuronal LDL receptor. Despite the considerable converging evidence that implicates ApoE and LRP in the pathogenesis of AD, the precise mechanism by which ApoE and LRP modulate the risk for AD remains elusive. Moreover, studies investigating expression of ApoE and LRP in AD brain have reported variable and contradictory results. To overcome these inconsistencies, we studied the mRNA expression of ApoE and LRP in the postmortem brain of persons who died at different stages of dementia and AD-associated neuropathology relative to controls by qPCR and Western blotting. Clinical dementia rating scores were used as a measure of dementia severity, whereas, Braak neuropathological staging and neuritic plaque density were used as indices of the neuropathological progression of AD. ApoE and LRP mRNA expression was significantly elevated in the postmortem inferior temporal gyrus (area 20) and the hippocampus from individuals with dementia compared to those with intact cognition. In addition to their strong association with the progression of cognitive dysfunction, LRP and ApoE mRNA levels were also positively correlated with increasing neuropathological hallmarks of AD. Additionally, Western blot analysis of ApoE protein expression in the hippocampus showed that the differential expression observed at the transcriptional level is also reflected at the protein level. Given the critical role played by LRP and ApoE in Aβ and cholesterol trafficking, increased expression of LRP and ApoE may not only disrupt cholesterol homeostasis but may also contribute to some of the neurobiological features of AD, including plaque deposition.
Recent studies have linked dopamine to differences in behavior and brain activity in normal individuals. We explored these relationships in older and younger adults by investigating how functional connectivity between the striatum and prefrontal cortex is related to caudate dopamine and verbal working memory task performance. We studied 12 young and 18 older participants with functional magnetic resonance imaging (fMRI) during this task, and used positron emission tomography with the tracer 6-[18F]-fluoro-L-m-tyrosine (FMT) to assess dopamine synthesis capacity. Younger adults had a greater extent of frontal-caudate functional connectivity during the load-dependent delay period of the working memory task than the older participants. Across all subjects, the extent of this functional connectivity was negatively correlated with dopamine synthesis capacity, such that participants with the greatest connectivity had the lowest caudate FMT signal. Additionally, the extent of functional connectivity was positively correlated with working memory performance. Overall these data suggest interdependencies exist between fronto-striatal functional connectivity, dopamine, and working memory performance and that this system is functioning suboptimally in normal aging.
aging; working memory; dopamine; functional connectivity; FMT
The arachidonate 5-lipoxygenase-activating protein (ALOX5AP) gene has been associated with stroke. The majority of the reported ALOX5AP associations have considered non-radiologically confirmed infarcts as the stroke phenotype. We assessed the association of genetic variants in ALOX5AP with stroke defined by the presence infarcts on brain Magnetic Resonance Imaging (MRI). We studied 202 persons with MRI-defined brain infarcts cases and 487 healthy individuals of Caribbean Hispanic ancestry. Another sample of European ancestry comprised of 1,823 persons with MRI-defined brain infarct and 7,578 controls. Subjects were genotyped for the four SNPs that define ALOX5AP HapA haplotype. No association was found between SNPs and MRI-defined brain infarcts. Our data do not support the hypothesis that variants in ALOX5AP are associated with risk of MRI-defined brain infarcts.
MRI-defined brain infarcts; ALOX5AP
The TgCRND8 mouse model of Alzheimer’s disease exhibits progressive cortical and hippocampal β-amyloid accumulation, resulting in plaque pathology and spatial memory impairment by 3 months of age. We tested whether TgCRND8 cognitive function is disrupted prior to the appearance of macroscopic plaques in an object recognition task. We found profound deficits in 8-week-old mice. Animals this age were not impaired on the Morris water maze task. TgCRND8 and littermate controls did not differ in their duration of object exploration or optokinetic responses. Thus, visual and motor dysfunction did not confound the phenotype. Object memory deficits point to the frontal cortex and hippocampus as early targets of functional disruption. Indeed, we observed altered levels of brain-derived neurotrophic factor (BDNF) messenger ribonucleic acid (mRNA) in these brain regions of preplaque TgCRND8 mice. Our findings suggest that object recognition provides an early index of cognitive impairment associated with amyloid exposure and reduced brain-derived neurotrophic factor expression in the TgCRND8 mouse.
PMID: 20447730 CAMSID: cams2277
Alzheimer’s disease; Object recognition memory; Entorhinal cortex; Hippocampus; Morris water maze; Optokinetic responses; TgCRND8 mice; Spatial memory; Amyloid precursor protein (APP); Brain-derived neurotrophic factor (BDNF); Real Time RT-PCR
Transgenic mouse models of Alzheimer's disease (AD) with abundant β-amyloid develop memory impairments. However, multiple nonmnemonic cognitive domains such as attention and executive control are also compromised early in AD individuals, but have not been routinely assessed in animal models. Here, we assessed the cognitive abilities of TgCRND8 mice—a widely used model of β-amyloid pathology—with a touch screen-based automated test battery. The test battery comprises highly translatable tests of multiple cognitive constructs impaired in human AD, such as memory, attention, and response control, as well as appropriate control tasks. We found that familial AD mutations affect not only memory, but also cause significant alterations of sustained attention and behavioral flexibility. Because changes in attention and response inhibition may affect performance on tests of other cognitive abilities including memory, our findings have important consequences for the assessment of disease mechanisms and therapeutics in animal models of AD. A more comprehensive phenotyping with specialized, multicomponent cognitive test batteries for mice might significantly advance translation from preclinical mouse studies to the clinic.
Alzheimer's disease; Mouse models; Attention; Response control; Touchscreen; Memory; Cognition; β-amyloid; TgCRND8
γ-Secretase, a multi-subunit transmembrane protease comprised of presenilin, nicastrin, presenilin enhancer 2, and anterior pharynx-defective 1, participates in the regulated intramembrane proteolysis of Type I membrane proteins including the amyloid precursor protein (APP). Although Aph-1 is thought to play a structural role in the assembly of γ-secretase complex and several transmembrane domains (TMDs) of Aph-1 have been shown to be critical for its function, the importance of the other domains of Aph-1 remains elusive. We screened a series of Aph-1 mutants and focused on 9 mutations distributed in 6 different TMDs of human APH-1aS, assessing their ability to complement mouse embryonic fibroblasts lacking Aph-1. We showed that mutations in TMD4 (G126) and TMD5 (H171) of Aph-1a prevented the formation of the Nct/Aph-1 subcomplex. Importantly, although mutations in TMD3 (Q83/E84/R85) and TMD6 (H197) of APH-1aS did not affect Nct/Aph-1 subcomplex formation, both mutations prevented further association/endoproteolysis of PS1. We propose a model that identifies critical TMDs of Aph-1 for associations with Nct and PS for the stepwise assembly of γ-secretase components.
γ-Secretase; Aph-1; Nct; PS; mutagenesis; transmembrane domain
We investigated relationships between glucose metabolism, amyloid load and measures of cognitive and functional impairment in Alzheimer’s disease (AD). Patients meeting criteria for probable AD underwent [11C]PIB and [18F]FDG PET imaging and were assessed on a set of clinical measures. PIB Distribution volume ratios and FDG scans were spatially normalized and average PIB counts from regions-of-interest (ROI) were used to compute a measure of global PIB uptake. Separate voxel-wise regressions explored local and global relationships between metabolism, amyloid burden and clinical measures. Regressions reflected cognitive domains assessed by individual measures, with visuospatial tests associated with more posterior metabolism, and language tests associated with metabolism in the left hemisphere. Correlating regional FDG uptake with these measures confirmed these findings. In contrast, no correlations were found between either voxel-wise or regional PIB uptake and any of the clinical measures. Finally, there were no associations between regional PIB and FDG uptake. We conclude that regional and global amyloid burden does not correlate with clinical status or glucose metabolism in AD.
amyloid plaques; amyloidosis; Alzheimer’s disease; glucose metabolism; Pittsburgh compound-B; Fluorodeoxyglucose; dementia severity; cognition
Compared with apoE3, apoE4 is associated with increased risk to develop age-related cognitive decline, particularly in women. In this study, young, middle-aged, and old female mice expressing human apoE under control of the mouse apoE promoter were behaviorally analyzed. Cognitive performance in the water maze decreased with age in all mice. Compared with apoE2 and apoE3 mice, apoE4 mice showed better cognitive performance and higher measures of anxiety than apoE2 and apoE3 mice. Measures of anxiety correlated with cognitive performance in the water maze and passive avoidance tests and might have contributed to the enhanced cognitive performance of the apoE4 mice. ApoE4 mice showed better water maze learning and higher cortical apoE levels than mice expressing apoE4 in astrocytes under control of the GFAP promoter. This was not seen in apoE3 mice. There were no line differences in either genotype in spatial memory retention in the probe trial following the last day of hidden platform training. Thus, the promoter used to express apoE4 critically modulates its effects on brain function.
Aging; Anxiety; Apolipoprotein E; Cognition
Excitotoxicity is thought to play a pathogenic role in amyotrophic lateral sclerosis (ALS). Excitotoxic motor neuron death is mediated through the Ca2+-permeable AMPA-type of glutamate receptors and Ca2+ permeability is determined by the GluR2 subunit. We investigated whether polymorphisms or mutations in the GluR2 gene (GRIA2) predispose patients to ALS. Upon sequencing 24 patients and 24 controls no non-synonymous coding variants were observed but 24 polymorphisms were identified, 9 of which were novel. In a screening set of 310 Belgian ALS cases and 794 healthy controls and a replication set of 3,157 cases and 5,397 controls from 6 additional populations no association with susceptibility, age at onset or disease duration was observed. We conclude that polymorphisms in the GluR2 gene (GRIA2) are not a major contributory factor in the pathogenesis of ALS.
Amyotrophic lateral sclerosis; excitotoxicity; GluR2; motor neuron
We investigated the relationship between regional atrophy rates and 2-year cognitive decline in a large cohort of patients with mild cognitive impairment (MCI; N=103) and healthy controls (N=90). Longitudinal MRIs were analyzed using high-throughput image analysis procedures. Atrophy rates were derived by calculating percent cortical volume loss between baseline and 24-month scans. Step-wise regressions were performed to investigate the contribution of atrophy rates to language, memory, and executive functioning decline, controlling for age, gender, baseline performances, and disease progression. In MCI, left temporal lobe atrophy rates were associated with naming decline, whereas bilateral temporal, left frontal, and left anterior cingulate atrophy rates were associated with semantic fluency decline. Left entorhinal atrophy rate was associated with memory decline and bilateral frontal atrophy rates were associated with executive function decline. These data provide evidence that regional atrophy rates in MCI contribute to domain-specific cognitive decline, which appears to be partially independent of disease progression. MRI measures of regional atrophy can provide valuable information for understanding the neural basis of cognitive impairment in MCI.
cortical thinning; cognitive deficits; naming; semantic fluency; verbal memory; executive dysfunction
Aged rhesus monkeys exhibit deficits in hippocampus-dependent memory, similar to aging humans. Here we explored the basis of cognitive decline by first testing young adult and aged monkeys on a standard recognition memory test (delayed nonmatching-to-sample test; DNMS). Next we quantified synaptic density and morphology in the hippocampal dentate gyrus (DG) outer (OML) and inner molecular layer (IML). Consistent with previous findings, aged monkeys were slow to learn DNMS initially, and they performed significantly worse than young subjects when challenged with longer retention intervals. Although OML and IML synaptic parameters failed to differ across the young and aged groups, the density of perforated synapses in the OML was coupled with recognition memory accuracy. Independent of chronological age, monkeys classified on the basis of menses data as peri/post-menopausal scored worse on DNMS, and displayed lower OML perforated synapse density, than pre-menopausal monkeys. These results suggest that naturally occurring reproductive senescence potently influences synaptic connectivity in the DG OML, contributing to individual differences in the course of normal cognitive aging.
delayed nonmatching-to-sample; disector method; estrogen; hippocampus; menopause; outer molecular layer; perforated synapse; post-synaptic density; recognition memory
Neuroimage measures from magnetic resonance (MR) imaging, such as cortical thickness, have been playing an increasingly important role in searching for bio-markers of Alzheimer’s disease (AD). Recent studies show that, AD, mild cognitive impairment (MCI) and normal control (NC) can be distinguished with relatively high accuracy using the baseline cortical thickness. With the increasing availability of large longitudinal datasets, it also becomes possible to study the longitudinal changes of cortical thickness and their correlation with the development of pathology in AD. In this study, the longitudinal cortical thickness changes of 152 subjects from four clinical groups (AD, NC, Progressive-MCI and Stable-MCI) selected from Alzheimer’s Disease Neuroimaging Initiative (ADNI) are measured by our recently-developed 4D (spatial+temporal) thickness measuring algorithm. It is found that the four clinical groups demonstrate very similar spatial distribution of GM loss on cortex. To fully utilizing the longitudinal information and better discriminate the subjects from four groups, especially between Stable-MCI and Progressive-MCI, three different categories of features are extracted for each subject, i.e., (1) static cortical thickness measures computed from the baseline and endline, (2) cortex thinning dynamics, such as the thinning speed (mm/year) and the thinning ratio (endline/baseline), and (3) network features computed from the brain network constructed based on the correlation between the longitudinal thickness changes of different ROIs. By combining the complementary information provided by features from all three different categories, two classifiers are trained to diagnose AD and to predict the conversion to AD in MCI subjects, respectively. In the leave-one-out cross-validation, the proposed method can distinguish AD patients from NC at an accuracy of 96.1%, and can detect 81.7% (AUC=0.875) of the MCI converters at 6-months ahead of their conversions to AD. Also, by analyzing the brain network built via longitudinal cortical thickness changes, a significant decrease (P<0.02) of the network clustering coefficient (associated with the development of AD pathology) is found in the Progressive-MCI group, which indicates the degenerated wiring efficiency of the brain network due to AD. More interestingly, the decreasing of network clustering coefficient of the olfactory cortex region was also found in the AD patients, which suggests the olfactory dysfunction. Although the smell identification test is not performed in ADNI, this finding is consistent with other AD-related olfactory studies.
Cortical thickness; Longitudinal analysis; Classification; Alzheimer’s disease; Mild cognitive impairment; Dynamics; Brain network
Although many Alzheimer’s disease (AD) patients have a family history of the disease, it is rarely inherited in a predictable way. Functional magnetic resonance imaging (fMRI) studies of non-demented adults carrying familial AD mutations provide an opportunity to prospectively identify brain differences associated with early AD-related changes. We compared fMRI activity of 18 non-demented autosomal dominant AD mutation carriers with fMRI activity in 8 of their non-carrier relatives as they performed a novelty encoding task in which they viewed novel and repeated images. Because age of disease onset is relatively consistent within families, we also correlated fMRI activity with subjects’ distance from the median age of diagnosis for their family. Mutation carriers did not show significantly different voxelwise fMRI activity from non-carriers as a group. However, as they approached their family age of disease diagnosis, only mutation carriers showed increased fMRI activity in the fusiform and middle temporal gyri. This suggests that during novelty encoding, increased fMRI activity in the temporal lobe may relate to incipient AD processes.
PSEN1; APP; fMRI; familial Alzheimer’s disease