Verbal paired-associate learning by APOE genotype in non-demented older adults: fMRI evidence of a right hemispheric compensatory response

Gray matter volume in women with the BRCA mutation with and without ovarian removal: evidence for increased risk of late-life Alzheimer's disease or dementia

OBJECTIVE

Ovarian removal prior to spontaneous/natural menopause (SM) is associated with increased risk of late life dementias including Alzheimer's disease. This increased risk may be related to the sudden and early loss of endogenous estradiol. Women with breast cancer gene mutations (BRCAm) are counseled to undergo oophorectomy prior to SM to significantly reduce their risk of developing breast, ovarian, and cervical cancers. There is limited evidence of the neurological effects of ovarian removal prior to the age of SM showing women without the BRCAm had cortical thinning in medial temporal lobe structures. A second study in women with BRCAm and bilateral salpingo-oophorectomy (BSO) noted changes in cognition.

METHODS

The present, cross-sectional study examined whole-brain differences in gray matter (GM) volume using high-resolution, quantitative magnetic resonance imaging in women with BRCAm and intact ovaries (BRCA-preBSO [study cohort with BRCA mutation prior to oophorectomy]; n = 9) and after surgery with (BSO + estradiol-based therapy [ERT]; n = 10) and without (BSO; n = 10) postsurgical estradiol hormone therapy compared with age-matched women (age-matched controls; n = 10) with their ovaries.

RESULTS

The BRCA-preBSO and BSO groups showed significantly lower GM volume in the left medial temporal and frontal lobe structures. BSO + ERT exhibited few areas of lower GM volume compared with age-matched controls. Novel to this study, we also observed that all three BRCAm groups exhibited significantly higher GM volume compared with age-matched controls, suggesting continued plasticity.

CONCLUSIONS

The present study provides evidence, through lower GM volume, to support both the possibility that the BRCAm, alone, and early life BSO may play a role in increasing the risk for late-life dementia. At least for BRCAm with BSO, postsurgical ERT seems to ameliorate GM losses.

Functional network centrality indicates interactions between APOE4 and age across the clinical spectrum of Alzheimer's Disease

Advanced age is the most important risk factor for Alzheimer's disease (AD), and carrier-status of the Apolipoprotein E4 (APOE4) allele is the strongest known genetic risk factor. Many studies have consistently shown a link between APOE4 and synaptic dysfunction, possibly reflecting pathologically accelerated biological aging in persons at risk for AD. To test the hypothesis that distinct functional connectivity patterns characterize APOE4 carriers across the clinical spectrum of AD, we investigated 128 resting state functional Magnetic Resonance Imaging (fMRI) datasets from the Alzheimer's Disease Neuroimaging Initiative database (ADNI), representing all disease stages from cognitive normal to clinical dementia. Brain region centralities within functional networks, computed as eigenvector centrality, were tested for multivariate associations with chronological age, APOE4 carrier status and clinical stage (as well as their interactions) by partial least square analysis (PLSC). By PLSC analysis two distinct brain activity patterns could be identified, which reflected interactive effects of age, APOE4 and clinical disease stage. A first component including sensorimotor regions and parietal regions correlated with age and AD clinical stage (p < 0.001). A second component focused on medial-frontal regions and was specifically related to the interaction between age and APOE4 (p = 0.032). Our findings are consistent with earlier reports on altered network connectivity in APOE4 carriers. Results of our study highlight promise of graph-theory based network centrality to identify brain connectivity linked to genetic risk, clinical stage and age. Our data suggest the existence of brain network activity patterns that characterize APOE4 carriers across clinical stages of AD.

Genetic Variants and Persistent Impairment Following Mild Traumatic Brain Injury: A Systematic Review

OBJECTIVE

The purpose of this review is to systematically assess primary research publications on known genetic variants, which modify the risk for symptoms or dysfunction persisting 30 days or more following mild traumatic brain injury (mTBI).

SUMMARY OF REVIEW

A search of PubMed and Embase from inception through June 2022 identified 42 studies that associated genetic variants with the presence of symptoms or cognitive dysfunction 30 days or more following mTBI. Risk of bias was assessed for each publication using the Newcastle Ottawa Scale (NOS). Fifteen of the 22 studies evaluating apolipoprotein E ( APOE ) ɛ4 concluded that it was associated with worse outcomes and 4 of the 8 studies investigating the brain-derived neurotrophic factor ( BDNF ) reported the Val66Met allele was associated with poorer outcomes. The review also identified 12 studies associating 28 additional variants with mTBI outcomes. Of these, 8 references associated specific variants with poorer outcomes. Aside from analyses comparing carriers and noncarriers of APOE ɛ4 and BDNF Val66Met, most of the reviewed studies were too dissimilar, particularly in terms of specific outcome measures but also in genes examined, to allow for direct comparisons of their findings. Moreover, these investigations were observational and subject to varying degrees of bias.

CONCLUSIONS

The most consistent finding across articles was that APOE ɛ4 is associated with persistent post-mTBI impairment (symptoms or cognitive dysfunction) more than 30 days after mTBI. The sparsity of other well-established and consistent findings in the mTBI literature should motivate larger, prospective studies, which characterize the risk for persistent impairment with standardized outcomes in mTBI posed by other genetic variants influencing mTBI recovery.

Cerebellar EEG source localization reveals age-related compensatory activity moderated by genetic risk for Alzheimer's disease

The apolipoprotein-E (APOE) ε4 allele is the greatest genetic risk factor for late-onset Alzheimer's disease (AD), but alone it is not sufficiently predictive. Because neuropathological changes associated with AD begin decades before cognitive symptoms, neuroimaging of healthy, cognitively intact ε4 carriers (ε4+) may enable early characterization of patterns associated with risk for future decline. Research in the cerebral cortex highlights a period of compensatory recruitment in elders and ε4+, which serves to maintain cognitive functioning. Yet, AD-related changes may occur even earlier in the cerebellum. Advances in electroencephalography (EEG) source localization now allow effective modeling of cerebellar activity. Importantly, healthy aging and AD are associated with declines in both cerebellar functions and executive functioning (EF). However, it is not known whether cerebellar activity can detect pre-symptomatic AD risk. Thus, the current study analyzed cerebellar EEG source localization during an EF-dependent stop-signal task (i.e., inhibitory control) in healthy, intact older adults (Mage  = 80 years; 20 ε4+, 25 ε4-). Task performance was comparable between groups. Older age predicted greater activity in left crus II and lobule VIIb during the P300 window (i.e., performance evaluation), consistent with age-related compensation. Age*ε4 moderations specifically showed that compensatory patterns were evident only in ε4-, suggesting that cerebellar compensatory resources may already be depleted in healthy ε4+ elders. Thus, the posterolateral cerebellum is sensitive to AD-related neural deficits in healthy elders. Characterization of these patterns may be essential for the earliest possible detection of AD risk, which would enable critical early intervention prior to symptom onset.

Sex differences in longitudinal changes of episodic memory-related brain activity and cognition in cognitively unimpaired older adults with a family history of Alzheimer's disease

Episodic memory decline is an early symptom of Alzheimer's disease (AD) - a neurodegenerative disease that has a higher prevalence rate in older females compared to older males. However, little is known about why these sex differences in prevalence rate exist. In the current longitudinal task fMRI study, we explored whether there were sex differences in the patterns of memory decline and brain activity during object-location (spatial context) encoding and retrieval in a large sample of cognitively unimpaired older adults from the Pre-symptomatic Evaluation of Novel or Experimental Treatments for Alzheimer's Disease (PREVENT-AD) program who are at heightened risk of developing AD due to having a family history (+FH) of the disease. The goal of the study was to gain insight into whether there are sex differences in the neural correlates of episodic memory decline, which may advance knowledge about sex-specific patterns in the natural progression to AD. Our results indicate that +FH females performed better than +FH males at both baseline and follow-up on neuropsychological and task fMRI measures of episodic memory. Moreover, multivariate data-driven task fMRI analysis identified generalized patterns of longitudinal decline in medial temporal lobe activity that was paralleled by longitudinal increases in lateral prefrontal cortex, caudate and midline cortical activity during successful episodic retrieval and novelty detection in +FH males, but not females. Post-hoc analyses indicated that higher education had a stronger effect on +FH females neuropsychological scores compared to +FH males. We conclude that higher educational attainment may have a greater neuroprotective effect in older +FH females compared to +FH males.

Interactive association of posttraumatic stress disorder, apolipoprotein ε4 genotype, and age on cognitive functioning

BACKGROUND

The ε4 allele of the apolipoprotein (APOE) gene and posttraumatic stress disorder (PTSD) are associated with cognitive deficits. Both associations may vary depending on age. No previous study has examined a possible three-way interaction between APOE ε4, PTSD, and age on cognitive functioning.

METHODS

Data were analyzed from 1244 European-American U.S. military veterans who participated in the 2011 National Health and Resilience in Veterans Study (NHRVS). Analyses of covariance were used to examine the main effects and interactions of APOE ε4, PTSD, and age on learning/working memory (LWM) and attention/psychomotor (APM) performance.

RESULTS

A significant three-way interaction between APOE ε4, PTSD, and age on the LWM composite (ηp 2  = 0.011) was observed such that the main effect of APOE ε4 on LWM was only significant for older participants with PTSD. A significant two-way interaction between PTSD and age on the APM composite (ηp 2  = 0.011) was observed such that the main effect of PTSD on APM was only significant in older participants.

CONCLUSION

Older APOE ε4 carriers with probable PTSD showed poorer LWM performance relative to other groups. Aging-related associations on APM performance were most pronounced in veterans with PTSD. These data are preliminary evidence that identification and treatment of PTSD may be beneficial for individuals at risk for age-related cognitive impairment.

APOE Genotype Modifies the Association of Fusiform Gyrus Cerebral Metabolic Rate of Oxygen Consumption and Object Naming Performance

BACKGROUND

The apolipoprotein E (APOE) ɛ4 allele confers risk for age and Alzheimer's disease related cognitive decline but the mechanistic link remains poorly understood. Blood oxygenation level dependent (BOLD) response in the fusiform gyrus (FG) during object naming appears greater among APOEɛ4 carriers even in the face of equivalent cognitive performance, suggesting neural compensation. However, BOLD is susceptible to known age and APOE-related vascular changes that could confound its interpretation.

OBJECTIVE

To address this limitation, we used calibrated fMRI during an object naming task and a hypercapnic challenge to obtain a more direct measure of neural function - percent change cerebral metabolic rate of oxygen consumption (%ΔCMRO2).

METHODS

Participants were 45 older adults without dementia (28 ɛ4-, 17 ɛ4+) between the ages of 65 and 85. We examined APOE-related differences in %ΔCMRO2 in the FG during object naming and the extent to which APOE modified associations between FG %ΔCMRO2 and object naming accuracy. Exploratory analyses also tested the hypothesis that %ΔCMRO2 is less susceptible to vascular compromise than are measures of %ΔCBF and %ΔBOLD.

RESULTS

We observed a modifying role of APOE on associations between FG %ΔCMRO2 and cognition, with ɛ4 carriers (but not non-carriers) demonstrating a positive association between right FG %ΔCMRO2 and object naming accuracy.

CONCLUSION

Results suggest that the relationship between neural function and cognition is altered among older adult APOEɛ4 carriers prior to the onset of dementia, implicating CMRO2 response as a potential mechanism to support cognition in APOE-related AD risk.

Altered functional connectivity pattern of hippocampal subfields in individuals with objectively-defined subtle cognitive decline and its association with cognition and cerebrospinal fluid biomarkers

Recent studies have shown that in the preclinical phase of Alzheimer's disease (AD), subtle cognitive changes can be detected using sensitive neuropsychological measures, and have proposed the concept of objectively-defined subtle cognitive decline (Obj-SCD). We aimed to assess the functional alteration of hippocampal subfields in individuals with Obj-SCD and its association with cognition and pathological biomarkers. Forty-two participants with cognitively normal (CN), 29 with Obj-SCD, and 55 with mild cognitive impairment (MCI) were retrospectively collected from the ADNI database. Neuropsychological performance, functional MRI, and cerebrospinal fluid (CSF) data were obtained. We calculated the seed-based functional connectivity (FC) of hippocampal subfields (cornu ammonis1 [CA1], CA2/3/dentate gyrus [DG], and subiculum) with whole-brain voxels. Additionally, we analyzed the correlation between FC values of significantly altered regions and neuropsychological performance and CSF biomarkers. The Obj-SCD group showed lower FC between left CA1-CA2/3/DG and right thalamus and higher FC between right subiculum and right superior parietal gyrus (SPG) compared with the CN and MCI groups. In the Obj-SCD group, FC values between left CA2/3/DG and right thalamus were positively associated with Auditory Verbal Learning Test (AVLT) recognition (r = 0.395, p = 0.046) and CSF Aβ1-42 levels (r = 0.466, p = 0.019), and FC values between left CA1 and right thalamus were positively correlated with CSF Aβ1-42 levels (r = 0.530, p = 0.006). Taken together, dysfunction in CA1-CA2/3/DG subregions suggests subtle cognitive impairment and AD-specific pathological changes in individuals with Obj-SCD. Additionally, increased subiculum connectivity may indicate early functional compensation for subtle cognitive changes.

Imminent cognitive decline in normal elderly individuals is associated with hippocampal hyperconnectivity in the variant neural correlates of episodic memory

The secondary prevention trials of Alzheimer's disease (AD) require an enrichment strategy to recruit individuals with imminent cognitive decline at the preclinical stage. Previously, we demonstrated a variant neural correlates of episodic memory (EM) function in apolipoprotein E (APOE) ε4 carriers. Herein, we investigated whether this variation was associated with longitudinal EM performance. This 3-year longitudinal study included 88 normal elderly subjects with EM assessment and resting-state functional MRI data at baseline; 48 subjects (27 ε3 homozygotes and 21 ε4 carriers) underwent follow-up EM assessment. In the identified EM neural correlates, multivariable regression models examined the association between hippocampal functional connectivity (HFC) and longitudinal EM change. Independent validation was performed using the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset. At baseline, the EM neural correlates were characterized in the Papez circuit regions in the ε3 homozygotes, but in the sensorimotor cortex and cuneus in the ε4 carriers. Longitudinally, the ε4 carriers exhibited a negative association of the baseline HFC strength in the EM neural correlates with annual rate of EM change (R² = 0.25, p = 0.05). This association also showed a trend in the ADNI dataset (R² = 0.42, p = 0.06). These results indicate that hippocampal hyperconnectivity in the variant EM neural correlates is associated with imminent EM decline in ε4 carriers, which may serve as a promising enrichment strategy for secondary prevention trials of AD.

Preserved Consciousness in Alzheimer's Disease and Other Dementias: Caregiver Awareness and Communication Strategies

Alzheimer's disease is an insidious onset neurodegenerative syndrome without effective treatment or cure. It is rapidly becoming a global health crisis that is overwhelming healthcare, society, and individuals. The clinical nature of neurocognitive decline creates significant challenges in bidirectional communication between caregivers and persons with Alzheimer's disease (AD) that can negatively impact quality-of-life. This paper sought to understand how and to what extent would awareness training about the levels of consciousness in AD influence the quality-of-life interactions in the caregiver-patient dyad. A literature review of multiple databases was conducted utilizing a transdisciplinary approach. The sum of findings indicates a positive relationship between enhanced caregiver awareness and training, positive interactions, and improved QOL measures among patients and caregivers. A multidirectional relationship was found among healthcare policies, training and education resources, caregivers, and persons with AD. Specifically, the current lack of policy and inadequate training and educational resources has various detrimental effects on patients and caregivers, while improvements in training and education of caregivers yields positive outcomes in communication and QOL. Furthermore, evidence of preserved consciousness in persons with AD was demonstrated from multiple disciplines, including neurobiological, psychological, and biopsychosocial models. The literature further revealed several methods to access the preserved consciousness in persons with AD and related dementias, including sensory, emotional, and cognitive stimulations. The evidence from the literature suggests a reframed approach to our understanding and treatment of persons with AD is not only warranted, but crucial to address the needs of those affected by AD.

Refined prefrontal working memory network as a neuromarker for Alzheimer's disease

Detecting Alzheimer's disease (AD) is an important step in preventing pathological brain damage. Working memory (WM)-related network modulation can be a pathological feature of AD, but is usually modulated by untargeted cognitive processes and individual variance, resulting in the concealment of this key information. Therefore, in this study, we comprehensively investigated a new neuromarker, named "refined network," in a prefrontal cortex (PFC) that revealed the pathological features of AD. A refined network was acquired by removing unnecessary variance from the WM-related network. By using a functional near-infrared spectroscopy (fNIRS) device, we evaluated the reliability of the refined network, which was identified from the three groups classified by AD progression: healthy people (N=31), mild cognitive impairment (N=11), and patients with AD (N=18). As a result, we identified edges with significant correlations between cognitive functions and groups in the dorsolateral PFC. Moreover, the refined network achieved a significantly correlating metric with neuropsychological test scores, and a remarkable three-class classification accuracy (95.0%). These results implicate the refined PFC WM-related network as a powerful neuromarker for AD screening.

APOE moderates the effect of hippocampal blood flow on memory pattern separation in clinically normal older adults

Pattern separation, the ability to differentiate new information from previously experienced similar information, is highly sensitive to hippocampal structure and function and declines with age. Functional MRI studies have demonstrated hippocampal hyperactivation in older adults compared to young, with greater task-related activation associated with worse pattern separation performance. The current study was designed to determine whether pattern separation was sensitive to differences in task-free hippocampal cerebral blood flow (CBF) in 130 functionally intact older adults. Given prior evidence that apolipoprotein E e4 (APOE e4) status moderates the relationship between CBF and episodic memory, we predicted a stronger negative relationship between hippocampal CBF and pattern separation in APOE e4 carriers. An interaction between APOE group and right hippocampal CBF was present, such that greater right hippocampal CBF was related to better lure discrimination in noncarriers, whereas the effect reversed directionality in e4 carriers. These findings suggest that neurovascular changes in the medial temporal lobe may underlie memory deficits in cognitively normal older adults who are APOE e4 carriers.

Connectome-based model predicts episodic memory performance in individuals with subjective cognitive decline and amnestic mild cognitive impairment

OBJECTIVE

To explore whether the whole brain resting-state functional connectivity (rs-FC) could predict episodic memory performance in individuals with subjective cognitive decline and amnestic mild cognitive impairment.

METHOD

This study included 33 cognitive normal (CN), 26 subjective cognitive decline (SCD) and 27 amnestic mild cognitive impairment (aMCI) patients, and all the participants completed resting-state fMRI (rs-fMRI) scan and neuropsychological scale test data. Connectome-based predictive modeling (CPM) based on the rs-FC data was used to predict the auditory verbal learning test-delayed recall (AVLT-DR) scores, which measured episodic memory in individuals. Pearson correlation between each brain connection in the connectivity matrices and AVLT-DR scores was computed across the patients in predementia stages of Alzheimer's disease (AD). The Pearson correlation coefficient values separated into a positive network and a negative network. Predictive networks were then defined and employed by calculating positive and negative network strengths. CPM with leave-one-out cross-validation (LOOCV) was conducted to train linear models to respectively relate positive and negative network strengths to AVLT-DR scores in the training set. During the testing procedure, each left-out testing subject's strengths of positive and negative network was normalized using the parameters acquired during training procedure, and then the trained models were used to predict the testing participant's AVLT-DR score.

RESULTS

The negative network predictive model tested LOOCV significantly predicted individual differences in episodic memory from rs-FC. Key nodes that brain regions contributed to the prediction model were mainly located in the prefrontal cortex, frontal cortex, parietal cortex and temporal lobe.

CONCLUSION

Our findings demonstrated that rs-FC among multiple neural systems could predict episodic memory at the individual level.

Apolipoprotein E ε4 Allele-Based Differences in Brain Volumes Are Largely Uniform Across Late Middle Aged and Older Hispanic/Latino- and Non-Hispanic/Latino Whites Without Dementia

Hispanics/Latinos are at an equal or a greater risk for Alzheimer's disease (AD), yet risk factors remain more poorly characterized as compared to non-Hispanic/Latino Whites. Among non-Hispanic/Latino White cohorts, the apolipoprotein E (APOE) ε4 allele is one of the strongest risk factors for AD with subtle declines in episodic memory and brain volumes detectable in the preclinical stages. We examined whether the APOE ε4 status had a differential impact on cognition and brain volumes among cognitively healthy and mild cognitively impaired Hispanics/Latinos (n = 86; ε4 n = 23) compared to a well-matched group of non-Hispanic/Latino Whites (n = 92; ε4 n = 29). Neither the APOE ε4 status nor the interaction between the ε4 status and ethnicity was associated with cognitive performance. The APOE ε4 status was associated with white matter and not with gray matter volumes. APOE ε4 carriers had a significantly smaller total brain white matter volumes, as well as smaller right middle temporal and left superior temporal volumes. The Hispanics/Latinos had significantly smaller left middle frontal gray matter volumes, yet marginally larger overall white matter volumes, than the non-Hispanic/Latino Whites. Exploratory analysis within the Hispanic/Latino sample found that those people whose primary language was Spanish had larger total brain white matter volumes compared primarily to the English speakers. Importantly, primary language differences only held for Hispanic/Latino ε4 carriers and did not differentiate Hispanic/Latino non-carriers, underscoring the need for further investigation into the impacts of language and acculturation on cognitive aging among the fastest growing ethnic minority group in the United States.

Value of magnetic resonance spectroscopy in geriatric patients with cognitive impairment

Background

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

Objective

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

Subjects and methods

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

Results

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

Conclusion

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

Risk for Alzheimer's disease: A review of long-term episodic memory encoding and retrieval fMRI studies

Many risk factors have been identified that predict future progression to Alzheimer's disease (AD). However, clear links have yet to be made between these risk factors and how they affect brain functioning in early stages of AD. We conducted a narrative review and a quantitative analysis to better understand the relationship between nine categories of AD risk (i.e., brain pathology, genetics/family history, vascular health, head trauma, cognitive decline, engagement in daily life, late-life depression, sex/gender, and ethnoracial group) and task-evoked fMRI activity during episodic memory in cognitively-normal older adults. Our narrative review revealed widespread regional alterations of both greater and lower brain activity with AD risk. Nevertheless, our quantitative analysis revealed that a subset of studies converged on two patterns: AD risk was associated with (1) greater brain activity in frontal and parietal regions, but (2) reduced brain activity in hippocampal and occipital regions. The brain regions affected depended on the assessed memory stage (encoding or retrieval). Although the results clearly indicate that AD risks impact brain activity, we caution against using fMRI as a diagnostic tool for AD at the current time because the above consistencies were present among much variability, even among the same risk factor.

Relationship between the Presence of the ApoE ε4 Allele and EEG Complexity along the Alzheimer's Disease Continuum

Alzheimer's disease (AD) is the most prevalent cause of dementia, being considered a major health problem, especially in developed countries. Late-onset AD is the most common form of the disease, with symptoms appearing after 65 years old. Genetic determinants of AD risk are vastly unknown, though, ε 4 allele of the ApoE gene has been reported as the strongest genetic risk factor for AD. The objective of this study was to analyze the relationship between brain complexity and the presence of ApoE ε 4 alleles along the AD continuum. For this purpose, resting-state electroencephalography (EEG) activity was analyzed by computing Lempel-Ziv complexity (LZC) from 46 healthy control subjects, 49 mild cognitive impairment subjects, 45 mild AD patients, 44 moderate AD patients and 33 severe AD patients, subdivided by ApoE status. Subjects with one or more ApoE ε 4 alleles were included in the carriers subgroups, whereas the ApoE ε 4 non-carriers subgroups were formed by subjects without any ε 4 allele. Our results showed that AD continuum is characterized by a progressive complexity loss. No differences were observed between AD ApoE ε 4 carriers and non-carriers. However, brain activity from healthy subjects with ApoE ε 4 allele (carriers subgroup) is more complex than from non-carriers, mainly in left temporal, frontal and posterior regions (p-values < 0.05, FDR-corrected Mann-Whitney U-test). These results suggest that the presence of ApoE ε 4 allele could modify the EEG complexity patterns in different brain regions, as the temporal lobes. These alterations might be related to anatomical changes associated to neurodegeneration, increasing the risk of suffering dementia due to AD before its clinical onset. This interesting finding might help to advance in the development of new tools for early AD diagnosis.

Lateralized memory circuit dropout in Alzheimer’s disease patients

Altered connectivity within neuronal networks is often observed in Alzheimer’s disease. However, delineating pro-cognitive compensatory changes from pathological network decline relies on characterizing network and task effects together. In this study, we interrogated the dynamics of occipito-temporo-frontal brain networks responsible for implicit and explicit memory processes using high-density EEG and dynamic causal modelling. We examined source-localized network activity from patients with Alzheimer’s disease (n = 21) and healthy controls (n = 21), while they performed both visual recognition (explicit memory) and implicit priming tasks. Parametric empirical Bayes analyses identified significant reductions in temporo-frontal connectivity and in subcortical visual input in patients, specifically in the left hemisphere during the recognition task. There was also slowing in frontal left hemisphere signal transmission during the implicit priming task, with significantly more distinct dropout in connectivity during the recognition task, suggesting that these network drop-out effects are affected by task difficulty. Furthermore, during the implicit memory task, increased right frontal activity was correlated with improved task performance in patients only, suggesting that right-hemisphere compensatory mechanisms may be employed to mitigate left-lateralized network dropout in Alzheimer’s disease. Taken together, these findings suggest that Alzheimer’s disease is associated with lateralized memory circuit dropout and potential compensation from the right hemisphere, at least for simpler memory tasks.

Cognitive and neuropsychological examination of the elderly

Neuropsychological assessment plays a prominent role in the evaluation and care of patients with neurodegenerative diseases throughout the dynamic course of disease. As a biomarker of disease, neuropsychological measurement can distinguish normal from pathologic aging processes. Further, neuropsychological data can help distinguish and classify underlying pathologies in dementing diseases, augmenting imaging and biofluid markers in this area. Neuropsychological data can predict increased or reduced risk for dementia conferred by multiple factors, and describe disease trajectory in affected individuals. Cognitive evaluation can also estimate and address functional outcomes that are most important to patients and their loved ones and that are clinically relevant to diagnostic staging. In informing intervention and patient care needs, areas of cognitive weakness highlight targets for support/intervention, while areas of cognitive strength can be capitalized upon to modify the clinical course of disease. These functions can be accomplished through the complementary use of brief screening tools and comprehensive test batteries. However, for neuropsychological data to serve these functions, it is critical to understand neuropsychological test properties and nondisease factors that can account for variance in test performance. This chapter concludes with directions for future research.

The role of education in a vascular pathway to episodic memory: brain maintenance or cognitive reserve?

Educational attainment is associated with cognition among older adults, but this association is complex and not well understood. While associated with better cognition among healthy adults, more education predicts faster decline in older adults with cognitive impairment. Education may influence cognitive functioning through mechanisms involving brain maintenance (BM: reduced age-related pathology) or cognitive reserve (CR: altered pathology-cognition association). We examined evidence for each mechanism by quantifying main and interaction effects of education within a well-studied pathway involving systolic blood pressure, white matter hyperintensities (WMH), and episodic memory in 2 samples without dementia at the baseline (total N = 1136). There were no effects of education on systolic blood pressure or WMH, suggesting a lack of evidence for BM. In the sample less likely to progress to dementia, education attenuated the effect of WMH on memory at the baseline. In the sample more likely to progress to dementia, education exacerbated this effect at the baseline. These moderations provide evidence for a CR mechanism and are consistent with previous findings of faster decline once CR is depleted.

Is brain connectome research the future frontier for subjective cognitive decline? A systematic review

OBJECTIVE

We performed a systematic literature review on Subjective Cognitive Decline (SCD) in order to examine whether the resemblance of brain connectome and functional connectivity (FC) alterations in SCD with respect to MCI, AD and HC can help us draw conclusions on the progression of SCD to more advanced stages of dementia.

METHODS

We searched for studies that used any neuroimaging tool to investigate potential differences/similarities of brain connectome in SCD with respect to HC, MCI, and AD.

RESULTS

Sixteen studies were finally included in the review. Apparent FC connections and disruptions were observed in the white matter, default mode and gray matter networks in SCD with regards to HC, MCI, and AD. Interestingly, more apparent connections in SCD were located over the posterior regions, while an increase of FC over anterior regions was observed as the disease progressed.

CONCLUSIONS

Elders with SCD display a significant disruption of the brain network, which in most of the cases is worse than HC across multiple network parameters.

SIGNIFICANCE

The present review provides comprehensive and balanced coverage of a timely target research activity around SCD with the intention to identify similarities/differences across patient groups on the basis of brain connectome properties.

Distinct neural correlates of episodic memory among apolipoprotein E alleles in cognitively normal elderly

The apolipoprotein E (APOE) ε4 and ε2 alleles are acknowledged genetic factors modulating Alzheimer's disease (AD) risk and episodic memory (EM) deterioration in an opposite manner. Mounting neuroimaging studies describe EM-related brain activity differences among APOE alleles but remain limited in elucidating the underlying mechanism. Here, we hypothesized that the APOE ε2, ε3, and ε4 alleles have distinct EM neural substrates, as a manifestation of degeneracy, underlying their modulations on EM-related brain activity and AD susceptibility. To test the hypothesis, we identified neural correlates of EM function by correlating intrinsic hippocampal functional connectivity networks with neuropsychological EM performances in a voxelwise manner, with 129 cognitively normal elderly subjects (36 ε2 carriers, 44 ε3 homozygotes, and 49 ε4 carriers). We demonstrated significantly different EM neural correlates among the three APOE allele groups. Specifically, in the ε3 homozygotes, positive EM neural correlates were characterized in the Papez circuit regions; in the ε4 carriers, positive EM neural correlates involved the lateral temporal cortex, premotor cortex/sensorimotor cortex/superior parietal lobule, and cuneus; and in the ε2 carriers, negative EM neural correlates appeared in the bilateral frontopolar, posteromedial, and sensorimotor cortex. Further, in the ε4 carriers, the interaction between age and EM function occurred in the temporoparietal junction and prefrontal cortex. Our findings suggest that the underlying mechanism of APOE polymorphism modulations on EM function and AD susceptibility is genetically related to the neural degeneracy of EM function across APOE alleles.

Medial Temporal Lobe Disconnection and Hyperexcitability Across Alzheimer's Disease Stages

 The posteromedial cortex (PMC) and medial temporal lobes (MTL) are two brain regions particularly vulnerable in Alzheimer’s disease (AD). We have reviewed the spatiotemporal patterns of amyloid-β and tau accumulation, local MTL functional alterations and MTL-PMC network reconfiguration, and propose a model to relate these elements to each other. Functional and structural MTL-PMC disconnection happen concomitant with amyloid-β plaques and neurofibrillary tau accumulation within these same regions. Ongoing disconnection is accompanied by dysfunctional intrinsic local MTL circuit hyperexcitability, which exacerbates across distinct clinical stages of AD. Our overarching model proposes a sequence of events relating the spatiotemporal patterns of amyloid-β and tau accumulation to MTL-PMC disconnection and local MTL hyperexcitability. We hypothesize that cortical PMC amyloid-β pathology induces long-range information processing deficits through functional and structural MTL-PMC dysconnectivity at early disease stages, which in turn drives local MTL circuit hyperexcitability. Intrinsic local MTL circuit hyperexcitability subsequently accelerates local age-related tau deposition, facilitating tau spread from the MTL to the PMC, eventually resulting in extensive structural degeneration of white and grey matter as the disease advances. We hope that the present model may inform future longitudinal studies needed to test the proposed sequence of events.

How pattern information analyses of semantic brain activity elicited in language comprehension could contribute to the early identification of Alzheimer's Disease

Alzheimer's disease (AD) is associated with a loss of semantic knowledge reflecting brain pathophysiology that begins years before dementia. Identifying early signs of pathophysiology induced dysfunction in the neural systems that access and process words' meaning could therefore help forecast dementia. This article reviews pioneering studies demonstrating that abnormal functional Magnetic Resonance Imaging (fMRI) response patterns elicited in semantic tasks reflect both AD-pathophysiology and the hereditary risk of AD, and also can help forecast cognitive decline. However, to bring current semantic task-based fMRI research up to date with new AD research guidelines the relationship with different types of AD-pathophysiology needs to be more thoroughly examined. We shall argue that new analytic techniques and experimental paradigms will be critical for this. Previous work has relied on specialized tests of specific components of semantic knowledge/processing (e.g. famous name recognition) to reveal coarse AD-related changes in activation across broad brain regions. Recent computational advances now enable more detailed tests of the semantic information that is represented within brain regions during more natural language comprehension. These new methods stand to more directly index how pathophysiology alters neural information processing, whilst using language comprehension as the basis for a more comprehensive examination of semantic brain function. We here connect the semantic pattern information analysis literature up with AD research to raise awareness to potential cross-disciplinary research opportunities.

Dissociable effects of the apolipoprotein-E (APOE) gene on short- and long-term memories

Short- and long-term memory performance as a function of apolipoprotein-E (APOE) genotype was examined in older, healthy individuals using sensitive and comparable tasks to provide a more detailed description of influences of the ε4 allele (highest genetic risk factor for Alzheimer's disease) on memory. Older heterozygous and homozygous ε4 carriers and noncarriers performed 2 tasks of memory. Both tasks allowed us to measure memory for item identity and locations, using a sensitive, continuous measure of report. Long-term memory for object locations was impaired in ε4/ε4 carriers, whereas, paradoxically, this group demonstrated superior short-term memory for locations. The dissociable effects of the gene on short- and long-term memory suggest that the effect of genotype on these two types of memories, and their neural underpinnings, might not be co-extensive. Whereas the long-term memory impairment might be linked to preclinical Alzheimer's disease, the short-term memory advantage may reflect an independent, phenotypical effect of this allele on cognition.

Current understanding of magnetic resonance imaging biomarkers and memory in Alzheimer's disease

Alzheimer's disease (AD) is caused by a cascade of changes to brain integrity. Neuroimaging biomarkers are important in diagnosis and monitoring the effects of interventions. As memory impairments are among the first symptoms of AD, the relationship between imaging findings and memory deficits is important in biomarker research. The most established magnetic resonance imaging (MRI) finding is hippocampal atrophy, which is related to memory decline and currently used as a diagnostic criterion for AD. While the medial temporal lobes are impacted early by the spread of neurofibrillary tangles, other networks and regional changes can be found quite early in the progression. Atrophy in several frontal and parietal regions, cortical thinning, and white matter alterations correlate with memory deficits in early AD. Changes in activation and connectivity have been detected by functional MRI (fMRI). Task-based fMRI studies have revealed medial temporal lobe hypoactivation, parietal hyperactivation, and frontal hyperactivation in AD during memory tasks, and activation patterns of these regions are also altered in preclinical and prodromal AD. Resting state fMRI has revealed alterations in default mode network activity related to memory in early AD. These studies are limited in part due to the historic inclusion of patients who had suspected AD but likely did not have the disorder. Modern biomarkers allow for more diagnostic certainty, allowing better understanding of neuroimaging markers in true AD, even in the preclinical stage. Larger patient cohorts, comparison of candidate imaging biomarkers to more established biomarkers, and inclusion of more detailed neuropsychological batteries to assess multiple aspects of memory are needed to better understand the memory deficit in AD and help develop new biomarkers. This article reviews MRI findings related to episodic memory impairments in AD and introduces a new study with multimodal imaging and comprehensive neuropsychiatric evaluation to overcome current limitations.

Faulty Adaptation to Repeated Face-Name Associative Pairs in Mild Cognitive Impairment is Predictive of Cognitive Decline

OBJECTIVE

We examined BOLD (Blood-Oxygen-Level Dependent) activity reduction upon stimuli repetition of face-name pairs in older adults with amnestic (aMCI) and non-amnestic (naMCI) mild cognitive impairment diagnosed using a comprehensive actuarial method, and relationships between activity reduction and behavioral indices.

METHOD

Twenty-nine cognitively healthy older adults (CHs) and 20 with MCI (n = 12 aMCI; n = 8 naMCI) underwent functional MRI event-related imaging, a comprehensive neuropsychological battery, and 1-year follow-up exam. During scanning, participants were shown face-name pairs 1-3 times and administered a post-scan recognition task.

RESULTS

The MCI group demonstrated less activity reduction upon repetition of face-name pairs within the MTL and other regions compared to CHs. Less activity reduction was associated with poorer Time 1 neuropsychological performance for the CH group and poorer post-scan recognition performance for the MCI group. Less activity reduction was related to poorer neuropsychological performance at Time 2 in the MCI group. Within MCIs, those with aMCI demonstrated less activity reduction upon repetition of face-name pairs than those with naMCI.

CONCLUSIONS

Distinct patterns of brain activity were identified in the MCI group compared to CHs, and aMCI compared to naMCI. Activated regions were not restricted to traditional memory circuitry, implicating a wider network of regions involved in the encoding of associative tasks. Findings add support to the hypothesis that lack of reduced BOLD activity reflects "faulty adaptation" to repeated stimuli and that reduction in activity represents successful encoding processes. They also provide further support for use of the face-name paradigm as a marker of prodromal Alzheimer's disease, and method to distinguish between MCI subtypes.

Pupillary Responses as a Biomarker of Early Risk for Alzheimer's Disease

Task-evoked pupillary responses may be a psychophysiological biomarker of early risk for mild cognitive impairment (MCI) and Alzheimer's disease (AD). Pupil dilation during cognitive tasks reflects cognitive effort until compensatory capacity is surpassed and performance declines are manifest, and reflects activation in the locus coeruleus, where degenerative changes have been found in the earliest stages of AD. We recorded pupillary responses during digit span recall in 918 participants ages 56-66. Despite normal performance, amnestic single-domain MCI (S-MCI) participants showed greater pupil dilation than non-amnestic S-MCI and cognitively normal (CN) participants at lower cognitive loads. Multi-domain MCI (M-MCI) participants failed to modulate effort across cognitive loads and showed poorer performance. Pupillary responses differentiated MCI and CN groups. Amnestic S-MCI participants required compensatory effort to maintain performance, consistent with increased risk for decline. Greater effort in CN individuals might indicate risk for MCI. Results are consistent with dysfunction in locus coeruleus-linked brain systems. This brief task shows promise as a biomarker for early MCI and AD risk prediction.

Subjective memory complaints are associated with brain activation supporting successful memory encoding

Subjective memory complaints, the perceived decline in cognitive abilities in the absence of clinical deficits, may precede Alzheimer's disease. Individuals with subjective memory complaints show differential brain activation during memory encoding; however, whether such differences contribute to successful memory formation remains unclear. Here, we investigated how subsequent memory effects, activation which is greater for hits than misses during an encoding task, differed between healthy older adults aged 50 to 85 years with (n = 23) and without (n = 41) memory complaints. Older adults with memory complaints, compared to those without, showed lower subsequent memory effects in the occipital lobe, superior parietal lobe, and posterior cingulate cortex. In addition, older adults with more memory complaints showed a more negative subsequent memory effects in areas of the default mode network, including the posterior cingulate cortex, precuneus, and ventromedial prefrontal cortex. Our findings suggest that for successful memory formation, older adults with subjective memory complaints rely on distinct neural mechanisms which may reflect an overall decreased task-directed attention.

The Effect of Apolipoprotein E ε4 (APOE ε4) on Visuospatial Working Memory in Healthy Elderly and Amnestic Mild Cognitive Impairment Patients: An Event-Related Potentials Study

Background: Apolipoprotein E (APOE) ε4 is the only established risk gene for late-onset, sporadic Alzheimer’s disease (AD). Previous studies have provided inconsistent evidence for the effect of APOE ε4 status on the visuospatial working memory (VSWM).

Objective: The aim was to investigate the effect of APOE ε4 on VSWM with an event-related potential (ERP) study in healthy controls (HC) and amnestic mild cognitive impairment (aMCI) patients.

Methods: The study recorded 39 aMCI patients (27 APOE ε4 non-carriers and 12 APOE ε4 carriers) and their 43 matched controls (25 APOE ε4 non-carriers and 18 APOE ε4 carriers) with an 64-channel electroencephalogram. Participants performed an N-back task, a VSWM paradigm that manipulated the number of items to be stored in memory.

Results: The present study detected reduced accuracy and delayed mean correct response time (RT) in aMCI patients compared to HC. P300, a positive component that peaks between 300 and 500 ms, was elicited by the VSWM task. In addition, aMCI patients showed decreased P300 amplitude at the central–parietal (CP1, CPz, and CP2) and parietal (P1, Pz, and P2) electrodes in 0- and 1-back task compared to HC. In both HC and aMCI patients, APOE ε4 carriers showed reduced P300 amplitude with respect to non-carriers, whereas no significant differences in accuracy or RT were detected between APOE ε4 carriers and non-carriers. Additionally, standardized low-resolution brain electromagnetic tomography analysis (s-LORETA) showed enhanced brain activation in the right parahippocampal gyrus (PHG) during P300 time range in APOE ε4 carriers with respect to non-carriers in aMCI patients.

Conclusion: It demonstrated that P300 amplitude could predict VSWM deficits in aMCI patients and contribute to early detection of VSWM deficits in APOE ε4 carriers.

APOE moderates compensatory recruitment of neuronal resources during working memory processing in healthy older adults

The APOE ε4 allele increases the risk for sporadic Alzheimer's disease and modifies brain activation patterns of numerous cognitive domains. We assessed cognitively intact older adults with a letter n-back task to determine if previously observed increases in ε4 carriers' working-memory-related brain activation are compensatory such that they serve to maintain working memory function. Using multiple regression models, we identified interactions of APOE variant and age in bilateral hippocampus independently from task performance: ε4 carriers only showed a decrease in activation with increasing age, suggesting high sensitivity of fMRI data for detecting changes in Alzheimer's disease-relevant brain areas before cognitive decline. Moreover, we identified ε4 carriers to show higher activations in task-negative medial and task-positive inferior frontal areas along with better performance under high working memory load relative to non-ε4 carriers. The increased frontal recruitment is compatible with models of neuronal compensation, extends on existing evidence, and suggests that ε4 carriers require additional neuronal resources to successfully perform a demanding working memory task.

Specific patterns of whole-brain structural covariance of the anterior and posterior hippocampus in young APOE ε4 carriers

Apolipoprotein E (APOE) ε4 has been associated with smaller hippocampal volumes in healthy aging, while findings in young adults are inconclusive. Previous studies have mostly used univariate methods, and without considering potential anterior/posterior differences. Here, we used a multivariate method, partial least squares, and assessed whole-brain structural covariance of the anterior (aHC) and posterior (pHC) hippocampus in young adults (n=97) as a function of APOE ε4 status and sex. Two significant patterns emerged: (1) specific structural covariance of the aHC with frontal regions, temporal and occipital areas in APOE ε4 women, whereas the volume of both the aHC and pHC in all other groups co-varied with frontal, parietal and cerebellar areas; and (2) opposite structural covariance of the pHC in ε4 carriers compared to the aHC in non-carriers, with the pHC of ε4 carriers covarying with parietal and frontal areas, and the aHC of ε4 non-carriers covarying with motor areas and the middle frontal gyrus. APOE ε4 has in young adults been associated with better episodic and spatial memory, functions involving the aHC and pHC, respectively. We found no associations between structural covariance and performance, suggesting that other factors underlie the performance differences seen between carriers and non-carriers. Our findings indicate that APOE ε4 carriers and non-carriers differ in hippocampal organization and that there are differences as a function of sex and hippocampal segment. They stress the need to consider the hippocampus as a heterogeneous structure, and highlight the benefits of multivariate methods in assessing group differences in the brain.

Disrupted Brain Structural Connectivity: Pathological Interactions Between Genetic APOE ε4 Status and Developed MCI Condition

The ε4 allele of the apolipoprotein E (APOE) gene and mild cognitive impairment (MCI) are both risk factors for Alzheimer's disease (AD). One factor is genetic, and the other is a developed condition during the aging process. The current study intended to discover the interactions of these two factors, which may be useful in the construction of a sensitive biomarker for early identification and intervention. Eight hundred eighty-five Chinese Han ethnic subjects (aged 55 and older) completed neuropsychological tests and APOE genotyping. One hundred ten of these participants underwent magnetic resonance imaging (MRI) for T1 structural and diffusion tensor imaging scans. Subjects were divided into four groups according to APOE ε4 carrying status and MCI condition: ε4+ MCI, ε4+ normal cognition (NC), ε4- MCI, and ε4- NC. In the studied Han population in Beijing, 16.9 % (ε2ε4 = 1.1 %, ε3ε4 = 14.8 %, and ε4ε4 = 0.9 %) carried at least one ε4 allele. Significant interactions between APOE ε4 and MCI were found in general cognitive function (p = 0.001) and white matter connectivity network (clustering coefficient, p = 0.004, and local efficiency, p = 0.011); the combination of ε4 positivity and MCI was accompanied by reductions in Mini-Mental Status Examination (MMSE) scores, global white matter network connectivity, and the right hippocampus (rHIP) nodal efficiency within that network (false discovery rate (FDR), p < 0.05). Our results suggest the presence of a genetic risk and MCI led to more severe pathological symptoms and could be informative in the implementation of clinical trials for early stages of AD.

Posteromedial hyperactivation during episodic recognition among people with memory decline: findings from the WRAP study

Episodic memory decline is one of the earliest preclinical symptoms of AD, and has been associated with an upregulation in the BOLD response in the prodromal stage (e.g. MCI) of AD. In a previous study, we observed upregulation in cognitively normal (CN) subjects with subclinical episodic memory decline compared to non-decliners. In light of this finding, we sought to determine if a separate cohort of Decliners will show increased brain activation compared to Stable subjects during episodic memory processing, and determine whether the BOLD effect was influenced by cerebral blood flow (CBF) or gray matter volume (GMV). Individuals were classified as a "Decliner" if scores on the Rey Auditory Verbal Learning Test (RAVLT) consistently fell ≥ 1.5 SD below expected intra- or inter-individual levels. FMRI was used to compare activation during a facial recognition memory task in 90 Stable (age = 59.1) and 34 Decliner (age = 62.1, SD = 5.9) CN middle-aged adults and 10 MCI patients (age = 72.1, SD = 9.4). Arterial spin labeling and anatomical T1 MRI were used to measure resting CBF and GMV, respectively. Stables and Decliners performed similarly on the episodic recognition memory task and significantly better than MCI patients. Compared to Stables, Decliners showed increased BOLD signal in the left precuneus on the episodic memory task that was not explained by CBF or GMV, familial AD risk factors, or neuropsychological measures. These findings suggest that subtle changes in the BOLD signal reflecting altered neural function may be a relatively early phenomenon associated with memory decline.

Effects of Ginkgo biloba extract EGb 761® on cognitive control functions, mental activity of the prefrontal cortex and stress reactivity in elderly adults with subjective memory impairment - a randomized double-blind placebo-controlled trial

OBJECTIVE

Cognitive control as well as stress reactivity is assumed to depend on prefrontal dopamine and decline with age. Because Ginkgo biloba extract EGb761 increases prefrontal dopamine in animals, we assessed its effects on cognitive functions related to prefrontal dopamine.

METHODS

Effects of 240-mg EGb761 daily on task-set-switching, response-inhibition, delayed response, prospective-memory, task-related fMRI-BOLD-signals and the Trier Social Stress-Test were explored in a randomized, placebo-controlled, double-blind pilot-trial in 61 elderly volunteers with subjective memory impairment.

RESULTS

Baseline-FMRI-data showed BOLD-responses in regions commonly activated by the specific tasks. Task-switch-costs decreased with EGb761 compared to placebo (ANOVA-interaction: Group × Time × Switch-Costs p = 0.018, multiple tests uncorrected), indicating improved cognitive flexibility. Go-NoGo-task reaction-times corrected for error-rates indicated a trend for improved response inhibition. No treatment effects were found for the delayed response and prospective-memory tasks and fMRI-data. A non-significant trend indicated a potentially accelerated endocrine stress-recovery. EGb761 was safe and well tolerated.

CONCLUSION

We observed indications for improved cognitive flexibility without changes in brain activation, suggesting increased processing efficiency with EGb761. Together with a trend for improved response inhibition results are compatible with mild enhancement of prefrontal dopamine. These conclusions on potential beneficial effect of EGb761 on prefrontal dopaminergic functions should be confirmed by direct measurements. © 2016 The Authors. Human Psychopharmacology: Clinical and Experimental published by John Wiley & Sons, Ltd.

Are the effects of APOE ϵ4 on cognitive function in nonclinical populations age- and gender-dependent?

APOE ϵ4 - one of three possible allelic variants (ϵ2, ϵ3 and ϵ4) of the polymorphic protein APOE - is well characterized in its role as the strongest risk factor (after old age) for sporadic Alzheimer's disease (AD). Perhaps less well known, and certainly less well characterized, is that this ϵ4 variant of the APOE gene also is a significant risk factor for age-related cognitive decline in nonclinical populations. This article considers APOE ϵ4 effects on cognition in people without dementia, the extent to which such effects may depend on age and on gender and other interactive biological systems that change across the lifespan.

Episodic memory in normal aging and Alzheimer disease: Insights from imaging and behavioral studies

Age-related cognitive changes often include difficulties in retrieving memories, particularly those that rely on personal experiences within their temporal and spatial contexts (i.e., episodic memories). This decline may vary depending on the studied phase (i.e., encoding, storage or retrieval), according to inter-individual differences, and whether we are talking about normal or pathological (e.g., Alzheimer disease; AD) aging. Such cognitive changes are associated with different structural and functional alterations in the human neural network that underpins episodic memory. The prefrontal cortex is the first structure to be affected by age, followed by the medial temporal lobe (MTL), the parietal cortex and the cerebellum. In AD, however, the modifications occur mainly in the MTL (hippocampus and adjacent structures) before spreading to the neocortex. In this review, we will present results that attempt to characterize normal and pathological cognitive aging at multiple levels by integrating structural, behavioral, inter-individual and neuroimaging measures of episodic memory.

A FDG-PET Study of Metabolic Networks in Apolipoprotein E ε4 Allele Carriers

Recently, some studies have applied the graph theory in brain network analysis in Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI). However, relatively little research has specifically explored the properties of the metabolic network in apolipoprotein E (APOE) ε4 allele carriers. In our study, all the subjects, including ADs, MCIs and NCs (normal controls) were divided into 165 APOE ε4 carriers and 165 APOE ε4 noncarriers. To establish the metabolic network for all brain regions except the cerebellum, cerebral glucose metabolism data obtained from FDG-PET (¹⁸F-fluorodeoxyglu-cose positron emission tomography) were segmented into 90 areas with automated anatomical labeling (AAL) template. Then, the properties of the networks were computed to explore the between-group differences. Our results suggested that both APOE ε4 carriers and noncarriers showed the small-world properties. Besides, compared with APOE ε4 noncarriers, the carriers showed a lower clustering coefficient. In addition, significant changes in 6 hub brain regions were found in between-group nodal centrality. Namely, compared with APOE ε4 noncarriers, significant decreases of the nodal centrality were found in left insula, right insula, right anterior cingulate, right paracingulate gyri, left cuneus, as well as significant increases in left paracentral lobule and left heschl gyrus in APOE ε4 carriers. Increased local short distance interregional correlations and disrupted long distance interregional correlations were found, which may support the point that the APOE ε4 carriers were more similar with AD or MCI in FDG uptake. In summary, the organization of metabolic network in APOE ε4 carriers indicated a less optimal pattern and APOE ε4 might be a risk factor for AD.

Spatial pattern separation differences in older adult carriers and non-carriers for the apolipoprotein E epsilon 4 allele

We examined the performance of healthy young (n=57) and older adults (n=43) genotyped as apolipoprotein E-ε4 (APOE-ε4) carriers or APOE-ε4 non-carriers on a delayed match-to-sample task involving varying degrees of spatial interference hypothesized to assess spatial pattern separation. Older adult ε4 carriers were further divided into "impaired" and "unimpaired" groups based on their performance on a standardized test of verbal memory. We found that performance on the spatial pattern separation test increased as a function of decreased spatial interference across all groups. The older ε4 carriers in the impaired group performed significantly worse (p<.05) than unimpaired ε4 carriers, ε4 non-carriers, and young adults. The data suggest that spatial pattern separation may be less efficient in a subset of healthy older adults with subtle memory decline who are carriers of the ε4 allele. However, pattern separation performance may be comparable to that of young adults in a subset of older adult ε4 carriers and more broadly among non-carriers. Our findings offer additional evidence that pattern separation may vary in older adults, and they provide novel insight into pattern separation efficiency in ε4-positive older adults.

Task-evoked fMRI changes in attention networks are associated with preclinical Alzheimer's disease biomarkers

There is a growing emphasis on examining preclinical levels of Alzheimer's disease (AD)-related pathology in the absence of cognitive impairment. Previous work examining biomarkers has focused almost exclusively on memory, although there is mounting evidence that attention also declines early in disease progression. In the current experiment, 2 attentional control tasks were used to examine alterations in task-evoked functional magnetic resonance imaging data related to biomarkers of AD pathology. Seventy-one cognitively normal individuals (females = 44, mean age = 63.5 years) performed 2 attention-demanding cognitive tasks in a design that modeled both trial- and task-level functional magnetic resonance imaging changes. Biomarkers included amyloid β42, tau, and phosphorylated tau measured from cerebrospinal fluid and positron emission tomography measures of amyloid deposition. Both tasks elicited widespread patterns of activation and deactivation associated with large task-level manipulations of attention. Importantly, results from both tasks indicated that higher levels of tau and phosphorylated tau pathologies were associated with block-level overactivations of attentional control areas. This suggests early alteration in attentional control with rising levels of AD pathology.

Rhinal hypometabolism on FDG PET in healthy APO-E4 carriers: impact on memory function and metabolic networks

PURPOSE

The ε4 allele of the apolipoprotein E (APO-E4) gene, a genetic risk factor for Alzheimer's disease (AD), also modulates brain metabolism and function in healthy subjects. The aim of the present study was to explore cerebral metabolism using FDG PET in healthy APO-E4 carriers by comparing cognitively normal APO-E4 carriers to noncarriers and to assess if patterns of metabolism are correlated with performance on cognitive tasks. Moreover, metabolic connectivity patterns were established in order to assess if the organization of neural networks is influenced by genetic factors.

METHODS

Whole-brain PET statistical analysis was performed at voxel-level using SPM8 with a threshold of p < 0.005, corrected for volume, with age, gender and level of education as nuisance variables. Significant hypometabolism between APO-E4 carriers (n = 11) and noncarriers (n = 30) was first determined. Mean metabolic values with clinical/neuropsychological data were extracted at the individual level, and correlations were searched using Spearman's rank test in the whole group. To evaluate metabolic connectivity from metabolic cluster(s) previously identified in the intergroup comparison, voxel-wise interregional correlation analysis (IRCA) was performed between groups of subjects.

RESULTS

APO-E4 carriers had reduced metabolism within the left anterior medial temporal lobe (MTL), where neuropathological changes first appear in AD, including the entorhinal and perirhinal cortices. A correlation between metabolism in this area and performance on the DMS48 (delayed matching to sample-48 items) was found, in line with converging evidence involving the perirhinal cortex in object-based memory. Finally, a voxel-wise IRCA revealed stronger metabolic connectivity of the MTL cluster with neocortical frontoparietal regions in carriers than in noncarriers, suggesting compensatory metabolic networks.

CONCLUSION

Exploring cerebral metabolism using FDG PET can contribute to a better understanding of the influence of genetic factors on cerebral metabolism at both the local and network levels leading to phenotypical variations of the healthy brain and selective vulnerability.

Genetic risk for Alzheimer's disease alters the five-year trajectory of semantic memory activation in cognitively intact elders

Healthy aging is associated with cognitive declines typically accompanied by increased task-related brain activity in comparison to younger counterparts. The Scaffolding Theory of Aging and Cognition (STAC) (Park and Reuter-Lorenz, 2009; Reuter-Lorenz and Park, 2014) posits that compensatory brain processes are responsible for maintaining normal cognitive performance in older adults, despite accumulation of aging-related neural damage. Cross-sectional studies indicate that cognitively intact elders at genetic risk for Alzheimer's disease (AD) demonstrate patterns of increased brain activity compared to low risk elders, suggesting that compensation represents an early response to AD-associated pathology. Whether this compensatory response persists or declines with the onset of cognitive impairment can only be addressed using a longitudinal design. The current prospective, 5-year longitudinal study examined brain activation in APOE ε4 carriers (N=24) and non-carriers (N=21). All participants, ages 65-85 and cognitively intact at study entry, underwent task-activated fMRI, structural MRI, and neuropsychological assessments at baseline, 18, and 57 months. fMRI activation was measured in response to a semantic memory task requiring participants to discriminate famous from non-famous names. Results indicated that the trajectory of change in brain activation while performing this semantic memory task differed between APOE ε4 carriers and non-carriers. The APOE ε4 group exhibited greater activation than the Low Risk group at baseline, but they subsequently showed a progressive decline in activation during the follow-up periods with corresponding emergence of episodic memory loss and hippocampal atrophy. In contrast, the non-carriers demonstrated a gradual increase in activation over the 5-year period. Our results are consistent with the STAC model by demonstrating that compensation varies with the severity of underlying neural damage and can be exhausted with the onset of cognitive symptoms and increased structural brain pathology. Our fMRI results could not be attributed to changes in task performance, group differences in cerebral perfusion, or regional cortical atrophy.

Beta-amyloid associated differential effects of APOE ε4 on brain metabolism in cognitively normal elderly

OBJECTIVE

Although apolipoprotein (APOE) ε4 allele is a well-established risk factor for late-onset Alzheimer disease (AD), the mechanism of its effects on AD pathogenesis is not fully understood. We aimed to investigate the effects of APOE genotype on regional cerebral glucose metabolism in cognitively normal (CN) elderly. We further tried to elucidate whether or not such effects are associated with beta-amyloid protein (Aβ) deposition.

METHODS

31 CN elderly participants underwent clinical examination, a range of neuropsychological tests, APOE genotyping, and Pittsburgh compound-B- and fluorodeoxyglucose-PET scans.

RESULTS

17 APOE ε4 carriers and 15 non-carriers were included. Both hypometabolic and hypermetabolic regions were observed in ε4 carriers compared with noncarriers when age, education, and sex were controlled. When the degree of global cerebral Aβ deposition was adjusted, the hypometabolic regions in the temporo-parietal area (i.e., BA 22 and 39) largely disappeared, whereas the hypermetabolic regions persisted in medial frontal and anterior temporal areas (i.e., BA 38, 11, and 39). Behaviorally, verbal episodic memory scores of APOE ε4 carriers were slightly lower than those of noncarriers, though still within normal range.

CONCLUSIONS

Our findings indicate that decreased cerebral glucose metabolism in the temporoparietal junction associated with APOE ε4 in CN elderly appears to be mediated by Aβ deposition, and the effect of APOE ε4 on hypermetabolism in the frontal and anterior temporal regions is independent of Aβ and may be associated with presence of compensatory mechanism in CN elderly with the ε4 allele.

The effect of alcohol consumption on the adolescent brain: A systematic review of MRI and fMRI studies of alcohol-using youth

Background

A large proportion of adolescents drink alcohol, with many engaging in high-risk patterns of consumption, including binge drinking. Here, we systematically review and synthesize the existing empirical literature on how consuming alcohol affects the developing human brain in alcohol-using (AU) youth.

Methods

For this systematic review, we began by conducting a literature search using the PubMED database to identify all available peer-reviewed magnetic resonance imaging (MRI) and functional magnetic resonance imaging (fMRI) studies of AU adolescents (aged 19 and under). All studies were screened against a strict set of criteria designed to constrain the impact of confounding factors, such as co-occurring psychiatric conditions.

Results

Twenty-one studies (10 MRI and 11 fMRI) met the criteria for inclusion. A synthesis of the MRI studies suggested that overall, AU youth showed regional differences in brain structure as compared with non-AU youth, with smaller grey matter volumes and lower white matter integrity in relevant brain areas. In terms of fMRI outcomes, despite equivalent task performance between AU and non-AU youth, AU youth showed a broad pattern of lower task-relevant activation, and greater task-irrelevant activation. In addition, a pattern of gender differences was observed for brain structure and function, with particularly striking effects among AU females.

Conclusions

Alcohol consumption during adolescence was associated with significant differences in structure and function in the developing human brain. However, this is a nascent field, with several limiting factors (including small sample sizes, cross-sectional designs, presence of confounding factors) within many of the reviewed studies, meaning that results should be interpreted in light of the preliminary state of the field. Future longitudinal and large-scale studies are critical to replicate the existing findings, and to provide a more comprehensive and conclusive picture of the effect of alcohol consumption on the developing brain.

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A large proportion of adolescents drink alcohol.

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Studies show how alcohol affects human adolescent brain development.

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This includes a systematic review of MRI and fMRI studies in alcohol-using youth.

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Changes in structure and function are observed in the brain in alcohol-using youth.

Imaging markers of structural and functional brain changes that precede cognitive symptoms in risk for Alzheimer's disease

Neuroimaging has rapidly advanced investigations into dysfunction both within and emanating from the hippocampus in early Alzheimer's disease . Focusing on prodromal subjects, we will discuss structural changes to hippocampal subregions, alterations to functional activity both within the hippocampus and elsewhere in the cortex, as well as changes to structural white matter connectivity and changes to functionally correlated patterns during memory performance. We present ample evidence that asymptomatic subjects demonstrate substantial identifiable brain changes before the onset of cognitive decline, but suggest there is significant work yet to be accomplished before applying these findings to individual patients.

Prospective randomized trial to assess effects of continuing hormone therapy on cerebral function in postmenopausal women at risk for dementia

The objective of this study was to examine the effects of estrogen-based hormone therapy (HT) on regional cerebral metabolism in postmenopausal women (mean age = 58, SD = 5) at risk for development of dementia. The prospective clinical trial design included pre- and post-intervention neuroimaging of women randomized to continue (HT+) or discontinue (HT−) therapy following an average of 10 years of use. The primary outcome measure was change in brain metabolism during the subsequent two years, as assessed with fluorodeoxyglucose-18 positron emission tomography (FDG-PET). Longitudinal FDG-PET data were available for 45 study completers. Results showed that women randomized to continue HT experienced relative preservation of frontal and parietal cortical metabolism, compared with women randomized to discontinue HT. Women who discontinued 17-β estradiol (17βE)-based HT, as well as women who continued conjugated equine estrogen (CEE)-based HT, exhibited significant decline in metabolism of the precuneus/posterior cingulate cortical (PCC) area. Significant decline in PCC metabolism was additionally seen in women taking concurrent progestins (with either 17βE or CEE). Together, these findings suggest that among postmenopausal subjects at risk for developing dementia, regional cerebral cortical metabolism is relatively preserved for at least two years in women randomized to continue HT, compared with women randomized to discontinue HT. In addition, continuing unopposed 17βE therapy is associated specifically with preservation of metabolism in PCC, known to undergo the most significant decline in the earliest stages of Alzheimer's disease.

Trial Registration

ClinicalTrials.govNCT00097058