Executive functioning in Alzheimer's disease and vascular dementia

Memory self-efficacy and working memory

Dementia affects multiple aspects of cognitive functioning, including working memory and executive functioning. Memory self-efficacy (MSE) has previously been related to episodic memory performance and to executive functioning, but little research has examined the relations between MSE and working memory. United States older adults (N  = 197) were recruited via MTurk to complete an MSE questionnaire before completing a digit span working memory task. Hierarchical regression results revealed that the model accounted for a significant amount of variance in working memory performance after statistically controlling for several covariates, F(11, 179) = 4.94, p < .001, adjusted R2 = .19. MSE explained a large and unique portion of variance (B = 1.02, SE = 0.17, p < .001). Based on our findings, one's beliefs about their memory are positively associated with their working memory performance. These novel findings provide support for neuropsychologists to consider using MSE measures and utilizing MSE interventions.

Neuropsychological differential diagnosis of Alzheimer's disease and vascular dementia: a systematic review with meta-regressions

Introduction

Diagnostic classification systems and guidelines posit distinguishing patterns of impairment in Alzheimer's (AD) and vascular dementia (VaD). In our study, we aim to identify which diagnostic instruments distinguish them.

Methods

We searched PubMed and PsychInfo for empirical studies published until December 2020, which investigated differences in cognitive, behavioral, psychiatric, and functional measures in patients older than 64 years and reported information on VaD subtype, age, education, dementia severity, and proportion of women. We systematically reviewed these studies and conducted Bayesian hierarchical meta-regressions to quantify the evidence for differences using the Bayes factor (BF). The risk of bias was assessed using the Newcastle-Ottawa-Scale and funnel plots.

Results

We identified 122 studies with 17,850 AD and 5,247 VaD patients. Methodological limitations of the included studies are low comparability of patient groups and an untransparent patient selection process. In the digit span backward task, AD patients were nine times more probable (BF = 9.38) to outperform VaD patients (β g = 0.33, 95% ETI = 0.12, 0.52). In the phonemic fluency task, AD patients outperformed subcortical VaD (sVaD) patients (β g = 0.51, 95% ETI = 0.22, 0.77, BF = 42.36). VaD patients, in contrast, outperformed AD patients in verbal (β g = -0.61, 95% ETI = -0.97, -0.26, BF = 22.71) and visual (β g = -0.85, 95% ETI = -1.29, -0.32, BF = 13.67) delayed recall. We found the greatest difference in verbal memory, showing that sVaD patients outperform AD patients (β g = -0.64, 95% ETI = -0.88, -0.36, BF = 72.97). Finally, AD patients performed worse than sVaD patients in recognition memory tasks (β g = -0.76, 95% ETI = -1.26, -0.26, BF = 11.50).

Conclusion

Our findings show inferior performance of AD in episodic memory and superior performance in working memory. We found little support for other differences proposed by diagnostic systems and diagnostic guidelines. The utility of cognitive, behavioral, psychiatric, and functional measures in differential diagnosis is limited and should be complemented by other information. Finally, we identify research areas and avenues, which could significantly improve the diagnostic value of cognitive measures.

A cognitive neurogenetic approach to uncovering the structure of executive functions

One central mission of cognitive neuroscience is to understand the ontology of complex cognitive functions. We addressed this question with a cognitive neurogenetic approach using a large-scale dataset of executive functions (EFs), whole-brain resting-state functional connectivity, and genetic polymorphisms. We found that the bifactor model with common and shifting-specific components not only was parsimonious but also showed maximal dissociations among the EF components at behavioral, neural, and genetic levels. In particular, the genes with enhanced expression in the middle frontal gyrus (MFG) and the subcallosal cingulate gyrus (SCG) showed enrichment for the common and shifting-specific component, respectively. Finally, High-dimensional mediation models further revealed that the functional connectivity patterns significantly mediated the genetic effect on the common EF component. Our study not only reveals insights into the ontology of EFs and their neurogenetic basis, but also provides useful tools to uncover the structure of complex constructs of human cognition.

From aMCI to AD: The Role of Visuo-Spatial Memory Span and Executive Functions in Egocentric and Allocentric Spatial Impairments

A difficulty in encoding spatial information in an egocentric (i.e., body-to-object) and especially allocentric (i.e., object-to-object) manner, and impairments in executive function (EF) are typical in amnestic mild cognitive impairment (aMCI) and Alzheimer’s disease (AD). Since executive functions are involved in spatial encodings, it is important to understand the extent of their reciprocal or selective impairment. To this end, AD patients, aMCI and healthy elderly people had to provide egocentric (What object was closest to you?) and allocentric (What object was closest to object X?) judgments about memorized objects. Participants’ frontal functions, attentional resources and visual-spatial memory were assessed with the Frontal Assessment Battery (FAB), the Trail Making Test (TMT) and the Corsi Block Tapping Test (forward/backward). Results showed that ADs performed worse than all others in all tasks but did not differ from aMCIs in allocentric judgments and Corsi forward. Regression analyses showed, although to different degrees in the three groups, a link between attentional resources, visuo-spatial memory and egocentric performance, and between frontal resources and allocentric performance. Therefore, visuo-spatial memory, especially when it involves allocentric frames and requires demanding active processing, should be carefully assessed to reveal early signs of conversion from aMCI to AD.

Context value updating and multidimensional neuronal encoding in the retrosplenial cortex

The retrosplenial cortex (RSC) has diverse functional inputs and is engaged by various sensory, spatial, and associative learning tasks. We examine how multiple functional aspects are integrated on the single-cell level in the RSC and how the encoding of task-related parameters changes across learning. Using a visuospatial context discrimination paradigm and two-photon calcium imaging in behaving mice, a large proportion of dysgranular RSC neurons was found to encode multiple task-related dimensions while forming context-value associations across learning. During reversal learning requiring increased cognitive flexibility, we revealed an increased proportion of multidimensional encoding neurons that showed higher decoding accuracy for behaviorally relevant context-value associations. Chemogenetic inactivation of RSC led to decreased behavioral context discrimination during learning phases in which context-value associations were formed, while recall of previously formed associations remained intact. RSC inactivation resulted in a persistent positive behavioral bias in valuing contexts, indicating a role for the RSC in context-value updating.

Loneliness, Sense of Control, and Risk of Dementia in Healthy Older Adults: A Moderated Mediation Analysis

Objectives: Despite the rising prevalence of dementia, little research has been conducted to identify modifiable psychological factors that alleviate the risk of dementia in older adults and the underlying mechanisms. Given that loneliness is, in part, concomitant with a weakened sense of control, we examined whether sense of control would mediate the relation between loneliness and dementia risk. Further, considering that working -memory capacity is a critical cognitive resource that serves as a buffer against age-related cognitive decline, we examined a second-order moderated mediational model whereby working-memory capacity moderates the relation between control beliefs and dementia risk in older adults.

METHODS

We administered a series of measures to older community-dwelling adults (ages 60-93; N = 69), including the participant-rated AD8 to assess the risk of dementia. Using the PROCESS macro, we examined the moderated mediation model for the relation between loneliness, sense of control, and dementia risk.

RESULTS

We found that sense of control significantly mediated the relation between loneliness and risk of dementia. Moreover, the indirect effect of loneliness on dementia risk via lowered sense of control was significant only in individuals with poorer working-memory capacity. Notably, these findings held true when important covariates were controlled for.

CONCLUSIONS

Our findings underscore the critical role of control beliefs and working memory in protecting against dementia risk.

CLINICAL IMPLICATIONS

Our findings have implications for intervention programs that target alleviating dementia risk and promoting healthy aging in older adults by improving socioemotional health and cognitive functioning.

Predictors of cognitive decline in a multi-racial sample of midlife women: A longitudinal study

Objective: Hypertension, diabetes, depressive symptoms, and smoking are predictors of cognitive decline in late life. It is unknown if these risk factors are associated with cognition during midlife or if the associations between these risk factors and cognition vary by race. This longitudinal study examined (a) risk factors for decline in episodic memory, processing speed, and working memory in midlife women and (b) if the associations between risk factors and cognitive decline were moderated by race. Method: Participants (aged 42-52) were European American (n = 1,000), African American (n = 516), and Asian American (n = 437) women from the Study of Women's Health Across the Nation. Two-level hierarchical linear models tested risk factors, race, and their interactions as predictors of cognitive change over time. Results: African Americans had poorer baseline episodic memory, processing speed, and working memory and greater episodic memory decline compared to European Americans. Asian Americans had poorer episodic memory and working memory, but better processing speed than European Americans. Depressive symptoms were associated with poorer episodic memory and processing speed at baseline; further, diabetes was associated with poorer processing speed at baseline. Greater depressive symptoms were associated with poorer episodic memory at baseline for African Americans but not European Americans. Conclusions: Our study results highlight racial disparities in cognition during midlife. Depressive symptoms may be particularly detrimental to the cognitive health of African Americans. Clinical and public health interventions for healthy cognitive aging should be tailored to the unique risks of racial groups. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

A community-based computerised cognitive training program for older persons with mild dementia: A pilot study

OBJECTIVES

Computerised cognitive training programs can improve cognitive function in patients with moderate-to-severe dementia or brain injuries and healthy older adults. However, most previous studies were not randomised controlled trials and did not examine older adults with mild dementia. The current study sought to analyse the effects of a computerised cognitive training program using a randomised controlled trial.

METHODS

In a single-blinded randomised clinical trial, 30 older individuals with mild dementia were split into an experimental (n = 15) and a control (n = 15) group to analyse the effects of a computerised cognitive training program. Outcomes were assessed before and after each program session, and 1 and 3 months afterwards.

RESULTS

Participants in the experimental group had better overall subjective memory, subjective retrospective memory and global quality of life, with fewer depressive symptoms than those in the control group 3 months following the program.

CONCLUSIONS

Our computerised cognitive training program improved subjective memory and quality of life in patients with mild dementia and decreased their depressive symptoms. These results may be useful for health-care providers caring for people with mild dementia.

Metabolic Syndrome and Physical Performance: The Moderating Role of Cognition among Middle-to-Older-Aged Adults

OBJECTIVE

Mobility limitation and cognitive decline are related. Metabolic syndrome (MetS), the clustering of three or more cardiovascular risk factors, is associated with decline in both mobility and cognition. However, the interrelationship among MetS, mobility, and cognition is unknown. This study investigated a proposed pathway where cognition moderates the relationship between MetS and Mobility.

METHOD

Adults ages 45-90 years were recruited. MetS risk factors and mobility performance (Short Physical Performance Battery (SPPB) and gait speed) were evaluated. Cognition was assessed using a comprehensive neuropsychological battery. A factor analysis of neuropsychological test scores yielded three factors: executive function, explicit memory, and semantic/contextual memory. Multivariable linear regression models were used to examine the relationship among MetS, mobility, and cognition.

RESULTS

Of the 74 participants (average age 61 ± 9 years; 41% female; 69% White), 27 (36%) participants manifested MetS. Mean SPPB score was 10.9 ± 1.2 out of 12 and gait speed was 1.0 ± 0.2 m/s. There were no statistically significant differences in mobility by MetS status. However, increase in any one of the MetS risk factors was associated with decreased mobility performance after adjusting for age and gender (SPPB score: β (SE) -.17 (0.08), p < .05; gait speed: -.03 (.01), p < .01). Further adjusting for cognitive factors (SPPB score: explicit memory .31 (.14), p = .03; executive function 0.45 (0.13), p < .01; gait speed: explicit memory 0.04 (0.02), p = .03; executive function 0.06 (0.02), p < .01) moderated the relationships between number of metabolic risk factors and mobility.

CONCLUSION

The relationship between metabolic risk factors and mobility may be moderated by cognitive performance, specifically through executive function and explicit memory.

Cognition at Each Stage of Lewy Body Disease with Co-occurring Alzheimer's Disease Pathology

BACKGROUND

Alzheimer's disease neuropathologic change (ADNC) may contribute to dementia in patients with Lewy body disease (LBD) pathology.

OBJECTIVE

To examine how co-occurring ADNC impacts domain specific cognitive impairments at each pathologic stage (brainstem, limbic, cerebral cortical) of LBD.

METHODS

2,433 participants with antemortem longitudinal neuropsychological assessment and postmortem neuropathological assessment from the National Alzheimer's Coordinating Center's Uniform Data Set were characterized based on the evaluation of ADNC and LBD. Longitudinal mixed-models were used to derive measures of cumulative cognitive deficit for each cognitive domain at each pathologic stage of LBD (brainstem, limbic, and cerebral cortical).

RESULTS

111 participants with a pathologic diagnosis of LBD, 741 participants with combined LBD and ADNC, 1,357 participants with ADNC only, and 224 with no pathology (healthy controls) were included in the analyses. In the executive/visuospatial domain, combined LBD and ADNC showed worse deficits than LBD only when Lewy bodies were confined to the brainstem, but no difference when Lewy bodies extended to the limbic or cerebral cortical regions. The cerebral cortical LBD only group exhibited greater executive/visuospatial deficits than the ADNC only group. By contrast, the ADNC only group and the combined pathology group both demonstrated significantly greater cumulative memory deficits relative to Lewy body disease only, regardless of stage.

CONCLUSION

The impact of co-occurring ADNC on antemortem cumulative cognitive deficits varies not only by domain but also on the pathological stage of Lewy bodies. Our findings stress the cognitive impact of different patterns of neuropathological progression in Lewy body diseases.

Donepezil down-regulates propionylation, 2-hydroxyisobutyrylation, butyrylation, succinylation, and crotonylation in the brain of bilateral common carotid artery occlusion-induced vascular dementia rats

Vascular dementia (VaD), caused by stroke or small vessel disease, is the second-most common type of dementia after Alzheimer's disease (AD). Donepezil is an acetylcholinesterase inhibitor that is currently used in patients with mild to moderate AD, and has recently been shown to improve cognitive performance in patients with VaD. In this study, we evaluated the effects of donepezil on VaD, and investigated the underlying molecular mechanisms of action. VaD was established by ligation of the bilateral common carotid artery occlusion (BCCAO). Executive function was tested by the Morris water maze (MWM) test and the attentional set shifting task (ASST). Our results showed that donepezil improved executive dysfunction and cognitive flexibility in BCCAO rats. In addition, we showed that donepezil treatment decreased the level of Aβ1-42 in BCCAO rats by enzyme-linked immunosorbent assay. Post-translational modifications (PTMs) are known to be critical mechanisms in the regulation of various cellular processes. Furthermore, PTMs have been linked to the central nervous system, which highlights the importance of PTMs in neurodegenerative diseases. In this study, we used western blot analysis to identify several novel PTMs in the hippocampus of BCCAO rats that were treated with or without donepezil. The data revealed that lysine propionylation, 2-hydroxyisobutyrylation, butyrylation, succinylation, and crotonylation were elevated in the hippocampus of BCCAO rats when compared to sham rats. This increase was abolished by donepezil treatment. Taken together, we speculate that donepezil treatment improves cognitive function in our animal model of VaD, possibly by reducing aberrant acyl-PTMs.

Impaired Reversal Learning in APPPS1-21 Mice in the Touchscreen Visual Discrimination Task

Preclinical-clinical translation of cognitive functions has been difficult in Alzheimer's disease (AD) research but is crucial to the (predictive) validity of AD animal models. Reversal learning, a representation of flexibility and adaptability to a changing environment, might represent such a translatable feature of human cognition. We, therefore, examined visual discrimination (VD) and reversal learning in the APPPS1-21 mouse model of amyloid-based AD pathology. We used touchscreen operant cages in novel and translationally valid, as well as objective testing methodology that minimizes within- or between-trial handling. Mice were trained to associate a visual cue with a food reward (VD learning), and subsequently learned to adjust their response when this rule changed (reversal learning). We assessed performance at two different ages, namely at 6 months of age, considered an early disease stage, and at 9 months, a stage of established pathology. Both at 6 and 9 months, transgenic animals needed more sessions to reach criterion performance, compared to wild-type controls. Overall, transgenic animals do not show a general cognitive, motivational or motor deficit, but experience specific difficulties to adapt to reward contingency changes, already at an early pathology stage.

Can adults living with dementia complete pure-tone audiometry? A systematic review

OBJECTIVE

It is estimated that over 60% of adults with dementia will also have a hearing impairment, resulting in a dual sensory-cognitive communication disability. Hearing interventions may lessen the impact of hearing impairment on a communication disability; yet, for audiologists to recommend appropriate hearing interventions, the individual's hearing thresholds must first be accurately established. The gold standard test for establishing hearing thresholds is pure-tone audiometry (PTA). However, the ability of adults with dementia to successfully complete PTA is uncertain. This systematic review examined studies of adults with dementia to better determine the proportion who could complete PTA.

DESIGN

Systematic review.

STUDY SAMPLE

Studies were included that assessed hearing in older adults who were reported as having mild and greater dementia. From a total of 1,237 eligible studies, only three were found to meet all inclusion criteria.

RESULTS

Across these three studies, the proportion of adults with dementia who could successfully complete PTA ranged from 56% to 59%.

CONCLUSIONS

Further research is needed in this area, particularly for adults with moderate and severe stages of dementia. Future research should also consider the feasibility of complementary, non-behavioural hearing tests. This systematic review was registered with the PROSPERO database, registration number CRD42017073041.

Alpha desynchronization during simple working memory unmasks pathological aging in cognitively healthy individuals

Our aim is to explore if cognitive challenge combined with objective physiology can reveal abnormal frontal alpha event-related desynchronization (ERD), in early Alzheimer's disease (AD). We used quantitative electroencephalography (qEEG) to investigate brain activities during N-back working memory (WM) processing at two different load conditions (N = 0 or 2) in an aging cohort. We studied 60-100 year old participants, with normal cognition, and who fits one of two subgroups from cerebrospinal fluid (CSF) proteins: cognitively healthy (CH) with normal amyloid/tau ratio (CH-NAT, n = 10) or pathological amyloid/tau ratio (CH-PAT, n = 14). We recorded behavioral performances, and analyzed alpha power and alpha spectral entropy (SE) at three occasions: during the resting state, and at event-related desynchronization (ERD) [250 ~ 750 ms] during 0-back and 2-back. During 0-back WM testing, the behavioral performance was similar between the two groups, however, qEEG notably differentiated CH-PATs from CH-NATs on the simple, 0-back testing: Alpha ERD decreased from baseline only in the parietal region in CH-NATs, while it decreased in all brain regions in CH-PATs. Alpha SE did not change in CH-NATs, but was increased from baseline in the CH-PATs in frontal and left lateral regions (p<0.01), and was higher in the frontal region (p<0.01) of CH-PATs compared to CH-NATs. The alpha ERD and SE analyses suggest there is frontal lobe dysfunction during WM processing in the CH-PAT stage. Additional power and correlations with behavioral performance were also explored. This study provide pilot information to further evaluate whether this biomarker has clinical significance.

Dose-Response Relationship between Exercise Duration and Executive Function in Older Adults

This study aimed to determine the dose-response relationship between exercise duration and task switching in older adults. Acute moderate intensity aerobic exercise for 20 min resulted in shorter response times than control and 10-min sessions in the heterogeneous, non-switch, and switch conditions, but not in the homogeneous condition. Additionally, linear and cubic trends between exercise duration and global switching performance as well as local switching performance were revealed with faster times being predicted by longer duration exercise; however, the cubic relationship resulted in performance following the 45-min session being not significantly different from the other three sessions. Acute aerobic moderate intensity exercise for 20 min is an effective duration to improve task switching. Although a longer duration of exercise is not optimal for benefiting task switching, it does not harm task switching in older adults and hence may be of value for other health-related reasons.

Frontal Assessment Battery as a Useful Tool to Differentiate Mild Cognitive Impairment due to Subcortical Ischemic Vascular Disease from Alzheimer Disease

BACKGROUND

Prominent executive dysfunction can differentiate vascular dementia from Alzheimer disease (AD). However, it is unclear whether the Frontal Assessment Battery (FAB) screening tool can differentiate subcortical ischemic vascular disease (SIVD) from AD at the pre-dementia stage. In addition, the neural correlates of FAB performance have yet to be clarified.

METHODS

Patients with mild cognitive impairment (MCI) due to SIVD (MCI-V), MCI due to AD (MCI-A), and demographically matched controls completed the Mini-Mental State Examination, Taiwanese FAB (TFAB), Category Fluency, and Chinese Version of the Verbal Learning Test, and underwent magnetic resonance imaging. White matter hyperintensities were rated according to the Scheltens scale.

RESULTS

TFAB total scale and its Orthographical Fluency subtest were the only measures that could differentiate MCI-V from MCI-A. Discriminative analysis showed that Orthographical Fluency scores successfully identified 73.2% of the cases with MCI-V, with 85.0% sensitivity. Orthographical Fluency scores were specifically associated with lesion load within frontal periventricular, frontal deep white matter, and basal ganglia regions.

CONCLUSION

The TFAB, and especially its 1-min Orthographical Fluency subtest, is a useful screening procedure to differentiate MCI due to SIVD from MCI due to AD. The discriminative ability is probably due to frontosubcortical white matter pathologies disproportionately involved in the two disease entities.

Assessing Executive Dysfunction in Neurodegenerative Disorders: A Critical Review of Brief Neuropsychological Tools

Executive function (EF) has been defined as a multifaceted construct that involves a variety of high-level cognitive abilities such as planning, working memory, mental flexibility, and inhibition. Being able to identify deficits in EF is important for the diagnosis and monitoring of several neurodegenerative disorders, and thus their assessment is a topic of much debate. In particular, there has been a growing interest in the development of neuropsychological screening tools that can potentially provide a reliable quick measure of EF. In this review, we critically discuss the four screening tools of EF currently available in the literature: Executive Interview-25 (EXIT 25), Frontal Assessment Battery (FAB), INECO Frontal Screening (IFS), and FRONTIER Executive Screen (FES). We first describe their features, and then evaluate their psychometric properties, the existing evidence on their neural correlates, and the empirical work that has been conducted in clinical populations. We conclude that the four screening tools generally present appropriate psychometric properties, and are sensitive to impairments in EF in several neurodegenerative conditions. However, more research will be needed mostly with respect to normative data and neural correlates, and to determine the extent to which these tools add specific information to the one provided by global cognition screening tests. More research directly comparing the available tools with each other will also be important to establish in which conditions each of them can be most useful.

Can a tablet-based cancellation test identify cognitive impairment in older adults?

Background and objective

There has been a growing interest in using computerized cognitive assessment to detect age-related cognitive disorders. We have developed a tablet-based cancellation test (e-CT), previously shown as a reliable measure of executive functions and free of effect of familiarity with computer-based devices in healthy older adults. This study aimed to investigate the influence of demographics and current daily use of computer-based devices in older adults with Mild Cognitive Impairment (MCI) and Alzheimer’s disease (AD). We further studied the ability of the e-CT to discriminate MCI and AD patients from older adults with normal cognition (NC).

Methods

The e-CT was administered to 325 older adults (NC = 112, MCI = 129, AD = 84). Subjects also performed the K-T test, a paper-and-pencil cancellation test from which the e-CT was developed. Multiple linear regression analyses were conducted to assess the contribution of demographics and current daily use of computer-based devices on the e-CT in patient groups. The Receiver Operating Characteristic (ROC) curves and the Area Under the Curve (AUC) were established to compare the efficacy of the e-CT and the K-T test to classify subjects into diagnostic groups.

Results

In the MCI group, age (B = -0.37, p<0.001) and current daily use of computer-based devices (B = 5.85, p<0.001) were associated with the number of correct cancellations of the e-CT. In the AD group, only current daily use of a computer-based device was a significant contributor (B = 6.28, p<0.001). The e-CT (AUC = 0.811; 95% confidence interval [CI]: 0.756–0.867) and the K-T (AUC = 0.837; CI: 0.787–0.887) showed good and comparable diagnostic accuracy to discriminate between MCI and NC subjects. To discriminate between NC and AD, both tests showed high diagnostic accuracy, with the AUC values of 0.923 (CI: 0.876–0.971) and 0.929 (95%CI: 0.886–0.972) for the e-CT and the K-T, respectively.

Conclusion

The e-CT presents satisfying discriminative validity and is a promising tool for detection of early cognitive impairment in older adults.

Cognitive profiles in degenerative dementia without evidence of small vessel pathology and small vessel vascular dementia

Although a large number of studies have examined possible differences in cognitive performance between Alzheimer's disease (AD) and vascular dementia (VaD), the data in the literature are conflicting. The aims of this study were to analyze the neuropsychological pattern of subjects affected by degenerative dementia without evidence of small vessel pathology (DD) and small vessel VaD subjects in the early stages and to investigate differences in the progression of cognitive impairment. Seventy-five patients with probable VaD and 75 patients with probable DD were included. All the subjects underwent a standard neuropsychological evaluation, including the following test: Visual Search, Attentional matrices, Story Recall, Raven's Coloured Progressive Matrices, Phonological and Semantic Verbal Fluency, Token, and Copying Drawings. The severity of cognitive impairment was stratified according to the MMSE score. Fifteen subjects with probable DD and 10 subjects with probable VaD underwent a 12-month cognitive re-evaluation. No significant difference was found between DD and VaD subjects in any of the neuropsychological tests except Story Recall in the mild cognitive impairment (P < 0.001). The re-test value was significantly worse than the baseline value in the MMSE (P = 0.037), Corsi (P = 0.041), Story Recall (P = 0.032), Phonological Verbal Fluency (P = 0.02), and Copying Drawings (P = 0.043) in DD patients and in the Visual Search test (P = 0.036) in VaD subjects. These results suggest that a neuropsychological evaluation might help to differentiate degenerative dementia without evidence of small vessel pathology from small vessel VaD in the early stages of these diseases.

A comparison of the diagnostic accuracy of the AD8 and BCAT-SF in identifying dementia and mild cognitive impairment in long-term care residents

We compared the accuracy of the Brief Cognitive Assessment Tool-Short Form (BCAT-SF) and AD8 in identifying mild cognitive impairment (MCI) and dementia among long-term care residents. Psychometric analyses of 357 long-term care residents (n = 228, nursing home; n = 129, assisted living) in Maryland referred for neuropsychological evaluation evidenced robust internal consistency reliability and construct validity for the BCAT-SF. Furthermore, hierarchical logistic regression and receiver operating characteristic curve analyses demonstrated superior predictive validity for the BCAT-SF in identifying MCI and dementia relative to the AD8. In contrast, previously reported psychometric properties or cut scores for the AD8 could not be cross-validated in this long-term care sample. Based on these findings, the BCAT-SF appears to be a more reliable and valid screening instrument than the AD8 for rapidly identifying MCI and dementia in long-term care residents.

Dopamine Burden Triggers Neurodegeneration via Production and Release of TNF-α from Astrocytes in Minimal Hepatic Encephalopathy

Dopamine (DA)-induced learning and memory impairment is well documented in minimal hepatic encephalopathy (MHE), but the contribution of DA to neurodegeneration and the involved underlying mechanisms are not fully understood. In this study, the effect of DA on neuronal apoptosis was initially detected. The results showed that MHE/DA (10 μg)-treated rats displayed neuronal apoptosis. However, we found that DA (10 μM) treatment did not induce evident apoptosis in primary cultured neurons (PCNs) but did produce TNF-α in primary cultured astrocytes (PCAs). Furthermore, co-cultures between PCAs and PCNs exposed to DA exhibited increased astrocytic TNF-α levels and neuronal apoptosis compared with co-cultures exposed to the vehicle, indicating the attribution of the neuronal apoptosis to astrocytic TNF-α. We also demonstrated that DA enhanced TNF-α production from astrocytes by activation of the TLR4/MyD88/NF-κB pathway, and secreted astrocytic TNF-α-potentiated neuronal apoptosis through inactivation of the PI3K/Akt/mTOR pathway. Overall, the findings from this study suggest that DA stimulates substantial production and secretion of astrocytic TNF-α, consequently and indirectly triggering progressive neurodegeneration, resulting in cognitive decline and memory loss in MHE.

Forebrain deletion of the vesicular acetylcholine transporter results in deficits in executive function, metabolic, and RNA splicing abnormalities in the prefrontal cortex

One of the key brain regions in cognitive processing and executive function is the prefrontal cortex (PFC), which receives cholinergic input from basal forebrain cholinergic neurons. We evaluated the contribution of synaptically released acetylcholine (ACh) to executive function by genetically targeting the vesicular acetylcholine transporter (VAChT) in the mouse forebrain. Executive function was assessed using a pairwise visual discrimination paradigm and the 5-choice serial reaction time task (5-CSRT). In the pairwise test, VAChT-deficient mice were able to learn, but were impaired in reversal learning, suggesting that these mice present cognitive inflexibility. Interestingly, VAChT-targeted mice took longer to reach criteria in the 5-CSRT. Although their performance was indistinguishable from that of control mice during low attentional demand, increased attentional demand revealed striking deficits in VAChT-deleted mice. Galantamine, a cholinesterase inhibitor used in Alzheimer's disease, significantly improved the performance of control mice, but not of VAChT-deficient mice on the 5-CSRT. In vivo magnetic resonance spectroscopy showed altered levels of two neurochemical markers of neuronal function, taurine and lactate, suggesting altered PFC metabolism in VAChT-deficient mice. The PFC of these mice displayed a drastic reduction in the splicing factor heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1), whose cholinergic-mediated reduction was previously demonstrated in Alzheimer's disease. Consequently, several key hnRNPA2/B1 target transcripts involved in neuronal function present changes in alternative splicing in VAChT-deficient mice, including pyruvate kinase M, a key enzyme involved in lactate metabolism. We propose that VAChT-targeted mice can be used to model and to dissect the neurochemical basis of executive abnormalities.

Confirmatory factor analysis of the ADNI Neuropsychological Battery

The Alzheimer's Disease Neuroimaging Initiative (ADNI) is a large multi-center study designed to develop optimized methods for acquiring longitudinal neuroimaging, cognitive, and biomarker measures of AD progression in a large cohort of patients with Alzheimer's disease (AD), patients with Mild Cognitive Impairment, and healthy controls. Detailed neuropsychological testing was conducted on all participants. We examined the factor structure of the ADNI Neuropsychological Battery across older adults with differing levels of clinical AD severity based on the Clinical Dementia Rating Scale (CDR). Confirmatory factor analysis (CFA) of 23 variables from 10 neuropsychological tests resulted in five factors (memory, language, visuospatial functioning, attention, and executive function/processing speed) that were invariant across levels of cognitive impairment. Thus, these five factors can be used as indicators of cognitive function in older adults who are participants in ADNI.

The overall impairment of core executive function components in patients with amnestic mild cognitive impairment: a cross-sectional study

Background

It remains unclear how executive function (EF) is affected in the stage of amnestic mild cognitive impairment (aMCI). Previous studies using different methods to assess EF in patients with aMCI have reached inconsistent conclusions. The aim of the study was to explore the characteristics of EF impairments in patients with aMCI.

Methods

We investigated three core components of EF (i.e., working memory, response inhibition and task switching) based on the theoretical model of EF proposed by Miyake et al. (2000) in 34 aMCI patients and 36 healthy elderly controls using computerized tasks programmed with E-prime (the 2-back task and the keep track task for working memory, the stop-signal task and the Stroop task for response inhibition and the more-odd shifting task for task switching). The overall EF and the three individual EF components were compared between groups. For EF components that were impaired, the extent of impairment was compared using a paired analysis. The aMCI group was further divided into EF-intact and EF-deficit groups according to their performances on the EF tests in clinical neuropsychological assessments. We tested for group differences among the normal controls and the EF-intact and EF-deficit aMCI groups and paid special attention to the comparisons between the EF-intact aMCI group and the control group.

Results

Compared to the control group, overall EF was significantly impaired in patients with aMCI (Wilks’ λ=0.572,P<0.001). Four tasks (the 2-back task, the keep track task, the stop-signal task and the more-odd shifting task) that tapped the three core components of EF displayed group differences that favored the normal controls. The results of the Stroop task revealed no differences in performance between the two groups. The EF-intact aMCI patients also exhibited significantly impaired capabilities in the four tasks compared to the normal controls. There were no significant differences in the extent of impairment between the four affected tasks in the aMCI group, suggesting that the three core EF components were impaired to the same extent.

Conclusions

Both the overall EF and all of the core EF components in the Miyake model of EF (working memory, response inhibition and task switching) were significantly impaired in aMCI patients, regardless of whether they had shown obvious clinical executive dysfunction.

Verbal fluency and awareness of functional deficits in early-stage dementia

Assessment of activities of daily living is an important element in the diagnosis of dementia, with research suggesting a link between functional ability and cognition. We investigated the relationship between self- and informant ratings of instrumental activities of daily living (iADL) and verbal executive functioning in early-stage dementia. A total of 96 people with early-stage Alzheimer's disease or vascular or mixed dementia and their carers completed the Functional Activities Questionnaire; people with dementia also completed a test of letter fluency. Letter fluency was associated with self-ratings of iADL, while informant ratings of iADL were associated with the age and Mini-Mental State Examination score of the person with dementia. Self-ratings of perceived functioning suggested significantly less impairment than informant ratings. Those with impaired letter fluency rated themselves as having greater difficulties in iADLs than those who performed better. People with early-stage dementia vary in their subjective level of awareness of their iADL functioning, and difficulties with language production may contribute to better awareness of iADL impairments.