Factor structure of a modified version of the wisconsin card sorting test: an analysis of executive deficit in Alzheimer's disease and mild cognitive impairment

Improved Dementia Prediction in Cerebral Small Vessel Disease Using Deep Learning-Derived Diffusion Scalar Maps From T1

BACKGROUND

Cerebral small vessel disease is the most common pathology underlying vascular dementia. In small vessel disease, diffusion tensor imaging is more sensitive to white matter damage and better predicts dementia risk than conventional magnetic resonance imaging sequences, such as T1 and fluid attenuation inversion recovery, but diffusion tensor imaging takes longer to acquire and is not routinely available in clinical practice. As diffusion tensor imaging-derived scalar maps-fractional anisotropy (FA) and mean diffusivity (MD)-are frequently used in clinical settings, one solution is to synthesize FA/MD from T1 images.

METHODS

We developed a deep learning model to synthesize FA/MD from T1. The training data set consisted of 4998 participants with the highest white matter hyperintensity volumes in the UK Biobank. Four external validations data sets with small vessel disease were included: SCANS (St George's Cognition and Neuroimaging in Stroke; n=120), RUN DMC (Radboud University Nijmegen Diffusion Tensor and Magnetic Resonance Imaging Cohort; n=502), PRESERVE (Blood Pressure in Established Cerebral Small Vessel Disease; n=105), and NETWORKS (n=26), along with 1000 normal controls from the UK Biobank.

RESULTS

The synthetic maps resembled ground-truth maps (structural similarity index >0.89 for MD maps and >0.80 for FA maps across all external validation data sets except for SCANS). The prediction accuracy of dementia using whole-brain median MD from the synthetic maps is comparable to the ground truth (SCANS ground-truth c-index, 0.822 and synthetic, 0.821; RUN DMC ground truth, 0.816 and synthetic, 0.812) and better than white matter hyperintensity volume (SCANS, 0.534; RUN DMC, 0.710).

CONCLUSIONS

We have developed a fast and generalizable method to synthesize FA/MD maps from T1 to improve the prediction accuracy of dementia in small vessel disease when diffusion tensor imaging data have not been acquired.

The assessment of executive function abilities in healthy and neurodegenerative aging-A selective literature review

Numerous studies have examined executive function (EF) abilities in cognitively healthy older adults and those living with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Currently, there are no standard accepted protocols for testing specific EFs; thus, researchers have used their preferred tool, which leads to variability in assessments of decline in a particular ability across studies. Therefore, there is a need for guidance as to the most sensitive tests for assessing EF decline. A search of the most current literature published between 2000 and 2022 on EF studies assessing cognitively healthy older adults and individuals living with MCI and AD was conducted using PubMed/Medline, PsycINFO, Embase, Web of Science, and Google Scholar. Emphasis was placed on the EF's dual-tasking, inhibition, shifting or switching, and working memory updating. Many tasks and their outcomes were reviewed. Of particular importance was the difference in outcomes for tasks applied to the same group of participants. These various EF assessment tools demonstrate differences in effectively identifying decline in EF ability due to the aging process and neurodegenerative conditions, such as MCI and AD. This review identifies various factors to consider in using particular EF tasks in particular populations, including task demand and stimuli factors, and also when comparing differing results across studies.

Insulin and Disorders of Behavioural Flexibility

Behavioural inflexibility is a symptom of neuropsychiatric and neurodegenerative disorders such as Obsessive-Compulsive Disorder, Autism Spectrum Disorder and Alzheimer's Disease, encompassing the maintenance of a behaviour even when no longer appropriate. Recent evidence suggests that insulin signalling has roles apart from its regulation of peripheral metabolism and mediates behaviourally-relevant central nervous system (CNS) functions including behavioural flexibility. Indeed, insulin resistance is reported to generate anxious, perseverative phenotypes in animal models, with the Type 2 diabetes medication metformin proving to be beneficial for disorders including Alzheimer's Disease. Structural and functional neuroimaging studies of Type 2 diabetes patients have highlighted aberrant connectivity in regions governing salience detection, attention, inhibition and memory. As currently available therapeutic strategies feature high rates of resistance, there is an urgent need to better understand the complex aetiology of behaviour and develop improved therapeutics. In this review, we explore the circuitry underlying behavioural flexibility, changes in Type 2 diabetes, the role of insulin in CNS outcomes and mechanisms of insulin involvement across disorders of behavioural inflexibility.

Phloretin Improves Ultrafiltration and Reduces Glucose Absorption during Peritoneal Dialysis in Rats

BACKGROUND

Harmful glucose exposure and absorption remain major limitations of peritoneal dialysis (PD). We previously showed that inhibition of sodium glucose cotransporter 2 did not affect glucose transport during PD in rats. However, more recently, we found that phlorizin, a dual blocker of sodium glucose cotransporters 1 and 2, reduces glucose diffusion in PD. Therefore, either inhibiting sodium glucose cotransporter 1 or blocking facilitative glucose channels by phlorizin metabolite phloretin would reduce glucose transport in PD.

METHODS

We tested a selective blocker of sodium glucose cotransporter 1, mizagliflozin, as well as phloretin, a nonselective blocker of facilitative glucose channels, in an anesthetized Sprague-Dawley rat model of PD.

RESULTS

Intraperitoneal phloretin treatment reduced glucose absorption by >30% and resulted in a >50% higher ultrafiltration rate compared with control animals. Sodium removal and sodium clearances were similarly improved, whereas the amount of ultrafiltration per millimole of sodium removed did not differ. Mizagliflozin did not influence glucose transport or osmotic water transport.

CONCLUSIONS

Taken together, our results and previous results indicate that blockers of facilitative glucose channels may be a promising target for reducing glucose absorption and improving ultrafiltration efficiency in PD.

Impact of Intestinal Microbiota on Cognitive Flexibility by a Novel Touch Screen Operant System Task in Mice

Cognitive flexibility is the ability to rapidly adapt to a constantly changing environment. It is impaired by aging as well as in various neurological diseases, including dementia and mild cognitive impairment. In rodents, although many behavioral test protocols have been reported to assess learning and memory dysfunction, few protocols address cognitive flexibility. In this study, we developed a novel cognitive flexibility test protocol using touch screen operant system. This test comprises a behavioral sequencing task, in which mice are required to discriminate between the “rewarded” and “never-rewarded” spots and shuttle between the two distantly positioned rewarded spots, and serial reversals, in which the diagonal spatial patterns of rewarded and never-rewarded spots were reversely changed repetitively. Using this test protocol, we demonstrated that dysbiosis treated using streptomycin induces a decline in cognitive flexibility, including perseveration and persistence. The relative abundances of Firmicutes and Bacteroides were lower and higher, respectively, in the streptomycin-treated mice with less cognitive flexibility than in the control mice. This is the first report to directly show that intestinal microbiota affects cognitive flexibility.

Acquired Decline in Ultrafiltration in Peritoneal Dialysis: The Role of Glucose

Ultrafiltration is essential in peritoneal dialysis (PD) for maintenance of euvolemia, making ultrafiltration insufficiency-preferably called ultrafiltration failure-an important complication. The mechanisms of ultrafiltration and ultrafiltration failure are more complex than generally assumed, especially after long-term treatment. Initially, ultrafiltration failure is mainly explained by a large number of perfused peritoneal microvessels, leading to a rapid decline of the crystalloid osmotic gradient, thereby decreasing aquaporin-mediated free water transport. The contribution of peritoneal interstitial tissue to ultrafiltration failure is limited during the first few years of PD, but becomes more important in long-term PD due to the development of interstitial fibrosis, which mainly consists of myofibroblasts. A dual hypothesis has been developed to explain why the continuous exposure of peritoneal tissues to the extremely high dialysate glucose concentrations causes progressive ultrafiltration decline. First, glucose absorption causes an increase of the intracellular NADH/NAD⁺ ratio, also called pseudohypoxia. Intracellular hypoxia stimulates myofibroblasts to produce profibrotic and angiogenetic factors, and the glucose transporter GLUT-1. Second, the increased GLUT-1 expression by myofibroblasts increases glucose uptake in these cells, leading to a reduction of the osmotic gradient for ultrafiltration. Reduction of peritoneal glucose exposure to prevent this vicious circle is essential for high-quality, long-term PD.

Wisconsin Card Sorting Test reveals a monitoring advantage but not a switching advantage in multilingual children

The Wisconsin Card Sorting Test (WCST) is used to test higher-level executive functions or switching, depending on the measures chosen in a study and its goal. Many measures can be extracted from the WCST, but how to assign them to specific cognitive skills remains unclear. Thus, the current study first aimed at identifying which measures test the same cognitive abilities. Second, we compared the performance of mono- and multilingual children in the identified abilities because there is some evidence that bilingualism can improve executive functions. We tested 66 monolingual and 56 multilingual (i.e., bi- and trilingual) primary school children (M_age = 109 months) in an online version of the classic WCST. A principal component analysis revealed four factors: problem-solving, monitoring, efficient errors, and perseverations. Because the assignment of measures to factors is only partially coherent across the literature, we identified this as one of the sources of task impurity. In the second part, we calculated regression analyses to test for group differences while controlling for intelligence as a predictor for executive functions and for confounding variables such as age, German lexicon size, and socioeconomic status. Intelligence predicted problem-solving and perseverations. In the monitoring component (measured by the reaction times preceding a rule switch), multilinguals outperformed monolinguals, thereby supporting the view that bi- or multilingualism can improve processing speed related to monitoring.

Multivariate Base Rates of Low Scores on Tests of Executive Functions in a Multi-Country Latin American Sample

The objective of the study was to determine the prevalence of low scores in a diverse Latin American population for two neuropsychological commonly used tests to evaluate executive functions and to compare the number of low scores obtained using normative data from a Spanish-speaking population from Latin America versus an English-speaking population from U.S.A. Healthy adults (N = 5402) were administered the Modified Wisconsin Card Sorting Test and Stroop Color-Word. Low scores on measures of executive functioning are common. Clinicians working with Spanish-speaking adults should take into account the higher probability of low scores on these measures to reduce false-positive diagnoses of cognitive deficits in an individual.

Effectiveness of sorting tests for detecting cognitive decline in older adults with dementia and other common neurodegenerative disorders: A meta-analysis

The demand for simple, accurate and time-efficient screens to detect cognitive decline at point-of-care is increasing. Sorting tests are often used to detect the 'executive' deficits that are commonly associated with behavioural-variant frontotemporal dementia (bvFTD), but their potential for use as a cognitive screen with older adults is unclear. A comprehensive search of four databases identified 142 studies that compared the sorting test performance (e.g. WCST, DKEFS-ST) of adults with a common neurodegenerative disorder (e.g. Alzheimer's disease, vascular dementia, bvFTD, Parkinson's disease) and cognitively-healthy controls. Hedges' g effect sizes were used to compare the groups on five common test scores (Category, Total, Perseveration, Error, Description). The neurodegenerative disorders (combined) showed large deficits on all scores (g -1.0 to -1.3), with dementia (combined subtypes) performing more poorly (g -1.2 to -2.1), although bvFTD was not disproportionately worse than the other dementias. Overall, sorting tests detected the cognitive impairments caused by common neurodegenerative disorders, especially dementia, highlighting their potential suitability as a cognitive screen for older adults.

The Colorado Cognitive Assessment (CoCA): Development of an Advanced Neuropsychological Screening Tool

OBJECTIVE

The Colorado Cognitive Assessment (CoCA) was designed to improve upon existing screening tests in a number of ways, including enhanced psychometric properties and minimization of bias across diverse groups. This paper describes the initial validation study of the CoCA, which seeks to describe the test; demonstrate its construct validity; measurement invariance to age, education, sex, and mood symptoms; and compare it to the Montreal Cognitive Assessment (MoCA).

METHOD

Participants included 151 older adults (MAge = 71.21, SD = 8.05) who were administered the CoCA, MoCA, Judgment test from the Neuropsychological Assessment Battery (NAB), 15-item version of the Geriatric Depression Scale (GDS-15), and 10-item version of the Geriatric Anxiety Scale (GAS-10).

RESULTS

A single-factor confirmatory factor analysis model of the CoCA fit the data well, CFI = 0.955; RMSEA = 0.033. The CoCA factor score reliability was .84, compared to .74 for the MoCA. The CoCA had stronger disattenuated correlations with the MoCA (r = .79) and NAB Judgment (r = .47) and weaker correlations with the GDS-15 (r = -.36) and GAS-10 (r = -.15), supporting its construct validity. Finally, when analyzed using multiple-indicators, multiple-causes (MIMIC) modeling, the CoCA showed no evidence of measurement noninvariance, unlike the MoCA.

CONCLUSIONS

These results provide initial evidence to suggest that the CoCA is a valid cognitive screening tool that offers numerous advantages over the MoCA, including superior psychometric properties and measurement noninvariance. Additional validation and normative studies are warranted.

Normative data for tests of attention and executive functions in a sample of European Portuguese adult population

OBJECTIVE

The main goal of this study was to produce normative data for the Portuguese population on five neuropsychological tests frequently used to assess executive functions and attention: the Modified Wisconsin Card Sorting Test (M-WCST), the Stroop Color and Word Test, the Trail Making Test (TMT), the Brief Test of Attention (BTA), and the Symbol Digit Modalities Test (SDMT).

METHOD

The study included 300 individuals aged between 18 and 93 years, who had educational backgrounds ranging from 3 to 25 years.

RESULTS

The influence of age, education, and sex was explored for each measure, as well as their contribution to explain the performance variance.

CONCLUSIONS

The normative data are presented as regression-based algorithms to adjust direct and derived test scores for sex, age, and education. This study provides a calculator of normative data, derived from the results of the regression models.

Executive functions in the elderly with mild cognitive impairment: a systematic review on motor and cognitive inhibition, conflict control and cognitive flexibility

Background: Mild Cognitive Impairment (MCI) is a syndrome characterised by mild cognitive decline, on one or more domains, but which does not compromise daily functions. Several studies have investigated the relationship between MCI and deficit in executive functions (EFs) but, unlike robust evidence in the mnestic domain, the nature of executive deficits in the MCI population remains uncertain.Objectives: This systematic review aims to evaluate EFs in patients with MCI, considering inhibition (motor and cognitive), conflict control and cognitive flexibility.Method: The databases used for the search were PUBMED, PsycINFO, PsycARTICLES and MEDLINE. Eligibility criteria: use of specific paradigms for EFs assessment ('Wisconsin Card Sorting Test', 'Stroop Task', 'Go/No-Go Task', 'Flanker Task'); age over 65, studies published in English. Exclusion criteria: presence of dementia; psychiatric disorders; stroke; cranial trauma; inclusion of participants with MCI in groups with healthy elderly or those with dementia.Results: Fifty-five studies were selected, namely: Stroop Task (N = 30), WCST (N = 14), Go/No-Go (N = 9), Flanker Task (N = 2). Results have shown in people with MCI deficits in all the EFs considered.Conclusions: The results of this review support the applicability of the four experimental tasks examined for the study of EFs in people with MCI. These paradigms are useful in research, diagnosis and therapeutic purposes, allowing obtaining an articulated EFs profile that can compromise the daily life in elderly. These EFs are not generally evaluated by standard assessment of MCI, but their evaluation can lead to a better knowledge of MCI and help in the diagnosis and treatment.

Age, education and gender effects on Wisconsin card sorting test: standardization, reliability and validity in healthy Argentinian adults

The Wisconsin Card Sorting Test (WCST) is a widely used neuropsychological assessment of executive functioning. The aim of this study was to provide norm values and analyze the psychometric properties of WCST in healthy Argentinian adults aged from 18 to 89 years old (N = 235). Descriptive statistics are reported as means, standard deviations and percentiles, with the effects of age, education and gender being investigated by ANOVA, and with the effect sizes being calculated. The psychometrics were studied using the WCST structure, reliability, convergent validity, and discriminant validity, and WCST norms adjusted for age and educational level are proposed. This instrument is a reliable and valid tool for the assessment of executive functions. However, as the age- and educational-related effects were demonstrated, these characteristics need to be considered before interpreting WCST scores. Regarding gender, no differences were found. Our results expand the geographical and sociocultural applicability of WCST.

Executive Functions in Alzheimer Disease: A Systematic Review

Alzheimer's disease is a severe irreversible syndrome, characterized by a slow and progressive cognitive decline that interferes with the standard instrumental and essential functions of daily life. Promptly identifying the impairment of particular cognitive functions could be a fundamental condition to limit, through preventive or therapeutic interventions, the functional damages found in this degenerative dementia. This study aims to analyse, through a systematic review of the studies, the sensitivity of four experimental paradigms (Wisconsin Card Sorting Test, Stroop Task, Go/No-Go Task, and Flanker Task) considered as golden standard instruments for executive functions assessment in elderly subjects affected by Alzheimer dementia. This review was carried out according to the PRISMA method. Forty-five studies comparing the executive performance of patients with Alzheimer's dementia (diagnosed according to different classification criteria for dementia) and healthy elderly patients both over the age of sixty, were selected. For the research, PubMed, PsycINFO, PsycArticles databases were used. The study highlighted the importance of using standard protocols to evaluate executive dysfunction in Alzheimer's disease. The Stroop task allows discriminating better between healthy and pathological aging.

Identifying preclinical vascular dementia in symptomatic small vessel disease using MRI

Sporadic cerebral small vessel disease is an important cause of vascular dementia, a syndrome of cognitive impairment together with vascular brain damage. At post-mortem pure vascular dementia is rare, with evidence of co-existing Alzheimer's disease pathology in 95% of cases. This work used MRI to characterize structural abnormalities during the preclinical phase of vascular dementia in symptomatic small vessel disease. 121 subjects were recruited into the St George's Cognition and Neuroimaging in Stroke study and followed up longitudinally for five years. Over this period 22 individuals converted to dementia. Using voxel-based morphometry, we found structural abnormalities present at baseline in those with preclinical dementia, with reduced grey matter density in the left striatum and hippocampus, and more white matter hyperintensities in the frontal white-matter. The lacunar data revealed that some of these abnormalities may be due to lesions within the striatum and centrum semiovale. Using support vector machines, future dementia could be best predicted using hippocampal and striatal Jacobian determinant data, achieving a balanced classification accuracy of 73%. Using cluster ward linkage we identified four anatomical subtypes. Successful predictions were restricted to groups with lower levels of vascular damage. The subgroup that could not be predicted were younger, further from conversion, had the highest levels of vascular damage, with milder cognitive impairment at baseline but more rapid deterioration in processing speed and executive function, consistent with a primary vascular dementia. In contrast, the remaining groups had decreasing levels of vascular damage and increasing memory impairment consistent with progressively more Alzheimer's-like pathology. Voxel-wise rates of hippocampal atrophy supported these distinctions, with the vascular group closely resembling the non-dementing cohort, whereas the Alzheimer's like group demonstrated global hippocampal atrophy. This work reveals distinct anatomical endophenotypes in preclinical vascular dementia, forming a spectrum between vascular and Alzheimer's like pathology. The latter group can be identified using baseline MRI, with 73% converting within 5 years. It was not possible to predict the vascular dominant dementia subgroup, however 19% of negative predictions with high levels of vascular disease would ultimately develop dementia. It may be that techniques more sensitive to white matter damage, such as diffusion weighted imaging, may prove more useful for this vascular dominant subgroup in the future. This work provides a way to accurately stratify patients using a baseline MRI scan, and has utility in future clinical trials designed to slow or prevent the onset of dementia in these high-risk cohorts.

Diminished neural network dynamics in amnestic mild cognitive impairment

Mild cognitive impairment (MCI) is widely regarded as an intermediate stage between typical aging and dementia, with nearly 50% of patients with amnestic MCI (aMCI) converting to Alzheimer's dementia (AD) within 30 months of follow-up (Fischer et al., 2007). The growing literature using resting-state functional magnetic resonance imaging reveals both increased and decreased connectivity in individuals with MCI and connectivity loss between the anterior and posterior components of the default mode network (DMN) throughout the course of the disease progression (Hillary et al., 2015; Sheline & Raichle, 2013; Tijms et al., 2013). In this paper, we use dynamic connectivity modeling and graph theory to identify unique brain "states," or temporal patterns of connectivity across distributed networks, to distinguish individuals with aMCI from healthy older adults (HOAs). We enrolled 44 individuals diagnosed with aMCI and 33 HOAs of comparable age and education. Our results indicated that individuals with aMCI spent significantly more time in one state in particular, whereas neural network analysis in the HOA sample revealed approximately equivalent representation across four distinct states. Among individuals with aMCI, spending a higher proportion of time in the dominant state relative to a state where participants exhibited high cost (a measure combining connectivity and distance), predicted better language performance and less perseveration. This is the first report to examine neural network dynamics in individuals with aMCI.

Diffusion tensor image segmentation of the cerebrum provides a single measure of cerebral small vessel disease severity related to cognitive change

Cerebral small vessel disease (SVD) is the primary cause of vascular cognitive impairment and is associated with decline in executive function (EF) and information processing speed (IPS). Imaging biomarkers are needed that can monitor and identify individuals at risk of severe cognitive decline. Recently there has been interest in combining several magnetic resonance imaging (MRI) markers of SVD into a unitary score to describe disease severity. Here we apply a diffusion tensor image (DTI) segmentation technique (DSEG) to describe SVD related changes in a single unitary score across the whole cerebrum, to investigate its relationship with cognitive change over a three-year period. 98 patients (aged 43-89) with SVD underwent annual MRI scanning and cognitive testing for up to three years. DSEG provides a vector of 16 discrete segments describing brain microstructure of healthy and/or damaged tissue. By calculating the scalar product of each DSEG vector in reference to that of a healthy ageing control we generate an angular measure (DSEG θ) describing the patients' brain tissue microstructural similarity to a disease free model of a healthy ageing brain. Conventional MRI markers of SVD brain change were also assessed including white matter hyperintensities, cerebral atrophy, incident lacunes, cerebral-microbleeds, and white matter microstructural damage measured by DTI histogram parameters. The impact of brain change on cognition was explored using linear mixed-effects models. Post-hoc sample size analysis was used to assess the viability of DSEG θ as a tool for clinical trials. Changes in brain structure described by DSEG θ were related to change in EF and IPS (p < 0.001) and remained significant in multivariate models including other MRI markers of SVD as well as age, gender and premorbid IQ. Of the conventional markers, presence of new lacunes was the only marker to remain a significant predictor of change in EF and IPS in the multivariate models (p = 0.002). Change in DSEG θ was also related to change in all other MRI markers (p < 0.017), suggesting it may be used as a surrogate marker of SVD damage across the cerebrum. Sample size estimates indicated that fewer patients would be required to detect treatment effects using DSEG θ compared to conventional MRI and DTI markers of SVD severity. DSEG θ is a powerful tool for characterising subtle brain change in SVD that has a negative impact on cognition and remains a significant predictor of cognitive change when other MRI markers of brain change are accounted for. DSEG provides an automatic segmentation of the whole cerebrum that is sensitive to a range of SVD related structural changes and successfully predicts cognitive change. Power analysis shows DSEG θ has potential as a monitoring tool in clinical trials. As such it may provide a marker of SVD severity from a single imaging modality (i.e. DTIs).

Behavioural inflexibility in a comorbid rat model of striatal ischemic injury and mutant hAPP overexpression

Alzheimer disease (AD) and stroke coexist and interact; yet how they interact is not sufficiently understood. Both AD and basal ganglia stroke can impair behavioural flexibility, which can be reliably modeled in rats using an established operant based set-shifting test. Transgenic Fischer 344-APP21 rats (TgF344) overexpress pathogenic human amyloid precursor protein (hAPP) but do not spontaneously develop overt pathology, hence TgF344 rats can be used to model the effect of vascular injury in the prodromal stages of Alzheimer disease. We demonstrate that the injection of endothelin-1 (ET1) into the dorsal striatum of TgF344 rats (Tg-ET1) produced an exacerbation of behavioural inflexibility with a behavioural phenotype that was distinct from saline-injected wildtype & TgF344 rats as well as ET1-injected wildtype rats (Wt-ET1). In addition to profiling the types of errors made, interpolative modeling using logistic exposure-response regression provided an informative analysis of the timing and efficiency of behavioural flexibility. During set-shifting, Tg-ET1 committed fewer perseverative errors than Wt-ET1. However, Tg-ET1 committed significantly more regressive errors and had a less efficient strategy change than all other groups. Thus, behavioural flexibility was more vulnerable to striatal ischemic injury in TgF344 rats.

Progression of MRI markers in cerebral small vessel disease: Sample size considerations for clinical trials

Detecting treatment efficacy using cognitive change in trials of cerebral small vessel disease (SVD) has been challenging, making the use of surrogate markers such as magnetic resonance imaging (MRI) attractive. We determined the sensitivity of MRI to change in SVD and used this information to calculate sample size estimates for a clinical trial. Data from the prospective SCANS (St George’s Cognition and Neuroimaging in Stroke) study of patients with symptomatic lacunar stroke and confluent leukoaraiosis was used (n = 121). Ninety-nine subjects returned at one or more time points. Multimodal MRI and neuropsychologic testing was performed annually over 3 years. We evaluated the change in brain volume, T2 white matter hyperintensity (WMH) volume, lacunes, and white matter damage on diffusion tensor imaging (DTI). Over 3 years, change was detectable in all MRI markers but not in cognitive measures. WMH volume and DTI parameters were most sensitive to change and therefore had the smallest sample size estimates. MRI markers, particularly WMH volume and DTI parameters, are more sensitive to SVD progression over short time periods than cognition. These markers could significantly reduce the size of trials to screen treatments for efficacy in SVD, although further validation from longitudinal and intervention studies is required.

Latent profiles of executive functioning in healthy young adults: evidence of individual differences in hemispheric asymmetry

Two competing theoretical models of individual differences in executive functioning (EF) were examined: the Prefrontal Convexity Model and the Hemispheric Asymmetry Model. Neurologically healthy individuals (N = 315; mean age 20.8) completed a modified switching task (MST) and the Attention Network Test (ANT) in a single testing session. Data analysis was conducted in two phases. In the first phase (model identification), latent profile analysis was applied to MST variables measuring the abilities to form, switch, and maintain mental sets under conditions designed to tax left or right hemisphere resources. In the second phase (model validation), participant clusters obtained from the first phase were compared on the ANT. The Model Identification phase yielded a 3-profile solution consistent with the Hemispheric Asymmetry Model. Profile 1 (N = 203) was characterized by average EF performances. Profile 2 (N = 43) revealed a set maintenance weakness under non-verbal conditions. Profile 3 (N = 38) demonstrated weaknesses in cognitive flexibility combined with poor executive performances under verbal conditions. The Model Validation phase confirmed group differences. Profile 1 demonstrated average EF performances. Profile 2 demonstrated distractibility and decreased alertness, consistent with a right hemisphere weakness. Profile 3 demonstrated cognitive rigidity in the absence of external cues, consistent with a left hemisphere weakness. Individual differences in EF appear to follow a Hemispheric Asymmetry Model of EF among neurologically healthy adults. Investigating the relationship between hemispherically mediated executive functions and other individual difference factors known to confer health risk or resilience could inform numerous disciplines within the field of psychology.

Diagnostic Profiles of Patients Differentially Failing Executive Functioning Measures

OBJECTIVE

Limited research exists to explain differential executive functioning impairment in clinical populations, particularly between the Wisconsin Card Sorting Task (WCST) and the Trail Making Test (TMT).

METHODS

The distribution of clinical diagnoses was examined in patients failing none, one, or both tasks, and executive task performance was compared among dementia-related diagnoses. Two hundred and sixty-six participants received evaluations through an Alzheimer's Disease Research Center, which included executive tasks. Dementia-related diagnoses were established through consensus.

RESULTS

Chi-square analyses indicated that TMT failure, with or without WCST failure, possessed higher associations with dementia diagnoses. Repeated measures analysis of variance similarly indicated that participants with dementia, especially mild and moderate severity, performed worse on TMT.

CONCLUSIONS

Executive dysfunction was observed in dementia-related diagnoses, and TMT failure was implicated in dementia in higher proportions than WCST impairment. Trail Making Test appears more sensitive than WCST for assessing executive impairment across diagnoses, especially when time and resources are limited in screening and clinical settings.

Pattern and Rate of Cognitive Decline in Cerebral Small Vessel Disease: A Prospective Study

Objectives

Cognitive impairment, predominantly affecting processing speed and executive function, is an important consequence of cerebral small vessel disease (SVD). To date, few longitudinal studies of cognition in SVD have been conducted. We determined the pattern and rate of cognitive decline in SVD and used the results to determine sample size calculations for clinical trials of interventions reducing cognitive decline.

Methods

121 patients with MRI confirmed lacunar stroke and leukoaraiosis were enrolled into the prospective St George’s Cognition And Neuroimaging in Stroke (SCANS) study. Patients attended one baseline and three annual cognitive assessments providing 36 month follow-up data. Neuropsychological assessment comprised a battery of tests assessing working memory, long-term (episodic) memory, processing speed and executive function. We calculated annualized change in cognition for the 98 patients who completed at least two time-points.

Results

Task performance was heterogeneous, but significant cognitive decline was found for the executive function index (p<0.007). Working memory and processing speed decreased numerically, but not significantly. The executive function composite score would require the smallest samples sizes for a treatment trial with an aim of halting decline, but this would still require over 2,000 patients per arm to detect a 30% difference with power of 0.8 over a three year follow-up.

Conclusions

The pattern of cognitive decline seen in SVD over three years is consistent with the pattern of impairments at baseline. Rates of decline were slow and sample sizes would need to be large for clinical trials aimed at halting decline beyond initial diagnosis using cognitive scores as an outcome measure. This emphasizes the importance of more sensitive surrogate markers in this disease.

Attentional Set-Shifting Across Species

Attentional set-shifting, as a measure of executive flexibility, has been a staple of investigations into human cognition for over six decades. Mediated by the frontal cortex in mammals, the cognitive processes involved in forming, maintaining and shifting an attentional set are vulnerable to dysfunction arising from a number of human neurodegenerative diseases (such as Alzheimer's, Parkinson's and Huntington's diseases) and other neurological disorders (such as schizophrenia, depression, and attention deficit/hyperactivity disorder). Our understanding of these diseases and disorders, and the cognitive impairments induced by them, continues to advance, in tandem with an increasing number of tools at our disposal. In this chapter, we review and compare commonly used attentional set-shifting tasks (the Wisconsin Card Sorting Task and Intradimensional/Extradimensional tasks) and their applicability across species. In addition to humans, attentional set-shifting has been observed in a number of other animals, with a substantial body of literature describing performance in monkeys and rodents. We consider the task designs used to investigate attentional set-shifting in these species and the methods used to model human diseases and disorders, and ultimately the comparisons and differences between species-specific tasks, and between performance across species.

Autoimmune manifestations in the 3xTg-AD model of Alzheimer's disease

BACKGROUND

Immune system activation is frequently reported in patients with Alzheimer's disease (AD). However, it remains unknown whether this is a cause, a consequence, or an epiphenomenon of brain degeneration.

OBJECTIVE

The present study examines whether immunological abnormalities occur in a well-established murine AD model and if so, how they relate temporally to behavioral deficits and neuropathology.

METHODS

A broad battery of tests was employed to assess behavioral performance and autoimmune/inflammatory markers in 3xTg-AD (AD) mice and wild type controls from 1.5 to 12 months of age.

RESULTS

Aged AD mice displayed severe manifestations of systemic autoimmune/inflammatory dise6ase, as evidenced by splenomegaly, hepatomegaly, elevated serum levels of anti-nuclear/anti-dsDNA antibodies, low hematocrit, and increased number of double-negative T splenocytes. However, anxiety-related behavior and altered spleen function were evident as early as 2 months of age, thus preceding typical AD-like brain pathology. Moreover, AD mice showed altered olfaction and impaired "cognitive" flexibility in the first 6 months of life, suggesting mild cognitive impairment-like manifestations before general learning/memory impairments emerged at an older age. Interestingly, all of these features were present in 3xTg-AD mice prior to significant amyloid-β or tau pathology.

CONCLUSION

The results indicate that behavioral deficits in AD mice develop in parallel with systemic autoimmune/inflammatory disease. These changes antedate AD-like neuropathology, thus supporting a causal link between autoimmunity and aberrant behavior. Consequently, 3xTg-AD mice may be a useful model in elucidating the role of immune system in the etiology of AD.

Dynamic O-linked N-acetylglucosamine modification of proteins affects stress responses and survival of mesothelial cells exposed to peritoneal dialysis fluids

The ability of cells to respond and survive stressful conditions is determined, in part, by the attachment of O-linked N-acetylglucosamine (O-GlcNAc) to proteins (O-GlcNAcylation), a post-translational modification dependent on glucose and glutamine. This study investigates the role of dynamic O-GlcNAcylation of mesothelial cell proteins in cell survival during exposure to glucose-based peritoneal dialysis fluid (PDF). Immortalized human mesothelial cells and primary mesothelial cells, cultured from human omentum or clinical effluent of PD patients, were assessed for O-GlcNAcylation under normal conditions or after exposure to PDF. The dynamic status of O-GlcNAcylation and effects on cellular survival were investigated by chemical modulation with 6-diazo-5-oxo-L-norleucine (DON) to decrease or O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino N-phenyl carbamate (PUGNAc) to increase O-GlcNAc levels. Viability was decreased by reducing O-GlcNAc levels by DON, which also led to suppressed expression of the cytoprotective heat shock protein 72. In contrast, increasing O-GlcNAc levels by PUGNAc or alanyl-glutamine led to significantly improved cell survival paralleled by higher heat shock protein 72 levels during PDF treatment. Addition of alanyl-glutamine increased O-GlcNAcylation and partly counteracted its inhibition by DON, also leading to improved cell survival. Immunofluorescent analysis of clinical samples showed that the O-GlcNAc signal primarily originates from mesothelial cells. In conclusion, this study identified O-GlcNAcylation in mesothelial cells as a potentially important molecular mechanism after exposure to PDF. Modulating O-GlcNAc levels by clinically feasible interventions might evolve as a novel therapeutic target for the preservation of peritoneal membrane integrity in PD.

Strategic lacunes and their relationship to cognitive impairment in cerebral small vessel disease

Objectives

Lacunes are an important disease feature of cerebral small vessel disease (SVD) but their relationship to cognitive impairment is not fully understood. To investigate this we determined (1) the relationship between lacune count and total lacune volume with cognition, (2) the spatial distribution of lacunes and the cognitive impact of lacune location, and (3) the whole brain anatomical covariance associated with these strategically located regions of lacune damage.

Methods

One hundred and twenty one patients with symptomatic lacunar stroke and radiological leukoaraiosis were recruited and multimodal MRI and neuropsychological data acquired. Lacunes were mapped semi-automatically and their volume calculated. Lacune location was automatically determined by projection onto atlases, including an atlas which segments the thalamus based on its connectivity to the cortex. Lacune locations were correlated with neuropsychological results. Voxel based morphometry was used to create anatomical covariance maps for these ‘strategic’ regions.

Results

Lacune number and lacune volume were positively associated with worse executive function (number p < 0.001; volume p < 0.001) and processing speed (number p < 0.001; volume p < 0.001). Thalamic lacunes, particularly those in regions with connectivity to the prefrontal cortex, were associated with impaired processing speed (Bonferroni corrected p = 0.016). Regions of associated anatomical covariance included the medial prefrontal, orbitofrontal, anterior insular cortex and the striatum.

Conclusion

Lacunes are important predictors of cognitive impairment in SVD. We highlight the importance of spatial distribution, particularly of anteromedial thalamic lacunes which are associated with impaired information processing speed and may mediate cognitive impairment via disruption of connectivity to the prefrontal cortex.

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Lacunes are a predictor of cognitive impairment in cerebral small vessel disease

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Lacunes in the anteromedial thalamus are associated with impaired processing speed

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This region was identified to have connectivity to the prefrontal cortex

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We validate this finding with the help of a structural covariance analysis

Detection of early cognitive impairment using AD8 in a young patient with stroke with cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy syndrome: a case report

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) syndrome is a hereditary disease resulting from NOTCH3 gene mutation. The clinical presentations include migraine, recurrent stroke, and cognitive impairment. The severity of cognitive impairment varies in different stages, and early recognition poses a challenge. A 47-year-old lady presented with chronic migraine and sudden onset of hemiparesis. Magnetic resonance imaging revealed compatible findings of CADASIL, which was confirmed by mutation analysis of NOTCH3 gene. Early cognitive impairment was detected by her score of 3 in Ascertain Dementia 8 (AD8) questionnaire and confirmed by detailed neuropsychological assessments. After 21 months of follow-up, deterioration in her cognition and ability to perform instrumental activities of daily living were significant with a follow-up AD8 score of 7. Ascertain Dementia 8 questionnaire is an easy and valid screening tool for early cognitive impairment in patients with CADASIL syndrome.

Mechanisms of cognitive impairment in cerebral small vessel disease: multimodal MRI results from the St George's cognition and neuroimaging in stroke (SCANS) study

Cerebral small vessel disease (SVD) is a common cause of vascular cognitive impairment. A number of disease features can be assessed on MRI including lacunar infarcts, T2 lesion volume, brain atrophy, and cerebral microbleeds. In addition, diffusion tensor imaging (DTI) is sensitive to disruption of white matter ultrastructure, and recently it has been suggested that additional information on the pattern of damage may be obtained from axial diffusivity, a proposed marker of axonal damage, and radial diffusivity, an indicator of demyelination. We determined the contribution of these whole brain MRI markers to cognitive impairment in SVD. Consecutive patients with lacunar stroke and confluent leukoaraiosis were recruited into the ongoing SCANS study of cognitive impairment in SVD (n = 115), and underwent neuropsychological assessment and multimodal MRI. SVD subjects displayed poor performance on tests of executive function and processing speed. In the SVD group brain volume was lower, white matter hyperintensity volume higher and all diffusion characteristics differed significantly from control subjects (n = 50). On multi-predictor analysis independent predictors of executive function in SVD were lacunar infarct count and diffusivity of normal appearing white matter on DTI. Independent predictors of processing speed were lacunar infarct count and brain atrophy. Radial diffusivity was a stronger DTI predictor than axial diffusivity, suggesting ischaemic demyelination, seen neuropathologically in SVD, may be an important predictor of cognitive impairment in SVD. Our study provides information on the mechanism of cognitive impairment in SVD.

A high-fat-diet-induced cognitive deficit in rats that is not prevented by improving insulin sensitivity with metformin

AIMS/HYPOTHESIS

We previously demonstrated that animals fed a high-fat (HF) diet for 10 weeks developed insulin resistance and behavioural inflexibility. We hypothesised that intervention with metformin would diminish the HF-feeding-evoked cognitive deficit by improving insulin sensitivity.

METHODS

Rats were trained in an operant-based matching and non-matching to position task (MTP/NMTP). Animals received an HF (45% of kJ as lard; n = 24), standard chow (SC; n = 16), HF + metformin (144 mg/kg in diet; n = 20) or SC + metformin (144 mg/kg in diet; n = 16) diet for 10 weeks before retesting. Body weight and plasma glucose, insulin and leptin were measured. Protein lysates from various brain areas were analysed for alterations in intracellular signalling or production of synaptic proteins.

RESULTS

HF-fed animals developed insulin resistance and an impairment in switching task contingency from matching to non-matching paradigm. Metformin attenuated the insulin resistance and weight gain associated with HF feeding, but had no effect on performance in either MTP or NMTP tasks. No major alteration in proteins associated with insulin signalling or synaptic function was detected in response to HF diet in the hypothalamus, hippocampus, striatum or cortex.

CONCLUSIONS/INTERPRETATION

Metformin prevented the metabolic but not cognitive alterations associated with HF feeding. The HF diet protocol did not change basal insulin signalling in the brain, suggesting that the brain did not develop insulin resistance. These findings indicate that HF diet has deleterious effects on neuronal function over and above those related to insulin resistance and suggest that weight loss may not be sufficient to reverse some damaging effects of poor diet.

Perseverative errors on the Wisconsin Card Sorting Test and brain perfusion imaging in mild Alzheimer's disease

BACKGROUND

The Wisconsin Card Sorting Test (WCST) has long been used to investigate deficits in executive function in humans. The majority of studies investigating deficient WCST performance focused on the number of categories achieved (CA) and the number of perseverative errors of the Nelson type (PEN). However, there is insufficient evidence that these two measures reflect the same neural deficits.

METHODS

Twenty AD patients with high PEN scores, and 20 age- and sex-matched AD patients with low PEN scores were selected. All 40 subjects underwent brain SPECT, and the SPECT images were analyzed by Statistical Parametric Mapping.

RESULTS

No significant differences were found between high and low PEN score groups with respect to years of education, Addenbrooke's Cognitive Examination scores, and Mini-Mental State Examination scores. However, higher z scores for hypoperfusion in the bilateral rectal and orbital gyri were observed in the high PEN score group compared with the low PEN score group.

CONCLUSIONS

Our results suggest that functional activity of the bilateral rectal and orbital gyri is closely related to PEN scores on a modified WCST (mWCST). The PEN score on a mWCST might be a promising index of dysfunction of the orbitofrontal area among patients with mild AD.

The Wisconsin Card Sorting Test and the N-back test in mild cognitive impairment and elderly depression

The aim of this study was to assess cognitive functions in 30 non-depressed patients with mild cognitive impairment (MCI), compared with 30 age-, gender- and education-matched patients with acute depressive episode, and with 30 healthy subjects. Neuropsychological assessment included the Mini Mental State Examination (MMSE), memory tests as well as the Wisconsin Card Sorting Test (WCST) and the N-back test. Patients with MCI obtained significantly worse results on all domains of the WCST and the N-back test compared to both depressed and healthy subjects. Depressed patients showed significantly worse performance than controls on most scores. In the MCI group, no association with MMSE was found with any of WCST domains, or with reaction time in the N-back test. Three tests, WCST-P, N-back %CORR and WCST 1st CAT obtained highest ranks (>90) as predictors for differentiating between groups. The results suggest a usefulness of employing WCST and N-back tests for a neuropsychological evaluation of patients with MCI.

Current concepts in Alzheimer's disease: a multidisciplinary review

This comprehensive, pedagogically-oriented review is aimed at a heterogeneous audience representative of the allied disciplines involved in research and patient care. After a foreword on epidemiology, genetics, and risk factors, the amyloid cascade model is introduced and the main neuropathological hallmarks are discussed. The progression of memory, language, visual processing, executive, attentional, and praxis deficits, and of behavioral symptoms is presented. After a summary on neuropsychological assessment, emerging biomarkers from cerebrospinal fluid assays, magnetic resonance imaging, nuclear medicine, and electrophysiology are discussed. Existing treatments are briefly reviewed, followed by an introduction to emerging disease-modifying therapies such as secretase modulators, inhibitors of Abeta aggregation, immunotherapy, inhibitors of tau protein phosphorylation, and delivery of nerve growth factor.

Construct validity of the Neuropsychological Screening Battery for Hispanics (NeSBHIS) in a neurological sample

Epidemiological studies suggest that the Hispanic population is at increased risk for neurological disorders. Yet, few assessment measures have been developed for, adapted to, or normalized with Spanish-speakers. The Neuropsychological Screening Battery for Hispanics (NeSBHIS) was developed to address the lack of resources available to this underserved community. Although the NeSBHIS possesses robust construct validity and clinical utility in a community-based sample, these properties remain largely untested in neurological populations. One hundred and twenty-seven Spanish-speaking Hispanic patients with confirmed epilepsy (mean age = 37.8, SD = 13.3) were evaluated using the NeSBHIS. All participants self-identified as "Hispanic" and immigrated from Spanish-speaking countries. Data were analyzed using confirmatory factor analysis with the a priori assumption that variables would load according to theoretical expectations reported by Pontón and colleagues (2000). The overall model fit indices were in the desired range: Comparative Fit Index = 0.936, Tucker Lewis Index = 0.915, RMSEA = 0.090, and SRMR = 0.069. All NeSBHIS subtests loaded significantly (p < .001) on their respective factors; the standardized loadings were high, ranging from 0.562 to 0.995, with the exception of Block Design (-0.308). Overall, findings suggest that the NeSBHIS has robust construct validity in a neurological sample.

Predicting executive function task scores with the Rey-Osterrieth Complex Figure

The Boston Qualitative Scoring System (BQSS) is one of the scoring methods of the Rey-Osterrieth Complex Figure Test (ROCF). With BQSS, 17 qualitative ratings are generated, and subsequently 6 summary scores are calculated by combining several qualitative scores. Previously we showed that 5 of 6 BQSS summary scores were correlated with the scores of the several executive function tests in children. The objective of this study was to develop a new summary score which correlates with the executive function test scores more strongly than the existing summary scores. For this purpose, we conducted multiple regression analysis to predict PEN, CA, DSM of the Wisconsin Card Sorting Test Keio Version, and the Mazes scores from WISC-III, by the BQSS qualitative scores derived from ROCF drawings in copy condition. The subjects were 78 children with various neuropsychological disorders (5 years 5 months-14 years 11 months; mean: 9 years 2 months; F 22, M 56). Significant predictive models were generated for PEN, CA, and Mazes scores. Among them the models for the Mazes scores were the most accurate. The second model for the Mazes scores was most suitable for a new summary score. Its degree-of-freedom-adjusted coefficient of multiple determination and multiple correlation coefficient reached 0.467 and 0.695, respectively. A new summary score should be applied in future studies to evaluate its clinical usefulness.

Executive functions deficit in mild cognitive impairment

OBJECTIVE

To investigate whether patients diagnosed with amnestic mild cognitive impairment (MCI) have also impairment in attention/executive functions, and therefore to clarify whether all subcomponents of executive control are equally affected in MCI.

BACKGROUND

MCI refers to the transitional state between normal aging and dementia. Amnestic MCI is characterized by impaired episodic memory, although subtle impairment of executive functions has been noted on neuropsychologic tests.

METHODS

We investigated 20 MCI patients and 20 normal controls using episodic memory, attention/executive functions, language, and praxis tests.

RESULTS

MCI patients had significantly lower scores on all measures of the Free and Cued Selective Reminding Test (P<0.05 to 0.01) than controls. Furthermore, MCI had a greater number of perseverations (P<0.01) on Modified Card Sorting Test and the lowest performance on the Stroop Test (P<0.02).

CONCLUSIONS

Our findings showed impairment in episodic memory performance in MCI as compared with that of controls. In addition, MCI patients had problems with response inhibition, switching, and cognitive flexibility, which encompass various aspects of executive functions. This suggests that MCI may be identified by using a more detailed procedure for the assessment of cognitive decline than the evaluation of memory alone.

MCI is associated with deficits in everyday functioning

The purpose of the present study was to examine the types of impairments in everyday function that accompany mild cognitive impairment (MCI). Data for this study was collected from 434 individuals consecutively evaluated at a university-based Alzheimer's Center. A total of 96 participants were diagnosed with MCI, 105 were cognitively normal, and 233 had dementia. Informant ratings of participants' abilities were obtained across different functional domains reflecting everyday abilities related to memory, language, visual spatial abilities, planning, organization, and divided attention. As expected, the demented group was significantly more impaired than the healthy control and MCI groups across all of the functional domains. The MCI group also showed significantly more functional impairment relative to healthy controls in all of the functional domains. Examination of the effect sizes as a measure of the magnitude of functional impairment in the MCI groups relative to controls showed that the greatest degree of impairment occurred within the Everyday Memory domain. The current findings suggest that individuals with MCI demonstrate deficits in a wide range of everyday functions but that the magnitude of these changes is greatest for those functional abilities that rely heavily on memory.

Reliability and validity of the Japanese version of the Frontal Assessment Battery in patients with the frontal variant of frontotemporal dementia

Patients with the frontal variant of frontotemporal dementia (fv-FTD) exhibit deficits of executive functions. However, no single executive function task that might be used to detect the executive function deficits in fv-FTD patients has been established as yet. The frontal assessment battery (FAB) devised by Dubois et al. (2000) has been reported to be a quick and simple bedside screening test that is sensitive for differentiating between FTD and Alzheimer's disease (AD). The present study was conducted with the aim of ascertaining the reliability and validity of the Japanese version of the FAB among Japanese patients with fv-FTD. The Japanese version of FAB was given to patients with mild fv-FTD (n = 18) and those with AD (n = 18). The test-retest reliability was evaluated after a 3-week interval by the same interviewer. Data from the Wisconsin Card Sorting Test (Keio version: KWCST) were also collected to ascertain the validity of the FAB. The Japanese version of the FAB exhibited good internal reliability (Cronbach's alpha: 0.70, 95% confidence interval [CI] = 0.50-0.84) and good test-retest reliability (intraclass correlation coefficient: 0.89, 95%CI = 0.77-0.95). Significant correlations were observed between the total FAB score and the category achieved (r = 0.454, P < 0.05) and number of perseveration errors (number of errors that were perseverations; r = 0.719, P < 0.01) in the KWCST. A cut-off of 10 for the total FAB score yielded the highest sensitivity (85%) and specificity (92%) for discriminating between patients with fv-FTD and AD with the highest positive likelihood (12.0, 95%CI = 2.6-55.4). The Japanese version of the FAB offers promise as an easy and quick bedside screening test to distinguish fv-FTD from AD.

Heterogeneity in executive impairment in patients with very mild Alzheimer's disease

BACKGROUND/AIMS

The presence of executive impairment in mild Alzheimer's disease (AD) has primarily been demonstrated by means of group comparison. Whether executive dysfunction is a common feature of mild AD or only present in a subgroup of patients remains unclear. The aim of this study was to describe the frequency of impairment on a set of internationally well-known executive tests in patients with very mild AD.

METHODS

Thirty-six patients with very mild AD (MMSE scores above 23) and 32 healthy control subjects were administered a battery of 7 executive tests: Trail Making part B, Stroop Interference Test, modified Wisconsin Card Sorting Test (WCST), category- and letter-based verbal fluency, a design fluency task and the Similarities subtest from WAIS. Impairment was defined as a score of 2 SD or more below control means.

RESULTS

Executive impairment on at least 1 measure was seen in 76% of the patients, and 50% were impaired on 2 or more tests. Trail Making B and Stroop Interference Test were impaired in more than 40%, whereas only few patients were impaired on Similarities, WCST and design fluency. A wide variation of executive test profiles was seen among the patients.

CONCLUSION

Executive impairments are common in early AD and not just a feature characteristic of a subgroup of patients. Complex attentional skills are more frequently affected than other executive functions. There is, however, considerable heterogeneity among AD patients in the pattern of executive dysfunction.

Early discrimination reversal learning impairment and preserved spatial learning in a longitudinal study of Tg2576 APPsw mice

To understand the relationship between amyloid-beta and cognitive decline in Alzheimer's disease, we evaluated cortical and hippocampal function in a transgenic mouse model of amyloid over-expression in Alzheimer's disease, the Tg2576 mouse. Tg2576 mice and their non-transgenic littermates were assessed at both 6 and 14 months of age in a battery of cognitive tests: attentional set-shifting, water maze spatial reference memory and T-maze working memory. Spatial reference memory was not affected by Tg status at either age. Working memory was only affected by age, with 6-month-old mice performing better than 14-month-old ones. Older mice were also significantly impaired on reversal learning and on the intra- and extra-dimensional shift in attentional set-shifting. A significant transgene effect was apparent in reversal learning, with Tg2576 mice requiring more trials to reach criterion at 6 months old. These data indicate that the effects of normal aging in C57B6xSJL F1 mice are most pronounced on putative frontal cortex-dependent tasks and that increasing Abeta load only affects discrimination reversal learning in our study.

Mild memory impairment in healthy older adults is distinct from normal aging

Mild memory impairment was detected in 28% of a sample of healthy community-dwelling older adults using the delayed recall trial of a word list learning task. Statistical analysis revealed that individuals with memory impairment also demonstrated relative deficits on other measures of memory, and tests of executive function, processing speed and global cognition, as measured by the CERAD and CogState batteries and CANTAB paired associate learning task. These relative deficits cannot be explained by age-related changes, education, intelligence, mood, health-related factors, or the individuals' ApoEepsilon4 status. Memory-impaired individuals (n = 30) did not recognize the extent of their memory and cognitive difficulties beyond the general complaints expressed by normal elderly (n = 77) within the study and their apparent difficulties did not appear to impact on their participation in life activities. These findings suggest it is unlikely that the memory and cognitive difficulties demonstrated by individuals with mild memory impairment reflect normal aging. Rather it is possible that such impairment may signal early neurodegenerative processes worthy of further investigation.

The nature of lexico-semantic processing deficits in mild cognitive impairment

Lexico-semantic impairments in Alzheimer disease (AD) have been attributed to abnormalities in both intentional and automatic access to semantic memory. However, the order in which these impairments appear during the course of the disease is unclear. We sought to answer this question by documenting lexico-semantic impairments in 61 subjects with mild cognitive impairment (MCI), a pre-AD stage, and by comparing them to those of 39 AD and 60 normal elderly (NE) subjects. All subjects were tested with intentional access tasks (picture naming and semantic probes), automatic access tasks (lexical decision and priming), and executive function tasks (Stroop and Stroop-Picture naming). Results indicated that the MCI group was only impaired on tasks of intentional access relative to the AD group who was impaired on both types of tasks. Because most MCI subjects eventually develop AD, these results suggest that intentional access to semantic memory is impaired before automatic access. Further, impairments on the Stroop-Picture naming task but not on the Stroop task, suggest that lexico-semantic impairments in the MCI group may be related to inhibition deficits during semantic search. Findings are discussed in light of executive dysfunctions within the framework of semantic memory theories.

Mechanical stress and glucose concentration modulate glucose transport in cultured rat podocytes

BACKGROUND

Recent studies show that mechanical stress modifies both morphology and protein expression in podocytes. Ambient glucose is another factor modulating protein synthesis in these cells. In diabetes, podocytes experience elevated glucose concentrations as well as mechanical strain generated by high intracapillary pressures. Both these factors are responsible for podocyte injury, leading to impairment of kidney glomerular function. In the present study, we examined the effects of glucose concentration and mechanical stress on glucose uptake in podocytes.

METHODS

Following a 24 h pre-incubation in low (2.5 mM, LG), normal (5.6 mM, NG) or high (30 mM, HG) glucose media, cultured rat podocytes were exposed to 4 h mechanical stress. We used the labelled glucose analogue, [3H]2-deoxy-D-glucose, to measure glucose uptake. The distribution of facilitative glucose transporters GLUT2 and GLUT4 was assessed by flow cytometry.

RESULTS

In the control (static) cells, glucose uptake was similar in the three glucose groups. In mechanically stressed podocytes, glucose uptake increased 2-fold in the LG and NG groups but increased 3-fold in the HG group. In the NG cells, mechanical load increased the membrane expression of GLUT2 and reduced the membrane-bound GLUT4. In stretched HG cells, the membrane expression of both GLUT2 and GLUT4 was decreased. High glucose decreased the plasma membrane GLUT2 content in the stretched cells, whereas both static and stretched podocytes showed an elevation in GLUT4.

CONCLUSION

Mechanical stress potentiated glucose uptake in podocytes and this effect was enhanced by high ambient glucose. The decreased expression of GLUT2 and GLUT4 on the surface of stretched cells suggests that the activity of other glucose transporters may be regulated by mechanical stress in podocytes.

The cerebral correlates of different types of perseveration in the Wisconsin Card Sorting Test

OBJECTIVES

To explore the neural substrates corresponding to the perseverative errors in the Wisconsin Card Sorting Test (WCST).

METHODS

The study examined the correlations between the WCST performances and the SPECT measurements of regional cerebral blood flow (rCBF) in subjects with neurodegenerative dementia. Negative non-linear correlations between the rCBF and the two different types of the perseverative errors ("stuck-in-set" and "recurrent" perseverative errors) were calculated on a voxel basis and volume-of-interest basis in the mixed groups of 72 elderly and dementia patients.

RESULTS

The stuck-in-set perseverative error was associated with the reduced rCBF in the rostrodorsal prefrontal cortex, whereas the recurrent perseverative error was related to the left parietal activity but not to the prefrontal activity.

CONCLUSIONS

These findings augment evidence that the rostrodorsal prefrontal cortex crucially mediates attentional set shifting, and suggest that the stuck-in-set perseverative errors would be a true pathognomonic sign of frontal dysfunction. Moreover, this study shows that the recurrent perseverative errors may not be associated closely with the prefrontal function, suggesting that this error and the stuck-in-set error should be differentially estimated in the WCST.

[Methods for assessing cognitive function utilizing operant tasks in rats]

Most human behaviors (responses) are volitional, the frequency of which is changed based on stimulus presentations contingent upon the response, that is, operant behavior. It is considered that the findings on cognitive functions based on operant behaviors are more reliable in extrapolating the results to humans. Impairment of memory function, most notably the impairments of working memory and attention, is an important research focus to elucidate the mechanism underlying the core syndrome of Alzheimer's disease. Among various methods to measure working memory and attention, a delayed matching-to-sample paradigm utilizing operant chambers equipped with 3 levers and a choice reaction time paradigm have been proven to be very useful. Aside from these, adaptation to new environment is an important function for survival, and its impairment has been considered to be one of the factors inducing psychiatric disorders. Preclinical methods to measure the adaptation ability include a position reversal learning paradigm utilizing 2-lever operant chambers. Since the findings of studies on cognitive functions utilizing operant behaviors have been in good correlation with clinical findings, it would serve as a good strategy for elucidating the causes of such disorders as well as developing therapeutic agents.