Executive functions in patients with Alzheimer's disease, type 2 diabetes mellitus patients and cognitively healthy older adults

A systematic review of preclinical studies exploring the role of insulin signalling in executive function and memory

Beside its involvement in somatic dysfunctions, altered insulin signalling constitutes a risk factor for the development of mental disorders like Alzheimer's disease and obsessive-compulsive disorder. While insulin-related somatic and mental disorders are often comorbid, the fundamental mechanisms underlying this association are still elusive. Studies conducted in rodent models appear well suited to help decipher these mechanisms. Specifically, these models are apt to prospective studies in which causative mechanisms can be manipulated via multiple tools (e.g., genetically engineered models and environmental interventions), and experimentally dissociated to control for potential confounding factors. Here, we provide a narrative synthesis of preclinical studies investigating the association between hyperglycaemia - as a proxy of insulin-related metabolic dysfunctions - and impairments in working and spatial memory, and attention. Ultimately, this review will advance our knowledge on the role of glucose metabolism in the comorbidity between somatic and mental illnesses.

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.

Altered functional connectivity between the default mode network in diabetic retinopathy patients

OBJECTIVES

Previous studies have demonstrated that diabetic retinopathy is associated with cognitive impairment. This study aimed to investigate the intrinsic functional connectivity pattern within the default mode network (DMN) and its associations with cognitive impairment in diabetic retinopathy patients using resting-state functional MRI (rs-fMRI).

METHODS

A total of 34 diabetic retinopathy patients and 37 healthy controls were recruited for rs-fMRI scanning. Both groups were age, gender, and education level matched. The posterior cingulate cortex (PCC) was chosen as the region of interest for detecting functional connectivity changes.

RESULTS

Compared with the healthy control group, diabetic retinopathy patients showed increased functional connectivity between PCC and left medial superior frontal gyrus and increased functional connectivity between PCC and right precuneus.

CONCLUSION

Our study highlights that diabetic retinopathy patients show enhanced functional connectivity within DMN, suggesting that a compensatory increase of neural activity might occur in DMN, which offers new insight into the potential neural mechanism of cognitive impairment in diabetic retinopathy patients.

Type 2 Diabetes Comorbidity and Cognitive Decline in Patients with Alzheimer's Disease

BACKGROUND

Although insulin dysregulation and resistance likely participate in Alzheimer's disease (AD) etiologies, little is known about the correlation between type 2 diabetes mellitus (T2DM) and the progression of cognitive decline in patients with AD.

OBJECTIVE

To determine whether AD patients with T2DM experience more rapid cognitive decline than those without T2DM.

METHODS

All cognitive performance data and the presence or absence of T2DM comorbidity in patients with AD were derived from the US National Alzheimer's Coordinating Center's (NACC) Uniform Data Set (UDS). A search of the UDS identified 3,055 participants with AD who had more than one epoch completed. The data set culled clinically diagnosed AD dementia patients who were assessed for diabetes type identified during at least 1 visit. These patients were divided into 2 groups based on whether they had a diagnosis of T2DM. The data from these groups were then analyzed for differences in cognitive decline based on neuropsychological test battery scores and a Clinician Dementia Rating using a general linear model.

RESULTS

Comparisons of the mean scores for 16 selected tests from the neuropsychological test battery showed no significant differences in baseline scores and scores at subsequent visits between the T2DM and nondiabetic groups.

CONCLUSIONS

The results revealed no differences in cognitive decline metrics over the course of 5 visits in either study group. These data indicate that the presence of T2DM does not increase the rate of cognitive decline in AD. This finding contradicts expected disease burden and will need to be explored further.

Decision-Making in Alzheimer's Disease: The Role of Working Memory and Executive Functions in the Iowa Gambling Task and in Tasks Inspired by Everyday Situations

BACKGROUND

Alzheimer's disease (AD) negatively impacts patients' ability to make advantageous decisions, i.e., a core ability contributing to the preservation of autonomy.

OBJECTIVE

The present study aims to analyze the changes that occur in the decision-making competence (DMC) in AD patients and to determine if these changes are related to the deterioration of executive functions and working memory.

METHOD

To this end, 20 patients with AD and 20 elderly control adults were assessed using executive, working memory, and DMC tasks. The latter comprised the Iowa Gambling Task (IGT) and a scenarios task based on situations inspired by everyday life and performed under conditions of risk and ambiguity.

RESULTS

Results revealed lower performances in AD patients than in elderly control adults for all the tasks assessing cognitive functions. The AD patients also made more strategy changes during the IGT. In the scenarios tasks, the two groups took as many ambiguous or risky decisions, but AD patients tended to take more risks in the context of gain than elderly control adults did. Switching and updating ability, as well as working memory, appeared to be involved in decisions in tasks inspired by everyday life, while inhibition was more related to the IGT performances.

CONCLUSION

Working memory and executive functions seem to be involved in decision-making, but in different ways in gambling and daily-life situations.

Contributive Role of Hyperglycemia and Hypoglycemia Towards the Development of Alzheimer's Disease

Alzheimer's disease (AD) is one of the causes of dementia that results from several infections/biological conditions leading to either cell disruption or loss of neuronal communication. Studies have documented the accumulation of two proteins, beta-amyloid (Aβ), which accumulates on the exteriors of neurons, and tau (Tau), which assembles at the interiors of brain cells and is chiefly liable for the progression of the disease. Several molecular and cellular pathways account for the accumulation of amyloid-β and the formation of neurofibrillary tangles, which are phosphorylated variants of Tau protein. Moreover, research has revealed a potential connection between AD and diabetes. It has also been demonstrated that both hypoglycemia and hyperglycemia have a significant role in the development of AD. In addition, SUMO (small ubiquitin-like modifier protein) plays a crucial role in the pathogenesis of AD. SUMOylation is the process by which modification of amyloid precursor protein (APP) and Tau takes place. Furthermore, Drosophila melanogaster has proven to be an efficient model organism in studies to establish the relationship between AD and variations in blood glucose levels. In addition, the review successfully identifies the common pathway that links the effects of fluctuations in glucose levels on AD pathogenesis and advancements.

Prospective Metamemory Monitoring of Episodic Visual Memory in Community-Dwelling Older Adults with Subjective Cognitive Decline and Mild Cognitive Impairment

OBJECTIVE

Metamemory tasks have been utilized to investigate anosognosia in older adults with dementia, though previous research has not systematically compared memory self-awareness in prodromal dementia groups. This represents an important oversight given that remedial and interventional efforts may be most beneficial before individuals' transition to clinical dementia. We examine differences in memory self-awareness and memory self-monitoring between cognitively healthy elderly controls and prodromal dementia groups.

METHODS

Participants with subjective cognitive decline despite intact objective neuropsychological functioning (SCD; n = 82), amnestic mild cognitive impairment (aMCI; n = 18), nonamnestic mild cognitive impairment (naMCI; n = 38), and normal cognitive functioning (HC; n = 120) were recruited from the Einstein Aging Study for a cross-sectional study. Participants completed an experimental visual memory-based global metamemory prediction task and subjective assessments of memory/cognition and self-awareness.

RESULTS

While, relative to HC, memory self-awareness and memory self-monitoring were preserved for delayed memory performance in SCD and aMCI, these processes were impaired in naMCI. Furthermore, results suggest that poor metamemory accuracy captured by our experimental task can be generalized to everyday memory problems.

CONCLUSIONS

Within the framework of the Cognitive Awareness Model, our findings provide preliminary evidence that poor memory self-awareness/self-monitoring in naMCI may reflect an executive or primary anosognosia, with implications for tailored rehabilitative interventions.

Classification of type 2 diabetes mellitus with or without cognitive impairment from healthy controls using high-order functional connectivity

Type 2 diabetes mellitus (T2DM) is associated with cognitive impairment and may progress to dementia. However, the brain functional mechanism of T2DM-related dementia is still less understood. Recent resting-state functional magnetic resonance imaging functional connectivity (FC) studies have proved its potential value in the study of T2DM with cognitive impairment (T2DM-CI). However, they mainly used a mass-univariate statistical analysis that was not suitable to reveal the altered FC "pattern" in T2DM-CI, due to lower sensitivity. In this study, we proposed to use high-order FC to reveal the abnormal connectomics pattern in T2DM-CI with a multivariate, machine learning-based strategy. We also investigated whether such patterns were different between T2DM-CI and T2DM without cognitive impairment (T2DM-noCI) to better understand T2DM-induced cognitive impairment, on 23 T2DM-CI and 27 T2DM-noCI patients, as well as 50 healthy controls (HCs). We first built the large-scale high-order brain networks based on temporal synchronization of the dynamic FC time series among multiple brain region pairs and then used this information to classify the T2DM-CI (as well as T2DM-noCI) from the matched HC based on support vector machine. Our model achieved an accuracy of 79.17% in T2DM-CI versus HC differentiation, but only 59.62% in T2DM-noCI versus HC classification. We found abnormal high-order FC patterns in T2DM-CI compared to HC, which was different from that in T2DM-noCI. Our study indicates that there could be widespread connectivity alterations underlying the T2DM-induced cognitive impairment. The results help to better understand the changes in the central neural system due to T2DM.

Increased Brain Iron Detection by Voxel-Based Quantitative Susceptibility Mapping in Type 2 Diabetes Mellitus Patients With an Executive Function Decline

Purpose

Brain iron accumulation has been suggested as a pathomechanism in patients with type 2 diabetes mellitus (T2DM) with cognitive impairment. This research aims to examine the total-brain pattern of iron accumulation in relation to executive function decline in patients with T2DM by voxel-based quantitative susceptibility mapping (QSM) analysis.

Materials and Methods

A total of 32 patients with T2DM and 34 age- and sex-matched healthy controls (HCs) were enrolled in this study. All participants underwent brain magnetic resonance examination, and 48 individuals underwent cognitive function assessments. Imaging data were collected with three-dimensional fast low-angle shot sequences to achieve magnitude as well as phase images. Using voxel-based QSM analysis, we compared the voxel-wise susceptibility values of the whole brain among groups and explored whether the susceptibility values had correlations with cognitive data.

Results

Among the 66 participants, cognitive function was estimated in 23 patients with T2DM (11 males and 12 females; average age, 64.65 ± 8.44 years) and 25 HCs (13 males and 12 females; average age, 61.20 ± 7.62 years). T2DM patients exhibited significantly (t = 4.288, P < 0.001) lower Montreal Cognitive Assessment (MoCA) scores [T2DM, 27 (27, 28); HCs, 29 (28, 29); normal standard ≥ 26)] and higher Trail-making Test (TMT)-A/TMT-B scores [71 (51, 100)/185 (149, 260)] than HCs [53 (36.5, 63.5)/150 (103, 172.5)] (Z = 2.612, P = 0.009; Z = 2.797, P = 0.005). Subjects with T2DM showed significantly higher susceptibility values than HCs in the caudate/putamen/pallidum, frontal inferior triangular gyrus, and precentral gyrus on the right hemisphere. In contrast (HC > T2DM), no region showed a significant difference in susceptibility values between the groups. The correlation analysis between susceptibility values and cognitive function scores was tested by voxel-based susceptibility value with sex and age as covariates. After multiple comparison correction, in T2DM patients, the left thalamus showed a significant relationship with TMT-A (R ² = 0.53, P = 0.001). The right thalamus and left thalamus showed a significant relationship with TMT-B (R ² = 0.35, P = 0.019; and R ² = 0.38, P = 0.017, respectively). In HCs, the cluster of right precentral/middle frontal gyrus/inferior frontal gyrus/inferior triangular gyrus showed a significant relationship with TMT-B (R ² = 0.59, P = 0.010). No relationship was found between the susceptibility values with MoCA in the brain region in both two groups.

Conclusion

Patients with T2DM presented declined cognitive assessments and elevated iron deposition in the striatum and frontal lobe, suggesting that executive function decline in T2DM might be associated with the cerebral iron burden and that changes in susceptibility values may represent a latent quantitative imaging marker for early assessment of cognitive decline in patients with T2DM.

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.

Being in the Past and Perform the Future in a Virtual World: VR Applications to Assess and Enhance Episodic and Prospective Memory in Normal and Pathological Aging

The process of aging commonly features a gradual deterioration in cognitive performance and, in particular, the decline of memory. Despite the increased longevity of the world’s population, the prevalence of neurodegenerative conditions, such as dementia, continues to be a major burden on public health, and consequently, the latest research has been focused on memory and aging. Currently, the failure of episodic and Prospective memory (PM) is one of the main complaints in the elderly, considered among the early symptoms of dementia. It is therefore increasingly important to define more clearly the boundaries between normal and pathological aging. Recently, researchers have begun to build and apply Virtual Environments (VE) to the explicit purpose of better understanding the performance of episodic and PM in complex and realistic contexts, with the perspective of further developing effective training procedures that depend on reliable cognitive assessment methods. Virtual technology offers higher levels of realism than “pen and paper” testing and at the same time more experimental control than naturalistic settings. In this mini-review article, we examine the outcomes of recently available studies on virtual reality technology applications developed for the assessment and improvement of episodic and/or PM. To consider the latest technology, we selected 29 articles that have been published in the last 10 years. These documents show that VR-based technologies can provide a valid basis for screening and treatment and, through increased sensory stimulation and enriched environments reproducing the scenarios of everyday life, could represent effective stimulating experiences even in pathological aging.

Effects of multidomain versus single-domain training on executive control and memory in older adults: study protocol for a randomized controlled trial

BACKGROUND

Previous research suggests that both cognitive training and physical exercise help to maintain brain health and cognitive functions that decline with age. Some studies indicate that combined interventions may produce larger effects than each intervention alone. The aim of this study is to investigate the effects of combined cognitive and physical training compared to cognitive training and physical training alone on executive control and memory functions in healthy older adults.

OBJECTIVES

The main objectives of this four-arm randomized controlled trial (RCT) are: to investigate the synergetic effects of a simultaneous, group-based multidomain training program that combines cognitive video-game training with physical exercise, in comparison to those produced by cognitive training combined with physical control activity, physical training combined with cognitive control activity, or a combination of both control activities; to investigate whether event-related potential latencies of the P2 component are shorter and N2 and P3b components assessed in a memory-based task switching task are enhanced after training; and to find out whether possible enhancements persist after a 3-month period without training.

METHODS

In this randomized, single-blind, controlled trial, 144 participants will be randomly assigned to one of the four combinations of cognitive training and physical exercise. The cognitive component will be either video-game training (cognitive intervention, CI) or video games not specifically designed to train cognition (cognitive control, CC). The physical exercise component will either emphasize endurance, strength, and music-movement coordination (exercise intervention, EI) or stretching, toning, and relaxation (exercise control, EC).

DISCUSSION

This RCT will investigate the short and long-term effects of multidomain training, compared to cognitive training and physical training alone, on executive control and memory functions in healthy older adults, in comparison with the performance of an active control group.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03823183. Registered on 21 January 2019.

Phytochemicals of Minthostachys diffusa Epling and Their Health-Promoting Bioactivities

The genus Minthostachys belonging to the Lamiaceae family, and is an important South American mint genus used commonly in folk medicine as an aroma in cooking. The phytochemical-rich samples of the aerial parts of Minthostachys diffusa Epling. were tested for pharmacological and health-promoting bioactivities using in vitro chemical and enzymatic assays. A range of radical scavenging activities of the samples against biological radicals such as nitric oxide and superoxide anion and against synthetic 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radicals, the ferric reducing antioxidant power and the lipid peroxidation inhibition were determined and ranked using the ‘relative antioxidant capacity index’ (RACI). The ethyl acetate fraction showed the highest RACI of +1.12. Analysis of the various fractions’ inhibitory ability against enzymes involved in diabetes (α-amylase and α-glucosidase), and against enzymes associated with Parkinson’s or Alzheimer’s diseases (acetylcholinesterase and butyrylcholinesterase) also suggested that the ethyl acetate fraction was the most active. Liquid chromatography–tandem mass spectrometry analysis of the ethyl acetate fraction showed more than 30 polyphenolic compounds, including triterpenes. The inhibitory cholinesterase effects of the triterpenes identified from M. diffusa were further analysed by in silico docking of these compounds into 3D-structures of acetylcholinesterase and butyrylcholinesterase. This is the first study on pharmacological activities and phytochemical profiling of the aerial parts of M. diffusa, showing that this plant, normally used as food in South America, is also rich in health-promoting phytochemicals.

Increased Brain Iron Deposition in the Putamen in Patients with Type 2 Diabetes Mellitus Detected by Quantitative Susceptibility Mapping

BACKGROUND

The underlying brain structural changes in type 2 diabetes mellitus (T2DM) patients have attracted increasing attention. The insulin-resistant state causes iron overload in neurons and leads to lesions in the central nervous system. Quantitative susceptibility mapping (QSM) can provide a noninvasive quantitative analysis of brain iron deposition. We aimed to compare the difference of brain iron deposition in the gray matter nucleus between T2DM patients and healthy elderly individuals using QSM.

METHODS

Thirty-two T2DM patients and thirty-two age- and gender-matched healthy controls (HCs) were enrolled in this research. Twenty-three patients and twenty-six HCs underwent cognitive assessments. Brain QSM maps were computed from multiecho GRE data using morphology-enabled dipole inversion with automatic uniform cerebrospinal fluid zero reference algorithm (MEDI+0). ITK-SNAP was used to measure the susceptibility values reflecting the content of iron in the regions of interest (ROIs).

RESULTS

The study included thirty-two T2DM patients (20 males and 12 females; mean age of 61.09 ± 9.99 years) and 32 HCs (14 males and 18 females; mean age of 59.09 ± 9.77 years). These participants had no significant difference in age or gender (P > 0.05). Twenty-three patients with T2DM (11 males and 12 females; mean age, 64.65 ± 8.44 years) and twenty-six HCs (14 males and 12 females; mean age, 62.30 ± 6.13 years) received an assessment of cognitive function. T2DM patients exhibited an obviously (t = 3.237, P = 0.003) lower Montreal Cognitive Assessment (MoCA) score (26.78 ± 2.35; HCs, 28.42 ± 0.64; normal standard ≥26) and a higher Stroop color-word test (SCWT)-C score [87(65,110); HC, 63(60,76.75), Z = -2.232, P = 0.003] than HCs. The mean susceptibility values in the putamen appeared obviously higher in T2DM patients than in HCs (t = -3.994, P < 0.001). The susceptibility values and cognitive assessment scores showed no obvious association (P > 0.05). However, an obvious correlation was observed between the changes in the susceptibility values in the putamen and the thalamus/dentate nucleus (r = 0.404, P < 0.001; r = 0.423, P < 0.001).

CONCLUSION

T2DM patients showed increased susceptibility values in the putamen and had declines in executive functions, but the linear association between them was not statistically significant. Changes in susceptibility values in the putamen indicated increased iron deposition and might be used as a quantitative imaging marker of central nervous system injury in T2DM patients. QSM might be able to help probe micro neuronal damage in gray matter and provide information on diabetic encephalopathy.

Time-dependent impairments in learning and memory in Streptozotocin-induced hyperglycemic rats

The sedentary lifestyle is responsible for the high prevalence of diabetes which also impairs cognition including learning and memory. Various studies have highlighted the learning and memory impairments in rodent models but data regarding the timeline of their development and their correlation to biochemical parameters are scarce. So, the present study was designed to investigate the type of memory which is more susceptible to hyperglycemia and its correlation with biochemical parameters such as inflammatory cytokines, cAMP response element binding (CREB) and protein kinase B (Akt) activation. Hyperglycemia was induced using streptozotocin (STZ, 45 mg/kg i.p.) and confirmed by measuring fasting blood glucose levels after 1 week of STZ injection. Learning and memory deficits were evaluated using the Novel Object Recognition Test (NORT) and Morris water maze (MWM), and correlated with biochemical parameters (TNF-α, IL-1β, and dopamine) at 3, 6 and 9 weeks. STZ-injected rats after 3 weeks of injection demonstrated moderate hyperglycemia (blood glucose = 7.99 ± 0.62 mM) with intact learning and reference memory; however, their working memory was impaired in MWM. Severe hyperglycemia (blood glucose = 11.51 ± 0.69 mM) accompanied by impaired short, long, and working memory was evident after 6 weeks whereas learning was intact. After 9 weeks of STZ injection, hyperglycemia was more pronounced (13.69 ± 1.43 mM) and accompanied by a learning deficit in addition to short, long, and working memory impairments. The extent of hyperglycemia either in terms of duration or severity resulted in enhanced inflammation, down-regulation of the level of dopamine, protein expression of AKT and CREB, which possibly affected learning and memory negatively.

Changes in Theta but not Alpha Modulation Are Associated with Impairment in Working Memory in Alzheimer's Disease and Mild Cognitive Impairment

While several studies have found that neural oscillations play a key role in the functioning of working memory, the nature of aberrant oscillatory activity underlying working memory impairments in Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains largely unexplored. These individuals often display structural alterations in brain regions and pathways involved in working memory processes and therefore may also display altered oscillatory activity during memory activation. Electroencephalographic (EEG) activity was recorded during the N-back working memory task in three groups: AD (n = 29), MCI (n = 100), and healthy controls (HCs; n = 40). Theta (4-7 Hz) and alpha (7.5-12 Hz) modulation was measured in response to the stimulus presentation during correct and incorrect responses. This modulation represents the change in EEG activity associated with the stimulus onset and was measured as a ratio of post stimulus power to pre stimulus power. We also assessed the relationship between change in oscillatory power and working memory performance. Compared to HCs, the AD group demonstrated the lowest working memory accuracy and a smaller theta ratio for correct responses on the 2-back condition; the MCI group demonstrated a smaller theta ratio for correct responses on the 3-back condition. Finally, we observed that the theta ratio, but not the alpha ratio, was a significant predictor of working memory performance in the three groups for all conditions. Taken together, these behavioral and electrophysiological results suggest that in addition to impairments in working memory performance, modulation of theta, but not alpha power, may be impaired in MCI and AD.

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.

Glycation Damage: A Possible Hub for Major Pathophysiological Disorders and Aging

Glycation is both a physiological and pathological process which mainly affects proteins, nucleic acids and lipids. Exogenous and endogenous glycation produces deleterious reactions that take place principally in the extracellular matrix environment or within the cell cytosol and organelles. Advanced glycation end product (AGE) formation begins by the non-enzymatic glycation of free amino groups by sugars and aldehydes which leads to a succession of rearrangements of intermediate compounds and ultimately to irreversibly bound products known as AGEs. Epigenetic factors, oxidative stress, UV and nutrition are important causes of the accumulation of chemically and structurally different AGEs with various biological reactivities. Cross-linked proteins, deriving from the glycation process, present both an altered structure and function. Nucleotides and lipids are particularly vulnerable targets which can in turn favor DNA mutation or a decrease in cell membrane integrity and associated biological pathways respectively. In mitochondria, the consequences of glycation can alter bioenergy production. Under physiological conditions, anti-glycation defenses are sufficient, with proteasomes preventing accumulation of glycated proteins, while lipid turnover clears glycated products and nucleotide excision repair removes glycated nucleotides. If this does not occur, glycation damage accumulates, and pathologies may develop. Glycation-induced biological products are known to be mainly associated with aging, neurodegenerative disorders, diabetes and its complications, atherosclerosis, renal failure, immunological changes, retinopathy, skin photoaging, osteoporosis, and progression of some tumors.

Selective Impairment of Attentional Networks of Executive Control in Middle-Aged Subjects with Type 2 Diabetes Mellitus

Background

The influence of type 2 diabetes mellitus (T2DM) on attention has been elusive. The Attention Network Test (ANT) was developed to evaluate the functioning of 3 individual attentional networks: orienting, alerting, and executive control. The purpose of this study was to use the ANT to assess attentional function and its sub-components in T2DM patients ages 40–60 years.

Material/Methods

Thirty T2DM patients and 30 healthy controls ages 40–60 years were recruited in this investigation. The ANT was used to statistically compare the efficiency among 3 sub-components of the attention networks between middle-aged T2DM patients (n=30) and gender-, age-, and education-matched healthy controls (n=30).

Results

The ANT demonstrated a significant difference in executive control network between the T2DM patients and healthy controls (t=3.242, P=0.002), whereas no significant difference was observed regarding the domains of alerting (t=0.515, P=0.609) and orienting control (t=0.078, P=0.938) between the T2DM patient group and the healthy control group. Moreover, the mean reaction time in the ANT in the T2DM patients was significantly longer compared with that in the healthy controls (t=3.561, P=0.001).

Conclusions

The ANT reveals significant impairment in the executive control of middle-aged patients diagnosed with T2DM, whereas no significant impairment was observed in the domains of alerting and orienting.

Theta-Gamma Coupling and Working Memory in Alzheimer's Dementia and Mild Cognitive Impairment

Working memory deficits are common among individuals with Alzheimer's dementia (AD) or mild cognitive impairment (MCI). Yet, little is known about the mechanisms underlying these deficits. Theta-gamma coupling-the modulation of high-frequency gamma oscillations by low-frequency theta oscillations-is a neurophysiologic process underlying working memory. We assessed the relationship between theta-gamma coupling and working memory deficits in AD and MCI. We hypothesized that: (1) individuals with AD would display the most significant working memory impairments followed by MCI and finally healthy control (HC) participants; and (2) there would be a significant association between working memory performance and theta-gamma coupling across all participants. Ninety-eight participants completed the N-back working memory task during an electroencephalography (EEG) recording: 33 with AD (mean ± SD age: 76.5 ± 6.2), 34 with MCI (mean ± SD age: 74.8 ± 5.9) and 31 HCs (mean ± SD age: 73.5 ± 5.2). AD participants performed significantly worse than control and MCI participants on the 1- and 2-back conditions. Regarding theta-gamma coupling, AD participants demonstrated the lowest level of coupling followed by the MCI and finally control participants on the 2-back condition. Finally, a linear regression analysis demonstrated that theta-gamma coupling (β = 0.69, p < 0.001) was the most significant predictor of 2-back performance. Our results provide evidence for a relationship between altered theta-gamma coupling and working memory deficits in individuals with AD and MCI. They also provide insight into a potential mechanism underlying working memory impairments in these individuals.

Effects of Video Game Training on Measures of Selective Attention and Working Memory in Older Adults: Results from a Randomized Controlled Trial

Video game training with older adults potentially enhances aspects of cognition that decline with aging and could therefore offer a promising training approach. Although, previous published studies suggest that training can produce transfer, many of them have certain shortcomings. This randomized controlled trial (RCT; Clinicaltrials.gov ID: NCT02796508) tried to overcome some of these limitations by incorporating an active control group and the assessment of motivation and expectations. Seventy-five older volunteers were randomly assigned to the experimental group trained for 16 sessions with non-action video games from Lumosity, a commercial platform (http://www.lumosity.com/) or to an active control group trained for the same number of sessions with simulation strategy games. The final sample included 55 older adults (30 in the experimental group and 25 in the active control group). Participants were tested individually before and after training to assess working memory (WM) and selective attention and also reported their perceived improvement, motivation and engagement. The results showed improved performance across the training sessions. The main results were: (1) the experimental group did not show greater improvements in measures of selective attention and working memory than the active control group (the opposite occurred in the oddball task); (2) a marginal training effect was observed for the N-back task, but not for the Stroop task while both groups improved in the Corsi Blocks task. Based on these results, one can conclude that training with non-action games provide modest benefits for untrained tasks. The effect is not specific for that kind of training as a similar effect was observed for strategy video games. Groups did not differ in motivation, engagement or expectations.

Insulin resistance plays a potential role in postoperative cognitive dysfunction in patients following cardiac valve surgery

Severe insulin resistance (IR) promotes the development of Alzheimer disease. IR and postoperative cognitive dysfunction (POCD) are a common complication during the cardiac perioperative period. The authors hypothesized that IR of individuals with cardiac valve surgery would have increased the risk of POCD. The purpose of the study was to analyze the association of IR and POCD after cardiac valve surgery. Total 131 patients who underwent valve replacement via cardiopulmonary bypass (CPB) were included. Cognitive function was assessed by a series of neuropsychological measurements at 1day before and 7days after the surgery. 40 healthy volunteers as the control group also completed the neuropsychological assessment at the same time point. POCD was identified using the "Z score" method. Fasting blood glucose and insulin levels were detected before anesthesia and at 6h and 7days post-operation. Additionally serum levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) were measured at 6h post-operation. The insulin resistance index was calculated by "homeostasis model assessment 2" (HOMA2) software. The relationship between IR and POCD or TNF-α, IL-6 was then analyzed. At 7days after surgery, the incidence of POCD was 43.8%. The levels of HOMA2-IR in patients with POCD were significantly higher than those of patients without POCD at 6h and 7days after operation (P<0.05).The levels of serum IL-6 and TNF- α were positively correlated with HOMA2-IR value at 6h after operation (RIL-6=0.426, P<0.01; RTNF-a=0.381, P<0.01). POCD was correlated with the patients' education age (OR=1.062), CPB time (OR=1.018), self-rating depression scale (SDS) score after operation (OR=1.082), HOMA2-IR at 6h (OR=1.110) and 7days (OR=13.762) after operation, IL-6 (OR=1.036) and TNF-α (OR=1.039) at 6h after operation. Our study suggests that IR is correlated with the incidence of POCD and the increase of inflammatory factors.