Patterns of executive dysfunction in amnestic mild cognitive impairment

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.

Working Memory Precision and Associative Binding in Mild Cognitive Impairment

To better understand working memory (WM) deficits in Mild Cognitive Impairment (MCI), we examined information precision and associative binding in WM in 21 participants with MCI, compared to 16 healthy controls, using an item-location delayed reproduction task. WM, along with other executive functions (i.e. Trail Making Task (TMT) and Stroop task), were measured before and after a 2-h nap. The napping manipulation was intended as an exploratory element to this study exploring potential impacts of napping on executive functions.Compared to healthy participants, participants with MCI exhibited inferior performance not only in identifying encoded WM items but also on item-location associative binding and location precision even when only one item was involved. We also found changes on TMT and Stroop tasks in MCI, reflecting inferior attention and inhibitory control. Post-napping performance improved in most of these WM and other executive measures, both in MCI and their healthy peers.Our study shows that associative binding and WM precision can reliably differentiate MCIs from their healthy peers. Additionally, most measures showed no differential effect of group pre- and post-napping. These findings may contribute to better understanding cognitive deficits in MCI therefore improving the diagnosis of MCI.

Neuropsychiatric Symptoms and Caregiver Stress in Parkinson's Disease with Cognitive Impairment, Alzheimer's Disease, and Frontotemporal Dementia

BACKGROUND

A better understanding of factors associated with caregiver burden might facilitate the construction of coping strategies to improve their clinical outcomes and the comprehensive care model for dementia.

OBJECTIVE

To investigate the cognitive and neuropsychiatric domains that contribute to caregiver burden in three types of neurodegenerative disorders: Parkinson's disease (PD), Alzheimer's disease (AD), and frontotemporal disease (FTD).

METHODS

Eight hundred and fourteen patients and their caregivers were invited to participate; among them, 235 had PD with cognitive impairment; 429 had AD, and 150 had FTD. The evaluation protocol included the Neuropsychiatric Inventory (NPI), the Mini-Mental State Examination, the Chinese Version Verbal Learning Test, the modified Trail Making Test B, semantic fluency, and a geriatric depression score. Statistical comparisons of the cognitive tests, NPI total scores, and caregiver burden among the three diagnosed types of dementia, matched for a Clinical Dementia Rating (CDR) of 0.5 or 1, were performed, and multivariate linear regression models were used to evaluate the parameter significance.

RESULTS

Caregivers for patients with PD and FTD showed significant burden increments when the CDR scores changes from 0.5 to 1. For CDR = 0.5, the PD group had significantly lower caregiver burdens than the AD group, but the NPI total scores were significantly higher. Factors related to caregiver burden were the presence of delusion among all diagnosis groups, while the impact of NPI total scores related to caregiver burden was the highest in FTD, followed by AD and PD.

CONCLUSIONS

At the mild to moderate stages, our results suggested different degrees of significance in terms of the cognitive test scores or NPI subdomains for predicting caregiver stress among the three types of dementia.

Repetitive Transcranial Magnetic Stimulation (rTMS) of Dorsolateral Prefrontal Cortex May Influence Semantic Fluency and Functional Connectivity in Fronto-Parietal Network in Mild Cognitive Impairment (MCI)

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neuromodulation technique that is increasingly used as a nonpharmacological intervention against cognitive impairment in Alzheimer’s disease (AD) and other dementias. Although rTMS has been shown to modify cognitive performances and brain functional connectivity (FC) in many neurological and psychiatric diseases, there is still no evidence about the possible relationship between executive performances and resting-state brain FC following rTMS in patients with mild cognitive impairment (MCI). In this preliminary study, we aimed to evaluate the possible effects of rTMS of the bilateral dorsolateral prefrontal cortex (DLPFC) in 27 MCI patients randomly assigned to two groups: one group received high-frequency (10 Hz) rTMS (HF-rTMS) for four weeks (n = 11), and the other received sham stimulation (n = 16). Cognitive and psycho-behavior scores, based on the Repeatable Battery for the Assessment of Neuropsychological Status, Beck Depression Inventory-II, Beck Anxiety Inventory, Apathy Evaluation Scale, and brain FC, evaluated by independent component analysis of resting state functional MRI (RS-fMRI) networks, together with the assessment of regional atrophy measures, evaluated by whole-brain voxel-based morphometry (VBM), were measured at baseline, after five weeks, and six months after rTMS stimulation. Our results showed significantly increased semantic fluency (p = 0.026) and visuo-spatial (p = 0.014) performances and increased FC within the salience network (p ≤ 0.05, cluster-level corrected) at the short-term timepoint, and increased FC within the left fronto-parietal network (p ≤ 0.05, cluster-level corrected) at the long-term timepoint, in the treated group but not in the sham group. Conversely, regional atrophy measures did not show significant longitudinal changes between the two groups across six months. Our preliminary findings suggest that targeting DLPFC by rTMS application may lead to a significant long-term increase in FC in MCI patients in a RS network associated with executive functions, and this process might counteract the progressive cortical dysfunction affecting this domain.

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.

Early detection of cognitive disturbances in mild cognitive impairment: a systematic review of observational studies

Mild cognitive impairment (MCI) is an intermediate state between normal cognition and early dementia and is not considered as a typical outcome of brain aging. It has been estimated that 10% to 20% of individuals above 65 years of age will be diagnosed as having MCI. The increased rate of dementia and the importance of early detection of its forerunners have encouraged researchers to focus on detecting MCI and modifiable risk factors with the hope of developing better ways of managing dementia and its consequences. The main aim of this study was to systematically review the related literature concerning the cognitive changes in the spectrum of cognitive aging to cognitive impairment. Articles included in this review were identified through searching the databases of PubMed, Psych Info, Embase, ProQuest, and Scopus. Many domains like verbal memory, language, executive function, visual memory, attentional skills, and working memory showed acceptable predictive power. Testing subdomains such as executive function, speed of processing, working memory and semantic language are critical and others may indicate some suggestions for further clinical deteriorations in normal individuals. Although various cognitive instruments have been used for evaluation of impaired cognitive domains, it remains challenging to select the most appropriate ones having high-level accuracy and their related cognitive subdomains. It also revealed that none of the identified cognitive domains solely fulfilled the criteria for MCI screening; in clinical settings, multiple neuropsychological batteries may be used for one single cognitive domain, while longitudinal studies prefer the use of at least two cognitive measures for each domain to improve accuracy and research settings might focus on only a single neuropsychological test. However, along with episodic memory, testing for amnestic MCI, executive function could increase the chance of early detection of MCI. Executive control has been found to deteriorate the earliest in MCI patients.

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.

Perioperative cognitive protection

There is significant evidence that many older surgical patients experience at least a transient decrease in cognitive function. Although there is still equipoise regarding the degree, duration, and mechanism of cognitive dysfunction, there is a concurrent need to provide best-practice clinical evidence. The two major cognitive disorders seen after surgery are postoperative delirium and postoperative cognitive dysfunction. Delirium is a public health problem; millions of dollars are spent annually on delirium-related medical resource use and prolonged hospital stays. Postoperative cognitive dysfunction is a research construct that historically signifies decline in performance on a neuropsychiatric test or group of tests and begins days to weeks after surgery. This review focuses on the current state of information gathered by several interdisciplinary stakeholder groups. Although there is still a need for high-level evidence to guide clinical practice, there is an emerging literature that can guide practitioners.

Associations of Bcl-2 rs956572 genotype groups in the structural covariance network in early-stage Alzheimer's disease

Background

Alzheimer’s disease (AD) is a complex neurodegenerative disease, and genetic differences may mediate neuronal degeneration. In humans, a single-nucleotide polymorphism in the B-cell chronic lymphocytic leukemia/lymphoma-2 (Bcl-2) gene, rs956572, has been found to significantly modulate Bcl-2 protein expression in the brain. The Bcl-2 AA genotype has been associated with reduced Bcl-2 levels and lower gray matter volume in healthy populations. We hypothesized that different Bcl-2 genotype groups may modulate large-scale brain networks that determine neurobehavioral test scores.

Methods

Gray matter structural covariance networks (SCNs) were constructed in 104 patients with AD using T1-weighted magnetic resonance imaging with seed-based correlation analysis. The patients were stratified into two genotype groups on the basis of Bcl-2 expression (G carriers, n = 76; A homozygotes, n = 28). Four SCNs characteristic of AD were constructed from seeds in the default mode network, salience network, and executive control network, and cognitive test scores served as the major outcome factor.

Results

For the G carriers, influences of the SCNs were observed mostly in the default mode network, of which the peak clusters anchored by the posterior cingulate cortex seed determined the cognitive test scores. In contrast, genetic influences in the A homozygotes were found mainly in the executive control network, and both the dorsolateral prefrontal cortex seed and the interconnected peak clusters were correlated with the clinical scores. Despite a small number of cases, the A homozygotes showed greater covariance strength than the G carriers among all four SCNs.

Conclusions

Our results suggest that the Bcl-2 rs956572 polymorphism is associated with different strengths of structural covariance in AD that determine clinical outcomes. The greater covariance strength in the four SCNs shown in the A homozygotes suggests that different Bcl-2 polymorphisms play different modulatory roles.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0344-4) contains supplementary material, which is available to authorized users.

Disproportionate Decline of Executive Functions in Early Mild Cognitive Impairment, Late Mild Cognitive Impairment, and Mild Alzheimer's Disease

Background and Purpose

Many literatures indicate that executive dysfunction exists in mild cognitive impairment (MCI) as well as Alzheimer’s disease (AD). However, there are few studies that found how early the deficits of the executive function (EF) exist in MCI. The present study investigated the presence of executive dysfunctions in the earliest stage of MCI, and the sub-domains of EF which are disproportionately impaired earlier than others.

Methods

The participants were 41 normal elderly (NE), 86 with amnestic multi-domain MCI, and 41 with mild AD. The MCI group was further sub-divided into two groups: Early MCI (EMCI, n=45) and late MCI (n=41), based on the Clinical Dementia Rating-Sum of Boxes. All participants were given neuropsychological tests to assess the sub-domains of EF, such as verbal fluency, psychomotor speed, inhibitory control, and mental set-shifting.

Results

Impairment of semantic fluency was observed in EMCI, with gradual worsening as cases approached mild AD. Phonemic fluency and psychomotor speed were also impaired at the early stage of MCI relative to the NE, but maintained at the same level up to mild AD. EMCI exhibited the same degree of performance with NE for inhibitory control and mental set-shifting; however, they progressively worsened from EMCI to mild AD.

Conclusions

These results suggest that impairments of EF exist even in the earliest stage of the MCI, with a disproportionate decline in the sub-domains of EF.

Rule induction performance in amnestic mild cognitive impairment and Alzheimer's dementia: examining the role of simple and biconditional rule learning processes

INTRODUCTION

Rule induction tests such as the Wisconsin Card Sorting Test require executive control processes, but also the learning and memorization of simple stimulus-response rules. In this study, we examined the contribution of diminished learning and memorization of simple rules to complex rule induction test performance in patients with amnestic mild cognitive impairment (aMCI) or Alzheimer's dementia (AD).

METHOD

Twenty-six aMCI patients, 39 AD patients, and 32 control participants were included. A task was used in which the memory load and the complexity of the rules were independently manipulated. This task consisted of three conditions: a simple two-rule learning condition (Condition 1), a simple four-rule learning condition (inducing an increase in memory load, Condition 2), and a complex biconditional four-rule learning condition-inducing an increase in complexity and, hence, executive control load (Condition 3).

RESULTS

Performance of AD patients declined disproportionately when the number of simple rules that had to be memorized increased (from Condition 1 to 2). An additional increment in complexity (from Condition 2 to 3) did not, however, disproportionately affect performance of the patients. Performance of the aMCI patients did not differ from that of the control participants. In the patient group, correlation analysis showed that memory performance correlated with Condition 1 performance, whereas executive task performance correlated with Condition 2 performance.

CONCLUSIONS

These results indicate that the reduced learning and memorization of underlying task rules explains a significant part of the diminished complex rule induction performance commonly reported in AD, although results from the correlation analysis suggest involvement of executive control functions as well. Taken together, these findings suggest that care is needed when interpreting rule induction task performance in terms of executive function deficits in these patients.

Interictal serum brain-derived neurotrophic factor level reflects white matter integrity, epilepsy severity, and cognitive dysfunction in chronic temporal lobe epilepsy

OBJECTIVE

Most patients with temporal lobe epilepsy (TLE) have epileptic foci originating from the medial temporal lobe, particularly the hippocampus. Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin growth factor mainly expressed in the hippocampus, though it is not known whether the circulating level of BDNF reflects cognitive performance or white matter structural changes in chronic TLE.

METHODS

Thirty-four patients with TLE and 22 healthy controls were enrolled for standardized cognitive tests, diffusion tensor imaging, and serum BDNF measurement. The patients were further divided into a subgroup with unilateral TLE (n=23) and a subgroup with bilateral TLE (n=11) for clinical and neuroimaging comparisons.

RESULTS

There were significantly lower BDNF levels in the patients with TLE compared with the controls, with significance contributed mainly from the subgroup with bilateral TLE, which also had more frequent seizures. The BDNF levels correlated with epilepsy duration (σ=-0.355; p=0.040) and fractional anisotropy (FA) in the left temporal lobe, left thalamus, and right hippocampus. Using a regression model, BDNF level predicted verbal memory score. Further, design fluency scores were predicted by serum BDNF level via the interactions with left temporal FA.

CONCLUSIONS

Serum BDNF levels reflected longer epilepsy duration, impaired white matter integrity, and poor cognitive function in patients with chronic TLE.

Predicting the neural effect of switching from donepezil to galantamine based on single-photon emission computed tomography findings in patients with Alzheimer's disease

BACKGROUND

A number of neuroimaging studies have addressed the specific effect of treatment with cholinesterase inhibitors on the frontal lobe in patients with Alzheimer's disease (AD). However, the neural effects of cholinesterase inhibitors on both apathy and executive dysfunction remain unclear. We examined whether baseline regional cerebral blood flow, as determined by using single-photon emission computed tomography, is capable of predicting changes in apathy and executive dysfunction in response to AD patients switching from donepezil to galantamine therapy.

METHODS

We conducted a 24-week, prospective, open-label study of AD patients treated with galantamine who did not respond to previous treatment with donepezil. Single-photon emission computed tomography was performed at baseline, and behaviour and cognitive assessments including the Mini-Mental State Examination, the Japanese version of the Alzheimer's Disease Assessment Scale-cognitive subscale, the Frontal Assessment Battery, the Neuropsychiatry Inventory Brief Questionnaire Form, and the Dysexecutive Questionnaire were conducted at three time points (baseline and after 12 and 24 weeks of galantamine therapy).

RESULTS

After galantamine therapy, the Neuropsychiatry Inventory Brief Questionnaire Form scores (apathy, irritability, and aberrant motor symptoms) and the Dysexecutive Questionnaire score improved significantly. The single-photon emission computed tomography findings showed that lower baseline regional cerebral blood flow values in several frontal areas, including the dorsolateral and ventrolateral prefrontal cortex, the anterior cingulate, and the orbitofrontal cortex, predicted greater reductions in the score for apathy (distress) on the Neuropsychiatry Inventory Brief Questionnaire Form and the Dysexecutive Questionnaire score after patients switched from donepezil to galantamine therapy.

CONCLUSIONS

Our study suggests that galantamine therapy, unlike donepezil, is characterized by a dual mechanism of action that may increase acetylcholine and the nicotinic receptor-modulation effect within the frontal lobe, both of which are associated with apathy and executive dysfunction in AD patients.

Can Intraoperative Processed EEG Predict Postoperative Cognitive Dysfunction in the Elderly?

PURPOSE

Postoperative cognitive dysfunction (POCD) is a serious and costly complication of the elderly; even mild impairment has the potential to impact overall well being. Anesthesiologists continue to search for ways to manipulate intraoperative technique to optimize postoperative cognition in the elderly. Depth of anesthesia during surgery is an area that has shown some promise for short-term outcomes, such as delirium. However, excessive depth has both positive and negative associations with longer-term POCD. We hypothesize that this uncertainty is due to the inability of median depth to capture the amount of burst suppression or electrical silence. In this study, our purpose was to identify the intraoperative processed EEG parameters that are most closely correlated with POCD.

METHODS

To explore the association of several processed EEG parameters with POCD, we performed a retrospective analysis of a cohort of 105 patients aged >68 years scheduled for major surgery under general anesthesia. Intraoperative medications, hemodynamics, processed EEG and cerebral oxygen saturation were recorded. All patients had a cognitive battery before surgery and repeated at 3 months afterward.

FINDINGS

One hundred and five patients enrolled and 77 (73.3%) patients completed the 3-month cognitive testing. The incidence of POCD was 27%; the median Bispectral Index value for patients who developed POCD was similar to patients who did not (46 vs 42 minutes). However, patients who developed POCD spent less time with Bispectral Index <45 minutes (82.8 vs 122.5 minutes, P = 0.01) and burst suppression (35 vs 96 minutes, P = 0.04). Hypotension, cerebral desaturation, and use of total intravenous anesthesia were similar between patients with and without POCD.

IMPLICATIONS

Patients who developed POCD spent less time in EEG burst suppression and less time in deep states. Burst suppression may be protective for POCD. Further work is needed to definitively identify the role of burst suppression in the context of other patient and intraoperative variables to prevent POCD.

Cognitive severity-specific neuronal degenerative network in charcoal burning suicide-related carbon monoxide intoxication: a multimodality neuroimaging study in Taiwan

While carbon monoxide (CO) intoxication often triggers multiple intraneuronal immune- or inflammatory-related cascades, it is not known whether the pathological processes within the affected regions evolve equally in the long term. To understand the neurodegenerative networks, we examined 49 patients with a clinical diagnosis of CO intoxication related to charcoal burning suicide at the chronic stage and compared them with 15 age- and sex-matched controls. Reconstructions of degenerative networks were performed using T1 magnetic resonance imaging, diffusion-tensor imaging, and fluorodeoxyglucose positron emission tomography (PET). Tract-specific fractional anisotropy (FA) quantification of 11 association fibers was performed while the clinical significance of the reconstructed structural or functional networks was determined by correlating them with the cognitive parameters. Compared with the controls, the patients had frontotemporal gray matter (GM) atrophy, diffuse white matter (WM) FA decrement, and axial diffusivity (AD) increment. The patients were further stratified into 3 groups based on the cognitive severities. The spatial extents within the frontal-insular-caudate GM as well as the prefrontal WM AD increment regions determined the cognitive severities among 3 groups. Meanwhile, the prefrontal WM FA values and PET signals also correlated significantly with the patient's Mini-Mental State Examination score. Frontal hypometabolic patterns in PET analysis, even after adjusted for GM volume, were highly coherent to the GM atrophic regions, suggesting structural basis of functional alterations. Among the calculated major association bundles, only the anterior thalamic radiation FA values correlated significantly with all chosen cognitive scores. Our findings suggest that fronto-insular-caudate areas represent target degenerative network in CO intoxication. The topography that occurred at a cognitive severity-specific level at the chronic phase suggested the clinical roles of frontal areas. Although changes in FA are also diffusely distributed, different regional changes in AD suggested unequal long-term compensatory capacities among WM bundles. As such, the affected WM regions showing irreversible changes may exert adverse impacts to the interconnected GM structures.