Executive functions in clinical and preclinical Alzheimer's disease

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

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

Rationale and Design of the PARTNER Trial: Partnered Rhythmic Rehabilitation for Enhanced Motor-Cognition in Prodromal Alzheimer's Disease

BACKGROUND

Functional decline in Alzheimer's disease (AD) is impacted by impaired ability to integrate and modulate complex cognitive and motor abilities, commonly known as motor-cognitive integration. Impaired motor-cognitive integration occurs in the early stages of AD, prodromal AD (pAD), and may precede other symptoms. Combined motor and cognitive training have been recommended for people with pAD and need to be better researched. Our data suggest that partnered rhythmic rehabilitation (PRR) improves motor-cognitive integration in older adults with cognitive impairment. PRR is an ideal intervention to simultaneously target cardiovascular, social, and motor-cognitive domains important to AD.

OBJECTIVE/METHODS

We propose to conduct a 1-year Phase II, single-blind randomized controlled trial using PRR in 66 patients with pAD. Participants will be assigned to three months of biweekly sessions, followed by nine months of weekly sessions of PRR or group walking (WALK) with 1 : 1 allocation. Group walking in the control group will allow us to compare physical exercise alone versus the added benefit of the cognitively engaging elements of PRR.

RESULTS/CONCLUSION

Using an intent-to-treat approach, this innovative pilot study will 1) Determine acceptability, safety, tolerability, and satisfaction with PRR; 2) Compare efficacy of PRR versus WALK for improving motor-cognitive integration and identify the most sensitive endpoint for a Phase III trial from a set of motor-cognitive, volumetric MRI, and cognitive measures. The study will additionally explore potential neural, vascular, and inflammatory mechanisms by which PRR affects pAD to derive effect size of these intermediary measures and aid us in estimating sample size for a future trial.

The impact of mild cognitive impairment on decision-making under explicit risk conditions: Evidence from the Personality and Total Health (PATH) Through Life longitudinal study

OBJECTIVE

Previous research has indicated that cognition and executive function are associated with decision-making, however the impact of mild cognitive impairment (MCI) on decision-making under explicit risk conditions is unclear. This cross-sectional study examined the impact of MCI, and MCI subtypes, on decision-making on the Game of Dice Task (GDT), among a cohort of older adults.

METHOD

Data from 245 older adult participants (aged 72-78 years) from the fourth assessment of the Personality and Total Health Through Life study were analyzed. A diagnostic algorithm identified 103 participants with MCI, with subtypes of single-domain amnestic MCI (aMCI-single; n = 38), multi-domain amnestic MCI (aMCI-multi; n = 31), and non-amnestic MCI (n = 33), who were compared with an age-, sex-, education-, and income-matched sample of 142 cognitively unimpaired older adults. Decision-making scores on the GDT (net score, single number choices, and strategy changes) were compared between groups using nonparametric tests.

RESULTS

Participants with MCI showed impaired performance on the GDT, with higher frequencies of single number choices and strategy changes. Analyses comparing MCI subtypes indicated that the aMCI-multi subtype showed increased frequency of single number choices compared to cognitively unimpaired participants. Across the sample of participants, decision-making scores were associated with measures of executive function (cognitive flexibility and set shifting).

CONCLUSION

MCI is associated with impaired decision-making performance under explicit risk conditions. Participants with impairments in multiple domains of cognition showed the clearest impairments. The GDT may have utility in discriminating between MCI subtypes.

Medial septum activation improves strategy switching once strategies are well-learned via bidirectional regulation of dopamine neuron population activity

Strategy switching is a form of cognitive flexibility that requires inhibiting a previously successful strategy and switching to a new strategy of a different categorical modality. It is dependent on dopamine (DA) receptor activation and release in ventral striatum and prefrontal cortex, two primary targets of ventral tegmental area (VTA) DA projections. Although the circuitry that underlies strategy switching early in learning has been studied, few studies have examined it after extended discrimination training. This may be important as DA activity and release patterns change across learning, with several studies demonstrating a critical role for substantia nigra pars compacta (SNc) DA activity and release once behaviors are well-learned. We have demonstrated that medial septum (MS) activation simultaneously increased VTA and decreased SNc DA population activity, as well as improved reversal learning via these actions on DA activity. We hypothesized that MS activation would improve strategy switching both early in learning and after extended training through its ability to increase VTA DA population activity and decrease SNc DA population activity, respectively. We chemogenetically activated the MS of male and female rats and measured their performance on an operant-based strategy switching task following 1, 10, or 15 days of discrimination training. Contrary to our hypothesis, MS activation did not affect strategy switching after 1 day of discrimination training. MS activation improved strategy switching after 10 days of training, but only in females. MS activation improved strategy switching in both sexes after 15 days of training. Infusion of bicuculline into the ventral subiculum (vSub) inhibited the MS-mediated decrease in SNc DA population activity and attenuated the improvement in strategy switching. Intra-vSub infusion of scopolamine inhibited the MS-mediated increase in VTA DA population activity but did not affect the improvement in strategy switching. Intra-vSub infusion of both bicuculline and scopolamine inhibited the MS-mediated effects on DA population activity in both the SNc and VTA and completely prevented the improvement in strategy switching. These data indicate that MS activation improves strategy switching once the original strategy has been sufficiently well-learned, and that this may occur via the MS's regulation of DA neuron responsivity.

Higher levels of neuroticism in older adults predict lower executive functioning across time: the mediating role of perceived stress

Neuroticism has been associated with individual differences across multiple cognitive functions. Yet, the literature on its specific association with executive functions (EF) in older adults is scarce, especially using longitudinal designs. To disentangle the specific influence of neuroticism on EF and on coarse cognitive functioning in old adulthood, respectively, we examined the relationship between neuroticism, the Trail Making Test (TMT) and the Mini-Mental State Examination (MMSE) in a 6-year longitudinal study using Bayesian analyses. Data of 768 older adults (M age = 73.51 years at Wave 1) were included in a cross-lagged analysis. Results showed no cross-sectional link between neuroticism and TMT performance at Wave 1 and no longitudinal link between neuroticism at Wave 1 and MMSE at Wave 2. However, neuroticism at Wave 1 predicted TMT performance at Wave 2, indicating that the more neurotic participants were, the lower they performed on the TMT six years later. Additional analyses showed that this relation was fully mediated by participants' perceived stress. Our results suggest that the more neurotic older adults are the more stress they may perceive six years later, which in turn negatively relates to their EF. In sum, this study demonstrates that neuroticism may lead to lower EF in older age across six years. It further suggests older adults' perceived stress as mediator, thereby providing novel insights into the mechanisms underlying this relation. Possible intervention approaches to counter these effects are discussed.

Changes in Pronoun Use a Decade before Clinical Diagnosis of Alzheimer’s Dementia. Linguistic Contexts Suggest Problems in Perspective-Taking

The use of pronouns has been shown to change pathologically in the early phases of Alzheimer’s Dementia (AD). So far, the findings have been of a quantitative nature. Little is known, however, about the developmental path of the change, its onset, the domains in which it initially occurs, and if and how it spreads to other linguistic domains. The present study investigates pronoun use in six speakers of German a decade before they were clinically diagnosed with AD (LAD) and six biographically matched healthy controls (CTR). The data originate from monologic spoken language elicited by semi-spontaneous biographical interviews. Investigation of nine pronoun types revealed group differences in the use of three pronoun types: D-pronouns—a specific pronoun type of German for reference to persons and objects; the impersonal pronoun man ‘one’, and the propositional pronoun das ‘this/that’. Investigation of the linguistic contexts in which these three pronoun types were used revealed a correlation with declines in elaborative and evaluative information; that is, information the hearer would benefit from in creating an informed model of the discourse. We, therefore, hypothesize that the early changes in language use due to AD point to problems in perspective-taking, specifically in taking the hearer’s perspective.

Flexibility as a marker of early cognitive decline in humanized apolipoprotein E ε4 (ApoE4) mice

To test the hypothesis that ApoE4 may be involved in cognitive deficits associated with aging, we investigated the impact of APOE4 status and aging on the flexibility and memory components of spatial learning in mice. Young adult (6 months) and middle-aged (14 months) ApoE4, ApoE3 and C57BL/6 male mice were tested for flexibility in an aquatic Y-maze, and for spatio-temporal memory acquisition in the Starmaze. Our results revealed a flexibility deficit of the 6-month-old ApoE4 mice compared to controls. However, this deficit was not associated with spatio-temporal memory deficit at the same age. Importantly, the ApoE4 flexibility deficit did not increase with age, nor turn into memory deficit, or was able to predict individual variations of memory performance at 14 months. By contrast, control ApoE3 mice showed a decline of flexibility at 14 months resulting in performance similar to that of ApoE4. Overall, our results suggest that ApoE4 could be associated with an acceleration of the flexibility decrease otherwise observed in normal aging.

Evaluating the association between brain atrophy, hypometabolism, and cognitive decline in Alzheimer's disease: a PET/MRI study

Glucose metabolism reduction and brain volume losses are widely reported in Alzheimer’s disease (AD). Considering that neuroimaging changes in the hippocampus and default mode network (DMN) are promising important candidate biomarkers and have been included in the research criteria for the diagnosis of AD, it is hypothesized that atrophy and metabolic changes of the abovementioned regions could be evaluated concurrently to fully explore the neural mechanisms underlying cognitive impairment in AD. Twenty-three AD patients and Twenty-four age-, sex- and education level-matched normal controls underwent a clinical interview, a detailed neuropsychological assessment and a simultaneous 18F-fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET)/high-resolution T1-weighted magnetic resonance imaging (MRI) scan on a hybrid GE SIGNA PET/MR scanner. Brain volume and glucose metabolism were examined in patients and controls to reveal group differences. Multiple linear regression models were employed to explore the relationship between multiple imaging features and cognitive performance in AD. The AD group had significantly reduced volume in the hippocampus and DMN regions (P < 0.001) relative to that of normal controls determined by using ROI analysis. Compared to normal controls, significantly decreased metabolism in the DMN (P < 0.001) was also found in AD patients, which still survived after controlling for gray matter atrophy (P < 0.001). These findings from ROI analysis were further confirmed by whole-brain confirmatory analysis (P < 0.001, FWE-corrected). Finally, multiple linear regression results showed that impairment of multiple cognitive tasks was significantly correlated with the combination of DMN hypometabolism and atrophy in the hippocampus and DMN regions. This study demonstrated that combining functional and structural features can better explain the cognitive decline of AD patients than unimodal FDG or brain volume changes alone. These findings may have important implications for understanding the neural mechanisms of cognitive decline in AD.

Qualitative Evaluation Informs Understanding of Motor Cognition and Therapies in Older Adults with Mild Cognitive Impairment

BACKGROUND

10%to 20%of Americans aged 65 and older have mild cognitive impairment (MCI) with 10%progressing to Alzheimer's disease (AD) each year. Underserved groups, including African Americans (AAs), are among the most vulnerable to MCI and AD. Although evidence continues to amass, the benefits of exercise and movement for AD is still understudied in AD.

OBJECTIVE

Understanding the attitudes, perceptions, and beliefs about motor-cognitive integration and examining the physical activity of a sample of predominantly Black women community members with self-reported memory problems will allow improved recruitment and refinement of multimodal interventions designed to improve motor-cognitive and cognitive function.

METHODS

We conducted focus groups with older adults who reported subjective memory complaints (n = 15; Black: n = 12, White: n = 3, mean age 71.7±5.8).

RESULTS

Findings from thematic analysis showed most participants knew of benefits of exercise. However, most participants reported not getting adequate exercise due to factors such as pain, increased responsibilities, and fear of injury. Despite barriers, participants expressed enthusiasm for multimodal interventions designed to target body and brain health and provided several suggestions to improve or enhance the proposed interventions.

CONCLUSION

Results provide useful insights regarding improving participation among historically under-represented groups in clinical movement-based research. Participants' discussion focused primarily on the way motor-cognitive integration prevents falls, maintains memory, and provides a social benefit. The reported perceived benefits and limitations of exercise, as this population understands it, can help researchers and physicians better engage the community for lifestyle changes that will support greater motor-cognitive health.

Frontal Behavior Syndromes in Idiopathic Normal Pressure Hydrocephalus as a Function of Alzheimer's Disease Biomarker Status

OBJECTIVES

Cognitive impairment and apathy are well-documented features of idiopathic normal pressure hydrocephalus (iNPH). However, research examining other neuropsychiatric manifestations of iNPH is scant, and it is unknown whether the neuropsychiatric presentation differs for iNPH patients with comorbid Alzheimer's disease (AD) versus iNPH without AD. This study aims to advance our understanding of neuropsychiatric syndromes associated with iNPH.

METHODS

Fifty patients from Butler Hospital's Normal Pressure Hydrocephalus Clinic met inclusion criteria. Caregiver ratings on the Frontal Systems Behavior Scale (FrSBe) were examined to appraise changes in apathy, executive dysfunction, and disinhibition. Patients also completed cognitive tests of global cognition, psychomotor speed, and executive functioning. AD biomarker status was determined by either amyloid-beta (Aβ) positron emission tomography (PET) imaging or cerebrospinal fluid (CSF) total tau to Aβ-42 ratio.

RESULTS

Results revealed clinically significant elevations on the FrSBe's apathy and executive dysfunction scales and modest correlations among these scales and cognitive measures. Of the 44 patients with available neuroimaging or CSF draw data, 14 presented with comorbid AD. Relative to the iNPH-only group, the iNPH + AD group showed a larger increase from pre-illness to current informant ratings on the executive dysfunction scale, but not the apathy or disinhibition scales.

CONCLUSIONS

These results replicate and extend prior research by identifying apathy and executive dysfunction as prominent neuropsychiatric symptoms of iNPH and suggest comorbid AD exacerbates dysexecutive behaviors. Future research is warranted to examine the effects of comorbid AD pathology in response to shunt surgery for iNPH, neuropsychiatric symptom changes, and resultant caregiver burden.

Memory of decisions: Relationship between decline of autobiographical memory and temporal discounting in Alzheimer's disease

Temporal discounting refers to the tendency to attribute higher value to a reward received early than to one received later. We evaluated this tendency in patients with Alzheimer's Disease. We also evaluated whether temporal discounting is associated with decline in autobiographical memory (i.e., the ability to remember past personal experiences), with executive dysfunction, and/or with general cognitive decline. We invited patients with AD and control participants to answer binary questions involving the choice between receiving a smaller amount of money earlier or a larger one later (e.g., "Which do you prefer, 10 euros in cash right now or 50 euros in a month?"). Results demonstrated higher temporal discounting in patients with AD than in control participants. Temporal discounting was significantly correlated with decline in AM and general cognitive decline but not with executive dysfunction in patients with AD. The tendency to decide based on immediate rewards (i.e., temporal discounting) in AD is related with difficulty in remembering information about experiences of previous decisions, and/or their consequences (i.e., decline in autobiographical memory).

Reduced Capacity of Cognitive Control in Older Adults with Mild Cognitive Impairment

Cognitive control for the coordination of mental operations is essential in normal cognitive functioning of daily life. Although the decline of cognitive control in older adults with mild cognitive impairment (MCI) has been demonstrated, whether this decline is a core deficit in MCI remains unclear. In this study, we employed a perceptual decision-making task to estimate the capacity of cognitive control (CCC) in older adults with MCI (n = 55) and the age-, sex-, and education-matched healthy controls (HC, n = 55) selected based on a commonly used battery of ten neuropsychological tests in five cognitive domains. We found that the CCC was significantly correlated to the neuropsychological measures of the battery. The mean CCC was significantly lower in the MCI group (3.06 bps) than in the HC group (3.59 bps) and significantly lower in the amnestic MCI subgroup (2.90 bps) than in the nonamnestic MCI subgroup (3.22 bps). In detecting and classifying MCI using machine learning, the classifier with the CCC as the input feature outperformed the overall classification with neuropsychological measures in a single cognitive domain. The classification performance was significantly increased when the CCC was included as a feature in addition to measures in a single domain, and the CCC served as a key feature in optimal classifiers with inputs from multiple domains. These results support the hypothesis that the decline in cognitive control is a core deficit in MCI and suggest that the CCC may serve as a key index in the diagnosis of MCI.

Connectome-wide network analysis of white matter connectivity in Alzheimer's disease

A multivariate analytical strategy may pinpoint the structural connectivity patterns associated with Alzheimer's disease (AD) pathology in connectome-wide association studies. Diffusion magnetic resonance imaging data from 161 participants including subjects with healthy controls, AD, stable and converting mild cognitive impairment, were selected for group-wise comparisons. A multivariate distance matrix regression (MDMR) analysis was performed to detect abnormality in brain structural network along with disease progression. Based on the seed regions returned by the MDMR analysis, supervised learning was applied to evaluate the disease predictive performance. Nine brain regions, including the left orbital part of superior and middle frontal gyrus, the bilateral supplementary motor area, the bilateral insula, the left hippocampus, the left putamen, and the left thalamus demonstrated extremely significant structural pattern changes along with the progression of AD. The disease classification was more efficient when based on the key connectivity related to these seed regions than when based on whole-brain structural connectivity. MDMR analysis reveals brain network reorganization caused by AD pathology. The key structural connectivity detected in this study exhibits promising distinguishing capability to predict prodromal AD patients.

A Network of Genetic Effects on Non-Demented Cognitive Aging: Alzheimer's Genetic Risk (CLU + CR1 + PICALM) Intensifies Cognitive Aging Genetic Risk (COMT + BDNF) Selectively for APOEɛ4 Carriers

BACKGROUND

Trajectories of complex neurocognitive phenotypes in preclinical aging may be produced differentially through selective and interactive combinations of genetic risk.

OBJECTIVE

We organize three possible combinations into a "network" of genetic risk indices derived from polymorphisms associated with normal and impaired cognitive aging, as well as Alzheimer's disease (AD). Specifically, we assemble and examine three genetic clusters relevant to non-demented cognitive trajectories: 1) Apolipoprotein E (APOE), 2) a Cognitive Aging Genetic Risk Score (CA-GRS; Catechol-O-methyltransferase + Brain-derived neurotrophic factor), and 3) an AD-Genetic Risk Score (AD-GRS; Clusterin + Complement receptor 1 + Phosphatidylinositol-binding clathrin assembly protein).

METHOD

We use an accelerated longitudinal design (n = 634; age range = 55-95 years) to test whether AD-GRS (low versus high) moderates the effect of increasing CA-GRS risk on executive function (EF) performance and change as stratified by APOE status (ɛ4+ versus ɛ4-).

RESULTS

APOEɛ4 carriers with high AD-GRS had poorer EF performance at the centering age (75 years) and steeper 9-year decline with increasing CA-GRS but this association was not present in APOEɛ4 carriers with low AD-GRS.

CONCLUSIONS

APOEɛ4 carriers with high AD-GRS are at elevated risk of cognitive decline when they also possess higher CA-GRS risk. Genetic risk from both common cognitive aging and AD-related indices may interact in intensification networks to differentially predict (1) level and trajectories of EF decline and (2) potential selective vulnerability for transitions into impairment and dementia.

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.

Subjective rating of executive functions in mild Alzheimer's disease

OBJECTIVES

Subjective cognitive decline is considered to be a core feature of pre-Alzheimer's disease (AD) conditions, the vast majority of literature having focused on memory concerns. Neuropsychological studies have implicated executive dysfunction on objective performance measures in AD, but no research has evaluated whether individuals with AD have concerns about their executive functions and whether it differs from their caregiver's concerns. In the present study, we sought to evaluate self- and informant ratings of executive functioning in patients with mild AD.

METHOD

Participants were 23 patients with mild AD and 32 healthy elderly controls (HC) and their informants who completed the Behavior Rating Inventory of Executive Function - Adult version.

RESULTS

Patients with AD and their informants reported greater executive dysfunction than the HC group and their informants, respectively, and patients reported greater difficulty than their informants. The largest effect size for both self- and informant ratings was obtained for the Working Memory scale.

CONCLUSIONS

These findings indicate that subjective cognitive concerns in mild AD extend beyond the memory domain to executive functions. That greater difficulty was endorsed by patients than their informants suggests that at least in the mild stage of AD some awareness of executive dysfunction may be maintained in some patients. Implications for clinical care are discussed.

Dysexecutive syndrome in amnesic mild cognitive impairment: a multicenter study

BACKGROUND

Executive functions (EF) in Alzheimer's disease (AD), classically related to the prefrontal cortex, have been forgotten in mild stages, given more importance to temporal lobe associated disorders, such as memory. The study of disexecutive syndrome (DS) has been relegated to advanced stages of the disease. Our goal is to demonstrate that EF are already present in amnesic mild cognitive impairment (aMCI). Furthermore, we are interested in knowing whether poor scores in EF tests are related to the progression to AD or another kind of dementia.

METHODS

We studied patients with aMCI (n = 81) and healthy controls (n = 142) from neurological departments of several centers of Basque Country with a cross-sectional design. Patients underwent a complete neuropsychological evaluation, neuroimaging testing APOE genotype and 3 year of prospective follow-up.

RESULTS

In the first visit, patients with aMCI showed more alterations in tests that evaluate EF such as Stroop, trail-making and categorical verbal fluency. More alterations were also found in NPI scale (P <0.05). Stroop and Trail-Making test were not associated with the future development of AD, but fluency (p = 0.01) and apathy (p = 0.031) did. No patient developed a different kind of dementia different from AD.

CONCLUSIONS

DS is a broad concept not confined to frontal lobes, and can be found in early stages of aMCI. DS impacts negatively on patient autonomy and may have prognostic value.

Theory of Mind and social reserve: Alternative hypothesis of progressive Theory of Mind decay during different stages of Alzheimer's disease

Although Theory of Mind (ToM) is thought to be impaired in Alzheimer's disease (AD), it remains unclear whether this impairment is linked to the level of task complexity, the heterogeneity of the studied patients, or the implication of executive dysfunctions. To elucidate this point, 42 AD patients, divided into two subgroups [moderate AD (mAD) patients (n = 19) and early AD (eAD) patients (n = 23)], and 23 matched healthy older subjects (HO) were enrolled. All participants were given (1) a false-belief task (cognitive ToM), (2) a revised version of the "Reading the Mind in the Eyes" test (affective ToM), and (3) a composite task designed to assess ToM abilities with minimal cognitive demands. Participants were also given executive tasks assessing inhibition, shifting, and updating processes. We observed a significant impairment of cognitive and composite ToM abilities in eAD patients compared with mAD patients. There was no impairment of affective ToM. Stepwise regression revealed that measures of global efficiency and executive functions (EFs) were the best predictors of progressive decay of ToM scores. These results indicate that cognitive aspects of ToM are more sensitive to AD progression than affective tasks. They also show that ToM abilities are more affected by dementia severity than by task complexity. One explanation of our results is the presence of compensatory mechanisms (social reserve) in AD.

Proof-of-Concept Randomized Controlled Study of Cognition Effects of the Proprietary Extract Sceletium tortuosum (Zembrin) Targeting Phosphodiesterase-4 in Cognitively Healthy Subjects: Implications for Alzheimer's Dementia

Introduction. Converging evidence suggests that PDE-4 (phosphodiesterase subtype 4) plays a crucial role in regulating cognition via the PDE-4-cAMP cascade signaling involving phosphorylated cAMP response element binding protein (CREB). Objective. The primary endpoint was to examine the neurocognitive effects of extract Sceletium tortuosum (Zembrin) and to assess the safety and tolerability of Zembrin in cognitively healthy control subjects. Method. We chose the randomized double-blind placebo-controlled cross-over design in our study. We randomized normal healthy subjects (total n = 21) to receive either 25 mg capsule Zembrin or placebo capsule once daily for 3 weeks, in a randomized placebo-controlled 3-week cross-over design. We administered battery of neuropsychological tests: CNS Vital Signs and Hamilton depression rating scale (HAM-D) at baseline and regular intervals and monitored side effects with treatment emergent adverse events scale. Results. 21 subjects (mean age: 54.6 years ± 6.0 yrs; male/female ratio: 9/12) entered the study. Zembrin at 25 mg daily dosage significantly improved cognitive set flexibility (P < 0.032) and executive function (P < 0.022), compared with the placebo group. Positive changes in mood and sleep were found. Zembrin was well tolerated. Conclusion. The promising cognitive enhancing effects of Zembrin likely implicate the PDE-4-cAMP-CREB cascade, a novel drug target in the potential treatment of early Alzheimer's dementia. This trial is registered with ClinicalTrials.gov NCT01805518.