Amyloid induced hyperexcitability in default mode network drives medial temporal hyperactivity and early tau accumulation

Fibre density and cross-section associate with hallmark pathology in early Alzheimer's disease

BACKGROUND

Tau pathology in Alzheimer's disease (AD) propagates trans-synaptically along structurally connected brain networks and in synergy with amyloid pathology it induces synaptic damage. However, the in vivo relationship of amyloid, tau and synaptic density with white matter (WM) structural changes has been studied rather limitedly. Recent advances in diffusion MRI processing allow quantification of apparent fibre density and fibre cross-section on the fixel level, i.e., individual fibre populations within one voxel. The aim of this study was to investigate the hypothesis of axonal loss due to tau propagation and amyloid pathology and its association with synaptic density in early disease stages.

METHODS

Twenty-four patients with amnestic mild cognitive impairment (aMCI) and 23 healthy controls (HC) underwent baseline amyloid (11C-PiB/18F-NAV4694), tau (18F-MK-6240) and synaptic density (11C-UCB-J binding to SV2A) PET/MR in combination with diffusion MRI and cognitive assessments. A subset of 14 aMCI patients underwent follow-up visits after 2 years. First, a whole-brain fixel-based analysis was performed to identify differences in fibre density and fibre cross-section between HC and aMCI and longitudinally in the aMCI group. Next, a tract-of-interest analysis was performed, focusing on the temporal-cingulum bundle where most alterations have been shown in early AD. Tau and SV2A PET were quantified in the connected regions, i.e., hippocampus and posterior cingulate/precuneus (PCC-P). Amyloid PET centiloids were measured in the commonly used cortical composite volume-of-interest.

RESULTS

At baseline, multiple WM tracts showed lower fibre density and lower fibre cross-section in aMCI compared to HC, and these parameters further decreased longitudinally in the aMCI group. In the temporal cingulum bundle, reduced fibre density was significantly associated with reduced hippocampal synaptic density while increased hippocampal and PCC-P tau specifically correlated with reduced fibre cross-section. Increased global amyloid burden was associated with reduced fibre density and fibre cross-section in the temporal cingulum bundle.

CONCLUSIONS

Our results suggest that WM degeneration already occurs in the aMCI stage of AD and alterations in apparent fibre density and fibre cross-section of the temporal cingulum bundle are associated with AD hallmark pathology.

Sleep Alterations and Cognitive Decline

Sleep disturbances and cognitive decline are intricately connected, and both are prevalent in aging populations and individuals with neurodegenerative disorders such as Alzheimer's disease (AD) and other dementias. Sleep is vital for cognitive functions including memory consolidation, executive function, and attention. Disruption in these processes is associated with cognitive decline, although causal evidence is mixed. This review delves into the bidirectional relationship between alterations in sleep and cognitive impairment, exploring key mechanisms such as amyloid-β accumulation, tau pathology, synaptic homeostasis, neurotransmitter dysregulation, oxidative stress, and vascular contributions. Evidence from both experimental research and population-based studies underscores the necessity of early interventions targeting sleep to mitigate risks of neurodegenerative diseases. A deeper understanding of the interplay between sleep and cognitive health may pave the way for innovative strategies to prevent or reduce cognitive decline through improved sleep management.

Differential effects of 2 and 4 weeks repetitive transcranial magnetic stimulation inducing neuroplasticity on cognitive improvement

BackgroundRepetitive transcranial magnetic stimulation (rTMS) is an efficient intervention for alleviating cognitive symptoms in Alzheimer's disease (AD), but the optimal treatment duration for high efficacy remains unclear.ObjectiveThis study investigates the effects of 2-week and 4-week rTMS on neural network plasticity and cognitive improvement, aiming to identify the optimal treatment duration for cognitive impairment.MethodsrTMS was administered to cognitively impaired patients over 2-week and 4-week periods, exploring its effects on cognitive improvement and induced neural circuits. The study also examines the predictive value of these neural circuits for individual treatment responses.ResultsThe 4-week rTMS treatment significantly outperformed the 2-week course in improving cognitive function. Neural activity analysis identified the precuneus as a key region for episodic memory. Changes in brain regions, particularly within the default mode network (DMN), visual network (VN), and motor network (MN), were associated with cognitive improvements. Baseline functional connectivity in these regions predicted changes in general cognition (r = 0.724, p < 0.001) and episodic memory (r = 0.447, p = 0.022) after rTMS.ConclusionsExtended rTMS treatment enhances cognitive performance in cognitive impairment patients, with the 4-week course showing superior effects. Reduced connectivity in the DMN following rTMS was linked to cognitive improvements. The neural network baseline can predict patients' treatment responses.

Challenges and Frontiers in Computational Metabolic Psychiatry

One of the primary challenges in metabolic psychiatry is that the disrupted brain functions that underlie psychiatric conditions arise from a complex set of downstream and feedback processes that span multiple spatiotemporal scales. Importantly, the same circuit can have multiple points of failure, each of which results in a different type of dysregulation, and thus elicits distinct cascades downstream that produce divergent signs and symptoms. Here, we illustrate this challenge by examining how subtle differences in circuit perturbations can lead to divergent clinical outcomes. We also discuss how computational models can perform the spatially heterogeneous integration and bridge in vitro and in vivo paradigms. By leveraging recent methodological advances and tools, computational models can integrate relevant processes across scales (e.g., tricarboxylic acid cycle, ion channel, neural microassembly, whole-brain macrocircuit) and across physiological systems (e.g., neural, endocrine, immune, vascular), providing a framework that can unite these mechanistic processes in a manner that goes beyond the conceptual and descriptive to the quantitative and generative. These hold the potential to sharpen our intuitions toward circuit-based models for personalized diagnostics and treatment.

Heterogeneous brain abnormalities in subjective cognitive decline converge on a common network and their transcriptional signature

INTRODUCTION

Subjective cognitive decline (SCD) is increasingly recognized as closely related to future Alzheimer's disease (AD). Numerous neuroimaging findings in SCD are inconsistent. We tested whether the various findings localize to a common brain network.

METHODS

Using a novel coordinate network mapping approach, we delineated common brain damage networks that were functionally connected to reported neuroimaging findings. We then decoded these common networks using microscale transcriptomic and chemo-architectures and psychological processes.

RESULTS

We enrolled 45 studies comprising 2453 SCD patients and 3017 healthy controls. The identified SCD networks were largely localized in the somatosensory network (SMN) and default mode network (DMN). Both were robust to perturbations of analyzed parameters and in an independent validation dataset. Neurobiology correlation analyses identified some key biological pathways and neurotransmitters linked to these networks.

DISCUSSION

Our findings reconcile heterogeneous neuroimaging abnormalities in SCD and provide a richer neurobiological underpinning, which has implications for understanding patients with SCD.

HIGHLIGHTS

The heterogeneous neuroimaging findings on SCD were reconciled in a coordinate network mapping framework. The SCD-related functional network involves changes in the DMN, while the SCD-related structural network has changes mainly in primary sensory areas. The identified genes in the functional network were predominantly enriched in biological processes related to synaptic structure, calcium ion binding, and cellular metabolism. An ALE meta-analysis was conducted for comparison.

A Shift Toward Supercritical Brain Dynamics Predicts Alzheimer's Disease Progression

Alzheimer's disease (AD) is the most common form of dementia with continuum of disease progression of increasing severity from subjective cognitive decline (SCD) to mild cognitive impairment (MCI) and lastly to AD. The transition from MCI to AD has been linked to brain hypersynchronization, but the underlying mechanisms leading to this are unknown. Here, we hypothesized that excessive excitation in AD disease progression would shift brain dynamics toward supercriticality across an extended regime of critical-like dynamics. In this framework, healthy brain activity during aging preserves operation at near the critical phase transition at balanced excitation-inhibition (E/I). To test this hypothesis, we used source-reconstructed resting-state MEG data from a cross-sectional cohort (N = 343) of individuals with SCD, MCI, and healthy controls (HC) as well as from a longitudinal cohort (N = 45) of MCI patients. We then assessed brain criticality by quantifying long-range temporal correlations (LRTCs) and functional EI (fE/I) of neuronal oscillations. LRTCs were attenuated in SCD in spectrally and anatomically constrained regions while this breakdown was progressively more widespread in MC. In parallel, fE/I was increased in the MCI but not in the SC cohort. Both observations also predicted the disease progression in the longitudinal cohort. Finally, using machine learning trained on functional (LRTCs, fE/I) and structural (MTL volumes) features, we show that LRTCs and f/EI are the most informative features for accurate classification of individuals with SCD while structural changes accurate classify the individuals with MCI. These findings establish that a shift toward supercritical brain dynamics reflects early AD disease progression.

Precuneus Activity during Retrieval Is Positively Associated with Amyloid Burden in Cognitively Normal Older APOE4 Carriers

The precuneus is a site of early amyloid-beta (Aβ) accumulation. Previous cross-sectional studies reported increased precuneus fMRI activity in older adults with mild cognitive deficits or elevated Aβ. However, longitudinal studies in early Alzheimer's disease (AD) are lacking and the relationship to the Apolipoprotein-E (APOE) genotype is unclear. Investigating the PREVENT-AD dataset, we assessed how baseline and longitudinal precuneus activity during successful memory retrieval relates to future Aβ and tau burden and change in memory performance. We further studied the moderation by APOE4 genotype. We included 165 older adults (age, 62.8 ± 4.4 years; 113 female; 66 APOE4 carriers) who were cognitively normal at baseline with a family history of AD. All participants performed task-fMRI at baseline and underwent 18F-flortaucipir-PET and 18F-NAV4694-Aβ-PET on average 5 years later. We found that higher baseline activity and greater longitudinal increase in precuneus activity were associated with higher Aβ burden in APOE4 carriers but not noncarriers. We observed no effects of precuneus activity on tau burden. Finally, APOE4 noncarriers with low baseline precuneus activity exhibited better longitudinal performance in an independent memory test compared with (1) noncarriers with higher baseline activity and (2) APOE4 carriers. Our findings suggest that higher task-related precuneus activity during memory retrieval at baseline and over time are associated with greater Aβ burden in cognitively normal APOE4 carriers. Our results further indicate that the absence of "hyperactivation" and the absence of the APOE4 allele is related with better future cognitive outcomes in cognitively normal older adults at risk for AD.

Epileptic activity on foramen ovale electrodes is associated with sleep and tau pathology in Alzheimer's disease

Both sleep alterations and epileptiform activity are associated with the accumulation of amyloid-β and tau pathology and are currently investigated for potential therapeutic interventions in Alzheimer's disease. However, a bidirectional intertwining relationship between sleep and neuronal hyperexcitability might modulate the effects of Alzheimer's disease pathology on the corresponding associations. To investigate this, we performed multiple day simultaneous foramen ovale (FO) plus scalp EEG and polysomnography recordings and acquired 18F-MK6240 tau PET-MR in three patients in the prodromal stage of Alzheimer's disease and in two patients with mild and moderate dementia due to Alzheimer's disease, respectively. As an eligibility criterion for the present study, subjects either had a history of a recent seizure (n = 2) or subclinical epileptiform activity (SEA) on a previous scalp EEG taken in a research context (n = 3). The 18F-MK6240 standard uptake value ratio (SUVR) and asymmetry index (AI) were calculated in a priori-defined volumes of interest. Linear mixed-effects models were used to study associations between interictal epileptiform discharges (IEDs), polysomnography parameters and 18F-MK6240 SUVR. Epileptiform activity was bilateral but asymmetrically present on FO electrodes in all patients and ≥95% of IEDs were not visible on scalp EEG. In one patient, two focal seizures were detected on FO electrodes, both without visual scalp EEG correlate. We observed lateralized periodic discharges, brief potentially ictal rhythmic discharges and lateralized rhythmic delta activity on FO electrodes in four patients. Unlike scalp EEG, intracranial electrodes showed a lateralization of epileptiform activity. Although the amount of IEDs on intracranial electrodes was not associated to the 18F-MK6240 SUVR binding in different volumes of interest, there was a congruent asymmetry of the 18F-MK6240 binding towards the most epileptic hemisphere for the mesial (P = 0.007) and lateral temporal cortex (P = 0.006). IEDs on intracranial electrodes were most abundant during slow wave sleep (SWS) (92/h) and non-REM sleep 2 (N2, 81/h), followed by non-REM sleep 1 (N1, 33/h) and least frequent during wakefulness (17/h) and REM sleep (9/h). The extent of IEDs during sleep was not reflected in the relative time in each sleep stage spent [REM% (P = 0.415), N1% (P = 0.668), N2% (P = 0.442), SWS% (P = 0.988)], and not associated with the arousal index (P = 0.317), apnoea-hypopnoea index (P = 0.846) or oxygen desaturation index (P = 0.746). Together, our observations suggest a multi-directional interaction between sleep, epileptiform activity and tau pathology in Alzheimer's disease.

Amyloid-associated hyperconnectivity drives tau spread across connected brain regions in Alzheimer's disease

In Alzheimer's disease (AD), amyloid-β (Aβ) triggers the aggregation and spreading of tau pathology, which drives neurodegeneration and cognitive decline. However, the pathophysiological link between Aβ and tau remains unclear, which hinders therapeutic efforts to attenuate Aβ-related tau accumulation. Aβ has been found to trigger neuronal hyperactivity and hyperconnectivity, and preclinical research has shown that tau spreads across connected neurons in an activity-dependent manner. Here, we hypothesized that neuronal hyperactivity and hypersynchronicity, resulting in functional connectivity increases, constitute a crucial mechanism by which Aβ facilitates the spreading of tau pathology. By combining Aβ positron emission tomography (PET), resting-state functional magnetic resonance imaging, and longitudinal tau-PET in 69 cognitively normal amyloid-negative controls and 140 amyloid-positive patients covering the AD spectrum, we confirmed that Aβ induces hyperconnectivity of temporal lobe tau epicenters to posterior brain regions that are vulnerable to tau accumulation in AD. This was replicated in an independent sample of 55 controls and 345 individuals with preclinical AD and low cortical tau-PET uptake, suggesting that the emergence of Aβ-related hyperconnectivity precedes neocortical tau spreading . Last, using longitudinal tau-PET and mediation analysis, we confirmed that these Aβ-related connectivity increases in tau epicenters to typical tau-vulnerable brain regions in AD mediated the effect of Aβ on faster tau accumulation, unveiling increased connectivity as a potential causal link between the two AD hallmark pathologies. Together, these findings suggest that Aβ promotes tau spreading by eliciting neuronal hyperconnectivity and that targeting Aβ-related neuronal hyperconnectivity may attenuate tau spreading in AD.

Lower Network Functional Connectivity Is Associated With Higher Regional Tau Burden Among Those At-Risk of Alzheimer's Disease But Cognitively Unimpaired: Specific Patterns Based on Amyloid Status

Introduction

Functional connectivity within the medial temporal lobe (MTL) and default mode network (DMN) changes across Alzheimer's disease stages, influenced by and influencing cortical amyloid-beta (Aβ) and regional tau burden. Previous research highlights functional connectivity's role in Alzheimer's disease progression and the interactions of cortical Aβ and functional connectivity within and between the MTL and DMN, but their impact on regional tau deposition remains largely unexplored.

Methods

Cognitively unimpaired participants from OASIS-3 (AV1451 cohort, n=287) were classified into Aβ- (n=193) and Aβ+ (n=94) groups via amyloid-PET for cross-sectional analyses. Principal components analysis of functional connectivity identified two MTL-functional connectivity and DMN-functional connectivity principal components (PCs), which were correlated with regional tau per Braak stages 1-6 brain regions. Aβ status-specific robust regressions evaluated whether functional connectivity was associated with tau.

Results

In Aβ- participants, lower "MTL Integration Axis" functional connectivity (PC1) was associated with higher tau levels in the left entorhinal cortex. In Aβ+ participants, lower "MTL Integration Axis" functional connectivity correlated with elevated tau levels in the DMN's left lateral parietal cortex, MTL's right parahippocampal cortex, and Braak stages 3-6 brain regions.

Discussion

Decreased functional connectivity was associated with increased regional tau burden, showing Aβ status-specific effects. Enhancing MTL functional connectivity could be a therapeutic strategy and a promising direction for future clinical interventions.

Iron deposition is associated with motor and non-motor network breakdown in parkinsonism

Background

Iron deposition has been observed in Parkinsonism and is emerging as a diagnostic marker for movement disorders. Brain functional network disruption has also been detected in parkinsonism, and is believed to be accountable for specific symptoms in parkinsonism. However, how iron deposition influences brain network remains to be elucidated.

Methods

We recruited 16 Parkinson's disease (PD), 8 multiple system atrophy (MSA) and 7 progressive supranuclear palsy (PSP) patients. T1-weighted, susceptibility weighted images and resting-state functional MRI (rs-fMRI) were acquired. Quantitative susceptibility mapping (QSM) analysis was performed to quantify iron deposition in substantia nigra, putamen and dentate nucleus. Cerebellar network, sensorimotor network, default mode network and language networks were segregated using independent analysis. Network and iron deposition status were evaluated in relation to diagnostic groups, motor and non-motor symptoms. The relationship between quantitative iron deposition and brain network status was further interrogated. To further validate the findings, 13 healthy controls and 37 PD patients who had available T1 and rs-fMRI scans were selected from Parkinson's progression markers initiative (PPMI) database, and network analysis was performed.

Results

In local cohort, compared to PD, MSA patients showed greater iron deposition in putamen, while PSP patients had greater iron deposition in caudate nucleus and thalamus. Cerebellar and language networks showed significant difference across diagnostic groups, while default mode network and sensorimotor network did not. MSA patients had significantly impaired cerebellar network and language networks compared to PD patients. Cerebellar network was positively associated with motor symptom scores while language network was positively associated with MoCA scores in the patients. Iron deposition was negatively associated with both networks' activity in the patients. In PPMI cohort, impairment was found in both cerebellar and language networks in PD. Cerebellar and language networks correlated with motor and cognitive impairment, respectively.

Conclusion

Cerebellar network and language networks are differently influenced in MSA, PD and PSP, which can serve as potential diagnostic marker. Impairment of cerebellar network and language network are associated with motor symptoms and cognitive impairment, respectively. Moreover, dysfunction of the networks is associated with iron deposition in deep nuclei (SN, DN, Putamen).

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knockin mouse model of Alzheimer disease

The disease's trajectory of Alzheimer disease (AD) is associated with and negatively correlated to hippocampal hyperexcitability. Here, we show that during the asymptomatic stage in a knockin (KI) mouse model of Alzheimer disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma, and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer disease.

The metabolic costs of cognition

Cognition and behavior are emergent properties of brain systems that seek to maximize complex and adaptive behaviors while minimizing energy utilization. Different species reconcile this trade-off in different ways, but in humans the outcome is biased towards complex behaviors and hence relatively high energy use. However, even in energy-intensive brains, numerous parsimonious processes operate to optimize energy use. We review how this balance manifests in both homeostatic processes and task-associated cognition. We also consider the perturbations and disruptions of metabolism in neurocognitive diseases.

Association of precuneus Aβ burden with default mode network function

INTRODUCTION

It remains unclear whether the local amyloid-beta (Aβ) burden in key regions within the default mode network (DMN) affects network and cognitive functions.

METHODS

Participants included 1002 individuals from the Chinese Preclinical Alzheimer's Disease Study cohort who underwent 18F-florbetapir positron emission tomography resting-state functional magnetic resonance imaging scanning and neuropsychological tests. The correlations between precuneus (PRC) Aβ burden, DMN function, and cognitive function were investigated.

RESULTS

In individuals with high PRC Aβ burden, there is a bidirectional relationship between DMN local function or functional connectivity and PRC Aβ deposition across various cognitive states, which is also linked to cognitive function. Even below the PRC Aβ threshold, DMN function remains related to PRC Aβ deposition and cognitive performance.

DISCUSSION

The findings reveal the critical role of PRC Aβ deposition in disrupting neural networks associated with cognitive decline and the necessity of early detection and monitoring of PRC Aβ deposition.

HIGHLIGHTS

Precuneus (PRC) Aβ burden impacts DMN function in different cognitive stages. High PRC Aβ burden is linked to early neural compensation and subsequent dysfunction. Low PRC Aβ burden correlates with neural changes before significant Aβ accumulation. Changes in DMN function and connectivity provide insights into AD progression. Early detection of regional Aβ burden can help monitor the risk of cognitive decline.

APOE4 Increases Susceptibility to Amyloid, Accelerating Episodic Memory Decline

Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for sporadic Alzheimer's disease (AD). Individuals with one copy of APOE4 exhibit greater amyloid-beta (Aβ) deposition compared to noncarriers, an effect that is even more pronounced in APOE4 homozygotes. Interestingly, APOE4 carriers not only show more AD pathology but also experience more rapid cognitive decline, particularly in episodic memory. The underlying mechanisms driving this domain-specific vulnerability, however, remain unclear. In this study, we examined whether the accelerated decline in episodic memory among APOE4 carriers is due to increased Aβ deposition or heightened susceptibility to Aβ-related effects. Using data from the Alzheimer's Disease Research Initiative, we modeled amyloid duration, the estimated number of years an individual has been amyloid-positive, and its impact on cognitive trajectories. Our findings reveal that APOE4 is associated with more rapid episodic memory decline as a function of amyloid duration. This decline was dose-dependent, with APOE4 homozygotes declining more rapidly than heterozygotes, and it was consistently observed across multiple episodic memory tasks and measures. Importantly, this pattern was not observed in other cognitive domains, such as processing speed, executive function, visuospatial skills, language, or crystallized intelligence. These results suggest that cognitive trajectories in AD differ by APOE genotype, with APOE4 conferring increased vulnerability to hippocampal dysfunction early in the disease course. Future research should investigate whether these cognitive differences stem from distinct pathological cascades in APOE4 carriers.

Can brain network connectivity facilitate the clinical development of disease-modifying anti-Alzheimer drugs?

The preclinical phase of Alzheimer's disease represents a crucial time window for therapeutic intervention but requires the identification of clinically relevant biomarkers that are sensitive to the effects of disease-modifying drugs. Amyloid peptide and tau proteins, the main histological hallmarks of Alzheimer's disease, have been widely used as biomarkers of anti-amyloid and anti-tau drugs. However, these biomarkers do not fully capture the multiple biological pathways of the brain. Indeed, robust amyloid-target engagement by anti-amyloid monoclonal antibodies has recently translated into modest cognitive and clinical benefits in Alzheimer's disease patients, albeit with potentially life-threatening side effects. Moreover, targeting the tau pathway has yet to result in any positive clinical outcomes. Findings from computational neuroscience have demonstrated that brain regions do not work in isolation but are interconnected within complex network structures. Brain connectivity studies suggest that misfolded proteins can spread through these connections, leading to the hypothesis that Alzheimer's disease is a pathology of network disconnectivity. Based on these assumptions, here we discuss how incorporating brain connectivity outcomes could better capture global brain functionality and, in conjunction with traditional Alzheimer's disease biomarkers, could facilitate the clinical development of new disease-modifying anti-Alzheimer's disease drugs.

Medial Amygdalar Tau Is Associated With Mood Symptoms in Preclinical Alzheimer's Disease

BACKGROUND

While the amygdala receives early tau deposition in Alzheimer's disease (AD) and is involved in social and emotional processing, the relationship between amygdalar tau and early neuropsychiatric symptoms in AD is unknown. We sought to determine whether focal tau binding in the amygdala and abnormal amygdalar connectivity were detectable in a preclinical AD cohort and identify relationships between these and self-reported mood symptoms.

METHODS

We examined 598 individuals (347 amyloid positive [58% female], 251 amyloid negative [62% female] subset in tau positron emission tomography and functional magnetic resonance imaging cohorts) from the A4 (Anti-Amyloid Treatment in Asymptomatic AD) Study. In the tau positron emission tomography cohort, we used amygdalar segmentations to examine representative nuclei from 3 functional divisions of the amygdala. We analyzed between-group differences in division-specific tau binding in the amygdala in preclinical AD. We conducted seed-based functional connectivity analyses from each division in the functional magnetic resonance imaging cohort. Finally, we conducted exploratory post hoc correlation analyses between neuroimaging biomarkers of interest and anxiety and depression scores.

RESULTS

Amyloid-positive individuals demonstrated increased tau binding in the medial and lateral amygdala, and tau binding in these regions was associated with mood symptoms. Across amygdalar divisions, amyloid-positive individuals had relatively higher regional connectivity from the amygdala to other temporal regions, the insula, and the orbitofrontal cortex, but medial amygdala to retrosplenial cortex connectivity was lower. Medial amygdala to retrosplenial connectivity was negatively associated with anxiety symptoms, as was retrosplenial tau.

CONCLUSIONS

Our findings suggest that preclinical tau deposition in the amygdala and associated changes in functional connectivity may be related to early mood symptoms in AD.

Walnut-derived peptides cross the blood-brain barrier and ameliorate Aβ-induced hypersynchronous neural network activity

Walnut peptides exhibit promising neuroprotective effects; however, they must be absorbed in their intact form through the gastrointestinal tract into the bloodstream and brain. In this study, the effects of the walnut peptide TWLPLPR (TW-7) were evaluated in mice, including its absorption and distribution ability to cross the blood-brain barrier, and inhibitory effects on hyperactivity of primary hippocampal neurons. TW-7 was stable in plasma, and the peptide retention rate was 88.19 ± 0.70 % after 48 h. In vitro imaging indicated that TW-7 was distributed in the brain, liver, lungs, and kidneys of mice after gavage, and an immunofluorescence analysis indicated that TW-7 could accumulate in mouse brain parenchyma; in addition, TW-7 reached its maximum concentration (5.36 ± 1.59 µg/mL) in plasma 2 h after gavage, and reached its peak concentration (0.95 ± 0.19 µg/g) in brain tissue 4 h after gavage. Microelectrode array and immunofluorescence analyses confirmed that TW-7 ameliorates the overexcitation of primary hippocampal neurons induced by Aβ25-35 through inhibiting the excessive release of glutamate and protecting synaptic structure and function. These results suggest that TW-7 can penetrate the blood-brain barrier in mice and positively affect the electrophysiological activity of neurons. More broadly, these findings provide a theoretical basis for the development and application of walnut peptide-based functional food for Alzheimer's disease intervention.

Resting-state functional connectivity abnormalities in subjective cognitive decline: A 7T MRI study

Resting-state functional connectivity (FC) MRI is sensitive to brain changes in Alzheimer's disease in preclinical stages, however studies in persons with subjective cognitive decline (SCD) have reported conflicting findings, and no study is available at 7T MRI. In this study, we investigated FC alterations in sixty-six participants recruited at the Geneva Memory Center (24 controls, 14 SCD, 28 cognitively impaired [CI]). Participants were classified as SCD if they reported cognitive complaints without objective cognitive deficits, and underwent 7T fMRI to assess FC in canonical brain networks and their association with cognitive/clinical features. SCD showed normal cognition, a trend for higher depressive symptoms, and normal AD biomarkers. Compared to the other two groups, SCD showed higher FC in frontal default mode network (DMN) and insular and superior temporal nodes of ventral attention network (VAN). Higher FC in the DMN and VAN was associated with worse cognition but not depression, suggesting that hyper-connectivity in these networks may be a signature of age-related cognitive decline in SCD at low risk of developing AD.

Connectivity, Pathology, and ApoE4 Interactions Predict Longitudinal Tau Spatial Progression and Memory

Tau pathology spread into neocortex indicates a transition from healthy aging to Alzheimer's disease (AD). Connectivity between tau epicenters and later accumulating regions of cortex has been proposed as a mechanism of tau spread, but how this relationship changes with greater AD pathology burden or genotype is not understood. We investigated tau accumulation in two key regions, precuneus and inferior temporal cortex, using resting state functional connectivity (rsFC) and longitudinal PET imaging from a multicohort sample of cognitively unimpaired older adults. We examined how baseline tau PET, Aβ PET, and ApoE4 genotype status interact with rsFC between hippocampus and these downstream regions to predict rate of tau accumulation in neocortex. We found that the 3-way interaction between connectivity, baseline tau, and baseline Aβ or ApoE4 status was associated with neocortical tau accumulation in precuneus and inferior temporal cortex. In addition, baseline tau, Aβ, and ApoE4 status also moderated the association between connectivity and rate of memory decline. Together, these results suggest that the extent and distribution of future tau accumulation may be predicted by the interaction of baseline connectivity, AD pathology, and genetic risk.

Association of Seizure Foci and Location of Tau and Amyloid Deposition and Brain Atrophy in Patients With Alzheimer Disease and Seizures

BACKGROUND AND OBJECTIVES

Alzheimer disease (AD) is associated with a 2 to 3-fold increased risk of developing late-onset focal epilepsy, yet it remains unclear how development of focal epilepsy in AD is related to AD pathology. The objective of this study was to examine spatial relationships between the epileptogenic zone and tau deposition, amyloid deposition, and brain atrophy in individuals with AD who developed late-onset, otherwise unexplained focal epilepsy. We hypothesized that if network hyperexcitability is mechanistically linked to AD pathology, then there would be increased tau and amyloid deposition within the epileptogenic hemisphere.

METHODS

In this cross-sectional study, we performed tau and amyloid PET imaging, brain MRI, and overnight scalp EEG in individuals with early clinical stages of AD who developed late-onset, otherwise unexplained focal epilepsy (AD-Ep). Participants were referred from epilepsy and memory disorders clinics at our institutions. We determined epilepsy localization based on EEG findings and seizure semiology. We quantified tau deposition, amyloid deposition, and atrophy across brain regions and calculated asymmetry indices for these measures. We compared findings in AD-Ep with those in a control AD group without epilepsy (AD-NoEp).

RESULTS

The AD-Ep group included 8 individuals with a mean age of 69.5 ± 4.2 years at PET imaging. The AD-NoEp group included 14 individuals with a mean age of 71.7 ± 9.8 years at PET imaging. In AD-Ep, we found a highly asymmetric pattern of tau deposition, with significantly greater tau in the epileptogenic hemisphere. Amyloid deposition and cortical atrophy were also greater in the epileptogenic hemisphere, although the magnitudes of asymmetry were reduced compared with tau. Compared with AD-NoEp, the AD-Ep group had significantly greater tau asymmetry and trends toward greater asymmetry of amyloid and atrophy. AD-Ep also had significantly greater amyloid burden bilaterally and trends toward greater tau burden within the epileptogenic hemisphere, compared with AD-NoEp.

DISCUSSION

Our results reveal a spatial association between the epileptogenic focus and tau deposition, amyloid deposition, and neurodegeneration in early clinical stages of AD. Within the limitations of a cross-sectional study with small sample sizes, these findings contribute to our understanding of the clinicopathologic heterogeneity of AD, demonstrating an association between focal epilepsy and lateralized pathology in AD.

The interplay of age, gender and amyloid on brain and cognition in mid-life and older adults

Deficits in memory are seen as a canonical sign of aging and a prodrome to dementia in older adults. However, our understanding of age-related cognition and brain morphology occurring throughout a broader spectrum of adulthood remains limited. We quantified the relationship between cognitive function and brain morphology (sulcal width, SW) using three cross-sectional observational datasets (PISA, AIBL, ADNI) from mid-life to older adulthood, assessing the influence of age, sex, amyloid (Aβ) and genetic risk for dementia. The data comprised cognitive, genetic and neuroimaging measures of a total of 1570 non-clinical mid-life and older adults (mean age 72, range 49-90 years, 1330 males) and 1365 age- and sex-matched adults with mild cognitive impairment (MCI) or Alzheimer's disease (AD). Among non-clinical adults, we found robust modes of co-variation between regional SW and multidomain cognitive function that differed between the mid-life and older age range. These cortical and cognitive profiles derived from healthy cohorts predicted out-of-sample AD and MCI. Furthermore, Aβ-deposition and educational attainment levels were associated with cognition but not SW. These findings underscoring the complex interplay between factors influencing cognition and brain structure from mid-life onwards, providing valuable insights for future research into neurodegeneration and the development of future screening algorithms.

Structural and functional remodeling of neural networks in β-amyloid driven hippocampal hyperactivity

Early detection of Alzheimer's disease (AD) is essential for improving the patients outcomes and advancing our understanding of disease, allowing for timely intervention and treatment. However, accurate biomarkers are still lacking. Recent evidence indicates that hippocampal hyperexcitability precedes the diagnosis of AD decades ago, can predict cognitive decline. Thus, could hippocampal hyperactivity be a robust biomarker for early-AD, and what drives hippocampal hyperactivity in early-AD? these critical questions remain to be answered. Increasing clinical and experimental studies suggest that early hippocampal activation is closely associated with longitudinal β-amyloid (Aβ) accumulation, Aβ aggregates, in turn, enhances hippocampal activity. Therefore, in this narrative review, we discuss the role of Aβ-induced altered intrinsic neuronal properties as well as structural and functional remodeling of glutamatergic, GABAergic, cholinergic, noradrenergic, serotonergic circuits in hippocampal hyperactivity. In addition, we analyze the available therapies and trials that can potentially be used clinically to attenuate hippocampal hyperexcitability in AD. Overall, the present review sheds lights on the mechanism behind Aβ-induced hippocampal hyperactivity, and highlights that hippocampal hyperactivity could be a robust biomarker and therapeutic target in prodromal AD.

Cerebral hyperactivation across the Alzheimer's disease pathological cascade

Neuronal dysfunction in specific brain regions or across distributed brain networks is a known feature of Alzheimer's disease. An often reported finding in the early stage of the disease is the presence of increased functional MRI (fMRI) blood oxygenation level-dependent signal under task conditions relative to cognitively normal controls, a phenomenon known as 'hyperactivation'. However, research in the past decades yielded complex, sometimes conflicting results. The magnitude and topology of fMRI hyperactivation patterns have been found to vary across the preclinical and clinical spectrum of Alzheimer's disease, including concomitant 'hypoactivation' in some cases. These incongruences are likely due to a range of factors, including the disease stage at which the cohort is examined, the brain areas or networks studied and the fMRI paradigm utilized to evoke these functional abnormalities. Additionally, a perennial question pertains to the nature of hyperactivation in the context of Alzheimer's disease. Some propose it reflects compensatory mechanisms to sustain cognitive performance, while others suggest it is linked to the pathological disruption of a highly regulated homeostatic cycle that contributes to, or even drives, disease progression. Providing a coherent narrative for these empirical and conceptual discrepancies is paramount to develop disease models, understand the synergy between hyperactivation and the Alzheimer's disease pathological cascade and tailor effective interventions. We first provide a comprehensive overview of functional brain changes spanning the course from normal ageing to the clinical spectrum of Alzheimer's disease. We then highlight evidence supporting a close relationship between fMRI hyperactivation and in vivo markers of Alzheimer's pathology. We primarily focus on task-based fMRI studies in humans, but also consider studies using different functional imaging techniques and animal models. We then discuss the potential mechanisms underlying hyperactivation in the context of Alzheimer's disease and provide a testable framework bridging hyperactivation, ageing, cognition and the Alzheimer's disease pathological cascade. We conclude with a discussion of future challenges and opportunities to advance our understanding of the fundamental disease mechanisms of Alzheimer's disease, and the promising development of therapeutic interventions incorporating or aimed at hyperactivation and large-scale functional systems.

Digital cognitive assessments as low-burden markers for predicting future cognitive decline and tau accumulation across the Alzheimer's spectrum

BACKGROUND

Digital cognitive assessments, particularly those that can be done at home, present as low-burden biomarkers for participants and patients alike, but their effectiveness in the diagnosis of Alzheimer's disease (AD) or predicting its trajectory is still unclear. Here, we assessed what utility or added value these digital cognitive assessments provide for identifying those at high risk of cognitive decline.

METHODS

We analyzed >500 Alzheimer's Disease Neuroimaging Initiative participants who underwent a brief digital cognitive assessment and amyloid beta (Aβ)/tau positron emission tomography scans, examining their ability to distinguish cognitive status and predict cognitive decline.

RESULTS

Performance on the digital cognitive assessment was superior to both cortical Aβ and entorhinal tau in detecting mild cognitive impairment and future cognitive decline, with mnemonic discrimination deficits emerging as the most critical measure for predicting decline and future tau accumulation.

DISCUSSION

Digital assessments are effective at identifying at-risk individuals, supporting their utility as low-burden tools for early AD detection and monitoring.

HIGHLIGHTS

Performance on digital cognitive assessments predicts progression to mild cognitive impairment at a higher proficiency compared to amyloid beta and tau. Deficits in mnemonic discrimination are indicative of future cognitive decline. Impaired mnemonic discrimination predicts future entorhinal and inferior temporal tau.

Increased between-network connectivity: A risk factor for tau elevation and disease progression

One of the pathologic hallmarks of Alzheimer's disease (AD) is neurofibrillary tau tangles. Despite our knowledge that tau typically initiates in the medial temporal lobe (MTL), the mechanisms driving tau to spread beyond MTL remain unclear. Emerging evidence reveals distinct patterns of functional connectivity change during aging and preclinical AD: while connectivity within-network decreases, connectivity between-network increases. Building upon increased between-network connectivity, our study hypothesizes that this increase may play a critical role in facilitating tau spread in early stages. We conducted a longitudinal study over two to three years intervals on a cohort of 46 healthy elderly participants (mean age 64.23 ± 3.15 years, 26 females). Subjects were examined clinically and utilizing advanced imaging techniques that included resting-state functional MRI (rs-fMRI), structural magnetic resonance imaging (MRI), and a second-generation positron emission tomography (PET) tau tracer, 18F-MK6240. Through unsupervised agglomerative clustering and increase in between-network connectivity, we successfully identified individuals at increased risk of future tau elevation and AD progression. Our analysis revealed that individuals with increased between-network connectivity are more likely to experience more future tau deposition, entorhinal cortex thinning, and lower selective reminding test (SRT) delayed scores. Additionally, in the limbic network, we found a strong association between tau progression and increased between-network connectivity, which was mainly driven by beta-amyloid (Aβ) positive participants. These findings provide evidence for the hypothesis that an increase in between-network connectivity predicts future tau deposition and AD progression, also enhancing our understanding of AD pathogenesis in the preclinical stages.

Variable and interactive effects of Sex, APOE ε4 and TREM2 on the deposition of tau in entorhinal and neocortical regions

The canonical AD pathological cascade posits that the accumulation of amyloid beta ( Aβ ) is the initiating event, accelerating the accumulation of tau in the entorhinal cortex (EC), which subsequently spreads into the neocortex. Here in a sample of over 1300 participants with multimodal imaging and genetic information we queried how genetic variation affects these stages of the AD cascade. We observed that females and APOE- ε4 homozygotes are more susceptible to the effects of Aβ on the primary accumulation of tau, with greater EC tau for a given level of Aβ . Furthermore, we observed for individuals who have rare risk variants in Triggering Receptor Expressed on Myeloid Cells 2 (TREM2) and/or APOE- ε4 homozygotes there was a greater spread of primary tau from the EC into the neocortex. These findings offer insights into the function of sex, APOE and microglia in AD progression, and have implications for determining personalised treatment with drugs targeting Aβ and tau.

Myo-inositol and total NAA in the hippocampus are linked to CSF tau pathology in cognitively normal older adults

INTRODUCTION

Understanding relationships between in vivo neurometabolic changes and Alzheimer's disease (AD) pathology in the hippocampus, a region vulnerable to early changes in AD, will support early diagnosis.

METHODS

Two studies using 1 H-MRS examined concentrations of myo-inositol (MI), total creatine (tCr) and total NAA (tNAA) in the hippocampus. The first study compared hippocampal metabolite concentrations in healthy young and older adults and the second study assessed relationships between hippocampal metabolites and cerebrospinal fluid (CSF) measurements of Aβ42, phosphotau 181 (pTau181), and total tau (t-Tau) while adjusting for demographic covariates and spectral characteristics (linewidth, signal- to-noise ratio) in a separate group of older adults ranging from cognitively normal (CN) to AD-dementia.

RESULTS

Hippocampal MI, but not tCr or tNAA, was increased in cognitively normal older versus young adults. Within the second older adult group, MI and tNAA, but not tCr, were linked to increases in CSF pTau181 and t-Tau, but not Aβ42.

DISCUSSION

Tau deposition in cognitively normal individuals is associated with biochemical changes related to glial reactivity and neural integrity in the hippocampus.

Drosophila appear resistant to trans-synaptic tau propagation

Alzheimer's disease is the most common cause of dementia in the elderly, prompting extensive efforts to pinpoint novel therapeutic targets for effective intervention. Among the hallmark features of Alzheimer's disease is the development of neurofibrillary tangles comprised of hyperphosphorylated tau protein, whose progressive spread throughout the brain is associated with neuronal death. Trans-synaptic propagation of tau has been observed in mouse models, and indirect evidence for tau spread via synapses has been observed in human Alzheimer's disease. Halting tau propagation is a promising therapeutic target for Alzheimer's disease; thus, a scalable model system to screen for modifiers of tau spread would be very useful for the field. To this end, we sought to emulate the trans-synaptic spread of human tau in Drosophila melanogaster. Employing the trans-Tango circuit mapping technique, we investigated whether tau spreads between synaptically connected neurons. Immunohistochemistry and confocal imaging were used to look for tau propagation. Examination of hundreds of flies expressing four different human tau constructs in two distinct neuronal populations reveals a robust resistance in Drosophila to the trans-synaptic spread of human tau. This resistance persisted in lines with concurrent expression of amyloid-β, in lines with global human tau knock-in to provide a template for human tau in downstream neurons, and with manipulations of temperature. These negative data are important for the field as we establish that Drosophila expressing human tau in subsets of neurons are unlikely to be useful to perform screens to find mechanisms to reduce the trans-synaptic spread of tau. The inherent resistance observed in Drosophila may serve as a valuable clue, offering insights into strategies for impeding tau spread in future studies.

Medial amygdalar tau is associated with anxiety symptoms in preclinical Alzheimer's disease

BACKGROUND

While the amygdala receives early tau deposition in Alzheimer's disease (AD) and is involved in social and emotional processing, the relationship between amygdalar tau and early neuropsychiatric symptoms in AD is unknown. We sought to determine whether focal tau binding in the amygdala and abnormal amygdalar connectivity were detectable in a preclinical AD cohort and identify relationships between these and self-reported mood symptoms.

METHODS

We examined n=598 individuals (n=347 amyloid-positive (58% female), n=251 amyloid-negative (62% female); subset into tau PET and fMRI cohorts) from the A4 Study. In our tau PET cohort, we used amygdalar segmentations to examine representative nuclei from three functional divisions of the amygdala. We analyzed between-group differences in division-specific tau binding in the amygdala in preclinical AD. We conducted seed-based functional connectivity analyses from each division in the fMRI cohort. Finally, we conducted exploratory post-hoc correlation analyses between neuroimaging biomarkers of interest and anxiety and depression scores.

RESULTS

Amyloid-positive individuals demonstrated increased tau binding in medial and lateral amygdala (F(4,442)=14.61, p=0.00045; F(4,442)=5.83, p=0.024, respectively). Across amygdalar divisions, amyloid-positive individuals had relatively increased regional connectivity from amygdala to other temporal regions, insula, and orbitofrontal cortex. There was an interaction by amyloid group between tau binding in the medial and lateral amygdala and anxiety. Medial amygdala to retrosplenial connectivity negatively correlated with anxiety symptoms (rs=-0.103, p=0.015).

CONCLUSIONS

Our findings suggest that preclinical tau deposition in the amygdala may result in meaningful changes in functional connectivity which may predispose patients to mood symptoms.

Digital cognitive assessments as low-burden markers for predicting future cognitive decline and tau accumulation across the Alzheimer's spectrum

Digital cognitive assessments, particularly those that can be done at home, present as low burden biomarkers for participants and patients alike, but their effectiveness in diagnosis of Alzheimer's or predicting its trajectory is still unclear. Here, we assessed what utility or added value these digital cognitive assessments provide for identifying those at high risk for cognitive decline. We analyzed >500 ADNI participants who underwent a brief digital cognitive assessment and Aβ/tau PET scans, examining their ability to distinguish cognitive status and predict cognitive decline. Performance on the digital cognitive assessment were superior to both cortical Aβ and entorhinal tau in detecting mild cognitive impairment and future cognitive decline, with mnemonic discrimination deficits emerging as the most critical measure for predicting decline and future tau accumulation. Digital assessments are effective in identifying at-risk individuals, supporting their utility as low-burden tools for early Alzheimer's detection and monitoring.

Personalized whole-brain neural mass models reveal combined Aβ and tau hyperexcitable influences in Alzheimer's disease

Neuronal dysfunction and cognitive deterioration in Alzheimer's disease (AD) are likely caused by multiple pathophysiological factors. However, mechanistic evidence in humans remains scarce, requiring improved non-invasive techniques and integrative models. We introduce personalized AD computational models built on whole-brain Wilson-Cowan oscillators and incorporating resting-state functional MRI, amyloid-β (Aβ) and tau-PET from 132 individuals in the AD spectrum to evaluate the direct impact of toxic protein deposition on neuronal activity. This subject-specific approach uncovers key patho-mechanistic interactions, including synergistic Aβ and tau effects on cognitive impairment and neuronal excitability increases with disease progression. The data-derived neuronal excitability values strongly predict clinically relevant AD plasma biomarker concentrations (p-tau217, p-tau231, p-tau181, GFAP) and grey matter atrophy obtained through voxel-based morphometry. Furthermore, reconstructed EEG proxy quantities show the hallmark AD electrophysiological alterations (theta band activity enhancement and alpha reductions) which occur with Aβ-positivity and after limbic tau involvement. Microglial activation influences on neuronal activity are less definitive, potentially due to neuroimaging limitations in mapping neuroprotective vs detrimental activation phenotypes. Mechanistic brain activity models can further clarify intricate neurodegenerative processes and accelerate preventive/treatment interventions.

Adenosine deficiency facilitates CA1 synaptic hyperexcitability in the presymptomatic phase of a knock in mouse model of Alzheimer's disease

The disease's trajectory of Alzheimer's disease (AD) is associated with and worsened by hippocampal hyperexcitability. Here we show that during the asymptomatic stage in a knock in mouse model of Alzheimer's disease (APPNL-G-F/NL-G-F; APPKI), hippocampal hyperactivity occurs at the synaptic compartment, propagates to the soma and is manifesting at low frequencies of stimulation. We show that this aberrant excitability is associated with a deficient adenosine tone, an inhibitory neuromodulator, driven by reduced levels of CD39/73 enzymes, responsible for the extracellular ATP-to-adenosine conversion. Both pharmacologic (adenosine kinase inhibitor) and non-pharmacologic (ketogenic diet) restorations of the adenosine tone successfully normalize hippocampal neuronal activity. Our results demonstrated that neuronal hyperexcitability during the asymptomatic stage of a KI model of Alzheimer's disease originated at the synaptic compartment and is associated with adenosine deficient tone. These results extend our comprehension of the hippocampal vulnerability associated with the asymptomatic stage of Alzheimer's disease.

Native-state proteomics of Parvalbumin interneurons identifies unique molecular signatures and vulnerabilities to early Alzheimer's pathology

Dysfunction in fast-spiking parvalbumin interneurons (PV-INs) may represent an early pathophysiological perturbation in Alzheimer's Disease (AD). Defining early proteomic alterations in PV-INs can provide key biological and translationally-relevant insights. We used cell-type-specific in-vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state PV-IN proteomes. PV-IN proteomic signatures include high metabolic and translational activity, with over-representation of AD-risk and cognitive resilience-related proteins. In bulk proteomes, PV-IN proteins were associated with cognitive decline in humans, and with progressive neuropathology in humans and the 5xFAD mouse model of Aβ pathology. PV-IN CIBOP in early stages of Aβ pathology revealed signatures of increased mitochondria and metabolism, synaptic and cytoskeletal disruption and decreased mTOR signaling, not apparent in whole-brain proteomes. Furthermore, we demonstrated pre-synaptic defects in PV-to-excitatory neurotransmission, validating our proteomic findings. Overall, in this study we present native-state proteomes of PV-INs, revealing molecular insights into their unique roles in cognitive resiliency and AD pathogenesis.

Meta-Analysis in Transgenic Alzheimer's Disease Mouse Models Reveals Opposite Brain Network Effects of Amyloid-β and Phosphorylated Tau Proteins

Background

Cognitive deficits observed in Alzheimer's disease (AD) patients have been correlated with altered hippocampal activity. Although the mechanism remains under extensive study, neurofibrillary tangles and amyloid plaques have been proposed as responsible for brain activity alterations. Aiming to unveil the mechanism, researchers have developed several transgenic models of AD. Nevertheless, the variability in hippocampal oscillatory alterations found in different genetic backgrounds and ages remains unclear.

Objective

To assess the oscillatory alterations in relation to animal developmental age and protein inclusion, amyloid-β (Aβ) load, and abnormally phosphorylated tau (pTau), we reviewed and analyzed the published data on peak power, frequency, and quantification of theta-gamma cross-frequency coupling (modulation index values).

Methods

To ensure that the search was as current as possible, a systematic review was conducted to locate and abstract all studies published from January 2000 to February 2023 that involved in vivo hippocampal local field potential recording in transgenic mouse models of AD.

Results

The presence of Aβ was associated with electrophysiological alterations that are mainly reflected in power increases, frequency decreases, and lower modulation index values. Concomitantly, pTau accumulation was associated with electrophysiological alterations that are mainly reflected in power decreases, frequency decreases, and no significant alterations in modulation index values.

Conclusions

In this study, we showed that electrophysiological parameters are altered from prodromal stages to the late stages of pathology. Thus, we found that Aβ deposition is associated with brain network hyperexcitability, whereas pTau deposition mainly leads to brain network hypoexcitability in transgenic models.