How tau buildup shapes brain networks in dementia

How do tau filaments differ structurally and in isoform composition between Alzheimer's disease (AD) and progressive supranuclear palsy (PSP)?

AD is characterized by paired helical filaments containing both three-repeat (3R) and four-repeat (4R) tau, whereas PSP is characterized by straight filaments containing predominantly 4R tau.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI

Where do pathological tau deposits initially arise and spread in Alzheimer's disease versus progressive supranuclear palsy?

In AD, tau pathology begins in the transentorhinal cortex and spreads to limbic and cortical regions. In PSP, it is most prominent early on in the midbrain and deep brain nuclei before reaching cortical regions in advanced stages.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI

What in vivo imaging tool did the researchers use to estimate the regional burden of tau pathology in patients?

They used PET (positron emission tomography) imaging with the radioligand 18F-AV-1451.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How effectively does the 18F-AV-1451 PET ligand distinguish between Alzheimer's disease and PSP?

It effectively distinguishes between the two diseases based on both the intensity and the regional distribution of its binding potential.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

According to the trans-neuronal spread hypothesis of tau propagation, what relationship should exist between a node's connectivity and its tau burden?

Regions that are more strongly interconnected (nodes with a larger weighted degree) would accrue more tau pathology.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

If hub vulnerability to tau is driven primarily by high metabolic demands, how would this manifest in graph-theoretical metrics?

It would manifest as a positive relationship between tau burden and the participation coefficient of a node, which is closely correlated with metabolic activity.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

According to the trophic support hypothesis, how would a vulnerability to tau accumulation relate to the clustering coefficient of a brain region?

There would be a negative relationship, meaning nodes with less tightly clustered connectivity patterns (lower clustering coefficient) would show higher tau accumulation due to more vulnerable trophic supply.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What were the recruitment criteria for the Alzheimer's disease patient cohort in this study?

The cohort included 17 patients: 10 with a clinical diagnosis of probable Alzheimer's dementia, and 7 with a clinical diagnosis of mild cognitive impairment (MCI) and a positive amyloid PET scan.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

Why did the researchers choose to include patients with mild cognitive impairment (MCI) in the Alzheimer's disease cohort?

They included MCI patients to ensure the largest possible variability in tau burden within the Alzheimer's disease group.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What was the primary advantage of using multi-echo independent component analysis (ME-ICA) to preprocess the resting-state fMRI data?

ME-ICA classifies BOLD and non-BOLD signals based on echo-time dependence, providing an optimal way to correct for movement-related and non-neuronal noise, which is crucial when comparing clinical groups.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What brain region was used as the reference tissue to normalize 18F-AV-1451 binding potential, and why?

The superior cerebellum was used because it is considered to have no tau pathology in either progressive supranuclear palsy or Alzheimer's disease.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How is the "weighted degree" of a node defined in this study's graph theoretical analysis?

It is a measure of the total number and strength of functional connections involving each node.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What does the "weighted participation coefficient" of a node measure?

It measures the proportion of a node's functional connectivity that involves other nodes outside of its own community structure.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What does the clustering coefficient of a node signify in a brain network?

It represents the fraction of triangular connections formed by a node, meaning how many of its neighboring nodes are also connected to each other.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What relationship did the study find between 18F-AV-1451 binding (tau) and weighted degree in Alzheimer's disease?

A strong positive correlation was observed across all network thresholds, meaning the most highly connected nodes accumulated more tau pathology, supporting the trans-neuronal spread hypothesis.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

Did the progressive supranuclear palsy (PSP) group show a positive correlation between tau pathology and weighted degree?

No, there was no consistent relationship between tau burden and weighted degree in the PSP group.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How did the researchers rule out the possibility that the correlation between tau and degree in AD was driven solely by the default mode network (DMN)?

They repeated the analysis excluding the DMN nodes and found that the positive relationship remained strong, and was also present in 9 of 10 individual intrinsic networks examined.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

Why did the researchers evaluate 'nodal connectivity strength' in addition to weighted degree, and what did it show?

They evaluated it to ensure the results were not biased by the thresholding of the graphs, and it successfully replicated the positive correlation with tau in AD.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

Which models of hub vulnerability were supported by the findings in progressive supranuclear palsy (PSP)?

The findings in PSP supported models of hub vulnerability due to high metabolic demand and lack of trophic support, but not trans-neuronal spread.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How did increasing tau burden differentially affect average cortical functional connection strength in AD versus PSP?

In AD, connection strength decreased as tau burden increased. In PSP, connection strength increased in line with subcortical tau burden.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How did local tau burden correlate with node-wise changes in functional connectivity (weighted degree) in patients with Alzheimer's disease?

There was a significant negative correlation, indicating that higher local tau deposition leads to a local drop in functional connectivity strength.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What mechanism is proposed to explain why cortical functional connections increase in strength with higher subcortical tau burden in progressive supranuclear palsy (PSP)?

Subcortical pathology in PSP disrupts long-range pathways, necessitating a compensatory increase in the relative strength of short-range, indirect cortico-cortical connections.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How does global disease burden affect closeness centrality (and path length) in AD versus PSP?

Increasing disease burden led to decreased closeness centrality (longer path length) in PSP, but increased closeness centrality (shorter path length) in AD.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI

Although Alzheimer's disease showed increased closeness centrality with disease burden, what was the cost to local network structure?

It came at the cost of lower local efficiency, indicating that local networks became less robust to disruption.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How does average betweenness centrality change with disease progression in AD compared to PSP?

It decreases with tau burden in AD (representing reduced reliance on cortical-only paths) but increases with tau burden in PSP (representing greater reliance on indirect trans-cortical routes).

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What graph-theoretical finding in PSP explains the characteristic 'cognitive slowing' seen in subcortical dementias?

The increase in average path length (lower closeness centrality) due to information taking highly indirect, cortico-cortical routes rather than direct subcortical routes.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

How does increasing tau burden differentially affect the participation coefficient in AD compared to PSP?

Increasing tau burden leads to an increase in participation in AD, but causes a marked decrease in the participation coefficient in PSP.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What regional pattern of eigenvector centrality changes was observed as global tau burden increased in Alzheimer's disease?

The functional influence (eigenvector centrality) of frontal regions increased, while the influence of occipital regions decreased.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What biological explanation is proposed for why trans-neuronal tau propagation might be less prominent or slower in progressive supranuclear palsy (PSP)?

The straight 4R tau filaments in PSP may propagate less easily or require higher local concentrations to trigger aggregation compared to AD tau.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What is a limitation of using multi-echo fMRI for analyzing subcortical and brainstem connectivity in progressive supranuclear palsy?

Multi-echo fMRI may suffer from a poor signal-to-noise ratio in deep brain structures compared to cortical areas.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI

What does the hub compensation theory predict about functional connectivity in early versus late Alzheimer's disease?

In early disease (low tau), hubs compensate for damage by hyper-activating (showing higher connectivity), but this mechanism eventually breaks down (connectivity falls) as tau burden increases.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What is the main methodological limitation of using cross-sectional data to model the relationship between tau burden and functional connectivity?

It assumes a uniformity of disease effect across individuals, which lacks the causal validation that longitudinal or interventional studies would provide.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

What is a known limitation of the PET ligand 18F-AV-1451 in non-Alzheimer's disease tauopathies?

Its molecular binding target is disputed because of elevated 'off-target' binding in the basal ganglia of healthy controls and in non-tau (TDP-43) disorders.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI

Why might 18F-AV-1451 PET imaging underestimate the toxic effects of tau on synaptic plasticity?

It primarily detects aggregated tau in neurofibrillary tangles, but does not measure oligomeric or extracellular tau, which are believed to be the most toxic forms.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified

Why did the study focus on the top 1-10% of strongest connections, and what limitation does this impose?

It focused on strong connections to minimize noise and false positives, but this potentially misses important functional changes occurring in weak or medium-strength connections.

Source: Tau burden and the functional connectome in Alzheimer's disease and progressive supranuclear palsy · DOI · quote verified