Mapping amyloid plaques and brain connectivity in Alzheimer's

How many years before cognitive symptoms arise does amyloid-β accumulation and plaque formation typically begin?

It typically begins 20 to 30 years before cognitive symptoms arise.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How is the Default Mode Network (DMN) functionally characterized in relation to ongoing brain activity?

The DMN consists of frontal and parietal midline structures with high metabolic activity coupled by high, synchronous ongoing functional connectivity.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What are the two primary hypotheses proposed to explain the progression of amyloid-β pathology in relation to brain networks?

First, neurodegeneration progresses along network boundaries to functionally connected areas. Second, pathology is accelerated by local stress from lifetime metabolic activity and connectivity.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What dual, seemingly contradictory relationships exist between amyloid-β pathology and intrinsic functional connectivity?

At a local level, amyloid-β reduces intrinsic connectivity; however, globally, a positive relationship exists where areas with high baseline connectivity show greater amyloid-β accumulation.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How does ignoring the positive baseline correlation between amyloid-β and connectivity confound measures of disease impact?

High-connectivity patients accumulate more amyloid-β, which reduces connectivity; ignoring this baseline masks the reduction, making the negative impact appear less severe than it actually is.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Why might previous Alzheimer's disease research have disproportionately focused on the Default Mode Network?

The DMN has the highest baseline connectivity and amyloid-β accumulation, making pathology-related connectivity changes easiest to detect there compared to other affected networks.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How was prodromal Alzheimer's disease defined for patient recruitment in this study?

It was defined by the presence of mild cognitive impairment coinciding with at least one biological supportive sign of Alzheimer's, such as significant cortical PiB uptake.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What PiB-PET standardized uptake value ratio (SUVR) cutoff was used to define PiB positivity?

A neocortical standardized uptake value ratio cutoff of 1.15 was used to determine PiB positivity.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What chemical compound is represented by Pittsburgh Compound B (PiB) in PET imaging?

PiB represents the radioligand N-methyl-11C-2-(4-methylaminophenyl)-6-hydroxybenzothiazole.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Which brain region was used as the reference standard for normalizing individual PiB-PET voxel values?

All voxel values were normalized to the cerebellar vermis.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What were the resting-state fMRI exclusion criteria for excessive head motion?

Head motion was restricted to a cumulative translation or rotation of under 3 mm or 3 degrees, and a mean point-to-point motion of under 0.15 mm or 0.1 degrees.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Which analytical framework was used to extract intrinsic connectivity networks from the concatenated fMRI data?

Spatially independent component analysis (ICA) using the infomax algorithm and ICASSO was used to decompose the fMRI data.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Which intrinsic networks were selected as a priori networks of interest, and which was used as a control?

The anterior and posterior DMN, three attention networks, and the salience network were networks of interest, while the primary auditory network was the control.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Which specific regions showed reduced functional connectivity in prodromal AD patients using conventional two-sample t-tests?

Regionally reduced connectivity was observed only in the posterior parietal regions of the posterior DMN and the right attention networks.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How did PiB uptake vary across different intrinsic networks in the prodromal AD group?

Patients showed a gradient of plaque deposition across networks, with the highest median PiB uptake occurring in the posterior DMN.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What is the global spatial correlation (rGLOBAL) measure, and what does it reveal about amyloid-β in AD patients?

rGLOBAL measures the spatial correlation between PiB-uptake and connectivity across entire networks, showing a robust positive correlation in heteromodal networks.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Did healthy control subjects exhibit a positive global spatial correlation (rGLOBAL) between amyloid-β and connectivity?

No, global spatial correlations in the healthy control group did not statistically deviate from zero.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Why was the primary auditory network excluded from having a significant spatial correlation (rGLOBAL) in AD patients?

Sensory and motor cortical areas, including the auditory cortex, are relatively spared from plaque deposition during early Alzheimer's disease stages.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What was the relationship between overall network PiB-uptake and the strength of rGLOBAL in AD patients?

Average network PiB-uptake correlated positively with rGLOBAL, meaning networks with higher plaque loads displayed stronger positive spatial correlations.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What does rLOCAL measure using the searchlight approach?

rLOCAL measures the local spatial correlation between amyloid-β and connectivity in small, homogeneous neighborhoods (6-mm radius) around each voxel.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What mathematical technique was used to isolate the local negative impact of amyloid-β (rLOCAL) from the global positive correlation (rGLOBAL)?

Gram-Schmidt orthogonalization was used to decorrelate PiB-uptake and connectivity values across the entire network.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What was the searchlight radius and neighbor constraint for the local spatial correlation analysis?

The searchlight used a 6-mm radius (~100 voxels) and excluded voxels with fewer than 25 neighbors in their network to ensure reliable boundary estimates.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What did the local spatial correlation (rLOCAL) reveal about the impact of amyloid-β in patients?

It revealed a strong negative correlation between plaques and connectivity across heteromodal networks, peaking in the high-connectivity network cores.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How did the median rLOCAL values compare between patients and controls across the networks?

Patients showed median rLOCAL values significantly below zero across all heteromodal networks, whereas controls showed no deviation from zero.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How did local overall amyloid-β pathology levels relate to the severity of local connectivity reductions?

Local regions with higher overall plaque load exhibited a stronger negative impact of amyloid-β on functional connectivity.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How does accounting for the baseline positive plaque-connectivity correlation affect the sensitivity of detecting functional AD deficits?

It substantially increases the sensitivity of detecting negative amyloid-β impacts compared to conventional direct group comparisons of connectivity.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How do the study's findings of positive rGLOBAL correlations support the 'nodal stress' hypothesis of AD?

They suggest that regions with high lifetime functional connectivity and metabolism are selectively vulnerable to accelerated amyloid-β accumulation.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How many participants were excluded from the final analyses, and for what reason?

Five participants (one patient and four controls) were excluded because of corrupted PET imaging data.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What subsampling approach did the authors use to control for unequal group sizes?

They repeatedly selected a random, size-matched patient subgroup to re-compute statistics and ensure differences were not driven by group size imbalance.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

How does the extended network degeneration model apply the findings to atypical variants of Alzheimer's disease?

It proposes that the same network-spreading and local-decline mechanisms occur, but initiate in different brain networks first.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What temporal staging difference does the model suggest between network cores and peripheries?

Network cores show late-stage negative connectivity impacts earlier, while peripheral regions may remain unaffected or show early-stage positive correlations.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Why is within-subject correlation analysis of pathology and connectivity superior to between-subject designs?

It avoids confounding by general disease state and allows direct estimation of amyloid's functional impact at the single-subject, single-network level.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

Which three covariates of no interest were regressed out of the median PiB and spatial correlation data?

Grey matter density (atrophy), age, and gender were regressed out to control for potential confounding.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What medical exclusion criteria were applied to prevent non-Alzheimer's cognitive confounds in participants?

Exclusion criteria included other neurological, psychiatric, or systemic diseases (like stroke, depression, or alcoholism) or remarkable structural MRI lesions.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified

What did the authors propose as a crucial longitudinal step to validate their cross-sectional network degeneration model?

They highlighted the need for longitudinal studies to track the temporal progression of network impairments proposed by the model.

Source: Within-patient correspondence of amyloid-β and intrinsic network connectivity in Alzheimer's disease · DOI · quote verified