IC‐P‐144: Assessment of structural differences in normal aging and Alzheimer's disease: Quantitative and qualitative differences using subjects from the Alzheimer's Disease Neuroimaging Initiative (ADNI)
Bibliographic record
Abstract
It has been suggested that the changes encountered in AD are largely an amplification of lesser but similar changes constituting “cognitive aging”. New automated techniques and large sample sizes allow for a more precise examination of between group morphological differences. We propose to examine whether AD and “normal aging” are only quantitatively different with respect to their cortical thickness and white and gray matter density “signature”, or differ in fundamental ways between the two groups. T1 volumes (196 elderly controls, 160 age-matched AD subjects; age range 57-91, mean = 76) were acquired from the ADNI database, and processed at the Montreal Neurological Institute by a fully automated analysis pipeline. The resultant tissue classification volumes were used in the voxel-based morphometry (VBM) analysis; cortical surfaces were used to extract cortical thickness values. Statistical analysis consisted regressing cortical thickness or tissue density, onto age and diagnostic group. Regression of cortical thickness onto diagnostic group, demonstrated significant widespread cortical thinning in the AD group in all lobes, with relative sparing of sensory and motor areas. The largest absolute losses were seen bilaterally in middle temporal gyri, insulae, and along with the left supramarginal gyrus (> ¼ mm loss), and in the medial temporal cortex bilaterally (> ½ mm loss). Normal elderly subjects showed additional age-related thinning in primary sensory and motor areas, including primary visual and auditory cortices. The VBM analyses found that differences within the medial temporal structures were primarily quantitative in nature, with both groups showing significant bilateral hippocampal atrophy, in addition to a significant white matter loss in three regions: periventricular, callosal, and adjacent to the hippocampus. AD-related morphological changes are both quantitatively and qualitatively different from normal aging. Tissue loss within frontal and temporal association cortex, in addition to that observed within and adjacent to the hippocampus, reflects an exacerbation of normal age-related changes. Conversely, tissue loss within the insulae is only seen in AD, whereas significant thinning within the primary sensory and motor cortices is reflective of normal aging.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".