IC–P–024: MRI, MRS and clinical correlates in posterior cortical atrophy and typical Alzheimer's disease
Bibliographic record
Abstract
Posterior cortical atrophy (PCA) is a rare, slowly progressive, dementia characterized by the development of early visuospatial and visual perceptual deficits. PCA is often considered the 'visual' variant of Alzheimer's disease (AD), although unlike typical AD episodic memory loss does not occur until later in the disease. To compare the patterns of cerebral atrophy on MRI and neurochemistry on MRS in a large group of subjects with PCA to typical AD, and to assess correlations between clinical and MRI features of PCA. Voxel–based morphometry was used to assess regional patterns of grey matter atrophy on MRI in 38 subjects with PCA, compared to 38 age and gender matched subjects with typical AD and 38 matched controls. An optimized version of VBM was applied using customized templates and prior probability maps. Detailed clinical data was assessed in all subjects. Proton MR spectroscopy (1H MRS) data was analyzed in a subset of 19 subjects with PCA, 21 subjects with AD, and 22 controls. The PCA patients had early preservation of insight and episodic memory. Features of Gerstmann and Balint's syndromes were common. PCA showed a posterior pattern of loss on MRI, affecting occipital, parietal and posterior temporal lobes, compared to controls (Figure). The pattern was bilateral, but more severe on the right. The typical AD subjects showed loss predominantly in the medial temporal lobes and parietal lobes bilaterally compared to controls (Figure). The PCA subjects showed more atrophy in the primary visual cortex, visual association cortex, and right parietal lobe, than typical AD. In contrast, typical AD showed more atrophy in the left hippocampus than PCA. Single–voxel 1H MRS spectra obtained from the posterior cingulate gyrus were consistent with loss of neuronal integrity and glial activation in both PCA and AD compared to controls, with no difference between the two groups. The patterns of atrophy on MRI in typical AD and PCA differ. The right hemisphere dominance, prominent involvement of the primary visual and visual association cortex, and sparing of the left hippocampus in PCA, suggest that it should be considered a distinct entity from typical AD.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
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".