Long‐Term Effects of Severe COVID‐19 on the Hippocampus: A 7T MRI Comparison with Alzheimer’s Disease
Bibliographic record
Abstract
BACKGROUND: Post-COVID cognitive dysfunction is a critical extrapulmonary complication of COVID-19. A previous post-mortem study has shown neuroinflammation and loss of hippocampal neurogenesis in COVID-19 case. High-resolution 7T MRI enables detailed assessment of hippocampal subfields, providing insights into disease process and early changes. This study explores hippocampal subfield volumes using 7T MRI in Alzheimer's disease (AD) and post-COVID-19 conditions, examining potential similarities in brain degeneration. METHOD: We analysed hippocampal subfield volumes in four groups: (1) AD patients with confirmed CSF-Aβ status (n = 32), (2) individuals recovering from mild COVID-19 >6 months post-infection (Cv, n = 13), (3) individuals recovering from severe COVID-19 with ICU admission >6 months prior (ICU-Cv, n = 9), and (4) age-matched healthy controls (HC, n = 29). Cognitive assessments, including the Montreal Cognitive Assessment (MOCA), were performed within these groups. RESULT: AD patients exhibited significant atrophy in multiple hippocampal subfields, including the entorhinal cortex (ERC), dentate gyrus (DG), hippocampal tail (Tail), and cornu ammonis (CA), compared to HC and Cv. In ICU-Cv, ERC volume was significantly reduced compared to HC, while Cv showed no subfield differences from HC. AD patients had smaller ERC and DG volumes compared to ICU-Cv. Average MOCA scores were lowest in AD (13.52), significantly lower than HC (27.58), Cv (27.24), and ICU-Cv (24.78). ICU-Cv showed a trend toward lower MOCA scores than HC, but differences were not significant. MOCA scores for ICU-Cv were significantly lower than Cv. AD patients performed worse than ICU-Cv on multiple cognitive domains, including verbal fluency (vegetable and animal naming), working memory (the longest digit span backward), visuospatial function (Benson figure copy), and episodic memory (total story recall and verbatim scoring). ICU-Cv patients also scored lower on Benson figure copy (p = 0.048) and vegetable naming (p = 0.047) compared to HC. CONCLUSION: ERC, a key gateway for neocortical input to the hippocampus, is particularly susceptible in the early stages of AD, contributing to deficits in episodic memory and spatial navigation. In ICU-Cv patients, we found selective atrophy of the ERC. This finding suggests that severe COVID-19 may lead to targeted neurodegeneration through mechanisms distinct from AD but potentially overlapping in terms of hypoperfusion, inflammation, and metabolic stress.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".