Individual variability in the size and organization of the human arcuate nucleus of the medulla
Bibliographic record
Abstract
Abstract The arcuate nucleus (Arc) of the medulla is found in almost all human brains and in a small percentage of chimpanzee brains. It is absent in the brains of other mammalian species including mice, rats, cats and macaque monkeys. The Arc is classically considered a precerebellar nucleus, presumably motor in function. However, several studies have found aplasia of the Arc in babies who died of SIDS (Sudden Infant Death Syndrome) suggesting a very different role for the Arc in the control of respiration. Aplasia of the Arc, however, has also been reported in adults suggesting that it is not critical for survival. We have examined the Arc in closely-spaced Nissl-stained sections in human cases to acquire a better understanding of the degree of variability of its size and location in adults. We have also examined immunostained sections to develop a neurochemical profile of this nucleus. Our data suggest that the Arc consists of rostral and caudal subdivisions. There is some degree of left-right asymmetry in Arc position, size and shape at all rostro-caudal levels. Neurons in the Arc express calretinin (CR), neuronal nitric oxide synthase (nNOS) and nonphosphorylated neurofilament protein (NPNFP) but not calbindin (CB) or parvalbumin (PV). There is also immunostaining for GAD and GABA receptors suggesting inhibitory input to Arc neurons. We support the classical idea of the Arc as a precerebellar nucleus; its absence in SIDS cases may not be the cause of death but rather a correlate of other brainstem abnormalities.
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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 | 0.002 |
| 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".