A universal scaling law between gray matter and white matter of cerebral cortex.
Level 5 - mechanism / opinion, no new human data
Level 5 by design analogy (theoretical mathematical modeling and comparative cross-species data).
PubMed 10792049 · doi:10.1073/pnas.090504197
What was done
A theoretical mathematical analysis was developed to explain the volumetric relationship between neocortical gray matter and white matter based on the principles of local cortical uniformity and optimal compact spatial arrangement of long-range axonal fibers. The predicted scaling exponent was tested against empirical brain volume measurements across multiple mammalian species spanning several orders of magnitude in brain size, including humans and nonhuman primates.
What was found
The model derived a scaling power law where white matter volume increases with gray matter volume according to an exponent of 4/3 minus a minor correction for cortical thickness. The theoretical scaling exponent accounted for empirical mammalian data across multiple orders of magnitude of brain size. The abstract reports no specific numerical fit statistics, correlation coefficients, or species counts.
Why it matters
It offers a fundamental biophysical explanation for why large mammalian brains require disproportionately larger volumes of white matter connectivity relative to gray matter processing tissue.
Limits
The abstract provides no exact sample sizes, species lists, or quantitative error margins. The model assumes general cortical uniformity and compact wiring minimization, which may not capture regional heterogeneity, specialized microcircuits, or species-specific developmental variations.
Cited by
- contradicts White matter makes up approximately 60% of the human brain, which is a higher proportion than in other species.