Global and regional brain metabolic scaling and its functional consequences

TL;DR

This study reveals that brain metabolic rates scale with brain volume in mammals, showing regional uniformity except for white matter, and that total brain metabolism scales more steeply than previously thought, impacting understanding of brain function.

Contribution

It provides empirical evidence that brain metabolic scaling exponents are consistent across regions and exceeds the classical 3/4 power law, offering new insights into neurophysiological scaling laws.

Findings

Volume-specific metabolic rates scale with brain volume at an exponent of about -0.15.

White matter metabolism scales with an exponent of -1/4.

Total brain oxygen and glucose consumption scale with brain volume at approximately 0.86.

Abstract

Background: Information processing in the brain requires large amounts of metabolic energy, the spatial distribution of which is highly heterogeneous reflecting complex activity patterns in the mammalian brain. Results: Here, it is found based on empirical data that, despite this heterogeneity, the volume-specific cerebral glucose metabolic rate of many different brain structures scales with brain volume with almost the same exponent around -0.15. The exception is white matter, the metabolism of which seems to scale with a standard specific exponent -1/4. The scaling exponents for the total oxygen and glucose consumptions in the brain in relation to its volume are identical and equal to $0.86\pm 0.03$, which is significantly larger than the exponents 3/4 and 2/3 suggested for whole body basal metabolism on body mass. Conclusions: These findings show explicitly that in mammals (i) volume-specific scaling exponents of the cerebral energy expenditure in different brain parts are approximately constant (except brain stem structures), and (ii) the total cerebral metabolic exponent against brain volume is greater than the much-cited Kleiber's 3/4 exponent. The neurophysiological factors that might account for the regional uniformity of the exponents and for the excessive scaling of the total brain metabolism are discussed, along with the relationship between brain metabolic scaling and computation.