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Comparative Study
. 2007 May 9:5:18.
doi: 10.1186/1741-7007-5-18.

Global and regional brain metabolic scaling and its functional consequences

Jan Karbowski  1
Affiliations
Comparative Study

Global and regional brain metabolic scaling and its functional consequences

Jan Karbowski. BMC Biol. .

Abstract

Background: Information processing in the brain requires large amounts of metabolic energy, the spatial distribution of which is highly heterogeneous, reflecting the complex activity patterns in the mammalian brain.

Results: In this study, it was 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 of -1/4. The scaling exponents for the total oxygen and glucose consumptions in the brain in relation to its volume are identical, at 0.86 +/- 0.03, which is significantly larger than the exponents 3/4 and 2/3 that have been suggested for whole body basal metabolism on body mass.

Conclusion: 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.

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Figures

Figure 1
Figure 1
Scaling of the total basal cerebral metabolism with brain volume. The least-square fit line for the log – log plot yields the following. (A) For the total oxygen consumption rate, the scaling exponent was 0.86 ± 0.04 (y = 0.86x - 1.02, R2 = 0.989, p < 10-4, n = 7), and its 95% confidence interval was 0.75 to 0.96. (B) For the total glucose utilization rate, an identical exponent 0.86 ± 0.03 was found (y = 0.86x - 0.09, R2 = 0.994, p < 10-4, n = 10) and its 95% confidence interval was 0.80 to 0.91.
Figure 2
Figure 2
Scaling of the volume-specific glucose utilization rate, CMRglc, in cerebral cortex with brain volume. The specific metabolic scaling exponent, corresponding to the slope of the regression line, had the following values: (A) -0.12 for visual cortex (y = -0.12x + 0.02); (B) -0.15 for parietal cortex (y = -0.15x + 0.01); (C) -0.15 for sensorimotor cortex (y = -0.15x + 0.02); (D) -0.15 for temporal cortex (y = -0.15x + 0.07). (E) Average glucose utilization rate of the entire cerebral cortex yielded the specific exponent -0.15 (y = -0.15x + 0.03).
Figure 3
Figure 3
Scaling of the volume-specific glucose utilization rate in subcortical gray matter with brain volume. The specific metabolic scaling exponent had the following values: (A) -0.15 for thalamus (y = -0.15x + 0.03); (B) -0.14 for hippocampus (y = -0.14x - 0.13), which represents limbic structures; (C) -0.15 for caudate (y = -0.15x + 0.02), which represents basal ganglia; (D) -0.15 for cerebellum (y = -0.15x - 0.09).
Figure 4
Figure 4
Scaling of the volume-specific glucose utilization rate in white matter with brain volume. (A) Corpus callosum metabolism yielded the exponent -0.23 (y = -0.23x - 0.45), and (B) internal capsule had a similar exponent -0.24 (y = -0.24x - 0.41).
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