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Global and regional brain metabolic scaling and its functional consequences.

Karbowski J - BMC Biol. (2007)

Bottom Line: 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.The exception is white matter, the metabolism of which seems to scale with a standard specific exponent of -1/4.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Sloan-Swartz Center for Theoretical Neurobiology, Division of Biology 216-76, California Institute of Technology, Pasadena, CA 91125, USA. jkarb@its.caltech.edu

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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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).
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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).

Mentions: The cerebral cortex is a critical part of the brain responsible for integrating sensory information, and commanding behavioral and cognitive tasks. Regions of the cerebral cortex differ both in molecular detail and in biological function, which is manifested in a non-uniform distribution of neuronal activity and energy utilization throughout the cortex (Clarke and Sokoloff [5] and Additional file 1). However, despite this heterogeneity, values of the scaling exponents of the regional volume-specific glucose utilization rates on brain volume (CMRglc; glucose cerebral metabolic rate per brain region volume) are surprisingly homogeneous; they are either exactly or close to -0.15 (Figure 2, Table 1). Consequently, the average specific glucose utilization rate of the whole cerebral cortex also scales with brain volume with the exponent -0.15 ± 0.03 (Figure 2E), which is equivalent to the exponent 0.85 ± 0.03 for the metabolism of the entire cortical volume – the value close to that for the whole brain (Figure 1).


Global and regional brain metabolic scaling and its functional consequences.

Karbowski J - BMC Biol. (2007)

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).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1884139&req=5

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).
Mentions: The cerebral cortex is a critical part of the brain responsible for integrating sensory information, and commanding behavioral and cognitive tasks. Regions of the cerebral cortex differ both in molecular detail and in biological function, which is manifested in a non-uniform distribution of neuronal activity and energy utilization throughout the cortex (Clarke and Sokoloff [5] and Additional file 1). However, despite this heterogeneity, values of the scaling exponents of the regional volume-specific glucose utilization rates on brain volume (CMRglc; glucose cerebral metabolic rate per brain region volume) are surprisingly homogeneous; they are either exactly or close to -0.15 (Figure 2, Table 1). Consequently, the average specific glucose utilization rate of the whole cerebral cortex also scales with brain volume with the exponent -0.15 ± 0.03 (Figure 2E), which is equivalent to the exponent 0.85 ± 0.03 for the metabolism of the entire cortical volume – the value close to that for the whole brain (Figure 1).

Bottom Line: 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.The exception is white matter, the metabolism of which seems to scale with a standard specific exponent of -1/4.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Sloan-Swartz Center for Theoretical Neurobiology, Division of Biology 216-76, California Institute of Technology, Pasadena, CA 91125, USA. jkarb@its.caltech.edu

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.

Show MeSH
Related in: MedlinePlus