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. 2017 Jun 7;38(8):1339–1353. doi: 10.1177/0271678X17708691

Figure 4.

Figure 4.

Distributions of ATP usage of different cellular mechanisms in gray matter (GM) and white matter (WM) of the human brain. The cellular components in GM represent housekeeping (HK), resting potential (RP), action potentials (AP), glutamate (and GABA) recycling (glu), presynaptic calcium (Ca), and synaptic transmission (ST). The cellular mechanisms in WM represent housekeeping (HK), resting potential (RP), neuron signaling (NS), action potentials in nerves (APnerve), and astrocyte calcium (glial Ca). Distributions of energy budget for (a) GM and (b) WM are shown in pie chart format where 100% represent the awake resting values of CMRglc(ox) in each tissue type. Nonsignaling costs (i.e. RP and HK) account for 30.5% and 82.3% of GM and WM demands respectively, suggesting that the total signaling costs in GM and WM are the remaining 69.5% and 17.7% portions, respectively. While the signaling costs in GM are assigned to energy needs of synaptic activity (i.e. ST, AP, Ca, glu), the signaling costs in WM are assigned to energy needs of 2.7 billion unmyelinated axons and 41.7 billion glial cells (i.e. NS, APnerve, Glial Ca). (see SI Text, Section B for details). (c) Bar plots of CMRglc(ox) for human brain PET data (dark gray38,55) and calculated budget results (gray). For calculation, signaling (“sig” in the bar plot) and nonsignaling (“Nonsig” in the bar plot) components in GM and WM are shown in absolute value, and the nonsignaling component in GM is double the energy demand in WM. See Figure S3 for further details of GM and WM behavior at different levels of neuronal activity.