An energy budget for signaling in the grey matter of the brain

Anatomic and physiologic data are used to analyze the energy expenditure on different components of excitatory signaling in the grey matter of rodent brain. Action potentials and postsynaptic effects of glutamate are predicte d to consume much of the energy (47% and 34%, respectively), with the resti ng potential consuming a smaller amount (13%), and glutamate recycling usin g only 3%. Energy usage depends strongly on action potential rate-an increa se in activity of 1 action potential/cortical neuron/s will raise oxygen co nsumption by 145 mL/100 g grey matter/h. The energy expended on signaling i s a large fraction of the total energy used by the brain, this favors the u se of energy efficient neural codes and wiring patterns. Our estimates of e nergy usage predict the use of distributed codes, with less than or equal t o 15% of neurons simultaneously active, to reduce energy consumption and al low greater computing power from a fixed number of neurons. Functional magn etic resonance imaging signals are likely to be dominated by changes in ene rgy usage associated with synaptic currents and action potential propagatio n.