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Abstract
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 predicted to consume much of the energy
(47% and 34%, respectively), with the resting potential consuming a smaller amount
(13%), and glutamate recycling using only 3%. Energy usage depends strongly on action
potential rate--an increase in activity of 1 action potential/cortical neuron/s will
raise oxygen consumption by 145 mL/100 g grey matter/h. The energy expended on signaling
is a large fraction of the total energy used by the brain; this favors the use of
energy efficient neural codes and wiring patterns. Our estimates of energy usage predict
the use of distributed codes, with <or=15% of neurons simultaneously active, to reduce
energy consumption and allow greater computing power from a fixed number of neurons.
Functional magnetic resonance imaging signals are likely to be dominated by changes
in energy usage associated with synaptic currents and action potential propagation.