THE METABOLIC COST OF NEURAL INFORMATION

We derive experimentally based estimates of the energy used by neural mechanisms to code known quantities of information. Biophysical measur ements from cells in the blowfly retina yield estimates of the ATP req uired to generate graded (analog) electrical signals that transmit kno wn amounts of information. Energy consumption is several orders of mag nitude greater than the thermodynamic minimum. It costs 10(4) ATP mole cules to transmit a bit at a chemical synapse, and 10(6) - 10(7) ATP f or graded signals in an interneuron or a photoreceptor, or for spike c oding. Therefore, in noise-limited signaling systems, a weak pathway o f low capacity transmits information more economically, which promotes the distribution of information among multiple pathways.