Where do the brain's 20 watts go? · Grey Matter

Mostly into pumping ions back after signals.

Where do the brain's 20 watts go?

Mostly into pumping ions back after signals. In the budget Attwell and Laughlin built for rodent grey matter, the largest items are the currents through glutamate receptors at synapses and the sodium entry of action potentials, both repaid by the sodium-potassium pump, with smaller shares for keeping the resting potential, recycling transmitter and clearing calcium. Housekeeping that any cell needs (making proteins and lipids, maintaining the cytoskeleton) takes a smaller part. Because demanding tasks change the whole brain's consumption by only a few per cent, most of the 20 W pays for ongoing activity, whatever the person is doing.