Comment by gwern
10 years ago
The resting metabolism is very high, because the brain is expensive to build and run. But it's not much more expensive to run on one task rather than another. This is one of the major flaws in the blood glucose theory of willpower as discussed by Kurzban: some additional sugar can't be 'gasoline' for the brain because the brain doesn't use up that much more energy working on something than not working on something. (As one might guess from the basal rate of 20%! Not much room left. Or from thermodynamics: when you walk or do physical exercise, you can feel your body heat up from how much energy you are burning. Your head doesn't heat up while doing arithmetic.)
This assumes that fatigue is merely a thermodynamics problem. Fatigue could also be caused by the depletion of chemicals which take time to regenerate. Such effects would not be captured when looking at energy usage alone.
You assume merely logical work in the pre-frontal cortex. As soon as emotions come to play the body get's involved because heart-rate, body-temperature etc. is influenced.
And I don't mean emotions like anger, but less visible ones like disgust, which seem to be triggered during procrastinating.