What is the energy consumption of the brain, and is there a difference in consumption when waking and sleeping?

  • $\begingroup$ Do you mean the activity as visible in an EEG? Because the brain mainly uses up energy as far as I know. $\endgroup$
    – skymningen
    Apr 3 '14 at 11:20

I assume that you mean energy consumption.

Talking in round numbers the daily energy requirement of a sedentary human is 2,500 kcal. It's usually said that the brain uses 20% of this energy.

What does this mean in terms of power consumption?

500 kcal = 500 x 1000 x 4.2 J  -[1]
24 h = 24 x 60 x 60 s          -[2]   

1 W = 1 J/s

therefore brain power  = [1]/[2] = approximately 24 W

Most of the energy consumed by the brain is used in maintaining membrane potentials so energy is used continuously. I would think that there will be very little difference between waking and sleeping.

  • $\begingroup$ One ref for the breakdown of energy costs: Laughlin, S. (2001). Energy as a constraint on the coding and processing of sensory information. Current Opinion in Neurobiology, 11(4):475-480. $\endgroup$
    – Memming
    Apr 3 '14 at 13:22
  • $\begingroup$ The cortical activity pattern is measurably different between rest and sleep states. I think there would be measurable differences. $\endgroup$
    – Memming
    Apr 3 '14 at 13:23
  • $\begingroup$ Adding to this: There is a difference of active vs. inactive brain regions in terms of energy consumption. This is used in PET (positron emission tomography) scans. Here you enrich radioactive glucose in the regions which are more active (=need more energy) and make them visible. $\endgroup$
    – Chris
    Apr 3 '14 at 13:27
  • 1
    $\begingroup$ I'm not denying that brain activity will require more energy (to restore membrane potential), I'm just dubious that it will be a very big difference (the brain is active during sleep too). I await an answer that provides evidence about this. $\endgroup$
    – Alan Boyd
    Apr 3 '14 at 13:43

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