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I'm wondering about the human brain's energy consumption at different "uses".
If you use a muscle it uses more energy than if you hold it still. Is the brain like this, or is it "always on" like a kidney or heart? Does it use more energy when you're actively learning or solving a problem? Do intelligent people have more energy hungry brains?
If I'm to sum into a single question, is the brain's energy consumption largely static (individually and over the population), or does it vary?
This question covers only the sleeping aspect and the top answer doesn't source is conclusion of static energy use. I'm still largely interested in differences while learning or problem solving and differences between intelligent and average people.