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Old 06-02-2008, 12:55 PM
threemae threemae is offline
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Join Date: Jun 1999
Location: Philadelphia, PA
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I'm sorry, I cannot answer this question entirely, but energy requirements for the brain do vary considerably on a small-scale as activity paterns change. This is the basis for fMRI imaging; basically, as a certain part of the brain becomes more active blood-flow to that area increases (actually overcompensates) and this is the basis for the contrast of a functional MRI scan.

http://en.wikipedia.org/wiki/Functio...onance_imaging

This is on a sort of 10-15 second timescale; I cannot provide a good answer for longer time scales or tell you if it's calorically significant or if so by how much.
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