I sent the following email to Richard Cytowic, the author of The Man Who Tasted Shapes, but it occurs to me that someone who reads my weblog might know the answer to my question:
Dear Dr. Cytowic:
In your book The Man Who Tasted Shapes, on page 146 you say that the brain "consumes 25% of all the energy used by the body." Elsewhere in the book -- I can't find the reference right now -- you suggest that this is some kind of upper evolutionary limit, that as a species it is not possible to survive a brain that uses more than 25% of our engery.
This reminds me somewhat of the limits on brain size of the newborn and the size of women's pelvises. That there are ranges in the size of newborn heads and women's birth canals is obvious, as is the consequence of too large a head or too small an opening.
Is the brain's energy usage subject to similar limitations? What problems would a person have if his or her brain demanded too much energy or if a particular part of the brain consumed too much? What are the practical consequences of this limit?
How was the 25% figure arrived at? Is there much variation among individuals? How is it meansured?
Anyone know the answers?
UPDATE: Cytowic replies:
The limits you cite have to do with physical scaling, which is exponential, after which things just "fall apart" (in simple terms). So a google search on "Brain energy metabolism" for a variety of articles and resources on this topic.
FURTHER UPDATE: Having read around in the various things his suggested search turned up, I think the one word answer to my question is OXIDATION. If the brain metabolizes more than a certain amount of oxygen, it sustains too much free-radical damage.