Brain energy expenses
Richard L. Hall
rhall at webmail.uvi.edu
Fri Sep 1 19:46:38 EST 2000
> As I said, I
>could have understood wrong, but changing the usage level of the brain of
>course changes the energy consumtion. I can't see any logic in saying the
The brain functions continually with momentary increases and
decreases in regional energy consumption, but there is no evidence
that I know of that total brain expenditures of energy change
appreciably (within reasonable error). As a parable consider a
heating and cooling system that in winter expends more energy heating
and in summer expends more energy cooling...and the monthly bills are
just about the same.
Now if you put someone on speed you may see differences along with
parallel increases in total energy consumption. Most likely the
percentage of brain energy consumption would actually decrease due to
the FACT that the brain is only 2% of human body weight and that
muscle is much more metabolically active.
In normal function brain energy consumption must be essentially
constant. Why? There are no energy stores in the brain and
consequently the brain extracts energy moment by moment from the
blood. Since cardiac output to the brain does not increase during
intense calculations it is highly unlikely that total energy
consumption changes during extreme mentations. If brain consumption
did change in one region, there would be less energy available in
other areas due to blood shunting. Hence Richard Norman's opine has
some rationale although he may have pressed the point slightly. I
saw his response as a bit playful, and certainly inviting debate.
No one denies that regional fluctuations in energy consumption occur,
but total brain consumption of energy logically and experimentally
does not change significantly.
>The brain IS the most energy expensive organ, but not in a general context.
>I mentioned hard intelectual work wich requires comparatively huge amounts
>of energy, and the momentum energy consumtion is far greater in the brain
>than in the hearth. It is my point of view, but if you have made experiments
>with humans, that can prove the other way, or have any other proved
>information, say me and I will surrender to your opinion.
You have the irritating habit of treating a hypothesis as fact. You
can insist all you want, but YOU ARE MISTAKEN! Arm chair
speculations are fun, but it is not science. Read Peter Hochachka
(1981) Science 212:509-514. There are an abundance of papers on
blood flow to organ systems that also dispute your hypothesis...
Richard L. Hall, Ph.D.
Comparative Animal Physiologist
University of the Virgin Islands
2 John Brewers Bay
St. Thomas, U.S.V.I. 00802
rhall at uvi.edu
"Live life on the edge...the view is always better" rlh
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