IUBio

Brain energy expenses

Richard L. Hall rhall at webmail.uvi.edu
Fri Sep 1 19:46:38 EST 2000


Vytautas writes:

>  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
>oposite.

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...

rlh



>Respectfully,
>Vytautas.

Richard L. Hall, Ph.D.
Comparative Animal Physiologist

University of the Virgin Islands
2 John Brewers Bay
St. Thomas, U.S.V.I. 00802

340-693-1386
340-693-1385 FAX

rhall at uvi.edu

"Live life on the edge...the view is always better"  rlh


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