Brain energy expenses

Sid Chaudhury direwolfc at yahoo.com
Fri Sep 15 19:06:18 EST 2000


I don't think that brain dramatically increases its usage of energy.  Many
people in the thread have been comparing a brain at rest with a brain 'in
action'.  However, outside of a coma or similiar injury the brain is not
usually 'at rest'.  When we are not concentrating on a math problem or
something we are thinking of something else, our mind wanders in thoughts
and perceptions.  When we do concentrate on a problem, we direct our energy
to that problem, so in a sense we eliminate thought processes that are not
important to the current problem and spend more mental energy on the task at
hand.  But is generally known that the brain consumes large amounts of
energy when concentrating for long periods of time (such as MCAT exams).


""Richard L. Hall"" <rhall at webmail.uvi.edu> wrote in message
news:v0422080ab5d5eab54ec5@[146.226.154.76]...
> 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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