Brain Use

Krakatoa stephan at nospam.ucla.edu
Thu Dec 24 04:12:07 EST 1998


In article <75rna7$649$1 at nnrp1.dejanews.com>, sgarriott at my-dejanews.com wrote:

> I know that this may be a strange question, but I've always heard that old
> cliché that human beings on the average only use about ten percent of their
> brains. My kids and I were talking about that, them asking what the other
> ninety percent was for. But I guess my question is: What do "people" (namely,
> those who have some kind of background in neuroscience) mean when they say
> that we only use ten percent? Does that mean that there are actually places
> in everyone's brain that remain dormant, never, or hardly ever, used? Or does
> it mean that at any one time we have ten percent of our brain capacity
> functioning? It could also be some other perspective that I hadn't
> considered. It could also be just something that people say, but it's more
> mythic than anything else.
> 
> Anyone's ideas on this or a source I could consult for this would be
> appreciated.
> 
> sjgarr at NOSPAMhotmail.com
> 
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The question, which is common, actually reflects a basic misunderstanding
about the way the brain is organized. Most parts of the brain has
specialized functions which is the only thing (or collection of related
things) that part of the brain does. Some parts of the brain are more
domain-general, but they represent small parts of the brain, and they are
also probably used very heavily by everything.

So back to the original question, most of the brain is devoted to sensory,
motor, or regulatory function. For example, I think somewhere in the range
of half of the cortex is visual, so as long as your eyes are open you are
using half of the brain.  And even if you are making relatively small
coordinated movements you are recruiting several large areas involved in
movement (e.g., motor cortex, basal ganglia, cerebellum). And of course
you are generally recording some aspects of your experience, which means
you are involving several memory regions.  So yes, you are using most of
your brains capacity, most of the time. Even sleep requires a great deal
of brain function!  Hearing the phone ring, picking it up, having a short
conversation, and remembering 5 words of what was said probably recruits
95% of the brain.

Now as far as the 10% figure, this is just a myth. It is based on several
moronic assumptions all of which are untrue. One of these is that the
brain is domain-general and works by mass action; this is patently false,
at least for many brain regions, particularly those which occupy most of
the brain (sensory, motor, and regulatory functions). The second is that
all neurons can fire at maximal rates and can have maximal metabolism
simultaneously (because the 10% estimate is based on theoretical metabolic
maximums). Of course, the latter is totally false since this would only
happen during a life threatening grand mal seizure and would not reflect
higher brain function. 

So think about it this way, consider you are driving down the street in
your car at 30 mph. The car is a Camaro and is capable of 150 mph. The
heater is set to 72 degrees but is capable of heating the car to 105. The
radio is set to 85 dB but is capable of 110.  The A/C is off, but is also
capable of being on. The rear defroster is off, but is capable of being
on. The brakes are not being operated, but are capable of stopping the
car.  Do you get my picture? Do you really feel that driving the car at 30
mph is using only 10% of its capacity, or it being used to its full
capacity, even though many systems are not recruited to the arbitrary
theoretical maximum at any given time?

Cheers,
Stephan



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