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From: Robert McGee <rmcgee@clark.net>
Newsgroups: alt.folklore.urban
Subject: Re: Ten Percent of the Brain
Date: Mon, 29 Jul 1996 10:31:57 -0400

Chris Peek wrote:
>
[Whence the notion that we only use 10% of our brains?]

> As one research subject they happened on a student who was a math major
> making adequate (though not spectacular) grades in school. It was
> determined he had some form of micro cephalism and his entire brain was
> _much, much_ smaller than the mass of a normal brain and somehow was
> contained in a relatively thin sheet of brain tissue near his frontal
> lobe area.

One Dr. Barry Beyerstein discusses the 10% myth at some length in a _Rational Enquirer_ article; you can find the complete text at:

http://eslvcr.fireplug.net/bcskeptics/ratenq/Re3.2-Brain10.html

Citing both evolutionary theory and clinical evidence, Beyerstein dismisses as absurd the notion that 90% of a healthy adult's brain lies dormant, waiting to be tapped by yogic meditation, alpha biofeedback, or Neuro Linguistic Programming [tm]. He does acknowledge, though, that a brain damaged *early in development* can sometimes compensate so well that the individual functions in a normal range even though brain mass may be severely reduced. ("Compensate" is the key word; dead or missing brain tissue is NOT replaced.) He gives an example of this phenomenon that resembles the math major case described above:

[The 10% myth] was reinforced recently in an otherwise informative TV documentary aired on PBS and the Knowledge Network. It featured the British physician John Lorber and an extraordinary group of young patients. Referred to Lorber because of fairly minor neurological complaints, they were of normal or above-normal intelligence and were coping well, educationally and socially. Astonishingly, CAT-scans revealed that their cerebral hemispheres had been compressed into a slab less than an inch thick by enlargement of the underlying fluid- filled ventricles. This had occurred over an extended period as the fluid dammed up behind constricted outflow channels. The youths' lack of retardation despite this tremendous neural shrinkage led the producers to ask the misleading question that, unfortunately, became the title of the episode: "Is the Brain Really Necessary?"

Beyerstein adds the caveat that the patients' normalcy may have been overstated for dramatic effect, and at any rate their cases only demonstrate a young brains' ability to adjust to damage-- NOT that a substantial portion of our brain mass is really superfluous. As to the origins of the 10% figure, Beyerstein offers an explanation that I don't recall seeing yet in this thread:

misinterpretation of certain terms used by comparative neurologists may have compounded the error. With evolutionary advancement, the cerebrum of mammals has enlarged greatly but a progressively smaller proportion of it is concerned with strictly sensory or motor duties. This was demonstrated in the 1930's by electrically stimulating the exposed cortical surface in a variety of species. Because the current was unable to evoke obvious responses from these increasingly large non-sensory and non-motor areas, they were referred to as "silent cortex." As we have seen, they are anything but silent -- they are responsible for our most uniquely human characteristics, including language and abstract thought. Areas of maximal activity shift in the brain as we change tasks and vary attention and arousal but there are normally no dormant regions awaiting new assignments.

In other words, the "humans only use 10% of their brains" canard would more correctly be phrased "humans only use 10% of their brains for walking around and smelling things"-- the implication being humans, for their size, have an unusually large brain mass available for higher-level functions. (In contrast, elephants and certain whales have LARGER brains than we do, but they must devote a great percentage of brain mass just to moving their massive bodies around-- to say nothing of the mumble-thousand muscles in the elephant's trunk alone, or the sophisticated sonar abilities of toothed whales. That leaves them with less brain mass potentially available for reasoning and language.) Anyway, it's easy to see that a term like "silent cortex" would lend itself to misunderstanding on the part of lay persons; unfortunately, Beyerstein offers no cites to show that the term was in wide circulation among neurologists in the 1930's, nor that it appeared in science articles written for a popular audience.

Rob "Will move electric trains with my brainwaves for food" McGee