Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 alpha 4/15/85; site cbosgd.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!cbosgd!rbg From: rbg@cbosgd.UUCP (Richard Goldschmidt) Newsgroups: net.sci Subject: Re: darwinism Message-ID: <1248@cbosgd.UUCP> Date: Fri, 14-Jun-85 09:13:17 EDT Article-I.D.: cbosgd.1248 Posted: Fri Jun 14 09:13:17 1985 Date-Received: Sat, 15-Jun-85 09:16:52 EDT References: <783@oddjob.UUCP> <542@petsd.UUCP> <784@oddjob.UUCP> Distribution: net Organization: Columbus Bell Labs, Silver Lining Lines: 59 Let me start by saying that after ten years of doing brain research, and a Ph.D. in neuroanatomy, there is NO evidence that people only use some small fraction of thier brain cells. In article <784@oddjob.UUCP>, sandip@oddjob.UUCP (Sandip Chakra) writes: > > > ......why human evolved about six times > > >as that of an orung-otung and yet human uses only about 5 percent of the > > >brain cells? > ... I recently watched a PBS broadcasting on brains (a > series in fact), which showed with the example of four people that > even though their brains are virtually entirely damaged and only an > extremely thin layer of brain cells touching the skull is functioning > they are perfectly normal person. In fact, > the subjects did not know that their brains are > damaged at all. These people are adults and are doing their jobs in a rather > respectable fashion. Their intelligence also were found to be above normal > (if I recall correctly). The method used to check such "hollowness" of their > brain was Tomography (called CAT scanning, I suppose). The test was clearly > convincing, and I do not doubt that my assertions based upon what I have > observed are correct. > > I suppose this clarifies my issue. Doubly regards. > Sandip No clarification at all, just misunderstanding. It is true that people can function effectively with some degree of brain damage, but it depends greatly on the task and on their degree of experience with the task prior to brain damage. The classic series of experiments in this area were done by Lashley in the 20's and 30's. He found that if he trained rats in a visual discrimination task for thousands of trials beyond the criteria usually used to demonstrate learning, that he could still get criterion level performance after removing 95% of their cerebral cortex. However, without OVERtraining, this result can not be obtained. It is true that there is a certain level of redundancy in the brain so that it can still function at some level after injury, and there are also repair mechanisms which can sometimes contribute to recovery from injury, but you can also be certain that any injury to the brain reduces the level of functional ability in specific ways, depending on the location of the injury. All of the living neurons in your brain work, and contribute to the distributed processing and storage which make behavior, learning and thought possible. It is in the nature of the distributed architecture that some function is preserved even when some of the processors are removed, but that does not mean they don't normally contribute to the overall function. But to get back to the more interesting issue of brain evolution, the large growth of the brain is not spread out equally over all areas, but is concentrated primarily in cortex, and especially in a few areas called "association" cortex. So there has been a functional reorganization in the brain during evolution with an emphasis on particular areas, not simply an increase in size. This story is repeated over and over again in brain evolution, with new layers being added on top of older ones, such that the human brain is a hodge-podge of layers, with many sensations or functions being represented at many different levels. It is very complicated, and it amazing that it works at all, but if it didn't we wouldn't be here! Rich Goldschmidt {ucbvax,ihnp4,decvax,allegra,seismo} !cbosgd!rbg ARPA: cbosgd!rbg@seismo or cbosgd!rbg@ucbvax