Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/5/84; site steinmetz.UUCP Path: utzoo!watmath!clyde!burl!ulysses!gamma!epsilon!zeta!sabre!bellcore!decvax!mcnc!ncsu!uvacs!edison!steinmetz!stpeters From: stpeters@steinmetz.UUCP (R L StPeters) Newsgroups: net.sci Subject: Re: Re: darwinism Message-ID: <169@steinmetz.UUCP> Date: Tue, 9-Jul-85 23:06:41 EDT Article-I.D.: steinmet.169 Posted: Tue Jul 9 23:06:41 1985 Date-Received: Sat, 13-Jul-85 14:15:07 EDT References: <542@petsd.UUCP> <1477@bbncca.ARPA> <526@psivax.UUCP> Organization: GE CRD, Schenectady, NY Lines: 79 > >I don't know about the % of gray matter "normally" used, but ... > > > >Using recently developed (tomographic?) techniques for scanning > >the brain in detail along various physical variables, researchers > >found that a number of people who suffered massive brain damage > >at birth or early in life but who display not only above average > >abilities but high general intelligence (unlike the "calculating > >idiots") are using less than 10%, in some cases less than 5%, > >of their brain mass: the rest is clinically or effectively dead! > > > >I haven't though about how this relates to evolutionary issues, > >but it struck me that these simple facts must have a serious > >impact on various theories about how the brain works: ... > > > Actually, before any conclusions can be drawn more details > are needed. What proportion of the dead tissue was gray matter and what > white? How much was glial cells and how much neurons? What about the > density of neurons in the remaining tissue - the same or perhaps > higher? What sections of the brain were involved? Of course the > answers to some of these questions requires a biopsy or similar > invasive sampling technique, so we may have to wait until some of > these patients die. Also, why were they given a tomography(a > diagnostic test) if they were so normal? The patient's death is not all that necessary. My neurosurgeon and my tomographic pictures can both attest that a sizeable region of my own brain has not held working neurons since I had a significant subarrachnoid hemorrhage and subsequent open-brain surgery not quite a decade ago. I have had the enlightening opportunity to observe up close the nearly-complete restoration of lost functionality as the initial total paralysis of my left arm and hand have gradually given way to the point where I am touch-typing this posting (sneaking in an occasional peak at the keyboard). While the damage I suffered was nothing approaching 90% overall, it was 100% throughout a region large enough to make some impressive tomographic images. Given that central nervous system neurons do not recover or regenerate, this functionality must be being supplied by other neurons, presumably in the vicinity of the destroyed region, and also presumably neurons that were not already otherwise in use. (At least I like to think so.) This leads me to the conclusion that, however evolution has managed to do so, it has put all these extra unused neurons in there in the first place as spare parts. Recoveries of major losses of functionality that take a decade to occur are unlikely to have much evolutionary benefit, so they most likely are a side benefit of a mechanism whose purpose is continual maintenance: ongoing repair of minor damage. The image I have is one of steady loss of active neurons due to disease, chemicals (e.g. alcohol), physical blows to the head, etc., accompanied by their continuous functional replacement through activation of alternate neural channels using these pre-existing replacement neurons. Thus nature, faced with only one chance ever to grow neurons, grows enough initially to provide a lifetime of spares. More precisely, an adequate *density* of spares is provided. The numbers seem to suggest that perhaps around ten possible replacements are provided for each neuron. Carrying this one step further, one can then imagine that perhaps a part of the condition we call senility is when the loss of neurons from old age requires that the brain reach ever farther to find suitable neural replacements, and the neural pathways, like old code patched many times, become ever more tangled and spaghetti-like. While I described the hypothetical repair process in one-for-one neural replacements terms, I doubt the replacement of neural pathways is that simple. I've progressed from some observations and a few known facts into some pretty tenuous conjecture, and it's time I stopped. -- R. L. St.Peters (Dick) The "R" is for "Reptile". uucp: decvax!mcnc!ncsu!uvacs!edison!steinmetz!stpeters (uucp is forever) arpa: stpeters@ge-crd (federal express) "Any opinions expressed by my employer are probably not mine."