throopw@rtp47.UUCP (Wayne Throop) (07/10/85)
I'd like to expand a little on Stanley Friessen's notes in this thread of discussion. For those who tuned in late, the folk knowlege that "we only use <mumble> percent of our brain power" is questioned. The fact that some patients with known brain damage are nevertheless able to think and behave normally is used as a support for this thesis. Stanley's reply: > 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. And Sandip Chakra's reply to this: > This does not exclude the fact that they were able to do > above average level work with a few percent of their brain cells. > Suppose all of us were born with 95% of our brain cells damaged, then > since we would be working at an above average level anyway, how do we > know that we needed the other 95% of our brain cells ? Lacking a complete knowlege of what brain structure is "good for", both "sides" of this discussion are mostly speculation. However, I suspect that the folks who claim that "we only use <mumble> percent of our brain" are incorrect. I have (essentially) two reasons. First, the patients on the referenced Nova episode showed that with about (as I recall) 80% brain damage, they could perform quite normally. However, the metabolism of the remaining brain tissue was quite a bit higher than normal, suggesting that (perhaps) more of the "essential stuff" was crowded into the remaining 20% of surviving tissue. Second, redundancy is not "wasted" capacity. Let us assume that a computer has 9 bits to support each 8-bit byte of memory, the "extra" bit being used for error correction. Is the computer "wasting" 1/9th of it's memory? Not at all. Or consider a computer that is triply redundant, or has triply mirrored disk storage. Is it "wasting" 2/3rds of it's capacity? Again, not at all. I think that a similar effect applies to the brain. To be as reliable as it is, it probably is highly redundant. Redundancy is hardly "wasted"... it increases reliablity. Thus a "normal" person who suffers brain damage *can* continue to perform at the previous level of competence. This normally does not happen to adults who have already "parceled out" functions to particular bits of grey matter, but it *can* happen even to adults. It more often happens that children (the examples from Nova were all damaged in early childhood, for example) can re-allocate brain function after damage and have few or no perceivable side effects. Nevertheless, they are far more susceptible than normal adults to further damage. To summarize: - The Tomographic results cited in Nova do not unambiguously show that "brain capacity" was destroyed along with brain tissue. (This is essentially a restatement of what Stanley said). - Even if there is *redundant* brain capacity, it can hardly be said to be *wasted* brain capacity. And, getting back to the original question (how would excess or wasted capacity be selected for), *redundancy* is a valuable survival trait. -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw