X-Message-Number: 11420 From: Thomas Donaldson <> Subject: thanks to Jan Coetzee; much more is known about brains, too Date: Tue, 16 Mar 1999 23:57:44 +1100 (EST) Hi everyone! We should thank Jan Coetzee for his report of one side of the issue of brain repair. It's important here to understand that now, in animals such as cats, experiments are going on aimed at replacing neurons lacking because of earlier brain damage. Moreover, by now it's well recognized that brain areas which deal with visual recognition generally respond to several different classes of visual stimuli, rather than just one kind: yes, some neurons are particularly sensitive, for instance, to horizontal structures, but that does not imply that horizontal structures are the only visual phenomena to which they are particularly sensitive. In general terms it's been known for a long time that information is widely distributed in our brain. Since, after all, our brains are parallel machines (with far more processors than any present parallel computer --- the processors are neurons, in case you haven't guessed) it's very likely that information will be widely distributed. The earliest experiments suggesting this (which also seemed to negate the idea that brain regions were specialized --- which later was still found to be true) consisted of systematic ablation of particular brain areas in rats. Despite this, the rats could still limp or roll through a maze. The article reported by Jan Coetzee adds to the force of these early experiments. Yes, our neurons do specialize, but not on one task only... and they also retain information needed for other tasks (just how I do not know ... and suspect that no one else does, either, but one possibility would be the continued existence of "silent" connections between neurons). The real problem is that of obtaining this information so that new neurons introduced for brain repair will grow the proper connections and so respond to that previous information. This may turn out to be easy in some cases, but it seems to me unlikely that it will be easy in all ... or even in most cases. I will add, though, that many of our neurons play no direct role in storage of information, and repairing or replacing those neurons will still have lots of value. Neurons using dopamine as their transmitter, for instance, play a large role in organizing our emotions and our knowledge but play little direct role in information storage. For those who are interested, I have compiled a list of books and papers on how brains work and just what is now being done in brain repair. I can email it to individuals who ask for it. I am also well aware that some people believe that we will someday simply be read off into computers; I will point out here that in order for such read-offs to be successful, we will need much more understanding of how our brains work than we presently have ... even though the last 20 years have seen a big increase in our understanding. So knowledge of just how our brains work remains highly relevant even to those who might prefer to live in computers. Best and long long life to all, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=11420