X-Message-Number: 15375 Date: Wed, 17 Jan 2001 23:25:06 -0500 From: Thomas Donaldson <> Subject: more on brains and computers To further comments about brains and neurons: Given N neurons, the number of possible connections between them goes up like N!. This is greater than exponential. The fundamental issue here seems to be that of whether the neurons are modified when they lose a connection or make a new one. The computational (and all other abilities, which must not be forgotten though they are too often forgotten) abilities of neurons depend on their connections. These connections, according to the best evidence we now have, CHANGE in many neurons. The suggestion behind such changes is that they are themselves the formation of memory. If so, the connections of our brain bear a very close relation to our particular memories... and thus our ability to CHANGE our connections depends on the number of possible connections for each neuron, not a fixed number to a fixed set of other neurons. The above paragraph deserves a number of qualifications. As most people who've done some reading about actual brains will know, many connections seem to develop very early and remain fixed. Those involved with our personal memories come last, and they are the ones which change constantly. Basically this means that we cannot assume that ALL connections belong to our memories. Sorry, but so far as I presently know, no one has counted these enough for us to make some math formulas. Second, there is a theory of memories which would assume that all the connections remain fixed, with memories changing due to changes in the connections themselves. The problem with this theory is that synapses (connections between neurons) have been found to change constantly. Yes, no doubt this observation and others might have alternative explanations, but they look weak to me and I'm hardly the most prominent person who would say that they look weak. It's what I understand about how brains work that makes me believe that the math figure will come closer to N! than just to some power of N. Since we are talking empirical facts, all current theories may someday be seen to be faulty. Still, even a little reading about brains will suggest that they do not work like present-day computers, even parallel ones, and that changes in connectivity (not to mention production of new neurons!!!) make them at least quite different. Best wishes and long long life to all, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=15375