________________________________________ From: Tim Cutts [t...@sanger.ac.uk] Sent: Wednesday, February 16, 2011 08:03 To: Lux, Jim (337C) Cc: ariel sabiguero yawelak; beowulf@beowulf.org Subject: Re: [Beowulf] IBM's Watson on Jeopardy tonight
On 16 Feb 2011, at 15:20, Lux, Jim (337C) wrote: > Aside from how brains are "programmed" (a fascinating question) > > One big difference between biological systems and non-bio is the handling of > errors and faults. Biological systems tend to assume that (many) failures > occur and use a strategy of massive redundancy with fuzzy collective action. <biologist mode on> Actually, I'd quibble with that statement about redundancy. On the system level, there's very little redundancy in most [animal] organisms. You only have one heart. You only have one aorta, stomach, oesophagus and so on. Even when some things are paired, the loss of either one (such as severing a carotid or femoral artery) can in many cases result in total organism failure. :-) >>> I was thinking at a smaller scale.. you have many bone cells in a bone, so >>> if there's a microfracture, that's accommodated within the "design". >>> Likewise, I can kill off some brain cells and still remain reasonably >>> functional. Biological systems tend to be plastic and self-healing rather than redundant, I would have said. >>> a much better description than mine.. plastic.. works in the mechanical >>> sense too.. At the sub-cellular level, redundancy is much more widespread of course, with various protein families able to cover for each other, resulting in redundant biochemical pathways in many cases, although again not all. Consider the DNA repair disorder xeroderma pigmentosum; it's a failure of one particular DNA repair mechanism, and there are seven genetic complementation groups for the disease - in other words there are seven distinct genes involved in the process, and the failure of any one of them results in the failure of the entire process. There's redundancy in the fact that you have two copies of most chromosomes, of course, although you and I, being male, are a bit buggered if there's anything wrong with our X chromosome. Ask any haemophiliac. Plants of course do much better, and do tend to be massively redundant, both at the structural level of the whole organism, and also at the genetic level (they often have much larger genomes than us, and massively redundant). Ever tried eradicating bindweed from your garden? That stuff is just impossible to kill. But as to mental processing, I think one only has to look at what happens in brain injury cases like strokes to see that the processing is not redundant; a stroke can remove some particular processing ability. The brain however, has a lot of plasticity, especially when young, and other parts of the brain can learn to take over the functions. But I don't think that's quite the same as true redundancy; it's like re-programming another set of flash chips to take over. >>> But I think in a stroke, you're not talking about a generalized distributed >>> failure, but of the failure of a particular "region" of cells. One might >>> think of the brain, which although remarkably uniform in internal >>> structure, does have specialized areas.. some areas because that's where >>> sensory or motor nerves wind up (e.g. your optic pathways wind up at the >>> occiput, so that's where vision processing is done). I think of it as more >>> a collection of organs that all happen to look the same but do different >>> things. >> you raise an interesting point, though. Biological systems handle >> distributed failures better than localized failures. Sort of like in error >> correction coding, there are codes that deal with burst errors and those >> that deal with distributed errors. In coding, there are interleaving >> schemes to change one into the other, too. >> and of course, the brain (and other parts of your body, to a certain extent) >> is remarkably plastic, and even moreso at the higher "system level" (e.g. >> one can invent a wheelchair) _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
