X-Message-Number: 24060 Date: Fri, 7 May 2004 10:58:31 -0400 From: Thomas Donaldson <> Subject: CryoNet #24054 - #24059 Hi for those interested in making brains: Several points: 1. Yes, I did not consider the possibility of connecting the neurons by radio or some other method which does not involve direct connection. You'll still have to have very many connections. 2. OF COURSE we can have messages passing through several nodes. We do that right now with what we call telephones. However there is still a loss in speed and a significant amount of switching devices and software to connect the number of neurons in a human brain. Furthermore, if our device grows new connections rather than connects to them by a phone line, it will reach those to which it's connected much faster. The problem comes from the number of POSSIBLE connections such a machine can have. For any single instance, it's true that it will use only a small subset of those possible connections. However if we limit our machines to some arbitrarily chosen smaller subset, they will ALL be limited, which is hardly what we want. If on the other hand we give them the possibility of contacting all possible (or all reasonable) nodes, then they'll all be carrying around A LOT of unnecessary hardware. Hardly a good idea. 3. How important is speed here? I strongly suspect that natural selection has basically adapted us to an "appropriate" thinking and mental processing (most of our mental processing is unconscious) speed. Either running faster starts to become more expensive, or it gives no special advantage in the lives we now lead. Yes, there are occasions in which (if we could) it would be good to react faster, but those reactions also involve physical movement and not just the speed with which we think. And we could get into a long and involved discussion about how much mental and physical speed we might get with a redesign. We'd probably have to miniaturize ourselves to start. However I won't get involved in such a discussion in this message. I'll just say that optimal speed is rarely maximum speed. 4. It's important to consider BRAINS here rather than neural nets. Among their other features, neurons usually have many more connections than the nodes in a neural net, and those connections behave in several distinct ways depending on just which connection you're looking at. There are directly electrical connections and also those which use a transmitting chemical, of which there are a fairly large variety of different transmitting chemicals. So those connections for brains don't just send a single YES or NO signal. And yes, our neurons do grow new connections and our brain makes new neurons, too. To see all this, just get hold of a diagram of a pyramidal neuron, and remember that you're not looking at a generic neuron but one of a frequent, common, and important type but hardly universal. Not only that, but real neurons might be better represented as nodes with a large set of branches, with one branch (the axon) going out from one end and also ending in branches. If you wish to represent such a system as a neural net, it will have to have more than one node for each single neuron, and multiple versions of each connection for the different types of messages that a neuron can send or receive. 5. Yes, my calculations weren't quite correct, but here is a better version --- and note that you still get a good-sized object. If we work with square connectors and want our node to be a box, then the box will be a bit more than 10 microns on a side. In terms of making the circuitry in your node nanosized, you'll have to forget that; your node will be too big. The area of the surface of a box is 6 * N^2 where the box is N X N X N. If the connectors are square in cross section and 1 nanometer on a side, then if we line them all up we get a length of one meter. We don't want to line them up, we want to collapse them into a square. The square root of 1 billion (1 nanometer == 1 billionth of a meter) is ~~ 3 x 10^(-4.5) ~~ 10^(-4) ~~ 10 microns. This is a pretty good sized node for an electrical circuit --- especially remembering that it contains NO extra space. Most of all, remember that brains are not neural nets, nor are they any kind of computer yet made. And after all, just what is the objection to growing new connections, anyway? Best wishes and long long life for all, Thomas Donaldson Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=24060