[kurtosis]

Oy man, I'm not used to people getting this fired up over a back of the envelope calculation! I'm sorry if my post sounded arrogant - I'm just trying to have some fun here.

I don't think I can really comprehend what any of your objections are, but I can certainly think of some major flaws in the toy argument I gave, and maybe these are what you were getting at even if you couldn't really articulate them.

first, just saying the state of a brain is the state of each synapse assumes a fixed topology of the brain. This is obviously false - there is a lot of evidence that the topology of the brain is changed by experience e.g. the occular dominance columns. Okay, so how much extra space would we need to deal with this - not that much actually: how much space do we need to store an arbitrary weighted directed graph with 10^11 nodes and 10^15 edges? Well for each edge we need to know the two vertices and the weight. Give each neuron a unique id and this requires about 10-12 bytes per synapse instead of 1. This is only one order of magnitude difference between a fixed and arbitrary topology! And this is probably a gross overestimate of the storage space required because the topology of the nervous system is far from arbitrary - after all the thing is generated by a genetic code of very modest size. See my posts on why the large search space doesn't kill attempts to solve protein folding.

Obviously I ignore the functioning of the glia - I know for a fact that these are very important for the growth and development of the brain but I'm not sure they are the critical part of its computational function. If you know otherwise please point me to some references, I would love to know!

The reason that I mentioned the speed difference of electronics and neurons is that this is what makes it possible to update the state of those 10^15 synapses in real time. Of course it would be wasteful to use the standard PC architechture for this process, but still.

Hope this helps clear things up.