thanks for your reply.
"Richard Norman" wrote:
> The general "wiring diagram" of the brain may be coded in the genes,
> but certainly not the fine structure. Consider fingerprints, for
> example. Identical twins with the same genes still have different
> fingerprints because these are determined by localized and
> unpredictable (sort of "random") environmental cues at the size level
> of a millimeter in the development of the finger ridges. At the same
> size level in the brain, in one cubic millimeter, there are thousands,
> perhaps tens of thousands of neurons each synapsing with many
> thousands of neurons in its vicinity. Certainly the 40,000 genes in
> the human genome are not going to code for specific neuronal
> connections! But the large pathways with dimensions of many
> centimeters (to a specificity of a few millimeters) may be determined
So it means the neural pathways are there for some purpose.
Then it is important to figure out why they are connected this way.
Maybe neural network modeling can shed some light on this issue?
> There is also a great deal of evidence to indicate that a tremendous
> number of neurons form and interconnect with each other initiallly.
> Later experience whittles down (sculpts) these connections and cell
> numbers to a smaller but functionally important number. Again, the
> fine details may be determined by experience even though the overall
> grand scheme "determined" by genetics.
>> From what we know of development, a small number of rules can produce
> a highly organized pattern of structure. Since this organization
> occurs because of the interaction between cells, not because of the
> separate activities programmed into each separate cell, you could well
> call that an example of emergent properties.
I was actually thinking that some neural pathways are the emergent
results of a small number of genes or factors. But it looks like the
current findings about the formation of cortical pathways are not
enough to answer this yet.
By the way, is there anything on the web like a map of the complete
neural pathways in the brain? That could be useful for modeling.