An Endless Number Of Connections: Selection and the Brain

Alan Alda: But you've maintained that flashlight of selection. How does selection apply to the way the brain works?

Gerry Edelman: Well, of course, the brain is an enormously complicated system, so what I'm going to say will sound oversimplified in the effort to try to convey something. The idea is something like this. When the brain actually gets put together, in the initial period its structure depends upon the genes. But then shortly after that, neurons that fire together, wire together, and they do that contingently, depending on the exposure of that individual organism, so that no two brains are going to be wired alike. So selection is going on there, depending on what events are occurring. So out of all the possible ways you could wire in the microscopic sense, one guy will wire this way, the other guy will wire that way, even if they're genetically identical.

Alan Alda: This is in the early…

Gerry Edelman: Early fetal development, the uterus, the embryo. This first stage is called developmental selection. The next one's called experiential selection. You don't change the anatomy so much as you change the road pattern by changing the strength of which one will go where.

Alan Alda: That's where a map develops?

Gerry Edelman: That's right. And, in fact, you're born with a crude map, but then when you see the world, this second stage of experiential selection will then refine that map in your particular way. Even by the way in adult life, if you play the violin, for instance, in your left hand, these fingers will take over a good hunk of the map that a non-violinist doesn't have. But what coordinates the bloody thing? How does it go together?

Alan Alda: What coordinates what to what?

		Edelman on brain development:"This hand is one map, this hand is another"

Gerry Edelman: …Well, what coordinates the selection, so that you make sense? So when you move, you do something sensible. When I see you, I don't see a patch of brown plus some grass. There you need an organizing principle, and we believe it is not logic like a computer. Instead, we think it's a principle called re-entry. And at this stage, I have to wave my hand. It's a little like trying to explain quantum mechanics, but imagine the following. This hand is one map, this hand is another map.

Alan Alda: Ok, what's this map a map of.

"When I go like this" Edelman demonstrates, "certain things here will fire."

Gerry Edelman: This is a map of say, vision. Suppose that this is a map of all the lines that are oriented in different ways. When I go like this, certain things here will fire, when I go like that, certain others will fire. It's a map meaning that neighbors in my eye are generally neighbors here.

Alan Alda: So that allows you to see something. So what's this other map?

		Our mind maps are linked, forming a "hair-raising" number of neuronal connections

Gerry Edelman: Supposing this is another map, and supposing this map deals with movement of objects, whole objects, not just orientations. Now supposing these two maps are connected. Think of a bunch of hay bundles going back and forth. These are nerve fibers and nerve cells that are connecting one map to another. Now they're reciprocal, meaning some go this way and some go that way. Now imagine I put things into each map, signals into each map, that are quite separate, but when they go in, certain things happen simultaneously to strengthen the connections in these fibers between. Pretty soon the maps are mapped, and this happens constantly. And that's the principle we call re-entry. It's like going back in the room again, but a different route, going back again and coordinating the maps in space and time.

Let's look at the numbers. Your brain's cortex, the size of, oh, I don't know, a table napkin, has 30 billion neurons and a million billion connections. So the number of possible patterns of traffic in your nervous system is perfectly scary. There are certain constraints. You're a human being so you're going to wire up a certain way, but nonetheless, the number of possibilities is hair raising.

- - - - - - - - - - - -
5 pages: | 1 | 2 | 3 | 4 | 5 |