How does the brain know to put a nest basket cell here, a small basket cell over there, a large basket cell in the middle, a Martinotti cell on the left and a bi-tufted cell on the right, all wired up to pyramidal cells? There has to be a plan, doesn’t there?
..the body doesn’t just throw its inventory of brain cells out there like a bunch of pick-up sticks, to fall where they may, [does it]?
As it turns out, that may be almost exactly what the brain does.
Like so much else in capital-L Life, connections in the brain may be emergent: the developing brain lays out its thinking cells in a nearly random mixture, and then wires them up after the fact.
The Blue Brain group …has built a computer model of a 298-cell slice of rat cerebral cortex. The model distributed the 6 types of neurons randomly, according to their frequency in natural tissue. They tracked “the incidental overlap of axonal and dendritic arbors,” the tree-like branchings at either end of the nerve cell that reach out and form synapses.
It’s a case of, “Ready. Fire. Aim.” The cells are (mostly) laid out, and the synapses appear to grow when the right cells touch one another—with some small role perhaps played by chemical or other signals that cause a few cells to reach out to one another after the fact.