Genes controlling axon guidance and repulsive molecules play a role in forming specialized speech circuits.

“Genes that control what we call axon guidance and form neuronal connections, and what was interesting, it was sort of in the opposite direction that we expected. That is, some of these genes, actually, a number of them that control neural connectivity were turned off in the speech circuit, all right. And it didn't make sense to us at first until we started to realize the function of these genes are to repel connections from forming, so repulsive molecules. And so when you turn them off, they allow certain connections to form that normally would have not formed.”