Some symbols are stripped of all but the vaguest symbolic content in order to serve as switches - these are isolated like indexical functions but they are not grammar. Symbols are distributed. There is some neat stuff about first learning specific associations and then, as indirect associations are built up, unlearning the initial specific associations. Symbolic recoding eliminates the exponential explosion implicit in indexical association. Different languages have different processing demands and brains adapt to them.
Italian brains are different from English brains.
Poo-poo's pop theories of brain lateralization. Suggests mostly adaptive. Inportant but seriously misreprented in pop discussion. Good discussion of Baldwinian evolution, genetic assimilation. Strong evolutionary arguments that there has been brain evolution to support language but not grammar.