Language bootstrapping the brain

Language is one of the most demanding cognitive tasks faced by humans early in their development.

The classic language areas have their own developmental biases emerging from the functions of nearby cortical areas. The frontal cortex area immediately rostral to Broca's area develops earlier as a center for processing action sequences. Other areas involved in language processing lie usefully near auditory and association areas. The visual cortex seems like it should be outside the loop.

Language has sharp elbows. It muscles its way into the brain, crowding out other neural functions. Language has the most powerful weapons at hand -- a baby's first word prompts an entire language community to pull the dopamine and serotonin levers of emotion and attention.

A function that was strongly specified by genetics, patterned early in brain development, would not plant itself in spare neurons like a weed in a vacant lot. Only a system that bootstraps itself upon experiencing language inputs could have such plasticity. The structure of the language environment fosters the development of the classic language areas, biased to appear in those particular places by prenatal developmental trajectories, but not built according to a genetic blueprint.

The blind subjects tell us that the ground for language processing is almost as fertile elsewhere in the cortex. Many brain areas have the genetic equipment to recruit and organize neurons into useful circuits for language processing.

Language development is developmentally robust because it can rely on a rich language environment, not because of genetic standardization. The basic problems of language evolution must be explained by showing how robust language communities emerged. I don't preclude genetics, far from it -- weaker language environments may have become stronger because of evolutionary change. But that evolution must have been substantially domain-general, because language processing is not specifically canalized by genetics.

I like this scenario because it means we shouldn't be looking for lots of language-specific genetic changes in the last few hundred thousand years. The Neandertal genome suggests that there may not have been any at all.

My second speculation: If the language environment determines the instantiation of language processing, then brains must be substantially different in the way they process language.

Children experience different language environments -- not only different languages, but different microenvironments within language communities. Only strong genetic controls could canalize brains despite the differences in their language environments. In brains where language processing emerges readily in the visual cortex, genetic controls cannot possibly synchronize brains in the face of environmental variation.

http://johnhawks.net/weblog/reviews/brain/language/bedny-blind-visual-cortex-language-2011.html