Yet more people who know more than me
This new study deals primarily with the visual system, since its structure has been well investigated. The question at hand: How does visual input affect neural functioning on the molecular level? The findings: "[V]isual stimulus turns up the expression of some genes and turns down the expression of others, somewhat like a conductor cueing the members of an orchestra." Above and beyond the whole "neurons that fire together wire together" premise, stimulation also affects the expression of whole families of genes. It's quite complex really -- visual input affects gene activity, which affects the way the brain responds to visual input. Probably not a big surprise to some of you, since it's well-established that environmental influences affect gene expression (Anna just blogged about how this presents itself in the Harry Potter universe), but as someone who is merely a cog-sci hobbyist, I really hadn't thought about it in the context of the brain before. The practical upshot? Sure, genetics have an influence on brain activity, but the reverse is also true. In other words, genetic variation is not sufficient cause to assume cognitive differences.
So that's a better, more evidence-based, and more authoritative version of what I was intending to say. Thanks are due to JP for making it clear that I hadn't been clear.