There are a few recent genetics items which suggest that human brains have much more genetic diversity than the initial human genome release would have suggested. I have blogged before about aneuploidy (loss or gain of chromosome)which occurs in suprising numbers of normal mammalian brain cells, and the hints that these altered cells contribute to brain function.
More recently a human genetics meeting at Cold Spring Harbor was full of reports of fine-scale (up to several hundred bases) variation in DNA of normal humans, in some cases even affecting the copy numbers of whole genes. (The best known of these blips is a short inversion in chromosome 17 found in Icelanders by DeCODE genetics.) Some variations affect the interactions of humans with their environment-- including the immune and nervous systems-- and appear from population genetic data to be undergoing natural selection.
And lastly, in a topic which I hope to finish reading (and maybe blogging) this week, a really astonishing report in Nature last week that small pieces of DNA known as LINEs relocate themselves (Nature link) in the mouse nervous system. The sequences "jump" out from their place of origin and re-insert, frequently near genes which are active in the nervous system, changing that neuron's DNA relative to its neighbors. This means that even identical twins will not match between neurons and DNA content. (This was already known to be true for female identical twins because of differential inactivation of the X-Chromosome. What makes LINEs different is that the genetic variations are potentially a whole range of flavors rather than binary.)