One point of critical importance in the debate over how much our genes account for variability in intelligence (current status: no effect demonstrated in normal cognition) is that human brains are ridiculously plastic. As would be expected in an organism that can create and function in a wide variety of social structures, our brains can and do structure themselves on the fly. When you see a headline that says, “XYZ Rewires Our Brains!” the only appropriate response is, “Duh.”
A very recent study suggests that this plasticity may be more radical than we already knew.
McConnell has been exploring this phenomenon for more than a decade. In a 2001 paper, he and his colleagues found that individual mouse cells destined to develop into neurons contain substantial chromosomal changes called aneuploidy. A few years later, he showed that neurons with these changes are active in the mouse brain.
Because humans are born with most of the neurons they will use throughout life, genetic variability among them could have a long-lasting effect on how people behave, McConnell says.
To see if human brain cells are genetic mosaics, McConnell turned to induced pluripotent stem (iPS) cells. They are created by treating adult cells with a suite of reprogramming factors that transform the cells into an embryonic-like state in which they can form other tissues.His team transformed iPS cells from two people into neuron cells and then examined the genomes of individual neurons, looking for places where the a huge chunk of the genome is missing or duplicated.
No brain cell’s genome looked the same. They all contained numerous duplications and deletions, but never the same pattern. His team also examined the genomes of the adult cells that were reprogrammed into iPS cells and then neurons, and these cells contained numerous insertions and deletion, but not the same ones as the neurons. McConnell says that this suggests that cells acquire their own genomes as they turn into neurons.
We’re talking mouse brains, and we don’t know how active these changed regions are in brains, but if this pans out, it could explain how we start to generate plasticity and why fetal development appears to be so critical in these systems that change through our lives. In the meantime, however, just try not to use any brain tissue for DNA matching.