The Allen Brain Atlas just launched their first set of gene expression maps in the adult human brain, based on microarray data from over 700 different anatomical locations. It promises to be an invaluable resource for scientists trying to figure out how a text of base pairs constructs the most complicated machine in the known universe. I wrote about the construction of the human brain atlas last year in Wired, if you’d like to learn more about how the map was made. Although these genetic maps are just a first draft – one researcher at the Allen Institute compared them to those 15th century sketches of the New World – the data has already taught us plenty of interesting things about the three pounds of flesh in our head.
One unexpected–even disheartening–aspect of the Allen Institute’s effort is that although its scientists have barely begun their work, early data sets have already demonstrated that the flesh in our head is far more complicated than anyone previously imagined.
The brain might look homogenous to the naked eye, but it’s actually filled with an array of cell types, each of which expresses a distinct set of genes depending on its precise location. Consider the neocortex, the so-called CPU of the brain: Scientists assumed for decades that most cortical circuits were essentially the same–the brain was supposed to rely on a standard set of microchips, like a typical supercomputer. But the atlas has revealed a startling genetic diversity; different slabs of cortex are defined by entirely different sets of genes. The supercomputer analogy needs to be permanently retired.
Or look at the hippocampus, the crescent-shaped center of long-term memory. Until recently, this small fold of tissue in the middle of the brain was depicted as neatly divided into four distinct areas. But data from the atlas has rendered the old maps not only obsolete but flat-out misleading. Even a single hippocampal area can actually be subdivided into at least nine discrete regions, each with its own genetic makeup.
Scientists at the institute are just starting to grapple with the seemingly infinite regress of the brain, in which every new level of detail reveals yet another level. “You can’t help but be intimidated by the complexity of it all,” Jones says. “Just when you think you’re getting a handle on it, you realize that you haven’t even scratched the surface.” This is the bleak part of working at the Allen Institute: What you mostly discover is that the mind remains an immense mystery. We don’t even know what we don’t know.
See the whole gallery of gorgeously gruesome photos over at Wired.