There is nothing more humbling or more perception-changing than holding a human brain in your hands. I discovered this recently at a brain-cutting lesson given by Jean Paul Vonsattel, a neuropathologist at Columbia University. These lessons take place every month in a cold, windowless room deep within the university’s College of Physicians and Surgeons. On the day I visited, there were half a dozen brains sitting on a table. Vonsattel began by passing them around so the medical students could take a closer look. When a brain came my way, I cradled it and found myself puzzling over its mirror symmetry. It was as if someone had glued two smaller brains together to make a bigger one.
Vonsattel then showed us just how weak that glue is. He took back one of the brains and used a knife to divide the hemispheres. He sliced quickly through the corpus callosum, the f lat bundle of nerve fibers that connects the halves. The hemispheres flopped away from each other, two identical slabs of fleshy neurons.
