A Brief Guide to Being Shot in the Head

You know what this is about. I don't have anything especially useful to say about the recent tragedy, or the question of crazy vs. political: at this stage, it's all speculation. Let's wait for the trial.
But anyway, the incredible thing is that Rep. Gabrielle Giffords survived a bullet to the head. How?

One of the amazing things about the brain is that almost all of it is unnecessary. The bullet passed through Gifford's left cerebral cortex, various parts of which are responsible for moving the right side of the body, seeing and hearing things from the right, and, in most people, language. But the only part of the brain which you actually need in order to live is the brainstem, which forms the top of the spinal cord.

The main reason you need your brainstem is that it controls breathing. It also controls your heart rate and blood pressure, but your heart pumps itself, without any input from the brain: the brain just does the fine tuning. Breathing, however, is controlled directly by several brainstem nuclei, and if you stop breathing, your blood will run out of oxygen and you'll die (without artificial ventilation.)

Damage to any other part of the brain is survivable. Of course, you might just bleed to death from the head injury, or get an infection; there's also the risk of brain swelling which can be fatal by compressing the brainstem (amongst other problems). This is why doctors have removed a large part of Gifford's skull, to give the brain room.

But the brainstem can do a surprising amount on its own. In the early days of neuroscience, there was a bit of a fad for decerebrating animals, essentially removing everything except the brainstem. These animals were still "alive", at least in the sense that they weren't corpses; decerebrate cats can walk and run.

They don't walk to anywhere, but this shows that the spinal cord and brainstem can control movement and respond to sensory feedback. It's even on YouTube. The famous headless chicken that lived for over a year - that really happened, it's no myth - is another such case.