* Because the brain is not sensitive to pain, a lot of such surgery is done on patients who are awake (with their scalps anesthetized, of course). This is helpful, because prior to modern imaging techniques, surgeons often had to have the patient awake to guide what they were doing. Place an electrode in the brain, stimulate, the patient flops her arm. Go a little deeper with the electrode, stimulate, and the patient flops her leg. Quick, consult your brain road map, figure out where you are, go an inch deeper, hang a left past the third neuron, and there’s the tumor. That sort of thing.