What does a brain surgeon do?

Yes, but obviously not all of it. In a hemispherechtomy half the brain is removed. This may seem drastic, but you can operate just fine with one side of your brain. This is usually done when one side of the brain is malfunctioning in such a way as to significantly distress or threaten the life of the patient.

Sometimes bits of cortex (brain matter) is removed from those suffering from severe seizures. Most brain surgeons' work consists of traumatic injury, removing tumors or aneurysms.