In regard to brain injury and incapacitation there is always the true story of Phineas Gage who was a "Tamper" back in the day when blasting was done with black powder. It was his responsibility to compress the powder in the hole using a 1 1/2 inch 6' iron rod to pound the powder down. A charge spontaneously exploded and drove the rod diagonally through his skull where it lodged. He survived and the rod was cut off leaving the imbedded section intact. He lived the rest of his life fully functional with only a minor personality change.
I'm a retired paramedic and my company had a transport contract with an institution that had a custodial adult brain injury unit. Some of their clients were profoundly impaired and some were ambulatory; all had sections of their brains that were non functional. Some certainly were still capable to be in a gun fight.
My point is simply that brain trauma is not necessarily incapacitating; one must transect the spinal column fairly high up to shut the bad guy down. The spinal column is a hard target to hit. If one is close enough to pick a target the area just above the rib cage and below the Adams apple is a viable aim point; there are major blood vessels there and the spine is close to the surface. Good luck to all of us if and when we are called upon to defend ourselves with a gun.