Let that sink in for a moment. When the brain doesn't get oxygen, via the blood, for more than 5-10 minutes, the brain cells die en masse and then necrose. I once read an autopsy report for a person who was an organ donor. (Spoiler alert:this may be considered gross by people who aren't me) By the time the autopsy was started, a few hours after donation took place, the brain was already liquifying. See, it's not a theory. Your brain really dies. It's just that in most cases, the heart stops first, then the brain dies. Brain death, were blood flow to the brain stops due to cerebral edema following trauma or other brain injury, occurs in less than 1% o all deaths.
The heart can be restarted. Think open heart surgery-they actually stop your heart. But without blood flow to the brain, you're toast. Except in rare cases, like cold water drowning, where the brain metabolism is brought almost to a stop.
Remember history class? During the French Revolution when everyone was losing their heads, sometimes the executioner would hold the head up and the eyes or lips would still be moving.
The new debate about the machine began soon after the first few executions. One of the more recognized incidents involved Charlotte Corday. Charged with the death of revolutionary leader Jean-Paul Marat, Corday faced the guillotine on 17 July 1793. After being beheaded, the executioner’s assistant held up her head by the hair, showed it to the crowd, and slapped it across the face. The cheek turned red out of the indignity of the act or so the spectators thought. The scandalous moment upset the crowd and thus gave reason to investigate the matter further. (The Guillotine: A Look into the Machine Built for a Humanitarian Death by Jonas L. Bulman)
Gross. This is why when someone goes into cardiac arrest, you do CPR. Not to keep blood pumping to their heart, but to keep oxygen moving to their brain. Duh, right? If I had a quarter for every doctor who's told me, "But I can't sign the death certificate. Their heart's still beating." Well, I'd have enough to buy a grande latte. Because, of course when someone is going to be an organ donor, they are kept on a ventilator and given various medications to keep the heart pumping and the organs perfused. But their brain flow scan, if they had one, will look like the one above. White=blood flow.
So maybe we need to rethink the whole term "Brain Death". It certainly seems to confuse many, even medical professionals, into thinking it's different from "Real Death". Maybe we should just say they're dead.