How long is a severed head conscious for? The question has troubled students of the human body for centuries and generated countless, possibly mythical stories. History of medicine blog The Chirurgeon’s Apprentice has finally looked through the records to find out which of the accounts are based in blood-curdling fact.
A common tale involves someone trying to test the idea during the French revolution by taking a severed head directly after it has fallen from the guillotine and asking questions, with the unfortunate victim communicating via blinks until it loses consciousness.
We’ve covered exactly such a story previously on Mind Hacks, but historian of medicine Lindsey Fitzharris thought it sounded a bit too much like a tall tale and decided to find out if anything like this had ever actually happened.
She ended up on a wonderfully macabre journey through the science of consciousness after decapitation, involving everything from electrocuting severed heads to grimacing dead people:
The first to reportedly do so was a Dr Séguret, who subjected a number of guillotined heads to a series of experiments during the French Revolution. In several instances, he exposed their eyes to the sun and observed that they ‘promptly closed, of their own accord, and with an aliveness that was both abrupt and startling’. He also pricked one of the severed head’s tongue with a lancet, noting that the tongue immediately retracted and ‘the facial features grimaced as if in pain’. Was this my urban legend?
Right century, wrong story.
Fitzharris eventually finds the source of the story, but I wouldn’t want to spoil the, er, fun for you.
Link to ‘Losing One’s Head’ (via @TheNeuroTimes)
Mind Hacks 
There’s a related story here: http://wp.me/pd52p-dz4
Of course there is the classic tale of Antoine Lavoisier, the father of chemistry, having his assistant count the number of times he blinked after being decapitated as a measure of his consciousness. Lavoisier had held the position of the tax collector during the French Revolution, a most unfortunate social responsibility. But the tale has been considered debunked. I would guess that the drop in blood pressure would be so sudden and affective that the lose of consciousness would quickly follow being decapitated. But it still makes a great tale to tell high school chemistry students of a man who was a scientist to the bitter end.
I’ve always thought there should be a distinction here between functionality and consciousness. Blood pressure seems to need to be so balanced that even someone standing up too fast can get a bit woozy. I would think that a drop to 0 would cause massive failings in consciousness even if the brain can still partially function.
I observed a video of a beheading from Iraq. The person was from Napal. The victim was laying on his back,his head was tipped backward while he was beheaded from the front of his throat to his spine, with the spinal cord severed last. It took longer than one minute for the perpetrator to reach the victim’s spinal cord. During the time that he sawed through the victim’s neck with a large knife, even after the main vein and two arteries to the brain were severed, for several moments the person’s diaphragm and wind pipe spasmed in an effort to take in air. I would be more precise about the amount of time it took, but I don’t want to watch it again. The person’s body showed signs of distress for about one third of the beheading. The spinal cord seemed the most difficult part to sever, but by that time there were no other signs of life and large quantities of blood had been lost. It would stand to reason that under most conditions when the brain is deprived of that much blood the person would lose conciousness. I remember thinking to myself that had the beheading been as quick as with a gillotine, it would have taken at least a moment or two for the person to lose concsiousness as the blood drained from his head. If the head were upended, preventing rapid blood loss, it seems that it would be a few moments before total oxygen deprevation would occur. If he been beheaded quickly from the back of the neck, messages from brain/spinal cord would not have reached the diaphragm requesting it to suck in air, but it may have tried.
Many things can cause loss of consciousness but the first to arrive on the scene at a beheading is insufficient oxygen through loss of blood circulation. It is not blood pressure per se that is so immediately important, as that drops to zero very shortly after severance of the carotid arteries, and there have been reports of severed heads appearing to remain conscious for some seconds at least. While it is ultimately pressure of course that causes the blood flow needed to supply the oxygen in the first place, flow without oxygen is useless so the rate-limiting factor for consciousness in a beheading is really all about oxygen.
Similarly, fast decompression to vacuum or very high altitude results in a rapid decrease of blood oxygen concentration that allows a ‘Time of Useful Consciousness’ of about 10 seconds. That’s about how much time you have to get your oxygen mask on if you’re in an airplane at 30,000 feet, and why they tell you to put yours on first. However in that situation blood still flows to the brain while blood oxygen concentration tapers off. Although it does taper quickly that should provide at least a couple seconds of extra oxygenation time to the brain that an instantaneous beheading would not. So figure you get maybe 8 seconds of Useful Consciousness after your head gets chopped off.
After the Time of Useful Consciousness has passed however, there should follow some few seconds of delerium until complete unconsciousness occurs, but I don’t have any idea or data about how long that might be or how you would measure it. If you do, please share.
Instances where heads are sawn off over a period of time instead of an instant beheading by guillotine or other means can introduce a lot of ambiguity to the story. For example if someone’s carotid arteries are cut they’ll bleed out and go unconscious quickly but for a long time afterward their bodies will react with very strong twitches as their spinal cords are sawn through. Similarly, recently dead eyes can respond to light and ‘painful’ stimuli evoke unconscious withdrawal reflexes, so they are not good measures of consciousness after beheading. A good measure though would be what Mason Kelsey described above as Lavoisier’s method of counting blinks after he was beheaded. I wonder how many blinks he did do, or if the story is even true?
It is questionable that Lavoisier actually did that as a “last experiment”. But the myth is that he blinked from 8 to 15 times. That would mean that he remained conscious for 8 to 15 seconds, which I cannot accept as factual. The loss of blood pressure would cause a quick loss of consciousness. Any blinking would be some sort of reflex movement. But it made a great tale to tell my chemistry students.
Maybe somebody can be decapitated in an MRI, in the interest of science.