Hi,
I was curious to see these articles about people surviving horrific injuries to the head and surviving. This prompted my question as to how much/which parts of the brain are necessary to survive and function.
I look forward to your feedback.
I guess define “live”
This boy “lived” for 12 years with just a brain stem. There was a lot of intervention, including feeding tubes.
That’s important. If nutrition/hydration/hygiene are handled by caretakers, relatively little brain power is required to keep the body functioning properly. After Terri Schiavo died, an autopsy showed that her brain weighed half of what would be expected for an adult female.
Schiavo died after externally supplied nutrition/hydration was withheld; this was 15 years after the cardiac arrest incident that left her in a persistent vegetative state. I don’t know how much longer she would have lived. I recall hearing long ago that people with complete quadriplegia have limited life expectancy due to the absolute lack of physical activity; if true, I would expect the same problem applies to long-term PVS patients. There is a calculator here for estimating the life expectancy of patients with spinal cord injury; for a female aged 27 with a completely severed spinal cord at the C1-C4 level, it predicts 33.4 years of remaining life, implying that Schiavo may have been expected to live another 18 years or so, assuming her brain injuries weren’t compromising her physiological functions.
For chickens, not much at all: Mike the Headless Chicken - Wikipedia
A Frenchman fuelled what a lot of people suspect about government employment by keeping down a job with a 50-75% reduction in the volume of his brain matter.
Well, there is this case of a normal person living with no brain at all (well, some brain but a very small portion):
The doctors are anxiously waiting for the man to die so that they can investigate and see what is really inside the man’s skull. Whatever it is it certainly isn’t a normal brain.
For those that don’t check the links, neither the man nor his doctors had a clue about his unusual brain for many years. He is living a normal life with a family and a job. But he is doing it with nothing that we would call a normal-sized or shaped brain.
I really wish someone would just post a link to the New Scientist article about the French guy with the tiny brain already.
Before he started running for president, Dr. Carson did quite a few hemispherectomies - removal of half the brain - to stop otherwise uncontrollable seizures.
Most of the people for whom he did this lived varying degrees of normal life afterwards. Some years back, I saw a PBS show where they were at a reunion of some of Dr. Carson’s patients, and others who had undergone it, and all of them had some degree of hemiplegia and about half of them also had some degree of speech impediment. They ranged from people with a slightly twisted arm up to people who had to use motorized wheelchairs, and interestingly, about 90% of them were female. There was a simple explanation for that: boys who have that disorder usually die before they reach this point. However, the guest of honor was the first person who ever had this procedure - a man who had it done in the 1940s as a last ditch measure. He had a speech impairment and walked with a cane, but he also had a college degree and a driver’s license, was married with children and grandchildren, etc. and was a medical pioneer in his own right. 
Pretty much none.
Jeez. Doesn’t anyone read my posts anymore?
You don’t need a lot apparently. Thanks, Popular Mechanics!
Well darn! 
for some reason I thought my posting was to a different article and about a different subject. Perhaps I need to have my head examined…
Sorry about the double post.
Follow-up question: How much of a brain is necessary to post non-redundant comment responses? 