If all but the brain is removed, and...?

You would have to provide an artificial blood flow to provide the oxygen and energy, but let's say that is doable. The brain would indeed be alive, but the person would rapidly go insane. Without ears or eyes, without the rest of the nervous system to provide feedback, this is the ultimate sensory deprivation chamber. Our brains are used to processing information about our surroundings at all times. a disembodied brain is cut off from all of that.

If you could overcome that,(say allow artifical eyes and ears), the mental stability of the subject would still be in doubt. Now you have the same situation as someone with a severe spinal injury, or neuromuscular disease, who is trapped in their own bodies. on the plus side, our hypothetical support system is probably easier to maintain than an entire body that is wasting away because the muscles and nerves don't work. you reduce or eliminate the chance of infections, bed sores, and other complications of a bed ridden state. So, the person should be able to live at least as long as if in their body. Can they live longer? hard to say. We don't understand many things about the aging process in normal elderly. An isolated brain? Uncharted territory.

As long as the brain is functioning and the person is presenting with something approaching their normal personality, I would be inclined to call it human.

It simply wouldn't function, not even in the case of an ideal jar. The problem is that the brain's energy is not produced by itself, but the body, so even if it's preserved, those 15 watts would eventually and very quickly run out, besides, since the heart won't be able to pump blood to the specific regions of the brain, whenever some particular area is active (that's supposing there's still brain activity). Another problem, is that the brain's job is to keep the "body alive", therefore, without the body the brain would have no function.

The brain is in control of the body, that is its job. So, taking it out of the body would be pointless, because the only reason we have a brain is to keep the rest of our body alive. It has never been tried, but the brain would probably exist for as long as it would have lived inside the body. And that is only if we had a major improvement in technology, that could feed the brain what it needs to stay alive. It also needs nutrition, not just oxygen.

Honestly, since you would not be able to do anything except think, you'd go crazy if you were only a brain. The brain would be rendered nonhuman, because it could not speak to anything, feel anything, smell anything, taste anything, It would be the same as a stool or a table.

I like how you question life, and how you let your curious mind wander! Keep up with it, we need more people like that.

There is a video on youtube of an experiment in which a dog's head is cut off. The head was linked to tubes with oxygen and a blood pump. I do not know the other details.

Edit: Actually I found out how long the brain can live. Its 8 hours. Rodolfo Llinas was the man behind the experiment that was done in mid-1980s.

Source: Popular Science Sep 2012

I think we are all jumping to conclusions and basing our reasoning on the fact a brain seemingly is created to be in control of a human body. This probably is true but I don't think we can say that it would dry and die if it can not fulfill its purpose. I say carry out the experiment and await and see what will happen. The brain would still be capable of thinking, or else it would not go insane when it realized it had no body, but I don't think it would have to base its thinking on it former purpose. Brains go on even when their bodies have lost all their limbs in an accident. Maybe somehow it would somehow start a new line of thinking based on being in a jar. I read of a woman who was being driven insane because she felt a total responsibility to be everything for a large family of fifteen people.They put her in an isolation chamber where she could neither move, think, speak or react to any stimuli for a period of six months. When she came out of the chamber she returned to her family to find they did alright without her and that somehow prevented her from going insane and she assumed a different role in the family.

Someone once accused Steven King of not having a brain of a child.

His reply!

I do so have a brain of a child, in-fact, it is setting in a jar on my desk, right now.

So, ask Stephen King.

No it would not last longer because it is not as protected, unless it was in a heavy duty vault or something I would think it would be safer in a human head. I wouldn't call it a "human" because it has no voice or feelings and it just is'nt. Also I don't think it would function but rather just be living because it has no use anymore, no limbs to move or sights and sounds to process.

Without any method of receiving information from the world via the senses, it would have nothing to process.

we assume so. tests have been done on animals and show that it is possible as odd as that seems.