Wikipedia:Reference desk/Archives/Science/2014 September 25

= September 25 =

Sustaining a brain
What would you need to do to sustain a living brain? What does a brain need to keep being conscious? 49.183.204.22 (talk) 04:06, 25 September 2014 (UTC)
 * A body is useful. Or maybe not... -- Jayron  32  04:10, 25 September 2014 (UTC)


 * See head transplant and brain transplant. A brain will clearly need a functioning blood supply, and maintaining at an appropriate temperature, for a start. AndyTheGrump (talk)
 * See also Isolated brain.--Srleffler (talk) 04:34, 25 September 2014 (UTC)


 * A brain needs a body to live and remain conscious. Obviously various limbs can be lopped off and so forth, but that's the question of how much you can mutilate a person without killing him or driving him mad.  Sensory input is necessary to maintain consciousness, see sensory deprivation and the works of people like Antonio Damasio. μηδείς (talk) 17:14, 25 September 2014 (UTC)


 * I don't see a body as an absolute requirement, it's just that we haven't yet found a way to replace all the functions the body performs, which are necessary to maintain the brain. StuRat (talk) 04:28, 26 September 2014 (UTC)


 * The blood can't just be pumped in at a constant pressure, either. It needs a heartbeat, as all our blood vessels are designed to work with a pulse. The blood will need to be oxygenated before it's sent in, and the carbon dioxide removed when it leaves.  Hemodialysis would also be needed to remove other waste products from the blood.  And food (in the form of glucose ?), needs to be added to the blood, including all the amino acids, cholesterol, lipids, vitamins and minerals required to repair the brain.  StuRat (talk) 04:24, 26 September 2014 (UTC)


 * Stu, you do realize that you have just said that you do indeed find a full substitute for a body necessary? A brain is a complex of biological organs that needs a body to work, even if some or most of the body is cyborg.  The more perfectly the organic is mimicked, the better.   It is nonsense to say otherwise, assuming that is, one understands physiology at the graduate level.  Ignore the platonists Goedel and Turing.  Read the aristoteleans Searle and Quine.  The latter were human, the prior only imagined they were. μηδείς (talk) 04:53, 26 September 2014 (UTC)


 * No I didn't. A heart-lung machine does the oxygenation and provides the pulse, a dialysis machine does the waste removal, parenteral nutrition does the feeding part.  This would be a series of machines hooked up to the brain, not a cyborg.  It would not be capable of moving, feeling, etc.  Now, if you actually wanted to interact with the brain, then you'd need to connect at least some of the senses.  The eyes can apparently be replaced by a camera hooked to electrodes in the visual cortex, although so far only low res images have been attained this way.  The technology behind a cochlear implant could also add hearing.  As far as output from the brain, you could read nerve impulses sent out from the brain, or perhaps use some scanning technology (PET scan ?) to read the nerve impulses within the brain. StuRat (talk) 13:56, 26 September 2014 (UTC)


 * But you did. You have just admitted that you'd need a suite of effective organs to replace the original ones.  You are not addressing that things like maintaining his blood sugar, etc, would require replacements for the pancreas and thyroid.  Such a brain would never thrive or lean in such an impoverished habitat.  And if it didn't have sensory input and the ability to communictae voluntarily it would soon go mad.  The solution might be an interface which would allow it to control and receive inputs from a robot body.  But again, that's a body.  Brains are not computers that just sit there, and consciousness requires embodiment. μηδείς (talk) 17:41, 26 September 2014 (UTC)


 * There's no reason why those replacement organs need to be contained in a single "body". They are a series of separate machines, and can remain as such.  As for the pancreas, thyroid, etc., the hormones they produce (like insulin) could be delivered directly by IV, as required.  So, whatever the original source is for those hormones, the brain need not be connected to it.  (BTW, this doesn't sound like a good life to me, either.)   StuRat (talk) 18:02, 26 September 2014 (UTC)


 * It's a difference of definition. My main point is that a brain not only needs a support system, it needs a mode of sensing and interacting with the world.  You awake an chose each day what to do, whether to get out of bed, what food to eat, what work to do and what entertainment to enjoy.  A brain kept alive at the cellular level due to an oxygenated blood supply that couldn't sense and interact with the world physically would go into a hallucinatory state at best--that's not consciousness.  Yes, those components need not be in one organic package.  But the brain does need a physical interface with some sort of world it can sense and manipulate to remain conscious. μηδείς (talk) 01:25, 27 September 2014 (UTC)


 * Did you see the original Star Trek episode where Spock's brain was removed and used to run an underground city ? Most of that episode seemed rather plausible, to me.  There the city became the substitute for his body, where it provided input to his brain, and his brain provided control over the devices which ran the city. StuRat (talk) 01:42, 27 September 2014 (UTC)
 * Yes, I have seen that episode. The problems would be that his brain would need to be entirely rewired in order to readjust to the different sorts of inputs he would receive and outputs he would generate.  The brain is already mapped onto the body in the sensory and motor cortices.  Anything that required decision making would require learning beforehand--imagine a class of disembodied brains sitting in class learning, today we will learn how to run all the water and sewage in chicago.  There's no brain area that's already wired to do this.
 * The brain and body are fully integrated systems. The brain works and is conscious because it connects to sensory and motor nerves and gets feedback from the body and its environment.  You can put the engine of a sportscar in another sportscar, usually without the patient dying on the table.  But you can't put the engine block on the street and win races or expect it to power a 747.  It's only Platonic and religious mythology that makes us think the mind is separable from the body. μηδείς (talk) 16:42, 27 September 2014 (UTC)


 * I believe car engines are sometimes used to power airplanes, which is akin to the Star Trek example. I've also seen tractor engines removed and used to power stationary machines. As for running water and sewage systems, that's something like kidneys and the urinary system, so perhaps an adaptation could be made there.  Just as people learn to drive a car like it's an extension of their body, we may be able to adapt to far more. StuRat (talk) 20:55, 27 September 2014 (UTC)

India Mars Mission - Escape from Earth
The Indian spacecraft made several highly eliptical orbits around the Earth before it finally achieved escape velocity and headed off to Mars. This YouTube video gives a good summary. On each orbit, the rocket engine was fired for a period as it approached the Earth. It would then coast around the rest of orbit. This seems like a reasonable approach: you are going to get more speed when you accelerate a falling object than trying to lift a rising one. But is this correct? F=MA (Force equals Mass times Acceleration), so it shouldn't make any difference when you fire the rocket. I have faith that the Indians knew what they were doing, but I can't figure out exactly why their technique worked. - Pergelator50.53.245.175 (talk) 21:01, 25 September 2014 (UTC)


 * See Oberth effect for why it is beneficial to fire the rocket engine when the craft is traveling faster. Abecedare (talk) 21:10, 25 September 2014 (UTC)
 * Hohmann transfer is our article on this specific technique. Tevildo (talk) 22:45, 25 September 2014 (UTC)


 * Kinetic Energy! When you are traveling faster, the end velocity of the propellant is less, and since the total energy remains constant, the rocket gets a larger share than if it were traveling slower. This sort of makes sense in a weird kind of way. I'm going to have to think on it. Thanks. 50.53.245.175 (talk) 02:57, 26 September 2014 (UTC)