One of the major concerns that a friend of mine who is paralyzed from a spinal injury is the inability to tell when he's been injured below his torso. This may seem like a positive, rather than negative, aspect of paralysis, however quite the reverse is true. For instance, upon completion of the Twin Cities marathon he discovered that he had cut himself rather badly before the race had started, and as a result had lost a large amount of blood during it. His natural ability to react to pain in order to remove it, a sort of conscious homeostasis, was lost.
Of course there are other ways for the body to monitor itself. He probably felt thirsty because of the loss of blood pressure. He may have been more tired than normal. In the course of a marathon neither of these seemed unusual, and that was where the danger lay. None of the other homeostatic mechanisms were nearly so effective as that of the conscious awareness of, and desire to relieve pain.
How does this reflect on the involvement of behavior? It suggests that the spinal cord does not have the level of consciousness that the brain embodies. The spinal cord is able to begin movements, as shown by simple reflexes. And in most paralysis victims, the pathways between the legs are connected. If the legs were consciously aware of the pain, it would seem to follow that they would be able to maintain some level, however small, of conscious homeostasis, one of the most basic forms of conscious functioning. However, the injured racer's other foot did not make any attempt to aid the injured one, or even attempt any motion at all. Conscious homeostasis was not present in any form between the two legs. While this proves very little, it does suggest something that most of us have always simply assumed, that only the brain, and not the spinal cord or surrounding body, contains consciousness, or the I-function.
Fascinating and appropriate story, with very interesting thoughts about it. Yes, indeed, the upper part of your friends' nervous system lacks an important normal source of information about the state of his legs. I'm not entirely sure though that I would equate homeostatic abilities with consciousness. The spinal cord has some significant homeostatic capabilities on its own (which we'll talk about later), and there are additional homeostatic mechanisms dependent on the brain but which operate "unconsciously" (as we'll also talk about more later). Finally, we'll show some ways that "conscious" may counteract homeostasis, in some senses. Regardless, you've raised some very interesting questions and suggesteda very interesting way to think about them. I wonder if, unnoticed by your friend, one of his legs did some things (within limited homeostatic abilities) to assist the other? PG