How can thinking about the behavioral changes induced by the severance of the spinal cord inform our theories of "brain and behavior" and our definition of behavior?
As before, thinking through the definition of behavior can help us attack this question. Behavior can be characterized (although not very usefully) on the cellular level, as in "a certain input made this cell do that action", or on a variety of organismal levels, from "the animal lifted its right front leg ten centimeters off the ground and placed it down 20 centimeters north of its previous position" to "the animal indulged in walking behavior" to "the animal was attracted to the researcher and moved towards it", or even on a multi-organismal level, as in "the flies swarmed around the light".
These semantic niceties, I opine, exist for convenience's sake. A neurochemist and a psychologist would probably use different terms to describe a behavior of an animal, for example. These differences do not make one or the other scientist "correct", but simply reflect the differing types of question that each is seeking to answer and the different methods and styles of experiment that are available to each.
One's method of explanation would be cumbersome or inappropriate to the other--nevertheless, an awareness of each's methods can be useful to apply towards an understanding of the overall system. A good example of this is the mind-brain question. Where does one end and the other begin? Does the mind contain the brain, or is the mind a property of brains? These questions have no useful answer, but thinking about them can clarify, enliven, or assist the work of mind-scientists and brain-scientists.
Biology contains many styles of description of behavior, from the chemical to the ecological. In the case of a person with a severed or otherwise disconnected spinal cord (that is, a central nervous system in which the brain is not in direct contact with every part of the body--for the sake of this discussion I'll talk about a human, Pat, whose spinal cord has been severed around the fourth vertebra), some methods of describing behavior can be applied with only a slight change, and others cannot.
For example, Pat's sensory neurons will generally continue to fire according to the same rules as they did before. In some cases, like if Pat's hand is left on a hot stove, some of the same behaviors can be observed--the hand may jerk away from the heat. These neurons still function, of course. They have no reason not to; they are still receiving nutrients from the bloodstream, they are still connected to the spinal cord, which is capable of many such reflexive actions. But the lack of connection to the brain, which controls speech and voluntary motor control and the like, will mean that Pat will not be observed to display "organismal" behaviors like saying "ouch!" or turning off the stove or applying ointment to the hand.
Therefore, the case of the severed spinal cord leads us to a few possible classification schemes for behaviors. Behaviors like thought and breathing still occur, but a previous connection which existed between them is literally gone. Maybe we can think of behaviors in terms of the scope which they encompass, or the cultural purpose they serve, or the psychological need they fulfill. Instead of looking at an organism and thinking "what behaviors is it capable of?", this train of thought leads us to look at a "behavior" (from signal transduction to culture formation) and think "What organisms are capable of this behavior?"
A sidenote: another class of behaviors has been created by the modern world's conveniences. I thought of this in reference to, say, someone in a voice-powered wheelchair. They move in a way that is related to the function of their brain, but is not related to their legs. In this, such a wheelchair is like an extension of the brain side of the severed-spinal-cord duality. How are such behaviors to be classified? The use of the computer, too, has substantially changed many areas of human endeavour, but in the end humans are still doing what they always do when they work at computers. Right now, for example, I am indulging in a brand-new class of behaviors related to computing--email, typing, using a disk, and so on. But the larger umbrella of behaviors contains all this under "communication" or "science", making my typing a side effect of my communication or my scientific education.
How can this apply to biology? Perhaps some larger classes of behaviors also have many different underpinnings, like communication has typing and talking and body language. I think I most easily understand this in reference to affective, or mood, disorders. In them, people may show the outward signs of being in a certain mood that are indistinguishable from anyone else in that mood, but their causes may have genetic components, while someone else may be in a "bad mood" brought on solely by the environment. (Long-term observation can distinguish the two, but that is still another class of behavior--its duration).
Another level of this is realized by the discussion of mind-altering drugs--in them, a pretty "high-level" behavioral choice(getting and taking drugs, maybe involving behaviors like money-handling and car-driving and language) creates a "low-level"(biochemical) behavior change in the body (which may resemble a behavior that the body is already capable of, as with amphetamines and schizophrenia). Eating is like this--what we eat may influence our biochemical makeup and therefore our behavior.
In my discussion before, I was unconsciously considering only the cases where the lower levels have a unidirectional influence on the higher levels of behavior, but of course the other direction is possible as well--if higher-level behaviors _couldn't_ influence lower-level behaviors, there would be no nature vs. nurture debate. With this new way of thinking, then, the severed-spinal cord problem is cast in a new light. The low-level functionings of the brain cannot (well, perhaps hormonally) induce high-level body control and therefore some (but not all--see the "sidenote" paragraph) classes of high-level behavior, like walking or holding one's breath.
In a normally functioning animal, high- and low-level behaviors can influence each other, but in Pat and other such impaired animals, this influential balance is altered. This seems like a simple but powerful extension of the first way I discussed to classify behaviors, and it has scope--microbiologists can talk about how a pathway and a cellular environment change each other, psychologists can talk about how an individual alters their brains by their behavior, and anthropologists can talk about the interplay between culture and individual.
This also seems to be an interesting way to discuss "normal" and "abnormal" as concepts. In her essay last week, Erin Brown made a point that perhaps "abnormality" is a dysfunctional connection between the "boxes" that make up the nervous system. In this week's ramblings I have been suggesting that the size of the box we draw to separate the system (neuron, CNS, organism, social unit) from its surroundings will determine the type of behavior we observe. Combining the two ideas leads us to the conclusion that there are different types of communication breakdowns that lead to different types of "abnormality". I also, though, suggested that the communication is bidirectional. Perhaps the bidirectional component is "normal", while unidirectionality is "abnormal". But some diseases, like multiple-personality disorder, when the personality "fractures" as a survival mechanism in the face of severe abuse, are a result of the application of bidirectionality. So is unidirectionality what we usually think of when we say "normal"? I have purposely painted myself into ths corner to illustrate the weakness of the "normal/abnormal" constructs. If someone has an illness, it is normal for them. Normal, then, is a probabilistic, not deterministic, quality.
One more thought, gleaned from reading Margaret Gruen's Week 2 essay. "God is what happens when people combine in societies like neurons combine in the brain." I can understand God, scientifically, as I understand consciousness--as that which emerges when individuals create a group. It's pretty interesting that I had this thought; I'm not generally someone who looks for definitions of God. (more readings have found this thought in David Rakoff's statement, "Consciousness could be considered a social construct, where the society is comprised of about 10 E12 neurons.").
Enought for one week!
Indeed. But also enlightening, sophisticated, and much appreciated (presumably by your colleagues, who you have obviously been paying attention to, as well as myself).Needless to say, I share your inclination to see the usefulness of all levels of description, and to use this to make better sense of concepts like "normal" and "abnormal". A key point, which you argue strongly (and I think correctly) is that causal relations must be understood to run from higher levels of organization to lower as well as from lower to higher. The neurobiologist Roger Sperry was very concerned about trying to get people to understand this in his later years ... and it has an earlier history summarized in Koestler's Beyond Reductionism. PG