Sigmund Freud felt a need to clarify the concept of the subconscious mind, and invented a new terminology to differentiate between the counscious and non-conscious. For him, the conscious was limited to the things that are going on in our immediate mental environments, i.e., what we are thinking at any given moment. Anything else was non-conscious, although the 'upper' half of the non-conscious mind was designated the pre-conscious, things that could very easily be in our conscious should we choose to think about them...things that can often be recalled by questions, "What color is my radio?" "When did I get that phone call?" These are often things we tune out of our conscious minds, but are always available for consideration, sometimes with more difficulty than at others. The 'unconscious' for Freud encompassed what we typically refer to as the subconscious, hidden, repressed, traumatic, blocked, undercurrents, events and experiences that we can not think about or even know existed at all, but that are sometimes revealed through dreams, slips of the tongue, and extensive psychoanalysis. Autonomous nervous system activity was generally considered to be a part of the subconscious, and Freud extended his 'unconscious' to cover those functions, although in reality many of them could be better considered to be preconscious, in that when we think about our breathing and heartbeat, for example, we can become aware of their activity, and sometimes consciously alter it. Certain n.s. activities are beyond the control or comprehension of the conscious mind however, such as hormonal release by the hypothalamus, blood pressure, certain other homeostatic mechanisms, etc. The concept of the human with the broken neck presents a problem different from all of these levels of consciousness. Something that is sensed by the nociceptors, passed to the dorsal root ganglia, to the spinal cord, through the ventral root, back to the motor neuron of the neuromuscular junctions in the leg, is definite behavior, and since the connections to the most rostral end of the spinal cord (the brain) where "consciousness" as Freud defines it is localized for the most part, are non-functioning, this stimulus-response cannot really be said to fall under any of the categories of consciousness supra. Consciousness as we know it is so far removed from this activity that it may as well occur in another organism.
The implications that this has on the importance of communication between neurons and other neurons, and especially neurons and the I-function, are that if 'we' don't 'know' what is happening at least on some level of brain-consciousness, it may as well not be happening. When that person's neck is broken, the brain ceases to be part of a larger body and it's related nervous system, and becomes a head with a life-sustaining apparatus attached at the neck. The body that we would normally consider to be part of a human being, and have a mind and a soul, may as well be a nutrient bath/respirator/circulation system like something out of a bad sci-fi movie, with a disembodied head attached. Which begs the question...when are necks are whole, does are body really have a mind? Or just a head, which in turn has mind.
I think, as long as we have skin to sense, and/or fingers with which to manipulate our world, or feet to propel us around within the world, our body is part of our higher consciousness. Otherwise it may as well be a lump of dirt, as long as our head were kept alive.
We could proceed to remove parts of the head from consciousness, too. Taste and all of the skin sensations of the face and head could be cut with a couple of cranial nerves, and our minds would still be essentially human. As long as there is some, however limited capacity for input and output of language and other stimuli/response, the consciousness remains unaffected and recognizable. About what goes on with complete sensory deprivation, we have an idea, from astronaut training, etc, but once means of communication are cut, we have no way of knowing if consciousness still exists. If the brain were kept alive, but removed from all input/output, how long could it survive on just the energy inside it (imagine the brain feeding off of action potentials that propogate each other continuously). Would someone put in this kind of state go instantly insane? Would we even be able to recognize their insanity? Imagine that the brain, after a long period of deprivation, is put back into a body.
Perhaps a tangental idea gotten out of hand, but it's interesting, and a little haunting, especially to consider oneself in the situation.
Neither so tangential, nor so out of hand. Thanks for bringing Freud along, he certainly belongs in the conversation. I'm not entirely sure I understand Freud's different levels of conscious/unconscious, or yours, but I wouldn't dismiss out of hand efforts to draw connections between them and the paraplegic. In intact nervous systems, there are, I suspect, close parallels to the lack of communication between parts of the nervous system which can result from trauma, as well as to the kind of indirect transmission of information which corresponds to slips of the tongue and the like. As for the isolated brain/head, that too is not so farfetched. A classic literature on sensory deprivation makes it pretty clear that consciousness indeed persists in the absence of sensory input ... and there is good supporting evidence from being able to look inside the brain, which will get to later in the course. PG
The case of a person with a broken neck can really clarify a lot of things if one would assume that the behavior that survived the damage of the nervous system reflects the actual human behavior. Is there any reason to assume that the surviving behavior is not partly due to some weird reaction to the damage? If I was to look back on the model of boxes discussed previously and to consider the fact that the model allows for the alternative pathways from a box to a box, would not this seem logical that if some pathway of the system was damaged, the output from the box could follow an alternative one, that is possibly not used in the ordinary situations?
But if I assume that the surviving behavior that we see in the person with a broken neck is an accurate reflection of what is going on in the nervous system, there are many cases of behavior that could be explained by it. The fact that when a person's brain and spinal cord are separated a person/brain does not feel the pain in his legs and cannot consiously produce a motion with his feet indicates that the brain and the spinal cord are responsible for the different functions in the nervous system. It also shows that the nervous system does not work as a string of lights on a Christmas tree: if one part of it is damaged the whole thing does not stop working. And this is the thing that I find hard to accept myself--how can a person still function (jirk the foot upon the pinch) when the nervous system is desrupted. But this principle of separate functions of the nervous system and the localization of "self" in the brain illustrated on the example of the broken neck person can really help to understand many other cases of behavior:
--for examlple, consider a person visiting a dentist. Let's say a person has a bad tooth ache. When a dentist gives a person local anastesia, a person stops "feeling" the pain while a dentist fixes his teeth. Does a person really stop FEELING the pain? No. As in the example of the person with a broken neck, the brain is disconnected with the affected area, and because of this loss of the communication, the brain does not "know" about the pain that actually exists. This is the principle on which the common painkillers work. But the case of the tooth-ache person is a little different because the nerves that are affected are actually connected to the brain, and the anastesia makes them to be inert towards sending the outputs and/or receiving inputs.
--Another example would be a paralized person. If a person is fully paralized, and cannot either move or talk, but his brain is undamaged, he can still function as a person. What I mean is, the person does not become less of a person, even though he cannot move or talk. So, I do not think that the idea mentioned in class that just because we cannot talk to a spinal cord, a spinal cord also could contain the "I-function", is right. In the case of a paralized person who has a damaged spinal cord and related nerves the surviving function is the "I-function", which means that the spinal cord is not really related to it at all.
So, as one can see, considering the case of a person with a broken neck can help one understand the separation of the functions between different parts of the nervous system. It also helps one understand the "I-function" a little better. It is also interesting to consider the relations between the "I-function" and the rest of the organism. For example, by using one's brain power, one can make an organism do things that ordinarily would be very dangerous (i.e. yoga, eating disorders).
Appropriate critique at outset, and then appropriate extensions. Yes, IS possible that what we see following damage is something totally different from how system normally works. But ... things tend to make sense on presumption that what we're seeing does relate to disconnection of semi-autonomous parts. Dental anesthesia indeed a related pheonomenon as is paralysis. I wasn't saying the "I-function" WASN'T in the brain, I was just saying it could ALSO be in the spinal cord (COULD be,we don't have a way to find out). And yes, we'll want to talk a lot more about when/where/why I-function interacts with rest of brain/nervous system. PG
The man with the broken neck can not feel his foot, replies that he feels no pain when he is asked, but still withdraws automatically when his foot is pinched. What does this imply about the human nervous system? We know that there are two aspects of the central nervous system: the brain and the spinal cord. Many of the body's actions involve an extended process of signals, passing from the sensory modalities up to the brain and then back through the motor pathways to the organ that performs the action. But some processes seem to take place without any input from the brain. In instinctual situations, you are up and running the moment you see a bear, even before you process the bear's present actions-whether it is preparing for attack or just lumbering through without any notice of your presence. These actions occur with less processing of the input than actions such as watering a plant or kicking a soccer ball. The type of responses that occur in these instinctual situations must be processed in a different, more efficient way. After all, if the bear is about to attack you, you can't pause to think about its other options. The bear will not wait for you. Perhaps these types of responses don't involve as much (if any) processing by the brain, and are dealt with only at the level of the spinal cord, making them have shorter duration. This would explain the response of the man whose neck is broken. Connections between the brain and the spinal cord may have been severed or lessened, but the spinal cord is still able to have small amounts of communication with the parts of the body connected to it directly. So even though the brain and spinal cord are typically thought of as dual point processing centers, they each also have processes independent of the other, allowing for faster processing in situations that can not be delayed.
Interesting extension. Need to be careful, though, not to presume an equivlence between "instinctual" and spinal cord, and something else and brain. Brain and spinal cord can work independently of each other; that's the point of the observations on paraplegics, with each having its own inputs and outputs beyond the nervous system. The response to a bear (perhaps "instinctual") involves both brain and spinal cord, since the input (seeing the bear) actually arrives in the brain (optic nerve). And the spinal cord is pretty sophisticated, capable of doing a lot of things one wouldn't obviously call instinctual. We'll talk more about what "instinctual" means, but for the moment let's leave it aside and just say that brain and spinal cord are capable of working independently of one another. PG
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
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
The mind's power lies in its ability to change and search for proof, as such the body is the main collector of sensory input. In someone with a broken neck the connection between the body and the brain has been severed, the brain is not receiving the signals and thus cannot interpret the inputs. The brain and the body are both functioning as separate entities, but we can really only see the thinking patterns in the mind not the body. Are we led to understand that there are two levels of control in our body, that have evolved at different levels ? Is it that we needed some way to sense danger and the surface area of our body, our skin, served that purpose, and proceeding with better awareness off our surroundings, we were able to develop higher sense, the thinking and communicating part of our brain. On the same theme, language which is such an important part of behaviour has developed and is most certainly linked to neurobiology. The connections which form in infancy must serve us the rest of our lives, we must somehow learn to communicate and convey our thoughts. The action potential along neurons can be seen as the language of the body. It talks to different parts through the passing of waves of energy. Someone who's neck has been broken, will experience a complete loss of control, they will no longer be able to send signals to the rest of their body to carry out what their brain is thinking, whether or not their brain continues to image the body is an interesting question. The eyes and consciousness would almost certainly perceive the body as still being there, and vital life functions are still being carried out by the hypothalamus, but the control center is no longer active, messages are no longer being relayed. We can understand the behaviour of the brain but not that of the body, because we cannot talk to the body part of ourselves. Everyone else can thus be seen as a complete combination of brain and body, the mind is always still free to work, because of the cranial nerves, but the body must react to external stimuli on its own, it is no longer a protective mechanism, we cannot see danger coming and act appropriately to avoid it. Behaviour thus is a very important mechanism which has many, many inputs not only the body reaction to what it senses from the outside world, and communicating it to the brain, but within it there is also the generation of certain choices. The mind is capable of directing the brain, we are capable of manipulating ourselves, thus making us independent and completely autonomous.
Interesting and appropriate set of concerns/issues. They involve some dichotomies which we may have to re-examine. Mind capable of controlling brain, rather than mind as part of brain? Brain/mind as distinct from body, rather than being part of body? Spinal cord as controlling body with brain controlling spinal cord? Maybe both as part of body, interacting with other parts of body and each other, no one thing in control? We'll see. At least worth thinking through the various observations to date to see which summary better fits them. PG
I'am a bit confused about the discussion concerning the frog's ventral root and input/output. If the ventral root is severed and irritating stimulus is placed on the limb, then another limb will wipe off the stimulus. Then, this demonstrates that the ventral root is output and not input. Does this mean that the stimulus is received by the entire frog, but only the severed limb cannot respond to it? This leads to a question about the person with the broken neck. Does pain exist if a person cannot feel it? I'am sure the spinal chord would say "yes", if it could respond, if the person's toe was pinched. So, a person's body can receive a stimulus or feel pain(at least their spinal cord) without their sensing it because the connection between the lower and upper part of the body has been severed?
Also, in the discussion about the filament and the neuron, if there is constant voltage moving longitudinal external battery and a constant transverse battery, does that mean one part of the neuron is constantly in touch with the muscle(the internal constant battery), while it is awaiting outside stimulus(which accounts for the moving voltage)? It also paradoxical to say that the information that the neuron collects has no substance or energy to it. Aren't the resting and action potentials information that the neuron is receiving or transmitting? Hasn't the information we received, of say a pinch to our toe, been a result of neurotransmitters and chemical or electrical interactions in our body?
Actually means that input can get into the nervous system from the limb without the ventral root (need some additional observations to say that the ventral root carries output to the limb). Yes, limb can't respond to input (because ventral root cut, and therefore motoneurons can't affect muscles). Yes, obviously input can get to other places in nervous system (including those containing motoneurons for moving other limbf). Yes, upper part of nervous system (with motoneurons for saying ouch) can't get signals about toe pinch. Does spinal chord feel pain? Don't know (as discussed in class). A subject to return to.
Will talk much more about batteries (potentials). Depend on matter/energy (of course) but don't move either. No, constant transverse battery doesn't affect muscle (is only across neuronal membrane, will talk more about this). PG
It is understood that a person with a broken neck has severed the nerves between the spinal cord to the brain. Thus if you pinch the toe, the foot will withdraw but there is no way for the information to get to the motor neurons in the cranium. This may seem obvious, but if the person canUt say that they feel pain or do not feel pain from the pinching of the toe, then how do they know they can't feel their legs? What in the brain tells them that have lost feeling in their legs? Another question I was curious about was the situation of walking and running activating the same channels then how does a person know which they are doing?
In "How We Control the Contractions of our Muscles" by P.A Merton, it is stated that "...self-regulating properties on a muscle, causing it automatically to adjust to changes in load, without any need for the orders that the brain sends down to be altered." If the foot knows it is being pinched and withdraws and if the muscles are self-regulating then why can't the muscles of the foot and legs regulate themselves to the standing position, even though the brain may not know that person is standing? In the article "Brain Mechanisms of Movement" by Edward V. Evarts, I think this question is answered. He states that "the inputs from these various cortical and sub cortical structures work together to control the final outputs from motor cortex to the spinal cord and thence to the muscles". So even if the muscles are self-regulating they are so only in part and the other part needs the brain. In conclusion the behavior of a person with a broken neck can be explained by studying the outputs and inputs and the connection between the spinal cord and the brain.
Yep. But it does raise some interesting further issues, as you also note. Will talk more about capabilities of spinal cord (which include walking, running), but in general the only way the rostral part of the nervous system could know they were happening is by looking (or hearing). And the running/walking/muscle self-regulation would not, as normally, be modified by vision or by gravity/motion signals (8th cranial nerve). PG
To be a good scientist you need to suggest the simplest model. This is understood and confirmed by most scientists. It frusterates me however, to see so much emphasis placed on physical evidence. As the new millennium approaches many important figures are predicting a massive change. A change not only in the physical structure of the world's collective culture, but a change in the mind set of the world's people as well. Astrolgists, physicists, and even the President, are all anticipating this change. This change can only occur if we let it, as we enter an age where global enlightenment is possible. The world is becoming a smaller place, and by virtue of this wonderful thing called the internet, we may connect with those in other countries, speaking a different language, in another hemisphere. The evolution of a sort of "global knowledge" is among us. Not only are we looking to the physical relm for answers, but we are accepting the metaphysical relm to offer some as well.
This all struck me again, as the lesson on action potential was being discussed. It seems that the human race as a whole is starting to pull things together. Not only philosophy and biology, but other culture's beliefs with one's own. Technolgy in the past has tended to discriminate against those that did not use it's vocabulary, it's terms, or it specificity when speaking of the brain. Technology of the present encompases all languages and all descriptions. Looking at the larger picture is enabling us to understand that others are and were speaking of the same things as we. Although they may not have dictated the information in our technoligy-specific manner, they processed the knowledge in the ways they were taught.
As I was coming to understand how an action potential works, I began to make the connection between "action potential" and the Chineese "Chi", or the Buddhist "Sushumna", all which describe the flow of energy or energy potential through the body. For decades allopathic medicine has given us temporary solutions to the "problems" of nature, but now we realize that we must learn what is at the root of these "problems" and prevent ourselves from being infected with the sickness. This is why I find it very important to learn about behavior and its neurobiological components. Indeed the universe is composed of energy, in every form, undergoing constant changes, yet never can it be created or distroyed. This energy is flowing through our bodies as well. As each polarization and depolarization occurs, there is a flux and information is transferred.
Behavior may be either complicated or simple, it depends on how you choose to define it. Maybe someone should just invent a word which covers it all, like an universal constant, which has no other purpose than to help us understand the world around us. Should we just except the fact that we were created as perfect beings, along with all that is living around us, or should we question why we are perfect? Ever since the first generation was cast out of Eden we have been searching for the answers. May there still be something this age old paradox can teach us about the beauty of life itself?
All of that from thinking about action potentials? I would be pleased though if you thought that understanding the brain might in fact provide some sort of common language which allowed the better sharing of diverse perspectives. Maybe the searching is what life is all about? PG
The behavior of a person with a broken neck helps show that the communication between the spinal cord and brain are important, as are the individual components. But it also brings up questions about the exact function of the spinal cord and nerves. A person with a severed spinal cord can still communicate with others because the 12 cranial nerves leave the brain above the spine and are not effected by the break we are discussing. Additionally, the vagus nerve controls the heart and viserea, so their basic life functions continue. Also, their mucscles and limbs respond to touch and will withdraw from a painful touch. The person cannot feel the touch, nor can they control their limbs. So both their spinal cord and brain are intact, but they simply are not connected. In a person with a broken back, they will have all movement above the break in the spinal cord, but none below. Again, the lower extermities will move when touched, but the person will not be aware of the touch. So the situation is the same as the person with the broken neck. But movement and sensation are also effected by other things. In people with a stroke, there is loss of movement and sometimes of sensation. This is often because a whole side of the brain will be effected and this side has sensation input areas and muscle control areas. Their spinal cord is fine and the communication to the brain is fine, but their brain is damaged. Additionally a person with nerve damage may not be able to feel their limbs, or move properly. But their brain and and brain/spinal cord connection are intact. This shows that all three are important to the normal functioning of a person.
However, many people with strokes recover a lot of the function and feeling that they have lost. Other areas of the brain take over the responsibiliteis of the damaged area. Additionally, if the hypothalamus is suddenly disturbed, a person will die, but if there is a slow growing tumor in the area, the person will not be effected. The responsibilities of the hypothalamous transfer to other parts of the brain. So why does this not happen in the spinal cord ? The nerves in the damaged area of the brain do not grow back, nor do they heal. Their functions are just taken over. Since the rerouting is possible in the brain, but not in the spine, does this mean that something other than the spine is responsible for movement? Does this suggest that the neurons in the body are highly specific and non-adaptive, whereas the neurons in the brain can change their patterns of use much more readily? The vagus nerve is still intact, so why cannot the signals be rerouted to this nerve, which would then connect the body to the brain. Or perhaps the body is structured so that this would not be possible, and there is no bypassing of the spine. But then how do you explain quardraplegics who learn to walk, or regain thir feeling? Do they just have damaged spines, and then part of the spinal cord takes on the responsibility of the rest of it. What if the vertral side is damaged. Does that mean there is no output, or would the dorsal root shift to take on both responsibilities? The case of a person with a broken neck brings up many more questions of why there body cannot adapt, as well as how it changes their behavior.
Interesting take on the whole thing. There is a very substantial amount of anatomical specifity in the nervous system, which sharply constrains information flow paths (as we'll talk more about). At the same time, it is indeed true that abnormalities associated with damage to some areas lessen with time. This may be because of new connections, or old connections taking on new functions, as you suggest. But it may equally be because the damage to one area temporarily disturbs the function of other areas, with the recovery not involving any new or substantially reorganized connections at all. We'll try and talk more about this too. PG
When a a person is diagnosed with a broken neck it doesn't necessarily mean the end of the world. If the break is below the medulla then the only thing that happens is that the person has lost all nerve connections to the body, and the brain. When the body is tested for the sensation of pain it'll register in the leg and withdraw from the source of the pain but if you ask the guy he wouldn't have known that you even touched him. This is the kind of phenomenon that still boggles the mind of many scientists today.
When the leg is pinched it must register the pain nerves to be excited. So the nerves make the trip up to the spinal cord but can't make the rest of the trip because of the loss of the connections. Whether or not there is any research bing done in this area is still not known, but how would one person go about trying to figure out what the nerves are registering? Well one way would be to try to set up an experiment where the excitement of the nerves caused a light to go off, or a sound to be made, but only the nerves that had anything to do with the sensation of pain. With this information it would be known if the nervous system (spinal cord) still continued to function even if the connection between it and the brain were severed.
Lots of research in this vein. And KNOW the spinal cord will continue to function disconnected from the brain. Questions have to do with how MUCH function the spinal cord has, and the trend of the evidence is much more than one tends to expect. Question is, beyond what has been observed, what would one look for to answer the question does it feel pain? And that may, for the moment, not have a good answer, not because one doesn't know how to observe spinal cord activity but rather because "pain" isn't yet a well defined concept. PG
Thinking about someone who has a serious spinal cord injury allows us to evaluate behavior and illuminates the fact that the spinal cord is the main vessel through which information is channelled up to the brain or is received and sent back out to the extremeties as motor output. If the spinal cord is cut, from the damaged point down, the body is disconnected from it's command center, leaving it seemingly lifeless. Although the body is paralyzed, it can still receive environmental stimuli, even if it is not able to send this information to the brain and receive "acknowledgment", and inturn react. The separation of the body and the brain as is the case when the spinal cord is severed, serves as a model for other behaviors. If any of the infinite "boxes" that make up the brain were for some reason disconnected or became unable to respond to incoming information, the chain of action potentials or signals is broken and the behavioral outcome is different. More specifically, for example,depressed individuals have lower levels of some neurotransmitters in the brain. If we assume that these unusually low levels somehow contribute to the depressed behavior then we can integrate the above model. If a smaller than normal amount of neurotransmitter is released at the synapse, then the intended signal may not be passed along- or acknowledged by the adjoining neuron. This leaves the receiving pathway unstimulated, which results in an abnormal behavior, or one that deviates from the norm due to the pathways miscommunication.
Interesting and appropriate line of thought. Add one idea though, that the disconnected things (as in the case of the spinal cord) are not necessarily "lifeless". They may continue to act (foot withdrawing when toe is pinched) but no longer does so in appropriate relation to the actions of other things. "Blues" occur in most people's lives, but can be alleviated by various other factors. Perhaps depression is an active "box", no longer able to be turned off by other inputs? PG
Something struck me in class when we were talking about the battery that exists within our bodies, the axon. I found myself thinking about the complexity of the processes that occur within our bodies and the sophistication of the systems that carry out these processes. It seems incredible that the body has the capabilities that it possesses. It's amazing to think that the reason I am able to type this is that a billion of neurons are firing thousands of times per second in a specified pattern. Something so complex as human behavior and human thought can be explained in what seems to be the simplest of terms--the passing on of information by an electrical code generated by one neuron to the next. With all of our sophisticated technology, we still do not have the ability to create anything as complex and sensitive as our own bodies.
Yep. And it is not (necessarily) so much that the components aren't understandable (and potentially makeable) as that they are assembled in the most exquisitely detailed way. What seems simple is indeed, when one looks carefully at it, enormously rich and complex. Furthermore, it changes (as you type). PG
In the past I have considered the brain (alone, not the entire nervouse system) to be the place where all nerve responses both originated and were processed. But since a person whose neck has been broken still has behaviors while no information from the lower part of the body can be transmitted to the brain, some processing obviously takes place in the lower section of the nervous system. Although at first it may seem logical to question whether the withdrawl of the foot is due to an optical input, this is obviously not possible either because just as no information may travel up to the brain, likewise no response could be initiated from the brain to the lower limbs. So now it seems logical that motor and sensory neurons stemming from the lower part of the body are processed in the lower spinal cord.
More interesting is why the person moves his foot. Does he "feel" the pain of the pinch? Or does he move his foot simply because someone is touching him? We have discussed in class the "does he feel question", and come to the conclusion that there is no way to prove this one way or the other. But it seems that there must be either some feeling or thought process which causes the person to withdrawl his foot. I don't know if his response is a self-preservation type reaction or if he "feels" pain in a more involved way.
This example leads to other questions about the construction of the nervous system such as where are the neurons for feelings and other such intangibles located?
Nice point: visual information can't reach spinal cord just as nothing from spinal cord can reach brain. And yes, do want to know more about "feeling" and other intangibles. Will try and get to them. PG
The fact that a person with a broken neck does not say "Ouch" or feel when their toe is pinched, but pulls away their foot, indicates that there are certain behaviors that are totally independent of the brain and the I-function box in the brain. More specifically, it indicates that some behaviors, besides dreaming, do not involve consciousness or free will. In addition, this demonstrates how the behaviors are highly dependent on communication between the different "boxes" of the nervous system. This high dependence on communication accounts for the large number of interneurons. The mechanism by which a person with a broken neck, and any person for that matter, pulls away their foot when stimulated can be easily accounted for by simply looking at it as the communication of neurons. An input (pinching) to the toe causes the sensory neurons of the toe to send a signal to the motor neurons in the ventral horn of the grey matter. The motor neuron, transmits the signal to the muscle which ultimately makes the person contract their foot. In the case of the person with a broken neck a signal sent at the spinal cord by the sensory neuron does not reach the brain because the connection between the two is severed. My questions is, how does this signal in a normal person get translated into the person saying "Ouch" and feeling the pain? Put more broadly how does an input impulse(signal) translate into a behavior? Not just any simple behavior, but one which causes a person to connect the word "Ouch" with pain and then proceed to make the vocal cords move to say it. It seems to me that there are three types of behaviors that the case of a person with a broken neck brings about: one which is independent of the brain, one which is dependent of the peripheral nervous system, and one which is dependent on both. Now, what seems interesting to me is to see
Yes, we'll want to put things back together again. But you've understood the main point: the problem is understanding how the parts interrelate. Careful, though, about two things. First, the sensory to motor transformation in the isolated spinal cord is nowhere near as simple as you describe it, there are lots of interneurons involved. And two: we don't, for reasons discussed in class, know whether what the spinal cord does involves consciousness and free will or not. In fact, we'll use some of what the spinal cord can do by itself to try and develop a clearer understanding of what is meant by those terms. PG
A person whose spinal chord is broken but can still express emotions and think and have behavior raises the question, what exactly causes behaviour and if only their mind is working while the rest of their body remains stagnant, are they able to behave at all?
The first thing needed here is a definition of what behavior is. If we classify behavior as the response to a PHYSICAL stimuli, like withdrawing a foot from hot coals, then, ofcourse, this hypothetical body can perhaps experience a stimulus but not react, thus not exhibiing behavior.
However, If behavior can include mere thoughts in reaction to a color, action or something else in the environment, then by all means, Behaviour is possible in this hypothetical body. (I tend to lean towareds our latter definition.)
Since, in my eyes, a person can "behave" even without a spinal chord in tact, it leads one to the belief that the "I function" or the "person" within us all, lies somewhere in the brain. Whats interesting is that, with the additional loss of control of one body part and then another, we can prove that that is not where the Ifunction hibernates. It is a type of "process of elimination" which leads us to the emininent conclusion that such a function exists, and that it exists in the brain.
Science continues to explore new areas and correct previous theories with new knowledge, and I can't help but think that one day, a revelation in the I function will occur, and that this imaginary, or at least what I know now of it at this point, pretend human function, is actually something quite simple yet in a different sort of dimeension that nobody has yet thought to look. Then again, the mere thought of modern science begining to understand the i function, in terms of artificial intelligence and replication is frightening.....sometimes, what one doesn't know can't hurt you.
I think Iw ould like to continue studying human biology as it is now and let the I-function remain a mystery......
Understand your trepidation. On the other hand, what one doesn't know frequently CAN hurt one (and does). I'm not sure I am following your argument exactly, but the "process" of elimination does indeed provide an important way to locate things ... subject to the important reservation (discussed in class) that something may be said to be somewhere but not that it is not ALSO somewhere else. PG
Pain and suffering are usually described in different terms. Pain has a very definite biophysical, biochemical meaning. Pain receptors at various sites receive "painful" inputs from the internal or external environments of the body, the sensory neurons then transmit the impulses to the appropriate areas of the brain where they are processed, and one "feels" the sensation of "pain". An interesting observation is that the brain itself has no pain receptors, and so has no way of detecting inherent danger to itself. Pain, after all, serves as a survival mechanism, warning the organism to stay away from the danger that the input represents. Thus children who lack the appropriate receptors, or lack the ability to correctly process the incoming signals pose a great danger to themselves, for they have no threshold. The point is that while everything about the way pain works in the body and in the organism's interactions with its environment may not yet be clearly known, it is forseeable that everything about pain may one day be described in terms of neurons and action potentials and EPSPs and IPSPs.
Suffering, on the other hand, is more vague, and its source not so easily pinpointed. One might say that suffering is to behaviour what pain is to brain. However, the notion of "suffering" does not necessarily contradict the brain- behaviour equivalence. Perhaps suffering just represents an extremely complex pattern of multiple pathways numerous enough to pose severe computational difficulties. But for argument's sake, suppose that every pathway in the "complex" could eventually be mapped, and suffering was reduced to a complex algebraic series of EPSPs and IPSPs of action potentials, it might still seem prudent to forget that kind of a reductionistic description in order to be able to deal with the macroscopic realities that suffering induces in the daily lives of people.
Why, then, bother to map out all the pathways, if it serves our purpose better to treat the feelings and phenomena in a "holistic" manner? Certainly, detailed knowledge of the exact ways in which the various circuits function is intellectually stimulating, and has applications in the manipulation of behaviours by physicians and other health professionals. But is it truly worth manipulating the mind with behaviour- altering drugs to the extent that we have been doing? And what possible repurcussions can this have for future generations, who may have at their disposal a "happy" pill, and a "sad" pill, and an "angry" pill, and a "calm" pill?
Nice distinctions, at several levels. Indeed, "pain" is, at this point, better understood in terms of neurons than is "suffering", but one can at least glimpse how the latter might also be recognized as corresponding to patterns of neuronal activity. Is it worth it? I think so, because doing so will, I think, close off the thoughts of "happy" pills and all the associated (and appropriate) fears of mind manipulation. "Suffering" can be no less complex understood in terms of brain function than it is understood holistically (if brain is behavior), and so will continue to exhibit all of the questions inherent in it as a holistic concept (multiple causes, benefits and costs, contributions to/detractions from personal growth). And it will correspondingly involve lots of widely space neurons using lots of different transmitters, and so not be "correctable" using pills (or surgery). At least that's the way I think it will come out. PG
When considering a broken neck or a cut spinal cord, location of neurons and their ultimate destinations are fundamental. If the spinal cord is cut, the entire body does not become non-functional, but, as a result of the Law of Physical Continuity, certain actions of the body are affected and certain actions that tend to coincide may no longer do so. For example, if the spinal cord is cut right before the brain, then sensory neurons receive external information and transmit it to the spinal cord, but the transmission of the signal may not be continued to the brain because of the cut of interneurons that pass the signal to other interneurons and motor neurons in the brain. Therefore, although there may be an output from the body, it is in conjunction with neurons associated with the spinal cord, and not the brain. The reverse situation is also plausible, in which the brain receives input that requires an output from the body, and yet it cannot occur because if the interruption of the connection. Furthermore, the nervous sytem is a distributed system in which complete behaviors are often the result of the entire nervous system coordinating a single output that may involve many aspects of the body. This implies that a cut in the spinal cord may cause certain human behaviors to be partial or incomplete, such as when one may be able to scream in fear, but unable to run, indicating a seemingly incomplete action.
One of the implications of having a nervous system dependent on the localization of neurons and a distributed system is that, in the case of a neck injury, not all human function is damaged. Furthermore, the locations and functions of particular neurons becomes more accesible to the researcher. By determining which actions and behaviors are seemingly incomplete, one can determine some of the locations of certain neurons, and the realtionship that these neurons have to the body. A problem arises, however, being that neurons may affect one another even though they may not be directly linked. Because of the actions of one particular neuron, located in the brain, for example, another neuron associated with the spinal cord may act differently depending on whether or not it receives a signal, or whether or not a neuron associated with it receives a signal, and so forth. Therefore, determining the location and function of certain neurons may not be as simple as it appears.
Accurate and sophisticated summary of the situation. Yes, both distributed system and one in which elements differ and location of each is important. Important both for understanding system, and for interpreting observations on it. PG
In examining someone who has suffered a broken neck and is therefore paralyzed, we have discussed in class that it is the connection that passes the electrical impulses from the spinal chord to the brain (thalamus, hypothalamus, cortex, etc.) that is severed. This also means that neuronal signals cannot be transmitted from the brain back down the spinal chord either. These people are therefore paralyzed. The signals can travel through the sensory nerves into the spinal chord through the dorsal root but the reciprocating motor nerves will not be activated. We compared this to the studies done on the frog nerves entering the spinal chord, where either one root or the other was severed, thereby severely reducing capabilities while still leaving some functions intact. We could see the frog walking on the leg when he couldn't feel it and reacting to pinches when he shouldn't have been able to move it. Yet a broken neck eliminates all of these avenues. This evidence proves that the brain must still receive input when one of the roots whether it is dorsal or ventral is cut. If the brain can receive input, behavior can occur.
A person who has suffered this injury still performs some of the types of behavior we have discussed. The I function is still present, the personality is totally intact. We debated the idea of personality being in the spinal chord along with the brain but this idea does not stand up against the evidence presented in the case of para- and quadrapalegics. The distinction between action and behavior is an interesting idea which needs to be explored in greater depth.
Indeed we'll want to consider the relation between action and behavior in greater depth ... again and again as we go through course. Careful about use of terms like "paralyzed". Arms and legs CAN move in person with broken neck, and do. Sensory signals entering spinal cord can and do produce motoneuron discharges from spinal cord. What can't happen is sensory signals entering spinal cord producing motoneuron discharge from brain, and sensory signals entering brain producing motoneuron discharge from spinal cord. PG
i decided that i was going to stray from the suggested topic this week, because i have had something on my mind for a while now. What i have been wondering is: if life is random, then how could the nervous system, a very complex and intricate system, have just randomly come together and be able to do all that it does? I wonder why there are not any more problems that arise for the average person because there are so many levels at which information can be lost or mutated.
Every individual person is basically defined by their nervous system, for it controls all the behaviors that the person performs. It controls who we are and what we do. And the nervous system controls all this by transporting information in and out at an extremely rapid speed, and, on the average, with very little difficulty. The input usually remains intact when passed on from neuron to neuron, and produces the correct output. This is simply amazing to me. I don't understand how this can happen. For example, if you have ever played the game "telephone" where everyone gets in a circle, and one person starts out by saying a sentence, and the sentence is transfered from person to person, until it finally reaches the original speaker. I have never played this game and had the passed-around sentence be the exact same as the original sentence. Yet the nervous system effectively does this exact same thing, with few mistakes.
One of the things which i believe helps transmit this information so effectively is that the information is distributed throughout the nervous system and many neurons are activated with the same information. Maybe this allows for some neurons to lose the information and still have the end message arrive at its destination. It also probably helps that there are divided pathways for inputs and outputs so they don't get confused. Yet even with this information, i still don't see how more information doesn't get sent to the wrong location or that an incorrect message is sent. Its possible that there are millions of messages being transmitted, and maybe a good number of them do get lost, but the ones that are safely sent are enough to allow us to act properly, and we are able to tell carry out our every-day duties. the nervous system maintains the ability to move our arms so that we put food in our mouths instead of all over our faces. I just keep waiting for the day when too much of the information in my nervous system is blocked by some substance or a huge chain of neurons get confused and i start spasming in all kinds of weird ways. but for the time being, my neurons seem to be working fine, because i was able to type this essay and coordinate all the neurons in my brain with the ones in my fingers... but don't ask me how.
Very interesting (and appropriate) set of questions/concerns. Without a full answer, but we can (and will) talk about parts. The first thing to remember is that the nervous system isn't really in the business of faithfully transmitting signals from point A to point B to point C. It is instead using a variety of signals at each step to create new signals (so its not quite like the telephone game). Both at the steps and in the interactions of the steps there are homeostatic features, which tend to keep things reasonably constant even if burps occur. And there are regularities which emerge from having lots of noisy elements interact with each other. And .... ? PG
Behavior is dependent upon two big boxes which are the spinal cord and the brain being able to communicate with each other. If a person has a broken neck, he/she will lack in this ability. Therefore a person with a broken neck will express different behavior from a normal person. The connection between the brain and the spinal cord allows individuals to express various kinds of behavior. An individual with a broken neck will not have this particular connection and therefore will express certain behavioral differences.
An individual with a broken neck will not have control over his/her body. Physical movement will be greatly reduced. However the properties of the spinal cord allow for some movement in certain circumstances. For instance, if a person with a broken neck gets pinched in the foot, the foot will withdraw due to the spinal cord reacting in such situations. This individual will probably not be able to verbally express the pain since the information of the pinched foot has no way to reach the motor neurons in the throat which will allow for verbal expression. A normal individual in this situation will react with withdrawing his/her foot and will have the ability to verbally express their pain. This is since the normal individual has the connection between the brain and the spinal cord which allows for the information to travel between them.
An individual with a broken neck has control over his/her brain to think and express their mental thoughts verbally but can not express physical behavior concerned with the rest of his/her body. He/she can decide to move their limbs but will be unable to follow through with the actual action since the spinal cord will not be able to receive information from the brain. This individual has the ability to feel emotions and thoughts due to functions of the brain but may be restricted to physically express or feel these emotions ( such as physical pain below the neck). For instance, if the individual is deeply sad, he/she may be able to cry but will not be able to wipe their tears with their hands(which is a common reaction when crying) or express their sadness physically otherwise.
Every individual is unique and each individual has the capability to express different behavior. It is important for any individual to have the connection between the brain and the spinal cord in order to function freely. This essential connection between the spinal cord and the brain will allow people to express their mental and physical needs and actions.
Not wiping tears a very nice example of what's disturbed in paraplegics. Careful though about "an individual ... has control over his/her brain". Presumably (at least on brain=behavior presumption) the "individual" IS the brain (or some part of it), so who controlling who? PG
We've been discussing alot of information about the spinal cord, the brain, and the connections between the two that can produce observable behavior. The interesting pieces of the "nervous system puzzle" are those that deal with the abnormalities and phenomenons associated with behavior. The intricate communication between caudal and rostral to the medulla through to the telencephelon may not be observable, but the output it generates is: a behavior, an action, a feeling, a movement, a response.
After reading
This raises the whole issue of whether the brain simply processes incoming information and analyzes it accordingly OR whether the brain isn't as pasive as we (or I) had thought. Maybe it generates its own output which is just comlemented, not necessarily dictated, by sensory input. The article propses a whole genetically determined "matrix" which is unique for each individual. It networks the parietal lobe, the limbic system, and the sensory pathway. These incorporate the sensory stimulation, a sense of self, and a generation of impulses to reassure the body is one whole. The output from the matrix carries information about the sensory input, but it also gives validity that the sensation is indeed occuring.
So without any true input from a limb, since the limb isn't even there, the rest of the body perceives pain, other sensation, and most importantly (and strangely!!), it feels like the limb is actually still attached. The idea that the brain generates this without any input makes me wonder. Maybe humans really aren't simply machines which react to input and act because of random nerve firings. This hypothesis reworks that idea in that the brain itself is "in control". Although genetically programmed, the matrix functions autonomously sometimes with, sometimes without, external or real stimulation.
To move into stream of consciousness, this certainly brings my thoughts back to the possibility of mind, soul, and a being. If our brains can make us believe we have body parts that really aren't there, they may be more complex than networks of nerves.
You're ahead of us, but that's fine. Yes, indeed, a sense of limb location may exist in absence of any input from the limb. Part of why we're not there yet is that we need some things first to understand how that could happen with no mystery, simply as a consequence of "networks of nerves". So we'll come back to the issue in a bit. Meanwhile, though, your more general point is entirely appropriate: the nervous system (as we'll see again and again) is NOT a passive receiver of and reactor to sensory information. PG
The issue of where "the person" or the I-function resides in the nervous system has been bothering me. In class you said that we know that their is a I-fuction that feels and is able to express what it has felt in the brain. You also said that we have no way of finding out whether or not the spinal cord has such an ability because we have no way of communicating with the spinal cord. The way I see it, the brain and spinal cord, just like the heart and lungs, each have their individual functions. The heart will never control breathing and the lungs will never control the circulation of blood, eventhough each organ is dependant on the function of the other. I think that the same kind of distribution of function is true for the nervous system. I think that the I function depends on the inputs from the spinal cord, and that the spinal cord responds to inputs from the I fuction, but I don't think that the spinal cord also has a component I function. By taking a look at people in Persistive Vegetative State, ie people who have lost cortical fuction but have retained brainstem function, it is possible to examine what kind of role the spinal cord plays in term of the I function and conciousness. These people exhibit bodily functions such as breathing,gagging, coughing, but seem to have lost the ability to be concious and aware of themselvesaand their surrounding, the ability to comprehend, the ability to question, and so on. It is as if these people are living, but not really alive. I think by looking at these cases and examining the effects of the loss of cortical function, we can say with as much certainity as allowed in science that the I fuction does reside in the brain. It is true that we cannot say with complete certainty that an I-fuction does not also reside in the spinal cord. But chances are, the spinal cord, which is concerned with the more primitive life forces, is not complex enough to house an I function. I believe that the development of the brain, specifically certain regions of the brain,have evolved to take on this so called I function.
I'm inclined to agree with you, but I still think its important to understand that we don't yet have a definition of consciousness which would allow us to be certain about the capabilities of the spinal cord ... and that we could be missing something simply because the spinal cord doesn't "talk" in the ways we normally use to assess consciousness. My point is less that the spinal cord might be conscious than to critically examine what we MEAN by conscious. And that many important properties of things (including the spinal cord) have been missed because people didn't look for them in the right way and hence presumed them to be absent. You're right, though, that additional observations make consciousness in the spinal cord less likely. PG
This week's lecture has advanced us from a big box representing the nervous system to 10e12 smaller boxed interconnected components to even more specific terms of neurology. It's exciting to get closer and closer and to build up terms and vocabulary for the brain to help us understand brain and behavior, which can be a very dense and overwhelming topic.
This situation of the poor person with the broken neck has become a recurring example used to investigate the connections and intricacies of the nervous system through neurons when there is malfunction present in the information processing system. In this case, the person with the broken neck has an interruption between the cranial nerves and the spinal cord nerves. Thus the relay of information is handicapped, and we can explain why such a person would not say 'ouch' when their toe is pinched. We learned the basic responsibility of each of the 12 cranial nerves, and with this knowledge, we can see how the person would have no way of getting the motor neurons which control the throat and the tongue to say 'ouch' because information from the caudal end of the body could not be carried to the cranial nerves as a result of this gap in the system pathway. Additionally, if told to lift a leg, this person would not be able to perform such a task, because the cranial nerve which is responsible for auditory control is cut off from the caudal motor neurons. Thus we learn that there is a vital connection that must be maintained in the nervous system for it to properly work.
So, we can expect this person to have no control of the movement of their body below the neck region. Thus, I would conclude that this person would not be able to feel pain in the region of their body below the neck, such that if their hand was put in a flame, they would not sense the burn, and if they didn't know better from past experiences or from their own knowledge of the consequences of burns, they would not necessarily know to remove their hand from the flame. I bring this example up, because I remember hearing of a disorder which makes people insensitive to pain, who have to be very careful to not hurt themselves.
I can understand how frustrating this must be for the person with the broken neck because they can adequately hear and speak, but they still can't coordinate voluntary movement. It's difficult to understand, even with this basic knowledge of the nervous system, how although the person knows what to do, they are prevented from doing the task by this break in communication. We tend to think that such simple tasks are simply regulated, when in fact, there seem to be whole 'circuits' of information relay responsible for these actions.
The thought of the person with the broken neck is tragic- they can think and their brains still function in the previous capacity before the accident (if there was no damage to the head), thus they are able to perform 'higher thinking', but in a sense they are prevented from doing the most basic things such as simple movement.
It makes one wonder if there is such a way to 'learn' how to move again, as many healers promote faith and the thought of mind over matter, and in this case, the mind is intact and functioning.
Don't underestimate the spinal cord, which probably knows enough to pull the hand away from the flame whether or not the information about it reaches the brain. And there are, of course, ways that such people can move, using prosthetic devices. Maybe it could be done by mind over matter, but not if mind=brain=behavior. PG
What does the fact that the body still responds to input once the spinal cord is severed say about the "Brain is behavior" Theory?
If the spinal cord is severed at the neck, the hand will still respond to a feather on it, even if it is not felt by the brain. Along with this specific premise, the argument that the brain (which encompasses the entire Central Nervous System)is indeed behavior. Since the spinal cord in the thoracic cavity of the body can act in certain ways without the input of the lobes of the brain inside the skull, clearly the head is not needed to move the left hand to scratch the right when the spinal cord is severed.
However, I have a difficult time conceptualizing the actions with respect to the neuron activity within the nervous system. I accept that the four lobes of the brain are not needed for every movement that the body makes. However, the biology of the nervous system when it reacts to the input of a feather on the hand confuses me. Am I to assume that the sensory neurons on the back of my hand receive the input of the feather, travels along the axon that runs from my hand to my spinal cord, runs down the axon to my other hand, and tells it to scratch where the feather landed. Furthermore, while all of this is going on, the eyes see nothing and the brain does not tell the hand to scratch?
When I discussed this with Professor Grobstein, it all made perfect sense, now I am confused again. Do the electrical impulses running along the axons have the ability to force muscles to contract and extend without the use of the brain? Does the spinal cord posses "brain-like" qualities to allow this to happen? What are the "brain-loke" qualities that let the brain make the scratching decisions instead of the spinal cord? Do the other senses (sight, smell, hearing, tasting) go away when the spinal cord is severed, just as the lower part of the body loses significant mobility and sensory capability? Or are some parts of the brain inherently most important in the realm of senses? Basically, I am curious as to whether the touch sensation is more or less developed than other senses.
Confused by ...? Or simply surprised? Yes, spinal cord has "brain-like" qualities. Signals enter it on sensory neurons, are processed by interneurons, and leave it as organized patterns of activity in motoneurons (like using one limb to scratch where feather landed on other). Spinal cord loses "sight, smell, hearing, tasting" because those signals arrive on sensory nerves that enter brain, can't be communicated to spinal cord. Touch not "better developed" but simply a set of sensory signals that directly enter spinal cord. That help? PG
In an interview, Christopher Reeves and his wife announced that they were going to try to have children. Christopher Reeves is paralyzed from the neck down due to an accident. I wondered if the Reeves couple may have their hopes set a bit high. After all, all of the reproductive organs are located in the lower half of the body, and in Reeves' situation, the lower part of his body is disconnected from the brain. I began to think of the discussion in class about the accident victim with a broken neck. We concluded that if toe of such a victim is pinched, the leg will withdraw. We also concluded that the victim does not say ouch because the brain is not recieving the message that the toe has been pinched. What actually happens is that there are nerves that go into and come from the the caudal end of the spinal chord that control the legs. The nerve (axons) that run from the legs to the the dorsal horn of the spinal chord (sensory neurons that recieve message of the pinch) where they end and synapse with interneurons that in turn synapse with motor neurons that cause the leg to withdraw. The brain is not needed for this part of action. However, from the dorsal horn, signals also travel rostrally through the spine via white matter that in a normal nervous system would signal the brain that there is pain, and the "I-fuction" should say ouch, via the hypoglossal nerves in the medulla. The accident victin with the broken neck does not say ouch because nerves that run through the neck to the head have been severed and therefore the message does not reach the medulla. We also noted that if the victim is asked a question, he can answer, indicating that this action is not effected by the accident and funstions seperately from the spine.
With this bit of information, I think I can try to answer the question as to whether or not a person paralyzed from neck down has the ability to have sex. If in fact the male sex organs are controlled by sensory neurons running to the caudal end of the spine, and motor neurons running from the caudal end of the spine, with the brain playing no part, then stimulation of the sensory neurons should make it possible for the male to achieve an erection and have sex. However, there is a part of the brain that mediates arousal, and parts of the brain that would cause secretion of various hormones (the names of which I am not yet familiar), that may also need to be considered and we have already determined that the brain will not recieve any information, it is disconnected from information relayed fron the caudal nerves of the spinal chord. So it seems that the answer would be dependant on the role and how necessary of a role the brain plays. It is also apparent that having sex would be for the sake of reproduction only, because the rostral part of the nervous system, the brain, (where the I-function that we know of is located) will not know of any sensations transmitted because they will be cut off below the medulla.
It is also interesting to think about this: "If we do not need our brains, or to say, if we do not need the "I-function to reproduce", meaning to have sex only requires stimulation of sexual organs, than this should influence ones opinion in paternity suits, and other social functions. In other words cases of fatherhood and motherhood, and who has the rights to claim these titles.
An interesting, and highly germane set of concerns. Yes, indeed, some sexual function may be local to the spinal cord (though is possible, likely?, that in this case some kind of artifical insemination may be what is planned). And the fact that different parts of the nervous system can function to some extent independently of one another does indeed raise a host of legal/ethical issues that deserve some thought. PG
Generally I find the subject of paralysis and the interactions of spinal cord and brain extremely interesting. I had a personal experience of paralysis that was drug induced.
In order to have joint replacement surgeries I opted for an epidural. This procedure stops sensory feeling and motor functions from about the waist down by inserting a catheter directly into the spinal fluid by which passes such drugs of the opiate variety. Somehow, because the interaction occurs in the spinal cord, only (or mostly) my legs were involved. One of the side effects that I noticed was that for months (years) afterward I did not have complete feeling in my toes. Instead I would have a zinging or tingly sensation which was not painful but yet worse because it was "half" of a sensation. To this day I do not have complete restoration of feeling in my toes.
Since then, I wondered how the medications worked on the nerve cells and whether some sort of leftover sensation was the cause of strange sensory information felt months after the numbing effects of the epidural wore off. Also, what kind of imbalance was caused inside the entire spinal column because of the foreign chemicals?
In talking with my doctors I never got the feeling that they had complete understanding of why epidurals work. In fact, after being on an epidural for seven days I experienced an overdose (due to miscalculations) and as a result had two epileptic seizures. The fact that I had never had seizures before and that the doctors realized their error, pretty much indicated that the drugs in my spinal fluid interacted with my brain, as well, to cause an electrical imbalance. This means that the drugs were not only effecting my legs but were effecting my brain and probably circulating throughout my blood as well. But why, then, did not my whole body experience numbness?
There are so many more questions about how the spinal cord and brain and body interact. I am at a loss as to try to explain all that I experienced, such as a seven day memory loss after my seizures, but I might suggest that signals are possibly saved someplace in the body and resurface in a translated form. And could it be the case that spinal fluid carries its own form of communication to the brain, without the involvement of neurons, that is chemical in nature and could have caused my seizures? This is something I continue to think about.
Very much worth continuing to think about. Many thanks for the personal observations. Obviously, the intent of the epidural is to locally inactivate sensory pathways (taking advantage of the fact that they come into the nervous system at different locations, as we talked about in class). Equally obviously, as you say from your experiences, there was unintended broadening of the effects, both in space and in time. And, as you say, it was probably not general drug circulation, since you didn't have whole body numbness. Lots to think about (and yet to be understood), but yes, spinal fluid is continous with fluids bathing brain and can be a communication pathway independent of neurons (would bet though that there is neural communication involvement in symptoms you describe). PG
I was mesmerized when you brought up the idea that we do not know if the spine is conscious because we can only talk to the brain/head. This brings back some of the mysteriousness into what we are studying. The idea of what is consciousness and how the input/output system works is pushed to its limits by this idea (we do not know if the spine feels pain when we give it input because we can only talk to the part of the person that did not receive the input).
We also discussed the idea that by damaging the nervous system, the thing you took away is not necessary (from behavior after the damage, it will show that the part was not necessary). How does this relate to Lashley's experiments that involved him taking out huge chunks of a rat's brain, and it was still able to follow out the task at hand. In other words, how does all of this relate to our ability to localize behavior to a specific area of the brain or nervous system?
Good question. What Lashley's experiments clearly showed was that the ability to do tasks, as he defined them, was not localized. What he (or at least others) inferred from that was that all parts of the nervous system do the same thing (i.e. NOTHING is localized). The latter is clearly not true. Damage to different areas of the nervous system produces different deficits. Therefore the different areas are doing different things (though exactly WHAT they are doing can't be specified in this particular way). The great challenge is to understand how different parts doing different things can lead (in general) to distributed functions (i.e. many different brain areas contributing to most tasks, behaviorally defined). That help? PG
When a person's neck is broken, their behavior is altered, and we can say that some of the functions below the neck remain; these are due to the somewhat autonomous nature of the spinal cord. We cannot tell what has happened to the behaviors that are not exhibited anymore. The information needed to exhibit them might be disposed of, stored, or still dispensed and blocked along the way to its receiving point.
I am wondering about the effects of a similar separation of the nervous system at a point higher up than the neck. We have used the cut spinal cord quite often as an example of how each of the five sections of the nervous system acts on its own to an extent, but how representative really is that example? I can imagine many more complications we would have to account for if a cut was made, perhaps, between the diencephalon and telencephalon. Would this person be deprived of smelling since the olefactory nerve is on the telencephalon and the part of the brain that is most crucial to regulating body activity is the medulla (which contains the vagus to control the heart and other organs)? Would this person be deprived of thinking or of consciousness that they were thinking, since the neocortex is such a large area of input processing? Would this person be able to think and smell and do nothing else? Would this person be dead? (Where does the "person" exist?) Certainly the bundles of axons such as the spinothalamic fibers that ascend all the way to the neocortex would be interrupted. I am inclined to think that a cut at this location would result in an array of partial behaviors and complete chaos in the nervous system without the direction of the telencephalon and neocortex, rather than the simpler scenario of the two divisions continuing to function without communication as in the model we work with in class. It strikes me that there is some organization to the cranial nerves, with the less crucial nerves toward the front, but I do not think this implies that there are less crucial parts of the brain. All of the brain's wires appear so tangled and interconnected at this point that any disturbance could cause the entire system to crash.
Very nice extension of questions discussed in class to a new, entirely appropriate, and fascinating set of issues. In general, the spinal cord example is quite representative: the various "boxes" of the nervous system really ARE SEMI-autonomous (they go on working, though somewhat differently, in isolation), and we'll see this over and over again, including in cases which approximate what you've described (isolation of forebrain structures, to varying degrees, from more caudal structures). Classic experiments on the frog show some, but not a lot of difference in behavior when the forebrain is separated from the rest of the nervous system (I'm actually thinking about redoing some of those in light of some other work, want to help?). No, they're not dead (nor do they crash). Humans? I can make some guesses (the situation is different because of the neocortex) but don't know of clear clinical material that would answer your questions. It may exist though, and it would be worth looking at clinical publications to see how good a guess one can make. PG
When the spinal cord has been disconnected from the brain, we observe that the brain and the spinal cord continue to function independently of each other: the foot withdraws when pinched, and the head hears and speaks. If the brain attempts to initiate movement in the foot, however, there is no resulting movement. This is because the physical contiguity between these two parts of the NS has been interrupted; information cannot be transferred from the brain to the spinal cord (and, thus, to the foot). Observations of the same individual also reveal that the/an "I-function" exists in the brain, since it retains the ability to acknowledge and convey self-existence in a way that existence is recongnized by others--that is, the rostral region of the NS is able to talk.
We don't know, though, that there is no "I-function" in the spinal cord just because it won't respond to a question such as, "Are you there?" What is it that the "I-function" consists of? Is it solely the ability to be "aware"? Or does it require the ability to initiate behavior (create output w/out input)? Does the spinal cord ever initiate movement or other behavior?
What if there was a separation in the connection between, say, the midbrain and the thalamus (instead of between the spinal cord and medulla)? Would the individual lose more than his eye-sight and sense of smell? What about if the NS were cut in both of the aforementioned locations? I would predict (based on the behavior of the individual w/ a broken neck) that each part of the NS would be able to carry out its functions as long as it was still connected to whatever it was designed to control. ... But for some reason, it's hard for me to imagine one part of the brain doing anything without the rest of it...
P.S. I've heard that humans only use a fraction of their brain (something like less than 10%). What exactly does this mean?
Yeah, is hard to imagine, but is so. In the case described, and in others as well (as we'll see). Its important, and I think you'll get used to it after a while.
PS I've heard that too, don't know what it means, and suspect its more or less like one's mother or father telling one to pay more attention to what one is doing (which may, but doesn't necessarily, mean using more of one's brain (anatomically defined). PG
I am comfortable with the notion that brain=behavior. What I am uncomfortable with, or more specifically curious about, is our "man with the severed spinal cord." My question is, if the link between the brain and the rest of the body is severed, at least at the level of the nervous system, how does that body function at all? I understand that there are structures and regions in the brain that control specific parts of the body; for example, the cerebellum is involved in muscular coordination, the medulla in vital functions, the hypothalamus in basic biological needs...the list is endless. Now, I know that regions like the pituitary gland interact with other organs through the bloodstream. But is that the only way, after severing the spinal cord, that the brain can communicate with the rest of the body? Does the bloodstream need to work overtime? Or do most signals travel that way normally? I guess the brain probably doesn't need to go through the spinal cord to, say, tell the heart to beat or the lungs to draw in air; but it still seems difficult to me that a person could at all function in such a condition. Would he "know" that he was hungry or thirsty? What about temperature regulation? As I am writing this, I am reminded of the "autonomous properties" that we talked about, both in this class and in bio lecture. And although I am comfortable with that aspect of biological organisms, I still cannot help wondering how this situation would really work, or if it would really work at all.
Good questions/concerns. Both generally (how do semi-autonomous entities work in coordinated way?) and specifically. Don't myself know enough about it, but hunger and thirst interesting issues. To the extent that the relevant sensory signals have to enter via the spinal cord, these would be lost. However, some part of "hunger", "thirst" almost certainly has to do with sensory receptors monitoring blood sugar and osmolarity in the medulla, and these should be intact. I suspect one would see some retention and some loss similarly in the other situations you mention. PG
Again, I understand your assertion of the existence of an "I-function" in terms of a person who has a severed spinal cord, but the idea continues to be bizarre to me. The logic that there seems to be an "I-function" located in the rostral nervous system (because a paralyzed person will continue to assert that he is "in there" when asked), but that we cannot know for sure whether there is such a function in the caudal nervous system (because there is no way of asking), makes sense, I suppose, but does not seem to me to be particularly scientific. And then there is the question of the mind that we have discussed for the past three weeks. Is the "I-function" a "mind"? What biological purpose does it serve within your brain=behavior model? Perhaps if we turned more directly to the biology of the nervous system and the evidence that you find there for your model of behavior, it would do more to back up your argument than would further philosophising at this point.
Fair enough. Will though return to "I-function" and what it might be good for. And let's return as well at some point to the meaning of "scientific" and how/whether that's different from "makes sense". PG
A person whose spinal chord is broken but can still express emotions and think and have behavior raises the question, what exactly causes behaviour and if only their mind is working while the rest of their body remains stagnant, are they able to behave at all?
The first thing needed here is a definition of what behavior is. If we classify behavior as the response to a PHYSICAL stimuli, like withdrawing a foot from hot coals, then, ofcourse, this hypothetical body can perhaps experience a stimulus but not react, thus not exhibiing behavior.
However, If behavior can include mere thoughts in reaction to a color, action or something else in the environment, then by all means, Behaviour is possible in this hypothetical body. (I tend to lean towareds our latter definition.)
Since, in my eyes, a person can "behave" even without a spinal chord in tact, it leads one to the belief that the "I function" or the "person" within us all, lies somewhere in the brain. Whats interesting is that, with the additional loss of control of one body part and then another, we can prove that that is not where the Ifunction hibernates. It is a type of "process of elimination" which leads us to the emininent conclusion that such a function exists, and that it exists in the brain.
Science continues to explore new areas and correct previous theories with new knowledge, and I can't help but think that one day, a revelation in the I function will occur, and that this imaginary, or at least what I know now of it at this point, pretend human function, is actually something quite simple yet in a different sort of dimeension that nobody has yet thought to look. Then again, the mere thought of modern science begining to understand the i function, in terms of artificial intelligence and replication is frightening.....sometimes, what one doesn't know can't hurt you.
I think Iw ould like to continue studying human biology as it is now and let the I-function remain a mystery......
Understand your trepidation. On the other hand, what one doesn't know frequently CAN hurt one (and does). I'm not sure I am following your argument exactly, but the "process" of elimination does indeed provide an important way to locate things ... subject to the important reservation (discussed in class) that something may be said to be somewhere but not that it is not ALSO somewhere else. PG
We don't like the idea of a reflex becuase it violates the Harvard law. (any other reasons why?) When I prick the foot of a person who's spine has been cut they will not always pull it back or pull it back in the same way... however, that they can pull the foot back even though they cannot feel the foot implies that neurons can function in simplest terms wihtout connection (input from or output to) the rest of the NS. TO pull the foot back takes only a sensory neuron connected to a motor neuron. So this means that a neuron doesn't need to be apart of the biggest box in order to perform it's function and also, it can exhibit the Harvard law inconsistency as an indiivdual or very small group of 2. So the Law is active at the micro and macro level.
In Buddhist philosophy we spoke sopme about the issue of free will. the issue of mind/brain split comes up, and it is taken for granted by many that "science" sees the brain as a big computer. cut and dry--they have taken the soul out of man. There must be a mind a locus of free will, where "I" exist. it would seem that free will could be explained in terms of the harvard law...neurons will fire randomly or not at all sometimes for "no good reason" except that they damn well don't want to. perhaps we have found the ghost in the machine.
Nice question. Yes, there are more reasons than the Harvard Law to not like "reflexes", but I hadn't thought of the issue quite that way. Can work on it together. Reflexes tend to make one think of simple paths through the nervous system, rather than, as we'll see even more of, distributed processing systems with important parallel and recurrent pathes. That a beginning? Along which lines, pulling foot back requires MUCH more than a sensory neuron connected to a motor neuron, for reasons we'll come to (LOTS of muscles, need to be active in right pattern). But yes, groups of neurons can indeed work independently of other boxes. Whether they exhbit, at that level, the Harvard Law is another very interesting question, one we're actually doing some experiments on. No simple answer, but individual neurons do indeed exhibit "noise". And yes, I think that is an important part of finding the ghost in the machine. A PART. PG
For this week's essay I chose to continue our discussion regarding dynamical system's theory (Thelan, etc) and it's usefulness in terms of helping one to understand or conceptualize a view of the nervous system as boxes within boxes. You indicated that you would like to hear more about dynamical system's theory, and although I feel that I am only a novice in terms of understanding it, I will give it a shot.
Dynamical systems is a theory, as I know it, a theory developed to describes how development occurs and how behavior emerges and changes. It has been mainly utilzed (to my knowledge) to describe motor development and the development of motor control, as in how a child develops and refines walking (much of Ester Thelen's work has been on walking and reaching development). Dynamical system's states that "behavior is an emergent property of interactions of multiple systems. Because the behavior is not specified, but emergent, the system can be said to be self organizing" (Kamm, Thelen and Jensen, 1990, page 770). This theory has arisen from works on Chaos Theory and embraces the concept that patterns (in this case behaviors) arise from the cooperativeness of many elements. MY interpretation of this is that we strive to make sense of chaos by creating systems for looking at and understanding things. In this class, our way of understanding behavior is by examining how the nervous system works as a system of boxes within boxes.
Dynamical System's theory challenges the notion that behaviors arise as a result of nervous system maturation and suggests that behaviors (specifically movement) are influenced by many factors (such as biomechanics, gravity, motivation, arousal state, as well as neuromaturation). The task itself will influence the behavior because it will provide certian constraint which will determine how the behavior is performed. For example, if a child is reaching for a round rattle, the shape of the rattle itself will influence the grasping pattern that the child uses. It's attractiveness and appeal to the child will influence if the child attends to the rattle, etc. The environment and the organism also provide additional constraints. Can the child physically move their body to get to the toy; is the lighting in the room such that the child can see the toy?, etc. IN addition, the system is said to be self organizing and self modulating in that it will organize around the task to be performed (rather that being driven by the CNS), and it will be modulated by mechanisms at all levels, influenced by systems or structures horizontally as well as vertically. It is a non-linear system.
So you see the dynamnical systems theory is similar to the box within box theory of how the nervous system guides behavior because they both realize that behavior is organized around the task (not directed from above); that there are multiple factors that influence any given behavior; and suggest that any of these factors may take precedence or set limits on a specific behavior. They both allow us to appreciate the compexity (or chaos) of the nervous system while enabling us to conceptualize its compelexity (?). In addition, they allow us to appreciate behavior within the context of real life, with it's complexities, diversity and indivdualism. Although neither discounts the concept that there is some linearity in the nervous system (ie: the individual with a spinal cord injury can not move or feel senstation from their limbs because the information to and from the higher centers can not get through); they appreciate the activity that is occuring at other levels of the nervous system (brain stem to cortex) and how this activity can drive new behaviors to emerge. For example, the idividual with a spinal cord injury who wants to move their wheel chair independently so they can get to visit their girlfriend, can learn a new behavior: using a mouth stick to operate the wheelchair switches. The "person" has not been injured but spared; the motivation to accomplish a task is apparent and the behavior is organized around the task for success.
The box metaphor does indeed proceed from many of the same concerns that motivate complexity theory generally ... particularly with the idea that most behavior arises not from a single cause but rather from an interaction among a set of influences, and that behavior can reflect more abstract objectives rather than simply particular bits of "machinery". The question, as you put it, is whether complexity theory gives us a practical way to usefully conceptually complex systems ... i.e. is it more than simply an acknowledgement that things are complex. Hopefully, we can do better than this, at least in particular cases. Recognizing the independent capabilities of brain and spinal cord (with "normal behavior resulting from an interaction among them) is one example. Can you be more specific about how this approach helps to understand emergence of motor behaviors in a way different from more traditional approaches? PG
It was said in class that for a great many of our behaviors we utilize a big percentage of our neurons. This makes sense when we are talking about mechanical behaviors such as walking or driving. However, how can we be sure that we are indeed using all our nerve mass? We have no way of showing that when we listen all our neurons in the part of the brain dedicated to listening are really active. In fact, in the popular media it is often said that our species uses only a very small percentage of its brain nerve mass. There are hypotheses about how the exremely intelligent people, genii, have the ablity to use a quantitatively bigger portion of their brain. The problem, as I see it, is how do we test this idea. We still don't have a way of monitoring every individual neuron in our NS, and even if we did it couldn't be very practical considering the great number of neurons in our bodies.
Thus, the question of whether or not we use all of our neurons stays withot an answer. If we allow for the possibility that we do not use all the capacity of our NS, then we have to ask what is its purpose, why is it there? It is very unlikely that we have more than we need in such a highly developed and essential system because the evolution did an excellent job of cleaning out the unnecessary characteristics. A possible use for this excess nerve mass might be to provide a safety net in case the main pathways crash, but we can't say that it can replace the damaged mass. It would be interesing to know with certainty whether or not we use all of our neurons since this may allow for a better insight into ways the NS functions.
Yes, an interesting issue. Point in class wasn't that we use everything but rather that lots of things are used for almost anything. I've heard the popular press story that most people don't use all their brain, but I think that's an assertion that people could in principle act more wisely or thoughtfully rather than to be taken literally as a measurement of how many neurons are active. In principal, as we'll see, acting wisely or thoughtfully might mean either more active neurons or fewer. PG
Paralysis is defined as the loss or impairment of the ability to move a body part and/or the loss of sensation to a region of the body as a result of damage to it's nerve supply. There is a distiction however between the ability to move a body part and sensation in a region of the body. For example, a cat who has had all sensory nerves in it's leg severed, but still has an functioning output connection from the brain to its legs will be able to walk. (It will however have difficulting adjusting to uneven terrain.) Furthermore, in many animals the severing of the spinal chord may result in the inability to consciiously walk, but the walking motion and rhythm can still be induced by experimenters. This indicates two things: 1) There is no need for constant sensory input for the motion of the legs (in terms of walking) and 2) The spinal chord is responsible for generating the normal walking pattern.
I find these two facts very interesting in terms of the situation of the human paralysis and loss of motion. Furthermore the issue of conscious movement is an important one. How does what one feels relate to how one moves? Although a paralyzed person "feels" no pain the foot will still retract when pinched. This indicated that the conscious notion of pain is not necessary fot the body to try and protect it's tissues. I think that conscious movement and the issue of pain raise some very interesting questions and would like to read further on the subject. I also think that this subject has some interesting ramifications on the treatment of severe chronic pain.
Careful about defintion of paralysis, there are lots of different kinds, as we'll see as we continue talking. You're ahead of us a bit, but yes, an ability to walk autonomously is one of the properties of the spinal cord. As is, distinctly, an ability to walk without sensory input. Yes, indeed, the observations raise some interesting questions about the relation between consciousness and pain (and about how to treat pain). PG
During our class discussions, we have referred to behavior as patterned output using the example of various patterns/sequences of muscle innervation such as running, extending the arm, etc. These are all examples of physical behaviors and of patterned outputs from the biggest box, the nervous system. At the same time, during the first week we also classified mental functions such as thinking, feeling, dreaming, learning, etc. as behaviors as well. Given that we have dealt with behaviors as patterned outputs from the largest box involving muscular innervation, my question is whether we can extend this example of behavior as patterns of outputs to non-physical, mental behaviors as well. Mental functions such as dreaming, feeling, and learning involve measurable outputs produced by the visual cortex mediated by the pons, the amygdala, and the hippocampus respectively. Similar to the examples of muscular outputs characterized as behaviors cited above, cortical activity during REM sleep is patterned as are the theta rhythms and LTPs produced during learning. On the other hand, unlike these physical examples of motor outputs, cortical outputs involved in thinking, learning, feeling -- these mental behaviors -- are outputs from interneurons within smaller boxes of the central nervous system. How do we classify the nature of the outputs of the visual cortex activated during REM stage sleep or the hippocampus during learning or remembering? Are they considered behaviors despite the fact that they involve outputs from interneurons in the smaller boxes of the nervous system? Do we still classify them as behaviors? If so, then do we modify our concept of a behavior as patterned motor outputs from the nervous system to include patterned outputs of interneurons in smaller boxes of the nervous system to accommodate these mental behaviors?
Nice question, and obvious extension. Sure, once we get used to behavior as patterns of motoneuron activity it will make a lot of sense to at least entertain the idea that those things which don't involve motoneuron activity can also be thought of as patterns of neuronal activity. PG
What are the implications if the spinal cord is severed? The person is conscious, but cannot move their arms, legs, etc. In terms of behavior, the spinal cord injury offers a view into how the brain and spinal cord are two distinct "boxes." The spinal cord is semiautonomous in that it carries out synaptic reflexes between sensory and motor neurons without consulting the brain. This is important in the event that you touch a hot object. Your hand will move away quickly without "... wasting time with cerebral debate." (Wallace and Sanders, p.820). The brain is the "box" that contains consciousness.
So these two boxes "talk" to each other in order to make the body walk, run, laugh, etc. Though thinking about spinal cord injuries has helped me to see to an even greater degree the semi-autononmous qualities of the brain and the spinal cord, I am left with many questions. What does it mean- that the spinal cord is severed? Is it still functional, just unable to communicate? After all, the brain is still functioning. Also, does the lower part of the body still respond to certain stimuli? Shouldn't it if it's semi-autononmous? I think I need to puzzle through this a little more.
You're very much puzzling along the right pathes. There are some significant complexities but, to a first approximation, yes "functional, just unable to communicate". And does still "respond" to certain stimuli. Understand which ones? And how that relates to distribution of sensory nerves? And how that and distribution of motor nerves means that we can say that rostral box "contains consciousness" but not that spinal cord doesn't? PG
The nervous system controls all behavior... the nervous system IS behavior. An interruption of the connection neurons that communicate between the spinal chord and the brain leads to some confusing results. The communication between all parts of the nervous system is essential for "typical" behavior as we think we know it. We discussed the idea of an "I-function" in the brain as being the "person". And that we did not know if there was a similar function elsewhere.
I am still questioning the idea of a person with a broken neck being able to run. I feel as though he or she may be capable of firing all of the correct neurons, but they do not lead to the desired result. In a sense, I would think that this would be one of the more frustrating parts of paralyzation to overcome. The only ways to know that the initial neuron firings were not going anywhere would be through visual observation and lack of any responses from the spinal chord. If you tell someone to move their foot, they cannot because the message cannot get delivered from the ear to the motor neurons of the foot. But does that mean that in their "mind", in their brain, or within their I-function of the brain, there is no sensation of accomplishing a particular goal? Or that there is no capability of performing a particular action?
In the same way, is it possible to stimulate the neurons right above the base of the brain, where there is the sever, in order to make the brain think (or convince the brain) that it has actually performed an action that it has not physically accomplished? These are my questions... are they just hypothetical, or do we actually think we know the answers (not that they are "right" answers because that would be no fun!)? There is only one person who I know who has a severed spinal chord right near the back of the neck. Abram is aware of his ventilator, but not of any other part of his body. He has no control of his spasms and movements. I have never thought that his brain asks his body to do certain things, but I realize that that may not be true. Since the brain can respond to verbal stimuli and then transfer that to motor neurons, the cut off in the nervous system must be known. But known to him? to his brain? to his mind, although that is part of the brain? I wonder.
Worthwhile things to wonder about. And maybe to ask Abram about too. There are some missing steps to file in in your considerations (and in the course). It isn't actually the brain that tells the motoneurons how to fire to run. Its the spinal cord. The brain tells the spinal cord it would like to see running, the spinal cord tells the motor neurons what to do. Question is what is Abram's experience when his brain tries to tell the spinal cord to cause running ... or anything else. Will talk more about this general set of problems, but to foreshadow: can you imaginea situation in which the brain requests running, nothing moves, but the brain DOES get information indicating that running has occurred? When and how could THAT happen? PG
In consideration of the responses of the person with a broken neck, I feel the need to make a distinction between two pathways of response. That is in a normal person we think of the stimulus going into a sensory neuron then to intermediate neurons up the spinal cord to the brain, then back down the spinal cord to a motor neuron giving the visible response. Yet in the patient with the broken neck certain stimuli give visible responses and clearly the pathway for this cannot include the brain. It can include the spinal cord, so one inference is that in a normal person there are similar pathways of response whereby the stimulus goes into the sensory neuron to the spinal cord and intermediate neurons and then to the motor neuron. In addition, there are similar pathways which do not include intermediate neurons such as the monosynaptic reflex arc. I wonder if perhaps the rate at which stimuli elicit a response is related to the amount of intermediate neurons in that particular pathway. For example, a knee jerk response may occur faster than a withdrawal of the foot after stepping on a tack. This would be due to the fact that a knee jerk response goes through only a few intermediate neurons, whereas the foot withdrawal would go through an innumerable amount more intermediate neurons in the brain.
Interesting and appropriate thoughts. Indeed, an implication is that one can get from spinal sensory to spinal motor neurons without the "brain" (LOTS of ways, all polysynaptic, the monosynaptic reflex arc is an anomaly which we'll talk about later in the course, much talked about by neurobiologists because its (relatively) tractable but highly misleading for thinking about how the nervous system works in general). And yes, indeed, different routes take different amounts of time, in part because of the different numbers of axons and synapses needing to be crossed. But there are almost certainly even more significant reasons for varying time delays. If you want to think about those you'll really be at the cutting edge of neurobiology. PG