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An ongoing conversation on brain and behavior, associated with Biology 202, spring, 1998, at Bryn Mawr College. Student responses to weekly lecture/discussions and topics.

TOPIC 5 (a choice):

"Central pattern generation" and "corollary discharge" are concepts which arise from observations on the motor side of the nervous system but which seem to have broader implications for thinking about behavior generally. Discuss the validity and more general implications of one or both of these concepts.


"Motor systems" and "Integrating Systems: The Neural Basis of Behavior" are Parts IV and V of your textbook (Delcomyn, Foundations of Neurobiology) with "Sensory Systems" as Part III, whereas we have talked about "output systems" prior to discussing "input systems". Discuss the pros and cons of the two different approaches.

(As in weeks past (and future), students were free instead to write instead on any other subject that struck them as particularly interesting during the week).

Name: Christy Taylor
Username: ctaylor
Subject: Corollary discharge
Date: Fri Feb 27 19:37:44 EST 1998
I think the most interesting implication surrounding corollary discharge is the fact that no matter how hard a parent may work to raise their children with the same experiences, this will never occur. This simply stems from the definition of corollary discharge which defines it as signals from one place in the nervous system going to another place in the nervous system all the while never stemming from outside of the body. It is an internal bi-directionality.

This is fascinating to me because it just encompasses so much of psychology - and it really makes me evaluate the way that psychological studies are held and the validity of these studies. For example, how could we possibly EVER say that humans will react a certain way in a certain situation. Oh sure, we can make guesses and assumptions, but there will always be unexpected behavior seen in the human race simply because of all if the internal and unseen information that is being sent WITHIN the body.

I also have thought a lot about phantom pain since I first spoke of it with my dad. He mentioned, just like Dr. Grobstein, that often uncomfortable, sometimes severe, and incessant pain arises from these signals in the spinal cord. I am having a hard time understanding, though why this pain is sometimes so unmanageable. I guess it just shows once again how little we know about pain and pain killers and the complexity of corollary discharge. For instance, do we know specifically where on the spinal cord certain corollary discharge signals arise? Do they migrate depending on the signals being sent? Do these signals change with the environment? And why in the world do some people have more active corollary discharge signals within them? (e.g. car sickness)

I know there are probably few answers to these questions, but still it has me thinking. It amazes me how interconnected the body is and I sort of see the corollary discharge signals as a defense mechanism and security mechanism for the human body. It helps the human body stay connected with itself. Fascinating!

Glad you like it. Yes, more questions than answers, which is fine as long as it makes it possible to see old things in new lights. There is, of course, a lot of work being done on chronic pain, from lots of different perspectives (would probably make a good web paper). And, in that context, its worth noting that a "corollary discharge" explanation, as we talked about in class, "makes sense" but isn't the only perspective worth exploring. Similarly, I tend to agree with you that the corollary discharge signals suggest the important conclusion that one can't even in principle give different humans "identical" experiences. That doesn't, though, follow with absolute rigor from what we've talked about so far. One might argue (as others have previously in the forum) that it is still so that everything STARTS with experience, with inputs leading to outputs which in turn affect inputs and so forth. On this argument, maybe even the corollary discharge sigals could be attributed to experience? We'll talk more about this, with additional observations which suggest that even if corollary discharge signals can be affected by experience (which indeed they can), there is still a fundamental unpredictability about processes internal to the nervous system. PG

Name: Anne Frederickson
Subject: Choice and Corollary Discharge
Date: Sun Mar 1 13:36:29 EST 1998
I was intrigued by the discussion at the end of class on Thursday about what choice is and how it may relate to corollary discharge. In class, Prof. Grobstein asked whether the slug exhibited choice of movement and I think we pretty much concluded that it was not choice due to the corollary discharges that came from movement of the teeth. So what is choice in the face of this evidense? How do we know that our actions are a result of choice and not a series of bi-directional connections? Someone suggested that we would know if it was choice if we were able to control for all the corollary discharges and the organism still exhibited different behaviors in reaction to the same stimulus. I agree with this in principle but it would be almost impossible to do. In an organism with a simple nervous system, like the sea slug, it is relatively easy. However, in humans it is virtually impossible. Everyone has different connections in differing degrees. You could never control for it all. In the face of this, choice is a very difficult concept. This is frightening to me. As humans, I think we are used to thinking that we have a great deal of choice of behavior because we are "the most advanced organisms." Perhapes this isn't true. Is it possible that most of our behaviors are in fact controlled by various connections from other parts of the nervous system?

Then, as stated above, how do we handle psychology which attempts to explain many human behaviors by motivations and choices that people make in response to these motivations. This in fact cannot be the whole story if we are to accept the idea of bi-directional connections within the nervous system. However, it feels wrong to assume that all behavior is controlled by this. There has to be some kind of choice to our behavior. Perhaps choice is little more than a different pattern of activation instead of the independent decision. I am sorry that this is mostly questions and little substance but I am really bothered by the idea that we may have no "choice" as we think of it.

No apologies needed. Sometimes (usually?) substance results from being puzzled by observations that raise new questions, and you've done wonderfully at characterizing them. And yes, there is something a little bothering about having to confront what one means by "choice". Are we "the most advanced organisms"? Maybe we're just different, instead of "most advanced"? But if so, in what way different? Given that at least some "choices" might be accounted for by corollary discharge signals and related circuitry, maybe behavior IS the nervous system rather than being "controlled" by it? And, if so, maybe much of our own behavior is less "under our own control" than we sometimes think it is? I very much agree though with your thought that this "cannot be the whole story". Is there, in the nervous system, something that might correspond to "independent decision"? That's the key question, and we'll talk more about it. For the record, I think the answer is yes. PG

Name: Meera Sangaramoorthy
Subject: Death to Determinism
Date: Sun Mar 1 20:41:13 EST 1998
I believe that the whole notion of corollary discharge undermines the infamous theory of determinism. For example, if, indeed, there are connections within the nervous system which do not depend on external sources of input, then this can be stretched to imply that there might be the existence of "free will."

Thus, herein lies the greatest mystery of all...that we feel a "self" that is innate--uninfluenced---and entirely our own creation. I think that the fundamental flaw in the determinist theory is its blatant ignorance of the nervous system and its behavior (pattern of action potentials) within the human body. Sure, we know tons about society and all man-made social, economical, and political institutions that have a great effect on our lives, but analyzing the hell out of things outside our bodies gives little credit to the little "miracles" within us. We undermine the fact that perhaps nature and all the things that biology studies is more complex than we think. In fact, perhaps it is too complex for our endless scrutiny of an existence which we know so little of. Sure, the structures that we, as humans, create can be strong enough to kill the biological body and, thus, end our nerve impulses, yet in a reciprocal way, the biological body and those endless neurons are doing things that all of our analysis put together can never uncover.

I share your feeling that with all our information about external influences on individuals, there is a serious neglect of what goes on "inside" and of the importance of that for thinking about behavior. I also share your sense that our conversations to date do indeed have implications for thinking about both "determinism" and "free will". There are, though, some difficult issues yet to wade through. "Connections within the nervous system which do not depend on external sources of input" needs clarification. Certainly, there are signals in the nervous system which do not depend on input at the present or recent times. Showing that they don't depend on input at any prior point in the individual's life is a little tougher, but is certainly true in some cases where genetic information is clearly implicated. In some ways, though, that simply replaces one kind of determinism (environmental) with another (genetic). Is there a way to get to a "self" which is maybe not "entirely our own creation", but at least partly so? Maybe by understanding still more of what's inside? That's something we'll keep exploring. Any thoughts about what would have to be there? PG

Name: Meredith Ralston
Subject: corollary discharge
Date: Mon Mar 2 09:26:22 EST 1998
What is the benefit of corollary discharge in the case of the pleurobranchus? It seems that in the example given in class, it would make more sense for the snout to withdraw from potential danger than to go on eating.

But that's a side note. In the April 1992 Scientific American article on phantom limbs, the author hypothesizes that the brain contains a neuromatrix of neurons which, in addition to receiving sensory input, generate a pattern of impulses which indicate that "the body is intact and unequivocally one's own." He calls this pattern a neurosignature.

I'm working under the assumption that this would fall under corollary discharge- parts of the brain communicating with each other and saying what they're doing. Patients who have a lesion in a certain portion of their brain have been known to push their legs out of hospital beds, because they're convinced the leg belongs to someone else. It seems that this neurosignature would be an important part of our sense of "self," at least our physical self. Could a similar kind of neurosignature contribute to personality?

After all, we all have moments of not feeling like ourselves, of saying something and feeling as though someone else said it. Maybe the brain is constantly evaluating its own thoughts, and cross-checking them against past thoughts. We spend most of our time very aware of our sense of self, maybe the brain uses this constant self-evaluation of our physical and mental self as an extension of sensory perceptions of the world around us.

Very interesting and sophisticated set of extensions. Certainly it is worth thinking of something that keeps track of corollary discharge signals (and input resulting from output?) and attributes it to some agent (a "self"?), which it is always "evaluating" and perhaps extending? Can imagine thinking of this in terms of neurons and connections among them? We'll certainly talk more along these lines. PG

Name: LPernar
Username: lpernar
Subject: order
Date: Mon Mar 2 09:37:53 EST 1998
Even though it intuitivelly would make sense to approach input systems, before taking up an investigation of output systems, this intuition crumbles in the face of what we have learned in class.

The first presentation of how the nervous system works, i.e. box, inputs on one side, outputs on the other, supports the logic of discussing sensory detection prior to motor activity generation etc. However, within two classes, this simple approacvh was refutet and was replaced by the notion that a.inputs do not directly cause outputs, b. ouputs can be generated anywhere in the nervous system, and c. ouputs feed back to inputs and may alter them (this may have been two weeks later, but still.) This list of characteristsics for output generation, indicates that aproaching the workings of the nervous system from the output side first is not as counterintuitive as it may seem at first, but may in fact lay a basis for understanding idiosyncracies of sensory detection, that would be complicated to exemplify in the absence of an understanding of the concepts of, for example, corollary discharge.

Obviously, by other tokens, such as outouts typically are generated as a response to a sensory input, the more traditional approach as employed in the text book makes sense too. Both approaches have the advantage of making an understanding of what is exemplified second more readily available and complete. The shortcomings of either approach is, that whatever is presented first, is incomplete without the second item. Possibly an optimal, but rather complex approch to the subjket matter would be a balance between input and output system, where appropriate.

Sounds fair. My own guess is that the "best" approach depends to some extent on what people expect. If one is used to thinking of things going from input to output (as I think most people are), then it probably helps to emphasize the unexpected first? Still, I have a glimmer of a feeling that in some important biological sense, it is actually output that motivates input, rather than the other way around. That would be interesting to explore further and see if it can be made compelling. PG

Name: Rachel Mosher
Subject: math and the brain
Date: Mon Mar 2 11:14:51 EST 1998
I read an interesting article in the New York Times a couple weeks ago that I would like to summarize and comment about because I think it provides a a good argument on the brain = behavior subject we were talking about a few weeks ago. (Sorry its an old topic...)

The title of the article is "Useful Invention or Absolute Truth: What is Math?". The article gives arguemts from a variety of perspectives on whaere exactly math stems from. Are numbers and physics laws an etheral idea or a human creation? (did the brain make up math or would it have been a constant on earth without any life?)

The argument given by the neurobiologists was that mathematical ideas and concepts are basic fixtures of the earth but arise from the human body experience. Math is used by the brain to simplify the ordering of sensory experiences and has been hard-wired into the brain by evolution. The scientists found some evidence to prove this theory. The evidence included finding the area of the brain which seems to contain the arithematical nodule and positive experiements finding traces of a math nodule in other, more primitive,species.

This explanation seems to make sense until you listen to the physicists arguments. They say that if mathemeatics is really just a construction of man then why does it work so well in explaining the fundamental laws of the universe? If there are other ways the world could be perceived based on different experiences then the human one, would there be the same physics laws? Neurologists would say NO- different experiences, genes and environment would bring a whole set of perceptions and behaviors. They would probably have totally different 'laws' to explain the world. How would neurobiologists explain why man has founded quantum physics then? If the reason why we come up with different ideas and laws to base our lives around is ultimately for 'survival of the gene', we wouldn't discover quantum physics-- there's no survival value to it! IF the reason we discovered quantum physics was because it was just a natural law that matter followed in nature, it would make sense that we stumbled upon it.

Based on these different arguments, math is a creation of our brains used to help us make decisions which, in the long run, are beneficial for the survival of our genes. The universe does follow some natural order- the reason why our math laws seem to fit so perfectly is because we mold them to fit. (remember there are always exceptions to the laws) If we had a totally different system of thinking we woeuld probably have different laws to explain the same natural order that would fit just as well. As to why we have quantum physics even though there is no survival value to it? There is definetely survival value to it-- think of how rich publishers of of Quantum Physics Study Guides are!

Wheeee! A whole set of interesting issues. The New York Times article caught my eye too, and so I bought and have been reading The Number Sense: How the Mind Creates Mathematics by Stanislas Dehaene. It gives a nice (and I think compelling) set of observations/arguments implying that brains (both humans and animals) have an innate sense of number and number manipulation, i.e. that this exists prior to individual experience (and hence presumably reflects genetic information). This is terribly important, from all sorts of perspectives (including educational), but doesn't quite get to the deeper issue of whether mathematics is a fundamental characteristic of "the universe" which humans (and other animals) have discovered, or a creation of the brain. What is innate is, after all, arguably a reflection of (ancestral) experience, and so one could argue, as you suggest, that the brain "creates" mathematics because evolution learned to do so from experience. On the other hand, one can, I think, make a strong argument that brains are constantly "making up" all sorts of things that have, when they are made up, little or no relation to the "outside world" (we'll talk more about this as we go). Some of these are kept (by individuals and by culture) and others discarded. In this sense, one might retain the idea that things like mathematics are certainly "made up", rather than discovered. And what is subsequently "discovered" is not the thing itself but rather how useful particular made up things are in dealing with an external world. At this point, the question becomes is it the case that we will eventually make up enough to have discovered everything there is to know about the external world? You might enjoy an interesting debate about whether we're approaching the "end of science". My own argument is that understanding to varying degrees always changes the nature of the thing being explored, and so there is no end. All of this is another (longer) way of saying I agree with you (I think). We make things up to make sense of our experiences and so they come to be molded by whatever regularities we detect (which come, in turn to reflect, to some extent, the organizing principles we create). At the same time, my suspicion is that there are enough different ways to make sense of things that we would see both similarities and differences in how this is done if (when?) we encounter other species with whom we can effectively exchange perspectives. Which would both be fun (not everything, even in biological systems, is immediately related to survival value) and help to settle the question. PG

Name: Cedar McKay
Subject: free will
Date: Mon Mar 2 15:43:57 EST 1998
We seemed to conclude that since we can not always predict the reaction of an animal to stimulus, even under carefully controlled experimental conditions, that must be proof of free will. We supply the same set of stimulus to animals with very similar histories and sometimes they do different, unpredictable things. We conclude that something originating in the brain must have decided to do that.

Perhaps this is not really free will. Maybe what we think of as free will can be traced back to structural differences of the brain, subtle differences between individuals, too slight to be perceived by observers. Even if we could give two individuals identical brains at time=0, which we can't, two other factors would quickly act to create differences between the two brains, which we may attribute to free will. The first is random quantum effects (molecular dice), a concept in physics which dictates true random variation in the behavior of the universe if we get to a small enough scale. The second is corollary discharge. Even the most minute difference in experience, through corollary discharge can change the very structure of the brain, changing and strengthening some connections, weakening others. Maybe all we perceive as free will is really dependent on tiny differences in our experience. If we could make experiences exactly repeatable, down to the atomic scale, perhaps our behavior would be perfectly predictable.

Interesting, well-phrased issue, related to some of the thoughts of others above. The question, in an important sense, is what exactly do we mean by "free will"? I agree with you (for reasons we'll talk more about) that two absolutely identical individuals at a given time would quickly become different from one another and behave differently. I also agree with you that this, by itself, could be explained without appealing to "free will" in the sense that one usually uses that term. So what more would be needed if we wanted "free will" in the usual sense of the term? And can one imagine that being achieved by some assembly of neurons? PG

Name: ingrid katz
Username: ikatz
Subject: violent behavior
Date: Mon Mar 2 17:50:26 EST 1998
I am continuing my discussion on violence both from last week and my paper - specifically in relation to corollary discharge. Dr. Grobstein raised an interesting point last week in reference to to the topic of violence and the notion of responsibilty. If one assumes that there exists a possibilty that inputs which contribute to violent behavior are actually consequences of an individual's prior violent outputs, then a bi-directional model may apply. If one considers the concept of corollary discharge and the notion of internal bi-directionality, than one can essentially shift the burden of responsibilty almost entirely on the individual him or herself.

How, then, can we assess what indivudal responsibilty is and what, specifically, goes into a decision making process? A mental awareness of one's own actions can be broadly interpreted - specifically when one is considered to be "mentally incompetent" to be prosectued for one's actions. Can we still say that an individual is not entirely responsible for acting violently with the notion of corollary discharge in place? When does society accept blame over the individual and when is the inverse true?

Violent behavior, as has been shown in many pyschological and neurological studies, has multi-faceted causal links. Certainly, it would be myopic to simply state that the environment is entirely responsible for the actions of a given individual. Likewise, it would seem equally as near-sighted to assume that an individual who is mentally disfunctional is still entirely responsible for his or her violent actions. These raise some broad philosophical questions which, I hope, will continue to remain pertinent as we continue the course.

Pertinent indeed. So how do we go on sorting out the threads? Yes, individuals respond to inputs; yes, individuals cause inputs. And so we could, if we wanted place responsibility wholely inside or wholely outside the individual. Based on the observations, it seems to me to make more sense to regard the thing as a distributed system, one in which responsibility resides, to varying degrees, in both places. Which does, however, raise (or at least help to better define) a new question: what exactly do we mean with legal concepts like "responsible for one's own actions"? Can we find an aspect of neurobiology relevant to that? If brain=behavior, we should be able to, no? Suggestions? PG

Name: Julia Johnson
Username: jfjohnso
Subject: corollary discharge and puberty
Date: Mon Mar 2 17:50:51 EST 1998
Do you remember when you were 11 or 12 and you were constantly running into doors? Please tell me that you do and that I was not the only one. I have been wondering if this might have something to do with corollary discharge. Corollary discharge signals are responsible for much of the internally generated information that shoots around in the nervous system. If they are responsible for maintaining information about body part placement, etc., then, wouldn't it be the corollary discharge signals that are involved in predicting where body parts should start and end? Let's look at one day in the life of a pre-teen. If the arm ends at x meters on that day, the sensory input coming from the arm will be sent up describing this. Not long after, however, the arm is significantly longer. Maybe, the sensory information sent up now is no longer in agreement with the "expected" length of the arm. My hypothesis here is that this "expectation" is due to corollary discharge signals. The poor dear doesn't yet realize that his arm is longer than his brain expects it to be, that he is gangly and awkward. In all the neurological confusion, arm length is underestimated and he will slam right into the door or run over his own foot. With time, the sensory information about arm length will match the expected arm length and, thankfully, he will be 17.

Another possible explanation is very similar to the one describing how lovers find each others' lips. Maybe it just has to do with cell memory. Once the nervous system decision-making center receives sensory input about arm length, it assumes that it will stay that way and so, does not make the adjustments. With time, though, it does adapt. If the corollary discharge signals are genetically programmed, though, why is this not accounted for in their programming? Does anybody think that either of these explanations for neurological acclimation to growth spurts in viable?

Quite viable, and quite interesting. There are mechanisms in the nervous system to adjust corollary discharge signals as bodies change, but they are likely to be differently effective in different people and at different times. So yes, "awkward" might indeed relate to improperly calibrated expectations. I'm less sure about lips and "cell memory". PG

Name: jeremy hirst
Username: jhirst
Subject: the movies
Date: Mon Mar 2 19:48:51 EST 1998
At dinner tonight the topic of IMAX or OMNIMAX movies came up. these are the movie theaters with super huge screens usually showing stories with flying or exploring high places as a central theme. Everyone kept talking about the amazing feeling of actually moving, of flying through the movie.

one scene was described, "flying slowly up one side of the alps, putt putt putt, and then Wooosh! down the other side into a tremendous expanse of blue sky and white rocky mountain. I could just feel my butt lifting off the seat!!"

then another person described, "all the ups and downs and wooshing make me air sick, in the movie theater."

So, how do movie goers experience these real feelings of motion, motion sickness, and weightlessness?

it seems that our visual inputs are strongly connected to the sensation of movement. if our eyes pick up cues from the environment showing that we are moving then the rest of our body reacts in a way to correllate with these inputs, it says, yes, you are moving. the discharge associated with the moving visual cues must be setting off one of our many symphonies which elicit a sense of movement.

falling, being weightless, or Woosh! must all have centrally origenating scores for a symphonic nervous discharge which our brains recognize, truly, as those feelings occuring from the actual physical event of falling, weightlessness, etc. This idea of having corrollary discharge also helps to explain the sicknes felt by some. there is a mismatch of inputs, one set, our eyes say we are moving, and the other set, our inner ear, says we are not. as was stated before, this mismatch of information is completely revolting to our bodies.

is bidirectionality tied in as well? i think it must be. these input signals and there accompanying outputs of sensation must all be connected internally. there does not need to be, or appear to be, an apparent external path for these signals to relate to eachother. the patterns and path ways for the discharge to flow through must occur on a primarily internal set.

the ability of bidirectionality to modify a sensation or behavior is key to these sensations. it is appealing how these models of the nervous system support some common experiences.

Yep, and that's a good touchstone. When new observations help other things "make sense" one feels one is on the (at least temporarily) right track. You're right that visual input is a VERY potent indicator of self-movement and hence that IMAX etc movies are very good at giving a sense of movement. But, "setting off one of our many symphonies"? You want to be a little careful there. Motoneurons aren't actually firing to cause the movements, of course, so the inputs aren't causing "motor symphonies". They are, though, certainly creating more general patterns of activity in the central nervous system. The curious thing is that IMAX movies are actually an example of "mismatches" of corollary discharge signals and input, since the latter says movement and the former doesn't, right? So, in these terms, its actually somewhat surprising that one feels as much of a sense of movement as one does? PG

Name: Libby O'Hare
Subject: implications of corallary discharge
Date: Mon Mar 2 20:09:56 EST 1998
The concept of corallary discharge seems to me to be one of the most important characteristics of a nervous system. It is responsible for the complex integration that nervous systems are capable of. The signals of corallary discharge running throughout the body clearly are responsible for our physical sense of self, and may be responsible for our spiritual sense of self. As might be expected, there are a number of behavioral implications of this concept, so I will pick one to discuss.

Like many others, I was intrigued by the discussion of choice at the end of Thursday's lecture. I read the previous comments, and I agree with most of what was said on this topic. However I want to point out one thing that I think has been overlooked so far.

To choose something is to make a decision. If we choose to go to the movies, we have made a decision to physically transport ourselves to the theatre etc. In order to make a decision, one must be capable of analytical thought. When deciding to go to the movies or not, you might consider for example, how much money you have, or how badly you want to see the film. These factors (among others) contribute to your choice to go to the movies. Now, we haven't gotten to thinking yet, but my intuition tells me that Pleurobranchea is incapable of considering the future implications of withdrawing its proboscis or not withdrawing it immediately before the proboscis is withdrawn. This is not to say that humans are the only organisms capable of considering future implications of their own behavior--I'm not sure of that. Unfortunatly, I can't account for the observation that sometimes the proboscis is withdrawn and sometimes it isn't in an isolated nervous system. Could it just be random? I don't know. And what about reflex actions--in humans there is no decision involved in a reflex action, often your hands are out in front of you when you are falling before you even realize it--but reflexes must happen every time a situation demands that behavior. Does anybody else have any other ideas?

Nice addition (as you said) to some earlier comments trying to distinguish what Pleurobranchea does from what we would comfortably call "choice". "considering future implications of their own behavior" is an interesting (and I think appropriate) touchstone. The question, of course, is what does THAT mean in terms of neurons and circuits of neurons? I think we'll need to dissect it into some smaller parts, but we'll see. As for the proboscis withdrawal in the isolated nervous system, it is not random (at least not as observed in the experiments). Proboscis withdrawal occurs when the central pattern generator for chewing is not active, and does not occur when it is. Because, as you'll recall, of an inhibitory projection from one to another (which is the corollary discharge circuit in this case). PG

Name: Rachel Kaplan
Subject: heads or tails?
Date: Mon Mar 2 20:11:08 EST 1998
Cedar McKay in his essay for this week suggested that "if we could make experiences exactly repeatable, down to the atomic scale, perhaps our behavior would be perfectly predictable." I think this would be true to some extent. I hesitate to fully embrace the idea because I believe that our behaviors are often governed by random chance. I propose that if it were possible to create completely identical people (a & b) who would then be placed in the exact same environments, they would still respond differently when asked, for example, to guess a head or a tail outcome for any # of throws of a die. Perhaps their guesses would coincide more closely than the guesses of two complete strangers; however, the important point is that there would indeed be unpredictable variation.

I wonder what is responsible for this unpredictable variation. It might seem that the incoming stimuli, the question "heads or tails?," would be processed in the same way in both people, and therefore would evoke the same response. The same results would be found with two identical computers. I would not say that they were exercising choice, however, because they are predictable in their unpredictability; whereas, humans can opt randomly whether to be predictable or unpredictable (although, perhaps this can be programmed into a which case I need to come up with a different reason, something having to do with emotions.). One or both of the clones (a or b) can decide to repeat his responses over a number of trials. My predictions for this coin tossing experiment indicate to me that higher level animals do have choice, even if the exact reasons for a decision are unknown to the "decider" (the unconscious comes into play??).

I do not believe that a lower level animal such as the pleurobranchea has choice. Experiments have shown that it is possible to predict various actions of this animal. Evidence from these experiments runs counter to the Harvard Law of Animal Behavior. Researchers' ability to predict the movement of the invertible proboscis seems strong support for the idea that all actions of this animal can be predicted. Even if the human nervous system was broken down to the atomic scale, I still do not believe that every action could be predicted. The question becomes, where do we draw the line between animals with choice and animals without.

I think you, Cedar, and I are all in agreement that there is some inherent unpredictability in the system (though this is far from a consensus position and needs some observational support, which we'll come to). I'm less sure whether we are in agreement on what "choice" involves. My own sense is that what is normally meant by that term requies something in addition to unpredictability. And that, in turn, is relevant to thinking about where to "draw the line". As we'll talk about, unpredictability is a fundamental characteristic of all organisms, so if one wants to distinguish Pleurobranchea's "choice" from a human "choice", its going to have to be on some other basis. Maybe something along the lines of Libby's suggestion above? PG

Name: Ruchi Rohatgi
Subject: choice?
Date: Mon Mar 2 20:12:33 EST 1998
I understand that the concept of the sea slug not withdrawing its proboscis while eating on account of inhibitory signals from motor activity does not quite exhibit "choice." It seems that even if the animal wanted to withdraw its proboscis while eating, it couldn't because the motor activity involved in eating does not allow the proboscis to withdraw on account of corollary discharge signals. I may be getting a bit off track, but even if it was more favorable for the slug to withdraw its proboscis (if there was danger)- especially if the stimulus was strong enough, would it still withdraw? Is there some kind of additive signal method where if the sensory input was strong enough it would overpower the inhibitory discharge signal? I understand that the internal processes in the snail affect sensory input and that is why the snail responds so differently under the same sensory inout- but if the sensory input was strong enough it could change the internal environment surrounding motor activity, right? And this is an example of bidirectionality....

Going back to choice... it seems to me that choice then is something that an organism must completely be aware of. Thus, it could in some way be an aspect of the I function. The I function is independent of corollary discharge, but it is dependent on sensory does this work?

You're exploring an interesting area, but be a little careful. "even if the animal wanted to withdraw its probosicis while eating, it couldn't because the motor activity ...." sounds a little like you think there is a nervous system there and, separately, an animal which, separate from the nervous system, might want to "want" or "not want". One possibility, at least, is that "want" and "not want" are simply descriptions of the state of the nervous system, involving no inhibition and inhibition respectively. Yes, it might be that there is an excitatory system which could override the inhibtion and that might correspond to "want even more" (that wasn't explored in the studies I described). I like your thought that "choice" as we usually use the word means something more, maybe related to the "I-function" and to "be aware of". Can you imagine what this might be in terms of neurons? PG

Name: Chris Lord
Subject: I function and corollary Discharge
Date: Mon Mar 2 21:27:19 EST 1998
In a previous post someone wrote that the I function was independent of corollary discharge. Why? If the I function is receiving sensory input, why wouldn't it acknowledge corollary discharge. How did we know that when we were poking our eye Prof. Grobstein wasn't jumping around? A possible explanation might be that there was corollary discharge from the hand telling the I function that it was poking the eye, thus any movement would be due to that cause and not external movement. Corollary discharge provides the body with information about what its doing and how its doing it. That information can be useful on a number of levels. Normally, I would agree that the I function does not really pay attention to corollary discharge relying instead on sensory information to figure out what is going on, but I think the concept of corollary discharge is very important in understanding our sense of self. Our bodies are a major part of who we are, and technically it is what's inside that counts. Since corollary discharge is a way of keeping up with what's going on inside ourselves and what our body is doing, it would make sense that it would have an impact on us on every level, not just the unconcious level. Now when I say impact, I mean, I may not know exactly what corollary discharge is telling my fingers right now as they type, but I am using some of the information that is getting sent back in the my nervous system to govern my actions as I type. Thus my I function is taking some aspect of corollary discharge into account.

I don't recall someone asserting that the I-function was independent of corollary discharge signals, but certainly agree with you that there isn't in principal any reason why it should be. In fact, that amputees report feelings from missing limbs (rather than simply acting as if the limb is there) certainly suggests that the I-function gets corollary discharge information, since they aren't getting sensory information from it. There is, it suddenly occurs to me, an interesting question there which I'm not sure anyone has looked at. My bet would be that the motor behavior of amputees would show that some parts of the nervous system are actually "aware" of the fact that the limb is missing (even if the I-function isn't convinced). That would be worth looking into further. PG

Name: Elaine de Castro
Subject: Choosing wedding rings
Date: Mon Mar 2 21:46:07 EST 1998

Corollary Discharge, phantom limbs. Hmm.

I can see how the presented theory works for cases of extreme pain of phantom limbs, especially when regarding congenital deformities. But once upon a Haverclass, I was taught that the pain and other senses from phantom limbs were caused by denervation supersensitivity - that neurons were adding more receptors in response to decreased sensory input. An example of which I can envision this working and not the corollary discharge theory is when a person says he or she can feel a wedding ring on the finger of the amputated hand. How would corollary discharge be so fine tuned this way? Other than this one example, I feel the supersensitivity argument seems weak in comparison. How do these two work with or against each other?

Now, choice. Why would we have free will or choice? If that cute little pleurobranchus is such a simple animal and has behaviors controlled by his neurons, then why not us? Sure, we seem to have a lot more options, some would say choice, since we don't feel tied down to some sort of routine - but think of how much more complex we are than this slug. Perhaps all our behaviors and actions are already programmed into our nervous systems, and each time we make a different "choice", we're just activating different neurons and pathways. After all, doesn't the brain = behavior? "There's nothing but the brain..." ;)

Maybe we're shying away from the obvious. After all, it is a bit frightening to think we might not have free will or choice. But maybe it's a tad pretentious to think we're so much better than sea slugs.

Interesting set of issues. Yes, there have been a lot of suggestions about the origins of phantom pain ... and, as you might guess, the "reality" probably is that it has a variety of different explanations ("the nervous system always has at least seven ways ..."). Denervation supersensitivity is a real, well-documented phenomenon, as is corollary discharge. How much each (and a variety of other things) contribute to any particular situation is an open question. On the other hand, I'm not entirely sure why supersensitivity makes more sense of feeling the wedding ring, since one would expect it to occur in all of the neurons which have lost inputs and not only those which received input from receptors at the base of the middle finger.

As for Pleurobranchea, it does raise the possibility that we too are "just activating different neurons and pathways". And maybe it IS pretention to think we're better. But we could still entertain the idea we're DIFFERENT. And that "free will/choice" actually reflects something more going on in the nervous system than we have yet considered (and which may or may not be there in Pleurobranchea), no? PG

Name: Emma Christensen
Subject: Yet another opinion...
Date: Mon Mar 2 21:56:45 EST 1998
In response to both Cedar McKay and Rachel Kaplan's(and any others who I managed to overlook), I would like to add that I don't think that if we could make experiences exactly and completely repeatable, we could predict behavior. Maybe I'm missing something(and I probably am) but the one big factor that messes everything up is time. For all intents and purposes, we as humans/as animals/as beings are always moving in at a forwards-seeming rate through time. It is impossible to make experiences repeatable or to predict behavior because we are constantly moving through time, and so learning and creating new neurobio pathways and adding new scores to our motor discharge symphony. We might not react to the same situation next time--even if everything was the same down to the little corollary discharges and quantum effects--because we remember it happening before. We are constantly learning, we are constantly changing, and that is irrevocable and unchangable in time as we know it. We might appear to behave the same simply because there was no outward 'reason' to behave otherwise, but that does not guarantee the continuance of that behavior for all time. It's all probability when you get right down to it--some time those dice roll with you and sometimes they don't.

I would also like to briefly address the issue of "phantom pain." I am caught in a quandary between what to believe--either the explanation that there is discord between the sensory perception and the dialogue/corollary discharge between the neurons within the nervous system, or the alternate explanation that I discovered in my acupuncture research at Memory) which describes that pain(particularly chronic pain and phantom pain) may be caused by "reverberating neuronal circuits" or "persisting changes within the nervous system," meanin that the original trauma created a sort of "pain circuit" or a pattern of pain that persists within the nervous system after the original trauma has been absolved(or amputated, as the case may be. Ew.). Both of these explanations make a lot of sense to me, and in my admittedly limited capabilites as a neurobiologist, I am unable to distinguish whether either theory is "more true." Whew. This is exhausting.

What's exhausting? This is fun. Anyhow, thanks for the link. Its a nice one. As for alternative hypotheses to account for phantom pain, see my reply to Elaine, above. There are probably lots of different mechanisms operating, to varying degrees in various cases. And the interesting question is what kinds of observations would allow one to distinguish among them in any given case. "Reverberating neural circuits" might be ruled out if one could show that pain reappears following a period of complete cessation of relevant neural activity or substantial disruptions of its pattern (and my guess is that this is so). One can also test for dependence on the "original trauma", and that is unlikely in cases of congential limb absence.

I detect some previous course experience in your concern for time. Yes, we are constantly learning/changing, and so "can't go home again". But that doesn't quite speak to the question of whether one could, in principle, cause two different individuals growing up at the same time to have the same experiences and hence behave identically. And where, other than from Arcadia, did the dice come from? Hmmmm. Actually, there aren't any dice in Arcadia, as I remember it. But there is some pretty impressive coin flipping at the beginning of Rosencrantz and Guildenstern Are Dead. PG

Name: Alicia
Subject: corollary discharge
Date: Mon Mar 2 22:26:59 EST 1998
After having read the essays of many other people and after thinking about corollary discharges for a while, I started thinking about family values and the idea of disfunctional families. I'd like to start off by stating that I don't think the word disfunctional should be used to describe families. I think that all families have issues and just about anyone can find something disfunctional in thier families. In any case, when thinking about this I began to consider the argument that people's actions can be either caused by or seriously affected by their upbringing and their environment and that pyschosis, violence, and other social abnormalities can be the result of a "bad" upbringing. Though I think that a person can be influenced by their surroundings, when corollary discharge is brought into the argument, it must be looked a quite differently. Because corollary discharge signals do not originate outside of the nervous system, no one person can receive the same experiences as another person and people do not necessarily react the same ways in certain situations. As a result, I do not think that all actions of a person can be blamed on or excused by their upbringing.

Thoigh I think that the above arguments and considerations are quite interesting and can be quite helpful and important when studying psychological issues, I think these ideas can also be rather scary. The idea that no people react the same as each other to different stimuli and experiences is quite significant. As a result, a person accidently bumped up against in a crowd may continue on very normally while yet another may become violent, and yet another person may become paranoid. A perosn may be brought up in a perfectly "normal" environment, but may act in an "abnormal" way. Here the notion of family values becomes hazy for one may be raised with perfect family values, but may not necessarily follow them. What I want to know is whether a specific reasons that certain people are so quick to such "abnormal", emotional responses to certain things. Do these people have chemical imbalances? Can we even call them "imbalances" when no person's actions are actually "caused' by specific inputs?

Very rich and interesting set of connections. Thanks. Yes, the recognition of reciprocal influences can make one think differently about all sorts of things, including family influences (see A Paradigm Shift from Lines to Circles: Twelve Characteristics of a Family System. Certainly there is enough reciprocity in families (and enough differences among individuals for reasons within them) so that not all behavior should be "blamed on or excused by" upbringing. That is not to say that families don't have an effect on individuals but it is to say that individuals themselves influence those effects. And there is indeed something a little "scarey" about the realities of things going on inside people of which one is unaware, so that one can't ever know for sure what they will do (yes, I tend to try and avoid both dysfunctional and abnormal as concepts). On the other hand, that's also part of the fun of life, no? And certainly part of what makes it possible for people to learn from each other. PG

Name: Jonathan
Subject: Does it make sense to study the nervous system in isolation
Date: Tue Mar 3 01:05:56 EST 1998
Before we further debate the significance and implications of central pattern generators and corollary discharge I think we should examine more closely the methods in used to discover them. I am speaking of to the technique of isolating the nervous system from the rest of the body and then study the effects of certain inputs on now independent nervous system. Perhaps my biggest concern with this method of study is based on the Heidenberg’s Uncertainty Principle which states that you cannot simultaneously know the location of an atom and its direction of movement. The reason proposed for this logic is that the very act of observing an atom alters the natural state of the atom thus preventing one from studying its true motion. This is much the same way I feel about studies with an isolated nervous system; the nervous system almost never functions with out continuos inputs from the body and the environment so I wonder how “realistic’ the results gained from this method of study are. Even if the central pattern generator does exist in normal life, its operation maybe not at all similar to experimental conditions because the contingencies the nervous system experiences in each situation are remarkably different. In normal operation the central pattern generators may constantly be modified by inputs from other parts of the body and the environment.

Another concept that cause me to have trouble with the experimental procedure of nervous system isolation is the idea of establishing operations; an establishing operation is a stimulus or event which changes the effects of all subsequent stimuli. In this experimental paradigm the removal of the nervous system could serve as an establishing operation for the observed functioning of the central pattern generator. In other word the central pattern generator may be a default system that functions only when there are no other inputs to the nervous system.

A third problem is see with the removal of the nervous system is that we are unsure of the effects the process has on the nervous system. The nervous system isolation procedure was used in order to study the nervous system without interference from the environment, but I wonder if we can guarantee such a lack of interference from other parts of the nervous system. What I mean is that removing of sensory neurons from their receptors may cause them to fire in a patter which will be relayed to other parts of the nervous system, thus affecting this "isolated" nervous system as if there were environmental stimuli.

I am not arguing that central pattern generators do not exist, but rather there needs to be improvement in the methods with which they are studied before we try to postulate the implications of their existence on behavior.

Entirely appropriate criticisms. My only argument is with the suggestion that "there needs to be an improvement in the methods". I'd argue, instead, that what is needed is instead a better general understanding of the possibilities and limitations of interpretation of experimental findings. The findings themselves, in this case, are quite solid, as are the terms when understood as summaries of those experimental observations. What is at issue is only the relevance of those findings for better understanding what is going on in more "real" situations, i.e. when one puts the system isolated for study back in the context of its richer set of interactions. The "problem" is, of course, not specific to studies of the nervous system but instead is quite general and applies to any "reductionist" science. And the solution, at least in my experience, is not to deny the very real usefulness of such observations but rather to simply accept that "explanation" is not possible from such observations. What one is instead doing is testing their usefulness for "making better sense" of the more complex systems. Which, in general, they do. That help any? PG

Name: zermatt scutt
Username: mscutt
Subject: Choice
Date: Tue Mar 3 02:31:58 EST 1998
I don't think I can intelligibly approach this issue from the perspective of a pleurobanchea. I feel compelled to utilize human perspective and experience in looking at what is meant by choice. However, I found the case study of the behavior of the pleurobanchea mentioned in class to be quite interesting. The observation was that the pleurobanchea like any other animal follows the Harvard Law of Animal Behavior which predicts the animal to act however it chooses at times. In the case of the plerobanchea, it was observed that it would always withdraw its evertible probroscis(nose) whenever it found itself being unfairly and injustly banged upon by a research biologist. That response, however, varied when the pleurobanchea was in the process of using its evertible probroscis for feeding purposes. At those moments the pleurobanchea's evertible probrosis just went on about its eating business, paying no mind to the crazy scientist banging on it, for no good reason. The nose didn't retract. These questions were then entertained, "How can we make sense of this in terms of neurological processes? Is the pleurobanchea making a "choice" as to its response to the banging on its nose? What then is choice?"

With these questions in mind, it was then illustrated that in a situation where the pleurobanchea's nose was cut off from its body(again, I cry atrocity of the worst kind) and studied, some light was shed on what was going on. The understanding developed from the observations and studies pointed to a central pattern generator directing tooth movement in the pleurobanchea's nose as it fed itself. The pattern processing feeding through the nose was then interpretated as a silmutaneously inhibiting agent to the pattern of behavior which would allow the nose to withdraw. From this explanation of the withdrawal vs nonwithdrawal state of the pleurobanchea's nose, a question arose which wondered, "Is that then what choice is, can the concept of choice be reduced to the phenomenon of corollary discharge in which motor activity affects the sensory input?". Is the pleurobanchea essentially "choosing" to withdraw or not to withdraw its nose?

In the case presented here, my mind's reactionary response was a loud "No, of course not, the pleurobanchea is not "choosing" a thing". But then, once I passed the reactionnary phase, I started considering critically this idea in view of the observations. Yet I still couldn't convince myself of the conclusion that "Yes indeed it was making a choice". A couple of issues kept rising up in my mind. First of all, those observations alone are not enough criteria to entertain the idea that what is seen as "choosing" is reducible and unmistifyingly an example of corollary discharge, which is the pressupposition on which the question asked in class is developed, "Is that what we mean by choice?" From these observations alone the clear answer is, "NO", in the case of the pleurobanchea. Secondly, the capacity of the pleurobanchea's nervous system as described by the above observations seem to not even allow any room for the idea of "choice" as understood in terms of me, for example, consciously making a decision to wake up at 4:30 every morning (miracles can happen, you know) until I graduate from Bryn Mawr. You better believe it that my body's motor activities would be fighting this idea with all their might. Yet, in spite of the wishes of the physical, "I" can choose to make that decision a reality. In that sense, the unjustly abused pleurobanchea's nose doesn't appear to share a similar luxury of "choosing" to withdraw even though it is eating. It simply cannot and will not withdraw its nose because it cannot both eat and withdraw its nose at the same time. In the politically correct world, the poor pleurobancheans would have to be described as a "withdrawing and eating at the same time challenged species", in which case the idea of it "choosing" seem kind of nonsensical and irrelevant.

Nice summary of the issues. Key issue, of course, is your emphatic "NO" to the question "Is this what we mean by choice", and, even more importantly, WHY you are so emphatic. "First of all" says it, but doesn't explain it. "Secondly", though, raises some important points, to be added to those of some of your colleagues. Yes, "choice", the way we usually use the term, clearly relates to the "I-function", so we'll have to come back to it after we work more on the latter. There is something important to in "make that decision a reality", implying that, in some sense, one (unlike Pleurobranchea?) might in fact have acted differently. Can you imagine ways to interconnect neurons to make that concrete? And yes, there are some interesting broader implicatons of all this with regard to political correctness. Does ".... challenged" mean diminished capacity to choose? All very much worth thinking more about. PG

Name: Anneliese
Subject: anthropocentrism
Date: Tue Mar 3 11:03:03 EST 1998
I was very pleased to read Elaine de Castro's comments regarding choice and free will, because they correspond to my own attitude towards our tendency to see ourselves as superior to other organisms. I don't actually know whether the term "anthropocentrism" exists, but you all know what I mean by it, I suspect. I am very interested in anthropology, which makes a point of trying not to be ethnocentric, i.e., all cultures are relative and cannot be judged on any other terms but their own. Yet when it comes to other species and genera, we as humans have no qualms whatsoever placing ourselves at the top of the evolutionary hierarchy (I realize this is not true for all of us, for which I am glad). That is one of the reasons I am so intrigued by biology as a discipline, because it seemed to me that biologists had less of a tendency towards this kind of arrogance. Yet in class, I discerned this same arrogance (forgive the harsh term, but it is fitting) when posed the question of whether the infamous pleurobranchea was exhibiting choice or not, or, more specifically, whether choice could be broken down/traced back to patterns of activity in various neural circuits.

Think back to the Professor Grobstein's proposal to us at the beginning of the semester, that brain=behavior; it seems plausible to me that even concepts so important to us as choice and free will could conceivably be nothing more (?why such a negative qualifier) than interactions between neurons, influenced both by what is going on outside as well as inside the nervous system. If we want to avoid magical explanations, we're going to have to accept this. When you talk about choice and will, it sometimes sounds as if they were some kind of essences floating around or residing within our brains; I think we need to think of them a little more concretely, not as concepts, but as behaviors, which, like all behaviors, can be traced to neurons.

Why does the possibility that our selves are explainable by patterns of activity across neurons, influenced by both sensory and motor input, as well as spontaneous action, cause us to feel any less whole, any less individual, any less alive? It is obvious, by just looking around and making observations, that we aren't in any way akin to the machines we build, that we aren't robots. But we are inventions, we have component parts, there is a lot which is predictable about us. Saying that brain=behavior, that we can be explained by interactions of cells at multiple scales, should not scare us or make us feel any less whole; Nature is a far more skilled and ingenious scientist than we can imagine, and her (?) "machines" have properties we can only dream of giving ours.

Having studied some biology together, it comes as no surprise that we think much alike about these things, but its nice to have them so well said. Indeed, "her machines have properties that we can only dream of giving ours". But indeed we CAN dream of that, and even successively approximate it. No magic, no floating essences ... and yet, somehow, the Pleurobranchea circuit discussed in class DOESN'T seem to exhibit properties that are inherent in what we as humans understand by "choice" and "free will". So our problem is what are those missing properties (a number of suggestions have been made by your colleagues) and how might we get them out of circuits of neurons? That's a question we can explore without prejudging the issue of whether Pleurobranchea does or does not also have them (we only looked at one Pleurobranchea circuit), and hence without anthropocentrism (as long as we don't presume that something having those properties is "better" than something else). To put it differently, one can (and probably should) treat as separate questions the brain=behavior hypothesis and the issue of whether humans are or are not the same as other organisms. PG

Name: Bonnie Kimmel
Subject: thoughts
Date: Tue Mar 3 11:23:52 EST 1998
I am intrigued by the issue of choice that was brought up in several other entries this week, as well as how this extends to issues such as violent behavior. I also think it's interesting how differently society tends to place value or legitimacy on certain behaviors depending on how much of it can be attributed to internal vs. external factors, how responsible the individual can be held for their actions. If we didn't care about why someone behaved violently, but rather felt it was unacceptable regardless of its source, this wouldn't be such a huge question to ponder. It shows so much about societal views on responsibility and blame, and overall acceptance of scientific knowledge as truth. This can apply to almost anything, and really reflects our preoccupation with scientific explanations. Why do we care so much and what would it change if we knew that there was, say, a genius gene and that people had no choice over that either? Would we value the genius less since s/he really had nothing to do with it anyway?

I keep coming back to the notion that just because we prove the existence of one thing, we do not necessarily disprove the existence of something else. I sometimes get confused, then, why we are trying to attribute behavior to corollary discharge or central pattern generators. Since we are talking about this at every step along the pattern of activity that constitutes action, might not each possibility we have talked about have some role at some time?

Two interesting, distinct, but related issues. I very much agree that our culture has a tendency to conflate explanation, responsibility, and morality. That one can account for something (violence, for example) really oughtn't to make it more or less acceptable. And yes, we prove existence of one thing, without proving the non-existence of alternatives, so LOTS of things can simultaneously exist (and frequently do). From the two of which one might conclude that one should simply insist on the difference between right and wrong and stop doing research. Alternatively, one might conclude that there is no such thing as "Truth", but there is such a thing as getting wiser, which means continually collecting observations which allow one to make better and better sense of things, including one's own feelings about what is right and what is wrong and what to do about it. Particularly for the latter, one might want to know more about what "being responsible" means, so that one could deal more equitably with people who act in similar ways but for different reasons, and one could encourage educational/social systems which assure that everyone acts with maximal personal responsibility. Want to guess which conclusion I draw? PG

Name: Zach Hettinger
Subject: Neurological damage
Date: Tue Mar 3 11:43:02 EST 1998
I thought I would diverge from our topics this week to write about something that has always captured my attention, the area of treating nervous system damage. Right now I can hardly imagine how to treat something that is most often described as permanent, but at the same time it's easier to look at the big picture without the all the details.

I've been intrigued by the recent findings about telomeres and how they help the cell determine it's life cycle. There is a certain set life cycle for the cell and when that runs out, the cell dies. But scientists have been able to trick the cell and "reset" the telomeres so that the cells live twice or three times as long as they normally would. Many people are now theorizing that we could be living twice as long in the near future if we take shots or pills to reset our "biological clock".

I find the prospect of doubling the human life span a little scary in both biological and ethical considerations. But what does strike me is what this research could do for neurological damage. We all know that a lot of neurological damage that occurs to young children can be overcome to a great deal because their systems are still forming. But in adults the damage is often permanent because the path ways have already been created and are even starting to die off. So what if we could turn time around for the nerve cells surrounding the damaged area and have them think they are young again and start to reform those connections. Obviously it would take a lot of time and effort to take advantage of the new reconnections, but some connections have got to be better than no connections.

Well, it's just a thought about how to help something that has been difficult to treat in the past. I'm not even sure if telomere gene therapy could apply to nerve cells, since they don't really divide once they have established their position. I just like the idea of being able to help repair the damage and give people back some of the control over their own bodies that they once had.

It is indeed an interesting idea, though, as you say, one would first have to either return neurons to the mitotic cycle or find germinal populations (for which there is increasing evidence). On the other hand, there are, as you also say, troubling issues about life span enhancement, both ethical and biological. Certainly, to "give people back some of the control over their own bodies that they once had" would be an appealing outcome. At the same time, one suspects that here, as in most situations in biology, values in one realm associated with a particular change almost invariably exact costs in some other realm. It might be interesting/instructive to try and guess what the costs would be in this case. PG

Name: Akino Irene Yamashita
Subject: determinism and responsibility
Date: Tue Mar 3 22:05:01 EST 1998
This week's discussion on whether we have free will or not made me realize that although there is an age-old "nature vs. nurture" debate these two alternative explanations for behavior actually share a common assumption, which can both be considered deterministic and do not consider free will or responsibility for one's actions. In the "violent person" example, someone can say, "Well, it's in his genes to be violent, so he is not responsible", but someone could also say, "Well, he was abused growing up, or he watched too many violent movies, or he was stuck in a slum where violence was the norm, so it's society's responsibility that he wound up murdering someone, not his."

In either case, the person is seen merely in a passive role, either dutifully carrying out "instructions" encoded in his genes or being influenced by the environment and responding to it. And it seems that if the person was not acting out of free will, then it makes no sense to punish him. Although then we get into the entire issue of, what is the purpose of punishment? Societally mediated revenge? The removal of dangerous persons from society? Rehabilitation? Okay, I am way off the subject of neurobiology here, let me stop.

Now there are also people who say, "Well, I was abused by my parents but I did not become an abuser myself", or "Well, my father abandoned me but I did not become an unwed mother". (I am picking these examples because there are studies that have shown correlations for higher rates of abuse for abused people and a higher rate of unwed motherhood among children of single-parent families".) These people usually cite free will. But of course, not all abusive situations or single-parent households are the same. Perhaps these people had other support systems outside their families, for example.

Maybe this discourse is rambling, but my point is that whether we have free will outside our genes and environment isn't simply a philosophical question, but has large societal implications as well.

Another little example related to the topic: I have noticed that, whenever people sneeze, we always shut our eyes. It seems that we have no "choice" to keep our eyes open when we sneeze. So is this situation similar to that of the sea slug's nose? Obviously there are many instances of "reflexes" where the body acts in ways that are not controllable by the conscious mind/I-function. But, what about behaviors that we perceive control over, that seem to be mediated by the I-function? If even those actions are not determined by free will, then what is the pattern of neuronal activity that causes us to perceive that we do?

I'm with you. Genetics and experience can be seen not as opposites but rather as two forms of the same deterministic (and hence exculpatory) "explanation". And yes, you're not way off the subject of neurobiology: if behavior can be accounted for in either of these ways (or by their combination), then there is something odd about a social/legal system that depends on a concept of "personal responsibility" or "free will". Which, for me at least, in turn means that if one takes brain=behavor seriously (as I obviously do), then one suspects there must be something more to behavior (and its underlying neural organization) than is expressed by genetics and experience alone. Trying to say what that something is is a significant part of our semester's explorations. And yes, I think it has something to do with the "I-function" which, as you point out, seems to be something over and above closing one's eyes when one sneezes. PG

Name: rob miller
Subject: CPG's
Date: Tue Mar 3 22:13:19 EST 1998
Corollary discharge signals and central pattern generation undoubtedly have implications for behavior. For instance, let's consider the example of the sea slug withdraw (or not withdrawing) it's snout(I hate the word proboscis). Due to the inhibiting signal sent from the CPG of chewing to the CPG of snout withdraw, the observed behavior is the absence of the withdrawing motion while eating. Obviously the behavior was affected by the central pattern generators. Behavior, in a sense is simply a pattern of outputs. These outputs can be explained by patterns of neurons firing in the brain. Behind each pattern is a CPG, which causes the specific ordering of neurons firing, to create behavior. An example may be a person who is always whistling. This person may have a CPG which spontaneously fires the pattern to inhibit talking and begin whistling. In this case CPG cause behavior.

We included the topic of choice in our discussion as well. If the sea slug does not withdraw it's snout, did it choose not to follow its CPG that governs feeding? In my opinion, choice in the sea slug and all animals is at a basic level, an interwoven meshwork of CPG which send corollary discharge signals between each other all of the time. In more complex animals, there are more inputs going into the meshwork. Since there are more inputs, there are more corollary discharge signals which interact with other parts of the brain. More complex animals also have memory (which may also be considered CPG, I don't know yet) to mix in with the other CPG, and complicate decision making and behavior. The brain must act on these CPG and corollary discharge signals in the most appropriate manner. This is how I feel choice is created in the brain.

Choice and behavior are not the same thing. Choices arise from and also causes certain behaviors in animals. There may be much more to consider than just CPG and corollary discharge signals, but we have not ventured further. All there is to work with are action potentials and neurons, so the basic mechanisms of choice and behavior must originate from patterns of action potentials, otherwise we wouldn't have much to do in life.

Assuming we agreed (accepted as a working hypothesis) that there is nothing there than neurons and action potentials and the like, then clearly behavior in all its aspects must come from that. That is not, however, quite the same thing as saying that all aspects (such as choice, in the present case) come from CPG's and corollary discharge signals and (presumably) sensory input. CPG's and corollary discharge signals are concepts at a level of organization above neurons. And, at the moment, our question is do we need additional concepts at higher levels of organization to account for behavior or do we have enough? Which in turn, of course, means what would cause us to "venture further"? Choice COULD be, as you describe, just "more inputs into the meshwork"? Are there any reasons to think it might be more than that? PG

Name: Fumiko Konno
Subject: pros and cons...
Date: Wed Mar 4 09:31:36 EST 1998
I think that there are definite advantages in studying inputs before the outputs. That's because there are many behaviors that are triggered by our senses. Thus, in these terms, it is only natural to study them in order of how the behavior occurs. However, the problem about this order is that bidirectionality of the nervous system and the fact that outputs influence inputs. In this sense, the nervous system seem circular with many branches, so it is difficult to determine where to start studying. Also, what about those behaviors that are fairly independent from senseory inputs? There is a question of choice as well. It seems that we can't understand behavior based only on cause and effect, because of Harvard Law of Animal Behavior. For example, we talked about Pleurobranchea the other day in class. It seems that we can't pin point one input as a cause for an action. There are other complicated factors involved in it. These factors are the patterns in which the sensory input is processed. One sensory input may cause several behaviors. It seems to me that perhaps it is more efficient to back track (study the outputs first).

Interesting problem, huh? Circles don't have a starting point, so ... . I'm not quite sure how to decide what is "more efficient". And don't think "it is only natural to study them in order of how the behavior occurs" for the reasons you give. So what should we do? Maybe circles need a different way of teaching altogether? PG

Name: Eric Odessey
Subject: Memory
Date: Wed Mar 4 17:48:47 EST 1998
My essay this week is going to be phrased more as a question than any definitive statement. Again, I'm off topic, mulling over a few details on memory. Memory, I have heard, consists of neuronal loops which store information as continuously moving action potentials. These potentials are somehow released to the rest of the nervous system when needed. There are a finite number of neurons in the brain, so it seems intuitive that there would be a limit to the amount of information we can store as memory. So, my question is, "will any of us will ever reach that capacity?" I suppose this question is also related to the mechanism of forgetting. The way I see it, there are at least two possible explanations for how one forgets a piece of information. If the brain has not accessed a piece of information in a very long time (such as playing a piece on the piano you haven't played in 10 years), it loses the ability to access it, but the information remains stored in the brain nonetheless. This explanation has the mind-boggling implication that everything you have ever learned is still in your brain somewhere. The second possibility is that when the brain receives a new memory input, it selects a relatively unused area in the memory stores and replaces it. If this is the case, then how does the brain decide when it needs to start replacing memory, and what is the limit? The idealist in me likes to fantasize that we are only limited by the speed in which we intake information, not the number of neurons in our brains. I'm curious to see if anyone has an answer.

We'll talk about learning and memory later in the course (and you can, of course, read about it in advance, in the textbook, on the web, etc.). For the moment, let me try and give you a quick setting based on what we have already talked about. As you might guess, "memory" is not a thing but lots of things ("at least seven"), of which repeating patterns of activity are one but probably not the most common and certainly not the most stable. Hence, it is next to impossible to estimate a "maximal storage capacity". What makes it even less likely that this is a reasonable way to think about the matter is that, by and large, the brain does not have a clear separation between processing and storage areas (and hence is quite different from most existing computers); information storage generally involves changes in the processors (neurons and their synapses) themselves. And this leads to a third needed clarification about memory: in general, what is stored is not at all like what is stored on records, tapes, CD's, something isomorphic with the experience. Instead, what is generally stored are a large number of small (and individually meaningless) changes from which the brain doesn't so much recall as try to reconstruct prior experiences. That help any? PG

Name: Allison R.
Username: arosenbe
Subject: genetic cpg
Date: Wed Mar 4 20:40:55 EST 1998

Looking back a bit, we discussed learned versus genetic central pattern generation in class. Professor Grobstein stated that usually both genetic and learned actions can be accounted for in central pattern generation. We were discussing whether a bird learns to fly or if the pattern for flight is already built into a bird's system. By using straitjackets to prevent the birds from practicing to fly, we concluded that flight must be inherent in birds.

The point of this little synopsis: I recall someone requiring about the setup of the experiment. If the restricted birds watch their siblings learn to fly, does this have any effect on their own learning? I was reading an article by J.E. Mazur and found the answer to be no. Similar to birds, an experiment was done on squirrels to see if the animal's ability to perform a behavior is dependent on prior learning. By taking these squirrels out of contact with any other squirrels, they wanted to see if the maturing squirrel would display "nut burying" behavior.

The squirrels were deprived of all possible means to learn the behavior. They were fed only liquid food, so had no opportunity to handle food. They lived on a solid floor, and had no experience of digging. There was never a reason for them to bury or save food for later because they were always well fed. Once the squirrels matured, they were given nuts for food. After they were satisfied, they began taking the nuts and piling them in the corner of the cage. The squirrels began performing "nut burying" actions even though they served no purpose in the cage.

We can conclude from this that this type of activity is innate in squirrels, as I am sure flying is in birds. Even if the bird's had been isolated and straitjacketed, they would still be able to fly once they were mature enough. Learning plays no role in this inherent central pattern generation.

Nice story, good addition to the bird flight example. Many thanks. Want to give me the reference? How'd you happen to be reading it? PG

Name: Donald Ball
Subject: CDS and Choice
Date: Thu Mar 5 11:07:32 EST 1998
Variation in the kind and quality of corollary discharge signals are just one factor that plays a part in this difference of experiencing an event. The example we did in class, moving our finger in front of our eyes and focusing on an object behind it, demonstrates the effect of CDS on our interpretation of an event. The internal backwards signal that says to some part of our brain that the eye is indeed moving and that whatever sensory info received from the eye should acount for this fact, does dramatically effect the interpretation of that incoming sensory info and as a consequence our perceived reality of that event. This in turn could generate a set of actions to respond to that perceived event that calls into play a whole series of CPG's and out comes a response. If something is perceived as real, then it is real and we react to it as such. That is why hallucinations, a phantom event to everyone not having that particular illusion, can motivate behavior. The same can be said for any concept that has been internalized and taken for real (or perhaps synonymously and more dangerously as truth).

So, what does this all have to say about personality and choice? [o.k., I don't know what just happened but I lost the last two paragrpahs of my discussion - so I will try and ressurrect them from memory, ughh]. It has long been understood that two people can experience the same event (have identical input signals) yet perceive that event in dramatically different ways. Before I was introduced to the concept of CDS I would say that this difference in perception had much to do with the genetic makeup of the individual and the environment in which that person was placed. Personhood is a concatenation of genes and environment. Now, to this list of factors that define difference I would add CDS's. The amazing thing about them with regard to personality is that they are an internal feedback loop that erects this vast internal network that modifies how we perceive incoming sensory info and thus our sense of what is real and how we respond to such perceptions. What is also profound about this sysetm is that it is not static but evolves itself as it is called upon time and again to respond to the incoming sensory information that our acting in the world generates.

This internal system has a 'memory' of its own and can follow its own protocals in calling upon hardwired CPG's to respond to an event. The bottom line is that CDS's directly impact our version of reality and how we respond to it. So, what about this question of choice? I don't have any definitive answer, but I can say that there is certainly more to it than either the same person or two different people exhibiting different behavior under identical circumstances. The information that the person receives is modified by this vast system of CDS's, as well as by the excitatory and inhibitory CPG's present at birth and those developed as a consequence of learning, which in turn is a function of environment.

Interesting, thoughtful. I'm glad you share my sense that there is explanatory richness in the CD concept. There is though one problem that needs some more thinking through. CD's are not, at least obviously, a thing to "add" to genetics and experience, in the sense that their existence and function might actually be fully determined by genetics and experience and so they might not broaden the arena on that conceptual level. I say "might" because we haven't as yet talked about evidence that that there is anything other than genetics and experience (at that conceptual level). We will, though, and at that point your argument that CD's could be a reflection of a third thing will be quite relevant. Any thoughts about the third thing? You can get a preview of some of my thoughts on the matter to compare with your own PG

Name: Daniel Casasanto
Subject: Weekly Essay #5
Date: Mon Mar 9 16:51:34 EST 1998

Biology, at the sub-microscopic level, describes the motion and interaction of molecules that constitute living systems: chemistry is the physics of biology. As such, the study of these molecules, and of the organisms they compose, must be informed by modern physics. The new theories that remodel scientists' conceptions of nature -- from sub-atomic particles to universes -- apply to every aspect of biology. In recent decades, physicists have changed their methods of experimentation to accommodate emergent theories. Have biologists?

Among the implications of Heisenberg's uncertainty principle is that the act of observing alters both the observer and the observed. Accordingly, physicists have begun to consider themselves components of any experimental system: not observers, but participants. How can biologists do the same? How can one "participate" in photosynthesis, or synaptic transmission, and how to account for one's participation?

A strategy physicists use to mitigate the effect of the observer on the observed, or more correctly their mutual interference, is to spatially separate them. (Some quantum theorists would take issue with this statement, arguing the impossibility of fundamentally discrete objects.) Spatial separation necessitates the huge circumference of particle colliders. What is a practical analog for such separation in biology? Surely long-distance dissection poses logistical problems! Is quantum-relativistic experimental design possible for biologists? Is it necessary?

The "old" way of thinking suffices for lay people and scientists alike, in most situations. (There is no need to invoke the Lorenz equations to measure your Amtrack commute.) This is because, ordinarily, we interact with things that are big and slow compared to sub-atomic particles moving at the speed of light. Even molecules, the smallest constituents of biological systems, are relatively big and slow. Since Newtonian physics describes the big and the slow with high precision, why should biologists worry about quantum-relativity?

Because it's real. The action-and-reaction-driven world modeled by Newton is imaginary -- albeit a useful image, integral to our perception of reality. Furthermore, it may be regressive to consider the molecule fundamental; perhaps the electron is the most basic element of biology, in which case quantum electrodynamics must surely supplant Newtonian mechanics. To go one step farther, if one considers that biology describes complex, dynamical systems in which no element is fundamental, then Newtonian mechanics are irrelevant and quantum-relativistic explorations are obligatory.

The question remains: how, with our three-dimensionally conditioned words and senses, do we perform experiments that reflect four-dimensional reality? If biologists must continue to design experiments based on obsolete notions of observer and observed, cause and effect, we must recognize our reliance on an imperfect model, and treat all data as approximate. If we cannot modernize experimental techniques, we must modify the interpretation of experimental results. As physics shows, our observable approximations may be substantially different from the quantum-relativistic realities they prefigure.

"What we observe is not nature itself, but nature exposed to our method of questioning."

Werner Heisenberg, Physics and Philosophy

Heisenberg was right (or at least "less wrong"); we'll see abundant examples when we (shortly) get to the input side of the nervous system. And Newtonian physics is, as you say, proving to be a mindset of both real and limited applicability (see On Beyond Newton ...). And I share your feeling that this all means that, in general, we need to find new ways to both do experiments and interpret experimental results (From the Head to the Heart: ... significance for research methodology and biological theory). With all that agreed to, the tough questions become deciding when and where one has to worry about such things as indeterminacy and observer effects (and when and where one doesn't). To put it differently, the need is as it has always been: to figure out what particular new observations will lead to improved (not perfect) understanding, given what we currently think we understand. Newton did awfully well with that. If current science does even half as well, things will be fine. PG

Name: ruth czarnecki
Subject: choice
Date: Tue Mar 10 22:04:17 EST 1998
Something was brought up in class that i thought was very interesting was the concept of choice. First of all, I do not deny that in the discussed instances of pleurobranchia activity, there was no choice being made. However, does that indicate the fact that choice cannot be made by "lesser" species? I do not think so. Now, pleurobranchia is a comparitively simple organism. There aren't many choices that it can make. In fact, my take on the pleurobranchia, is that it was designed to have premade choices. In 5 billion years of evolution, i think that the choices made by pleurobranchia, have mostly evolved with him. For instance, being such a simple creature, he doesn't have much of a way to get around in order to find food, other than ocean current. Therefore, the choice to keep his nose out when attacked when feeding has probably been a choice made by evolution. the pleurobranchia just doesn't have to think about it anymore.

Another interesting thing that came to mind is, what does that say about higher organisms? What about humans? Could it be that many of our choices have already been made by evolution and we just refer to them as instinct? I think this is a very plausible explanation for action in all species. But then again, what choices do we make AND what has decided that we should still be allowed to make these choices? AND how do we make choices? Are new choices just a compilation of instincts that take a while to be put together? If so, what allows us to make an intellectual decision? By intellectual decision, I mean one on something purely or at least mostly intangible. A decision that exists only in your brain, i.e. what book should I read this week? Well, I guess that is all, it just got me thinking a little.

Thinking a little is fine, even desireable. And, in some ways, the very essence of the question, yes? "The Pleurobranchea doesn't have to think about it any more". Did it once have to "think about it"? Do we actually "think", or is that just "a compilation of instincts that takes a while to put together"? Interesting questions. Can you think of a way to get at them? Is that a meaningful question, and what does it mean? PG

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