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Remote Ready Biology Learning Activities

Remote Ready Biology Learning Activities has 50 remote-ready activities, which work for either your classroom or remote teaching.

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An ongoing conversation on brain and behavior, associated with Biology 202, spring, 1999, at Bryn Mawr College. Student responses to weekly lecture/discussions. A suggested topic was provided, but students were free to write about any other observations, ideas, or questions that particularly interested them.


Pleurobranchea might or might not withdraw its proboscis when it is hit, depending not on some other sensory input but rather on the presence or absence of a corollary discharge signal. Is this what we mean when we speak of "choice"? When I (or you) "choose" to do one thing or another is it because of corollary discharge activity, or is something else involved? If so, what?


We've begun to see that behavior (at least action) might be describable in terms of interacting, relatively simple, small circuits of neurons. Can you see ways to extend this to behaviors other than those we've talked about in class? to more complex (more interesting) behaviors? Are there aspects of behavior which you can't imagine accounting for this way? Why? What more might one need?

Name: adrianne
Subject: negative feedback
Date: Sun Mar 21 16:03:17 EST 1999
The knee "reflex" has a negative feedback loop because the knee wants to return to its natural position or state, in which it was in, before the extraneous force which acted upon it, caused the loss of the initial position. This can be seen as maintaining a type of homeostasis. The negative feedback loop comes in handy when a person is about to fall. When someone is walking, the leg is somewhat straight and is moving in this constant position. When an object blocks the leg's path the person initially begins to fall but the body compensates through negative feedback to change the leg's position from straight to bent as way to prevent the person from falling. If the body compensates for an imbalance such as this through negative feedback then why are there people who are complete clutzes (sp?). Are these people negative feedback loops inadequately developed? Or maybe the axons sending the signal to the brain is cross-wired and goes somewhere else before hitting the brain making the "repsonse" slower?....... (just thinking)

"Klutz", I think. And be a little careful: the knee doesn't "want to return to its natural position". The muscles of the knee have sensory and motor neurons connected in such a way that if disturbed the knee will tend to return back toward its original position. The situation where a leg movement is blocked is a little more complicated. The negative feedback loop will cause the muscle to generate more force (assuming the gamma motoneurons are active, hence defining an "original position" different from the blocked one), but this won't help if the blocking object is immobile. What is actually needed to keep one from falling in this case is a more complex change in the motor pattern, involving other muscles of the same as well as the opposite leg. The spinal cord is organized to achieve some of this (see section on "reflex reversal" etc in the textbook). But, depending on the extent of the problem, the cerebellum, vestibular system, and other descending signals probably are as well. My bet is that the degree of "klutziness" has to do with variations in the organization and efficacy of the ascending and descending signals, but its a less studied area than in probably should be. Interesting question. So, by all means keep thinking. PG

Name: Debbie Plotnick
Subject: negitive feedback loops, corollary discharges and choice
Date: Sun Mar 21 20:36:21 EST 1999
I've been thinking about both negative feedback loops and corollary discharges with regard to one another. Sexuality and reproduction is an area where I can imagine a set of operations controlled by negative feedback loops that might be mitigated by corollary discharges. This is an instance where the corollary discharge might be attributed to choice.

I would speculate that for the females the reproductive cycle series of "set points" that are controlled by negative feedback loops that regulates hormone levels. The fluctuation of the menstrual cycle is such an example. But with regard to sexual behavior it is my conjecture that the high hormone levels that would compel the female to engage in mating behavior could be subject to corollary discharges that cause choice. The female may decide that she does not like a certain male or males. She, in the case of human females, may experience corollary discharges resulting from previous patterns generated as learning (moral and or experiential as examples) related to the appropriateness of mating at the specific time in question or again with regard to a particular male. The same issues regarding choice because of learned behavior or fear of consequence would affect the males. In both sexes this would cause disequilibrium and a state of discomfort as the corollary discharges and physical sensory information are in conflict.

I also would suggest that there are various negative feedback loops that come in to play creating a series of set points during reproduction. The hormones of pregnancy and lactation would be a new negative feedback loop that would make new set points for menstruation.

Actually there are both negative and positive feedback loops involved in the menstrual cycle. The extent to which there are changes in the set points of these is an interesting question. As is the issue of the relation between hormone levels and mating behavior. I like your idea that, whatever that relationship, other patterns of activity can also influence whether one actually engages in mating behavior. Whether these ought to be called "corollary discharge" signals is a matter of definition. We developed that term from thinking about what additional signals pattern generators must be creating during movement, and probably one doesn't need to be moving in order to make mating choices. Maybe a more general idea would be that "thinking" (like moving) involves patterns of activity (within interneurons rather than motoneurons) and this may also be accompanied by signals sent to other parts of the nervous system which influence their function? I don't know of an existing term for the latter. Shall we call it "internal signalling"? or something like that?

Name: Alexandra Smith
Subject: Negative Feedback Loops
Date: Sun Mar 21 21:21:43 EST 1999
In my first paper on migraines, I discovered that a current theory about the origination of these excruciatingly painful headaches involved a positive feedback loop. It is believed that a certain trigger (varying according to the individual) causes the release of neuropeptides from the trigeminal nerve. These neuropeptides in turn cause inflammation of the surrounding nerve fibers which send pain messages into the brain. The pain signals cause additional neuropeptides to be released and thus a vicious cycle is established resulting in an uncomfortable migraine. While this is an example of a positive feedback loop, I found that it related to the idea of a negative feedback loop in that a trigger causes a chain of events with each intermediate step having some consequence on the following steps.

In thinking about other ways in which these cycles can explain behaviors, I thought back to my intro biology class and the idea of dehydration and ADH (or antidiuretic hormone). The body looses lots of water through the respiratory system and sweat glands and in other ways. In this cycle, the pituitary gland senses the loss of water in the body and secretes ADH. This hormone has an effect on the kidneys causing them to reabsorb more water and thus loose less through waste. By retaining more water, this negative feedback loop prevents against further water loss and dehydration.

Similarly, there is a complex set of feedback loops in the feeling of hunger, but specifically, there is a negative feedback loop, which tells the animal when to stop eating. A hormone called CCK (or cholecystokinin) is released from the intestine as food passes through the stomach. This signal sends messages to the brain telling the animal to stop eating by evoking a "full" feeling.

Negative feedback loops, or more generally, simple circuits of neurons, are critical to understanding behaviors because they clearly have many applications. Amazingly, an everyday behavior such as hunger, thirst, or mood, as brought up in class, can be broken apart into seemingly simple circuits of neurons.

There are indeed both positive feedback loops and negative feedback loops throughout both the nervous system and physiological systems in general. In fact, people interested in cybernetics and systems dynamics contend that a wide variety of systems, ranging from the biological through the economic, political, and social, have similar characteristics best appreciated in terms of interactions "through 'feedback' loops, where a change in one variable affects other variables over time, which in turn affects the original variable, and so on" (from the systems dynamic link above). Negative feedback loops, as we talked about in class, tend to stablilize systems around a given value. Positive feedback systems, on the other hand, tend to make systems move toward an extreme value. And yes, as embodied in small circuits of neurons, such loops do indeed make it possible to imagine new ways of thinking about lots of "every day" behaviors. PG

Name: Mary Bartek
Subject: choice
Date: Mon Mar 22 00:03:33 EST 1999
I still do not understand how the circuits we designed in class explain choice. While I see that the model could be made more complicated to explain a wider variety of behavior, I do not see how it relates to concious choice. In class, I gave a rather trivial example about chosing a seat on the Blue Bus. That morning, I was given the option of many seats. I saw two of my friends sitting in two seats, as well as lots of open seats. I chose to sit in an open seat next to one of my friends. Sitting in that seat rather than another did not seem to require separate central pattern generators, since only the only movement that differed was the duration of walking. I do not see how central pattern generators can exist to control how long we walk, because that would limit flexiblity. We would need an infinite number of central pattern generators. The model also did not relate cognition to decision-making. Given the choice on the Blue Bus, I conciously thought, "well, if I sit with this friend, the other might be offended, but if I sit with the other, the first friend would be offended." Perhaps central pattern generators control our thought, and that is possible, but they do not seem to provide the element of complexity or creativity evident in human thought and activity. Yes, central pattern generators explain many behaviors, but I do not see how they explain choice.

Ah ha ... "could be made more complicated to explain a wider variety of behavior, I do not see how it relates to conscious choice (emphasis mine)." That is indeed, as I see it, the crux of the matter. One could, in principle, imagine how a given input could have different possible outputs, based on corollary discharge signals and CPG's, but that doesn't SEEM to account for the experience of "thinking about something". Could we perhaps do it in terms of some generalization of CPG's and corollary discharge circuits as in my response to Debbie above? Or is something more still needed? PG

Name: Rachel Berman
Subject: The Dopamine phenomenon
Date: Mon Mar 22 00:31:03 EST 1999

From the discussion in class, I was also amused to how many complex behaviors Dopamine was linked to. I have been trying to make some sense of how a single chemical can have multiple affects on behavior....if it is possible to conceive of such a scheme.

Taking as a staring point that behavior is controlled by various chemical reactions in the brain and the communication pathways, the circuits of neurons, involve and are influenced by various chemicals that are produced. A single chemical is capable in participating in various chemical reactions that produce different products that can, depending on their reactive specificity, go on to react further and cause different products to form. Also various other factors such as relative size of ionization constants, temp, side products, etc., of these reactions could influence which reactions predominate and thus which products are present in greater amounts. Therefore, different behavioral patterns may arise depending on the chain of reactions caused by a chemical, say dopamine, and by the concentrations of various chemicals produced. It is conceivable that the chemical reactions behind these behavioral patterns can potentially start from the influence of a single chemical.

So could behavior be described by a particular influence of a single “starter chemical” whose medium is the “small, relatively simple circuits of neurons”. If we could trace the action of a chemical in this maze of circuits and have the knowledge of the various intricacies of chemical reactions, perhaps we will be one step closer to understanding what behavior is?!

If you’re interested in this, I did a chemistry project on a web site called “Love Molecules ( It talks of the same Dopamine phenomenon that was brought up in class. One of the discussions brought up is on the effect of a chemical called pheromone which is released by various organisms, including humans. It is released by the queen honeybee and a sniff of it causes the other bees to raise the queen’s young and basically do anything she pleases! Also, the chemical serves as a signal in various insects to attract members of opposite sex. Certain species of male beetles literally make “a chemical offering” to a potential mate and if the female finds the chemical compatible, she will continue to mate with him.....and the list goes on and on, connecting this chemicals to at least a dozen behaviors. Even to the sex life of elephants!

I'm enjoying your persistance in trying to find comfortable ways to connect behavior through the nervous system (thanks for including small circuits) to the chemistry you know about. Yes, of course, a given chemical can have lots of different effects. But be a little cautious about meta-problems too. "Pheromone" (nice article) is not ONE chemical, but a name for a biologically defined class of (chemically) diverse substances which have in common that they function as signallers between organisms. And, while I think dopamine is likely to be involved in a number of different behavioral functions, I suspect an additional reason for it turning up in lots of contexts at the moment is that it is "fashionable", i.e. lots of scientists have heard of it and there are lots of available protocols for working with it, so observations linking it to a variety of phenomena are readily made. It may well, in the long run, turn out that dopamine is less significant than other as yet less well-known materials in a number of these. Its a good idea to be both imaginative and skeptical in dealing with science. PG

Name: David Benner
Subject: posture
Date: Mon Mar 22 01:04:28 EST 1999
One example where negative feedback loops may affect behavior is posture (this may not be as interesting as anything that may or may not involve dopamine, but body position is important to me, as a rower, to my sister, as a ballet dancer, and to my father with his lower back pain). The body maintains a steady position through muscles in the legs, lower back, and neck which are regulated by the thalamus. We can make ourselves upright for a short period of time, if we consciously think about it, altough it requires a certain amount of strength to stand at attention, for example. If muscles are stronger, they will not need to shorten as much, resulting in less stimulation of alpha neurons. Posture, though, seems to be the product of more than relative strength. To maintain 5th position, there has to be a corollary discharge since a dancer is aware of his or her movements which are regualted by the thalamus. It is likely that there is a central pattern generator for the muscles that maintain our body position since it is the product of corrdinated muscle activity. It is likely, then, that radical changes in posture are not possible, although we can improve it by practicing sitting upright which strengthens relevant muscles.

In response to last week's question, then, corollary discharge must be the means by which we can change central pattern generators for their operation, giving "us" (the elusive agent) control over behaviors. Unless the brain gets input regarding something like posture, it cannot deliberatley set about trying to change it. Our ability to modify behavior of this sort is pretty limited, though. I don't see how we can alter preexisting CPGs, but we can change the muscles on which they act.

One question which interests me is how some zen monks can lower their metabolism until they appear dead. How is this possible since we can only act directly with *corollary discharge* on muscles which are innervated by neurons from the somatic nervous system? Is it simply an extreme form of the relaxation that comes with meditation? On a philosophical level, does this ability signify a greater understanding of the central nervous system than that of science? (Can you do this? Can they explain why it happens in terms of neurons?) This is a topic I would like to explore in my next web paper.

As usual, you're raising some very interesting questions, trying to use ideas we've developed in one context to see if they can help in additional, more sophisticated contexts. See my comments to Debbie for some cautions about the applicability of the terms central pattern generation and corollary discharge in such efforts. And I'm not sure I follow the argument that leads to "radical changes in posture are not possible". One can, presumably, develop new CPG's and corollary discharge circuits, which would make possible new postures, no? My guess is that something of this kind happens when one "learns" 5th position, or standing on one's head.

How the "elusive agent" ("I-function"?) plays into all this is a good question, which we'll come back to. And your extension if it to control of metabolic processes is appropriate. Why, though, do you presume that only the "somatic nervous system" (defined how?) can be influenced by "corollary discharge" or the "I-function"? There is certainly some implication of the latter kind in many textbooks, but what kinds of observations would support it? and what others may simply have never been made (in the "science" context?). Certainly, we all have the capability to influence some "vegetative" functions (such as heart beat), by deciding to sit down/relax/go to sleep, no? Could an enhanced expertise along these lines account for Zen monks? I don't know, but am looking forward to what you come up with on the matter. PG

Name: Lacey Tucker
Subject: complexities of corollary discharge and a connection with choice
Date: Mon Mar 22 15:34:59 EST 1999
In the past few weeks we have begun exploring neurobiological explanations for very complex concepts. Some of these concepts, like “choice,” are the very things that I have been most interested in hearing an explanation for, yet I am finding that, as we get further into these ideas, I feel more uncomfortable with the explanations than I have during any other discussion in this course. I found the ideas of neurons as the building block for everything that happens in the nervous system much more understandable than the circuits that we are building out of them. I think it is the concept of corollary discharge that I find so mysterious. As I understand it at this point, corollary discharge is a neuron (or series of synapted neurons?) that is attached to a localized central pattern generator which then takes the information from that CPG and passes it on, perhaps to a different localized CPG, perhaps to the brain. It is a way of linking together the smaller, repetetive circuits of the CPGs so that a larger circuit, which is ultimately the whole box, the whole input output system, is linked up. The actual pathways that make up these larger links seem undefined though, and maybe exactly where all the corollary discharges go and exactly how they link things up is not well understood. Is the idea of corollary discharge a general term to describe the notion of linking up CPGs, or is it more specific? Does it describe all types of linking of simple circuits? The part that I am especially still wondering about it an idea that we touched upon in class: that there is a difference between the input you give someone and the experience that they have because a perceived experience is based on more than just input. The perceived experience also has to do with whatever corollary discharge is happening at the time. In other classes I have learned that what a person perceives is an amalgamation of their experiences. Does it then follow that corollary discharges are set by experience? Is knowing how you feel about something that you have experienced before (like the pleurobranchea not eating a particular type of food because it has tried before and didn’t like it) due to how corollary discharge connects certain CPGs? Are these connections set as you store up experiences? Can you change them? How does the notion of the “strength” of a particular CPG fit into how things connect up, the role of experience, and the ultimate output? All of this comes down to trying to understand choice. I have no answers this week, only questions…

Questions are sometimes even better than answers. See my comments to Debbie above for an effort to clarify the issue of what is/is not a corollary discharge signal, and how one might usefully generalize from that. As for the issue of "an amalgamation of their experiences" and "connections set up as you store up experiences" see my reply to David. One might, I'm pretty sure, make a particular choice either because of genetic information or because of experience (or, more generally, because of a combination of both). I like the idea of trying to connect the messages of "other classes" with the neuronal circuits of this one. So keep it up please. Remember though that the categories one uses to make sense of behavior may be different in different contexts, and those used in one context (experience as an influence on perception) may not be related in a direct fashion to those used in another context (corollary discharge, which may be either experience or genetic) as an influence on perception). PG

Name: Deborah Silvis
Date: Mon Mar 22 20:19:08 EST 1999
This is slightly off the topic, but it is along the lines of the discussion that was begun at the beginning of the last class. We were talking about searching for the "answers" to questions about the nervous system, and the comment was made that there will never really be an end, an answer because simply asking the question changes the very system under investigation. I understand this point, however, the implications of it concern me. It makes me feel as if neurobiological research, and scientific research in general, for that matter, are not a means to an end but rather a perpetual game of hide and seek in which the "answers" keep changing hiding places in mid-game. And this doesn't seem right in a business in which conclusions based on experimentation and observation are expected. Can the conclusions section of every neurobiological research paper reasonabley disclaim that "nothing can be drawn from this study because the brain is constantly changing"? And if a researcher dares to report anything more conclusive and the brain is constantly changing, then what does that say about those conclusions? about the researcher? about the field in general? At any rate, whether and to what extent the brain is an ever-evolving system will certainly not deter the researchers from asking their questions, from doing their research. It's the business of science to ask these questions- whether or not there are answers out there, and, if so, whether or not the answers are knowable.

Not off the general topic, at least, at all. And will be even more germane to the specific topic as we move into sensory processing, and the relation between perception and "reality". I'm glad you picked up on the class discussion.

Science actually has two faces, and is best appreciated/understood by seeing both clearly, and the interrelations among them as well. One face is indeed "a business in which conclusions based on experimentation and observation are expected" and certainly the issue raised in class should not (and will not) "deter the researchers from asking their questions, from doing their research". The other face, seemingly paradoxically, is a much more skeptical one: one which is suspicious of all existing understandings, one which sees the task not as "getting it right" but rather as "getting it less wrong". The first face provides a basis from which the second can proceed in asking new questions; the second is the one which assures that the first doesn't settle for incorrect or incomplete understandings. The first face tries to get the answer, the second to define the next question, without any presumption that the process will eventually end (and, indeed, with some enjoyment of the possibility that it never will).

With regard to the brain specifically? For the moment, most of the kinds of questions one asks about how the brain works aren't likely to cause changes in those aspects of the brain one is studying, and so the problem doesn't exist. The more sophisticated the questions get, however, the more one is likely to find oneself in a place where new understandings do in fact change what one is studying. From the second face point of view, that's not so much a problem as a charm, but it certainly will require a new perspective on what one means by "conclusions". Or perhaps a clearer appreciation of what the second face of science has always understood about the meaning of that term.

Happy to talk more about these issues if you're inclined. Thanks again for raising them. PG

Name: feyza sancar
Subject: placeb and set point
Date: Mon Mar 22 20:20:59 EST 1999

In the last two class periods, certain negative feed back systems and their associated set points were discussed. From what I understood from class discussion, it was ultimately concluded that the set points and related negative feedback systems operate autonomously from the part of the nervous system that contains the I-function. In a sense, the negative feedback loop is governed mainly by involuntary mechanisms. One example brought up was the involuntary response of shivering produced during a fever. Here it seems perfectly reasonable to observe that the I-function-what makes us aware and consciously monitor our actions-is not involved in this particular behavior. It seems that the "I'' is not dictating when or how violently the muscles in the body will contract to produce shivering.

With this in mind, I began to wonder how the placebo effect relates to the idea of regulatory set points and negative feedback mechanisms. It could be argued that in this case (at least in the pathological condition) the body throws itself out of equilibrium in response to a placebo, to ultimately reach an "optimal level''. It could also be that instead of actually throwing itself out of its pathological equilibrium, the usual set point is altered to represent a more normative level. In either case, the negative feedback system is actively involved in the process. Assuming that the placebo effects the set point of a negative feedback system in this manner, it seems that the therapeutic effects of the placebo are more related to or mediated by the I-function than any other response rendered by a negative feedback system. For example, in a patient with depression, although a placebo has no chemical or qualitative effect on the chemistry of the brain (i.e.-it is an inert agent) the pathological set point for the release of dopamine (or seratonin) seems to be increased. As a result of this increased set point, a greater amount of dopamine will begin to be released to equilibrate at the new (more normative) set point. Unlike the set point example related to a fever, with placebo, it seems as though there is no involuntary, quantitative change in the body that triggers the alteration of the natural set point. Instead, the set point seems to be altered by a conscious cognitive effort on the part of the patient. It is assumed that the patient's belief that the placebo will produce a qualitative effect on mood is what actually changes the chemistry of the brain. In this case, is the negative feedback loop and set point more directly associated with the 'I' or self-function?

You're raising some very interesting issues. Yes, I agree that shivering when one has a fever involves a change in the set point of a negative feedback loop which isn't caused by the the "I-function" (and about which the I-function doesn't get any information about except for the result). I'm a little less certain about how you imagine a placebo to be acting via influence on the set point of a negative feedback loop in any particular case. It could certainly, though, do so in principle. Now the intriguing question: does it do so "by a conscious, cognitive effort"? If I understand you correctly, you're arguing that one has to "believe" in a placebo for it to have an effect. But then the issue becomes does "belief" require a "conscious cognitive effort"? My guess is that it can (as in "clap your hands if you believe in Tinkerbell"), but that it needn't. One can "believe" in things that one hasn't thought about, and that one is unaware of believing in, no? So maybe we have three situations: an agent acting directly on a regulatory system, an agent acting on a regulatory system by virtue of another system of unconscious beliefs, an agent acting on a regulatory system by virtue of conscious beliefs (the I-function)? PG

Name: Marion
Subject: negative feedback loops
Date: Mon Mar 22 22:28:00 EST 1999
Last week we talked about negative feedback loops, and the idea of a set point for things like muscle positions and body temperature and weight, and the concept of mood possibly having a set point. I think that maybe another kind of set point could be hormonal set points for different hormones. That could also relate to mood which we said might have a set point of sorts. Hormones control a lot of chemical reactions in the body and changes in the set points for hormones might account for mood swings and other reactions of the body.

I can't imagine accounting for any vocal reactions or conscious behaviors using the negative feedback loop. I guess that is because there isn't a set form for most of what I think of as behavior normally, like what I choose to do. I can see the things I can't control having set-points, but not other behavior. I don't know what more one might need, except to account for the influence of a person's conscious decision on his or her behavior. There must also be over-rides for the negative feedback loops, like we discussed in class, which allow someone to move their muscles from the set point, or to change their weight or mood consciously.

"To account for the influence of a person's conscious decision on his or her behavior" is a pretty big thing still to need, no? But what is that? how would we know whether or not it was there? Because there is not a "set form"? When you feel cold, you put on a jacket. Is that a "set form"? It probably is influenced by a negative feedback loop, no? To think more about ... and come back to. PG

Name: Patricia Kinser
Subject: negative feedback and menstruation
Date: Mon Mar 22 22:50:16 EST 1999
The concept of negative feedback loops as a contributing factor to elements of our behavior is both confusing and stimulating. This simple circuit of neurons can be used to explain phenomenons from the knee-jerk reaction to hunger, and beyond. Needless to say, the "beyond" is what is quite confusing-- can these circuits account for emotions, internal thought-processes? Indeed, we could say that in the case of depression these circuits are affected by variations in the levels of certain neurotransmitters... thus affecting emotion. Yet, it is easier to accept the idea that simple neuron circuits can cause a limb to be jerked up rather than the idea that our emotions, our thoughts, our "being" could be also defined by these circuits.

Another example of a system of negative feedback loops (that is easier to understand/ accept) is the menstrual cycle, which Debbie also discusses. I am particularly interested in the phenomenon of the synchronisation of menstrual cycles in women who live together. For the men in the class who may not be aware of this, very often women who live together for extended periods of time (say, on a dorm in college) will eventually experience some sort of coinciding cycles. There is still on-going research as to the exact mechanism for this synchrony, yet one fact that is essential to its' understanding is that the menstrual cycle is controlled by series of negative feedbacks on levels of hormones. It is believed that pheromones (chemicals secreted from the skin and detected possibly in a certain area of the nose) cause a neuroendicrine response involving an increase or decrease of release of a hormone involved in menstrual-cycle regulation. In other words, could it be that this type of chemical communication from one woman to another affects such a highly regulated system as the menstrual cycle, simply due to different chemicals affecting the integral negative feedback loops at the neuronal level?

It sure looks like it. See Jason Bernstein's web paper, and particularly his link to a description of a recent study on human pheromones. From limbs to menstrual cycles to ... emotions? thoughts? "being"? My guess is that we need something more than just negative feedback loops (together with other things we've talked about so far), but what? PG

Name: Joey Xiong
Username: jxiong
Subject: Hello
Date: Mon Mar 22 23:04:32 EST 1999
It has been a while since I last wrote in the forum, while being out with my little oral surgery and all, but I think that I am finally caught up in the class to adequately examine a lot of the ideas we have discussed lately. First, I am very happy to finally have a different view on the concept of a negative feed-back loop. Before I thought in simple terms that it dealt with a action which induces another action, or releases a chemical to go back and inhibit the first action. In redefining the notion of a (-) feed-back loop as being goal-oriented, I am happy to say that I understand (-) feed back loops a little better now.

Alright, I do have a few questions though, the first is that how do we figure out the set points for the (-)feed-back loops for such activities as weight control, or mood? Are there any methods that we can use? I am not sure if this is an example, but in terms of weight control, I think the environment has a great influence on how an individual weight may change. Well, the reason why I say this is because I have a friend who contracted a stomach virus a few years back. Before, he became ill, my friend was approxiamtely 5'6-7" and roughly close to 180 lbs. At the time he contracted the bug, he lost a huge amount of weight. Now, he weighs about 150 lbs. The day after class I told him about what we discussed in class on (-) feed-back loops, and he said that amazingly he has not been able to gain back any of the weight he lost. I was amazed and said that his body has found a new set weight. But I could only guess that one of the reason for his ability to sustain a lower weight was due to the bug, which may have offset his body's normal body weight before contracting the stomach virus.

Another, question which I was thinking about was that if there is a (-) feed back loop, there must be a (+) feed back loop? If so, I am assuming that it too is goal oriented. But the goal may not be to bring something that has been lured off its path back on; instead the purpose may be to keep influencing it to follow a different path. Sorry for the vagueness. But I only have a vague idea on how it could work.

Nice to have you back. And glad the "goal oriented" notion gave you some new insights into negative feedback loops. I can, out of my head, imagine what kinds of circuitry might constitute a set point for weight control, and perhaps (with more difficulty) for mood. But I don't know of any work which actually explores this question. It might be worth looking into for a web project (though one might turn up a blank). And yes, there are indeed positive feedback loops. One example is in the generation of the action potential: increasing sodium permeability leads to increasing inside positivity which leads to increased sodium permeability etc. Another is in the menstrual cycle, where increasing estrogen leads to increased release of estrogen stimulating hormones from the hypothalamus-pituitary axis. Your instinct is correct: positive feedback loops tend to drive systems to extreme values. PG

Name: Emma Kirby-Glatkowski
Subject: negative feedback systems
Date: Mon Mar 22 23:04:40 EST 1999

I've had lots of exposure to negative feedback systems in other classes such as biology and physics. I can see how these can be useful in cases of maintaining homeostasis. But it doesn't really make sense to me to that the set "normalcy" can be changed in certain circumstances. And I was having some difficulties in understanding the conditions of "setting the set point". Why can you change the position of your leg and not your body weight? The more I think about the example of the leg that we looked at in class the other day, the less sense it seems to make. It appears to be something entirely different than body weight. It seems to me that it's not actually possible to see my leg return to the exact possible position. I thin kit's more of a conscious choice of placement rather than a "return to normalcy". If I had my arm up in the air and someone put a weight on it to bring it down, my arm is not going to spring back up to the previous position unless I choose to bring it back there. Maybe I just misunderstood something in class, but this doesn't quite sit right with me.

If, however, this negative feedback system is in fact responsible for all that we believe it to be, it certainly does help to better explain behavior. An integration of many of these systems doesn't use too many neurons and could account for seemingly complex behavior. However, this all still seems too "predestined" for me. I don't see where choice comes into it. And without there is a loss of free will that I am not willing to give up.

So be stubborn. Actually, I'm on your side. It seems to me we need to find "free will" in there (here) somewhere too. For the moment, though, what's interesting is, as you said, how much negative feedback loops (and other things we've talked about) do "help to better explain behavior". Your arm is indeed going to spring back up toward its original position because of the negative feedback loop, UNLESS you choose otherwise. Which you can do (I think). So what does that mean? We'll come back to it (but you might want to check out Laura's thoughts in the meanwhile. PG

Name: lauren hellew
Subject: corollary discharge, (-) feedback loops, and choice
Date: Tue Mar 23 00:02:53 EST 1999
The nature of the relationship between conscious choice and neuronal processes such as corollary discharge and negative feedback loops is an interesting and troubling one. It seems to lead us back to a question which (I think) was raised when we discussed whether “brain equals behavior” at the very beginning of the semester: Is the brain responsible for our conscious thoughts?

The question of choice and whether or not it can be explained by corollary discharge and negative feedback loops is troubling because choice is generally something which we attribute to conscious processes involving thought. This makes it difficult to accept an explanation for choice which would equate it with unconscious “reflexes” and homeostatic processes such as temperature and weight regulation. In other words, it is difficult to believe that neuronal processes underlie a decision to sit in a particular seat on a bus because the relationship between such processes and the conscious activity which seems to lead to that decision is unclear. Whether or not conscious thought can be explained by neuronal processes is both a philosophical and neurobiological question for which we do not, as yet, have a good answer.

So, I guess I have some of the same concerns that other people have expressed with the explanation of choice in terms of corollary discharge and negative feedback loops. I see how these processes can help to explain some of the simpler behaviors discussed in class, however I am not sure that I accept them as an explanation for choice.

Fair enough. But at least they help to sharpen the remaining questions, yes? Not only "Is the brain responsible for conscious thoughts?" but also "what does one mean by conscious thoughts?" and, since we can make sense of lots of behavior without them, "what are conscious thoughts good for?". We'll come back to such questions in a bit. PG

Name: kathy
Subject: anti-placebo effect
Date: Tue Mar 23 00:18:29 EST 1999
I know that this is compltely off the topic, but hey, this is a forum. I just wanted to present a question to the group before I forged ahead with my second web project. Does anyone else believe that there is such thing as an "anti-placebo effect"? My last paper being on Melatonin: miracle vs. myth opened up the idea to me that maybe preconceived ideas could in fact cause a person to inhibit the effects of a particular drug/supplement. I know that it has been showed that there is such thing as a placebo effect. But, an anti-placebo effect? Maybe I am alone in thinking there is such a thing, before I throw myself any further into the web research, maybe I could get a little feedback?

But, as Feyza said, is a placebo effect just throwing everything out of whack, or is it an adjustment of the set point to a normative level? With an anti-placebo do we see anything in particular? Could we consider this a negative feedback loop? We are talking about something, take Melatonin for example, which in theory, should have an effect, but it some people, doesn't. Do we assume that the idea of "choice" will take some effect? "Choosing" to believe that something is not going to work... Maybe this line of thought is too sophisticated for the level that my biology expertise is at, therefore I cannot visualize how this could connect at the neuronal level. Maybe someone else has a couple of suggestions.

An interesting issue, particularly taken in combination with Feyza's thoughts, and some of my thoughts in reaction to hers. One can imagine a placebo acting on some other system (conscious or unconscious) to cause it to correct a problem elsewhere. An anti-placebo though, if I'm understanding you correctly, would have to act on some other system to prevent something from acting on a disturbed system which normally acts on it. Or, maybe, not to prevent it from acting but somehow prevent its action from becoming apparent in output? Either might, I suppose, happen, though the second seems more likely. One can, for example, concentrate and at least reduce the amplitude of the knee jerk when the doctor hits your knee. The "anti-placebo" notion is an interesting one; lots of therapies (even the better understood one) are more effective in some people than in others, for unclear reasons. I'm a little worried though about whether you'll be able to find enough on the web (or elsewhere) to explore the issue further. Maybe look more generally into the issue of "psychosomatic medicine"? There is an American Psychosomatic Society, and a Society of Behavioral Medicine, which might serve as starting points. PG

Name: Kimberly Bibbo
Subject: Bipolar connection to negative feedback loops?
Date: Tue Mar 23 01:15:00 EST 1999


Since I have relatively little knowledge about bipolar disorder, I thought of it more as an example of how a negative feedback loop MIGHT work in shaping outward behavior. I did attempt to look up some websites involving bipolar disorder and negative feedback loops on the same page, yet nothing seemed to link the two.

The negative feedback loops were perhaps to me one of the most interesting things we have learned so far in this course. I thought the analogy of a thermostat was an excellent one, where when a room gets too cold, heat turns on, but when the room gets to the set temperature, it then turns back off again. the idea of "set points" was particularly facinating, especially in regards to weight. If we do have such "set points," how are they eventually overcome? there are people, for example, who loose weight after altering their diet. Does that outward behavior, then, create a new set point internally?

I then had an idea that perhaps something like extreme cases of mania and depression, as in bipolar disorder, might occelate due to many little internal links of negative feedback loops. The chemicals in the brain that cause the mania might reach a set point, then shut off, and swing the other direction to depression, and so on. I definitely feel that it is possible for people to experience external behavioral changes due solely to a series of negative feedback loops that can alter behavior. Since the ideas I had were so incredbly speculatory, and most likely off the mark, I just wanted to share what was running through my head during class; and propose possibilities of disorder and instances where negative feedback loops could fit into the larger behavior of an organism.

Kim B

Disclaimers and apologies unnecessary. The forum is a place to think freely, so as to get some feedback (!), and to trigger additional thoughts in others. Along which lines ....

My intuition (speculation) is that bipolar disorder might relate to one "abnormally" functioning negative feedback loop, rather than to several which are successively turned on and off. What underlies this is the fact that negative feedback systems have a tendency to oscillate, if they are not tuned correctly (see Simple Feedback and Complex Feedback). Imagine, for example, a significant time delay between the thermometer and the heater/cooler. The room gets a little cold, the heater (after a bit) comes on, the temperature rises to the ideal temperature but then keeps rising (since it takes a while for the information to get to the heater/cooler). The same happens as the temperature then drops, so the actual room temperature oscillates around the ideal temperature rather than remaining constant at it. The greater the time delay, the greater the oscillation.

Could something like this account for bipolar disorder? I'm not sure, but it seemed worth looking to see whether it has been explored. Sounds like it isn't obvious on the web, so one might have to look elsewhere. How would one decide whether the intution/speculation is useful? PG

Name: ...sarah catherine nosal...
Subject: response...
Date: Tue Mar 23 04:04:02 EST 1999

a conscious choice...

this is in relation to emma kirby-glatkowski's ponderance as to the possibility of the body moving (or not moving) only as a mechanism of conscious choice...emma's statement made me think of a childhood amusment of standing in a doorway with your arms streched down and then pushing up on both sides of the door frame with your hands, palm up for about 60 seconds...then let go and step out of the doorway...

if you haven't before...give it a try...
Name: ...sarah catherine nosal...
Subject: ..."choice"...
Date: Tue Mar 23 04:39:06 EST 1999

The issue of how to define a word is callenged most often in those classes less grounded in the natural sciences. Again however, we find ourselves faced with redifining a word which has definite implicaitons in the societal realm, which seems thus far to differ greatly when understood in the scientific realm, particularly in the brain. Thus the question of how one might experience and comprehend "choice".

Human beings in large part seperate themselves from the rest of the animal kingdom on the premise that they are able to "think" and thus "choose" their destiny. This very concept of "chioce" and how tojustify the interpretaions of such a word in relation to the brain and nervous system remain to be reconciled. Thus far, "choice", at least in the traditional sense -- or by popular definition -- does not occur in the brain. The reasoning behind preforming on aciton over another is mearly the measurment and comparision of corolary discharge and a system of interacting pattern generators.

It has been postulated that true "choice" perhaps indicates the involvement of a wider range of interacting neuron circuits. Certainly, memories and previous learning all relate to the eventual "choices" one makes. While I do not deny the possibility of such a definition that relates one's experiences and desires to partially explain the phenomena of "choice" in the brain; I feel no need to deny the possibility that perhaps "choice" in its popularized understanding does not have a comparable feature/occurence in the brain.

Furthermore, a well integrated system of interacting neurons may in fact dictate all of our "choices" when influenced by the appropriate corollary discharge, although this may appear to many unsettling. Somewhat ironic then was the overwhelming assertion in the early weeks of class that "brain=behavior". If we all were so convinced of such, any component of choice might be eliminated from behavior, from the brain, thus reinforcing our belief.

Perhaps however, the very fact that people do not wish to accept such seeming logic proves indicative of some component of "thought" or "choice". I do not fear the absence of such things. I am willing to accept that me, myself, and I are no more than the compelation of behaviors, or firing neurotransmitters. What you ~chose~ to be beleive, however, is not for me to decide.

Yep, science does indeed include "redefining a word which has definite implications in the social realm". And yep, there are issues of similarity or difference between humans and other animals. What I can't quite tell is whether you're ready to accept a redefinition of choice as corollary discharge related interactions among neurons (with the attendent thought that we and other animals are not so different) or whether you think there is something more ("proves indicative of some component of "thought" or "choice") and what that might be. Could you make a choice to proof-read or not to proof-read? Might that be relevant? PG

Name: carly cenedella
Date: Tue Mar 23 08:34:15 EST 1999
Most types of epilepsy are associated with the motor or sensory cortex. For instance, tumors growing near the motor cortex may irritate the neurons that they discharge and initiate convulsions. Posttraumatic epilepsy, a frequent complication of severe head injuries, may be the result of scar tissue formation near motor or sensory cortex.

The motor cortex and sensory cortex are interdependent. Inputs reaching cerebral cortex, particularly the tactile and propprioceptive impulses condition the response of the motor cortex. Therefore, an epileptic fit can involve muscular convulsions and peculiar sensations or hallucinations. Electroencephalograms show high voltage and high frequency waves during grand mal seizures and high voltage low frequency waves during petit mal seizures.

The cerebral cortex is involved in various types of epilepsy as shown by abnormal electroencephalograms. However, the motor and sensory areas may not be the primary initiators of epileptic fits. It is possible that the cortex is driven by subcortical discharges.

In most of the books that I have been reading about epilepsy, the motor cortex and the sensory cortex play a large role, as I expected. Some books, however, referred to temporal lobe epilepsy. This seemed similar to what we had been talking about in lecture when two different neurological problems are given the same label because the behavior is the same. I seems like temporal lobe epilepsy and the epilepsy involving cerebral cortex could be different neurologically but similar in presentation.

Additionally, this makes me wonder if photosensitive epilepsy is different neurologically than other types of epilepsy. So far, I have been considering what I found on epilepsy in general to be true for photosensitive epilepsy. Perhaps this assumption is invalid.

Hmmmm. I'm a little puzzled by "most types of epilepsy are associated with the motor or sensory cortex" and "the motor cortex and the sensory cortex play a large role, as I expected". Why did you expect that? And what evidence is there that it is so? My sense has been that epilepsy, from the perspective of a neurobiologist, is local abnormal activity (because of either local abnormalities or subcortical abnormalities) in the neocortex (which includes the temporal lobes), and that it may (grand mal) or may not (petite mal) spread to involve additional cortical regions. Depending on where in the necortex the local abnormality occurs, it may produce various different kinds of hallucinations (visual if in visual cortex, for example) or muscle activity (if in motor cortex), or less well-defined odd "feelings" (temporal lobe epilepsy). When it spreads, motor cortex (as well as other cortical areas) become involved, and the most prominent manifestation is convulsions. From this perspective, the motor cortex (and the various sensory cortices) play no greater a role in epilepsy than do other cortical areas, it is just that the consequences of abnormal activity there are more easily observed and reported. Does this fit what you're finding from your reading, or do I need some re-education? Fine either way it comes out, of course. PG

Name: Nicki L. Pollock
Subject: corollary discharge and choice
Date: Tue Mar 23 08:40:18 EST 1999
I believe that most of us would like to think that we actually think when making a choice, and that it is not just a function of what pathways your neurons are firing through. I do believe that some "choices" just happen so quickly that they do not heavily involve the brain (things we are not currently allowed to call reflexes). But decisions which we mull over for days and days certainly involve more brain activity and how that actually occurs and what is going on is probably very complex. I skimmed through a little of chapter 21 which talks a little more about higher neural functions and choice, but the exact mechanism of choice (Iam thinking more of complex thinking processes) were not explained there. Corollary discharge and negative feedback loops can definitely be a part of making decisions, but I think it would have to be on a much larger scale than just a few. There must be many pathways to allow for the tremendous amount of behaviors, particularly in humans, that can be observed. Choice, at least how I think about it, is about taking in and "processing" different inputs which will eventually generate an output (which can be very different for everyone depending on how their neurology is set up).

An interesting question: is "thinking" just negative feedback loops, corollary discharge signals, and so forth "on a much larger scale than just a few", or does it involve something more? Yes, taking in and "processing" different inputs which will eventually generate an output, and yes, different in different people. But that we can in principle account for, no? Is there something more? PG

Name: Beth Varadian
Subject: love
Date: Tue Mar 23 09:06:26 EST 1999
In terms of everything that we've been talking about, I am curious as to how "love" can be explained. By love, I mean the tickly stomack feeling, the extreme euphoria, the comfort and relaxation, and the need to be as close to someone as possible for extended periods of time. I was thinking that maybe certain aspects of love could be explained by corellated groupings of neurons in similar circuits. Maybe a feedback loop could be casuing certain reactions so that procreation will occur (a purpose). I don't understand how these explanations account for homosexual behavior though. Maybe they occur through corollary discharge? Is there really "choice" involved in love? Do emotions follow the same idea of "setpoint," where after extreme changes, the body will try to return to its original state? Is it possible that "love" changes the set point? These are just some ideas that I was tossing around in my head...

I am, as you know, willing to take on some not unsophisticated aspects of behavior (choice, free will, consciousness, self ...). But ... love?! Gulp ... alright, alright, brain=behavior, and so ... Let's see ..... Uh .... Yeah, the tickly stomach feeling, extreme euphoria, comfort and relaxation, need to be as close to someone as possible for extended periods of time ... Hmmmm .... MUST be corellated groupings of neurons in similar circuits, no? .... with a negative feedback loop or two (no I don't think it reduces to procreation either) .... and changes in LOTS of setpoints (in my experience at least). Dare you to write a web paper on this one. PG

Name: laura gosselink
Subject: choice & destiny
Date: Tue Mar 23 09:57:10 EST 1999

It makes sense to me to investigate the neurological building blocks of behavior (neurons and central pattern generators, etc.) as an approach to developing some perspective on the nature of behaviors such as those that might be identified as involving "choice." Why are some people resistant to this approach?

I have sort of cornered a friend of mine into listening to my current thoughts concerning "brain = behavior" class a couple of times. This may not be an exact quote, but his opinion is essentially this: "I don’t like to think of human "choice" being reduced to a set or sets of interactions between neurons. I believe any system, including the human brain, is more than the sum of its interrelated parts." When encouraged to explain why he feels this way, my friend scowled and appeared to be deep in thought for long enough that I decided he was not going to be able to come up with any reasons. Finally, he gave me an example -- what he thinks is an analogous type of problem intrinsic to a sort of microcosmic approach. For example, he said, take a computer program consisting of thousands or hundreds of thousands of lines of code and sub-routines. If we examine only one or two sub-routines or two or three lines of the program – we would have no idea how the computer program would "act" or "react" (can we use the word "react" in brain=behavior class?) to input from the environment. We would only know what a particular subroutine would "do" – we would not know how the entire system would function if the entire set of programming details were understood, taken into account, and allowed to function in its entirity. In the same way, my friend explained, he is much more comfortable discussing human behavior in terms of broader psychological and sociological concepts. A person seems to be who he or she is because of their entire biological profile interacting with their total environment.

I thought about my friend’s response and decided that he was not really opposed the study of neurons and central pattern generators as a valid approach to understanding choice. His reaction seemed more emotional than anything else. I asked him if his discomfort reflects a need to point out that it is sometimes easy to lose sight of the forest for the trees. He decided that was a fair description of his feelings.

It seems that whether behavior is looked at from a broad sociological perspective or from the microcosmic level of neurons similar conclusions about choice and determinism can be drawn. If a neuron simply quantifies the relative strengths of inhibitory and excitatory input, it then fires or doesn’t fire in the one and only possible way it can as a result. There is only one thing the neuron can do given the situation. So then, can any given neural symphony be said to be destined to occur given everything that has happened up to the moment of its occurance? Pulling back for a more expansive view of behavior can also support deterministic ideas about behavior or what could be called "destiny." We are certainly born into a particular social strata that will affect how we "choose" to spend our lives – as well as being born with certain biological predispositions (possibly affecting mood, intelligence, etc). Though both environment and biology are involved in our acquisitions of mood and intelligence. I think if each one of us were looked at -- when we were born, gathered enough information about our families – where we were born in the social strata – and examined aspects of our personalities (how often we cried, how much we moved in our cribs) – it would be possible, I think, to predict relatively well in what type of circumstance each one of us will be found in twenty, thirty, or forty more years (barring the unknown of accidental death, disease, etc).

I am the sum of my biology and my environment. Did I really have a "choice" whether to write this essay? Given who and where I am, the answer is no. Everything that makes me who I am, compells me to write this. If I had unlimited freedom of choice, I could be lying on the beach in the sun instead.

I for one am glad you were here rather than there. Nice essay, thanks to you and friend for laying argument out so clearly. BUT ... I'm not sure it will satisfy Emma. And, to be honest, it doesn't quite satisfy me either. No, I don't think we have "unlimited freedom of choice". And I agree that it is actually sort of nice to be oneself, a unique combination of "biology and environment". But maybe with a LITTLE bit of choice thrown in? Something along the lines of this? Determinism is AN approach to life, but there are non-mystical others, as we'll get to. PG

Name: Jason Bernstein
Date: Wed Mar 24 02:01:28 EST 1999
Last week I talked about a unique motor learning experience that I once had that involved juggling. I'm still wondering about this topic. I was able to learn this week that my conception of CPG's was somewhat off. I think that I was attributing movements that were too complex to single CPG's. CPG's produce movements that are specific, simple, and often rythmic. These movements can take place in the absence of sensory feedback. A good example is the one discussed in class today of the clasping and unclasping of the hand--all the fingers moving in unicen unless specific effort is made to divert from the group movement. To say that I developed a CPG for club juggling is nonsense. "Researchers understand well how reflexes work to maintain ballance in a person standing still, but far less is known about how the nervous system orga
Name: Jason Bernstein
Date: Wed Mar 24 02:16:02 EST 1999
Sorry about being cut off there--my netscape is having technical difficulties. I was quoting a passage in the book which said "Researchers understand well how reflexes work to maintain ballance in a person standing still, but far less is known about how the nervous system organizes a movement like a pirouette. Reflexes are obviously used during such a movement, but they cannot account for it completely." So, I'm not the only one who isn't sure how people learn to juggle. Like a pirouette, juggling involves organizing a complex pattern of movement. Although I've never tried to execute a pirouette, and I'd like to assert my masculinity now by saying that I will never attempt one, I'm pretty sure that juggling is an even more complex pattern. Also, the demands it places on the perceptual part of the nervous system are great.

One question I have is about the time frame necessary for structural changes to take place in the brain. I claimed that overnight, I somehow improved my juggling ability. Can new circuits be made overnight? Are they different from the kind of circuits that are made immediately when you learn a new motor task in

Name: The guy with the annoying juggling story
Subject: This is the last one, I promise.
Date: Wed Mar 24 02:35:15 EST 1999
Sorry again about the cutoff. I was questioning what it means, from a cellular standpoint, to learn a new pattern of movements, like typing your name, learning a keyboard piece, or juggling. What is the timeframe for the making of these circuits? Can changes take place overnight that can't happen in the half an hour that you have to practice. Something tells me it is somewhat like the benefits of exercise--one won't start reaping the benefits of a hard workout immediately-it takes time for cellular changes to take place. My juggling story, which you are by now very tired of reading about, is good evidence for giving yourself time between studying and taking an exam.

Juggling intrigues me as well. I haven't tried clubs but enjoyed teaching myself with bean bags. And yes, you're right, there is certainly more involved than central pattern generation. Juggling clearly depends on an output/input interaction, so what is learned is not a sterotyped motor pattern but rather some kind of motor pattern coupled with expectations of and corrections for varying inputs. An interesting topic for a web paper, maybe. Some papers by people exploring the problem: Amazeen and Schaal. Motor learning is also an interesting problem, involving, almost certainly, a variety of mechanisms operating over a number of different time courses. Motor performance can indeed improve over a period of time subsequent to actually engaging in motor activity. A paper by Marc Jeannerod gives some relevant discussion and references. PG

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