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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.


Thinking of the nervous system in terms of "stimulus" and "response" inclines one to believe that what happens on one side of the nervous system in caused by what happens on the other, an idea which might, to some extent, persist even when replacing the terms "stimulus" and "response" with "input" and "output". In class, it was suggested that the organization of the nervous system actually yields bidirectional causation, with output affecting input as well as input affecting output. Discuss the legitimacy and usefulness of this suggestion, and its possible significance for how one thinks about behavior.

(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: Mindy
Subject: input/output
Date: Fri Feb 13 13:06:01 EST 1998
I like the idea that that inputs and outputs equally affect each other. This makes some actions of the nervous system cyclical rather than linear, which is how a stimuls/response model portrays it. This new, self-perpetuating model brings the nervous system somewhat more in line with other continual biological processes which are also cyclical (how many "cycles" do you learn in intro bio?!?!). Thinking about the NS this way gives another explanation for "autonomous" behavior, I believe, in that constant external stimulus is not required to explain all intermittent behaviors. Spontaneous potentials give an explanation for behaviors that occur autonomously and constantly. The feedback loop (as it were) of the NS can explain behaviors that occur inconstantly or infrequently, or only once, for which there is no observable related stimuli or inputs. A single input or set of inputs could occur at one point in time which causes certain outputs which cause more inputs and so on, so that an observed behavior can be "caused" by an external input that happened long, long ago.

My question about looking at the NS, from either end, is what about those potentials that go nowhere? Looking from the output side, you may never encounter those senory signals which never caused a response. Looking from the input side, you may never encounter those spontaneous potentials. Unless we consider it as a bidirectional loop...

Interesting issues, but I also got a bit lost in the loops. Maybe a little more specifics would help? Yes, lots of cycles in biology, which means/implies? What more concretely is odd/different about cycles? that is common to all of them? I see indeed the interesting thought that "an observed behavior can be 'caused' by an input long ago, via a continuing output/input/output/input iteration. But "behaviors that occur inconstantly or infrequently"? Oh ... you mean ONE of the outputs in a long and changing string of them due to ....? Hmmmm, could be. Hadn't thought of that. And yes, I think that's a separate, distinct set of phenomena from things which either end in or start in the middle of the nervous system. We'll get back to those. PG

Name: Christine (Chris)
Subject: Scores
Date: Fri Feb 13 13:33:38 EST 1998
The part of class that really interested me was our discussion on the symphony that we discussed on Thursday. We began discussing whether or not there was a score to the performance. As Prof. Grobstein reached for the cup, was there a plan of action for the motion? I think the answer is yes. While the NS has the ability to change its behavior based on its own output, i.e. changing your grip on the cup as you grasp it to get a firm but gentle hold on it, the NS also seems to operate most actions with an already pre-determined form. Think in your own life how you begin reaching for something or doing something without thinking and then cannot stop yourself once the action has begun, but you know you don't want to perform the action. A good example for me is when I'm working at my computer and get into a rhythm of pushing keys to do keyboard commands. Sometimes I need to change the order, but once the sequence was initiated I cannot stop what I am doing. If you play sports, like Basketball or Football, you might have done similar things when going for a pass. Obviously not all of our behavior is once started, cannot be stopped. We do stop in mid-step, we do change direction quickly depending on what is coming toward us. However, I think that there is a point in these scores where you cannot abort the action. You must actually continue with the action. This would actually make sense in the system. Instead of having to take all the time to constantly readjust and require all the input, the system can now just execute without expending too much effort. If something does happen to cause it to readjust, it can. Either way you don't use up a lot of processing and you still get the benefit of a wide variety of actions with the ability to modify the action if necessary. Cool.

Indeed. Glad you liked it. And nice description/extension into things everyone more familiar with. Certainly centrally pattern generated movements have some "inertia" to them, since they are a playing out of internally stored patterns, and one can notice this from observing cases "where you cannot stop the action". Remember, though, that the strict definition of central pattern generation has to do with the existence of some independence of motor patterns from sensory input. Independence from "you" is, strictly speaking, a different, though equally (more?) interesting issue. That has to do with the "I-function" and we'll talk more about that interaction as we go on. PG

Name: Anne Frederickson
Subject: bidirectional
Date: Fri Feb 13 19:47:42 EST 1998
I am interested in the idea that there is a bidirectional cause and effect relationship between the input of the NS and the output. It solves the problem of of how the body keeps track of itself, in the sense that the body becomes aware of behavior in some form and reprocesses this information. But I am not completely sold on the idea because once this information cycles back into the NS it becomes the ignition for a whole new set of behaviors. Like the first woman stated, it is all a bunch of cycles. So I guess I am really having a difficult time believing that there are spontaneously generated behaviors. There always seems to be some kind of stimulus for things that we do. Something triggers us to act which in turn triggers sensations, thoughts, and other actions. These all generate more behaviors. We do not stop behaving until death. One thought or sensation may produce several behaviors or a stimulus may die out in the NS. It is hard to believe that things begin on their own, however. Sure, we have behaviors that are rare and inconsistant but we never encounter the same situation twice. So basically, I think that the bidirectionality of the NS is only helpful in explaining how one behavior or output can affect the NS. It does not explain the spontaneous generation of outputs sufficiently enough for me to believe in them.

Fair enough. As I said above, we have two separate ways to possibly account for "spontaneous" behaviors, i.e. behaviors that don't seem to result from an input at the time they occur. One is genuine spontaneous activity in the nervous system (due to stable high permeabilities), as we talked about earlier. And the other is the output/input/output chaining that recognition of bidirectionality makes possible. The first certainly exists, as we have talked about and will some more. In all honestly, I hadn't thought a lot about the second until Mindy raised it, so I'm not sure I have a dramatic example at hand. The output/input/output chaining is certainly real, as we talked about in the case of earthworm locomotion. One actually sees a similar thing in eye/head coordination when you look toward something. The eye movement is adjusted based on input signals resulting from the head movement. In a broader context ... if I type a particular thought and later read it a new idea comes to me? PG

Name: Kristin Chimes Bresnan
Username: kchimes
Subject: Information as a third thing
Date: Fri Feb 13 20:23:09 EST 1998
One of the ideas which has most captured my imagination is the idea that information, not matter or energy, is what flows through our axons. I like very much the idea that information constitutes a kind of "third thing" in the universe, and the questions I have been asking myself all have to do with finding a way to characterize the storage and flow of information.

The two systems I have thought about are language; and the genetic code of DNA. What do they have in common?

1. a set of building blocks: our language uses both the alphabet of 26 letters, and a set of accepted sounds; DNA uses the four nucleotide bases read as non-overlapping triplets to code for the arrangement of 20 amino acids.

2. the reciprocal traits of stability and variable expression. Language is stable in two ways: through time over the course of generations, and in our own memories (for example, words do not change shape or meaning in our memories; they are stored there, ready for use as needed). It varies in the same ways: over time, language slowly changes its shape to adapt to changing environments (old English is different from middle English is different from modern English); and it varies in the way we use it in any given moment (the way we can arrange words is like a mathematical limit approaching infinity). The stability of DNA is in its architecture and in its base-pairing system, and in its mode of reproduction; its variability is in both its differential expression and in its mutability.

There are, I think, more and subtler ways in which DNA and language can be compared to each other. (What I haven't been able to decide is whether DNA is merely analogous to language, or if they can actually be grouped together as modes of information storage and transport.) If we allow for a few minutes the idea that they both might be different ways of doing similar things, then the nervous system is yet another way of doing these things. Would one say that its building blocks are axons, or ions and variable permeability, or transient charges, or neurotransmitters? Or the sum of these things? Are its stability and variability merely a result of its hard-wiring, so to speak? (anatomical specificity and responsiveness to particular stimuli).

One other thing which has influenced my thinking about all of this is a bit of an essay I came across, which described language as "transcending the machine of its own reproduction". What does this mean? It means that the motor neurons which tell our mouths to speak and the auditory neurons which record and translate that speech, as well as books, typewriters, recordings etc, are all parts of the machine of reproduction which convey and store language, but language itself "transcends the machine"; it is more than the sum of its parts. Is the same true of information, then? And doesn't the analogy also suggest that the "self" might also "transcend the machine"? That any system of storing and transporting information might, by virtue of what it does, have a "transcendent" component? Is this what it means to have information be a third component, next to matter and energy, of which the universe is made?

Interesting, and very rich set of thoughts, as we've talked about on a couple of occasions since you wrote this. For others' interests, the language/DNA parallel possibility is one that a number of people are interested in, including the Cal Tech neurobiologist Marty Sereno, an outline of whose thoughts are available on the web. Also for other peoples' interests, the "transcending the machine of its own reproduction" line is from our own Nancy Vickers. PG

Name: rani shankar
Username: rshanka1
Date: Sat Feb 14 15:15:22 EST 1998
The idea of information flow in the nervous system is very interesting to me too. Though, I still find it difficult to conceptualize, or even visualize, action potentials and “current flow”. I realize that there is not any voltage being exchanged, however, even with these chains of permeability changes and charge build-up, I find it difficult to believe that there isn’t any current passed...

So, assuming there is some sort of an action potential, now, how do we make sense of the passage of information in patterns between neurons? Could it be some sort of neuronal morse code- patterns of pauses, accents, crescendos, fortes? I, too, like the motor symphony analogy to explain the complexity of neuronal patterns and signal transduction. The interactive nature of an orchestral movement nicely parallels the idea of bidirectional causality. However, I find the question of "who wrote the score?" and the answer- that no one, or there is no score- a little problematic, especially in light of evolution. It was brought up by someone in class that there must be some sort of score, based on the observation that there are obvious similarities in neuro behavior in species. I mean, it's not like humans are swinging from the trees like monkeys- I know we aren't anatomically capable or built of swinging from trees like monkeys but the fact that babies, once they reach a certain age (1 year?), can learn/teach themselves how to walk bipedally is proof that this sensory direction and perception, walking on two legs, is an innately human characteristic. The sensory neurons located in the joints must somehow direct/integrate positional information to enable a baby to start walking one day. Also, I remember reading in some psych textbook how babies have an advanced depth perceptive field at an early age, since they know not to crawl too close to stairs, etc. Is every species capable of this? Surely, other animals have different wirings, arrangements, and templates that their neuronal signals are based's not like everyone and everything is born with a blank slate...

Yes, VERY much not the case that everyone "is born with a blank slate", as we've talked about a bit since you wrote this. And will talk some more about (see From Genomes to Dreams for a preview). In lots of situations, there certainly IS a score, written to varying degrees from information in the genome (itself resulting from evolution) and from individual experience. In others ... the symphony is actually written (again to varying degrees) as it is played. PG

Name: Dena Bodian
Subject: "Potentials That Go Nowhere"
Date: Sun Feb 15 01:53:04 EST 1998
This is a response to Mindy's question: what happens to potentials that go nowhere? I think this can be explained in a few ways: first of all, not necessarily all stimulus is internalized. Many times, potential output will go way over our heads, completely ignored because of other, more important (or more interesting) stimuli. Although there is an input, it may not be received, which could account for the lack of output. A second possibility is the strength of the stimulus. A fly buzzing around your nose might upset you much more than one on your arm -- perhaps you see the one by your nose, hear it louder because it is closer to your ears, or are more impeded by an object in front of your face than one lower on your body. There is also the chance that, although your nervous system processes the information, some other part of your brain will cause you to rationalize the effort involved in brushing the fly away. You may decide that the chance of swallowing a bug is great enough to make you move from a comfortable position in order to swat the bug. Or you could reason that the effort involved in flicking the fly off your arm isn't worth stopping whatever you were doing. Therefore, although the input was processed, the stiulus wasn't powerful enough to elicit output. There may be some perfectly rational reasons for why we don't always observe an output in response to a stimulus.

Yep, but NOW ... can you rephrase all of those possibilities in terms of neurons, receptor potentials, action potentials, synaptic potentials? THERE's the key. For example, some outside events never become inputs because there are no transducing permeability changes for those events corresponds, I think, to your "not received". Can you do that for "strength of the stimulus"? For "rationalize the effort"? PG

Name: ingrid katz
Username: ikatz
Subject: the bidrectional model and violent behavior
Date: Sun Feb 15 12:35:13 EST 1998
The notion of bidirectional causation has certain advantages when considering the myriad of intricate actions and responses humans perform each day. How then does this relate to the notion of the "I - box" in our original discussion of brain and behavior? Let's consider the example of an indivudal who is prone to violent behavior (my future paper topic) and the motivation for such actions. One can assume on the physiological level that perhaps a certain firing of neurons has occurred that has triggered a response in certain indivudals who feel an urge to beat or kill other indivudals. This would be an argument for a unidrectional model - neuron fires and the indivudal reacts. A bi-drectional model, however, takes into account the stimuli that this individual has been receiving throughout his or her life. Stimuli of abuse and/or trauma could account for possible "inputs" that might cause this indivudal to react on supressed desires of violence.

This model is certainly the more wholistic one when assessing an individual's desire to commit a violent act. Still, it leaves open the question of just how essential the brain is during the decision making process of whther or not to act violently. In other words, how much of a role does the input play vs. what effect is simply based on the mental awareness and capacity of the indivudal? Certainly this is a contentious issue - one that is often presented during trials of individuals accused of murder. Can this person be held responsible for his or her actions? If so, how much can be attributed to continued inputs of violence this individual has experienced him or herself?

If indeed one adopts the bidrectional model, one is left then with the question of where the self truly lies. If the self, or the "I box" exerts as large a guiding force as initially asserted, then the bidirectional model may be a less than useful one. If, however, one asserts that the "I" is not the initator but rather the processing center of information (much like the central nervous system is when receiving stimuli from sensory neurons), then, in fact, the bi-directional model can be a useful tool in examining people's behavior.

Hmmmm. Am very intrigued with the issue of accounting for "violent behavior" and associated concerns about the grounds for being "held responsible". Looking forward to your paper. Am less sure how the bidirectional model relates specifically to this. As you say, one can use a unidirectional model to acccount for violent behavior (many people do) and that alone seems to me to pose most of the subsequent questions you're raising (should one accept that violence results from/is excused by previous experiences?). What it seems to me the bidirectional model does is to (potentially) return some sense of responsibility to the individual, in the sense of raising (though not settling) the possibility that the inputs which contributed to the violent behavior where themselves consequences of the individual's prior outputs (yes, not "politically correct", and I stress "raising (though not settling)". That, though, still leaves entirely open, it seems to me, the deeper question of what do we mean by "being responsible". For that, we need a clearer understanding of what we mean by "decision making", "mental awareness and capacity". Which we're working toward, and will get back to. PG

Name: Rachel
Subject: more on scores
Date: Sun Feb 15 14:51:56 EST 1998
I would also like to write about the question, is there a prewritten score to all/some of our actions? Someone posted a comment earlier saying that there must be scores based on psychological experiments that proved early depth perception in humans. Also the fact that language is so systematically learned by infants leads to the conclusion that some sort of language-learning score exists in all of us. So, I believe there are some intrinsic neuron associations which make certain behaviors pratically automatic from birth. I also believe that there are some 'learned' neuron associations for frequently done behaviors that allow us to do things without even conscioulsy thinking about them other than to briefly initiate the action. I have my own naive opinion on what exactly these scores are comprised of. I think the scores that are built into us that we use for early behaviors are simply a well-organized path of neurons. For instance, take the score for learning how to comprehend and communicate a first language. The ealry nervous system takes in the inputs of parents/people talking to them and the sensory system initiates a path through neurons to figure out what to do with the input. The neurons have been set up in a biased way so that they will synapse and carry their information through particular sets of cells (because they are the closest together and easiest to get to) that create the 'learning' response. (This is how I think the comprehension part of the 'language score works: The 'learning' response stores the new words and associations which will lead to their future comprehension. If that word is used again, it will meet the previous word in storage and compare and contrast associations and try to reach a conclusion on what the word means. The more times the same word comes back to this storage bin, the clearer its meaning becomes.) Anyway, this sort of intrinsic score is probably just from the biased organization of neurons. The scores that are learned are a little bit different. The first time a particular behavior is done, there is a lot of effort put into it. (Think of a baby trying to eat with utensils!) This is because the correct neurons are not lined up in a simple way and the nervous system has to pay attention to what is actually going on outside the body to get feedback on which neurons it has to go to. The neurons are not already connected in a loop. The first time you do an action, you have sort of tied the neurons together with a loose thread. Each future time you do the same action yo u add another thread. Eventually, the neurons are connected by a large number of 'threads' and pulled closer together. The body has no problem enacting this behavior because as soon as it starts on the path, it easily follows the thread to the resulting behaviors. Besides initating the path, there is almost no need for this behavior to even be conscious, unless the behavior is to be altered. IF the behavior is to be altered, like if you decide that you do not want to bring the cup to your mouth after beginning the action, it is not a big problem to stop it. The system stops the action potentials in the threaded path and tells them that they need to change route. They move on to a different set of neurons which enact the stop the cup and bring it back down to the table behavior. So, I think there are intrinsic and learned scores of behavior. The ability for action potentials to stop on their path and change directions if it receives 'stop' information, makes the scores seem reasonable.

Very nice and quite sophisticated laying out of what "scores" might consist of and how they might be created. The details well worth exploring in cases you've mentioned (language development, in particular, is a ripe and active area), as well as in others. "Paths" is probably too simple an image in general, and there is still an issue with what "you decide" means (the I-function problem), but the general characterization fits well with where we're going (I think). PG

Name: Emma Christensen
Subject: stream of consciousness
Date: Sun Feb 15 19:35:28 EST 1998
The idea that the inputs and outputs of the nervous system affect and shape each other and the idea that the "musical score" of the central pattern generation go hand in hand. As the inputs and outputs are feeding back on eachother, the patterns traversing the nervous system are modified and altered as needs be; they are in a constant state of composition--not exactly improvisational, but more like a kind of "beat writing" for the brain. The way beat is a sort of stream of consciousness for hipsters, the conversation between the inputs and outputs is a stream of consciousness for the nervous system.

This explanation assuages the slight sense of unease(woah, go me with the alliteration!) I felt when we were discussing several weeks ago the evolution of behavior--the fact that we are in a constant state of learning and because of this, our behavior as well as our brains are constantly changing and being modified. The ambiguity arose in trying to explain exactly how this happened and why. It makes sense, then, that changes in our outward behavior and modifications in the grand picture of our brains and nervous systems actually are the reflections and repercussions of the minute changes taking place in this symphony of pattern generation that is being composed during every second of our existence.

I like your "in a constant state of composition-not exactly improvisational, but more like a kind of "beat writing" for the brain". There is both freedom and constraints, and, indeed, outward changes are "reflectings and repercussions of the minute changes" (at least so far as I know). Glad this assuages some unease. On the other hand, it creates some problems, no? You say "modified and altered as needs be (boldface mine). What makes sure that the modifications are that way, as opposed to random and/or destructive? Is that something special, an additional thing, or does it somehow emerge in the details, the different time courses along which things change and the different mechanisms involved in them? PG

Name: Libby O'Hare
Subject: applications of bidirectionality
Date: Sun Feb 15 19:52:01 EST 1998
The bi-directionality operation principle of the nervous system is a very useful way for understanding both basic and complex behavior. If, as Mindy said above, the nervous system can be thought of as a cyclical system, in which input can affect output and output can affect input, we might have a way of conceptualizing the process of thinking and analyzing. For example, when you are reading a really good novel you might think about the story line even when you are not actually reading the book. This thinking seems to just start, without an actual concrete stimulus. Is it possible that thinking is an example of a series of spontaneous potential occuring throughtout the nervous system, and that these potentials in turn generates outputs that then affect further inputs? This may or may not turn out to be true (we'll find out as the course continues), but nevertheless, it is a an interesting way to think about the higher functions of the brain and complex behavior.

Application of the bi-directionality principle also raises some concerns/questions for me. When you are talking about autonomous behavior, you start to run into some problems. Does the spontaneity of the nervous system take away from each individual's responsibility for their own behavior? (I'm thinking here about criminals and the like, but this could also apply to everyday life.) Another interesting aspect of this model is that by allowing outputs to affect inputs, you are saying that the brain changes with every action that it coordinates the body to perform. That means that the brain is constantly changing, but it also means that patterns of behavior can be established pretty quickly. I'll argue that all behavior is ultimately a pattern (for an individual). So, does that mean that this might be a way to understand the way identity is formed and representated in the brain? I'm asking a lot of questions that I can't answer. Does anybody else have any thoughts on these ideas?

Lots, whether your other colleagues do or not. I'm particularly intrigued by your thought that "identity" might be formed as a consequence of patterns of activity both generated by and in turn modifying patterns of connections. It fits some other thinking I've been doing, and raises the question of whether the patterns need to involve sensory input or not. Thinking about a book when you're not reading it might depend on bidirectionality (you act out something which creates a sensory input which reminds you of the book?) or might simply be, as I think you're saying, a pattern of activity which arises internally which reflects the previous input of reading the book. The latter would be "thinking" in exactly the sense you characterize it. And what DO we mean by "responsibility", if everything is just patterns of activity in neurons? Nice question. We'll get back to it. PG

Name: Rachel Kaplan
Subject: get the beat
Date: Sun Feb 15 21:16:58 EST 1998
As I was thinking about the "motor symphony" concept, I was reminded of a semi-related, most amazing story I just recently heard. About a week ago my mom read about a man with an irregular heartbeat who decided to take matters into his own hands. He decided, for reasons unknown to me, to listen to a metronome in the morning, noon, and night. He found an electronic metronome, set it to 30 beats per?, plugged earphones into it, and tuned in for the long haul. As it turns out, his heart started beating regularly and at the same rate as the metronome setting even after he stopped using the device. He is convinced that the steady, external beating saved his life. Of course it is possible that he simply went into a spontaneous remission.

A person who is very dear to me is now trying out this man's technique. I'm hoping and praying that there was something to his alternative treatment.

I am fascinated by this man's account. I am a strong believer in the body's ability to heal itself, with perhaps a little low-tech help, and I would like to explore a mechanism by which the outcome could have been achieved: The sensory input patterns (the beating of the metronome) enter via the ears and are rapidly processed in the brain, after which they are sent down the ventral roots to various effectors, including the heart muscle. The contractions of the heart are either affected alone or the most visibly. Perhaps the stimuli is not strong enough to affect any other effector...or, maybe other effectors are affected imperceptibly. When I listen to music I often get the urge to dance, but that urge is definitely under voluntary control. I know, however, that when I hear a very loud sound, regardless of whether I am expecting it, my body reacts involuntarily in some way, whether it be the tensing of facial muscles, the tightening of stomach muscles, or etc.(the ole "fight or flight" response). Even if the loud sounds occur over and over, I feel a change in myself; I start to feel as if the beat is resonating inside me; perhaps at these times, without my realizing it, my heartbeat has followed suit. I suppose this is part of why drumming or listening to drumming can be such a powerful experience; people's heart rates increase with the drum beats. (aside: In various cultures throughout history, drumming has been disallowed due to the leaders' fear that it would incite rebellious actions amongst the people).

This does not explain, however, why the heart sometimes responds in a more permanent way to the external beats. I think the key to this treatment is definitely in the consistency of its administration. The recipient hears the beats incessantly for an extended period of time.

I would love suggestions anyone might have on the subject!

Very interesting story, rich with issues. As you say, it may have been a spontaneous remission. On the other hand, we all have experiences (like music) in which particular input patterns have rather compelling general affects. Strobe lights, as a particular case, will trigger epilepsy in some people. And particular patterns of stimulation of the heart are not uncommonly used by cardiologists to restabilize it in cases of irregular heartbeat. What's less clear is the basis for effects being both general and locally specific, and that's worth exploring further. Try patting your stomach and simultaneously rubbing your head. Why does a pattern in one limb interfere with one in the other? Not sure what you would find on the web about drumming, related things, but might make a nice paper topic. Hope, in meanwhile, that something (this or otherwise) has helped in the case of someone dear to you. PG

Name: Allison R.
Username: arosenbe
Subject: inputs and outputs
Date: Sun Feb 15 23:33:35 EST 1998

I can completely understand how the nervous system yields bidirectional causation. It is easy to see how inputs effect outputs within our box by looking at any stimulus- response occurrence. If we step on a nail, the inputs to our sensory neurons will be activated, telling our motor neurons to take quick action, which will result in our foot immediately retracting, perhaps with a verbal "ouch" response going along with it. Here, we can plainly see how inputs effect outputs.

I think though, that it might be a little harder to see how our outputs can continuously and equally effect our inputs from the outside of our box. Perhaps I am wrong in thinking this, but I think that this type of pattern can be looked at as a positive feedback mechanism. For example, if a child watches a scary movie late at night, it is very possible that this input will result in his inability to fall asleep at night. Since he is so scared, this in turn, sharpens his senses and he becomes even more attuned to the noises and odd- shaped shadows lurking around him. Having this sensitivity to the stimulus around him, will in turn make him even more frightened. This pattern might continue until he can no longer stay in his room and runs, screaming, into his parents bedroom. This pattern shows that each output can in turn result in even stronger inputs which result in stronger outputs, and so on.

I think this example illustrates that the nervous system can definitely be considered bidirectional. I understand how positive feedback works in this method, so I'm sure there must be an example for negative feedback too. Wherever there is one feedback mechanism, the other is always possible too. Perhaps we will discuss this later on.

Indeed we will. Nice extension: bidirectionality makes possible both positive and negative feedback systems (among other things). And nice example of something resulting from input which in turn affects input, probably because of bidirectionality within the nervous system (which we now know exists in terms of corollary discharge). That's a little different though from the output affecting input "outside of our box". How about the following modification of your story? Child watches scarey movie, pulls blanket over head (output) which makes everything darker (input), which makes child even more scared. In this case, the output is, outside the box, affecting the input. PG

Name: jeremy hirst
Subject: bidirectional
Date: Mon Feb 16 10:59:35 EST 1998
The idea that nervous system outputs can affect the behavior of the organism is not new. For example, in histology we learned that when food is put in our mouth glands begin to secrete digestive enzymes. The acidity in our stomach is changed by other secreting glands, blood flow is redirected to areas used for digestion, and many other responses are made to the introduction of food. This all means that the behavior of eating causes many other things to happen. A nervous system output (similar to the example in class of grabbing and lifting a cup to our mouth) which brings food to our bodies results in the production of inputs, and many within-the-box generated outputs.

These non externally generated outputs (I mean outputs not generated from externally originating inputs) lead me to the very convincing conclusion that our now familiar arrow filled box is a two way street. A street with a very small median, such that information traveling down one side of the road can seriously innate, interact with and alter the information traveling the other way.

This two way info idea is very useful. It allows for the explanation of much more complicated behavior than a simple, if this-then that, idea of behavior. This idea lets us discuss how complicated behaviors such as eating, digesting, thinking, running, and balancing can occur. All of these behaviors seem like they would be too complicated to exist if they relied on one way, if then, statements. We can now account for behaviors, which are constantly being modified, such as standing up.

We don't fall over because our bodies are constantly adjusting which muscles are tense and relaxed. Shifting our weight forward and backward, side to side. With out some system of feedback we would most likely fall over.

This bidirectionality allows us to perform in the living world. Behavior is complicated and requires an intricate, revisable method of explaining its origins. I am not convinced that even this bi-directional method is sufficient. Hopefully with further investigation we will develop a more satisfying perspective on how behavior is formed.

Nice, concrete, relevant examples of bidirectionality. And yes, of course, its a property of many biological systems. Interesting, perhaps, to see if one can make a rigorous argument that things ought to be that way, instead of one-directional, in some terms that generalizes across biological systems. Appreciate as well your continuing skepticism, but it would be nice to have some more explicit "alright, now I can account for this, but not THIS". Then you (and I) would have a clear sense of what we might need in addition to bidirectionality. PG

Name: Rachel Kaplan
Subject: Re: get the beat
Date: Mon Feb 16 13:13:18 EST 1998
I just wanted to add a quick note to my "get the beat" posting. It occured to me that another way to regulate your own heartbeat is through biofeedback. I wonder whether this method would be more effective than the "metronome method." The biofeedback technique seems as though it would at least be less of a hassle. Any ideas?
Name: Mindy
Subject: re: Dena's response
Date: Mon Feb 16 14:26:44 EST 1998
Just to clarify, my question was not "what happens when stimuli don't produce a response?" but rather "can we really study the NS from either back to front (output to input) or front to back (input to output)?" I think that either way, if we look only linearly we will miss one type of action of the NS. If we follow the NS from its outputs, we will miss the inputs which caused no output (or no ascertainable outputs). If we follow it from inputs, we will miss those outputs which are "spontaneous." It was a comment on ways of looking at the NS, Thats all.

I've been thinking more about the issue of "spontaneous" action, and I must reiterate/agree with Anne F. that this input/output cycle shows that many actions that may be considered spontaneous are actually sparked by inputs which occured so far back in time that they seem unconnected.

Name: L Pernar
Username: lpernar
Subject: thinking
Date: Mon Feb 16 14:52:25 EST 1998
A bidirectional connection between inputs and outputs definetly aids in understanding and grasping the functionning of the nervous system beyond the linear notion that is put forth in texts etc at first.

But is it really quite correct to think of inputs affecting outputs and outputs inputs? And if one desires to think about it in such a manner, what sort of loops is one considering? Short feedback, long feedback, is the feedback negative or positive? Does the feedback actually cause anything? All these are important questions that need to be considered more as one choses to view the inputs affecting the outputs and vica versa.

What the consideration definetly yields is a better approach to understanding behavior in its nuances, and precisely why some inputs are terminated rather than responded to with an output, similarily, why outputs do not recquire inputs.

Can you be more specific about what nuances it helps us understand (and hence what additional nuances we have yet to make sense of)? Are you persuaded that indeed outputs do affect inputs? PG

Name: Anneliese
Subject: score
Date: Mon Feb 16 16:34:40 EST 1998
I definitely do not believe that there is a pre-written score to the motor-symphony which gives rise to behavior...that wouldn't allow for learning, outside influences, etc. But I was thinking, maybe the score is begun, I'm not sure how early, but after that continues to be written as long as we live, never reaching completion. It is always being revised, parts of it rewritten or even erased, always changing, but building upon what's already there. I think I noted a hint of this idea in some other people's comments, too. Kind of like predeterminism--I don't believe our lives are mapped out, our fates sealed before we ever set foot on this earth.

Is there a score? I think so, at least in a very loose sense. My conviction rests on observations of habitual, repetitive behavior, learned processes, memory...I do not, however, believe there exists anything analogous to an actual score-sheet, but rather that the notes and phrases are distributed throughout the nervous system. But if there's a score, what about a conductor? That's where the notion of a motor symphony begins to cause potential trouble; though I have no proof, I strongly suspect that there is no central conductor, that everything is regulated by and regulates everything else around it. In addition to self-regulation, perhaps.

I just started reading chapter 16 in our textbook, and for just a moment realized how incredible it was that our neurons can take a single sensory stimulus and react to it by activating and inhibiting the right muscles at the right time in the right order with the right amount of force...HOW??? It's easy to lose sight of the big picture and get stuck in particulars, so it was nice to have this moment of bafflement. It's beautiful, in a way, that something so perfect, so efficient exists naturally, for no other reason than chance experimentation (?).

I'll leave the "for no other reason" part for others. Yes, the functional "specificity" (orderliness) of nervous system responses is stunning ... and largely (though not entirely) to be accounted for in terms of a corresponding anatomical specificity. And, by now, you're comfortable that your lack of conductor speculation was valid? As for the "prewritten score", you're generalizing interestingly but well beyond the facts at hand. The nervous system of any given organism certainly contains pre-written scores for a whole series of different movements, but it also has the capacity to write new ones, and to use existing ones in ones such that the performance varies depending on the circumstances. Can all of an individual's behavior over a lifetime be, as you suggest, a playing out of a very large prewritten score (of which all the smaller ones are parts)? I suspect not, but it pays to explicitly identify the various reasons in terms of neurons. We've started doing that, and will do more as we go along. PG

Name: Julia J.
Username: jfjohnso
Subject: Back on the Love Train
Date: Mon Feb 16 17:30:44 EST 1998
Bidirectionality did not really get me going this week but I was doing a little looking around from last week and found some interesting thoughts. I apologize for the tardiness, but I would like to jump back on the love train for a few minutes here. The author of the Inquirer article wrote that "Americans want love to remain a mystery." I throw my hat in with that group of brave Americans who neither need nor want to think about the role of the frontal lobe in motivation and commitment or about the ways and means of dopamine and vasopressin in the act of falling and being in love. It is not that I don't believe it or even that I don't find it interesting. I do. It is truly fascinating. I know it is there and I know that the nervous system plays an integral part in the whole love gig. I reserve the right, though, to turn my back on it when it does not suit my needs.

I believe, and I think it was Rachel Kaplan who first said it, that there more to it than that. Nothing concrete. Nothing quantifiable. Maybe I am a sucker, but I think most people are. Who wants to believe that the repulsion they feel for their usual fried egg sandwich breakfast with SPAM the day after they meet Guy or Gal Fantastic is due to a bunch of firings and misfirings? How utterly boring! Of course that is largely the reality of the situation, but am I the only one who doesn't need only reality on this issue? I can look past it and choose to believe that something larger is taking over in the act of falling in love. This is not unlike many other people's comments about their belief in the existence of God. Naive, ignorant, romantic. Throw them at me. I am proud and honored to snub my nose at the pheremones and let them do their thing while I go on believing in things that noboby can prove.

I also have a hard time with the tone of the Inquirer article. Something about "examining love with the cold, rational eye of science could someday alleviate the scourge of romantic rejection." Bitter much? The cold, rational eye of science does not necessarily preclude that there is not a larger essence out there that is love. I know that. This is not a confrontation. It is just that I am right and everybody else is wrong.

So be it. Everybody should have a bottom line where they are what is right for them. In this case, though, what you're asserting isn't actually so idiosyncratic; lots of people share your view (as you point out). And there are some interesting deeper issues. I too bridle at "the cold, rational eye of science", and am dubious that it could ever "alleviate the scourge of romantic rejection", but for reasons somewhat different from yours. I presume that "falling in love" is indeed a pattern of activity (and chemicals) in the brain, one so complex, special, and distinctive that it produces all the effects one experiences when engaged in that activity, both the ecstacy and the agony. Were it one pheromone, one might feel diminished, and have prospects of controlling it pharmacologically. If it is an enormous number of interacting signals and chemicals in highly specific patterns, then it simply is what it is, neither artificially creatable nor artificially manipulatable, to be lived and coped with, as we do. "The cold, rational eye" is not that of science, but rather of some scientists (and some non-scientists), who would prefer to have reality be simpler than it actually and demonstrably is. PG

Name: Bonnie Kimmel
Subject: some thoughts
Date: Mon Feb 16 17:33:04 EST 1998
I recently received an e-mail from a friend of mine describing her current state of depression. In my response I asked her if a particular event had triggered her state, or if she had "become depressed" in general and that this was consequently causing other aspects of her life to seem grim. As I thought about it in this cause and effect route, it got me thinking about what we have been discussing in class re: inputs that have no outputs, why and when delays in output occur, and what the links are between depression and memory. Was this depression an output from something that had occurred a long time ago? Was a traumatic emotion or event of the past repressed, stored in the brain, and the memory of it triggered much later somehow? And if so, why was her circuitry rerouted?

Somewhere along these lines, there was an article in the Sunday New York Times that I would highly recommend to everyone in the class titled "Our Memories Our Selves". The article discusses the development of mind-enhancing drugs, initially intended for use with Alzheimer's patients. (The person who wrote last week about her grandmother's memory loss might want to check it out. It makes some distinctions between long and short term memory and learning i.e. being able to remember events from childhood versus more recent ones such as where you put your keys.) The article states that "behavior has always been critical to the scientific study of memory." Memory is such a huge part of who we are, so much a part of our notion of self. If we did not remember, say an abusive relationship or a traumatic experience, who we are and how we act would be so drastically different. Memory = all our baggage (and much of the good) we bring to our experiences. And since memory can largely be explained at the cellular level, there's another facet of our self that hangs its hat in the brain.

Yes, an interesting article in the New York Times Magazine, both in its own right and in connection with larger issues, as you describe. Indeed "memory" is an important part of "self", and so we'll want to talk more about it in the course (and will). Can prior events have long term and major effects on subsequent behavior? Yes, of course. And, indeed, that is consistent with what we know of cellular processes, so "there's another facet of our self that hangs its hat in the brain". Can depression be among such effects? Almost certainly. Does depression REQUIRE such effects? Almost certainly not. A tendency to at least certain forms of depression runs in families, implying some genetic influence. Which, of course, oughtn't to surprise us. Cellular processes reflect both the genome and prior activity (experience). It is worth noting explicitly, though, that quite similar effects (such as depression) may in different cases have quite different causes. Measles may imply a particular virus, but depression doesn't similarly imply a particular cause. PG

Name: rob miller
Subject: love again
Date: Mon Feb 16 17:53:23 EST 1998
I would like to revisit one of the topics brought up in last week's forum, love. Since valentines day was this weekend, it has been on my mind. I am in agreement with Pribram, the author quoted last week, that there are many pathways involved with being attracted to someone. However, I feel as though the author does not make the distinction between attraction and love. Physical attraction can be studied as a series of hormonal and chemical signals triggered by the sight (or other senses) of someone who is "attractive." It seems logical that that a stimuli can bring about a heightened state of reproductive preparedness. This is how most animals go about finding a mate.

But I think to discuss love is more complicated and can never be fully understood. Of course the argument hinges on a definition of love, which is always subject to interpretation. First off, love should not be confused with sexual attraction, infatuation or romance. I feel that physical attraction is a part of love but cannot be mistaken for love. Romance, or the idea of romance is a fictional idea about what love should be, and usually confused with real love.

I think our discussion in class about love left out that fact that another brain must be involved in the process. Love is not a series of inputs and outputs in a brain, rather it is input from two brains working simultaneously. The brains involved must evolve during the process, not only react to inputs. I think falling in love with someone takes a lot of time and is much like the learning process in the brain. One must learn about someone, and continue learning as time goes on. The stimulus is always changing, therefore the love response or output is changing as well. Love as a neurological function is not about a series of reactions leading to an output, love. This idea also relates to the concepts of bidirectionality and interconnectedness covered in class this week. So, it is obvious that there is much more to love than can possibly explained through neurological pathways, confined in specific regions of the brain. I like it better that way anyway.

A nice extension of the conversation to include more recent topics. Indeed, I suspect you're right taht there is not only a need for two brains but also a fundamental "bidirectionality" involved in love. The output of each brain is of course the input for the other, and the input of each the output of the other. And each then comes to increasingly change in correlated ways? PG

Name: Eric Odessey
Subject: anecdote
Date: Mon Feb 16 19:27:52 EST 1998
An interesting story. I was sitting alone a few days ago, eating a meal at the coop, when someone who generally makes me nervous walked in. I looked up from my meal, and the instant my eyes focused on this person, my stomach started to twist in knots and slam around in my body as if it really wanted to get out. I know that everyone has had this sensation at one point or another; I'm pretty sure it has to do with a release of adrenaline (maybe other hormones, too). The part of the whole experience that really struck me, however, was that I didn't consciously recognize the person for a few seconds after my stomach went nuts. It was as if I were receiving output from within my body about my environment. By that point, I had to try to cover the look of severe pain that had swept over my face so as not to seem rude. It's amazing, though, that your nervous system can recognize and translate an input full seconds before your consciousness (using this term loosely) figures out how to interpret it. What are the implications of this observation? Well, the one that really gets me is the level of complexity (or possibly redundancy) of the nervous system. In only a few seconds, the immensity of the number of neurons that can fire is staggering. This means that likely billions of neurons needed to fire before I realized who was standing before me. I like to believe that means the brain has an exceedingly complex and highly ordered set of pathways, eventually ending at the thalamus (I think) to signal the release of adrenaline. There is also the possibility that the signal enters our brain and gets stuck there in a series of redundant pathways, but I like to think that evolution has helped to correct that condition. Sorry I can never seem to stick to the topic given, but I’m constantly amazed as I learn more of what the brain can do.

No apologies needed. Valuable story, useful contribution, from lots of points of view. Yes, HIGHLY ordered set of pathways, with enormous numbers of active neurons and very sophisticated processing (object recognition, response choice, output) in a very short time. The REALLY interesting thing, though, as you say, is that all that happened before YOU recognized the person. Which is highly germane to our past and future discussions of the "I-function" which, from your observations (as from others we've talked about) is not synomous with nervous system activity as a whole and therefore must instead relate to a subset of nervous system activity (be a smaller box). What you might also want to think about is what was involved in YOU (the I-function) "recognizing" the person. By the time you did it, you had a lot of sensory inputs over and above the visual image of the person, including some generated by your own output (input from the stomach). Maybe those contributed to "I-function" recognition? PG

Name: Jonathan Ball
Subject: Negative Feedback Systems
Date: Mon Feb 16 19:41:27 EST 1998
The notion of bi-directional causation is essential for understanding the functioning of an organism. The nervous system in isolation may be able to function without bi-directional inputs, but in order to produce the complex patterns of operation associated with behavior, feedback is necessary. Every output from the nervous system changes its perspective on the current situation, so the outputs need to be constantly modified in order to achieve the desired goal. Take for example Prof. Grobstein picking up his coffee mug, the output of moving his arm changed the sensory information entering his brain which then changed the output to his muscles so he was able to stop his arm at the proper distance to grab the cup. Without the motion of the muscles telling the nervous system how much it moved, the nervous system would never know when it need to stop. It is only through continuos communication and modification that the nervous system can coordinate then multitude of minor operations that go into creating an observable behavior. This system of outputs becoming inputs which in turn modify inputs is known as a negative feedback system. The negative feedback loop has been shown to be one of the most efficient and practical methods of output control and it is utilized in many systems both organic and non; that is why I believe it is a legitimate model for the functioning of the nervous system.

There is indeed a close relation between "bidirectionality" and "negative feedback" and we'll talk more explicitly about this. At the same time, there are other things that can emerge from the output/input/output circularity (as others have noted), and we'll talk about those as well. While it is true that picking up my cup involved lots of sensory input, it is also true that similar movements (as in the case of the monkey we discussed) can and do stop in the absence of sensory input, so the "continuous communication and modification" you describe is not quite as generally needed as you seem to imply. PG

Name: Ruchi Rohatgi
Subject: is there a score?
Date: Mon Feb 16 19:43:08 EST 1998
In class it was said that maybe there isn't a score for a motor "symphony." Maybe then movements/behaviors are just a complex pattern of discharge in motor neurons that are constantly being written. In some respects I agree with this but I am confused with the idea of learned behaviors. Through the process of learning, there is actually synaptic growth as certain synpatic transmissions are used more. So if an input or stimulus is repeated over and over, the same behavior response (and thus the same complex pattern) occurs. The behavior is now learned and can even be elicited more quickly. Does that mean a new score is still being written, even for behaviors that are already learned? What about something like a habit? Is the same pattern being written over and over again? Then can one really ever "learn" to do something???

But what about behaviors that occur without an input or stimulus? An example could be an instinctual behavior. I understand how these behaviors can begin in the middle of a system and be carried out, but I don't understand why they would just happen. However, I don't think that there is a score stored in the nervous for behaviors such as these. We know that behavior is a complex patterned activity and that changes in behaviors are changes in these pattered acivities. maybe instinctual behaviors are underlying patterns- almost like patterns that come easiest to neurons and to which they have certain proclivities towards.... it's kind of like two puzzle pieces fitting exactly together and not forced together- do you kind of see what I am saying?

Yes, I think so. Let me see if I can sort it out in pieces, since you're touching on a variety of related but distinguishable important things. A "score" may exist in the nervous system for entirely genetic reasons, either being a consequence of "patterns that come easiest to neurons" or being a pattern that has been selected for during evolution. This helps one to understand "innate" behaviors, those that seem common to many organisms and to appear without prior experience. A score may also exist as a consequence of use, in the way you describe or other ways. And, of course, the two things may interact, with both genetic information and use influencing a given pattern (probably by far the most common situation). That all ok? PG

Name: Elizabeth Windsor
Username: ewindsor
Subject: bi-directionality
Date: Mon Feb 16 19:52:34 EST 1998
I agree that the nervous system can operate as a two way street, with inputs affecting outputs and vice versa. Even so, it does not seem to operate equally both ways. The few examples already given to support the idea that outputs can affect inputs have an input as the initiator. In the example of picking up a glass of water, the action is initiated by input from the body telling the brain that it is thirsty. This begins the whole series of outputs affecting inputs affecting outputs which leads to picking up the glass of water. I don't know if this can work the other way; if a series of outputs and inputs affecting each other could begin with an output instead of an input. In class we've talked about the existence of outputs that originate in the middle of the nervous system. Perhaps some of these outputs might initiate a series of inputs and outputs affecting one other. Even so, the two way street is not equal. The majority of these series of outputs and inputs are initiated by an input. However, this does not mean that we should not study the nervous system from the perspective of outputs affecting inputs as Prof. Grobstein suggested. I have to admit that I have a problem imagining outputs that do not originate in some way from previous inputs. We've talked about mechanisms in the nervous system that could account for behavior originating in the nervous system so I believe that it is possible, I'm just not sold on the idea yet. Perhaps this is because prior to this class I always thought of behavior in terms of stimulus and response. Maybe I just need a clear example of an output that originates in the nervous system ?

I am also very interested in the relation between learning languages during early childhood and the idea of a "score" that we talked about in class. There is a question of whether children can learn to speak after the age of ten or eleven if they never learned before then. I saw a documentary once about a twelve year old girl whose parents had locked her in a spare bedroom for most of her life and who had never learned to speak. The program followed specialists as they tried to teach her to talk. It was a very sad story and the girl never did learn to speak. There was a question of whether this was due to retardation or because she had passed the age when languages can be learned. This will probably be dealt with later in the course.

Interesting and appropriate concern, thanks for making it concrete. Yes, one might imagine that all all outputs have an input as their origin somewhere back in time, and I wasn't very clear about concrete examples where that wasn't so. I'll try and do better as we go on. Interestingly, language development provides a likely (though not definitively demonstrated) example. Humans pass through a "babbling" stage, out of which definitive speech emerges, and there are reasons to suspect that this "babbling" has its origins inside the nervous system rather than being a "response" to a "stimulus". While hearing adult speech is obviously important to development of speech in children, there is also reason to believe that hearing one's own speech is also important. Some song birds, for example, will not develop normal song if prevented from hearing their own immature songs. Putting all this together, one might suggest that adult speech motor patterns depend as much on output/input relations as they do on input/output ones. We'll talk about other places where the output/input relation seems critical as we go along. PG

Name: Doug
Username: dholt
Date: Mon Feb 16 20:17:14 EST 1998
I have to admit that I am having a challenging time imagining bidirectional causation. In the example of the coffee cup that was used in class, each ne of the actions that is necessary could be broken down into separate and distinct actions that are precipitated by stimulus. The initial action was the decision to reach for the cup. Even after this decision was made, the eyes provided the direction and distance information that allowed the brain to decide how far and for what it ws reaching. With the eyes closed, the brain would presumably interpret signals coming from stretch receptors in the muscles of the back and arms etc.. to compute how far the arm was from the body.. but this is done from internal stimulus (as opposed to external stimulus).. so as a feedback mechanism I haven't really made the differentiation between that and external senses. Where this model does appear to be more logical, but definitely a lot harder to show is the thought process within the brain. I feel that it is more understandable as a method of explaining how information flows from one box to another and then back again without having any visible external output (or input for that matter). Other than that, output is just new input for the brain to digest and act upon.

I think we've been back over this a couple of times since you wrote. Content with the demonstration that indeed some complex movement patterns do NOT require feedback from stretch receptors etc? Yes, the bidirectionality is at least as significant in terms of internal signals, as we've now talked about. PG

Name: jenn snavely
Username: jsnavely@bmc
Subject: bidirection and music
Date: Mon Feb 16 21:39:44 EST 1998
Wow lots of interesting stuff to read this week. i have to say that the bi-directional nature of inputs and outputs can help us a lot and is very important. I think this helps us understand why sometimes a stimuli or input causes us to behave certain ways and some times it does not. If inputs only affected outputs than we would always do the same thing. Every time we heard a loud noise we would be startled...but sometimes we are not, because perhaps our outputs feed back and change further imputs or perhaps the inputs were not strong enough to influence outputs at the time or whatever. I don't know if this example makes any sense or is relevant but the point is that sinse impulses go both ways we can account for many more behaviors and outputs without imputs and visa versa. I have to agree with emma when she says that the idea of a musical score for behavior goes hand in hand with the bi-directional idea of impulses. when listening to music it is not just the notes we hear by themselves, we hear notes linger and resonate affecting the notes that follow just like an impulse can come in as an imput and it does not just disappear when it becomes an output. The original output can come back to effect other things that are going on. I don't know about this but this seems a lot to me like the chaos theory. that all we do starts with one single event that goes around and around and comes back to effect us again. One impulse can cause an output that changes a future imput that changes an output and so on. And the same thing does not necessarily happen each time but there is a definate underlying and complex pattern. Well the two concepts just seemed kind of similar to me so i thought i would mention it. Anyway this was one of the most facinating topics for me to ponder and i hope i did not sound to rediculous with my feverish babbling.

Babbling is not always bad (see above). Generating outputs is often a good way to get interesting inputs. Yes, bidrectionality can make things less stereotyped (although you may want to be a little clearer on exactly why). And the music issue is a good one. Singers (and talkers) do much less well if they can't hear their own voices (even worse if one deliberately distorts the input which results from the output). As for chaos theory, there is a relation, in its dependence on repeated iteration. That, though, sometimes does and sometimes does not yield a definite, underlying, and complex pattern". PG

Name: Alicia
Date: Mon Feb 16 22:37:40 EST 1998
The concept that inputs and outputs can affect each other makes perfect sense to me. Though it is easier to think about inputs affecting outputs than to grasp the idea of outputs affecting inputs, I feel quite comfortable with this cylic(as I believe someone called it before) system. It helps to explain how seemingly spontaneous reactions result. This concept also helps to explain the concept of our everchanging memories, our concepts of our past experiences and actions as a result of them, and the way we learn.

Interesting how outputs affecting inputs seems obvious to some people, not to others, no? Careful, though, about the "seemingly" spontaneous; some things ARE. Can provide some examples of why it makes sense, how it helps to explain the things you mention? PG

Name: jen
Subject: inputs and outputs
Date: Mon Feb 16 23:31:10 EST 1998
I can understand why inputs and outputs affect each other in a continuous cycle, but I can't see how outputs affect inputs. We learn from our behavior which changes or sometimes stays the same. When I get nervous like when I am on an airplane, the same things happen to me every time: my hands start sweating, my stomach feels sick, and my voice cracks. Although, I am not clear though on how these actions affect inputs in my brain...

Fair enough. Let's see. How did you know you started sweating, felt stomach to be sick, voice cracked? Each of those things happens because of an output from the nervous system. For you to KNOW they happened, maybe you had to hear your voice, get sensory input from your stomach, see or feel your sweat? That (assuming it is what happened) would be output causing input, no? PG

Name: Christy Taylor
Subject: Bi-directional causality
Date: Mon Feb 16 23:48:10 EST 1998
I definitely agree that the organization of the nervous system leads to bidirectional causation. Inputs influence outputs just as much as outputs influence future inputs. The nervous system can be seen as a symbiotic relationship - directing outputs based on previous outputs and current inputs.

I think an interesting way to think about this is how no two people are the same and the reason for this unique quality is the fact that their nervous systems are unique to each individual.

No two people will ever see a problem or situation in exactly the same way simply because of the previous outputs and inputs that the nervous system has performed in the past.

I think that I can make an argument that the nervous system has a sort of "memory". In class we were shown that even when Dr. Grobstein closed his eyes, he could still find a coffee cup at the end of his desk. Furthermore, we were told about a monkey whose dorsal roots were cut allowing no incoming information from the arm, and yet the monkey was still able to point to a light with his arm in order to receive a treat.

What does this mean for you and me? This means that everything that we have done, said, or experienced is a part of who we are and is also a part of our nervous system. I believe that the nervous system has an enormous ablity to store and retrieve information. Have you ever had a response to a situation that you could not explain only later to realize that you had been exposed to a a similar situation but had just "forgotten" about it? Well, your nervous system did not forget!

Interesting sequence of thoughts, and where it takes you I think is true and significant. There are some steps along the way, though, that could have branched in other ways. People ARE different, and some of that may have to do with outputs causing inputs, but that doesn't follow necessarily, and there are some other possible explanations of differences. Similarly, me and the monkey could be accounted for by changes in the nervous system due to the past, but could also be accounted for in other ways. Finally, you need an "I-function" in there to explain how "you" can forget things but your nervous system remembers, yes? PG

Name: Akino Irene Yamashita
Subject: scores, more on love
Date: Mon Feb 16 23:50:04 EST 1998
The feedback loop topic doesn't energize me that much. However I will point out that in our newest drawing of the "box model" the arrow going from outputs to inputs is drawn outside the box representing the NS. I think sometimes we tend to think of inputs as all coming from outside the human body, when actually they include inputs that come from outside the NS but are generated by the body itself, like how much muscle fibers are stretched. And, how does the body generate these inputs? By behavioral actions, of course. And what's responsible for the actions? Motor neurons. So stated that way, the bidirectional model makes sense.

Anyway, on to juicier topics. The "scores" model also seems quite interesting, and I would agree that these "scores" are not predetermined from birth but are constantly written and rewritten as we live our lives. This model would explain the many behaviors that are not quite involuntary but which we do not really consciously think about, such as walking, chewing, and for people who have learned swimming, skating, and other sports that require certain similar repetitive motions to be performed. When I was learning to skate the guy who helped teach me kept saying that I would skate better if I did not think about it, this made no sense to me at the time but now that I know how to skate (though I am not very good) it does, I really have stopped thinking about it. I realized this when I was trying to help someone else learn to skate and I could not describe exactly how.

I think that in many instances the phrase "use it or lose it" applies quite well to the brain and the mind. I once read about an experiment conducted on newborn kittens, who were divided into groups, the first experimental group being raised in a room in which the only visual input made available was horizontal lines and the second with only vertical lines as input. When the kittens were placed in a normal environment, the kittens who had been raised in the horizontal-line room seemed to be unable to see vertical lines, and vice versa for the group raised in the vertical-line room. It does seem that there is a critical learning period early in life where the new scores seem to be easier to "write" than later.

Okay, now, love, again. It occured to me that maybe love is also an example of a "score", and maybe this can explain why many people have long-lasting relationships even though, as the Inquirer article said, genetically people may be programmed to stay in relationships only long enough to raise offspring when they need parental nurturing. Now maybe this is just me, and I beg forgiveness if what follows is completely off the wall. However, I have noticed that often one initially finds a person attractive for certain, often superficial things like the sound of their voice or their sense of humor. However, once one is "in love" many other attributes of the person become attractive as well, even when you find out new things about the person that change your initial perceptions of them.

So maybe, at first the initial inputs cause the "in love" score to be "written", or processing unit and neural circuits for feeling love for a person are formed. Then further inputs from the source are all processed through the same "in love" box and result in the output of feeling attraction or love. Maybe this is why some people continue to feel love even after many later inputs from the same source that would provoke a very negative output if coming from someone new, and I will not go into further detail on that, for reasons of privacy. But maybe it is possible to actually be "addicted to love"!

Lots of interesting pieces. I'm not sure skating is a "repetitive activity" necessarily, but your next points are quite significant in a different context. Both difficulties telling someone how to do something and the need to "not think about it" are examples of things that point to the "I-function" as a distinct part of nervous system activity. We'll get back to this. And to the "use it or lose it" issue (which has a grain of truth, but is, as usual, more complex). As for love ... sure it grows, matures, changes. Doesn't everything? At least if it is the nervous system? PG

Name: Moriah McSharry McGrath
Date: Tue Feb 17 00:06:05 EST 1998
I am all over the bidirectional causality thing - it makes me think of feedback loops. As I'm sure a lot of people who have taken multiple introductory biology classes are sick of discussing, many processes in the body are maintained by these homeostatic systems in which the output of (for example) a given hormone is determined by the level of another hormone. Each of these levels fluctuates, but together they remain in a relative equilibrium due to the feedback one exerts on the other. These systems are described as loops because the inputs and outputs circle into each other, creating a cycle that is not directly cause-and-effect.

These systems of negative feedback loops allow an organism more flexibility to adapt to its environment because they are more fluid than, say, cascade reactions, which build up as they progress. Their greater interactivity can be more effective than such a unidirectional process, which is why I think it would make sense for the nervous system to be bidirectional.


"Loopiness" is indeed closely related to "feedback systems", not only negative but also positive, and we'll talk more about that. "More fluid", "greater interactivity" though are a little vague as explanations for why they "make sense". Let's see if we can be a little more specific as we explore further. PG

Name: Kristen Reiff
Subject: Symphony
Date: Tue Feb 17 09:15:31 EST 1998
I really like the concept of the "motor symphony". I think it is undeniable that there are a lot of agents at work for even the most seemingly simple action. I also like that this model provides for when accidents happen, to a certain degree. For example, a person with bad hand-eye coordination could be explained by suggesting that their motor symphony is "out of tune".

I also think that the score can be rewritten and is continually being added to. We are very capable of learning new ways of doing things, although for some this is harder than for others. Actions that are done routinely, like walking for example, could be said to be already written and just repeated, but when an action is done for the first few times, that is when the score is being written.

This model does leave some questions in my mind, though. An orchestra has only one conductor. From what I can tell so far, this is not the case with the nervous system, if the nervous system can be said to have a "conductor" at all. Does action in the nervous system arise the way patterns do in complex systems, or is the action directed by a leader. If there are multiple leaders, how is the action coordinated by all of them? Is one leader in charge of the other- if conflict arises between the leaders, who resolves it?

Nice questions, which we've talked about since you wrote this, yes? Are you comfortable that, at least in many cases, there is no conductor? Instead, the players simply listen to one another? PG

Name: Liz Shafer
Subject: which direction to study the nervous system
Date: Tue Feb 17 10:55:15 EST 1998
As far as which way to study the nervous system, by following the firing of neurons from inputs, or tracing the steps backwards from the noticeable outputs, I think the picture would not be complete (if there is such a thing) without approaching the study of the nervous system from both directions. There are certainly many things which can be learned from either approach. Just as it may be discovered where signals for outputs arise from within the nervous system without any outside stimulus, it may also be discovered what events give rise to the sudden (or perhaps not so sudden) stop of an input signal, preventing any noticeable output. If the "musical score" (the motor symphony) is written as it goes along, this means (or does it?) that at every instant there is feedback to the nervous system from the momentary output, which then influences the next "note." The next note is somewhat dependent on what the output in the form of a new input tells the nervous system. If all this is the case, in a sense, studying the nervous system from outputs back to inputs is the same thing as the other way around. Once you follow an output back to the influencing input if there is one, you may end up at a prior output and begin the circle again. This loop can even become confusing as to what is the "input" and what is the "output" as these labels are essentially arbitrary.

Yes, they may be "essentially arbitrary" labels in terms of causation, which could be confusing and is certainly meaningful. Fortunately, there are not arbitrary in terms of nervous system anatomy. Inputs are sensory neurons, outputs are motor neurons. Convenient to help keep track of things, no? PG

Name: zach hettinger
Subject: bidirectional causation
Date: Tue Feb 17 11:18:51 EST 1998
I think that the concept of bidirectional causation lends an even greater legitimacy to the model that we are slowly building up in class. In fact, I couldn't even imagine an organism without some kind of bidirectional causation. An organism wouldn't be able to adapt and survive, it would keep acting, but without any reference or any information about how successful its actions were the organism couldn't survive, it couldn't learn from it's actions. I'm sure there are some exceptions to that, but having a reference feedback seems necessary in the ability to learn. I remember when my younger cousin was little, he use to just run off small stairs and fall on his face or he would just walk into a wall and then fall down and then do it again. It seems possible that he wasn't making the connection between running into something and the consequences that arose from those actions, it's also possible that he didn't feel pain, but that’s another situation. Eventually he made the connection that running off stairs makes you fall down, which then should cause some level of discomfort. This is a very elementary example of what goes on in the body, but I think it at least points out bidirectional causation's importance in learning and adapting.

Nice point, and I agree with you. An output/input coupling is absolutely essential for learning. Interesting thing is that much of educational theory implicitly supposes that learning occurs simply as a consequence of inputs. PG

Name: Emily Varani
Subject: Instincts?
Date: Tue Feb 17 11:29:16 EST 1998
In thinking about different types of behaviors this semester, I have often found myself distinguishing actions that are made through active decision from actions that occur without pre-thought (I am hesitant to call these actions instinctive or reflexive because these word has broader implications, though these are easy ways to think of them).

The idea that information flow in the nervous system is bidirectional lends an interesting fold to the difference between these two types of actions. If, indeed, information flow can move both forward to response and/or backward to cause another stimulus, one can imagine two actions arising from a single initial input. The first action would be the "true" response of the nervous system while the second action, more delayed due to longer processing time, would be the result of the "true" response causing a secondary reaction.

Truth be known, I am not entirely clear about how I can reconcile these different behaviors to the different functionings of the nervous system. Perhaps, given the longer processing time, the secondary reaction allows the nervous system to feel that it is making a decision while the inital reaction feels reflexive or instinctive. If anyone has any ideas about this subject and its relation to bidirectional information flow, please let me know.

Very interesting thought. Yes, indeed, there is a distinction between "active decision" and without "pre-thought" movements. And very interesting effort to link that to output/input/output sequences with delays. We'll suggest quite soon another basis for the distinction (maybe more clear?), using the "I-function". PG

Name: Kristin Chimes Bresnan
Username: kchimes
Subject: bidirectionality, language, other kinds of communication
Date: Tue Feb 17 11:30:46 EST 1998
One of the things which pleased me most about last week was the idea of the bidirectionality of the nervous system, mostly because I had been wondering about chimney swallows and the way they sweep around together in what seems to be a unified motion that is not strictly patterned. That is, the group moves as one body but not in a clearly defined and level circle; there is a lyrical, uneven swooping to their motions which is what makes them so beautiful to watch. Anyway, as I saw them I was wondering about what particular link-up of neurons made such group action possible, and the bidirectionality model gives me some food for thought. Then I came across the following lines by Rilke: "What birds plunge through is not the intimate space / in which you see all forms intensified." Which got me wondering about the area of our brains associated with consciously identifying and naming things as a kind of "intimate space"; and all of the communication which occurs outside of that "intimate space" which seems to constitute so much of the inputs of our nervous system. I am still wondering about language, and I am seeing the bidirectionality concept as relating directly to conversation and also accounting for kinds of group action or mass participation in a coordinated event.

Also, I've been thinking more about what I wrote about last week and I am not sure that "transcendent" is the best way to discuss the flow of information across its media. Mostly, I am trying to figure out what it means that language exists as a diffuse network in all of our brains at the same time. Maybe it doesn't mean much in the consideration of our nervous system, but the idea is suddenly under my skin. Any ideas would help!

Maybe slow down a step or two? :) Bidirectionality very directly related to birds flocking. And yes, it is almost certainly, as I think you're implying, a leaderless bidirectionality (have a look at boids) operating outside "intimate space", the outputs of one organism affecting the inputs and hence outputs of another. As for language, it has a LOT to do with the brain, both as a creator of language and something modified in turn by it. Along which lines, you (and others) might enjoy Origins of the Modern Mind, by Merlin Donald (Harvard University Press, 1991). PG

Name: Rupa Hiremath
Subject: input-output
Date: Tue Feb 17 14:09:54 EST 1998
I think that the suggestion of "input" and "output" is a good place to start understanding the nervous system. However, I do believe that there has to be something more than this rational. In regard to bidirectional causation, this concept seems too simple in itself. Output affecting input as well as input affecting output. I am wondering if there is such a thing as polydirectional causation. It would include bidirectional causation in addition to the concepts of output affecting output and input affecting input. And how would this occur? I am, of course, not certain. However, there may be certain chemical relays that prompt such signals between each occurrence. This was simply some food for thought at my moment of pondering more about the nervous system.

Nice thought. One needing more development with some specifics. If we have only "input" and "output" to work with, then its hard to imagine there are are more than two directions. But, if, as we've been talking about, there are lots of different boxes within the box, including for example, an "I-function" then one can imagine that inputs affect outputs and vice versa, and any given box can affect, be affected by others .... then one has "polydirectionality"? PG

Name: Rehema Imani Trimiew
Subject: 2 of the same?
Date: Wed Feb 18 01:54:04 EST 1998
I still am not confident about the score, symphony, an bi-directional causality. The worm does not have a main brain that controls everything, would the "brain" be at each of the little clusters of neurons? Could each group send out its own pattern or symphony to the neurons involved in contracting? Or is there only one neuron and one "muscle" so that there is no pattern needed because 1 direct signal could be sent. Is there any reason to believe in bi-directional causation? If each unit is like a brain then it could receive an input from the stretch cells, make a decision and then send out a pattern to move. So are they both used at the same time, bi-directional causality and a pattern? Input can cause a pattern to be sent out and the result of that can instigate another pattern being sent out. How big does it get? If I don't do my work, I get a bad grade so I do more work and then get a better grade and then really work for the best grade. That is a continuous reading of the output of how I do my work and then getting the input, adjusting, and responding.

I can not recall ever doing something and not being able to stop, with the exception of emotions. I've played sports, typed and quite frequently walked and never have I not been able to stop something that I was doing. Possibly, the brain has the power to override any pattern that has started. Is hypnotism an example? I went to a show featuring a hypnotist and he called me on stage. Sometimes I would automatically do what he said until I thought about it, then I had to conscious continue the activity, my body would not automatically as others would. Or were they not aware/conscious of what they were doing? I understand how one can have a symphony going on without conscious awareness ( I frequently dance in my seat, while singing to the music, tapping to the beat with my hands, while focused on my reading and only really paying attention to the reading), but if I want to stop I automatically do though my body has been in a singing/dancing/taping mode. A thought occurred to me that if there are set patterns that control an entire behavior and the patterns are started by action potentials or electrical stimulation, then could they be controlled? Leonard part 6 (an old movie starring Bill Cosby) had the evil woman who wanted to take over the world controlling animals in a similar fashion. She had a device that when activated would send out some sort of signal that would trigger a pattern to be released in the animal (the behavior was mostly to bite anything that was near it). Thus all of the animals that had an implant or injection of some kind would attack when the signal was sent out. I saw a special on TV where they cut the top of a man's skull off, exposing the brain and then sent a small electrical pulse through different regions of the brain. The man was conscious and when they would tap the instrument to one part of the brain he might move or feel something in his hand or have problems identifying things. They went through the surface of the brain labeling each are based on what it did my the man's responses. Could a program one day be put into people so that the standard way of learning is not necessary and that it would invoke already formed patterns in a way that had never been done before (ex. riding a bike or flying a plane). Anyway, all of this neuro stuff is fascinating.

I can tell, not only from what you write but from some of the talking we've been doing in the halls. Pleased/delighted. Yes, of course, work on something (generate output), get less than you wanted in response to it (the resulting input, a grade, or?), work differently on it (a new, resulting output) is a good example of bidrectionality. As for the "stopping something", that's a concept which has as much to do with the "I-function" (not the "brain", but a part of it) as with central pattern generation (see some earlier comments this week). It has, as you say, to do with "consciousness", which we'll talk a lot more about. Yes, one can indeed, trigger behaviors by stimulating various places in the nervous system. When done in humans, people generally report that "they" didn't do it. And lots of "learning" involves minute, specific, widespread changes in the nervous system, so much so that it is inconceivable that they could ever be mimicked by direct electrical stimulation of a specific location. That give you more to think about? PG

Name: Anuja Ogirala
Subject: bidirectional causation
Date: Wed Feb 18 23:52:54 EST 1998
I found the suggestion of polydirectional causation rather interesting because it destroys the idea of a linear relationship between our NS and our environments. I am intrigued by the notion that we could have a number of varying inputs that could lead to one output. I wonder if it would be possible for different outputs to be generated simultaneously with perhaps the existence of some hierarchy. This order would preclude the execution of low-ranked outputs while emphasizing the terribly distinguished outputs from a higher strata.

Perhaps bidirection is a more plausible mechanism by which our NS operates. Epileptic seizures would be a flaw in the polydirectional causation theory since they arise from rapid simulataneous neural activity in certain parts of the brain. This cacophony generated by multiple neurons firing can throw our bodies into utter chaos. It is really interesting to consider the various ways in which we relay inputs and outputs through our NS and the effects that these communications have on our behaviors.

Glad you like it. Me too. Where did you get the idea that different inputs could lead to the same output? Its true and important. Similarly, a given output can yield different inputs, and that's important too. And the thought of a "hierarchy" so that one ouput precludes others, where did that come from? Notice that the Pleurobranchea case we just discussed is sort of like that? PG

Name: ruth czarnecki
Subject: the score
Date: Fri Feb 20 01:22:55 EST 1998
Please pardon the tardiness of my post- my brain lost the score for how to write comprehensive, English sentences for awhile.

I really enjoy the idea of a "score" that the nervous system plays to create behavior. Naturally, there are instances in which the score is initially created st the moment of behavior, but overall, I believe that a score is the way most behaviors happen. I also think it is interesting that the score is veryy much genetically based. Because many scores are of genetic origin, I contend that they are bound by the laws of evolution and that they improve with time. An example of this would be the use of tools. Chimpanzees will use rocks every so often to open hard fruits or nuts. Early homonids used tools that consequently became more and more specialized. We use such complicated tools as computers and ovens. Granted, much has to do with the ability to create technology, however, I contend that the score for "tool use" became more and more specialized through evolution.

I also find it interesting that there are so many scores stored in our nervous system. for instance, babies know how to walk before they are even close to having the muscular and skeletal structure needed. (if anyone knows of a website that has info on this, please tell me. i want to do my research on it) Things like this lead me to wonder how much is really passed down from our parents. For instance, is it just a coincidence that a friend of mine's father, uncles, and grandfather are all orthodontists? Or could it be that the behavior of orthodontics was passed down in the form of a score? i doubt that every act they perform was passed down, but perhaps a certain attitude, or a demeanor, or even one type of behavior predisposed them. Knowing that these scores can be passed down and attempting to see how they are remembered open up new doors to understanding behavior. I just thought these things were really interesting. I apologize for the incoherence of it all.

No apologies needed. It is indeed interesting to entertain the possibility that motor scores may have a genetic component, and, generalizing, that broader behavioral patterns may as well. The latter is certainly the implication of information about similarities among identical twins reared apart. Whether things actually "improve" with time as a consequence of evolution is an interesting subject/ it is not so clear as you imply that that is so. To talk/think more about (though not necessarily in this course). PG

Name: Daniel Casasanto
Subject: Weekly Essay #4
Date: Tue Feb 24 22:55:46 EST 1998

The experiments performed on the isolated nervous system of the crayfish, described on 19 February, showed some surprising results, from which we must draw conclusions that contradict our intuitive sense of bodily organization and hierarchy.

In non-scientific contexts, the human brain is often compared to a "switchboard operator", and thought to be the "Commander in Chief" of the body. Our intuitive understanding is that information is generated by the brain, distributed by the nervous system, and acted upon by the muscles and limbs. This paradigm is similar to one which accurately describes the commercial distribution of electricity by utility companies; the current is generated at the power plant, distributed through power cables (which ramify into smaller conducting wires), and put into action by the appliances in homes located far from the power plant. It is absurd to think that the cable is responsible for generating current, or that the appliances could function when cut off from the central distributor of current. It is for this reason that the "power plant" analogy does not parallel brain function.

The experiments that show central pattern generation to be localized in the caudal part of the crayfish nervous system indicate that the brain is not the coordinator and disseminator of all information: that a rostrally located "Conductor" is not necessary for "motor symphonies" to be played by caudally located neurons. Moreover, that the neurons are more than conduits through which signals travel from sender to receiver: they are themselves senders and receivers. Localized central pattern generation endows peripherally located neurons with a kind of "intelligence" we intuitively reserve for brain cells.

The idea of a distributed system, as opposed to a centrally controlled system, accords with emerging theories that seek to explain not only the functioning of the body, but the functioning of the universe. Common to several emerging organizational schemes is the proposal of dynamic systems instead of static structures. Whereas "structures" comprise parts, "dynamic systems" comprise processes. Perhaps future medical students will not take separate courses in anatomy and physiology, because it will become clear that anatomy is physiology.

You've certainly gotten the point, both specifically and more generally. The idea of "distributed systems" is being widely recognized as giving a new and useful handle to exploration of a variety of phenomena. Serendip has a section on this topic, I'm teaching another course more or less on it, and there's a nice Exploring emergence" interactive web essay from the MIT Media Lab. The question, of course, as with all ideas, is how productive it proves to be in the long run. PG

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