Topic 5: What significance do the neurobiological concepts of central pattern generation and corollary discharge have for thinking about behavior?


The most important way in which knowledge of corollary discharge signals and central pattern generators alters the understanding of behavior is by further spotlighting the enormous amount of coordination which occurs among the nervous system's elements in producing behavior. We have already observed one example of this coordination in that there are many neurons involved in any given behavior. In fact, it may be more accurate to say that every neuron has an input to any given behavior, with the input of some neurons being their very state of inactivation. Were these neurons active, the behavior that manifested would be different from the one which would arise if they were inactive. (The epitome of this, of course, would be the simultaneous activation of every neuron, which would result in a grand mal seizure.) Therefore, the coordination of activity or inactivity of neurons is important to behavior.

Not only do the specific set of neurons active at any given point determine which behavior will be manifested, but also the amount of activity within each neuron relative to the others. The coordination of the neurons' activities is dictated by the neurons' corollary discharge signals. This shows another level at which coordination of nervous system elements is important to behavior.

If this high degree of coordination in both the neurons involved and their relative degrees of activity is so imperative to behavior, it appears that anything which would affect this coordination would affect behavior. It therefore seems likely that separate central pattern generators which are active simultaneously should exert an influence on each other. The input a given neuron (A) receives from the corollary discharge signal of another neuron (B) can cause neuron A to be active in a particular fashion. Neuron A adjusts its period to be a "compromise" between its own natural period, and the period which emerges as a result of the coordination of the rest of the neurons involved in that particular motor symphony. Now assume that a new motor symphony begins while the first symphony is still active (i.e., walking and chewing gum at the same time). It seems logical that the corollary discharge signals of the second symphony would also exert an influence on neuron A's period. If neuron A's period were to change, then the corollary discharge signals of neuron A should also change the periods of other neurons involved in the first motor symphony. This effect would be magnified by the fact that there would probably be more than one neuron which was involved in both motor symphonies. The change in the period of the motor symphony should result in a change (which may or may not be overt) in the behavior. It therefore appears possible that given behaviors are not distinct entities, but rather, have a coordination of their own.

Raises some very interesting and appropriate general issues. The thoughts about inactivity as well as activity contributing to behavior patterns suggests the possbility of a REALLY abstract characterization of behavior in terms of possible patterns across all neurons. And the interaction of entities does indeed suggest that behavior itself can be thought of appropriately both as the result of interactions and a contributor to a still greater web of interactions. Now the question is, can one translate those ideas into experimentally approachable new questions? PG


I would like to go back to the discussion two weeks ago when we first began discussing central pattern generation. Besides the examples such as the swimmerets of crayfish we also brought up the discussion of athletes as having to create CPG's during their lifetime. I would agree that this makes sense as far as athletes being able to complete actions theyve done thousands of times with close perfection. My question, which was not answered in the next weeks lecture would be how do you create a CPG. My best hypothesis is that you force the same pattern of action potentials through your brain that after a while all you have to do is start it on its road and it will complete the action unless you stop it. So instead of having to create all new connections you are merly hot wiring the ones allready there. This would explain why if you had to similar actions to perform you sometimes do the one you told your body to do but you sometimes do the one that is closely related. Say these are two actions you have repeated tons of times therefore you have set up a pattern that will go to completion once initiated. Its easy to see that if the pattern starts at the same place it could get side tracked to the wrong CPG. Does this creation however block out other action potentials? Or is everything held with the same weight ? Actually to answer my own question it appears that the CPG holds more weight because there is a huge lag when you tell yourself to stop doing a practiced behavior versus a non-practiced behavior.

VERY interesting set of questions. Large enough to make a career out of, which is to say many answers don't yet exist. We'll talk more later about what is currently known about how activity can modify nervous system function in general. But your question opens some more sophisticated, not yet really asked questions about how patterns of activity and modification relate to one another. For which your own experiences may well be relevant insights. Would like to hear more about what you mean by a "huge lag" when you try and stop a practiced versus a non-practiced behavior. And talk more about what actually happens when you practice something. It MAY be "stamping in" an activity pattern, but my own instinct is that it also involves exploring the usefulness of alternative activity patterns. PG


"Corollary Discharge and the Multiplication Tables"

In last week's Philadelphia City Paper there is an article on Waldorf schools. On a typical day the children start the morning with multiplication tables: they are said while clapping out a rhythm. These two behaviors, saying the tables and clapping, are thus linked. So I have been wondering where the linkage between the patterns occurs, what kind of combination between reafferent signals or corollary discharge is it?

Corollary discharge by definition occurs when central pattern generation is present. So first I must decide whether CPG is in any way part of saying the tables and clapping. It is easier to imagine a CPG for the clapping behavior. Rhythms produced thanks to CPG's are not unknown to the body, take a heartbeat for example. So a rhythm made with hands could also be internally generated. And thus would require interaction, corollary discharge, between the CPG's in charge of the clapping rhythm and behavior. Saying the multiplication tables takes memory, and I do not know enough about that yet to make more than uninformed guesses. But I am imagining that the memory is a way of making CPG's, and thus over time, the multiplication tables and the behavior of saying them could become a function of a CPG. Now, how could a link between two different behaviors, most likely generated in two different parts of the body (saying the tables from the brain, clapping the rhythm from the rostral end of the spinal chord) spring up?

To think this one out, I will imagine the very first time the child tries to put the two behaviors together. I believe that for the first time, most of the communication going on in the nervous system is due to reafferent signals. Although a rhythm might be generated within the nervous system, the child must watch and listen to the rhythm to coordinate it with the tables she is saying, at least in the beginning. And especially if she does not know her tables well. In that case, the the speed of the rhythm will depend on how fast she can say the tables. And all of this information is more easily assimilated if the child can hear and see what she is doing. But as the child improves, she doesn't have to "think" about what she is doing.

Does this memorization of the coordination of the two patterns come from decreasing dependence on reafferent signals and increasing dependence on CPG's? If so, then there must be communication between the CPG's of each pattern of behavior. The final speed of the clapping/table-saying behavior will be a coordination of the speeds of the individual behaviors due to corollary discharge. As I mentioned before, the faster she can do her tables (the better she "knows" them, or the better functioning the CPG is) the faster she can clap.

Finally, I can look at the entire classroom as individual CPG's talking to each other. The students can all do the clapping multiplication tables individually. But, each student's rhythm and speed also depends on the rhythm and speed of all the other students. The corollary discharge in this model would actually be the sight and hearing of the students, which, taking in information about the other speeds and rhythms in the room, uses the input to adjust their own patterns. The entire pattern of clapping and saying the tables in the room depends on the communication and information processing of each student, of each CPG. In that way, the behaviors of clapping and saying the multiplication tables are connected both inside and outside the students.

VERY interesting, pretty set of thoughts/extensions. Thanks. Now want to go on to why this might be a good educational strategy? PG


In light of our current understanding regarding the narture of corollary discharge, many interesting ideas emerge. In attempt to anticipate the various functions of this neural system, certain areas of interest emerge. Specifically, questions of conciousness and visual input pose many area of discussion. Regarding the question of the function of conciousness in conjunction with corollary discharge, one wonders on the nature with which the neural connections communicate between themselves. For instance, studies have attempted to determine the ways in which our brains are able to make connections and thereby retrieve information quickly and efficiently. Obviously, the brain is not orgainzed like a computers retrieval system, in which information is scanned, so to speak, until the correct answer is attained. The brain hypothetically connects many seemingly unrelated associations in an attempt to achieve answers by the coming together of many various parts. An interesting concept produced by Melzack in his study of phantom limbs is the idea of pre-formed conncetions in the brain, dubbed the neomatrix, which links areas of the limbic system, cortical networks, somatosensory receiving area and the adjacent parietal cortex together to form a complex web of various inputs. This area is supposedly responsible for conveying an awareness to the body of self and non-self in an effort to coordinate the actions coherently.

The idea of the neomatrix, while fascinating, poses quite a few complications in terms of studying the actions of the various parts. The visual sensory area, on the other hand, provides perhaps more concrete facets of study. For example, the blind spot of the fovea must use some sort of corollary discharge system for the neurons to fill in the missing spots in our field of vision. Another example would be the actions of optic illusions in which the brain must reconcile the disparity between the two seemingly conflicting bits of information by communicating between the neurons.

The intricacies of corollary discharge leave many questions to be resolved. Among them, the workings of conciousness and visual processing, but even more so, the capabilities not even realized or studied as yet.

Like "the capabilities not even realized or studied yet" and the general sense that CD opens up questions in your mind (as it should). I'm a little less clear about the logic across the middle ground between the CD idea and your geneal enthusiasm. Try and make that a little clearer? We'll come to phantom limbs and blindspots more as we go on. CD is clearly a useful concept for the former, but you may be overgeneralizing it for the latter. We'll see. PG


Whoever would have thought a person could gain fame and fortune by poking himself in the eye! Yet Herman Helmholtz's observations regarding visual perception led him to be the first to infer that some kind of communication *within* the nervous system must exist. Today we refer to that kind of communication as *corollary discharge*. We have seen in the crayfish that the metachronal beat of swimmerets is controlled by a series of ganglia--each one associated with one swimmeret--and the connectives between these ganglia. The ganglia are the CPG's (central pattern generators) which control the beat of individual swimmerets, and the connectives carry the corollary discharge signals that coordinate the movements of all the swimmerets. It should not be surprising that CPG's are distributed throughout the nervous system and not localized solely in the brain. The chicken running around with its head cut off does so without information from the brain, and running is a rather complex movement. At the end of class on Thursday, it was pointed out that most of the studies done on the nervous system tend to be on the brain-controlling aspect of behavior, not on distributed CPG's. This is simply because studying a centralized controller is easier for scientists and does not mean that CPG's are of less import or not as common.

Just the opposite, holds Professor Grobstein--distributed CPG's are probably *more* relevent. I'd like to argue this point. The nervous system is very redundant to ensure against damage. It is fully possible that ordinarily the brain controls the cooridination of swimmeret beat (or whatever behavior you want to study), and the CPG's only take over in times of need. Also, how are the distributed CPG's and their connecting neurons carrying corollary discharge signals organized in the first place? Are they inate? Many behaviors are *learned*. The monkey who can still point to the light even after its dorsal roots have been severed (thus leaving no reafferent signals)could NOT do so if it had previously executed that behavior. This implies that the behavior had to be learned--that the CPG for pointing to the light had to be formed--and the brain could easily be responsible for this.

Finally, when the crayfish's nervous system is lying in a dish, you do not see the output pattern for the metachronal wave unless neurotransmitter is added. How is this n.t. made available in the body? Perhaps the *brain* controls how much should be synthesized, dependant upon a negative feedback system. For these reasons, I cannot yet believe Pr. G when he states that distributed CPG's are more responsible for behaviors than the brain.

You raise some very interesting issues. Yes, given what we've talked about, it COULD be the case that interactive CPG's are a device to assure redundancy and a second order mechanism that comes into play when some master controller fails. This isn't though a REQUIRED conclusion from any of the arguments you've made (any more than its converse is required by what we've talked about). You're drawing a contrast between CPG's and "the brain" which I never intended. Its true that the CPG's we've talked about are located in more caudal parts of the nervous system, but CPG's are found throughout the nervous system (including its most rostral parts), which is to say that one probably ought not try to say that CPG's can do things and "the brain" can do other things; its all the same nervous system. The deeper question you're raising though is whether there is some "master controller" SOMEWHERE which could do what the CPG's do if they didn't do it, and which is NECESSARY for the origin and activation of the CPG's. As you point out, CPG's can emerge from genetic information or from experience. The latter, it turns out, does not NECESSARILY require a master controller: interacting groups of neurons can acquire pattern generating (and recognizing) properties simply because of their interactions. As for the neurotransmitter necessary for swimmeret beat, it certainly is true that more rostral parts of the brain may use descending pathways with that neurotransmitter to active CPG's, but that is quite different from telling them HOW to do their job. THAT information is in the CPG's. PG


Topic: Central Pattern Generators and Corollary Discharge

Thinking about the Central Pattern Generation as a product of simultaneous processes in each separate ganglion first seemed quite contra intuitive to me. During the inclass discussion about what can be the reason for Distributed Control in CPGeneration, I felt very frustrated, because nobody could see what then seemed obvious to me: there is a pattern of input/output activity and, therefore, something central must be coordinating this pattern. I found an analogy to myself - the patterns created by a large number of people at stadiums etc. When a person is a part of such a pattern, she can not see the pattern and regulate her movements according to others - she just performs movements that she was told to perform by central coordinator, who is above (or far away) from each individual and thus can coordinate the temporal relations of movements of each individual. I thought that central coordination was necessary for a pattern to exist. Just because none of the ganglia in the crayfish have the information obtained by view from above and thus should not know that the neurons should fire .5 second after the neurons in the preceding ganglion have fired.

Then we learned about corollary discharge (communication signals between ganglia) and everything seemed clear for a while. The periods of sodium inactivation in different oscillators are coordinated and, as a result, the synchrony of the resulting activity comes about.

Later, I have thought about the issue little more and it seems to me that something is still missing. I am looking for some larger box, which would determine specific pattern for each pattern generator, i.e. how long should the periods of sodium inactivation be, how long should be the time lag of signals sent by the consecutive neuron. I am missing something that would say: this is the pattern each pattern generator will follow and this is the relation between them.

For example, the current behavior a person is performing is walking. Suddenly, the person decides to run. The signal of this decision travels down to the dorsal root ganglia, to motor neurons. Now, how does each particular neuron know what pattern corresponds to running. What initiates the first change in the generated pattern? A good analogy is the marching of a group of soldiers. Yes, they can coordinate the timing of movements according to their neighbors - but there has to be somebody to set the time when the group stops or changes pace. Moreover, each individual soldier has known beforehand the patterns correspondin to each command - start marching with right (or left) leg, certaing way to turn around etc. These patterns were decided centrally.

Overall, I am feeling quite uncomfortable with an organized system which has no hierarchy. Being equal in terms of capabilities, the units of the system should not be able to organize themselves without prior instructions or initial example from one (first, thus in some sense superior) unit. Is there another box that has this function?

VERY worthwhile set of questions/working through things. Thanks. Football stadium analogy worth extending. If everyone in the crowd knows to stand up and then sit down in response to someone to the left of them standing up, a "wave" will travel around the football stadium. The "wave", visible from above, need not be in anyone's mind, either in the crowd or anywhere else, but will simply happen because of the "stand up/sit down" pattern in each individual, and the signalling among them (notice when someone to your left stands up). From this, however, follow two questions: how did the simple instructions get in the minds of any individual? and why does someone stand up in the first place? Do either of these require a "central coordinator" or could they too simply be expressions of interacting simpler entities? For the former, its worth thinking about the mechanisms of evolution. For the latter: maybe someone got excited by a play on the field? PG


The idea that each individual's preception of reality is partly influenced by what is going on inside the nervous system is a very interesting one, and slightly alarming. It brings up the interesting if not unanswearable question of what is reality. I was talking about this same question with a friend of mine the other day. We both had very different experiences with the same person, and one of us thought he was a jerk, while the other thought we was a great guy. There is no objective reality. Two people can look at the same thing, and come up with very different interpretations. I guess that is what keeps this world interesting. If everybody agreed on everything, life would be very boring.

But back to neuro-biology, the fact that our preception of reality is influenced by our nervous system has many impacts on behavior. Maybe people from different backgrounds can take in the exact same inputs, and interpret it in different ways. Additionaly, this new information complicates the picture even more. It is now harder to explain then ever why certain action potentials are interpreted in different ways.

The first part IS neurobiology. And yes, there IS an interesting question worth thinking more about: given the influence of internal states on the interpretation of incoming information, what DOES one mean by reality? Any ideas? As for the second part: how does it "complicate" things? and why does it make it harder to "interpret" action potentials? Make it harder for who? The nervous system or the experimenter? PG


We have, over the last couple of weeks gone through several phases in our interpretation of what behavior is and how it is broken down in the nervous system. We started out with the notion that behavior is nothing but a bunch of chemicals in the nervous system. We then moved on to say that any given behavior is actually a pattern of action potentials within the nervous system. What came out of this theory was the idea that behavior is a pattern, but we referred to that pattern as a "motor symphony"; a pattern of action potentials in motor neurons that get translated into muscle movement, thereby creating any given behavior. What we have done by introducing the idea of pattern generators and corollary discharge, is gone another more detailed step in determining where behavior comes from and what it consists of. Corollary discharge is nothing more than the signals between pattern generators in the nervous system. These signals, however, greatly influence and affect the other pattern generators they come into contact with, thereby affecting behavior as well. So one can argue that the important basis of behavior is the pattern generator itself. It seems that without pattern generators we have no behavior. A couple of interesting questions are raised by this interpretation. Where are the pattern generators located in the body? Could they be centralized in the brain or the spinal chord? Also, what does the variance in the amount of pattern generators within the nervous system say about the "intelligence" of the organism? Perhaps a greater number of pattern generators allows us as humans to have access to a wider range of behavioral patterns and therefore allows us to respond more productively to a problem or situation presented to us. Perhaps the only advantage we have over lower life forms is our number of pattern generators. This idea would certainly put a whole new spin on the our whole concept of choice as well.

Interesting questions (though there is more to the story than just pattern generators). It would certainly be worth having a way to try to determine how many patterns are stored in various nervous systems, and to try and relate that to behavioral complexity or adaptability. And yes, it does potentially relate to choice, and through that probably to the degree of responsibility we feel various organisms have for their behavior. PG


Central Pattern Generation implies that there is a great deal of stored information in the nervous system and that behaviour need not have to come from the outside - has its origin in the nervous system. Infact to me it says that all of our behaviours are a result of stored information. If this is true, then it means that much of who we are is a result of learning by the nervous system, the question to me then remains is how does the nervous system learn? If we were to take away all sensory input at a very early stage in our childhood, would the nervous system still be capable of learning? How much information is stored in the nervous system at this stage (ie how much do we learn and how much is already contained within us)? But then again, is it not also a behaviour to be able to learn - how does that then fit in with everything else?

Each intermediate box or each CPGenerator is capable of doing its own thing, of generating one line of an entire pattern. This fact enhances in my mind the assertion we had already made of the importance of communication between different regions of the nervous system. There are many different ways in which one CPGenerator can affect another, and as a result there are many patterns that may be produced by one particular set and thus there are many different behaviours possible for one particular set of CPGenerators interacting in different ways. If like we said in class, walking, running, jogging and so forth are all the result of the same set of oscillators producing different patterns, then if we say change the way that we normally walk, that would be a change in behaviour ie a change in the pattern, but how does this pattern change? How do the CPGenerators store all of this information and what makes them change it?

Since the nervous system is capable of learning, it also means that it is capable of changing and this supports the fact that behaviours are always changing. Right now what is difficult for me to comprehend is how so much information can be stored in our nervous system and how do the CPGenerators know which pattern is appropriate for a particular situation, even if it is not a result of any input. Slowly however, all the pieces seem to be coming together, and things seem to be making a lot more sense, they are getting more complicated but slowly making more sense!

Glad its more complicated AND making more sense. Yes, we still have to account for learning, and for how it comes to be that particular CPG's are activated at particular times. But, at the same time, we can see both how there could be lots of behaviors and something of how one can change from one to another (by neuronal signals that alter forms of interaction among CPG's). PG


The existence of multiple Central Pattern Generators helps to explain behavior which occurs without any sensory input. Patterns like that of walking, breathing, etc. are generated in the Nervous System from the stored information, and so there is no need for any input into the "box". The fact that there are series of interacting CPG's can probably be used to explain the coordination between some patterns, and the complex behavior that results. It is hard to accustom myself to the notion that there is no most important Central Pattern Generator which would guide all the other ones, because the coordination of different patterns and their timing appear very complicated. Since it is true, however that there is no such thing as central CPG, then the corollary discharges must be very important in the functioning of nervous system. TThings starting inside the box don't have to be random or unpredictable, because they can be patterns of the CPG, and the information for them is stored inside the system. It is interesting to see how the more we learn about nervous system the clearer is the fact that it doesn't rely as much on the input and is in some ways self-sufficient, because in the beginning of the course exactly the opposite appeared to be true.

Nice connection of CPG, CD notions to broader insights into behavior. Agree that the absence of a master CPG counterintuitive for most people, can't help wondering why, whether that more a function of culture or of innate brain organization. Interesting thoughts about relation between CPG/CD and internal spike generation/randomness (still haven't gotten to that last, but will). PG

I'm not sure about the expirement by Herman H. which was described in the last class and the interpretation of its results. Is there also anything I could read about corollary discharges?

Good point. Helmholtz's experiments tend not to be described in neurobiological contexts. Should be, though, in almost any psychobiology text, and I should (but don't) have a good reference for it. Stop by sometime and I'll rummage one up.


In my opinion, the central pattern generation is a very interesting and fascinating phenomenon. Even in the beginning of the course when I tried to logically follow how the nervous system and behavior could be the same, I thought that behavior was due, in part, to the brain. However, the crayfish example proved that to be wrong. In the crayfish, it was proven that there was a CPG in each of the organism's swimmerets. And when the head was removed, the organism was still capable of generating the motor pattern to move. This example also leads to additional evidence that there is no mind. Usually the term mind refers to something other than the brain, but still located in the head. Aside from the fact that there is no separate structural support for the existence of a mind in the head, the idea of multiple CPGs also lends support to its nonexistence. So if the head (brain) was not necessary for the organism's movement, then a mind must not have been either. Therefore, the fact that such behavior can still occur without a brain and is due to the number of CPGs in the various parts of the nervous system is an interesting way in which the nervous system and behavior work and gives evidence showing that there is no such thing as a mind which controls behavior.

For some reason the concept of central pattern generation (CPG) makes behavior seem somewhat mechanical and automatic. Yet, it also gives support to the argument that behavior is the nervous system. Essentially, CPG is when the nervous system contains all the necessary information to generate output patterns or motor symphonies. Since the nervous system has these "memorized" patterns through CPGs, it is the nervous system initiating the movements/behavior without the need of any sensory inputs. This makes behavior seem somewhat mechanical and, in a way, automatic too, because there is some delay time when stopping such a behavior that results from the memorized ouput pattern. For example, when one plays the piano and wants to stop, the person will go further with the piece (play some more notes) before stopping due to a CPG. Furthermore, from the numerous stored motor patterns, it seems as though behavior has much of its origin in the nervous system.

A series of (somewhat disconnected) interesting thoughts. The "automatic" character of behavior due to CPG's is both true and not so true. As we'll see, most actual behaviors don't involve JUST CPG's, but CPG's interacting with input signals. What really intrigues me though is your set of thoughts about "mind" which emerge from the swimmeret story. I'm not sure that we want "mind" to just disappear entirely; its too much a part of everybody's own experience. Can you imagine a way to keep it around which would be consistent with the distributed character of CPG's? PG


From this week's discussion of central pattern generators(CPGs) and corollary discharge signals, I realized that motor behavior can be independently generated from the involvement of an extremely small portion of the nervous system. Originally, I assumed all behavior, even the simplest forms of behavior would require the cooperation and synchronization of inputs and outputs of many boxes in the nervous system, both large and small. However, given the example of swimmerets in crayfish, how the repetitive oscillating motion of swimmerets is generated by cooperation of CPGs in each individual swimmeret and those individual swimmerets are in turn able to independently generate the full motion of the swimmeret it is connected to causes me to change my perception of motor behavior.

The localization and fragmentation of motor control indicates that even small boxes contain an amazing variety of capabilities. A CPG must contain all information necessary for certain motor behaviors, including information needed to generate corollary discharge signals, imput information into the limbs or organs involved in the behavior, receive feedback from the environment, and receive feedback from the motor behavior generated. The concept of the CPG gives further implication that the nervous system is indeed capable of generating all behavior in an organism because such a small portion of the nervous system is able to perform such complex functions needed to exhibit an entire motor behavior. This leaves great potential for larger boxes in the nervous system to perform far more complex behavior such as dreaming and learning.

Nice set of thoughts. A bit ahead of where we actually are (we haven't yet shown that CPG's can do ALL the things you claim for them), but very much in accord with general message of course: yes, fairly simple elements can do what seems at first surprisingly sophisticated things. Which then means that there is room to identify and account for still more sophisticated pieces of behavior. PG


A behavoiral system which uses both central pattern generation and corollary discharge seems very plausible. It only seems logical that some intergal components of behavoir would be "built-in" or genetically programmed into the organism(cpg).Corralary discharge is another form of a built in behavoiral system which is not dependent on external cues. It makes senses that the behavoiral sytem which evolved would use these innate behavoiral programs in conjunction with afferent signaling in order to produce behavoir.

In the complex and industrial world of taoday we can verify the existence of this system by the feelings elicited by a numebr of unnatural phenomena(at least in an evolutionary sense of the species) When we are riding in a car or in space, the external and the internal workings of the nervous sytem are not in accord and as a result a "wierd" feeling is produced.

In a way this is also scary since it diminishes the percieved plasticity of our species. If all of these communications and functions of the nervous system are hardwired then there can in fact be flaws in programming of an individual by genetic mutations or perhaps even environmentally induced. If, however, these flaws are hard wired into the organism the prognosis for the individual modifying its behavoir is not very favourable.

As an aside, I felt the discusiion on where the cpg was located in the crayfish was very intersting and revealed some of the pedagogical techniques employed in this country as well as the proclivities of the models wich exist in both biological and other sciences, which cause us to believe that an entity exists entirely in one compartment. Or that every region in an anatomical or other structure can be assigned a specific and unique role

Thanks. I too am always bemused by/intrigued with the inclination of people to expect/look for a "master controller". The related thought of looking for a particular task for each entity hadn't occurred to me but is so. A very interesting question is whether that inclination is entirely a cultural artifact or has as well a genetic basis. My suspicion is that both are involved, largely because the inclination seems to differ in different individuals within our culture.

The extension to other examples of "wierd" states is appropriate, and we'll talk more about this. As for "hard wiring", I wouldn't worry too much about that, and hopefully you won't either by the end of the course: there is a big difference between knowing how things work and there being inevitable and determined. PG


What is interesting about corollary discharge and its effect on our theory of behavior is that it does not now seem possible to just say simply that the brain equals behavior. So far, I have been able to agree that a series of action potentials, etc. work together to make behavior, but, now, it is apparent that so many various pieces are working together in the nervous system that we cannot describe behavior in simple terms/language - that there is not just one part that causes behavior.

The general description of the effect of corollary discharge is that there are synchronized patterns of behavior that are independent of one another yet still manage to work together. In the case of the crayfishes swimmerets, in order to keep the overall movement in synch with each swimmeret, we learned that there were oscillators that were entrained or in other words slowed or speeded up so the time interval between each swimmeret moving was kept even. It is not really very complicated structures so that I cannot understand what is happening for the behavior to occur but it is definitely not very simple (i.e. - we cannot just explain the phenomena as the crayfish wills itself to contract its swimmerets one at a time for there are so many more pieces in order for the movement to occur). The fact is that with the description of corollary discharge we finally do get the better understanding that there exists intermediate sized boxes inside the bigger box. First, we discussed the smallest box (the neuron) to see how we get behavior but we realized that there had to be more than just these neurons going about and doing everything which to me seems proven by the patterns and sequences provided by corollary discharge because it explains the sort-of independence as well as dependance of the whole system.

Like your "sort-of independence as well as dependence". That is indeed the essence of what we've begun to get accounted for. I'm a little more puzzled by increased skepticism about brain=behavior expressed at the beginning. I agree things aren't "simple", but am not sure why that (apparently) means there must be something other than the nervous system. Maybe what's bothering you is you see less clear "causes" for behavior? That's the word you actually use, and it certainly is less clear that one can point to one "cause" in a complexly interacting system. So maybe what you're saying is that CPG/CD notions don't fit well with an instinct of yours that each behavior should have a single identifying "cause" instead of emerging from a set of interactions? PG


The concepts of the central pattern gererator and corollary discharge signals are helpful in that they bridge the gap between neurons and the concept of the nervous system as a whole. After we learned that the neuron is the building block of the nervous system and that the only thing it does is to generate and conduct action potentials, which are the same in all neurons, it was hard to imagine how the system could create all of the behaviors possible in a human being. Central pattern generators helped us to understand how patterns of neuronal firing can be stored within ganglia and can, without any sort of external input, create behavior. Thus, they are a good model for intermediate boxes - groups of neurons which, as a group, have a specific function within the nervous system.

Next we discovered that central pattern generators actually function as a group of CPGs interacting to make a pattern. Metaphorically, the master CPG is like a script that allof the actors are holding, but each particular actor reads only one part of the script in order to reproduce the play. At this point, we had to look at what we learned about neurons in order to explain the interaction of the ganglia and their neurons. We knew that neurons could have an excitatory or inhibitory effect on each other, so the task was to imagine a circiutry of interconected neurons which would be able to account for the synchrony between the individual CPGs. To return to the metaphor, each small box had to be assigned a role so that all of the CPGs would "speak" atthe right time. At this point, we were able to use more of our knowledge about neurons to understand the interactions. We needed to take account of the refractory period in order to synchronize the firing. We had to consider selective permeability in order to invisage a potential neuron which was always firing due to a constant high Na+ permeability.

Thus, the corollary discharge signals led us to integrate our learning about neuronal caracteristics and to apply it to a practical problem. In the process, we came to understand how neurons create diverse signals, other than simply atering intensity through rate of firing, when all they have to work wwith is an action potential. We are now closer to grasping what goes on in the big empty box inbetween input and output.

Very pretty summary of where we are at the moment. I particularly like your drama metaphor. No thoughts about where we should be going, or what we've missed/failed to make sense of? PG


"How Has the Concept of Central Pattern Generation Changed Your Perception of Behavior?"

I was quite awed by the new revelation that individual experience is not fully dependent on input, but is also influenced by what's already going on in the nervous system. This is not to say that I was unaware of the influence that the chemical environment of the nervous system exerts, but rather that I was amazed to learn that our bodies contain "instruction manuals" in the form of central pattern generators. Central Pattern Generation (CPG) is the production of a motor output pattern in the absence of any input pattern. The information necessary to "compose" certain behaviors is thus stored in the nervous system. We are not simply reacting to the world; instead, we are also "controlled" by the inner workings of that infamous "other" self.

As exemplified when observing a pianist, the rapid finger movement of the pianist is difficult to interrupt because a central pattern is directing the behavior. This suggests that just as an exercised heart increases the efficiency of oxygen transfer, an exercised neuron will also perform at a higher level. It seems that the old expression "practice makes perfect" applies to the nervous system and to behavior too. The internal "instruction manual" is thus also developed by practice and holds the potential for developing acquired behavior.

With these discoveries, I have found myself grappling once again with the old assumption that behavioral practices are culturally and socially taught. This notion is truly transparent in light if the CPG. On a different note, though, the CPG is not the "great" conductor of the nervous system. A solo CPG is not the supreme director and an output pattern is not the consequence of a single CPG. A segment of a CPG carries not the entire code, but rather the processing potential to generate a fragmentary sequence in a long course of events. It is imperative that these central pattern generators are connected, for it is through communication between the CPG's that recognizable output is achieved. This group interaction seems to bring us back "full circle," for the grand "Big Brother" is still out of reach.

In a way, I find this reassuring!

NICE set of general thoughts from CPG, CD. Though "This notion is truly transparent in light of the CPG" not entirely clear. What's the relation to a presumption of behavior as largely "culturally and socially taught"? Challenges or supports that assumption? PG


As we begin to understand the concept of corollary discharge signaling in nervous systems, I ask myself where lies the main impact of this concept on our quest to understand behavior. We know that basically, corollary discharge signals (CDS) inform other neurons of the sending neuron's current disposition and activity so they may perhaps act in a more coordinated fashion based on this information. This type of principle in not new to either man made or natural systems. Many machines from the microprocessors in our auto engines to molecular sized machines in living cells make use of information exchange and feedback to regulate processes. It is really no surprise that the neurons of our nervous system would operate using this technique as well.

When pondering what the presence of CDS means to our understanding of the nervous system, I realized it may have impact regarding our question of who or what is "in charge" of the system as a whole. Professor Grobstein has already stated that he will ultimately show that nothing is actually "in charge" overall. I believe that the presence of CDS may be evidence for this. At a minimum CDS enables neurons to communicate and thus act in concert apart from other influence. This obviates the need for a central component that is "in charge" because it allows for neural symphony based on interactions between multiple components isolated from the rest. But does it prove that nothing is in charge? The answer hinges in the light of the evidence that is used to examine the problem. The knowledge that CDS exists does not disprove the possibility of there being something in charge of the overall system. In order to eliminate the possibility of a component that is in charge, we must examine how individual and groups of boxes within our system interact to create behavior. This is easier to do in simpler systems like the swimmerets of a crayfish. Interaction involving CDS allows for the coordination of swimmeret movement (metachronal wave). This can be demonstrated in the absence of the rest of the nervous system, providing an example of a motor symphony without a sole conductor. How similar is this to some of our own behavior? Ours is certainly more varied and complex, but perhaps our brain, rather than having an area that is "in charge," may actually operate like a vast collection of ganglia in the abdomen of a crayfish, with sheer numbers of boxes and connections allowing for the diversity of behavior observed.

Yep, worth considering the possibility. No, not proven (maybe not provable?), but clearly so in some respects, a (for most people) novel way of imagining how things MIGHT be, and will look more and more like this as the course goes on (and as research on brain and behavior goes on). PG


the term Central Pattern GenerAtion very directly suggests a property that is centrally located and possibly singularly positioned; just as the central nervous system, however extensive, is a tangibly singular complex. in reference to the discussion about why there are many CPG's located within the N.S., yes the crayfish does not have to worry about losing a ganglion and thus losing it's CPG. But there is an underlying common thread woven throughout the natural world and its systems that strongly supports the notion that i recall another student made in class. i.e. redundancy as a safeguard against failure. although we're are beginning to see that this concept does not pertain to CPG and its reasons for multiplicity, i was interested in its relevancy to other natural systems. the analogy of the CPG to the flocks of flying feathered friends parallels the idea of endurance in numbers by the fact that if one birdie is lost, shot down, or whatever suits your fancy to get him out of the formation, the rest og the formation adjusts to compensate for the lack of bird. the interesting part is the inherent ability of the rest of the birds to adjust to such a loss upon their immediate interaction.

Hmmm. "singular", "tangibly singular" not entirely clear to me. Am interested in the "redundancy" issue, and do agree that an ability to compensate for disappearance of parts is a common thread through biology. The interesting question is whether that is because losing elements is a common selection pressure or whether instead there is some deeper explanation. Can imagine any? PG


The concepts of a central pattern generator and corollary discharge signals do not change my thinking about behavior, but instead affirm what seems to me like common sense. Behavior like walking could not possibly be controlled by constant sensory input. A central pattern generator controls the pace, the stride length, the pattern of leg movement, etc. Sensory input can change the pattern, such as when the foot is lifted higher to avoid an obstacle in the path. It is easy to think of the nervous system as a big box having control over the little parts but when common behaviors like breathing are considered, they really could not be sufficiently controled without a reflex like pattern. Why take something relatively simple to understand on an undetailed level and make it so complicated?

VERY interesting issue. Science frequently proceeds by disproving the (to some people) intuitively unlikely and supporting the (again to some people) intuitively obvious. At that level, the important point is that people are different, what is "intuitively obvious" to some is "intuitively unlikely" to others, and what science does is to create some common set of experiences to mediate between different intuitive perspectives. What's interesting about the particular case of central pattern generation is that most neurobiologists actually thought it was intuitively "likely" that motor symphonies had their origins in sensory feedback, CPG's for neurobiologists were the "unlikely" and in some sense revolutionary possibility. There are interesting and complicated reasons for this, which one might boil down by saying that scientists (and many non-scientists) found it easier to believe in (and explore) forms of organization which had a clear explanation in terms of sensory input. Which then leads to the next point: even when supporting the "intuitively obvious (to some people)", science usually turns up additional things which even those to whom a particular something is "intuitively obvious" hadn't yet recognized. Recognition of CPG's, for example, clearly implies a remarkable amount of stored information in the nervous system, makes clearer the importance of coordinating information within the nervous system, and, generally, inclines one to think somewhat differently about how and why particular behaviors are exhibited at particular times. PG



It has been very interesting to learn about the central pattern generator (CPG). During the first day of class when we were trying to define behavior, I remember thinking that it was difficult to do because many words can describe/define behavior, but there didn't seem to be an all encompassing definition. Now, I can understand more and more why our behaviors are so rich, why it was difficult to define behavior, after learning about how the nervous system can store or generate patterns of action potentials corresponding to a particular behavior without any external input.

Glad its helping to think about behavior. But can you be a little more concrete, give some more details about exactly how? What new issues does it raise in your mind? PG

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