As the mystery of behavior unravels, it is important to see that corollary discharge is yet another concept that effects behavior. In normal behavior, there is a different time relation between certain parts of the body. For example when an action potential is fired, it doesn't simultaneously produce the behavior desired. It starts a chain of reactions. This is an important concept to understand because behavior revolves around this very aspect of neural communication. The small boxes each have to communicate with each other in order to successful produce the right behavior. A copy of a signal is sent from one box to another saying that it has come to a decision. This is the concept of corollary discharge. To further understand corollary discharge, the idea of central pattern generation is also important to look at. CPG is a motor symphony, pattern of connections through motor neurons. A CPG relys a message and the CD fulfills the wish. In the end it is important to see that communication among the neurons is pertinent to behavior. If the neurons didn't communicate, the idea of autonomy would not exist, and neither would the ideas of choice, and purposefulness. CD signals create a set of expectations which can be used for interpretation in the nervous system, ultimately leading to a certain behavior. In essence, CD's are the very path that ultimatley wind down the many different possiblities of many outputs from one input. It gives the NS a sense of direction.
Some appealing poetic images. Yes, CD contributes very importantly to coherence/coordination of nervous system activity. Have ways to relating this more specifically to, for example, the vaguer ideas of "choice", "purposefulness"? PG
Corollary discharge signals both help us to account for the complexity of behavior and also raise many ethical questions.
First of all, CD signals account for the differences of people's responses to the same input. In general, it is very hard to predict how a person will react to a specific input, and there is no guarantee that two different people will react similarly.
Also, CD signals help us understand such phenomena as the motor sympony (different muscles contracting at the specific times to one another, and how the complex behavior can be broken down into several CPG's of the simpler behaviors that are communicating with each other by the means of CD signals). An example of such would be a person learning to play accordeon. Let's say, he learns to play the left hand and the right hand separately. By doing this, the person modifies the existing CPGs to form two CPG: the right hand playing, and the left hand playing. But then, in order to put them together the person has to use his CD signals to produce the movements that would be timed relatively to one another and the right music would be played.
Also, CD signal help us to understand "phantom limbs" and related phenomena. One of such related behaviors is having one's limbs asleep. For example, if one were to sit in an uncomfortable position for a long period of time, one's foot would "fall asleep". When such a person would get up and try to move, he would be able to produce the general movenment he would produce normally (motor symphony is present), but he would not be able to adjust to random position of the foot efficiently (inputs are inhibited). But CD signals sent from the foot would nevertheless tell a person the position his foot should be at.
CD signals also help explain the behaviors that are produced by the mismatches between CD signals and the input signal: motion sickness, astronaut sickness, etc.
Some of the questions that arise in my mind are:
Why are some people able to consciously control their motion sickness? Does I-function play a role similar to the one that input signals play in the motor simphony: the one of adjusting otherwise ready output?
Also a question about choices:
If we were to think of choices as involuntary (biologically determined) actions, this would relate to an issue of fatalism and free will. Such a view would support a theory of fatalism, as in : "Everything that happened was meant to happen and one could not do anything to change it". The main objection that i have to such a view on choosing is that to me it seems that at a particular point I could choose either option, and that it is me (the I-function), not my nervous system, who does the choosing.
Nice CD thoughts/questions. I'm not sure though about the foot asleep one. In that case, there is no (or reduced) sensory input, but one can (I think) still move the limb. Hence there would be both movement and appropriate CD's, no? As for fatalism: that's important and we'll get to the question of whether there is something "choosing", as opposed to just CD's and CPG's. Yes, the "I-function", but no not "me versus the nervous system" (since its all one thing). That be ok? PG
In general, corollary discharge signals help to understand inconsistent behaviors in experimental conditions where everything is pretty much controlled for, but differences still occur between trials. One thing that I'm not certain about is the connection of the corollary discharge with the I-function. One interpretation is that corollary discharges are spontaneous excitations of the neuron that lead to output occurring without any related input. Or, could it be that corollary discharges are related to an organism's predispositions, such as their genetic makeup or experiential influences. The second idea seems like it would have more influence on output by the effects it has on the processing of specific inputs. But maybe this is an additional aspect of corollary discharge. I guess I'm just not sure how encompassing the idea of the corollary discharge really is. Overall, it does help in my understanding of behavior, but I think it would help more if I had a better understanding of it.
Fair enough. Has gotten any better since you wrote this? Regardless, your prior points quite good ones. Yes, CD could help account for variations in behavior which don't seem to have any explanation in terms of input signals. And, they don't bear any clear relation to the "I-function", which is to say they can exist independently of it (but also might contribute to it, and be a tool of it, as we'll come to later). How encompassing an idea? The strict definition of the term is "signals generated by pattern generating circuitry which go to circuitry other than motoneurons and influence their function". They might, or might not, arise spontaneously. It is worth, though, thinking about intercircuit coordination in cases in additional to pattern generating circuitry, and how this might help to explain behavior. That help? PG
erin hunter and I have been going through our notes and discussing possible topics for the last 45 minutes. We were going to write another dialouge on the general topic of CDs and how understanding them makes sense of behavior. Basically, we have reached the conclusion that CDs are communication between CPGs (the level of boxes one step above neurons) and that acknowledging their existence is another step away from the linear, causal "stimulus-response" model of behavior towards a more interconnected model. This wider, more permissive model allows for phenomena like phantom limbs, motion sickness, etc. erin wants to say something about choice--that CDs also affect how one must consider the philosophical discussion of "choice" in behavior. (amber: "how so?")
erin: to what effect is the i-fcn controlling behavior, and to what effect is the I-fcn just CPGs and CDs?
amber: every phenomen we discuss will prolly continue to erode the I-function and assign it fewer and fewer functions until it disappears. The I-fcn (in my opinion) is an umbrella under which to put all the behavioral things we don't understand yet.
erin: so do you think that each person's unique behavior can be explained by the individual set-ups of neurons, cpgs, etc. instead of the i-fcn?
amber: couldn't have said it better myself. But I also think that "explanation" of that is near impossible--it's too complex, so much so that it might not even be considered as an option.
erin: i'll be the first to admit that i don't really understand it well enough to explain it.
amber: ok, then I'll be the second. :)
And may never. Indeed, won't ever if it is really true that brain=behavior. Understanding changes brain which in turn changes what is being studied. An infinite loop (seriously). And I think it is true that I-function will get smaller and smaller. For a while. But betcha it DOESN'T disappear. Not, at least, as a distinguishable box. Which, yes, has the same things making it up as the rest of the brain, but which bears a distinctive relation to the rest of the brain. PG
The concept of central pattern generation and corallary discharges seems both absolutely amazing and yet completely logical to me. The idea of such a delicate and complex amount of control existing in the nervous system seems flabbergasting, but it's form and system are so clearly functional that it removes the mystique. It follows perfectly the metaphor of communicating boxes made out of smaller boxes that comprises the brain and nervous system.
This gives much credence to the old cliche "practice makes perfect" in that the continued use of a CPG and the corollary discharges would naturally lead to increasing accuracy of movement. It also helps me to understand why it is that memory of physical movement such as tying shoes is not affected in the same way that memory of intellectual things such as dates, names, etc. Movement and actions that are performed without thought, such as absent mindedly scratching an itch, or sleep walking, are easy to account for in terms of monitoring by corollary discharges and CPGs.
One thing I am curious about in relation to the subject of CPGs is the length of time that the pathways are in exsistence when not in use. Another cliche pops into mind, 'It's like riding a bike; once you learn you never fall off.' Is this true, do you never forget? No, this can't possibly be true, after all, it only takes a couple of months of not playing a guitar to lose the ability to perform anywhere near the former level. Perhaps this is related to the complexity of the pattern. Hmmm. Just a thought.
And what's the deal with complexity, anyhow? Does something really complex mean that it has a lot of associated actions, or that it requires more concentration? Is tying a knot more complex a movement than splitting a hair? I guess I would need to define complexity before I rambled on too much farther, so I won't go too far. But it seems as if the level of complexity in the really vague way that I am thinking of it may be measured in the amount of corollary discharges needed. But then again, I'm also combining proprioception, CDs, and autonomy. I guess I'm not being coherent enough to continue this, but that's my question about behavior... I guess... sort of.
No need for diffidence. An interesting and appropriate line of thinking. But you need to fill in some details. How does CPG and CD help with "practice makes perfect"? Yes, it does suggest a difference between some kinds of memory/skills and others (we'll talk more about this in a while). And that does lead on to why some things are more stable, others less so (will do some of this, but there's lots of room here for you/others to come up with new ideas). As for complexity ... that too is open and interesting turf. Yes, I suspect there is SOME relation to numbers of semi-autonomous parts, and hence to importance of interactions (communicating pathways, CD's). PG
A corollary discharge is necessary in conjunction with a central pattern generator, because it seems to be the integration factor. The nervous system will always have something being generated internally. This is necessary because there is an intermediary between what is happening in the outside world and what goes on inside the brain. Already in the transmitting of information from the outside world to the inner cognitive centers of the brain there has been some sort of paradigm or "character" given to the message. The pattern in which the neurons fire, is already imparting some sort of subjective character to the message, thus when it arrives in the brain, there must be some way to begin to interpret and integrate this message. A corollary discharge is just such a signal. Because behaviour is a result of our genes and the influences that the external world exerts upon us, this integration is vital for producing some sort of output. Of the control exerted the most important is that of lateral inhibition, allowing one motor symphony to proceed, but not having discordance by having all the possible patterns occurring. In this situation, for any particular output there must only be one coordinated and integrated pattern within the individual. Thus the corollary discharge signals ensures that we are not exploding into all the realistically possible pathways. The corollary signal is what distinguishes within ourselves between actuality and possibility. It is this distinction which is vital in producing some sort of behaviour.
As humans the different regions of our brain is capable of imaging all sorts of things and communicating it to other parts of the brain. A corollary discharge relays the message and acts upon the appropriate symphony for response, whether it be the generation of another idea, or the movement of the muscles. Thus the corollary discharge is the integration unit of the mind.
A very sweeping, broad, and intriguing assertion. It is certainly true that corollary discharge signals constrain and coordinate what different parts of the brain are in principle capable of doing independently, and so in the absence of coordination among them. And that is almost certainly true not only for the clear cases of coordination among CPG's and action circuits in general, but perhaps for various more abstract thoughts and drives as well. I'm less certain what you mean by a "subjective character" in incoming signals, why this requires corollary discharge, and how it acts, but will think about that as well. PG
It seems that CD plays a very significant role in explaining behavior since it helps coordinate information between CPG and other boxes, and it also effects sensory input. It also explains the body's awareness of itself without the "I-function" being active. Perhaps, some of the unexplainable human behaviors, such as "phantom limb" sensations can be revealed by CD. Perhaps our body can function entirely on its own without even the "I-function" being turned on or us being conscious of what our body is doing? For example, when sleepwalking, our "I-function" is not on, but we are able to wander through our own house with our eyes close and are able to open the refrigerator and pour ourselves something to drink. Can this be explained by CD? We are not actually obtaining any inputs from ourselves, nor are we fully conscious of our behaviors and thus have little or not control of it. This must mean that something, such as CD along with CPG, is directing our body to do such things.
Very nice idea/extension. Will talk about sleep-walking a little later in course, precisely in context of absence of "I-function". So yes, lots of coordinating signals without that. PG
If all circumstances in our memory (our experiences) inhibit some action in some way, what we call a "choice", may not be a "choice" at all. With corrilary discharge, we see certain actions or recollections inhibiting future actions. We see past events having a direct influence on present events. And in a way, if this world (this reality) is nothing more than what we create, could all our actions be indefinetly dictated starting with the beginning of time?
This seems an obsurd presumption, but when we break the process down, and work backwads, we see that each event is directly or indirectly influenced by a previous event. Indeed the only difference between humans, and a mammel of "lower" intelligence, is that we are conscious of our thought process. This consciousness is what we call "choice."
So, if our brain interpreted our "choices" differently, producing different actions , would we have created a different reality for ourselves? Because our brain is simply a record of past events, and quite possibly a code for future events, could changes in our interactions with this world and the people in it yeild a change in a collective reality?
With every supporting case I find for this hypothesis, I also learn of a contradicting one. Maybe it is not quite contradicting though. Maybe that case simply deals on a microcosmic level, where the details become amplified until they are out of context. And we look at these details as if they were the entire picture. In some ways, science has become a type of religion because of this. Science seeks to take the collective whole and encompass everything in this reality, when in fact it works at such micro or macro levels, that true meanings (in relation to this reality) become obscured.
When confronted with the possibility of a corrilary discharge, we are encompassing the micro, macro and real cosms all at once. There are the electrons, quarks and leptons that make up an action potential, and there are the brain's effects on it's outside environment, or reality, as well as the entire universe. There is nothing in this world that does not feel the effect of even the smallest change in space or time.
I look at corrilary discharge and am overwhelmed by the possibilities that extend in each direction. Afterall, we are after the best model, should not look inward as well as outward?
Indeed, ought to look in all directions ... and keep adding observations indefinitely. Which, of course, changes the thing (the nervous system) which both makes and interprets the observations. So maybe things aren't quite so determined by the past as you suggest ... and science isn't so limited. All that triggered by a discussion of corollary discharge? Must be good for something, huh? PG
Corollary discharge is an interesting mechanism, and helps explain several areas of the nervous system. It makes sense of the phenomena of phantom limbs, and also helps explain several types of motion sickness. The mismatching signals that the brain receives from corrolary discharge and input create the pain and the sickness. But it seems odd that the body has a mechanism that causes unreasonable pain or sickness. The important point with the symptoms of motion sickness and photntom limbs is that both of these situations are not normal, or expected to the body. So they represent a malfunction in a normally smooth running information collection and comparision process. These symptoms can be examined, and through them, you can see how the nervous system normally works.
The motion sickness problem is recent problem, that has only been encountered by modern societies. It is a reminder that while we may become more advanced in our technology, we cannot go beyond the limits of what we were originally adapted for. Originally, people just propelled themselves. So all of our nervous mechanisms are for walking or moving oursleves, and coordinating our movement. But with the advent of technology, we have begun to be moved by things other than ourselves. This causes confusion for our nervous systems. Also, we are spcifically adapted to the gravitational pull on earth. So when astronauts go into outer space where the gravitational pull is different, they also become sick. Small conflicts like this remind us that we are only human, and that there are limits to what we can technologically do.
Very much agree with your point, an important and subtle one, that our culture puts us in situations which are novel in terms of evolution and hence we may not have the responses appropriate for it. What's additionally interesting though is that "feeling sick" motivates us to find equally novel ways to deal with the novel circumstances. So maybe we can both be "only human" and have some hope, at any given time, of being more than that (or at least more than what that means at any given time)? PG
Correlary discharge helps to make better sense of behvior. When a neuron is activated, before it carries out it's specific pattern and function, it sends another message to other areas of the brain to have a copy of the command"on file". It makes it possible for the body to have have a back-up copy or a "double check" system, to make sure that the proper action or system of actions was activated. Motion sickness helps to clarify this; the muscles of our body aren't registering any movement so our brain doesn't get any messages telling us that we are moving, yet our inner ear senses the swaying and we become ill. It makes sense that a back up system to monitor our intended activities (neuron activity) and the outcome of our neurons activity, considering the vast responsibilities that our brain must carry out.
Its not so much a "backup" system, in the sense of keeping a copy of the command stored somewhere in case its needed again. Better to think of it as notification by one part of the brain to another that the first has done something, and the second may want to do something differently because of that, or should expect something because of it (like an input from the inner ear). That make sense? PG
It is interesting to think about the evolutionary implications of the development of a center in the brain that monitors and contrasts sensory input with the corollary discharge signals. That we have developed this center and that we are still affected by itin the cases of motion sickness, jet lag, and phantom limb syndrome, for examplesuggests that it is a part of the human experience to have a view of "reality" that differs from the reality of "reality". Put in more comprehensible terms, it seems that humans, as a species, have found it adaptive to maintain a system to check our perception of the outside world. This would suggest that our perceptions, our internal reflection of our world, tends to vary with the original input. The higher levels of processing may therefore interpret original sensory input to a degree that its reflection of the input is weakened. The system of checking the outside input with our internal reflection of this input also suggests the need to maintain a feel for the outside inputthat our tendency to stray from the original outside input and to create internal models that stray further and further from the original idea is selected against. It is to say that it is beneficial if not necessary to keep in touch with the "outside world" and it is not possible to function at our best while living in a world that exists entirely within our heads without regard to the external input that bombards us constantly. This argues against the idea that we exist as figments of our own imaginationsthat the world is because we think it is. That we feel ill at ease when we our internal perceptions stray from the input received more directly from the external world suggests that there is an external world from which to stray. Perhaps there is an external reality after all.
Yes, indeed. Or at least you've given the best evidence for it that I know. I don't think though that the necessity for checking is because our perceptions tend to "vary with the original input". An alternate possibility is that the internal model is more fundamental, and that we simply use input to check/update it. Possible? Anyhow, nice thinking through of interesting problem. PG
Corollary discharges help better understand behavior for several reasons. They provide the connection between CPGs and other parts of the nervous system. This affects how the nervous system processes information and what outputs it has. For example, when I run the images of my surroundings appear to be moving. I know that in fact it is my body that is moving because corollary discharges from my CPGs for my running pattern are sent to the rest of my body telling it I am moving. This message reaches my box for vision and tells my eyes how to interpret the movement that is perceived. This is how I know that I am moving and not my surroundings.
The connection created by corollary discharges between CPGs and other "boxes" of the nervous system also helps account for the different behaviors exhibited by one organism to the same input. A female cricket might not respond to the male song not because it does not hear it or is not inclined to do so, but simply because it might be carrying out some other behavior. The corollary discharge created by that behavior, inhibits an output to the male song.
Corollary discharge signals also help explain why people and organisms in general react differently under the same circumstances. Corollary discharge signals are different in every person, which makes everyone's perception of reality different. This unique perception of the reality makes every organisms inputs and outputs distinct.
Corollary discharge signals help better understand certain patterns of behavior and how it is that the connections between boxes of neurons create behaviors. There still remains much to be accounted for in the understanding of behavior and the workings of the different levels of organization of the brain and the nervous system.
Crystal clear summary of what we talked about. So ... you REALLY think that doesn't account for ALL of behavior? How come? Pg
So we've learned that corollary discharge is responsible for a certain type of neuron communication. It signals when to fire and provides feedback about which neurons have fired and when. It may explain how a message travelling towards more than one other neuron is only passed on by one neuron. That neuron signals, through corollary discharge, that the others don't need to fire because it has. I wonder now if corollary discharge has something to do with willpower or inhibition and subtle movements.
There could be some neural activity that is increasing the likelihood that the person will engage in a behavior, say, eating. If this behavior is a motor symphony, it is possible that the activity that we interpret as desire is regulated by not just a single pathway but a whole network. Perhaps corollary discharge signals from one neuron to others prevents the desire from being too strong by inhibiting some neurons farther in the pathway. This could prevent the eating behavior. Corollary discharge, in a similar way, may be responsible for inhibition of say overtly displaying sexual desires.
Most interesting is how corollary discharge signals may function in subtle movements. Just as good and rapid piano playing supports the idea of a central pattern generator, soft piano playing supports corollary discharge. To be able to press a key with the precisely desired force at a very specific pace is very difficult. I would imagine that as the finger approaches the key there is constant regulation of the speed and force with which it nears the key. There must be corollary discharge signals that let one neuron know that, say, too many others fired and the finger is approaching too rapidly so the anchor(last) neuron must compensate by perhaps not firing at all. If good piano playing requires a high quality of motor symphony and thus a specific central pattern generator, and if such playing must be learned, is it that CPG isn't present from birth and develops as we "learn". It's not genetic but I still don't know if its potential to bring on motor symphony is there from birthand "learning" means turning off that which inhibits the CPG or if CPG itself, from the beginning, can affect behavior but only once sufficient corollary discharge signals have developed("learning"). So is "learning" the rise of the CPG or the rise of CD to coordinate the CPG?
Probably both ... and some other things as well (remember the nervous system does anything at least six different ways?). You've got some interesting and very subtle ideas out of our CD discussion. Simple CD signals tend to coordinate activity in groups of neurons, but yes indeed it is possible that similar signals may help to adjust and compensate even CPG patterns as they are being played out. And yes, of course, they may help to explain regulation ("inhibition") of various motivational states. PG
The idea of corollary discharge signals, signals from one central pattern generator to another, or from one ganglion to another, that inform the recipient of the actions of the sender, does much to explain many aspects of behaviour that our model previously was unable to incorporate into its predictions.
The phenomenon of the "phantom limb" has very many interesting observations, and many equally interesting conclusions can be drawn from them. It allows us to practice our methodology of determining function by effect of absence, without involving the experimenters in ethical issues. The information that amputees provide, that they feel the presence of the limb even in its absence, even when they cognitively know that it is no longer there, and that they often feel discomfort in the limb, implies that most of the motor patterns that involve movement of the particular limb are the results of central pattern generators, and that somehow these CPGs still exist after amputation. Also, they are able to communicate well with other CPGs and with the brain, including the I- function of self- awareness, that makes the "person" aware of the feeling of substance of a limb that no longer exists. Corollary discharge patterns fit nicely into the communications niche; the person hence knows where the limb is without sensory input because of the still- functioning firing system of corollary discharge signals.
Corollary discharge signals, coupled with central pattern generation, indicate the functioning of a higher level of organisation within the nervous system. They can be thought of as communications pathways, or methods, or processes for and between central pattern generators that are inclusive of the universality of the basic structural unit (the neuron) and the basic functional unit (the action potential), and the variations observed in behaviours that have the same inputs. They can sometimes serve as the input itself into CPGs, that the immediately modifies the interpretation by the nervous system of the state of the outside world. Hence interpretations of exactly the same sentence or word can be widely varying between two different individuals.
What happens, for example, when one walks off a treadmill upon which one has been walking for a while at a reasonably rapid pace, faster than normal walking gait? You still feels as if the body is moving through space in the smooth, rapid manner as the pace set by the machine, while at the same time your feet are telling your brain that they are not really moving as fast as before! Your feet try to move at the same rate as before, but the ground simply won't provide the same give as the treadmill does, i.e., the treadmill moves along with your legs, and so you are able to take large strides and not feel the effect of dragging your body against gravity in tune to those large strides. Off the treadmill, you has no such luxury, and gravity catches up with you, although your brain has not yet realized it.
In other words, the central pattern generator still continues to fire and create a motor symphony of large strides, while sensory inputs inform the brain that the ground isn't moving as fast anymore- there is a disjunction between the sensory inputs and the corollary discharge signals that the central pattern generator sends to the other parts of the body and the I- function, and so you feel like you're still moving through space at the same rate as you were before. Thus the feeling of sudden physical disorientation one experiences as a result of perturbations of the inertia of motion could be explained by incomparable inputs and corollary discharge signals from the central pattern generators that initiate the motor symphonies in question.
Sophisticated review, with nice extension. Yes, lots of situations in which we "notice" a mismatch between input and expectation. Might even, in fact, be a general lesson about the "I-function" there, one we'll try and come back to. PG
Corollary discharge signals help explain many of the previously unexplainable and incomprehensible components of behavior in the "brain is behavior" model. One of the overwhelmingly apparent aspects of behavior is that the nervous system often produces different outputs for the same set of inputs, and such a system is more easily justifiable with the presence of corollary discharge signals. Since such signals reach many more neurons than the average action potential, it is possible for differnt outputs and motor symphonies to be produced because a greater number of neurons may be activated at differnt times. Corollary discharge signals therefore expand on the concept of the "boxes" of the nervous system. Although one still recognizes that there are distinct "boxes" of various sizes that comprise the nervous system, the links between them are multiplied with the existence of corollary discharge signals.
Another function of corollary discharge signals is that they are continuous monitors of sensory input in that they provide a set of expectations for what the sensory should be and compare in relation to what it is. Such a function helps explain multiple examples of behavioral phenomenon, most specifically the discomfort felt by amputees in their amputated limbs and various cases of motion sickness.
The most fundamental function of corollary discharge signals is to provide a basis for central pattern generaters to work together without relying on control from any other source. Some of the specifics of how this system works have been previously explained and it is evident that corollary discharge signals account for much of the unaccounted for in a more simplistic "box" model of the nervous system, such as the presence of outputs without inputs, coordinated outputs and other behavioral patterns. In viewing the brain (or nervous system) as behavior, the function of CD signals becomes essential because they justify that much of the source of behavior is purely biological and they show the vast connections of all the parts of the nervous system.
Nice description of both some specifics and generalities. Can imagine any additional things CDs might help explain? PG
So, I have been thinking about a few things in relation to Central Pattern Generators and Corollary Digschages (cPGs and CDs respectively)
The first thing comes from reading a few of the essays that were written by last year's folks. One woman talked about a group of children who were taught their multiplication tables by doing them along with clapping. The question was asked at the end about why that might be a good way to teach them. I wonder. I think that in many ways, it is beneficial. Corollary Discharge depends on a CPG and can then seemingly go on without the person being "conscious" of it (okay, loaded statement, I know) What I am thinking about is the way that an athelete can routinely perform a certain activity at a certain level. Or, something that I can relate to more, when a pianist can play a piece over and over without thinking about it. CDs are involved in this process. However, if that pianist starts to think to hard about what she is doing, sometimes a problem can arise as the process is no longer automatic. Why does that happen? Learning the multiplication tables with clapping means that clapping may elicit the recitation of the tables in one's head, or out loud, but if asked to really think about them, it might be more difficult. Still it seems like a good way to start. The alphabet song is another one of these types of things. If I'm asked to alphabetize something, I find myself singing that song. There are some letters that I can't remember their order without singing it. Okay, I don't know where I was going with that. I'm sorry, if I sort it out, I'll write more. The other thing that i have been thinking about is phantom limbs. I mostly have questions about that. I still don't understand why the feeling would be unpleasent and uncomfortable (for the limb, I do understand why it might be unplesant for the person to experience something in a limb that isn't there.
"From the attic came an unearthly howl. The whole scene had
an eerie, surreal quality, like when you're on vacation in
another city and "Jeopardy" comes on at 7 P.M. instead of 7:30."
--Deep thought from a random high school student
Yep, internal model, against which input tested, yielding distress when they don't match. Phantom limb discomfort the same? Can't be "for the limb", since perception is a function not of limb but of nervous system. But can be "referred" to limb, since that's the object exhibiting a mismatch of CD and input. That OK? And yes, lots of things not only don't depend on "consciousness" ("I-function" a safer term). We'll talk more about that. PG
The corollary discharge signal, as I understand it, seems to be an internal signal that "informs" a neuron of its neighbors' actions and thus allows coordination of various behavioral patterns. In other words, it allows different bhavioral patterns to arrange themselves in what can be seen as an acceptable motor symphony, rather than a discordant jumble of "notes". Earlier in the course, you mentioned that the corollary discharge signal was not a sensory signal. In the case of stretch receptors, however, the sensory neuron directly contacts the motor neuron. Here, the motor neuron is "informed" of an action affecting its neighbor (the sensory neuron) and it goes on to act in a coordinated manner. Wouldn't the signal it receives from the sensory neuron be an example of corollary discharge also, and if so, couldn't it be termed a sensory signal as it is coming from a sensory neuron?
CD most typically a signal from one GROUP of neurons to another GROUP of neurons, but yes, you've got the important idea. Yes, sensory neuron to motoneuron is, in a sense, one neuron telling another what it is doing. One tends to use CD for signals which originate inside the nervous system, rather than in sensory pathways, to try and emphasize the extent to which internal organization/coordination can be independent of sensory input. Hence, one wouldn't normally call the sensory to motor signal a CD (but there is indeed some fuzziness in definition there, as is always the case when terms have arisen in different contexts for different purposes). PG
As we have become more specific about the concepts that are associated with the production of behavior, the idea of corollary discharge and central pattern generators addresses this issue in a new light. It would seem that a lot of behavioral information is then stored in the nervous system somewhere, so that these signals can be generated. Corollary discharge sends the impulses through to the ganglions, yet they are not seeing the whole picture of how their individual signals are affecting the behavior. Where is the ultimate CPG then for these types of actions? Is it in fact the brain, or does this governing force lie somewhere else within the body? We've talked about how the brain is not the be all end all of behavior...can the spinal chord be responsible for the action we may see generated before us? Where is it that we learn all of these behaviors that end up being stored to automatically occur anyway? The process of learning behavior so that it becomes automatic is an interesting process. It would seem to me that these behaviors do NOT always have this CPG/corollary discharge system. Something must be done prior to that so that the behavior can set up the map that it then follows. The biology behind that is absolutely fascinating. The impulses are like a stream of water that is running down a sand pile. After a bit of time, the water has created a groove for itself and it doesn't have to do the work anymore; it just flows right on down to the bottom. So is the process of learning these automatic behaviors. If you tilt the bucket of sand, or put a rock in the way of the path of water, it is going to have to re-route before it can be comfortable again. This happens when a behavior has to be modified due to any of the possible circumstances. The old tract will still be present for a while which means that the behavior can slip back into its old groove it the switch is soon enough. When the tract does not get used for a while it might begin to fill in, but will be easier to carve out again if needed. So it seems to happen with respect to behavior. This is especially true with respect to addiction. Although it might be questionable as to whether or not the addictive behaviors have been taken over by corollary discharge due to the enormous amount of factors involved with this particular example, the CPGs seem to be sending ( or forced to send) these signals indicating severe need. I question how much of our behavior is being generated by central pattern generators and corollary discharge. We seem to act so differently to situations depending on our mood, the weather, what happened at lunch, that a great deal of what we do seems like it must be generated on the spot without any direct sort of model. It's not even the differences between people that scare me, I can understand that people will not see and react to situations in the same way due to the multitude of individual differences, it is when we, ourselves, start changing everything around. When we don't produce these same behaviors each time, it makes me wonder where the boundaires lie with respect to how much of our behavior can be thought of as a stored resevoir wating to be tapped.
Lots of different, interesting ideas, needing to be disentangled at bit more (which is fine, that's what the class is all about). Yes, lots stored in the nervous system. No, probably no "master CPG", but only a lot of semi-autonomous parts (we'll like more closely at the brain to show this). And yes, what we are is changing all the time. Boundaries? Worth thinking more about. You want some, or not? PG
Corollary discharge signals are composed of internal signals within the nervous system in which its function is to coordinate what's going on in the central pattern generators. Corollary discharge determines what kind of behavior to be expressed. That is probably why we all show various kinds of behavior since each of our corollary discharge signals seem to be different.
We are all generally composed of similar substances and have similar functions. However, each of us express various kinds of behavior and have differnt experiences. Some of us feel nauseous when we are on boats and some of us feel fine. This is because although we may be in the same environment, our nervous systems have different corollary discharge signals so that we each may have varied experiences. Corollary discharge signals are also important in the correlation with movement thorugh the nervous system. In walking we are able to to use corollary discharge signals which enable us to walk in a coordinated pattern (left leg out first then right leg out next..). The corollary discharge signals allow us to distinguish the left leg from the right leg in walking. We all have this general tendency in walking but we each may have dffernt ways in walking. In a sense we are all the same in our makeup but different in how each of our components work at different times which makes every individual unique in his/her behavioral patterns.
The interaction between sensory input signals and corollary discharge signals allow us to observe behavior which is influenced by these conflicting signals. In a moving car, sensory input signals report that the individual is moving all over the place while the corollary discharge signals report that nothing is moving. These conflicting signals may result in car sickness but differs with each individual.
Corollary discharge signals which interact with central pattern generators in the nervous system help make a little more sense of how the nervous system works in determining behavior. The choice of what behavior to express also depends on corollary discharge signals. We now know that the nervous system has the capability to produce outputs not necessarily having to do with sensory inputs and that the nervous system is organized in a way that we can not predict the specific input. This allows for individuals to express bhavior in different ways to which the corollary discharge signals respond and interact with the nervous system to produce behavioral outputs.
Pretty good summary of various things we talked about. Yes, indeed, corollary discharge signals can help explain why people are different from one another. Can imagine significance for additional aspects of behavior? things you have yourself experience, wondered about? PG
We've determined that corollary discharge is responsible for virtually every movement from co ordinated, complex mostions to (ugghhh! i don't want to use it, but i'm going to dare to) "reflexes". No behavior can exist without some pattern of activity, and hence, without a CD. CD's are the determining factor in output considering that they can overrule input and they can exist without input. The scary thing is that they are located outside the I-function which supposes that CD's can trigger behavior regardless of what you choose to do.
I'm beginning to think of CD's as a god--they have supreme rule over the nervous system. I use this idea for explaining the phantom limb phenomena. People with phantom limbs might choose to move their non-existent arm in order to get through a door way, but CD's don't coincide with this choice, so they body senses that the arm is still in danger of hitting the door frame. Possibly, the proprioceptors in the phantom limb are not receiving the information that signals the absence of a limb so they still feed input into the CD circuit which tells the body that the limb is present and needs to be moved. The CD takes action and the pattern it generates continues, but since there is no limb to be moved, the proproiceptors do not detect the change in limb position that normally would occur. CD's have control over the phantom limb but because the output doesn't reach the limb (since it isn't there), the CD generates continuously. I am a little confused about how CD's relate to cloning. I find the topic of cloning extremely interesting, but I am not sure where CD's fit into all of this. Are CD's genetically determined? And how, if there are billions of neurons in a cloned body, could CD's not exist? I don't think of CD's as an addition to the basic nervous system, I tend to think of them as simply a result of the nervous system: if you have a network of nerves, then inevitably, CD's are present. If I take that spporach, then CD's don't pose problems for cloning--a scientist creates a pattern of nerves, then he creates CD's as well.
What would be amazing/ fascinating and TERRIFYING would be when scientists do indeed clone and then they can begin to program their own CD's such that they can ellicit certain behaviors. Of course, it would be impossible to completely replicate all behavior since no circuits are identical, but similar human behaviors might be able to be manipulated from a cloned "body".
i'm not quite sure whether to fear or look forward to the day.........
Glad you like CD's (so do I, obviously), but don't get TOO carried away. As you say, they are "simply a result of the nervous system". And, hence, as you say, they bear the same relation to cloning as any other aspect of the nervous system (and, like any other aspect, they move emerge from genetic information, from experience, and most typically from both). As for clones, remember that there are different kinds. The recent news reports have to do with making embryos which are genetically identical to donor adults. By the time those grow up, they are likely to be no more like the donor than identical twins are like each other. As for the possible of make people who BEHAVE identically, using ANY technique, that's unbelievably unlikely, for reasons we'll get to as we go on (and are nicely described in an article by George Johnson "Don't Worry. A Brain Can't be Cloned" in the New York Times Week in Review, Sunday, 2 March, 1997). PG
It seems to me that saying CDs are responsible for a choice reaction makes it difficult to pose a belief in an I-function. An I-function proposes a concept of autonomy within the nervous system...if this autonomy is depicted> as a CD or a neoru-process, the entire system becomes a mechanicalk system and then we might as well be robots, functioning as we are programmed to do so. A Pleurobranchea will not respond when eating but will otherwise...this observation does not imply a choice? in higher organisms choice is an everyday , opngoing process....whether it be what to wear or what to drink. If one chose a purple shirt to wear there is no CD that made him wear it? it is a choice factor - an I function.
my proposition is simply that CDs cannot be held responsible for every and any action that is not processed by thought and analysis.
Interesting set of issues. CD's and "I-function" are not mutually exclusive ideas (they better not be, since there is strong evidence for both). What thinking about CD's does is to show to what extent behavior which LOOKS like "choice" may have its basis in CD. And that, in turn, can help try and figure out what is (and is not) distinctive about the I-function, as well as what we normally MEAN by the word "choice". PG
One way in which corollary discharge helps make sense of behavior is that it helps to coordinate different aspects of behavior. It is important to realize that behavior is not just action potentials sent from one neuron to a motor neuron. Instead behavior is a coordinated circuit of neurons, or motor symphonies. Also a behavior may involve several different motor symphonies. Who is responsible for coordinating these? Corollary discharge. It is one very important way that the nervous system talks to itself.
Corollary discharge is one way the body can detect that there is something wrong with another part of the body. For example, when the body doesn't do what the nervous system tells it to do, the mismatch between corollary discharge and sensory input tells the body there is something wrong. This is why people get motion sickness.
Corollary discharge also explains one reason why the body does not respond to input in the same way every time. In the Pleurobranchea may not withdraw its proboscis when it is eating because it receives corollary discharge signals that tell it that it is eating. So the one sensory input, hitting the proboscis, may result in two behaviors, withdrawing proboscis or not withdrawing.
These are two ways corollary discharge helps to explain behavior we will probably encounter many more.
Actually, you have three. And will encounter more. Don't want to make any guesses/suggestions yourself? PG
Corollary discharge signals play a major role in the interpretation of sensory information. It can also be said that corollary discharge signals themselves can function as a sort of internal input. This concept can explain why no two individuals can ever have the exact same experience. Since every person's nervous system is different, the corollary discharge signals generated amongst the different CPGs will also be different. Therefore, even if two individuals are put into the same environment, their interpre- tation of that environment will differ. This brings forth the interesting question of what reality actually is. Since reality is subject to interpretation, can we then even say that a reality exists? Due to the fact that at a given time, every person will be transmitting different corollary discharge signals, it should be the case that every person's interpretation of a particular object should be unique in some way. So maybe the reason why many of us can agree on the identity of particular objects is because of the similarities (more or less) in corollary dis- charge signals or sequences of corollary discharge signals. It should follow that if the corollary discharge signals in an individual are very abnormal, then that person's view of reality should be very distorted. My question is- is there such a disorder?
The importance of corollary discharge signals also lies in the fact that they form a set of expectations which are used as a framework for the interpretation of sensory information. When these expectations lead a person to interpret one thing, when in actuality it is really something else, then their is a discrepancy between the expectations held by corollary discharge signals and the sensory input. This sort of discrepancy can explain the existance of otherwise seemingly peculiar behavior such as motion sickness.Therefore, broadly speaking, the concept of corollary discharge signals can be used to explain the existence of certain behaviors and to explain the variance in the expression of behaviors among people.
Wonderful set of issues/question. A disorder with severe distortion of reality? Schizophrenia perhaps? Reality? Maybe that which lots of different people agree on despite variations in CD's? And may also be true that CD's reflect experience, so mismatches between expectation and input might lead to discomfort and modification of CD's? Which would in turn make the expectations closer to "reality"? PG
Corollary discharges, on one level, resolve many questions about behavior, but on another level, pose many questions as well. Corollary discharges provide a very interesting explanation about astronaut flight sickness, jet lag, and motion sickness, as discussed in class. The introduction of CDs helps to make more order in our structure of the nervous system, such that behavior may be considered to be interactions of central processing generators, with CDs as communicators between CPGs. For example, in the poking eye experiment, a CD sends a signal to the brain from the eye to tell you that the image is not really moving (when one closes 1 eye and waves one finger around and follows finger movement with eyeball, activating a CPG, images other than finger appear stationary).
CDs appear slightly mysterious to me. I don't know exactly what constitutes these 'signals', except that they are action potentials in axons, just like everything else, but they seem to be a big part in understanding our nervous system, with a certain job which does make them different from ordinary action potentials. We haven't really described the signals, nor their mechanism, nor have we tried to quantify them. We've gone from the quantity, 10^12 neurons, to something quite intangible, something that has multiple linkages and multiple effects. The statement in class, "your perception of the world is colored by CDs," suggests to me the idea that perhaps you can control mind over matter in some situations, as we try to do when we fly across time zones and turn off the lights in the plane and try to change the body's internal clock to alleviate jet lag.
Yes, there is some abstractness in the CD notion, but that shouldn't be mysterious. There is nothing special about the neurons or action potentials involved, only something special about the interconnections, and the fact that because of them the neurons carry information about the current state of particular parts of the nervous system rather than information about external inputs. That ok? PG
I think that the concept of corralary discharge is very interesting while trying to understand behavior. A few example of different physiological phenomena strike me as appropriate in discussing CD's.
1)While sneezing, your eyes are always closed. Someone once told me, and I have run this experiment several times on my own, that when you sneeze, you can not open your eyes. While this really makes no sense to me, I have tried it, and you can't open your eyes. This doesn't seem to serve much of a purpose, so it makes no sense for us to evolve this silly quirk in our sneezing.
2)In contrast, when we swallow food, we can not intake oxygen at the same time. This would make sense. We have this epiglottis to direct traffic into and out of our respiratory system and our digestive system. I tfollows that we would have evolved this anatomical structure rather than a CD which would prevent the two activities from occurring simultaneously.
Do we develop a CD over time like we evolve an epiclottis? Are CDs some sort of "crossed wires" that have seemingly unrelated functions--seeing and sneezing? Do we evolve needs and not CDs?
Nice thoughts. CD's may also help understand why difficult to pat head and rub tummy at same time? Am not being facetious. Even if we don't have evolutionary story for why particular organizations exist, its nice to be able to infer their existence. Evolve needs or CD's? Are perhaps more or less the same thing, no? PG
I have been thinking about central pattern generators and corollary discharge signals in regard to phantom limbs, phantom pain, and the possible relationship to chronic pain.
Because of central pattern generators (or what I believe are referred to as neurosignatures in the article "Phantom Limbs") and their corollary discharge signals, the nervous system is able is able to send messages to various parts of the brain that lead the brain into believing a missing limb is present or in the case of paraplegics that limbs are felt. Not only are the CPG's able to remeber that an arm was once present, they are also able to remember pain that was once felt in that limb, phantom pain. Apparently after pain is felt for a period of time CPG's are developed (or enhanced) in a similar manner as CPG's are developed for motion itself. In many cases, I believe most, the phantom pain is untreatable. Narcotics, anesthetics, cutting nerves in various regions, all result in little or no relief of the pain. However, there is one treatment that was developed that resulted in relief for about 60% of the patients treated called DREZ. Interestingly, the treatment relieved the patient of phanton pain, however, the phantom limb remained present.
I believe that there may be a connection between phantom pain and chronic pain. This connection is based on the fact that the nervous systems of vertebrates, (even invertebrates) are very similar. If the nervous systems of vertebrates are similiar, ie , dogs, monkeys, humans, than certainly the nervous systems within the human species are the same, and for that reason, there is no reason to believe that the nervous system between an amputee and a non-amputee are different. Therefore, the ability of an amputee's nervous system to develop CPG's that memorize (so to speak) pain that was once felt in the limb, then a person who suffers from chronic pain (for example, chronic back pain) may be suffering from phantom pain as well. The pain is very real, just as it is for amputees, and as it turns out, many chronic pain sufferers also benefit very little from neuronal surgery to cut nerves, anesthetics, and narcotics. For many chronic pain sufferers, even morphine offers no relief. This similarity among symptoms of pain between amputees and non-amputees triggers the possible connection that at least some of the pain felt by those who suffer chronic pain may very well be a result of CPG's and the corollary discharge signals sent to other parts of the nervous system, just as in phantom pain.
One of the problems doctors face in treating patients with chronic pain is that they do not want to anesthetise the patient to a point that they no longer feel a part of their body. I am thinking that the DREZ treatment should be tested on non-amputee's if it hasn't been already. My reasoning is that although the the phantom pain was relieved, the position of the limb in space and time did not disappear. Possibly, this is indicative that if a limb is present, that the patient will not lose feeling in the limb but may in fact get relief from the pain. Whatever part of the brain is saying "I know where the arm is and what its doing" just may do the same thing in non-amputees.
I am suggesting that since there is so much research in hopes of relieving phantom pain, than perhaps chronic pain should be incorporated into these studies as well, with the thought that the sources of pain are similarly derived and we can therefore work to help two or more populations of people suffering at the same time.
VERY interesting idea, worth someone pursuing (if they aren't currently). Be a little careful though about details. CPG's aren't "memorizing" pain. At least not as we currently understand things (they are just circuits of neurons producing action potentials which cause motoneurons to fire in a particular pattern, and causing other neurons to carry information about their activity to other parts of the brain, the CD). What MAY however be happening in both phantom limb pain and chronic pain is some kind of mismatch between sensory signals and CD's. If this is so, then standard pain relieving procedures may not work, and one wants something that instead affects (possibly) the mismatch detectors (their sensitivity or output). I don't know anything specific about DREZ, but its relief of pain without disturbing sense of existence is very intriguing ... and it might on that account well be explored for possible use in chronic pain. PG
While sitting in the audience of an orchestra concert, I am amazed that the different instruments and sections manage to begin their parts at just at the right time, with perfect volume, and pitch compared to their musical companions. But if I analyzed the symphony in a nitty-gritty matter, their intricate communications would be revealed and their secrets known.
You see, an orchestra cannot function without a director or without particular cues that function as hints to tell the other players when to come in and maybe even when to stop. I even remember from my high school band days that if we needed to play a certain sequence in repetition then the number of times was memorized and the musicians would follow through this way. Such cues are not alone found in music but can be used in plays so that players know what to say when a certain line is stated by a certain actor. This is how corollary discharges can be used as well ..
Because corollary discharges are integral parts of behavior (neurons need to communicate with each other in order to produce behavior) we can further understand behaviors by detecting corollary discharges. It is necessary for the nervous system to have very detailed communications not only externally (via sensory neurons) but internally as well so that cooperation can occur between systems. Corollary discharges are at least partially responsible for the knowledge we have about where our limbs are placed (even without seeing with our eyes) and for other such coordinations such as walking exhibited in crayfish. We cannot find one possible source for these feats so this organization is clearly a function of ganglion communicating between each other (corollary discharges) and not a dictation from some "upper level system".
Corollary discharges make great sense of behavior because it means that we are interactively organized. This means that many, many inputs from many, many ganglion "talk" about what is going on--there will not always be the exact "conversation" or reaction to the same stimulus. Behaviors can now be extremely varied and yet some things can be exactly the same all the time, such as walking patterns, or movements performed daily (such as getting dressed in the morning). But things can also be wildly different, not only between different people but on different days of the week when faced with the same stimulus--it all depends on what the corollary discharges are "saying" at the time. Behaviors can now be better explained because of these communications but it also becomes easier to see the varieties that we perceive in other's behaviors and our own idiosyncrasies.
Yep, CD's a lot like the various cues used by symphony players (though not necessarily like having a conductor). Nice analogy. And yes, can make life more interesting, differences among people as well as in one's self. PG
Corollary discharge is the signalling or communication between boxes within the nervous system. In multicellular organisms, behavior is the result of the coordination between many cells. It is the communications between the boxes within the nervous system that provide for the coordination > of the cells. In the example of the crayfish, the five abdominal ganglia are responsible for the swimmeret movement. The stimuli of the abdominal ganglia was recorded and it was found that the each of the ganglia had the same pattern, but each of them were delayed a little after the ganglia before it. So when a cut was made between the first and second ganglia, the first ganglia did not have a pattern that coordinated with the other four. In this case, corollary discharge makes it so that when the first box, or in this case the abdominal ganglia gets a signal to stimulate the swimmeret, it not only signals the swimmeret, but signals the next box (abdominal ganglia #2) so that it can stimulate the swimmeret and signal the next box. Together, all the boxes communicating to the next, and stimulating the swimmeret, produce the behavior of swimming in the crayfish.
Corollary discharge allows for the pattern generations between boxes in neurons. Without communication between the many cells that are involved with one behavior, the simple behavior could not occur. If there is no coordination of the cells involved in a specific behavior, then the cells would randomly stimulate a part of the muscle and nothing would occur. This was the case for the first abdominal ganglia when it was stimulating the swimmeret without the coordination of the other four ganglia. If there existed a cut between each of the abdominal ganglia then each of them would stimulate the swimmeret regardless to how the ganglia before it was working, because there is no connection between the neurons and thus no corollary discharge which is essential for behavior to occur.
Good focus on a paradigmatic example. Can now imagine similar arrangements as basis for explaining other sorts of behaviors? PG
Just when I thought it was safe to believe that we may have more "I" in our behavior than I thought, we started talking about corollary discharge signals. For example, sea sickness or motion sickness in general has been something that has plagued my life incessantly...When I think more about it, the incongruent signals (in which I have very little "I" function involvement) can control my behavior for vast amounts of time.
And the knee "dare I say reflex" I am still thinking about its purpose, and why for example "reflexes" can be dull after car injuries or head injury. I realize that we do not have a great deal of control over behavior in many curcumstances (like the knee reflex) because we cannot control which corrollary discharge signals make it back to register information. And our conscious awareness does not seem able to register CD's for the most part.
I am still thinking about the moving eye/hand example and why two similar images on the retina are changed by the brain due to CD's. It seems that much of our brain's perception is regardless of the "I" function. We can't consciously feel propriorecepters for example. And we cannot control Cd's and we are not aware of which Cd's are functioning and which are not- and ironically much of behavior seems based on them.
Interesting and appropriate wonderings. It IS significant how much of behavior can be accounted for without invoking an "I-function". Not only to "know thyself" (and others) better, but also because it helps to clarify what IS meant by an "I-function" and, ultimately, what it IS useful for (and how best it can be used). PG
I am thinking about the relationship of corollary discharges to the I-function, which we defined in class as the "box" where consciousness exists. What got me started on this was when we said that when the eye muscle(s) moved, a corollary discharge signal was sent back from the muscle which said, "*I* moved." The sensory neurons in and around the eye were what said, "You moved." Somewhere in the brain, the two pieces of information combined and a decision was made that the eye had actually been moved. As the case of the person with carsickness shows, the two stories told might have conflicted. Here the person would have felt an "*awareness*" of discomfort or nausea--depending, we conjectured, on how involved the I-function is. The two starred words above are emphasized because they so strikingly relate to our definition for the I- function. The corollary discharges that come together with sensory input somewhere in the brain could even be part of the I-function.
I'm sure the actual process is more complicated than what I have described, but I will go ahead anyway with a few conjectures about the mental aspects of corollary discharge that have grown from my thinking about the physical aspects. What is memory? I do not imagine that memory of a fact or event is stored passively until needed, like the information on a computer's disk. Instead I imagine it as potentials circulating in loops over and over again where it is stored and dispatched when needed. When you remember something you have done, wouldn't there be an accompanying corollary discharge to say "I remembered that," "I did that," or "I thought that," or else how would you be aware that it is a memory? The same would apply to thoughts. Right away you can differentiate a thought you are having as being your own or someone else's, because something (the corollary discharge?) says, "I thought that-- as far as I know, the content of the thought did not come from the memory part of my brain but the thinking part." So maybe corollary discharges are used within the brain as signals about the state of the mind it directs. If this is not at least a part of the I-function, then I am still mystified as to where to begin describing it.
All along in our class you have been saying, "How do we know that the cricket (or another animal) does not have an I-function?" Well, the cricket has corollary discharges just like we do to tell it what is going on in its body. It can probably also combine its sensory input and corollary discharges as its activities are normally highly coordinated with its environment. The cricket can have an awareness of itself through its corollary discharges, which may or may not include its thoughts and memories just because of the limited size and capabilities of its brain. How much different, though, is this "primitive" I-function from ours? We have the luxury of being able to analyze and comprehend through our I-function, but without corollary discharges it would seem that crickets and humans would be on equal ground--without the physical (and mental?) awareness that the I-function depends on.
Very interesting thoughts, anticipating directions we will (I think) be moving. Indeed, corollary discharges can well be thought of as signals from the nervous system to the nervous system about its own state ... and, in this sense, might well help us to make sense of the "I-function". At the same time, the "I" of "watch out, I moved the eyes" isn't quite the same "I" as the one in "I saw that" or "I am going to walk". In fact, the first "I" probably shouldn't have been used; it was my way of describing dramatically what is instead simply action potentials from an eye-movement CPG going to some area of the brain that also gets action potentials from the eye. So the referent for "I" in that case would simply be the CPG, whereas "I" refers in common speech to something more global. Crickets and humans ARE on the same ground with respect to corollary discharge; they both have and use it. And CD could certainly play a role in the "I-function" but maybe there's something more needed? Which humans have (judging from our own experience), and crickets might or might not have? PG
In one of my past essays I talked about the importance of the communication between neurons, as well as that amongst larger boxes. Through the notion of a corollary discharge, that communication is making more sense, and becoming more concrete. Along with sensory inputs, motor outputs, CPGs, etc., our original idea of the brain(nervous system) equalling behavior is becoming more convincing. In terms of the CD itself helping us to understand behavior, I think one of our best examples has been the phantom limb phenomenon. The whole fact that a person can be receiving no sensory inputs(in this case because the limb doesn't even exist!) and yet report that the limb is there, and even report that it is in an uncomfortable position, is just fascinating to me. It is due to these internal communications I spoke of earlier that allows for this. The CPG sends the message that it has told the "limb" to move, and the CD receives that message. But when nothing comes back saying that it agrees with what the CD thinks should be the input, something is wrong, and for the CD to say that something is wrong, it sends out a signal of pain(which is why they report discomfort). This is all well and good, but how does it help explain behavior? Well, I think the phantom limbs show a good example of the connections and communications within the nervous system. And, because we understand that everyone's nervous system is different, it makes sense that these communications and connections would be different. So, if given the same exact situation or even to develop in the same environment, two people would not report having the same exact experiences, due to this CD difference. Once we begin talking about autonomy, choice, and the I-funcion, the issues become more cloudy. I think it is altogether possible to explain both autonomy and choice using the CD, but I would like to see how the I-function interacts with the CD(even though I know we said you don't need it to explain many behavioral observations). So, CD helps explain behavioral differences between people and the behaviors that arise with no sensory inputs. But where does that I-function come in?
Glad you like CD's (obviously, so do I). Be a little careful though about the details of how you use the term. Strictly speaking the CD isn't what receives the signal form the CPG, but rather the signal itself, which might be received by another CPG or by some sensory structure or by ....? Maybe the I-function? Question, of course, is what is THAT? and what can IT do with the CD signal? We'll get there, maybe? PG
I can buy corollary discharge signals and central pattern generators as explanations for behavior in lower animals like pleurobranchia, but I still cannot help but find it overly simplistic for humans and for higher animals. I am anxious to begin discussing the I-function in terms of neural construction and functioning, because so far it is a very nebulous concept that definitely needs better definition. And I still haven't dropped the idea of consciousness, mostly because it is such a salient aspect of experience (not that introspection is a great way of substantiating theories), but also because it does have incredible adaptive/evolutionary possibilities in terms of expanding behavioral possibilties beyond those which are afforded by innate neural connections.
Don't too quickly equate what we've been talking about with "innate" neural connections. Remember CPG's can be acquired from experience (and presumably CD's as well). Furthermore, there's a lot "innate" about the "I-function", and "consciousness" (which no, you shouldn't give up). And don't presume we haven't yet been exploring things relevant to understanding the latter two concepts. Its important to know what can be done without an "I-function", both because it helps to define what might be special about it and, it will turn out, because you can't have an "I-function" without the things we've been (and will be for a while) talking about. PG
In some ways, my view of the nervous system has become my dichotomous. I tend to think of the correlary discharge as a means whereby certain controlling or overseeing parts of the brain can monitor what other parts are doing. On the other hand, the correlary discharge seems to interconnect different parts of the NS in a meaningful way.
While we, perhaps naively, first think of the NS as a one-to-one, stimulus/response, spaghetti network, we then shifted our view to encompass the Harvard law and the fact that neurons almost always make thousands of connections and receive thousands of inputs.In other words, the NS can create it's own signals and is an active processor, not a passive reciever. However, we also introduce the notion that the NS is really just a mind-boggling massive number of interconnected neurons.
This more complex view was at first quite confusing, because it is hard to imagine how such as system could keep track of itself- how it could operate coherently, let alone evolve and develope reliably.The notion of Central pattern generation adds a degree of organization by explaining that neurons although autonomous to some degree, can function as units in a coalition or circuit of neurons. Some of the interconnections can be accounted for by thses circuits. By noting that there are correlary discharges, we account for even more of these thousands of interconnections, as well as a collection of behaviors mentioned in class. (motion sickness etc.)
These corrolary discharges can be seen as the way that circuits of neurons communicate with each other and also as the means by which neurons that comprise a circuit may communicate with each other. We would expect that a circuit needs to be aware what its parts are doing, and also what other circuits as a whole are doing. Please let me knwo if this overall view is correct. have I charecterized the CD properly? have i left out important details? Where types of research are being done that have relevance to the above discussion? I'll lok on the web myself, but please mail me any links you know of. Thanks.
Sounds pretty good to me. Yes, recognition of groups of neurons interconnected in particular ways helps to account for coherence of activity (as in CPG's), and interconnections between such groups of neurons, informing each other of their current state, further helps to account for coherence. Just be careful of "aware of", since what we are of course really talking about (at least at this point), is neurons, synapses, action potentials, and the like. Not sure of relevant web sites, but happy to have any you run onto, and to keep my eyes open. PG
Corollary discharge is activity in the nervous system whereby one neuron or pattern of activity causes an efferent discharge. This efferent discharge goes to another area of the CNS, or back to itself, to tell it what is going on. For example, there may be an output from the Central Pattern Generator (CPG) for walking that triggers a corollary discharge (CD) activity that causes inhibition to the quadriceps (to stop hip flexion) and that also sends signal to other parts of the CNS to tell it what is going on. CD is different than sensory input in that it is generated from within the nervous system and is not dependent on sensory input; but also in that it does not give sensory feedback (such as proprioception) but rather is activity output that informs and influences the nervous system in a way different that sensory input.
In terms of how CD helps explain aspect of behavior, I have delineated 4 possibles ways that I will present and discuss below.
1. CD provides an additional explaination for a way to get activity in the CNS other than through sensory input or autonomously. Through CD the nervous system has the capacity to facilitate or inhibit. For example, if a given CPG turns on (either from sensory input or autonomously), the CD pattern that arises from that activity might inhibit the CPG from further discharge. This may be what is occurring with the crayfish swimmerette activity when it is activated by a CPG but then inhibited momentarily by the CD from that CPG. Similarly, this may be what is occurring in human walking patterns when the CPG for the Quads is initiated during the swing and stance phase of gait and then inhibited to allow the hamstrings activity to occur.
2. A second way that CD explains behavior is that it allows a motor symphony to be enacted without there being a central command center. In other words, a motor symphony can be initiated and than carried out at subcortical level without ongoing commands from the cortex. For example, a CPG for walking can be initiated based on the desire to get somewhere(cortical activation), but then enacted at a subcortical level through CPG and CD which provides ongoing information about the motor symphony and which provides a mechanism for coordination of the motor symphony (ie: balance of facilitation and inhibition).
3. CD affects the interpretation of sensory input and is an active component of our perception of reality. This is best explained by Helmholtz's observation regarding eye movements where when the eye is moved passively by pulling at the corner of our eye, the images we see is interpreted to be moving and that the eye is still because we are not getting information from the eye that the eye is moving (ie: there is a lack of CD). Whereas, when we actively move our eyes across a visual field the CD activity tells us that our eye is moving and therefore the visual image is still. The CD from the eye muscles, therefore, affected how we interpreted the sensory input from our visual field. (this concept brings up a question for me: what is the difference between CD and proprioceptive input? When this question was posed in class you responded that CD is from within the CNS whereas sensory input is from without the CNS. But isn't proprioception from "within"? and if so, what distinguish the feedback that we get from proprioception from CD?).
A second example of how CD affects interpretation of sensory input is the phantom limb experience. Melzack suggests that even in the absence of the limb (and therefore in the absence of sensory input), neural networks that continuously generate a characteristic pattern of impulses about the body continue to fire. He calls these neurosignatures. In the absence of sensory input, according to Melzack, cells in the CNS become more active and...."the brain's intrinsic mechanism transform that neuronal activity into meaningful experiences" p 123. In other words, the brain interprets the arm as being there and perhaps as moving. However, as we discussed in class, there is a dissonance created between the perceived sensory input and the expectation of what the sensory input should be from CD pattern. thus, although the individual seems to "feel" the limb because of neursignature patterns that continue to fire, they do not get the typical CD pattern that would emerge when the arm moved. Hence, a dissonance is created and may cause pain.
4. Finally, CD explains one aspect of the capacity for choice in organisms, Albeit at a very primative level. For example, in the pleurobrancha, although a stimulus to the proboscis will usually elicit a withdraw response, when the P. is chewing the stimulus does not elicit withdraw because of a CD pattern from the chewing CPG inhibits the withdraw reaction. Does this account for choice? I feel that in some respects it may, while in other, more complex behaviors it may not. For example, is it possible that a baby, when presented with a novel and interesting toy may mobilize oneself to get the toy and play with it in one instance(ie: when it feels comfortable with its surroundings and the people in it and feels free to explore); and inhibit that behavior in another situation (ie: when an unfamiliar babysitter is with the child and they feel inhibited to explore)? Is this choice a result of a CD pattern that inhibits exploration in the child????? Or is the supression of the drive to explore, a much more complex "I function" interaction of limbic system cues and cortical cues which may result in the baby choosing not to explore?
I will look forward to our discussion on purposeful behavior to add further dimension to this discussion.
Nice summary, with some interesting/appropriate questions/extensions. Proprioceptive is "from within" in one sense, that the signals originate from within the organism rather than from outside the organism. But, they originate from outside the NERVOUS SYSTEM, ie they originate in sensory receptors, unlike CD signals which originate from within the nervous system. That distinction clear? Is worth making, not only to counter the impression that brain activity is dependent on outside input but also because much "proprioceptive" information actually comes not from "enteroreceptors" (like muscle spindles) but also from "exteroreceptors" (like the eyes). Yes, indeed, the responses of a baby under some circumstances and not others may reflect CD's (as may similar observations on adults). Which the, of course, raises your question: what is the role of an "I-function" (you're not prepared to attribute "purposeful" behavior to negative feedback circuits?). PG
The phantom limb phenomenon is extremely surprising at first, however taking into account what we've learned about central pattern generators and corollary discharge it makes sense. Though the limb has been lost its connections to the rest of the nervous system still remain. Those connections are kind of like loose wires in a machine that keeps sending electricity towards another part of the machine without realizing that the other part is not receiving the electricity. Instead the electricity is being given off as sparks. The machine may keep sending electricity out until it breaks down or somebody turns it off.
The person can feel their missing limb because their nervous system tells them where the limb would be doing and what it would be doing, through the corollary discharge that the remaining central pattern generators (the remaining connections)send to surrounding neurons. This means that our perception of where our limbs are and what they are doing is a combination of sensory input we receive from the limb and other sources of sensory input as well as the information our nervous system receives from corollary discharge. Corollary discharge also represents what our nervous system wants our limbs to do, it is the message it is sending to the motor neurons. What happens however when the motor neurons can't do exactly what the nervous system tells them to do? What if they don't receive the message or if the muscles are not working properly? Who does the nervous system "believe", the corollary discharge that says that the limb has moved or the propioceptors that say the limb has not moved?
If the nervous system believes the propioceptors and the sensory input from the eyes, then the person should be able to convince themselves that the limb hasn't moved for some reason. If this is true then a person who faces the phantom limb syndrome should be able to convince themselves that their limb does not exist therefore they shouldn't be experiencing any sensation from it.
If the nervous system believes the corollary discharge signals then the person would have a very warped sense of reality and what is actually happening with their bodies in the world around them. This must be the dillema the person with phantom limbs must experience. They must be somewhere in between these two extremes.
Nice phrasing of the problem. Be a little careful, though, about details. The motoneurons are still around (though not connected to the muscles, which are missing). The CD signals almost certainly don't come from the motoneurons, but rather from CPG's which still also activate the motoneurons (actually, the motoneurons may, in time, disappear, and other secondary reorganizations may also take place in the nervous system). PG
The phenomenon of corollary discharge has some interesting ramifications on the model of the neural system which we have been building in class. It means that the behavior of central pattern generators is controlled by other central pattern generators in addition to self-firing neurons and external input. Since behavior is regarded as a complicated subject it makes sense that one would required a complex system for modeling behavior (i.e. the nervous system).
The presence of corollary discharge also makes the nervous system more difficult to study in an experimental setting. Generally an experimenter is forced to work within a limited and somewhat simple set of parameters. The complexity of the nervous system in which central pattern generators can be affected by each other, external information, or self-firing neurons makes the identification of cause and effect relationships within the nervous system much more difficult; narrowing the number of variables down such that one still can obtain significant data becomes the most important task. An effect with multiple causes is much more difficult to explain. Are all variables of equal importance? If not, which variables are more important and why?
In class we have discussed the problem of motion sickness and it's causes. An individual suffering from motion sickness is receiving contradictory information from the external sensory system and from corollary discharge signals. The external sensory system is telling the nervous system that the person is moving whereas the corollary discharge signals are telling the nervous system that the person is not moving. The nervous system becomes "confused" resulting in dizziness, headaches, and even nausea
Here, it's shown that the corollary discharge signals and the external sensory signals both contribute to a person's sense of motion. However, there still remains the issue of those who do not get motion sickness. Do they have faulty sensory signals or are they receiving fewer corollary discharge signals? If they are receiving fewer or discarding the information transmitted via corollary discharge, how and why? It seems likely that a person who does not suffer from sea-sickness receives the same amount of corollary discharge signals, but that the central nervous system does not process these signals in the same manner that the sea-sick individual does. Eventually, those who suffer from sea-sickness will recover from it if left at sea for a lengthy period of time. Therefore it stands to reason that the individual is processing the corollary discharge information that was confusing her/his nervous system in a different way. It seems likely that the corollary discharge information resulting in the motion sickness are being discarded in a manner not unlike olfactory desensitization.
Yes, its probably true that the nervous system is more complex in its causal relations than most experimenters are entirely comfortable with. So, simplify to get reliable results? Or try and develop ways to characterize its complexity? Nice problem. So too the differences in susceptability to motion sickness. Seems to me worth noting that there ARE at least two possibilities: people less prone to seasickness MIGHT, as you say, have less potent CD signals. OR the same signals might have less effect. Which would suggest different possible forms of therapy. How might one distinguish among these (and other) possibilities in terms of additional observations? PG
Professor Grobstein told me last week about a recent article reporting a finding that merely thinking about a motor behavior improves one's coordination in the performance of that behavior at a later time. He cited this finding as support for the existence of an I-fnc. While I am still not completely convinced of the existence of an I-fnc per se, it is my interest here to further explore this notion of the I-fnc as it relates to CPGs and CDs, which we have outlined as being the communication between the CPGs and between the I-fnc and the CPGs. The first question is obvious, what exactly is this I-fnc? How does it interact with internal "noises" to influence patterns of outputs from and the processing of inputs to the NS? Per usual, this raises the question of whether it is feasible to observe this I-fnc at work or even within ourselves? A concrete example:
One interesting behavior -- which while not as straightforward an example as that of the Pleurobrachia pileus' not withdrawing its proboscis when you hit it while it is eating -- involves the physiological response to exercise stress and the modification in behavior which occurs with repeated exercise. One interesting observation has been that the behavior of habitual exercise -- while eliciting the physiological stress response -- actually increases a person's ability to cope with psychological stressors. A number of immediate neuroendocrinological changes lead to long-term changes: alterations in resting peripheral catecholamine levels, in central monoamine levels, increased central opioid activity, cardiovascular changes, etc. -- the list goes on and on. And in fact, one of the strongest pieces of evidence for a biological basis for this phenomenon is that there might be long-term changes in the HPA axis in highly trained athletes which actually results in an elevated threshold of the degree of physical or psychological stress required to elicit the physiological stress response (Wittert etal., 1996).
One common observation is of the "runner's high" which is well known to be associated with an overall elevation in affective state. At the basis of this elevation in affective state is believed to be an elevated level of endogenous opioid activity -- commonly known as the endorphins and enkephalins -- which has been observed in highly trained athletes and fitness fanatics. In an article in Medicine and Science in Sports and Exercise, Thoren etal (1990) propose a physiological basis for the activation of the opioid systems with exercise. They hypothesize that sustained rhythmic motion of the skeletal muscles activates mechanoreceptors (ergoreceptors) in the skeletal muscles with contraction and flexion. These afferent fibers synapse on the raphe nucleus, the brain's broadcast center for seratonin, as well as on the periaqueductal gray which has a concentration of opioid receptors.
In light of these observations, then it is even more intriguing to learn that not all people have the same affective response to exercise stress, and in fact, personality behavior pattern appears to influence the affective and physiological effects of exercise stress. When Hardy etal (1989) exposed Subjects who display extreme type A or type B behavior patterns to exercise stress, they found that at the lower exercise intensity levels, type As rated themselves as higher in affect than Bs. On the other hand, during and after high intensity affect, type As actually showed a greater degree of epinephrine responsivity to exercise stress and a lower self-reported affective state. Other similar questions regarding the role of individual differences in how training affects the mind > and body have been raised by the observation that some highly trained athletes suffer from bouts of overtraining syndrome and others do not.
These elegant examples of how the motor outputs provide inputs to the nervous system which alter the nature of how a person processes inputs from her environment and in turn how a persons personality affects the nature of the mental impact of these changes. The release of endogenous opioids in response to exercise stress can be concluded as being rewarding (for reasons not addressed herein -- refer to ICSA and motivated behavior experiments for more information), reinforcing the behavior of exercise and increasing the likelihood of that behavior. But exactly how that habitual behavior affects the body appears to depend upon something greater than personality -- possible an I-fnc.
Hardy, Charles J., Robert G. McMurray, & Sue Roberts. (1989) A/B types and psychological responses to exercise stress. Journal of Sport & Exercise Psychology, 11, 141-151.
Thoren, Peter, etal. (1990) Endorphins and exercise: physiological mechanisms and clinical implications. Medicine and Science in Sports & > Exercise, 22(4), 417-428.
Wittert, Gary A. etal (1996) Adaptation of the hypothalamopituitary adrenal axis to chronic exercise stress in humans. Medicine & Science in Sports & Exercise, 28(8), 1015-19.
Very interesting set of issues, and a nice example of output causing input which in turn causes changes in the nervous system itself. Important. Less clear where CD fits into the whole thing. And, very intriguing in relation to your opening questions: "thinking about doing something" would seem to involve/require "I-function", whereas it isn't obvious (to me, at least) that the exercise effects you talk about do. Maybe that helps us to further specify what is meant by an "I-function". Yes, of course, we'll talk more about that. PG
We know that CDs coordinate CPGs and affect sensory input. The goal is to understand all complex behavior and how it relates to the brain. My thoughts on CDs are not very focused, and my thoughts on how we are stepping closer to understanding behavior are random as well. I think that there are different ways to study the brain and behavior. We are obviously taking one route that not many others would necessarily take. Good for some and bad for some. At this point with CDs, I am probably a little bit unclear with certain aspects of it. For example, we did a good job figuring out the answer to one of the posed questions: to what extent is our sense of what is reality a result of CD vs sensory input. But I cannot quite grasp exactly what a CD is. CDs are signals, but from where do they come? I almost feel as though things are slightly abstract and that may be why I cannot focus so well.
Perhaps this question too: are CDs a generally well-accepted way of thinking about the brain and behavior? And their whole connection with CPGs...? I do not think that I am lost, but perhaps in need of a little bit of something. Any comments?
Hmmm. You think there is something idiosyncratic in what I'm teaching? Could be. And maybe its too abstract? Yeah, I worry about that sometimes too. So let's go back to the particulars. Swimmerets, lots of CPG's, CD's the signals from one to another that report timing of activity in one, and influence timing of activity in another. Stability of visual images: signals from CPG for eye movement that influence another part of the nervous system's interpretation of input signals. Pleurobranchea: inhibition of one sensori-motor circuit resulting from activity in a CPG. THOSE help? And, by the way, are NOT idiosyncratic: well and carefully described pieces of research, well known by most neurobiologists with interests in the areas. Now, what we MAKE of them? to try and understand behavior more generally? There's the question: how much DOES it help? And the answer? Well, that's your job (and everyone elses). PG
Corollary discharge is significant in terms of accounting for behavior in that it accounts for greater variability in terms of behavior. That is, without corollary discharge the nervous system appears to be made up of many CPGs that respond to input by producing or not producing some behavior. With corollary discharge, the nervous system seems more complete as it can now account for its actions in terms of communicating between CPGs. Thus, more complex behaviors can be account for as the nervous system can now supply itself with the input of its own actions.
A good general point. Have in mind some concrete illustrations? From in class but also from your own experiences, thoughts? PG