Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!

Nervous system architecture: from the output side

Paul Grobstein's picture

Welcome to the on-line forum associated with the Biology 202 at Bryn Mawr College. Its a way to keep conversations going between course meetings, and to do so in a way that makes our conversations available to other who may in turn have interesting thoughts to contribute to them. You're welcome to post here any thoughts that have arisen during the course this week (and to respond to thoughts others have posted).

We've begun to move on from the building blocks of the nervous system to its architecture.  So if you need something to get you started ... In what ways do reafferent loops, central pattern generation, and/or corollary discharge help us further bridge the gap between neurons and behavior?  What new questions do they in turn raise?

K. Smythe's picture

Pain management

In continuing to think about phantom limbs, pain, neuron firing etc., I was reminded of a paper from a while ago that I thought at the time was very interesting and now think is relevant to our discussion of pain.  It is interesting to me that we can manage pain in this way and what is says about our voluntary control of the nervous system/nervous firings:

Mahvish Qureshi's picture

On the topic of the

On the topic of the existence of a conductor, I agree with what one person said in class, which was that maybe there is an initial conductor which gets taken away as the activty is picked up.

It seems that a conductor is only needed to start the pace of an activity such as the clappingin unison however once it got started the conductor was necessary.

This conductor may not necessarily be a specific person and could just be that eveyone is conducting themselves based on the auditory feedback, and adjustments of whether they should clap faster or slower.

Nelly Khaselev's picture

everyone is conducting

well if everyone is conducting themselves based on the auditory feedback wouldnt that just be what the corollory discharge is? with my understanding corollory discharge is the process of different parts of the nervous system talking to each other providing feedback. When I hear a pase of clapping, the message is passed on and I am able to form the same clapping pase.
heather's picture


that could be a plausible reason for how, but why do we tend toward synchrony?
Lyndsey C's picture

Today in class we covered a

Today in class we covered a lot of interesting topics that i wanted to comment on briefly. The first is in regards to our discussion about bird migration and the lack of a conductor, which may seem counterintuitive at first, but appears more convincing with further examination of neurological factors. I have heard that since geese must travel hundreds of miles at a time, they take turns leading the flock. The first goose must work the hardest and expend the most energy, so once it's term has expired, it slows down and acts as the caboose of the flock iun the back of the line, and this pattern continues. In this example, all of the geese work together to maximize the efficiciency of travel. (It reminds me of the Indian Sprint Drill) We can conclude that there is no presence of a conductor, and that it only appears as such because of the V-shape made by the flock (which is employed for increased efficiency. i suppose the geese could fly horizontally, but that would be less optimal.)

Related to th idea of a conductor, we touched on the idea that some organisms follow the behaviors of others, which may appear to lend support to the conductor theory. however, we learned through the clapping excercise that this is not so. one classmate mentioned that if one person in an elevator turned to the left, the rest of the people in the elevator would follow suit. i dont agree with this, but i also want to point out that if it WERE to occur, it would do so as a result of social desirability. in other words, it is a function of conformity, which i do not personally classify in the same category as conductance.

In the beginning of the semester when we began discussing the I-Function, one of our main arguments was that it sets us as humans apart from animals and other organisms. At first, i thought the I-function was therefore the conductor mechanism. then, we identified many examples of animal behaviors which were possible without the I-function, so clearly my initial thoughts were wrong. however, now i am left with the notion that the I-function is NOT what controls many of our conscious outputs. this is somewhat disconcerting to me because i do not like to think of the I-function as simply being a box that does not neccessarily have as much control of output (or input) than i previously imagined.

lastly i was just wondering what would happen if there WAS a conductor mechanism in our nervous systems. obviously the absence of one is more ideal, but i wonder how our behavior would change if the I-function functioned as a conductor or if certain living things were predestined to be conductors. how would this effect the rest of us?

Simone Shane's picture

Mirror Neurons and Phantom Limbs

Earlier in the forum a lot of people were discussing phantom limbs. There was actually a very recent article in the BBC regarding treatment for phantom limb pain ( ), which basically stated that, in conjuncture with the mirror box treatments, watching someone else rub their hands together can also help relieve the phantom pains. They seem to think that this might be due to mirror neurons firing when the patient watches another's actions. An excerpt from the article explains mirror neurons:


"Mirror neurons in the brain fire up when a person performs an intentional action, such as waving, and also when they observe someone else performing the same action.

They are thought to help predict the intentions of others by simulating the action in the mind.

Similar cells exist for touch, and become active both when a person is being touched and when they watch someone else being touched.

Researchers at the University of California, San Diego, say the reason people do not constantly feel what they observe happening to others is that a person's sensory cells do not give the right signals, so they know it is not happening to them."

These researchers argue that, since, the amputated arm is not giving these signals to the brain that the rubbing is not actually being felt, the brain does not receive the feedback that their arm is not actually being rubbed.

Reading this article made me think beyond phantom limbs to mirror neurons. I recall talking about mirror cells when learning about language acquisition in young children. In fact, it is thought that mirror neurons are whant enable us to learn how to move our mouth in ways to make specific sounds. Also, when you make faces at a young infant, they will mimmic your expression, also presumably due to mirror neurons. Yet, when children grow older, they no longer automatically mimmic expressions. This lead me to wonder whether we are just controlling ourselves from mimicking others as adults through feedback or whether the feedback system between the child's brain and their muscles is not yet strong enough.


In any case, it seems we have another little sub-symphony going on here between mirror neurons and sensory neurons to determine behavior.

I really hope we come back to the topic of mirror neurons as I find them so interesting!

nasabere's picture

Harvard Law of Animal Behavior and "noise" in the NS

Check out this Nature article; the researchers attribute behavioral differences to "noise--" defined as "random disturbances of signals" --- in the nervous system.

merry2e's picture

CDs and Auditory Hallucinations in Schizophrenia

If anyone is interested, I came across an interesting article on CDs and auditory hallucinations in schizophrenic patients...


PS2007's picture

I was also really

I was also really interesting in our discussion of phantom limbs on Thursday. I left class wondering about limb transplants. How does the brain come to incorporate this new body part? I know that sometimes limbs are rejected, but it is my understanding that this has to do with the immune system and not the brain. Why do some transplanted limbs function better than others?

I was reading abotu some different treatments for phantom limb pain, and I was suprised to find that there has been some use of virtual reality to treat this condition. Researchers at the University of Manchester used virtual reality to create the illusion that both limbs are still attached. This illusion helped people suffering from this condition feel like they had control over their phantom limb, and they could move it into more comfortable positions. This was interesting to me because they sort of tricked the brain on some level into believing that the limb was still there, even though obviously they knew on another level it was not.


Lyndsey C's picture

phantom limbs cont'd

I am really interested in our class' evolving discussion about phantom limb pain (and pleasure). It is an interesting concept that I have not thought about much until now, but increased attention to treatment options seems to be a growing concern. To understand this topic a little better, i thought I might look up some articles online, and I missed class on thursday so I might be repeating some things, but I found a lot of interesting. One article by TOni Ray explains that "When a body part is lost the corresponding part of the brain is not able to handle the loss and rewires its circuitry to make up for the signals it was no longer receiving from the missing digit...Perhaps nerve impulses in the sensory cortex begin to course down previously untraveled pathways. The second theory is that neighboring neurons in the cortex may actually invade the territory left fallow because sensations are no longer received from the missing limb." I don't really understand why the implications for the second theory would cause a phantom sensation or why our brains would find this adaptation useful.

Next, i found an interesting discussion on cultural differences of phantom limb sensation experience. Nicola Diamond discusses several drawbacks to the western perspective regarding this subject, and i found this slightly intriguing because i had never before analyzed the perspectives used to explain this phenomenon. For example, she mentions that in some african societies, "phantoms of the body –affects/sensations and images –are not set up in contradistinction to the actual body, but are taken as bodily because they are lived as such and there is a fluidity between bodily attributions and actual bodily states. Belief that the spirit is possessing the body is fluid with images of the body, to that of trance states and muscle and nervous activity ect." This is a very distinct way of thinking as compared with our own, and I believe it stems from a presence of different types of warcraft and religious beliefs. its a wonder that such societies perceive limb loss not as a loss but as an intangible extension of the self.

Mahvish Qureshi's picture

As odd a comparison as this

As odd a comparison as this may be I kind of see the phantom limb phenomenon similar to the straight-jacketed birds.

People who were born without limbs still have the sensation of their limbs presence, because it is in a sense hardwired into the system, in the same way birds that may have never stretched their wings before still have the ability and sensation of how to fly because this is something that is hardwired into them. The birds improve their flying with time, so would that mean if a prosthetis of sorts was put on as replacement for the lost arm, that motion would be gained just as quickly as flying was for a bird?

ptong's picture


In class the other day, we were asked to clap syncronously without someone directing us. I found it was intriuging that it was an everyday thing that we can do without really thinking about. Also it made me wonder what other interactions our bodies can do with one another without a "conductor" or IS there a conductor, just that we can't see it or isn't the same definition as we think it is. Is it possible for a higher order in our system, that controls these things?
nasabere's picture

To be honest

Right--to be honest, I was not entirely convinced that there was no "conductor" in the clapping activity; I felt like someone established a steady rhythm and slowly we all adopted it as our own. Had we done this activity without any sort of auditory or visual feedback, a clapping “pattern” would be none existent. I feel like there may be a conductor, one that doesn't manifest itself in the form that we are use to thinking of, but rather, one who's role is fairly transient and only necessary in certain situations.

Tara Raju's picture

I dont think we have it all yet...

I really enjoy the questions that have been brought up by Angel, EB and Jenn. There are so many questions that have yet to be answered that it seems almost asinine to assume that we found the big picture in regards to behavior. Like obviously, as brought up that experiment in Jenn's post, some behavior is in fact genetic and influenced by outside factors. The brain is different for everybody so what really accounts for the uniform behaviors that all of us, fofor the most part, have like walking, talking, etc. To what extent are our behaviors influenced by genetics, actually neurology and all of that craziness? How and why to they influence/define our behaviors only to the extent that they do?
anonstudent01's picture


In class we learned that Corollary Discharge Signals from one part of the Nervous System tell a different part of the Nervous System what it's doing. How can we know for certains that these CDS's always work correctly? Our behavior is dependant on their communication within the nervous system- do those who we believe to exhibit abnormal or unsynchronized/uncontrolled behavior have miscommunicating CDS's? Or in fact do we? How can we know for sure that both the Corollary Discharge Signals and the Central Pattern Generators are in fact normal and can that explain why so many accidents happen due to momentary disorientation or uncoordination?
merry2e's picture

Many questions???

I had to leave a few minutes early on Thursday, so if I am asking something that was talked about, someone please fill me in!

I have been thinking about central pattern generators and would it not make sense that if they are thought to be responsible for many behaviors: walking, breathing, swallowing, that these CPG’s would be found in the parts of the brain such as the brain stem for breathing or swallowing that we know control these functions, just as the CPG for walking is found in the spinal cord?

I am a bit lost and need help with the connection of the RA loop and CPG’s…can the RA Loop initially generate a CPG and once stored, then a CPG no longer needs the RA loop? Or are we born with the CPG’s? And if we are born with these CPG’s, do they have the ability to be inherited? Have you ever noticed two family members who have a very similar gait? And you definitely know they come from the same family? Is this learned or is it already built into our storage system within the CPG?

And if CPG’s have to do with storage and memory, it seems to me that the “I” function and CPG’s have a lot to do with one another…thinking about OCD and other similar disorders, I wonder if CPG’s play a part in the repetitive nature of handwashing, etc…

Madina G.'s picture

I-functions and corollary discharges

I found the discussions last week about corollary discharges really interesting. What struck me the most intriguing was the idea that no single part of the nervous system is in charge. This is a new concept for me and will take a while to let it sink in, since I'm used to considering the brain as the "control center" of the entire nervous system but I can see its direct application in nervous system functions. For example a study was completed to see if schizophrenia, a mental disorder in which the patient will often have auditory hallucinations, can be attributed to a failure in the presence of corollary discharges that are responsible for inhibiting a response to self-generated speech sounds, and concluded that this hypothesis held true(
To perhaps address the question of the I-function in this case, it is this particular lack of corollary discharges that allows for someone to believe that they are hearing voices. Part of our understanding of the I-function is that it all depends on whether or not the "cable" is connected from one area of our body where the sensory input occurs to the head where a speech output is generated. Similarly since corollary discharges are signals that transmit information to the brain that in turn generate a response, any disruption with the normal activity of corollary discharges has consequences on the I-function; in the case of schizophrenia, one would claim to hear voices, when someone who does not suffer from the disorder would have normal corollary discharge activity and consequently does not have the same claim.
Angel Desai's picture


I am increasingly interested in the idea of neuronal arrangements being the distinguishing factor among people. I wonder if it is too easy to buy into the idea that arrangements have the final say in behavior. How does that account for similarities among people (is it that some of the arrangements are similar and others different) or that tastes change (behavior influencing arrangements?) It's true that probability wise there are many, many different arrangements that can occur to account for why everyone is different...but in the span of thousands of years of human history, is there no overlap at all? And if there is, how is it that someone from the present time could act similarly to a person from an ancient civilization based only on groups of neurons alone? I guess this ties into the ideas presented by jwong etc....
EB Ver Hoeve's picture

Missing parts of the story ?

I am very much intrigued by our newest approach to understanding the Nervous System. Especially in regard to understanding behavior, the notion of the NS generating outputs in order to receive inputs seems very promising. And on Tuesday and Thursday we began to explore how the NS is organized to produce action (output). I appreciate the image of the stored “motor symphony” but want to continue to discuss the question of what is it that tells the “players” to play at particular times. The only problem that I am having with the direction of our discussion is that while I understand concepts of, say, the reafferent loop (for example) from a biological standpoint, I am not yet satisfied. I agree with the conclusions we are making from observations of the swimmeret’s and I am deeply interested in the big idea concepts, but I want to follow it through completely. For instance, let’s re-open the example of how talking creates input. I want to know the specifics. I want to know the specifics because I want complete understanding. I am not interested in surface level biology.

There is no conductor. This, as you said in class, is a hugely important and extremely interesting point. But can we delve into the specifications of communication? How is it happening?

cheffernan's picture


The idea of reafferent loops at first was counter-intuitive, however, when I left class this week thinking about how an output could also be an input, I thought about it and how when we move our hand, there is a whole new set of sensory inputs that need to account for the change in location of your hand. This need for accounting is important especially when considering a fear response. Let’s say that you burn yourself, your nervous system quickly gets the sensory input to move your hand, and produces an output to move your hand, but without the reafferent loop, the nervous system would not know whether the hand needs to be moved more or if the hand was safe.

Central pattern generation (CPG) is a genetic or learned behavior that requires coordination of various parts of the nervous system, and this coordination would not be capable if it were not for reafferent loops. In the example that Prof. Grobstein gave in class, the crayfish has a nervous system produces swimming behaviors, which requires the coordination of movement of many legs. Reafferent behavior feeds into this because before CPG can occur to tell another leg to begin its swimming movement, the sensory neuron sends a signal back to the nervous system informing it of the leg’s new location. Once this information is received, the next leg moves and allows for coordination to occur.

I am now able to understand how the coordination of the nervous system translates into the coordination of the organism, but how does the nervous system establish CPGs? Is it like conditioning, where once a behavior is reinforced enough the neurons become connected to produce the behavior without thought?

maggie_simon's picture

The role of corollary discharge in the interruption of sleep

A few weeks ago I began wondering what is going on in the brain and nervous system when people fall asleep in class.  I had a friend who could not stay awake in one of the classes that we had together.  There was something about the room such that about half an hour into every class she couldn’t keep from falling asleep (one might argue that it was the lecturer, not the classroom, but the lecturer changed from class to class; although this doesn’t rule out other options such as the course subject…).  She would do the typical head bob where she would just barely be asleep and then her head would slowly roll forward, and then more quickly jerk back, usually partially waking her up.  Of course, I have also had this experience and I know how annoying, yet natural this bobbing behavior is.


It only occurred to me now that it can possibly be explained as the brain and the I-function shutting down (in the sense of going to sleep) while the nervous system is still awake, ready to receive external stimuli.  In fact, I began to wonder if it was actually corollary discharge (related to balance?) that was causing the head to jerk back in the opposite direction of the way that it is falling.  Another question this raises in my mind is whether the nervous system really ever goes to sleep because it seems that nerves get plenty of time to rest when they are not firing, although the idea of corollary discharge suggests that there may be some neurons that are working or are ready to work all the time.


An observation that I have with respect to the nervous system going to sleep: I am a light sleeper, so my response to external stimuli is usually that my brain wakes up, while my sister is a much sounder sleeper and if I were to poke her while she was sleeping, she might respond without her brain being fully awake, or not respond at all.  I also know that there are times when I have really been out, and probably haven’t responded to stimuli, so that suggests to me that there are different degrees to which the nervous system shuts down to sleep.  I wonder what the advantages between these differing degrees or levels might be and why someone might be more inclined than another to sleep at a certain level?  (Some mildly related questions: why do we need to sleep?  What needs to sleep?  And of course: what is sleeping?)

Jackie Marano's picture

Selectivity of the Nervous System

I have found our class discussions this week about central pattern generators in the nervous system quite fascinating. We can apply such a topic to everyday tasks such as picking up a coffee mug, or somewhat less common practices, such as playing the piano. I mentioned in class that I can now view my experiences from playing the piano in a more scientific context. I mentioned that, in the past, I have played innumerable songs infinite times, and that I could cut off certain sensory 'inputs' (visual and/or auditory) and still play the exact song with reasonable accuracy. such as visual and/or auditory. I realize that the idea of 'muscle memory' is quite a hot topic in the forum, and I cannot really say whether my ability to have this specific experience is a result of nature or nurture (both my father and my brother play, and we all share this experience). I may do some additional research on this topic at some point...

I am also beginning to think that while the nervous system has multiple ways of performing some function, it definitely contains some element of selectivity with respect to its performance of these functions. For example, in high school I began practicing and working on a difficult piano piece by George Gershwin 1.5 years in advance for a school talent show. I practiced this song daily until the show. In the later portion of this 1.5 year committment, I had pretty much memorized the song for its sound (auditory), for its presence on a score of music (visual), and for the way that this song felt on the piano keys (tactile). I could do any combination with these three inputs to generate a very respectable performance of the song, and it became so easy that I didn't even have to think about it...but only when I practiced at HOME!

However, when I attended practices at school (change in environment and audience), and even the real event itself...I found that these multiple well-established 'patterns' of playing the song would temporarily disappear or 'malfunction'. My muscle memory would fade somewhat, I found that my eyes would jump from the keys to the music in confusion, and that I was not as quick to fix/realize any mistakes that I heard. While this may be explained most simply as a classic case of pre-performance nervousness or is really very interesting. It always used to annoy me that I could return home the night of a show or concert and that my central pattern generator would function perfectly.

If I practiced in front of large audiences more often, would I be training my nervous system to balance/compromise its functions differently? Probably. My anxiety would likely decrease, and then maybe my pattern generator functions would not temporarily malfunction? In this case, would I be influencing my central pattern generator? Is this even possible?

llamprou's picture

The Function of the I-function

I am also a little confused about the I-function. It may sound weird but even as a write this post the words are going through my mind before I am able to type them out on my laptop. I always considered this voice inside my head as my I-function. But I now find myself perplexed, if the I-function is interpreting signals or 'inputs', then isn't it just another 'box' hardwired into the human body, am I attributing the voice in my head to the I-function even though it should not be? Actually after finishing this post I find myself becoming more and more confused about what the I-function actually is and how it functions!
Sophie F's picture

I-function, etc.

If the nervous system, through its complex network of boxes and connectivity assimilates information both from within the system (the nervous system) and without the system (the environment), as the corollary discharge signals and central pattern generators work in tandem, how might the corollary discharge signal reconcile external input that is in conflict with the signal it is receiving from within the nervous system that is not strictly sensory information? This issue makes sense as we explored in class using the two different eye experiments, one poking our eyes and the other closing one eye and following a finger. Does this, however, account for messages that we send ourselves, so-called “self-talk?” For example, someone with an eating disorder, who may be visibly emaciated to outside observers, but “believes” herself and may even “see” herself as being overweight. And what about people with schizophrenia who have more than one “voice” in their heads? Which signals are enhanced or inhibited that may lead to this?

Like Skye, I also had some questions about the I-function. How does the I-function come into play in terms of interpretation or signals, or is the I-function merely an audience to the symphony?

Simone Shane's picture

Just another member of the band

Both Sophie and Skye's comments got me thinking about the I-function's role in the "conductorless symphony"of neuronal output. Indeed, the I-function often feels like a conductor when it engages in what Sophie calls "self-talk" in instances such as when one tells oneself to relax in order to deactivate the sympathetic nervous system. But is the I-function conducting or just sending merely another message, say, the feedback of discontent and desire for physiological change? Indeed, this message does not always work (as I'm sure we all know), which leads me to believe that it is not a conductor. Moreover, it seems like even the I-function is subject to feedback from other stronger signals that may be saying "too bad, this is what we have to do right now."
Skye Harmony's picture

I-function; genetic CPGs

In class we decided that no one part of the nervous system is “in charge,” but rather, all the different boxes communicate with each other via corollary discharge signals. I suppose having a central control box that signals were sent to would add another step and decrease efficiency, but I wonder what we consider the I-function? Have we not been describing it as some sort of control module? Maybe, though, like all boxes, it just gets information from all the other parts of the nervous system, but it does more with the information it receives… does that make sense?

mcrepeau, that’s a really interesting question about vestigial flight patterns. I wonder what kind of CPGs are genetically transmitted and how they come to be genetically transmitted. We talked a little bit about human walking, but what about swimming? It seems less natural, but is still a skill that many people have- if there’s a culture in which swimming is important and necessary, can that ever become incorporated into the genetic code? How, and how long does it take?

Emily Alspector's picture

Mind=corollary discharge?

So I acidentally just closed out my post before I posted so I'll try and remember everything I had said.

I think it's really interesting our discussion has led to phantom limbs. I am currently doing a project for my senior seminar, and the concept of corollary discharge is, on the contrary, not really discussed in much detail. According to wikipedia, corollary discharge "refers to the ability to differentiate one's own movements and responses to external motor events." One of the leading theories behind phantom limbs was introduced by Ronald Melzack, and is based on our genetically pre-wired awareness of ownership of our limbs and other body parts (phantom sensations have been seen in sexual organs as well). What is interesting is how this relates to I-function and the mind (or spirit, soul, what have you). Is this feedback system all that accounts for our mind? It seems unlikely, but plausible. Also, there is a similar disorder known as somatoparaphrenia where the patient rejects ownership of a body part; it would be interesting to see where corollary discharge plays a role in such cases.

We also discussed a central pattern generator and the reafferent loop, which I still don't completely understand in terms of inputs and outputs. In class Professor Grobstein made the point that the nervous system is both cause and effect, so is the loop just the mechanism behind this idea?'s picture

architecture and higher probabilities

The discussion of the brain being a structure of many different neurons makes the explanation of our minds and souls being results of different combinations of chemical functions and physical functions a more probable hypothesis.

Not only are there so many different kinds of neurons and different ways to extract a specific output from one neuron, combining those individual combinations and multiplying those combinations by the numerous ways that these enurons can function as a whole just adds more and more infinite explanations to explain the variety of human behavior.

Yes, we do have the ability to trigger the same output with the same brain everytime, however, there may be many different ways to trigger one output. Also, maybe the reason why humans are so likely to make mistakes may also be due to the fact that as much as there are many ways to produce one output, there are so many ways to mess up and backfire, causing an output that was not initially intended.

And for muscle memory and memory "scores" with the neurons acting as an orchestra, there may be an original song, then a remix, a variation, etc. WHich is why, those who are more familiar with certain patterns of action can adapt easier to certain actions, such as dancers, pick up on choreography easier than those who have never danced before.

Anna G.'s picture

I think what we talked

I think what we talked about this week in class was really fascinating. I like the idea of a "score" that we have, that we then continually modify. But my only question is, if we have this motor symphony that we create through patterns of actions is this different from an ideal, AI computer? When we talk about computers in class, we limit ourselves to the personal computers that we all use everyday. But this is only one type of computer. One of the main reasons why computers don't "learn" as we learn, I think, is because of the materials used. Wires that conduct current are limited, especially compared to living cells, with synapses and channels and proteins and plasticity, etc. However, when manufacturing and engineering gets even more precise, whose to say we can't engineer these?


What I think would be really interesting to delve deeper into though is the level of responsibility for action the central pattern generators have and the level that actual learning and experience plays. For example, we talked about birds that don't need to jump out of nests, but do. I don't know if a similar study has been conducted in humans (I can't imagine it would be very ethical to keep a baby tied down) but it would be interesting to see how much of that trial and error is actually necessary.


Caitlin Jeschke's picture


I am also interested in the relative importance of CPG's v. practice/experience when it comes to behavior.  In class, we have discussed the importance of communication between centers of pattern generation, and also of proprioception, which provides additional feedback to the body.  One advantage that I see of "experience" is that it would allow an organism to become familiar with both the proprioceptic feedback and the corollary discharge associated with a particular "score."  This would enable the organism to sense any unusual sensations (possibly indicating injury) right away, and could also make it more inclined to alter its behavior (make a necessary deviation from the score) if some type of obstacle was encountered. 

Even some of the most common, well-practiced behaviors such as walking in humans (which might be a "centrally-stored pattern" just like flying in birds) become extremely difficult if proprioception is taken away.  One particular incident comes to mind in which I attempted to stand up out of a chair and walk forward, not realizing that one of my legs had fallen asleep, and proceeded to fall flat on my face. 

This makes me wonder what would have happened if some of the baby birds in the experiment we discussed in class had encountered such difficulties (ex: a local anesthetic applied to a portion of one wing or something). I guess this experiment would be difficult to design, as it would require inhibiting proprioception while leaving corollary discharge unaffected.  And I don't know if that's possible.  So, again, it all boils down to the whole "CPG v. reafferent loop" problem which has yet to be resolved.  Anyway, just some thoughts I had. 

mcrepeau's picture

What if...

Continuing on this mode of experimentation what would happen if you ablated the wings entirely, i.e. if you removed the entire AER of the wing bud during embryonic development...would the chick experience the notorious phantom limb syndrome and could one (despite the absence of the wings themselves) still find evidence of an internal CPG, of an internal score for wing movement during the correct developmental phase when the chick would have been learning to fly (in the same way that one can find evidence of the spinneret and swimmer responses in crayfish and leeches that have either never developed the appendage for the corresponding activity or have been isolated from an environment in which the corresponding activity would have been implemented). What of flightless birds? Is there any evidence of vestigial "flight" patterns indicative of an internal genetically directed score in bird species in which evolution has favored the loss of functional wings (how similar are the swimming pattern of penguins for instance to the neurological signals associated with flight?)

Caroline Feldman's picture

Phantom Limbs

I was intrigued to learn more about phantom limbs after class on Thursday. I have heard of the term in other psychology classes that I have taken, but have not had the opportunity to explore the issue more fully. Not only do those who have had a limb amputated feel sensations in their phantom limb, but also children who are born without a limb at all. This suggests “that perception of our limbs is ‘hard-wired’ into our brain” (Cole, Jonathon. “Phantom Limb Pain” The Welcome Trust. Therefore, it is probable that our brain is the cause of the phantom limb because it is still receiving signals from the area around the limb. People continue to feel and perceive the missing limb, and often feel strong pain that must be treated with prescription pain killers. The most difficult thing about losing the limb is usually not in dealing with the reduced quality of life, immobility, or feelings of low self-esteem, but rather the pain itself.

In order to reduce the pain suffered by those with a missing limb, neurologists Ramachandran and Rogers-Ramachandran created a device called the mirror box. (
Essentially, the patient looks at the side of the mirror with his good limb and sees a reflection. Thereby in his/her mind, they have two good limbs because of what they see in the reflection. When the patient moved their good limb, they were “fooled” into believing that it was their amputated arm that had moved, which seemed to have reduced the pain in many patients. It has been suggested that attempts like these to link “the visual and motor systems might be helping patients recreate a coherent body image, and so reduce pain as a result of reduced and disordered input”. ( The brain must be re-trained in order to alleviate the pain felt by these patients, and has therefore become the main source of looking for treatment.

mcrepeau's picture

Where the reafferent loop comes in?

Perhaps the visual input produced by "seeing" the missing limb in the mirror, thus producing input from an imaginary output, serves to reinforce the importance of the joint role of CPG's and the reafferent system, as well as the overall redundancy of the nervous system, to comment on Zoe's post. In this case the visual "input" is able to mimic part of the reafferent loop and compensates for the discrepancies in the corollary discharge networks by producing a "direct" input that "reports" on the missing limb. Even though the communication amongst the components of the internal score that report on the status of the missing limb sense a problem (i.e. they are not receiving reports from that limb and thus report to the brain and its higher levels of organization that something is wrong via the dummy-light system i.e. the sensation of pain) the visual input that reports on a) the "physical presence" of the missing limb and b) on changes...i.e. if you move the hand being enough to trick the nervous system, especially the brain, into acting as if everything is alright and functioning normally.

jwong's picture

From our discussion on

From our discussion on Tuesday about inputs being a result of outputs, I began to think about these central pattern generators and the analogy that they resemble an orchestra, creating a “motor symphony” of movement, a pattern of action potentials that are based on memory. This idea of a prewritten score was very interesting to me because of the visual that I got from it; from it I began thinking back to when we described the brain as a computer with preprogrammed programs already existing inside of it. By equating behavior with a “motor symphony,” we assume each motor neuron produces different patterns and the mixture of these patterns constitutes behavior. These motor neurons derive instructions from the central nervous system, where sensory organs contain specific sensory neurons called receptors. The receptors then continue on to translate information from the nervous system to different parts of the body in the form of nerve impulses. Seeing such a mechanism made me wonder about how such a complex system could be initiated by experience or whether or not it was a result of genetics. In some readings I found online, I learned that CPGs are actually developed during early embryonic maturity, where efficient motor patterns are initially developed by neural circuitry. An example of this “learning” is demonstrated in the instance of a young bird learning to fly; in the particular experiment, the newborn birds were constrained in straight jackets. After the period of time during which a bird would normally learn how to fly, the jacket was removed and the young birds still had the ability to fly. Thus the motor patterning that determines this characteristic of birds was proven to be of a genetic factor, and that such patterns are not necessarily learned patterns.

Molly Pieri's picture

I-functions and CPG's...

Wow... first of all, I'd love to read a write up of that experiment. I'm glad to hear that the birds didn't seem to suffer any long-term damage. But feelings of sympathy for little birds in straight jackets aside, the study raises some really important questions concerning how much of our behavior "we" (that is, our I-functions) can be held responsible for...

Let's say, for argument's sake, that some human behavior is at least semi-analogous to a birds ability, according to this study, to fly. If, as this study suggests, such an ability is 'pre-programed' into an infant's nervous system, we might decide to call it an "innate behavior", that is a behavior which we are hard-wired to perform, regardless of upbringing or personal choice.

Now, when we're talking about baby birds learning to fly, that seems like a pretty innocent statement, after all like the old saying goes, "fish gotta swim, birds gotta fly". But what if we were to find that some of the uglier aspects of humanity were similarly hard-wired into our neo-natal brains? What about concepts like racism, xenophobia, sexism? Certainly, these questions must be raised in relation to the idea of CPGs- especially if we are going to assert that such neural pathways are developed during embryonic development.

If we are to accept that some patterns of behavior are innately programmed into our nervous systems, then I think that we must at the same time take up the question as to whether life truly is "nasty, brutish and short." If we'd like to conclude otherwise, I think we'd better start searching for biological justification of an I-function pretty soon, because without it I don't see much hope for any argument to the contrary.

Jen Benson's picture

genetics and behavior

Some evidence, has in fact explored genetic predispositions for negative behaviors, such as alcohol and drug abuse and Tourette's syndrome. Having a biological parent with alcoholism increases the chances of drug abuse even if the child is raised by different parents, and the proclivity to use cocaine and opiates also appears to be heritable (Breedlove, Rosenzweig, and Watson, Biological Psychology). Certain environmental factors can of course interact with preexisting genetic components to make certain behaviors more likely.
Personality variables such as extraversion, agreeableness, and neuroticism have also been speculated from twin studies to be about 50% heritable, which can certainly impact the likelihood of certain negative behaviors. Broken families, poor relationships with parents, and the presence of an antisocial sibling are also associated with drug abuse. I just think it is valuable to consider the environmental affect on the expression of genetic factors, including those that developed during embryonic development. Fetal alcohol syndrome research, for example, certainly posits a relationship between prenatal development and later behavior.
maggie_simon's picture

hard-wired tendencies of the central pattern generator

Perhaps there are other mechanisms in play that can inhibit, control, or modify hard-wired tendencies?

It was mentioned in class that walking may be a result of the central pattern generator.  In my experience walking styles can change as a result of social or other environmental influence.  I wonder to what extent those tendencies controlled by the central pattern generator can be changed.  Are they permanently changed, or just overshadowed or modified by something else?

nasabere's picture

No conductor to this motor symphony?

In class, Professor Grobstein provided the examples of swimmerette movement and human locomotion as a testament to our understanding of CPGs. But, aren't these "patterns" subject to external conditions? If such movements are truly regulated by said "patterns" we should continue walking in situations when it might be advantageous to stand still or hide from a potential predator. It seems to me that there are so many external factors that regulate how and when we walk and I'm having a hard time attributing the variety of animal movement to a fully autonomous "pattern generator." Perhaps the conductor here is the environment??? Or maybe even the I-function (although it is interesting to ponder that if the CPG before the I-function is aware of it) in some instances. Some other variable must account for our ability to produce a wide range of movements.

Interestingly, these circuits are able to foreshadow events to come and don’t necessarily require feedback from the I-function. But at the same time our I-function must have some sort of control over the CPG for locomotion—when my I-function suddenly feels the urge to stop walking and jump up and down for five seconds, my locomotion CPG obeys (or does my I-function obey it?). This all seems so convoluted to me, and for this reason I am not yet able to attribute the human experience to a bunch of mechanized CPGs.

Zoe Fuller-Young's picture

Multiple ways?

I am still not exactly clear how the reafferent loops influence the input and output, and how the output can change input, but I would like to comment on our ending remarks in class. We spoke about the knee reflex, and how the stretch reflex is unusual. Then we looked at an earthworm and the thoeries about its stretch reflex. We concluded that the earthworm may have a stretch reflex, but can also still function (move forward) without the connection needed for the stretch reflex. Therefore, are there really multiple ways in which our nervous system can produce the same output? (assuming it is inside, input, that is dictating output, ie muscle movement) How does this correlate to humans? If our spinal cord is severed, are there ways of repairing it? I have heard of paralysis recuperation, is this like the earth worm being partially cut?
Paul Grobstein's picture

fixed action patterns: resurrecting the homonculus?

See Jessica before this forum got put up.