Neurobiology and Behavior, Week 8

The concept of patterned outputs of the nervous system sheds new light on our capabilities and also our limitations. Central pattern generators may help us and other organisms function more quickly and efficiently and in a more coordinated manner, but I would think patterns can also be very limiting. For instance, when I used to play a musical instrument I would often need to memorize the pieces of music I was learning. I occasionally had difficulties keeping the different pieces separated, especially if they had phrases or rhythms in common. I’d begin playing one piece and end up playing a different one because I was relying on the patterns I’d formed for each piece and paying less attention to my performance.

I would imagine that patterns of inputs could be even more limiting than patterns of outputs. Many optical illusions rely on the brain filling in information that it thinks should be there when it is not. Olfactory memory works a similar way: we smell something and the brain responds by setting off a cascade of stored experiences associated with that scent. These examples seem trivial now that I’m thinking about them. However, other patterns of associations and behavior can be detrimental. Stereotypes are made up of patterns, as are superstitions. A great deal of harm can come from someone receiving a specific set of inputs and automatically assuming that other situations they associate with those inputs also exist when they very well may not.

On the other hand, more dramatic disadvantages can occur when patterns are interrupted. For instance, if a person suffers neuronal damage that disrupts the CPG of their walking behavior, that person has to re-learn how to walk. If a person uses addictive drugs, those drugs create patterns of neuronal activity that wreak havoc on that person if they stop using those drugs.  Despite their drawbacks, pattern generators seem pretty essential for regulating behavior.

As several of others mentioned in the forum, I found the discussion about infants don’t learn to walk but born with central pattern generator for walking.  Since it takes awhile for infants to learn to walk and there are steps they have to develop in order to walk, I never thought there would be a system “pre-installed” in our brain that makes you walk, even before you know how to walk. For the case of breathing, as it is another example for CPG, infants don’t require practice or experiences to have CPG for breathing to take a place. Then is that mean some CPGs require experiences, like walking, and some don’t, like breathing? Also, is this because there are less muscle movements to be learn to breathe than to walk, therefore can be done faster?

Another sets of questions I have for CPG are, so if you were not born with central pattern generator for certain activities, you won’t be able to create CPG for an activity of your choice? Meaning, does CPG always have to be there from the birth or can it be created from experiences, repeated actions, etc? So for example, as we discussed, is playing a piano without thinking an example of CPG that is created after birth? If it is, then shouldn’t we say that CPG can be “learned”?

Sort of along the lines of what a few other people have been addressing here, to me the most interesting thing that came out of Thursday's discussion was the concept of Central Pattern Generators, which for me seems to really destabilize a lot of our most common notions about what it means to "learn" something.

I feel like there's a linguistic or conceptual issue at the root of this idea of Central Pattern Generators—that is, what is "learning?" If, for example, a CPG exists for walking, does that mean children do not "learn" to walk? Can we "learn" a new action if the blueprint for that action is already present in our nervous system, just waiting for us to use it? What exactly is going on as children try and try to walk—or as birds try, over and over, to fly out of their nests those first few times?

I would say that our impulse, after Thursday's class, to reject the idea that such efforts constitute "learning" is premature. Maybe what we require is a more specific vocabulary to describe how exactly we acquire and store information, because "learning" as a catch-all term is clearly causing us problems here.

On a related note, I'm interested in how CPGs become part of the nervous system. It seems like there are some that we have from birth—walking, for example, or other subconscious neural and bodily activities—but that there are others we are able to acquire through experience. What's the distinction between these two types of CPGs—say, learning to walk vs. learning to play an instrument? How is it that some CPGs are passed on to future generations and seem to be part of our genetic structure while others are only acquired?

I guess overall it seems like there must be some kind of spectrum, a continuum of learned behavior ranging from the most instinctual to the most acquired, and that various types of CPGs would lie at different points on that spectrum. I'm interested in investigating this further.

Finally, I'm curious about the CPG as a metaphor—because that's essentially what it is, right? In class, we used CPGs to talk about activities ranging from breathing or our hearts beating to playing a sport or instrument. The brain must have different ways of handling such diverse phenomena, and so I'm interested in what differences are paved over by the concept of the CPG—that is, a metaphor for some kind of activity becoming more-or-less permanently "engraved" (or something) in the pathways of the nervous system.

Hearing about the experiment with the birds in straightjackets and its affect on its ability to fly made me think of another behavior in a particular kind of bird that I now recognize as a central pattern generator. The Cuckoo is an interesting species in that it is a brood parasite species, meaning that the offspring of the Common Cuckoo require parental care from unrelated host parents (usually a Reed Warbler) while the host parents gain no reproductive rewards from the cuckoo nest-invader. A female Cuckoo simply drops its egg into the nest of a Reed Warbler and leaves it there to be raised by host parents. The parasitized nest is detrimental to the host species because the Common Cuckoo not only requires food and care from its host parents, but it also ejects the eggs of the host parents out of the nest within hours of first hatching.

Upon hatching in the Reed Warbler’s nest, the baby Cuckoo, blind and featherless, begins what is believed to be a natural instinct for baby Cuckoos. Unsteady and wobbling, the baby Cuckoo positions the unhatched host’s eggs onto the dip in its back and pushes them toward the edge of the nest and with a determined thrust, expels the egg out of the nest.  The Cuckoo repeats this action until all the remaining eggs are rid of the nest. (If you want to see this behavior for yourself, watch this http://www.youtube.com/watch?v=DbvDQjhO9nY&feature=player_embedded)

I found this behavior quite fascinating. At first was hard for me to understand how a newly hatched Cuckoo could carry out such a complex, nonlearned behavior.  I now see that it is a central pattern generator, or a circuit of neurons, that allows this behavior to play out so early in life. The egg-ejecting behavior is clearly a highly developed survival mechanism and I am interested to learn more about how evolution shapes the formation of central pattern generators.  

 

To me, the idea of innate central pattern generators (CPG) and their coordinated control of specific actions, like walking, is startling but makes sense. I always thought that children learning to walk, or reaching out to grab anything within reach was a visually learned process and that their development of these behaviors would be different if they grew up in a different situation (without human contact, etc.). Despite this, there are clearly behaviors that we (our neurons, muscles, bodies) can just do. Breathing, the beating of a heart, and flinching away from something hot or sharp are not learned actions, nor are they controllable by an “i-function”. The motor symphonies for these actions have already been composed by our genes.

I find the ability of organisms to create new CPGs for other behaviors fascinating as well. I began playing soccer when I was six and it was definitely not an innate set of actions. Kicking a ball, aiming my passes, and using my non-dominant foot were awkward, frustrating actions. I knew what a specific move looked like but, no matter how hard I tried, I could not will my body to to recreate it smoothly and skillfully. It took me a while to realize that if I practiced passing, shooting, or even certain moves over and over again, they would become almost instinctual when I played with my teammates. And so I began creating CPGs that worked together to create a motor symphony of soccer skills. Now, when I come back from a few months off from soccer, it takes only a couple of days to get my feet moving fluidly again. I wonder if, having now created these CPGs, they can ever be destroyed? Does disuse of a certain CPG over a long period of time affect its existence? Or, can the CPGs we create during our lifetime become as innate as those responsible for breathing? In other words, when someone sits back at the piano bench after fifteen years without practice, is it just the motor neurons that aren’t used to being utilized in that manner or is it the CPG that has become weaker?

 

        It seems like we moved into a pretty big seemingly empty space. The starting point are billions of neurons of different sizes and shapes that each function in the same way collected into discrete groups and connected to each other. Their outputs are specific activities. How their output are specific activities. How we get from the starting point to behavior will fill in the empty space. Central pattern generation and corollary discharge functional ways of organizing some neurons. In central pattern generation there seems to be a fairly fixed protocol for a set of neurons which produces a specific repetitive output such as the song of a cricket or contraction of an organ resulting in speech or locomotion. Depending on the input the input the output can be modified or shared. In corollary discharge neuron sets are organized to preserve a copy of actions for comparison purposes. Organization of neurons to produce specific activities helps fill in the space, but there are still a lot of activities to be explained such as consciousness, culture, reality, and purpose and meaning.

After reading the notes and some of the comments posted, I have many questions on CPGs. CPGs make sense to me as patterns of neuronal activity that are stored and then create a physical action (i.e. typing, picking up objects). However some of the comments suggest CPGs may be involved in non-physical brain activities like thinking and learning. While this is an interesting notion, I find it difficult to understand. Thinking can't be caused by a CPG, maybe the act of thinking, like knowing when to think, but maybe not the actual thoughts. Thinking never occurs in the same manner though. I am confused on this.

Furthermore, I have questions:

What is the prerequisite for creating a CPG?

Are there disorders where motor symphony doesn't occur?

How common are CPGs in the nervous system?

I like the fact that we have AN explanation for the large percentage of interneurons in the nervous system(CPG) and circuitry.

The concept of "muscle memory" raised some interesting questions for me. Because we have memory stored in the form of central pattern generators in parts of the nervous system other than the I-function, I finally was able to convince myself that a paraplegic dog does in fact have the ability to wag its tail.  Perhaps the dog has sensory neurons located caudally that respond with tail movement when the dog is pet; therefore, the dog is not necessarily wagging its tail because the dog is happy, but because an external stimuli is generating the firing of central pattern generators that produce tail wagging. Thus, I guess it could be said that the dog's spinal cord was happy and not the dog itself. Another explanation could be that the dog, in the presence of food, gets excited and induces a firing of neurons that create a hormonal output that generates tai wagging.  This leads me back to Christopher Reeves.  If Reeves became sexually stimulated would his brain activity generate hormones that then induce an erection?  Based on the dog model, I would say yes.  Can quadriplegics and paraplegics have sex?  

Additionally, in response to "muscle memory", I began thinking about the influences of drugs.  I was thinking about different eras of music, i.e. Bebop jazz, when heavy drug usage was common for the musicians.  I was wondering if a lot of the creativity that came from this era of music partially resulted from this heavy drug usage that I believe could have led to a detachment from the I-function and greater reliance on central pattern generators.  Drugs, may perhaps, have the power to inhibit the I-function and enhance musical or artistic creativity by giving the individual the ability to escape themselves and their inhibitions and trust the musical/artistic patterns and abilities located elsewhere.  We kind of touched on this during class when we talked about how in order to play a memorized musical piece accurately and convincingly one had to detach themselves from the situation and just let it happen.  I wonder if drugs provide one with the increased ability to do so. 

          I found the experiment with the baby birds in straightjackets to be very interesting. Unfortunately, I could not find video of it, but I can imagine this would have been pretty funny to watch. It is fascinating that the baby birds, like babies, have a certain innate ability to walk. In this sense, “learning” to do something like this seems to be more of a time-activated genetic feature. What are the limits of this innately-acquired skill set? If babies intrinsically know how to walk, and birds intrinsically know how to fly, then surely there are other skill sets we unknowingly possess in our genetic code. What if we innately “knew” how to ski or how to shoot a bow and arrow? I’m curious as to how this applies to swimming. For evolutionary purposes, certainly we must have some basic ability written into our genetic code.

          Jeannette raised an interesting point about “unlearning” these skills stored in the central pattern generators. Perhaps these motor pattern scores are archived in our CPGs, but can become “dusty” if not used for extensive periods of time. [Maybe this explains what people say about learning a second language- if you don’t use it, you’ll lose it.] So why is it that these motor scores can atrophy with time? Imagine a young boy who likes to run a lot. His motor score for running is routinely being accessed, and his nervous system is extremely adept at performing the set of actions called for by the CPG. Now imagine he doesn’t run at all for a few years. If he were to try to run again, it would be the same impulses as always, and the CPG would be sending the same set of commands. However, he has grown a lot, things have changed, (size of limbs, chemistry of his body, etc) and now the old score is not as appropriate for his new bodily conditions. In other words, maybe the CPGs dictate very precise signals that are attuned to bodily conditions. If bodily conditions change and CPGs do not change with them, we may not be able to execute the motor symphony as adeptly. It would be like playing the same old song but with a different instrument; it may not work as well at first.

          I am excited to learn how this all integrates with mental scores. Just as we have physical motor scores, we probably also have mental scores. Maybe this explains why certain things are engrained in our brain and it doesn’t take cognitive effort to recall them. If you ask a small child their address, they would probably give it to you in one unbroken continuous memorized sentence. This bit of information may be stored in a mental score, just as the swimmeret movement is stored in localized CPG. The mental scores seem a little more ambiguous at first, but I’m sure we’ll get to them soon.
 

Central pattern generation and corollary discharge go a long way towards bridging the gap between neurons and behavior. They give a good explanation of how a pattern of activity in motor neurons can cause a coordinated physical action, even in the absence of some overall guiding force (a conductor). What they don’t really explain all that well is how thinking is a pattern of neuronal activity. Physical activities require similar patterns each time they are enacted, throwing a ball, even if you change the angle or the force, is the same base action each time, so it makes sense that it involves a definable pattern of activity in motor neurons. Thinking, however; doesn’t seem like it should work that way. Even if we think about the same idea more than once, we think about it in different ways each time and while changes in physical actions tend to be based on changes in sensory inputs that is not usually the case with thinking.

On a somewhat related note, Thursday’s discussion made me wonder why we tend to forget memorized information so much more easily than memorized physical actions. It’s not very difficult to ride a bicycle again after several years of not having done so, but much more difficult to repeat a poem you memorized in the 5^th grade. Why do these types of memory work differently? And how does forgetting actually work? If a memory is a network of connected neurons, and remembering is an activation of that network, then is forgetting just a loss of one or more of the connections in the network, or is it more complicated than that? Does a stronger memory equate to stronger connections in the network?

 CPGs make sense to me for motor function. Our actions are based on sensory input for direction/purpose; however, they cannot be purely based on sensory input, because certain actions can happen without "thinking", like we talked about in class and like what others have been mentioning on the blog thus far. Our actions must have some intuitive quality. While I think we have a pretty good understanding of motor functioning now,  I do not think CPGs fully explain interconnected neuronal circuits in general. Our actions are very fluid; we can most often move without thinking about it. But what about THINKING? Of course thoughts are influenced by other inputs, certainly sensory, but are there CPGs for thoughts as well? Are CPGs specific to motor functioning or can they be applied to different functions within the brain, even more "intangible" things? I was talking about memory in last week's post and the idea of learned CPGs causing memory make sense to me: a memory is just a learned pattern of activity, so when we are reminded of a certain thing, it is just that pattern being activated, so potentially a running CPG. 

On another note, I am not sure I completely understand the full definition of corollary discharge. Something to do with the "coordinated performance of independent players", a motor symphony without a conductor (sort of like Stomp?). What specifically does corollary discharge refer to?

Lastly, I just wanted to share my experience applying this class to daily life! This past Monday I got a concussion in lacrosse practice, and in the context of this class, I have been thinking about what is going on inside my head. My symptoms are very mild: "pressure" in the head, photosensitivity, and headaches from the photosensitivity. But what is going on in there??? "Pressure" in the head -- what is that, in terms of neurons? Why am I sensitive to sunlight, when I was hit in the front of my head and not the back of my head where info. from eyes are first processed? In more extreme cases of concussions: people lose memory, but are able to get that memory back...if memory is based on CPGs, or something of that sort, how could a pattern be "lost" and then returned? I think it may have been Jeanette who mentioned in her post that she used to play the piano and now she hardly remembers anything besides a few melodies...I am sure if she wanted to learn piano again it would be very easy for her to improve. How can something that was so ingrained and then lost come back to us? Does "practice" strengthen neuronal connections that were once strong and had been weakened/turn off inhibitors?

            I think that the connection between central pattern generation and learning is very interesting. As we discussed in class, there are some things that require learning and will later establish their own central pattern generations. For example, someone would have to learn piano, and after sometime, they would develop a muscle memory for the songs that they play. They wouldn’t even have to think about them. This means that they now have a central pattern generation for playing those songs. The thing I’m curious about is the “unlearning” of this muscle memory; is it possible to get rid of central pattern generations? Based on my own experience, I would think that it is. I took piano for several years; I would say that I was even pretty good at it. I quit it in 10^th grade, but a few years later, I tried to sit down and play it again (without touching it since that period). I could only play simple melodies. This makes me think that I could have lost the central pattern generation for it, or at least for anything complex. However, there is a part of me that thinks, perhaps, it is not that I lost it, but that it is weakened. I don’t know if it’s possible to weaken a central pattern generator or not, but I do know that I could still play the piano after several years of not playing it, even if not well, and if I tried to learn the songs that I knew before, they came much more easily than they did the first time. I think that it’s possible that the connections could still be there even when they aren’t being utilized-they just might be weakened. Practicing again could help strengthen them again. But I still have to wonder, is it possible to loose central pattern generators in ways that don't involve massive brain damage? Is it possible to weaken them?  And if so, how and why would this happen? Would there actually be an advantage to getting rid of some of these “motor symphonies?” 

In class, we discussed how behaviors are either learned or acquired through genetics. It's interesting to think that something perceived as such a critical learning process in our lives is really not learned at all, but would be reached eventually anyway. What other processes are actually inborn in us? 

It is also interesting to me from a developmental perspective. Humans are not able to walk until a certain point in their lives, usually around the one year mark. When horses are born, they can walk right away. What developmental differences exist between these two species that allows one to walk right away but the other to grow and change before walking? Are there brain connections that need to be made in humans after birth before they are able to implement the process of walking?