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Any sort of complete understanding of the workings of brain and behavior will, in my opinion, require knowledge of many different levels of organization within the system. I've gotten the impression that many researchers in different branches of the neural and behavioral sciences decide that their loyalty belongs either to top-down or to bottom-up studies of neural systems. Of course everyone can't do everything at once, but I'd hate to turn my back on either one of these approaches as some tend to do.
Understanding the functions of neurons not only as boxes but as the cognitive scientist's famous and impenetrable "black box" would be useful for some forms of explanation and useless for others; it's certainly necessary to go beyond this and discuss the neurons' inner workings as well. For example, thinking of a neuron as a black box that somehow passes on a signal might do for a simplistic explanation of excitatory communication, and perhaps we could explain much of the brain's activity using only this model. But it would be wrong. Pharmacological work and closer inspections of neuronal function are necessary to uncover the complexity at microscopic levels of the nervous system.
Learning is another example; cognitive studies of learning (and behaviorist-style learning theory as well) have uncovered a great deal of information about how learning takes place at a higher level. But their models, when they try to identify a neural basis for their findings, require the information collected in smaller-scale studies of synaptic changees like long-term potentiation in order to be falsified or supported.
I think it's critical to know what the nervous system can and cannot accomplish using the materials at hand when attempting to model its function. Some of the fields I'm interested in (cognitive science, AI, computational neuroscience, biorobotics) don't necessarily tend to pay attention to the actual body while modelling it; I suppose it depends on the goal of one's research, but I'd prefer to have a strong background in the function of the living system and to keep this in mind even when I'm not working with it directly.
I share your field interests, and your belief. NOW the question is, more concretely and more in details, WHY is it necessary to move among levels of organization and for WHAT? (I've actually written on this subject, somewhat obscurely, but happy to give you a reprint if you're interested ... or you can find the article at http://serendipstudio.org). PG
The Importance of Understanding Neurons
If the brain is behavior, and neurons constitute the brain, then of course it is necessary that one have a decent working knowledge of neurons in order to understand behavior. As the basic premise of the course is that the brain/behavior relationship exists, an understanding of neurons is imperative. Even if one does not espouse this relationship, one must know enough about neurons to be able to argue why the relationship does not need to exist.
I feel that what is most important about learning about neurons is dependent one's personal interest--particularly, what one is trying to get out of it. For me, the amount of diversity that can be generated by the different things we talked about (i.e., the sheer number of neurons, neurons that have different built-in permeabilities, etc.) was the most interesting factor. As the range of possible behaviors is so great, and very small variations on the same behavior can occur, I questioned that this diversity could be accounted for without the existence of a mind. That possibility is much more salient to me now, although I still have difficulty accepting that nagging feeling of "self" as merely the product of neuronal interaction. I still have my ghost question as well...
I'm also interested in behavior modification through physical manipulations--of neurotransmitters or otherwise. (Although I don't know how capable we are of the "or otherwise," yet.) For example, learning about the neurotransmitter dopamine led to great advances in the treatment of schizophrenia and Parkinson's disease. This, to me, is strong proof that an understanding of basic neural functioning is important to understanding behavior, and treating behavioral disorders.
Many people wouldn't agree with the "of course", so its worth developing stronger and more explicit arguments (if one cares about the matter, which of course I and you do). The clinical issue is clear, though its worth thinking more about WHY studies of individual neurons turn out to be clinically useful (and when they don't). The more general arguments have to do with the sorts of issues raised by your variability considerations: maybe studying neurons helps make vague beliefs about behavior more certain. Yes, we'll get to "self" (and maybe ghosts). PG
The thought that some neurons have regions of high sodium permeability does help me get away from the circular problem I was having last week. The brain would still be behavior but not in the conscious way we are use to looking at it. Its sort of a biochemical situation that develops without effort. I dont know Ill have to come back to this topic my thoughts are too scattered right now to orient them into anything coherent. As far as your question in class on whether understanding neurons is important in understanding behavior I would have to say yes. It allows us to understand how we as humans can have so many complex behaviors when we realize that this behavior is based not on one neuron but instead on the pattern of a possible 10^12 neurons. As well learning about how the total added effect including inhibitory needs to break the threshold point explains how the same or simular stimulus can result in different responses from the same organism. In essence we make decisions at the action potential level, the firing of all the different neurons results in our behavior not just one neuron. Seeing the neuron as the propigator of an electrical charge also makes it easier to believe that a action potential can be started without a stimulus, as mentioned last week. Therefore, I think it is this littlest box that is the key to understanding behavior.
Glad things are fitting together, helping to make sense of each other. Interested in hearing more about "but not in the conscious way we are used to looking at it". What IS that way, what's the new way? "Biochemical situation that develops without effort" a little vague. But fine, for now. Is something we can come back to several times. PG
"Was it worth it to learn about the smallest denominator of the Nervous System, the neuron?"
The most important thing I learned about the nervous system during these past two weeks concerns the "pattern of activity across a large number of elements." I have been trying to play with the concept of these patterns and how they might result in a behavior. I resolved myself that the pattern was more complicated than an uninterrupted chain of neuron firings. But I had no idea that there is more complexity than that. According to class on Thursday, one neuron has very little effect on the firing of a neuron connected to it by a synapse. The firing of a neuron depends on the collective information passed by all 1000 other neurons connected to it. So the chances are very, very low that there is a certain neuron-to-neuron linear pathway composing the "pattern of activity" that leads to a behavior.
This complexity gives rise to a couple of conclusions, but more questions. The patterns can definitely have more variety as each neuron is "listening" to a host of others. There are more checks and balances along the way, as the summation of information from the other neurons can result in turning off a neuron, too. There is also more choice of what the "message" will be: at any neuron the pattern can change slightly.
However, the question of whether there are "start" and "stop" neurons that determine the "end" or "beginning" of a pattern leading to behavior becomes more complicated. If we hear a sound, where did the pattern for that behavior start? The sensory neurons in the ear had to have received input first. But, each of those neurons are also receiving information from 1000 other neurons. So, the firing of an ear sensory neuron did not necessarily occur just because there were sound waves in the air that influenced them. So where did the hearing pattern really start? The sound at the sensory neuron was just a part of information continuously received by that neuron. Can I say that that ear sensory neuron was already a part of a larger pattern, and this hearing pattern was a sub-pattern that helped result in the "hearing" of a sound? The same situation must occur at the "end" of the pattern, when the "hearing" has occurred. The place in the brain where this pattern of activity ends, if the pattern even "stops" anywhere, is also influenced by thousands of other neurons. The ending must just be part of a larger pattern as well.
It is interesting to think that each entire pattern of activity depends on information that comes from all over the nervous system. In order for any pattern to occur, other patterns must be occurring that will influence it. I already knew that the path in between the beginning and end of a pattern is complicated, but now this part of the pattern resulting in behavior seems even more nebulous. I would assume that for a sound to be heard, the pattern would not go from the ear to the toe to the stomach to the brain for it to result in hearing. Yet, how can we know? At the very least, the pattern will be influenced, at least indirectly, by the entire rest of the nervous system. Does this make the capabilities of the nervous system more or less delicate and vulnerable?
I do not know that working knowledge of the neuron has really gotten us anywhere besides telling us what does not happen (though isn't most science like this?) We already knew that the nervous system was like a box taking in input, processing it by means of other little boxes within it, and resulting in an output, a behavior. We know by what means the information is digested and transmitted by the little boxes. But I am back where I started, in awe of the whole complexity of these deceivingly simple boxes.
Lovely set of thoughts, very much belying the notion that you are "back where you started". Yes, no linear pathway. Yes, patterns affected by other patterns. Probably (at least usually) no end or beginning (at least not in the sense of a single neuron from which things start or on which they end; why should there be? input is a pattern across many neurons, so is output). But some substantial specificity in networks, at least toward periphery, so activity in some neurons primarily due to input signals, in others intended exclusively for muscles. What is talked to, heard from is not a random 1000 other neurons but particular populations. PG
The details of neural function leave many questions unanswered. The most provocative of which is the existence of areas on the neurons which inhibit many sorts of behavior. If so, one begins to wonder about the functionings of the id from a psychological perspective, for example. Are manifestations of the id merely action potentials that managed to slip through the cracks, so to speak, and if so, what causes this to happen with greater frequency in certain individuals and not in others? In a like manner, what factors are responsible for this supression of action potentials: environment, conditioned behavior, faulty neurological connections, etc.? One begins to wonder how inhibited behavior would be selected for and if so, would behavior that was consider "socially unacceptable" in context be selected against? Also, since many neurons exist in localized regions that produce action potentials automatically, are there analogous regions where the corresponding inhibitory neurons exists?
Another area of interest is the velocity with which action potentials travel along the neurons. Does an overall pattern emerge throughout human evolution pointing in the direction of faster signal transmission? Or is the speed of an impulse somthing which the individual must perfect on their own? However, does the relatively slower paced life of humans today as opposed to our rugged primordial ancestors set the stage for a degeneration in the speed of action potentials?
True, two weeks appears to be a long time to spend in a detailed study of anything, but knowing the basic mechanics of neurons sets the stage for a more in depth study of the nervous system.
Interesting questions, indeed. Inhibition raises all sorts of issues, neurobiological and psychological (like the connection to the id). Suspect answers as they evolve (in course and elsewhere) will make id (and neuroanatomy) a blend of excitation and inhibiton, rather than one or the other in some localizable and distinct way. We'll see. And that action potential speed is only one of many factors which are likely to be under selection pressure in connection with the speed (or lack of it) in human behavior. You really think we have a slower paced life than our ancestors? Seems to me incredibly (perhaps undesireably) fast. PG
On Tuesday it was discussed that the nervous system works in real time, not instantaneously. While voltage change and passive current flow are essentially instantaneous, the change of the membrane permeability is not. Therefore, neither is the action potential. Instead, it has a conduction velocity somewhere between 0.1-10 meters per second. The example given of a signal for a giraffe to move its foot would take a whole two seconds to travel from the spinal cord to the muscles in the foot if it had a conduction velocity of 1 m/s.
Then the question of whether or not it is possible to improve one's quickness was proposed. Certainly the answer is yes. Rebecca Lobo (basketball player and female Athelete of the Year, 1995) can grab a rebound with amazing swiftness, but she could not do it as well when she first entered UCONN. Over her college career, her speed, agility, and performance improved. Practice makes perfect, right? If it were simply that she could oly throw the b-ball faster and harder, it would be logical to say the changes were solely in the muscle tissue. Her sharpened alertness on the court, however, implies that the nervous system is involved.
Eric's notes inform me that there is no axon adjustment that improves quickness. This means that each neuron has a certain rate that is inate to it, that it was "Born" with, and that will not change. That can explain why some people have quicker reflexes than other, are better natural athletes. But then how do we account for IMPROVEMENT in quickness??? We could say that more synapses are created, but unless neuron A synapsed on neuron B who is faster than neuron C--what good does that do? And why wouldn't A synapse on C to begin with--wouldn't that have been more advantageous for the animal?
Perhaps the number of receptors on a post-synaptic membrane is increased, or perhaps these receptors increase their infinity for their neuro- transmitter. This would then shorten the time it takes for synaptic transmission, and quickness would be somewhat improved. I still, however, do not see why it is impossible for the axon itself to adjust to a faster conductive velocity.
Glad you're back. Stop by if conversations with others haven't cleared up unclarities in Erica's notes (or my lectures). The issue of speed improvement raised in class is an interesting one. I didn't mean to say that axonal conduction velocity was fixed at birth, but only that for complex behaviors there were undoubtedly a number of additional factors contributing to "quickness", and it was probably more likely one or more of those was contributing to acquired athletic skills. It would make an interesting (and maybe even doable) little experiment to test out in some simple case. PG
In this essay I will answer the following question: was the study of nervous system on the micro level worth it. I believe it was worth it. We have explored the micro foundations of a complex system (in this case nervous system/human behavior), which is very important in study of any macro-phenomenon. Before diving into the complexities of nervous system and trying to model/predict behavior, one should know what the nervous system consists of. Having familiarized ourselves with the functions of the simplest particle of the system - the neuron - we can now proceed and generalize this knowledge for systems of neurons (boxes), systems of systems of neurons (larger boxes) etc. all way up to the nervous system as a whole. As of now, we can translate complicated questions into the micro level and seek our answers there. Or , in the opposite direction, take issues from the neuron- world and ask ourselves what do they mean in terms of behavior.
I would like to analyze one such question that caught my interest during the past several weeks. It is the issue of variability of membrane potential, caused by some properties specific to the neuron. The existence of this variability means that the output of the neuron does not correspond only to the given input, but also to some other properties of the neuron, independent of the input. The first thought that occurs to me is that we should be able to generalize this result to more complicated systems, all way up to behavior. The result that we would obtain on the level of behavior would be the Harvard law of animal behavior, which states that under controlled conditions, animals will behave in an unpredictable fashion. This, however, seems too simple and straight forward. My problems with this direct generalizations are as follows:
Although we can separate the portion of the output caused by input on the level of neurons (detect an output in isolated neurons with no input), I donÕt believe it is possible to do so on the macro level. Behavior is so complex that it seems impossible to control for all the inputs at any given time. Thus, the unpredictability of behavior can be due to the difference of Òother inputsÓ at the given moment. As an antient philosopher has taught us, ÒYou will never step into the same riverÓ. In the same way, there are no two states of the nervous system that are completely identical. The nervous system changes over time and differs across individuals. How can we control for all these variables? It seem that variability in human behavior is not random, but is a result of a particular combination of inputs from present and past. This brings me to my big question: how is our past experience ÒcodedÓ in the nervous system? How are the present outputs dependent on the inputs from the past? (I think nobody will argue that our behavior is independent of former experience). How are the new inputs ÒprocessedÓ through the former inputs and outputs on the level of neurons?
Serious and important issue, one which research in my lab has had to confront (stop by and I'll give you a reprint). I think your argument is more correct than you think it is, both generally and specifically. Variability of neuronal behavior does provide a basis for macrolevel inquiry, and there is at least in principle a way to (more or less) step in the same river twice. Can guess it, from what we've so far talked about? Irrespective of that, it is obviously important to know how the nervous system stores acquired information, and we'll get to it (though not with any deeply satisfying Ah HA answers, can you guess why?). PG
Although the material is starting to get awfully complex, I still find your class very interesting. The idea of having neurons that are always turned on and of inverse synaptic potentials brings up many interesting possibilities. If these two abilities essentially lower or raise the threshold needed to cause an action potential, is the body able to prioritize it's neurons. In an area of the body that is very important for survival (the brain? an important organ?), maybe the synaptic potential is lowered so that it needs less of a stimulus to provoke a response. Then less priority could be placed on neurons in regions that are less important for survival, or maybe are stimulated more often. In that way the body could better use its resources and would cut back on unneeded signals.
I am still confused about the idea of multiple chemicals, so hopefully we will go over them in class on Tuesday. Tell me if this is the sort of thing you are looking for, or if it is inadequate. Thanks a lot!
Is fine, whatever the class makes you think/wonder about is what I'm looking for. Ask if the multiple chemicals idea still doesn't make sense (actually, we'll get back to it in a few weeks). In meanwhile, try thinking about an interactive system in which there isn't anything that "prioritizes" everybody else, they just all talk to each other constantly. PG
It is important, when dealing with a living organism, to understand how all the parts of the system fit together in to one working unit. In order to do this you have to go to the smallest unit of the entire system. Through a better understanding of the base level we are better able to determine what would cause an organism like ourselves to have a system failure, and what our bodies can or can not do.
I think the basic unit of the nervous system is generally thought of as the neuron. But one can make the argument that one unit is not that important, because the removal of a neuron does not cause the entire system to break down. In fact many neurons are lost everyday (some days more are lost than others ie. Mondays).
When talking about the behavior of an organism we do not necessarily need to know about the individual neuron works or what sort of activity or change in membrane potential is taking place at the neuronal level. However once we get into trying to manipulate behavior and change behavior through artificial means (medication) that is when knowledge of how the "littlest box works" is a good thing. When exploring knew technologies in behavior manipulation it is always good to know what is happening right down to the smallest neurotransmitter molecule, just in case something goes wrong.
Interesting thoughts, worth trying to make them more concrete/rigorous. On the one hand, you're arguing that of course you need to understand the smallest parts (but this leads to needing to study the atoms, no?). On the other, you're (appropriately) arguing that individual neurons may be irrelevant. One relation between the two conflicting arguments is the medical/practical one: the results of studying neurons is useful. But why? And how does it relate to the conflict between the two arguments? Can one construct a still more general argument which resolves the two? PG
You asked us to reflect on how signals starting in the middle of a box affects behaviour. When we addressed this topic, I was under the impression that such signals were not influenced directly by any input from outside. There are many behaviours that are not in response to an external input. Such behaviours include emotion, thought and so forth but what about the little habits and mannerisms that we perform continuously without realising it or consciously telling ourselves to do so. Do these fall under this category also? This assertion though does imply that a much larger overall number of behaviours is possible now.
The second thing you asked us was if an action potential can be behaviour. I find it difficult to consider APs as behaviour because I guess I am not as yet prepared to sum my entire self up to something tiny and electrical. When I think however of how muscles are stimulated it seems a bit more feasible that all the physical (action) aspects of behaviour may be attributed to action potential patterns of activity and their interaction. I do not think that any single AP can be responsible for bringing about any form of behaviour for the mere reason that you have continuously stated that behaviour requires combined activity and pattern of activity. I do not understand though, how an AP (an electrical impulse) or a collection of APs could be responsible for other behaviours such as the entire personality of a person, the emotional aspects of it. I mean, how could an electrical impulse cause you to hate or love or think? There has to be more to the entire thing. What about receptor potentials and synaptic potentials and so forth? They have an effect to. Without sensory transduction we wouldn't respond to external stimuli such as touch and so forth and that is a behaviour too. APs can be considered to have a lot to do with behaviour but there are a whole load of other things involved too. On its own it is just an electrical impulse that would die without synaptic potentials and so on.
If the assertion is that we are our brains and brain = behaviour and the brain is a part of the nervous system and the functional unit of the nervous system is the neuron then I definitely think it is worth learning about them. Neurons are the tiniest boxes within the big box, they are a means of communication between the other medium boxes and therefore worth the study. If the entire box is made up of tinnier and tinnier boxes and behaviour is the result of interaction between all these boxes and inputs and outputs (but not necessary) and neurons are such an integral part of contiguity then they are fundamentally important. If we find that there is an "abnormal" behaviour being exhibited it may have something to do with this intense and extremely complicated communication system and therefore worth understanding. There is so much involved in this system, it is so delicate and intricate that I can sort of perceive that if there were to be some defects in the network, it could eventually have reprocussions on behaviour. For example, in muscle stimulation, if a particular neurotransmitter were to for some reason, no longer be released (in a certain region only) then this could inhibit the conduction of impulses to a muscle and thus not cause a certain behaviour. Right at this moment I still do not really see that neurons have anything much to do with behaviour but I think they are the tools to finding out what does and how.
Nice to have your thoughts back, and all at once on several topics. There is a consistent pattern of doubt, which is useful and appropriate. Middle of the box sounds fine. Action potential question wasn't meant to excluse other kinds of potentials, and I'm not entirely sure whether your argument here relates to those or to a more general skepticism about the possibility of a material reality for behavior. Your last paragraph suggests the latter, but without a particular arguement. Want to try and make one? Or just keep going with course and THEN see where you come out? PG
Perhaps the most important thing I learned about behavior by learning about the smallest boxes, neurons, is that is not random; which however does not mean that it is easily, if at all, predictable. We learned that not all impulses which originate on the neutrons are propagated to other neutrons, and that even those that are propagated can not achieve a lot by themselves, as each neuron listens to a thousand of others and decides what to do based on their collective input. Which seems to mean that in order for some action or a thought to begin, a lot of neurons have to coincide in the firing of their signals, which probably explains why we don't have a lot, if any, random thoughts. Another phenomenon bringing more order into our conception of the nervous system is the presence of the inhibitory synaptic potentials. Whereas before it seemed that the behavior could not be ordered because of the multitude of the signals originating in a random order on random neutrons, that notion is altered if the inhibitory synaptic potentials are considered. Therfore, if some neurons start working, there are others which ttell them to stop. This might mean that the behavior is more controlled and ordered than previously thought, yet I don't see how this might help explain or predict it. Yet another order-bringing factor in the nervous system is that there are "established" pathways by which signals propagate, and that there is therefore selectivity: -- depending on the place where the signals originate they are either propagated or not. But on the whole, even though the nervous system seems to be much more ordered, it is still difficult to imagine that all behavior could be explained or predicted in its terms. SSpecific and not very complex patterns in behavior can probably be explained by some particular interconnections between the neurons; while more complicated processes, like that of thought ( they seem to iherently have a lot more randomness), can be partly dependant on some chance occurences in the nervous system. >Usual behavior patterns, like feeding, and socializing, appear to be at least to some degree explainable in terms of the neurons and the specific passes by which their signals propagate. But what about things which are not usual and demand a totally new and different response, something which has never before happened, for example a human seeing something for the first time. Do new passways for the propagation of signals for some specific response form, or are they just a little modified, does the same signal acquire a different frequency, is the event governed by some rules, or is basically random.
Also, if there are established passways for the propagation of signals, and a lot of neurons with inhibitory synaptic potentials telling others to stop firing, doesn't that mean that a response would be very similar or the same in a variety of somehow similar (or not very different) situations? However when I think about the fact that my responses to different situations are quite different every time, it seems that there should be a baffling number of different neurons connected into specific passways of propagation, and that even with a lot of order-instituting events, the nervous system is still too complicated to explain, or predict behavior, with quite a bit of randomness present.
In my opinion, understanding how the 'littlest boxes'(neurons) work and what they do are important in order to understand behavior. Since we are working under the assertion that the nervous system is behavior, then it would follow that understanding the nervous system also means understanding the behavior we exhibit. Therefore, since the neurons are the basic functional unit of the nervous system, understanding them would lead to understanding the nervous system and hence behavior. In addition, learning the mechanics of the neurons may be helpful to learn about how certain behaviors are caused. For example, if someone has a continuous twitch, then it may be due to the regions of membrane which are constantly generating action potentials (due to the Na ion permeability) or for some other mechanical reason (such as inhibitory synapses). Also we would know where certain inputs come from and how they are produced to create ouputs which are essentially behavior. Furthermore, as in the article about the crayfish, it was important to know about neurons and neurotransmitters to explain and to understand their dominant and submissive behaviors.
Another example that shows the need of understanding neurons to know about behavior is neural networks. They are computer models of neurons which are used to predict behavior and associate memories. So the physiological aspects of the neurons and their interconnections to each other have to be understood to make such a model which will then give a predicted output with all the given information. Finally, it is important to understand neurons for the simple fact that a number of weeks were spent on neurons (and the course is called neurobiology AND behavior).
An Aside: Recently, I was talking with a friend about the nervous system and behavior and an interesting question arose. It was said that people have different brains. What about identical twins who are brought up in the same environment, like say a bubble? Would they have different brains? It would seem like they would have different brains since they would be different people, but then since they would have the same experiences it seems like their brains might be the same.
I'm not sure I follow the logic of your general argument (lots of people think the smallest boxes are irrelevant, doesn't your argument imply we should study atoms?), but the specifics are nice. Yes, some aspects of the smallest boxes show in behavior, and yes, knowing small box properties helps in trying to study the big box. The twin question is a wonderful one, one that has been on my mind for many years. I'm pretty sure we'll have an answer for your friend by the end of the course. In fact, we could pretty much give an answer now. Want to try? PG
While the amount of time spent on the micro-model of nervous system structure and function seemed appropriate, some facets of reductionism seem to disturb me. Namely, it seems as if the trend in science today is to study something on a smaller and smaller scale. One first attempts to ascertain a cellular description, then an molecular version, and then and atomic version, it seems today with the excessive specialisation in the sciences that we are not any closer to uncovering the "truth" about a process, we are solely able to describe it at a more miniscule level.
Nevertheless, being able to understand the processes of the nervous system on such a scale has both educational and clinical ramifications. Extensive studies of the biochemistry of neurotransmitters have produced drugs which specifically target molecules like seritonin, and have been effective in treating both affective and cognitive disorders.
In a way, it seems as if some of my concern from the biological reductionist approach, stems from an ingrained fear that one day we might be able to understand such complex entities like thoughts, emotions, and feelings, on a purely biological level. There are certainly implications, when a feeling of joy can be explained by the release of a certain molecule in the brain, while feelings of jealousy might trigger the release of another. In a way, the prospect of understanding something as complex as the neural arrangements(there are as many neurons in the brain as there are stars in the solar system) in the brain is very scary. Concepts such as individuality, free will, determination and desire might in fact only be certain innate neuronal arrangements or biological proclivities.
However, at the same time, an understanding of the fundamental processes of the brain might bring relief to millions of people who are affected with diseases ranging from alzheimers to anxiety disorders. If relief is sought, then one must surely have a firm grasp on the fundamentals of the explanatory model. Concepts such as depolarization, concentration gradients, and action potentials must be understood fully.
Thanks. At two levels. Am enjoying having you in the course to make important arguments on my own behalf. At the same time, I detect some gratifying sharpening and softening of your concerns, which I hope will continue (as mine have). Offensive (and logically incoherent) reductionism presumes that properties at high levels of organization will correspond in some one to one fashion with properties at lower levels of organization (I actually wrote a paper more or less on this subject, stop by if you'd like a reprint). That's in general demonstrably not so (despite some clincal successes based on this mind set). On the other hand, some understandings of lower level properties turn out to be helpful for clarifying questions about higher level properties. In the end, I think we'll conclude that an understanding of the nervous system does help to make better sense of individuality, free will and the like (some more reprints, if you're interested). They are, after all, biological phenomena (and chemical/physical phenomena). Making sense of does not, however, equate to "reducing" or making disappear. PG
Spending the last two weeks studying neurons in order to understand behavior as a whole was a very important foundation for the course. All along we have been stressing that the idea of behavior is a very broad topic - are we referring to what we consider to be "behavio"r (i.e. - what actions does it constitute) or how we actually act/respond or the questions can go on and on . . . If our focus is how we get the responses we have, then, of course, it is necessary to examine the numerous pieces of the nervous system and how they act alone and eventually together as part of the larger unit of the nervous system in order to get the so-called "bigger picture" of behavior. As we have learned, neurons represent the tiniest part of the nervous system that acts like the whole system. This fact is extremely important because once we know what causes neurons to carry their messages and even how this feat is accomplished, we can get a general picture for the entire nervous system. Since nervous transmissions are sent from neuron to neuron (maybe from a sensory neuron straight to the brain or from one motor neuron to another) in order to get the intended response, the fact that we learn about the various sorts of actions potentials, receptor potentials etc. and how they transmit across the membrane is useful for the overall understanding of behavior. Once we get an idea of signals are carried by the smaller units, we can then study how the larger parts actually carry out the action. Another aspect to consider why these last two weeks have been important in our attempt to consider behavior is the plain fact that not everyone in the class may have studied neuron behavior in depth before. Not only do the various students in the class have different backgrounds but just by explaining the important aspects to neurons and how they play a part in behavior, everyone will have at least a common idea of the nervous system.
Glad you found int worthwhile, and agree that a common foundation is useful. Many people studying behavior would, however, argue with your first point: "that it is necessary to examine the numerous pieces". Why not just get on to the "bigger picture"? Does it really matter for that what the little pieces do? PG
Studying the little boxes was essential to understanding the complexity of human behavior. Whwn one starts studying the neuron and the action potential, it doesn't seem that it will be leading anywhere - it is all so simple that every excitation in the nervous system is produced bythe same size and duration of a permeability change. It is probably very important, however, that things are so simple at that level. The more complicated things are, the more possibilities of malfunctions. It would be devaYYYY]l:s /oa`:}sqx"*JTpx!H1 U]~ >were to go awry. Proof of this withinthe system comes in the form of inhibitory and homeostatic mechanisms. If it were not important how many action potentials took place,$({ok >why would there be regulation of neurotransmiteEk1V/{eMoeEkoYE23+jU um, sorry - i thinksomeone picked up the phone.
I was saying that regulatory systems such as autoreceptors are there inorder to prevent action potentials from going awry. What I mean to say is that all action potentials are the same because the system is less fallible that way.
Once one understands the mechanisms of permeability change and such, one can move onto the mechanisms withinthe nervous ssytem which lead to the stunning complexity of behaviors. Even though the same signal spreads commun- ication from neuron to neuron,the signals are by no means similar. Here we come to the main sources of variability - the receptor and the transmitting chemical. As you pointed out, we only actually need one neurotransmitter and two recept- ors: inhibitory and excitatory. Why then are there so many neurotransmitters as well as hormones and neuropeptides to relayinformation? Why are there so many versions of receptor for each chemical? Why, according to the two-state theory, can each receptor be in an agonistic (R) or antgonistic (T) state. It is apparent thatthere is this great amount of possible interactions between all of the possible types of receptor and chemical for a purpose. It is here that we get the explanation for the complexity of behavior that human beings are capable of. If we had never studied the little boxes, we'd be stuck calling it a miracle, which is hardly what scientists aim for.
Yes, I think that spending two weeks talking about the neuron was beneficial and NOT a waste of time, but I can't say why right now because that kind of ties in with what I think the most important things we learned about behavior through studying the neuron are. I think that the most important things we learned about behavior in terms of the neuron are the different types of neurons and action and resting potentials. First of all, on a broad basis, 10E12 neurons have to be responsible for something pretty big. You said in class that behavior can be thought of as a conversation going on inside the brain, rather, communication going on between the different types of neurons. These different types of neurons are something that I consider an important piece of evidence to prove that behavior is created by neuronal interactions, and also a good way to learn about how inputs and outputs are processed in the nervous system. The interconnection between sensory neurons that recieve information from outside the nervous system, local and projection interneurons that start and end inside the box and convey information to different areas throughout it, and motor neurons that send the information to an area outside the box, proves that there is a sort of network of communication that goes on between the different types, and that they do have a sort of conversation between them. When that connection or conversation is interrupted, there are interruptions in our behavior, such as in the case of the paraplegic.
Two other topics that I consider important in understanding behavior through the neuron are action and resting potentials. I know that resting potentials are transverse longitudinal batteries that exist because of concentration gradients, specific membrane permeability, and passive electrical spread, but I think that the things we learn form experiments involving these potentials are both interesting and important in learning about behavior. You know what I mean- I feel like I understand concentration gradients and what they do, but I think the more general concepts of action and resting potentials are pretty convincing in terms of understanding what they have to do with behavior. The whole light bulb thing really impressed me- the way it lights up just before the muscle twitches. That's an indication right there that charged particles are moving down the axon of the motor neuron, and that they're not only causing a light to go on, but they're causing a muscle to twitch. So there has to be some source of energy, a battery, inside the neuron. Then I was really conviinced about that part where more than one bulb was attached to the neuron and they all flashed in succession, then the muscle twitched at the end. They were all the same brightness, which we said indicates a moving battery of fixed size, and weak batteries made weak lights and strong batteries made strong lights. This idea of action potential is really important for understanding behavior- it just proves that there is an electrical impulse that is responsible for muscle twitches, and, while muscle twitches aren't behavior so to speak, it's not that hard to make the connection that the integrated communication network of 10E12 neurons all working together and in a coordinated pattern could communicate the impulses and potentilas necessary for movement and behavior.
Interesting. Thanks. Worth making more focused/coherent argument. What I gather MOST impresses you (the lightbulbs) is the evidence that small, material elements ARE involved in behavior. Is a good point, one of enormous historical importance though not frequently noticed explicitly. PG
"Was it Worth it to Consider and to Explore Behavior in Terms of the Neuron?"
I would have to express wholeheartedly that exploring the smallest box, the neuron, was crucial to beginning the quest for understanding the nervous system. To begin, I have always been somewhat daunted by the mysteries of the brain and the workings of the nervous system. By "reducing" our initial exploration to a single unit, the neuron, it became clear to me that the search need not be one of infinite complexity and confusion. This is not to ignore the intricacies of the nervous system, but rather to assert that by highlightin g the neuron I have become more comfortable with the fact that there is an underlying explanation and order to the great system.
By analyzing the neuron I have come to appreciate a number of events that underlie behavior. First, behavior can start within the nervous system. This seems to imply that there is in fact an "inner self" that orchestrates and conducts a high degree of our actions. To carry it a step further, this also suggests that in our control-oriented society, we do not have the ability to exert complete control at the most basic level, within our own body. In many cases, this "inner controller" is essential because it organizes such processes as heart beat and breathing patterns, but it also implies that there is a potential for the great Freudian slip!
A neuron's ability to selectively categorize, differentiate,and sort incoming messages, heeding only certain calls, is truly amazing as well. Our body seems to actively limit our "true experience." It is essential, however, that our body exert such control. If our brain had to address all of the perceptions and emotions experienced during the course of the day, we would surely be unable to function. Then, one must ask how the decisions deciding a signal's importance are determined and what that suggests about free will. Perhaps, this is the key to individuality.
By exploring the neurons, I have also come to appreciate the important fact that neurons do not work in isolation. Instead, messages are conveyed through particular pathways. To attempt to understand the neuron, it is also important to evaluate the universal signal, the action potential, that travels between all neurons. Once behavior is considered in light of neurons and actions potentials it becomes clear that behavior is generated on a simple level. Now, with the confidence that there are universal staples, I feel inspired to uncover the secret ingredients, including the effects of receptors and neurotransmitters!
Wow. Now THAT's an argument (a set of arguments) for being sure to cover the neuron in thinking about behavior. Thanks. In some contexts, there are people convinced that studying neurons is a waste of time. Mind if I use your arguments in such contexts? PG
We are constantly reminded "don't lose the forest for the trees," but can we truly know the forest if we don't know the trees? I believe that in order to have a full understanding of the big picture, it is indeed important to know the smaller components of it. As we begin our exploration of neurobiology and behavior, it seems proper that we should begin with an understanding of the small parts that will define the greater whole. Understanding what a neuron looks like, how big it is, how many we have helps to place into perspective possibilities for an explanation of behavior. How could we understand behavior in terms of "patterns of action potentials" without understanding an action potential and how one is formed in a neuron? Although surely a significant amount about behavior and the nervous system could be learned without an understanding of the neuron, it would be somewhat incomplete without it. Two weeks on the neuron at the outset of this course is time well spent in preparation for the quest of behavior. We can certainly better understand the forest by spending some time lying under the shade of a tree.
Yes, but ... Lots of people don't buy the argument that you have to understand neurons to understand behavior. And your argument, in its bare bones, would require us to understand atoms and quarks too, no? Germ of a stronger argument: yes, couldn't appreciate "patterns of action potentials" without knowing what action potentials are. PG
When I began this course I thought that the nervous system and behavior had some kind of connection to one another, I just had no idea where that connection lay. After a month of studying the nervous system in more detail (focusing on concentration gradients, changes in permeability, current flows, and the various kinds of potentials that exist in a neuron), I know that behavior is connected to the functioning of the nervous system. This does not mean that I believe the nervous system and behavior to be the same thing. But upon understanding the brain's connection to behavior and vice-versa, we can begin to lay a foundation in understanding if they are in fact the same thing.
>The nervous system is a complex network with many intricate parts involved in it's functioning. Some parts are more significant than others (in relation to behavior), but each part is needed to create the system itself and to carry out the system's function--basically telling the body what to do. The reason we studied action potential for two weeks (and will continue to study it) is so that we can begin to understand the signal an action potential relays and how that signal affects behavior. When we discussed two processes where action potential was involved (i.e. we see lightning and we hear thunder) we had to ask ourselves, What distinguishes these two experiences? We began to look deeper into action potential and found that maybe the difference in experience was caused by a difference in the patterns of action potential. Maybe the nervous system interprets signals differently in relation to where they originated and what their destination is. We found that the significance(in regard to behavior) was not the action potentials themselves, but rather the pattern of connectivity in the nervous system, thus affecting patterns of behavior. We went further to discuss synaptic potentials and the fact that a change in permeability affects the transmitter release, in turn affecting the length of the synaptic potential. The length of the synaptic potential is relative to the length of the output given (thus behavior). These are concepts that I do not fully understand, but I am intrigued by. They definitely force me to question my belief that behavior is mostly socially constructed. It is amazing to think that such a complex structure, like that of the nervous system, has a reason for everything that it does. I have only used two small examples to depict the nervous system's influence on behavior. But even they illustrate the importance of understanding the brain and something as miniscule as a neuron to gain a better understanding of one's behavior.
we spent two weeks discussing the smallest boxes in the N.S. was it worth it? well, we are much closer to understanding behavior than we were two weeks ago, but we have simultaneously opened a Pandora's box of more intricate mysteries of the N.S. but i am enthused by the possibility of what is to come. i am revelling in the fact that i am beginning to better understand the nature of humans. this is a big part of my long journey towards healing ailing human conditions through the practice of medicine. i've have been anxious to get to the heart of my academic ambitions. requirements to get here are nearing completion, now i have the chance to study what interests me most. i'd like to take this opportunity to thank you now for the education that you are offering us. i apologize that this is short and simple, but i have been very sick. thanks
Everyone gets sick now and then, no problem. Short, simple, gratifying, and also intriguing. I can't help but want to know more about why it feels to you like you're getting (finally?) to the heart of what interests you. PG
When examining any system, including the nervous system, it helps to reduce it to the smallest part in order to understand the whole. If we did not know that the neuron can start an action potential without initiation from the outside, we could not understand or explain how the nervous system controls behavior that could not be catagorized as a response. By understanding that behavior is the chemical movement of ions at its simplest level, we can begin to understand it at higher levels. Examining the neuron has not answered all my questions about the nervous system and behavior, but has led to more questions. For instance, if a person learns to change their response to a stimulus, is that a result of a change in permeablility of the axon? Can learning cause chemical changes and if so how do the neurons change their permeability to send a different message? The study of the neuron is certainly an integral part of understanding the nervous system, but it leads to more questions to which the neuron may or may not be part of the answer.
Lots of people don't agree with your general point, that it helps to reduce things to their smallest parts to understand the whole. But you've given two good reasons why that is true in this specific case. Aspects of the parts are visible in the whole (spontaneous behavior), and raises new questions to ask of the whole. Thanks. Worth trying to generalize to other cases. PG
I think that it was tremendously worth the time and effort to spend the past 2 weeks on the littlest boxes, the neurons. During this time, I learned how the neurons communicate with each other, and I began to understand more about the idea of how behavior is a pattern of large number of interacting elements in the nervous system. I am also beginning to see how there can be freedom of choice in the nervous system when I look at how individual neurons are "listening" to 1,000 other neurons and then deciding to "speak". The neuron can repeat what others are saying or it can say something different, something new. Before, I had the notion that the same message was relayed from one neuron to another, and that the patterns arose from the different connections in which the message traveled.
All makes sense, glad it worked. Can you be more explicit about how this makes a difference in thinking about behavior? What new questions come to mind because of what you've understood? PG
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