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From last week's dialogue. . .
Hmmm. If brain=behavior, how can there be "an interface between [the brain's] mechanisms and our perceived mental states"? Presumably, perceived mental states are themselves brain mechanisms? So what is the real problem in characterizing consciousness as a brain process? Glad you like Dennet, I did too. But even he doesn't, it seems to me QUITE put his finger on the problem, as pointed out by John Searle in a two part NY Review essay (starting 2 Nov 1995). Have you seen it? Sure, it has something to do with verbal report, but I think there are some additional subtleties. Let's keep the question (and ambition) in mind, and see where we are at the end of the semester. PG
Well, one of the problems I had with Dennett was that he denied the existence of qualia by saying that they only seem to exist...but isn't that the point? How can qualia not exist if they are really defined as the sensory experiences we have...and we do have them. Their "seeming" is sufficient evidence in favor of their existence to allow us to refer to them. We need some way of referring to the perceived mental states..and I do believe that brain=behavior, but that it is also valid to speak of our subjective experiences as something separate from the mechanisms that they _are_, because what they are is not what they seem to be. I just think we should keep in mind that this separation is simply useful for our discussion, not a representation of reality. But then you're right; if I speak of "perceived mental states" this way there is no interface - that was a poor choice of words. Perhaps "relationship" would have been more appropriate. I don't think we can deny the existence of a relationship.
I haven't seen the Searle, but I take it that he and Dennett don't quite get along. Do you happen to have a copy?
Have the originals, from which copies can be made. Searle has the same problem with Dennet you do, accusing him of trying to make the qualia experience disappear. And I agree with you (I think) that making them disappear is missing the point. If brain=behavior, then something about the brain has to explain what gives rise to the experience of qualia. That's the additional subtlety. Any idea how to deal with this? PG
Any idea how to deal with it? I wish that the brain-qualia connection were one that I had some sense of. But I suppose lots of people would love to know what's going on with this one... It seems as though it would be awfully difficult to deal with qualia without regressing to the old, long-discredited introspectionist psych techniques. I agree with Dennett that if we knew _everything_ about the workings of the brain, as in the case of Mary the color scientist, we'd know how qualia worked. But he still evades the point. And I can't just say that if we keep plugging away at neurobiological, cognitive, etc. studies we'll get there someday. There has to be a shortcut. We can't need to know everything about the brain before we can understand qualia or other intriguing little things about consciousness.
This sort of leads into essay #2, which I was going to post on the newsgroup, if it exists yet, but my newswatcher disk is suddenly unreadable for some reason.
The sheer number of smaller neuron "boxes" that exist in the structure of the larger "box" of the brain (and spinal cord) could evoke conflicting thoughts about the idea that brain=behavior. There are so many neurons that one might be tempted to think that surely they must be able to account for all the subtleties of behavior - even that there might be specific neurons that perfrom very specific tasks, as in the case of visual perception and Barlow's "grandmother cell" theory. But behavior itself is such a huge category that we can't visualize how much must be involved in its production. The computational problem of combinatorial explosion, along with experimental evidence, has shown that the brain=behavior view is far more consistent with the idea that patterns of activity, rather than individual pathways, produce behavior. Actually, "produce" isn't the word I want to use, but I also have the same problem with the linguistic inaccuracy of saying "the brain equals behavior" that I have with Dennett's dismissal of qualia because they only seem to be there. So I'll say "the patterns of activity manifest in behavior," for lack of a better term, but I don't think I've missed your point about avoiding separation of behavior and the brain. Even assuming that patterns rather than direct input--- output progressions of activity are behind behavior, it's difficult for us to conceive of a way in which this could come about. But this is because if the extent of our behaviors is hard to imagine, so is the huge number of possible patterns that nervous system activity could actually form. Since there are so many neurons to begin with an each one possesses thousands of connections, it seesm to me that we must forget the intuitive resistance we feel when confronted with the idea that our brains could be everything that we are - behavior, consciousness, thought - and accept that sufficient conplexity of connections, combined with hierarchical and parallel brain organization, could account for more than we may readily grasp.
I'm still thinking about possible ways to deal with the qualia problem. Last semester I read an article by Davida Teller on linking propositions (associations between physiological states and perceptula states) and their necessity in vision science. An example would be the perception of Mach bands and their relation to the cells that are responsible for this perception, or edge detection and center-surround activation, etc. The article said that most vision scientists accept the idea, at least for vision, of the "bridge locus" - one specific mapping point in the brain at which a physiological state is mapped onto a perceptual state. Thinking about a bridge locus in terms of consciousness is completely contrary to Dennett's entire claim about the nature of consciousness; I suppose he'd deny the vision bridge locus as well - he'd have to. I wonder if this denial is premature?
More than intriguing conversation, looks like we have a lot of thoughts in common. Not sure whether this is your third essay, or a bonus response to my response to your second, but doesn't matter much. Accept your concern about "linguistic inadequacy" of brain=behavior together with agreement that brain/behavior not separable. Would like (both of us) to better understand "linguistic inadequacy", not as challenge to its validity but because it might point us in direction of some issues yet to be resolved. Would also be interested in reading the Teller article, to understand better what is meant by "bridge locus". Am persuaded that the qualia problem looks and feels to many people like a critical problem requiring new insights. Am myself less sure that's so, more inclined to believe that all the pieces to understand it are already available. Is part of what course is building to. Want to try and guess how it will come out? And then we can get on to whether it actually resolves the problem? PG
The Uniformity of Action Potentials, the Summation Effect, and Their Implications
Behavior as the result of "a bunch of identical action potentials" fits well with the summation effect I discussed in the previous essay. If action potentials have no character of their own, it would seem that the only way to get variations in behavior from these identical subunits would be to vary the amount of input that each subunit would have in a given behavior, if it has an input to that behavior at all. This could take the form of a 1:1 influence: neuron A fires an action potential, causing neuron B to fire; or a less direct influence: neuron A fires, but its input alone isn't enough to make neuron B fire. An additional input from neuron C, or having neuron B already be partially activated (slightly depolarized), is necessary in order to make neuron B fire.
The latter method has implications for the equation of brain and behavior. While a given input could be what caused neuron A to fire, neuron B's partially activated state could be completely independent of outside input. Similarly, neuron B could just as easily be in a constant state of hyperpolarization, making it difficult or impossible to make it fire. This would be independent of input from other neurons which may be influenced by information from outside the nervous system. If that is the case, then the brain (as represented by neuron B) is behavior. It is what has the ultimate say in whether or not a behavior is carried out. IIf the brain is behavior, then one might wonder if it would be possible to manipulate behavior by manipulating the brain. That has been demonstrated by manipulating neurotransmitter levels to change behavior. Drugs like Prozac are often effective in treating depression by altering serotonin levels in the brain. Similarly, manipulating dopamine levels has helped treat many schizophrenics. Is it possible that we'll eventually be able to identify the neurons associated with specific behaviors and manipulate their resting potentials directly? Perhaps we could artificially block some of their receptor sites. If this could be done, we could produce a lasting effect on behavior, and eliminate the necessity of patients taking a particular drug for the rest of their lives.
Yep, summation significant. In fact, is very rare for an action potential in one neuron to cause by itself an action potential in another (as we'll see). I'm not sure though that I follow your brain=behavior argument. A neuron or "the brain" has "ultimate say in whether a behavior is carred out" isn't clear to me: the brain (neurons collectively) IS the behavior being carred out, no? Yes, of course, an implication of all this is that physical influences on the nervous system can alter behavior. What KINDS of effects they can have is a subtler question. Remember that in general behavior corresponds not to whether individual neurons are or are not active but rather to patterns of activity over very large numbers of neurons. PG
Sorry about the last message, I sent it to the wrong address then it was sent back to me and I forwarded to you.
I have a feeling there is a relation between starting an action potential via a sensory neuron and starting one in the middle of the brain. Normally an action potential is started by a mechanical, checmical, etc. deformation of the neuron allowing the permeability of the neuron to change. So what other causes are there that could produce the same action without an external input? Mechanical would be difficult but a chemical change would make more sense in the brain. Actually what exactly is a behavior started inside the box? How about the relization that you are in a bad mood but you are going to make yourself be happy because you know that there is no good reason for you to be in the bad mood. Focusing in on the point where the person decides to change their mood will help divulge the answer to my question. Is it as simple as the statement the brain is behavior? Does that mean that behavior is the brain? I guess you can't propigate a behavior without the brain but it is apparent that your behavior can effect how you feel, ie. your brain. UGHHH! This seems like a circular argument that can never be solved. I suggest that the neocortex is the propigator of these action potentials. This doesn't explain how the neocortex works but it does explain why there is such a difference between mammals and all other animals, insects, etc. If the neocortex was involved with selfrecognition it would be the guardian over the rest of the brain allowing it to override the brains instinctive behavior. In that case the self would be the hybrid of the neocortex, brain and spinal cord. Each controlling there own area, the spinal cord taking on outputs that do not have to go to the brain, the brain dealing with more complex, multiple variables situations and the neocortex recognizing self and working out processes where a new action potential pattern is necessary.
Interesting and appropriate thoughts/extensions along multiple box line. Sure we need "cause" for action potential without external input? Could just be that particular neurons have regions of high sodium permeability, no? But yes, indeed, could explain why feeling bad in morning even if nothing has happened. CHANGING that a different problem, related to the "I- function", which we'll get back to later in the course. Will (I think) give us a way to break sense of circularity. Actually, you're already moving in that direction, with your thoughts that the neocortex interacts as a distinct entity with other parts of the nervous system. Its NOT the only brain region that can start its own action potentials though. Can you think of any other thing it could be doing to break the circularity? PG
"What about those signals that start inside the nervous system?"
According to the article "The Chemistry of the Brain" by Iverson, the brain is the most active energy consuming organ in the body. Its rate of metabolism (20% of the body's total resting energy uptake) is constant and may even increase during sleep. This is incredible considering that sensory and motor neurons, whose firing are most easily interpreted as the starting and ending points of a behavior, seem least likely to be active when the human is asleep. This information is evidence that the behaviors due to the activity of the neurons of the brain do not necessarily depend on the amount of input given initially to sensory neurons. So, some activity must be originating not at the sensory neurons, which touch the exterior of the nervous system, but at the interneurons, which lie only inside the system.
But wait a minute, how do those interneurons "know" to fire? A "behavior" is a pattern of activity across a large number of elements, thus there must always be a starting element and an ending element in this activity. When a sensory neuron is involved, then the starting point for the behaviour is obvious: the firing begins at the neuron touching outside the nervous system, the neuron which has received a message from the outside to fire. However, it is not that obvious when a pattern of activity supposedly starts within the nervous system. Does this then mean that although specific neurons can not be labeled as "behavior=laughter" neurons, for example, there are, indeed specific "start" and "stop" neurons? And what starts and stops them?
Here is another angle. What if those "start" and "stop" neurons were at one time sensory neurons? I am thinking of human development from conception (about which I know nothing sophisticated) and that there has to be a first neuron. This neuron must be all three types at once: sensory, inter-, and motor. Then at some point, there are three neurons, which gives rise to the possibility that one is an interneuron. Could that one have been the first sensory neuron, just moved inside the system? A neuron which was "used to" certain processes being carried out in the embryo? If so, maybe it would "know" what it needed to be doing, which patterns to start, without being signaled first by the sensory neuron.
I do not know if this scenario really makes sense, but I would like to continue playing around with it if it is not way off base. Very interesting, thoughtful. Sure, play more with it. Connection to Iverson entirely appropriate. Interesting issue is whether ANY neurons "know" what to do, as opposed to simply doing what they do because of their permeabilities. And, if the latter, how does the whole thing (the pattern across all of them) have any coherence? From this perspective, the issue is more what gives rise to coherence than whether interneurons start out life as sensory neurons (I doubt it, though the question is not one which any one else ever raised in quite the sense you do), since the same coherence question exists whether the action potentials start in sensory neurons or interneurons. PG
Knowing that certain regions of neurons are constructed with open sodium channels, one would logically wonder which functions and which area these particular areas control. The first area that comes to mind is the brainstem in which the most primative of responses may be found. Here, neurons could initiate action potentials to maintain breathing, pulse rate, blood pressure, etc. for basic life functions. However, one runs into problems considering that the sino-artial node of the heart functions independently of the nervous system. Even more interesting, how did this arrangement come about? Does the same structural phenomenon hold true with other orgainsms besides humans?
The heart, as a muscle, would undergo less dramatic morphological changes over time than the nervous system. Thererfore, it would seem much safer to make a process as vital as cardiac contractions independent of the nervous system. Or, this area of the heart could perhaps be a vestigial structure of the nervous system which has since evolved into a separate entity. Another advantageous aspect of this arrangement could be the location of the sino-atrial node as opposed to a cardial structure connected to the nervous system. Considering the fact that our early ancestors led extremely difficult lives; the incidence of head injury and trauma would have been much higher than it is for the average person today. Damage could occur and thus affect the individual's heart permanently. Therefore, placing control of heart beat regulation under autonomous control would be a much better option than neurological control. TThus, one still wonders if there are any other vital life functions which, like the heart beat regulators, has evolved independently of the nervous system in a manner like the open soduim gated neurons.
Interesting issue, both specifically and generally. Heart does indeed have autonomous action potential generation. Question is whether that is because of natural selection (better because of head injury?), or because of some more general reason. Truth is that autonomous action potential generation is pretty ubiquitous. Many muscles, and many, many different nervous system regions. We'll see this as we go along. What it suggests, of course, is that "autonomy" is in some sense a characteristic of the primitive elements out of which things are built, common to most things (certainly not restricted to humans), rather than being a response to particular selection pressures. PG
At the end of class on Thursday, the "possibility" was presented that one source of action potentials is that the proteins which make up the Na+ channels are stimulated by other proteins simply "floating" around. These two proteins have a lock-and-key fit so that when the two join up, the Na+ channel is activated; it opens up, allows Na+ to flow in, and thus creates the action potential. This idea appears to be a good explanation of why there are sometimes outputs of the nervous system without any apparant inputs--why "some things start inside the box."
Where do dreams come from? How do you get ideas from seemingly nowhere? Why do you get a sudden chill in a warm room? Now we have a way to tidily explain away all these phenomena. John Lennon's creativity and Albert Einstein's genius can be simply due to an excess of those floating proteins or to mere luck that they happened to meet up with the proteins of Na+ channels. It's a rather humbling thought. However, it gives hope to the people who have uncontrolled movements as the outputs of someting that began within the box; it gives them something tangible to blame, and hopefully, to fix.
Interesting, appropriate extension to creativity (and problems). Careful though about origins of spontaneous action potentials. Needn't (though might) have to do with proteins (chemicals in general) "floating around" and sometimes contacting proteins in membrane. Can instead be simply that cell is built with particular proteins (open sodium channels) yielding a constant high sodium permeability. PG
Professor Grobstein, I am sending you only a short (unfinished) set of thoughts because I feel bad about turning my essay in late again. I will write more tonight. You can just count the current version for my final grade - I think that would be fair. Hana
In my third essay I would like to consider the case when "behavior starts from inside the box". As we have learned during the last class, the proteins which determine sodium permeability carry specific genetic information. Consequently, the action potential depends on genetic coposition. Does this mean that the same input generates different outputs in different individuals only because the genetic information is different? If, hypotheticaly speaking, we take two individuals with identical genetic information and identical input, does that guarantee identical output? I was not quite sure in the last class what exactly is the role of these proteins in determining behavior. I am still wondering about the interaction of genetic and learned bases for behavior.
No problem. But do enjoy hearing your thoughts, and setting them down regularly will help you get the most out of the course, so try and give yourself scheduled time for them.
Proteins don't so much "carry genetic information" as result from it (or express it). That point aside, your questions are appropriate, ones that have always interested me, and (I think) answerable ... once we have talked more about the relation between neuronal activity patterns and behavior. The twin question is one that has intrigued me for years. If you'd like a foreshadowing of where we're going, there are some articles I've written available on the web at http://serendipstudio.org. Or stop by my office sometime and I'll give you a reprint or two. PG
I am not really sure what you are looking for, so I'm just going to write my feelings, and maybe you can tell me if I am doing this right or wrong.
First off I would like to thank you again for letting me enrole in your class. I am telling the truth when I say that I am really enjoying it. It is different from most other classes I've had, in that it really is a discussion. Even though I missed the first weeks of class, I am very able to follow along in class. Even though it is a science class, you do a great job of just lecturing without writing anything on the board or without a book.
Probably the thing I like best about the class is the way everything fits together. The human body is SO complex, with so little margin for error, yet most of the time everything works. If someone were to sit down and try to develop a system as complicated, as interwined, and yet as efficient as the human body, it would be impossible. A couple years ago I heard a scientist speak at my Mom's office, and he was saying that the more he learned about science, the more religious he became. He was convinced that there must be something greater that could have created all of this. It just boggles the mind. There is such a delicate balance involved in resting potential, in potassium pumps, in selectivly permeable membranes, it is all truly amazing.
I stumbled across your articles in the serendip home page, and some of the things you said really interested me, especially the article about learning how to think. As a future teacher (knock on wood), I think I would like to discuss some of the things you said at some point.
I will see you tuesday, Dan Feinberg
Thanks for the kind words; they pleasingly express my aspirations for the course. The religious issue (can such order and balance emerge without anybody being in charge?) is an appropriate one to have in mind, and I'd be pleased to talk more as well about teaching and its importance, a matter about which I feel very deeply.
So, with those general agreements, let's ALSO try and talk more about the specifics and details of what "fits together" and what doesn't. I'm not so much concerned about whether you know the details. Your questions in class seem to indicate you're not having any trouble with the material. In a very real sense, though, the ability to make greater sense of the general issues depends on and emerges from seeing how the details work out, what makes sense and what doesn't. WHAT fits together (and what doesn't) in your mind, and in the class? PG
As was discussed earlier, we have been able to roughly categorize behavior as a result of many different patterns of neuronal firing. The knowledge of how an action potential works simply reduces behavior to a smaller unit of action (from neuron firing to an electrical current/chemical exchange). I have a bit of trouble accepting that behavior is able to be reduced to chemistry. When I think of electrical current or ion exchange or any chemical activity of that sort, I think of uncontrollable actions. We always think of electricity as something that we have to keep under control, and by keeping it in control we make it useful. In that way I am able to accept that there is electrical current in our nerves, but I am wary to accept that this is the foundation for our behavior. I would be more ready to accept that something in our nervous system (the brain) controls or generates this electricity as signals FOR our behavior not as signals that ARE our behavior.
Are SERIOUS skeptic. Is fine. Keep us honest. In turn, be a little careful. Action potentials aren't electricity, they are permeability changes which can be observed as electrical events, and which have electrical consequences. That said, your concern about needing to control electricity is still valid, at least metaphorically. The issue in thinking about brain=behavior is precisely the question of whether order depends on someone being in control, or whether it can instead emerge from lots of different elements doing their own things and talking to one another about it. Let's see whether your feelings change as we talk more about it. 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
It seems that the start of an action potential can be an almost random event starting in the "box"in such cases when it is not stimulated by some outside input. It appears to be random because it occures when some particular region of a neuron's membrane has an increased number of Na+ channels, therefore being a continuing generator of action potentials. I have trouble imagining how action potentials generated in some of the vast numbers of regions on the vast numbers of axons can end up as something like thought. Perhaps because the process of thinking seems to be quite ordered, and thoughts seem to be always brought up by some association with other thoughts, I don't understand how they can just appear unless there is some order in the generation of action potentials (I think I might be mixing two different things -- how the thoughts begin, and what happens to them afterwards). But if there is a very large number of regions on the neurons where a very large number of action potentials can appear, a lot probably at the same time, I don't understand how any coherent thought can ever start (and why sometimes there don't seem to be any thoughts present). II have trouble understanding behavior in terms of action potentials. (I think I just distinguished between thinking and behavior) If behavior is based on the appearance of action potentials, then it should be very random and almost unpredictable, unless there is some order, some semblance of a pattern in their emanation. Perhaps some regions on some particular neurons are more active than others, or may be action potentials originating on some neurons are not "taken as seriously" as some others. But even then, I don't see how it is possible to be able to understand the behavior in terms of an immense number of action potentials which can originate in many different locations on the neurons, and at any time. (If a behavior is a response to some particular input it seems to be easier to understand than if it just originates inside the box.) A lot of behavior is learned (?), and does that mean that with time some regions on the membranes of neurons with a lot of Na+ and K+ channels become more active than the others, or that those neurons which generate unneeded action potentials die?
Interesting, appropriate questions. General issue is how get order in patterns of action potentials? Agree it has to be there (though perhaps less of it than one might think at first). Any idea how it could come about? Let me know if we don't adequately deal with the matter. Notice that it all being action potentials, the border between "thinking" and "behavior" (or anything else) starts to get pretty fuzzy? PG
During the last part of class, it was briefly explained how 'signals start in the box' (as mentioned earlier in the semester). Now, knowing and understanding the mechanism behind how these action potentials start in the nervous system (without the presence of an input), it seems as though signals (action potentials) actually can and are started from within. In my opinion, accepting this new information leads to further support of the assumption that the brain and nervous system are behavior. Since action potentials can be generated in the nervous system due to the permanent regions of sodium ion permeability that are constantly "on", an output can occur without resulting from some external input. Therefore, if action potentials originate from the organization of the nervous system itself, then the resulting behavior is (and is from) the nervous system, and the nervous system alone. Hence, the argument that the nervous system is behavior is strengthened.
In the cases where the action potentials in the nervous system correspond to some external inputs (i.e., noise, smell), the argument seems to be further substantiated. These action potentials may also result in some output/behavior. Since the action potentials are what correspond to such external inputs, it again leads to the nervous system being behavior, because the action potentials are what corresponds to them and then some type of behavior results. From all the information, it seems as though the nervous system is behavior, but more specifically, it seems like the action potentials are behavior.
It was mentioned that these action potentials are all the same signals. Basically, they are just waves of sodium ion permeability. This suggests that on the level of action potentials, they can not be distinguished to what behavior they may lead. So, then how do action potentials lead to a certain behavior? Is it due to the pattern of action potentials, or does it depend on the location, or something else?
Good summary (if slightly wordy in the middle). Good questions, with some appropriate possible answers. Will get to them. PG
NOTE: Sorry, this is e-mailed late. I had some problems with sending e-mail and couldn't get it fixed until someone at the desk in the computer center knew what the problem was.
No problem. Good summary of where we are. How do you feel about it? No new questions in your mind? What do you think we should do next? PG
From the discussion of action potentials and how they function this week, I come to two conclusions. One, that behavior can start in the middle of the nervous system. This occurs when there is a region on the axon of a neuron built with high sodium permeability which would self generate constant action potentials. The significance of this conclusion is it confirms the assertion that behavior is not a bunch of imputs connecting to corresponding outputs but behavior can start in the middle of the nervous system.
With the assertion that behavior is the nervous system, and the nervous system is made up of many boxes called neurons(the smallest boxes in the nervous system), and the only activity occurring in these boxes are action potentials, then behavior must be derived from patterns of the same action potentials in neurons which cause messages to travel between neurons. This leads me to conclude that behavior is not as complex as one may think without having thoroughly studied behavior and that to study behavior, a large part of that studying would have to be focused on the pattern of action potentials that cause a certain behavior.
In the true spririt of biological reductionism, the complex behaviors of our species have been reduced to electrochemical phenomenon occuring on the membrane of the axon. This pattern of reductionism is indicative of a larger trend in the natural sciences which attempts to explain all physiological processes first in a gross sense and then in a cellular one.
Complex machinery has revealed that electrical events are actually transpiring. Electricity provides us with a feasibole explanatory model which allows for rapid reaction times. Nevertheless, the claim that all behavior is traceable to solely the brain and spinal cord has not been established. It sems as if all we have done is simplified our model of behavior from a gross model to a micro model.
We now know that there are quingillions of cells called neurons which commmunicate using an electrical medium. When I think there is an electrical current going through some of the neurons in my head, when I throw a baseball a current is flowing in neurons in my arm. We have also devised a model which helps us to explain those behaviors which originate in the brain. It appears that what has been established is that these cells communicate in acertain way--but how, why, and when they communicate has not been explored. In other words, we know they are using ATT to call Kansas but we don't know why the call is going there yet or how our call is interacting with the call of a neighbor to California.
I would HATE to be seen as a champion of biological reductionism. At the same time, the evidence suggests that what the brain consists of is in fact nothing more than a lot of neurons sending action potentials to one another. This is important precisely because it defines the properties of the elements from which behavior must emerge. What is does not do, as you correctly point out, is explain how or why particular messages are sent at particular times in the large array of neurons which constitutes the nervous system. We'll get on to that but needed to know what the elements and messages are first to be able to pose the higher order problems in an answerable way. Ready? PG
I do not think the fact that behavior can now be thought of as a series of action potentials alters the idea that the brain equals behavior. It might not sound as pretty or it may even just sound much too succinct to describe the entire process as a series of action potentials yet the idea makes sense to a certain degree; considering that the role of action potentials is to send messages over a long distance, it is not that hard to consider that they make/result in behavior. These messages from one neuron to anothercause the body to act (i.e. - behave). As the brain is what seems to be used to process all these messages being sent around the body, the brain still can be considered overall "behavior." AAs the neurons are the smallest unit of the nervous system that "behaves"/performs the duties of the nervous system, their communication through action potentials results in what we would term "behavior." Because of the cooperation of neurons, we act, we move, etc. I still get a little fuzzy when we consider how we "think" or "philosophize" but the fact remains that basically the action potentials across membranes eventually lead to some sort of response or even just a complete lack of response to an input. What is interesting to consider is that all sorts of sensory trandusctions must become an action potential in order for the information to be relayed across the body. Such an idea furthers the notion that the action potentials are what causes behavior as any sensory input in order for the body to respond to it must become an action potential and move across the membrane.
In general, this thinking is actually helping me to understand how the system works more and more. As I consider what is going on, the fact that it can be described in more specific terms helps shape how brain equals behavior in my mind. Each week we seem to be going more in depths (not all too surprising but . . .) so instead of just thinking of the nervous system as boxes, it is now neurons that can communicate due to action potentials. It will be interesting how this notion is even more clarified.
***************cccccccccccccccccccccccccccccccccccccccccccc***************** **One day! one day who knows. Someday! someday I suppose. There was a verse that I was going to write. I haven't yet but there's still a chance that I might. - Mighty Mighty Bosstones ***************cccccccccccccccccccccccccccccccccccccccccccc*****************
AM glad that it feels like we're getter deeper and deeper. And yes, of course, there is (should be) some fuzziness still to clarify. Best done by trying to be as concrete as possible about what you DO know/understand, AND (even more importantly) what you don't. Can be more concrete about how various things make YOU more comfortable with brain=behavior? And about where the fuzziness is? PG
Preliminary thoughts on the signals which start in the middle of the box:
If one thinks generally about the implications of "spontaneous" action potentials arising from within a neuron and spreading from there, one might think that problems would result. It might be rather chaotic if neurons all over the brain were deciding to fire at random since there is such a high degree of interconnection. Why aren't people twitching and hallucinating all over the place? Furthermore, could some of the behaviors we explain in terms of some input or "cause"actually be completely spontaneous and without cause other than a neuron with an area of the membrane significantly permeable to sodium?
So now that one is all worked up with the possibilities,one has to consider the probable. Many action potentials die on the vine. They might make it across a few neurons, but not have the impetus to be considered "enough to be excited about" when some neuron sums the input at the postsynaptic area. In that case, it may not ever make it to amotor neuron or a sensory neuron or even do enough that there will be any sort of tangible result to us. I'm limiting things a lot, I realize, by talking only of what the person who owns the nervous system _detects_. Furthermore, it unlikely that a spontaneous action potential is going to generate the pattern of excitement that will result in a complex behavior like walking.
Now to consider the uses of these action potentials. Perhaps they can help to explain dreaming and such difficult things as imagination. When we imagine something, we probably feel as if it all started with some input - something triggers a memory or an image in our head. Sometimes, though one just thinks of something and has no idea whene it came from. The middle of the box perhaps? Dreaming is another matter - where on earth would that input come from? Since our senses are operating at a limited state -our eyes are closed etc - it is unlikely that the triggers of the dreams are exter- nal. There is, of course, the case in which you have to go to the bathroom, so you dream about doing so (dangerous in small children), but most dreams are not this trackable. Perhaps these action potentails play a role in the often unpredictable quality of behavior, which, as I mentioned in an earlier essay, is rather adaptive. They could be another mechanism to produce variability. In any case, they are useful in order to exaplin some of the complexities of behavior which are not so easily explained.
Nice thoughts. Not so "preliminary". Yes, indeed, can account for some intriguing aspects of behavior (dreaming, imagination), AND raises some new questions about how the whole thing can work coherently. PG
Behavior is a series of action potentials. Action potentials are waves of sodium permeability whose signals are indistinguishable They function as a longitudinal battery along the axis of the axon. There are an infinite number of different kinds of longitudinal batteries characterized by the permeability of their membrane. Moreover, genetic information results in regions of high sodium permeability in the neurons; therefore action potential can be generated inside the box without input from the sensory neurons.
This is what I understand to be an action potential as described in class. I am not sure how this translates to a particular behavior. Each time I place my hand in fire, does this input correspond to identical permeability along the neurons and therefore the identical behavior of quickly moving my hand? I am also not clear as to how information is processed. If all action potentials are the same, how is this related to a wide variety of behavior? With certain types of input- the heat from a stove, I will have the same behavior, but what about a particular input which results in different responses in each situation? How does sodium permeability lead to various behaviors? I am sure you will clear everything up and I will be a believer by the end of course. Or maybe not.
Good summary, and good questions. Not sure we'll clear EVERYTHING up, but when one knows the questions, one has a better chance of making sense of the whole thing. Tuesday discussion helped? More on synaptic potentials should too. And then still more when we start looking at groups of neurons (next week). Don't be shy about keeping me posted on whether its getting better or not. PG
Thoughts and Reflections for Week 3
"Can Behavior Come from Nothing More or Less than Action Potentials?"
As a traveling messenger, the action potential is the basis for communication within the nervous system, traveling between neurons and muscles While the signal emanating from the action potential remains relatively isolated within the domain of an axon, action potentials are continuously created and "passed along". One could assert that action potentials are similarto the universal currency known as the dollar bill. Every action potential like every dollar bill may carry the same value, but the potential use for eachform of currency is boundless.
It seems quite rash to limit and to explain behavior in the simple term of a universal currency called the action potential. If one is to propose that the action potential leads to behavior, I believe that there must be sseveral other layers of control that add variation to the system. The action potential may in fact be a universal messenger, but the manner in which it interacts with the boxes of the system must surely alter and modify its mmessage. For example, the order in which action potentials trigger certain boxes may endow the action potential with different characteristics. The number of action potentials generated per unit of time may also alter the mmanner which the action potential is decoded.
On a more localized level, I believe it is important to consider the mmanner in which the action potential is received by the receptor. For example, perhaps the synaptic junction that conveys the action potential, whether between axon and axon or between axon and cell body, plays a role in how the action potential is interpreted. The chemical transmitters released ffrom the synapse may also hold a key to better understanding how a universal code, the action potential, could lead to diverse and varying responses.
Appropriate, thoughtful. Yes, there must be ways in which the same action potential can "mean" different things. We'll talk more about this, including some of the things you mentioned. PG
Two interesting questions arose over the past week: one regarding an explanation of behavior in terms of patterns of action potentials and the other regarding the spontaneous generation of action potentials within the nervous system. I see these two areas of interest as being more closely related than they might appear at first glance. What gives meaning and effect to action potentials that may arise from within is not the action potential alone and independent, but rather its manifestation in the larger pattern of many action potentials.
To begin to understand behavior in terms of patterns of action potentials it may be a good first step to consider the mathematics taking place which governs the patterns. I'm no mathematician but I can recognize the staggering potential in sheer numbers when you consider 10^12 neurons in the human system each receiving input from as many as 1000 others and in turn distributing output to as many as 1000 others. The number and variety of possible patterns is essentially incalculable.
I am eager to explore the relationship between patterns of action potentials and the behavior they define. Obviously we must begin with the simplest models and expand on those. I'm not sure if the human mind will ever be able to comprehend the full potential of itself, however. Perhaps their is a sort of neurological Heisenberg uncertainty principle. . .
Nice point, the relatedness of spontaneous activity and of distributed representations. The significance of the former indeed depends on the latter, both the meaning of individual action potentials AND their effect. Yeah, we'll go on to patterns, where they come from. And yes, there IS a Heisenberg uncertainty principle for the nervous system. Have seen my article on "Variability in brain function and behavior"? Is on serendip, can also give you reprint. And that in turn DOES relate to whether the brain can ever "comprehend the full potential of itself". The answer, I THINK, is no. But not simply because of the combinatorial explosion. There is a deeper issue at stake, which is the existence or non-existence of boundedness in that potential. In either case, it is certainly true that for the foreseeable future every advance in understanding the brain modifies it and hence increases its potential (making the answer to the question a moving target). PG
in recollection of your last response to last week's essay (re: the choice neurons make in the N.S.) i found it very interesting that many neuronal pathways are designed or determined at an early age in a person's life (if i understood you correctly). one of the articles on reserve touched on this topic briefly, it mentioned that although science has not made terrific headway on how such choices are made, so far it is believed that "cell-cell" recognition depends on membrane proteins that are associated with unusual carbohydrates. Although you probably already know that, i thought it was interesting.
on to this week's material:
we have learned that that the current that results from an action potential can only flow in one direction due to the fact that Na channels immediately shut off as soon as they have turned on (or opened up) thus preventing backward flow. my question pertains to an exception to this case. what would result from a malfunctioning Na channel that does not shut off quickly enough to prevent the passage of current in the other direction? i would conjecture that there exists a clinically determined disfunctional behavior/disease?, that would result from such a case. are seizures caused by similar circumstances?
A thought proposed in class: signals CAN start in the middle of the N.S., where might be some such origins? If the compression of the skin membrane can instigate signals, then I see how techniques like acupuncture can be effective. If we are speaking of the internal area of the body, the spinal cord area, as the middle of the nervous system, I have some ideas about the possible commencements of signals. e.g. the flow of various other chemicals in the bloodstream may influence or be the cause of an onset or signaling/ the concentration of various chemicals in the vicinity of the neuron/ the movement of different molecules in the glia/ the chemical reaction of certain compounds with others near or with the cells of the myelin sheath surrounding the axon. (REMINDER: I'm lacking the foundations of intro. bio. therefore some references might not be accurate.) there must be a variety of surrounding cells that transport materials and other compounds near the neurons which might onset the transportation of info. i'm going to take a wild stab at meningitis here. i know that meningitis is the attack of a bacteria on the meninges that lie within the brain encasement. the reason why this illness hits so quickly is because the meninges are exposed to a fluid that separates the brain from the skull. once the bacteria reaches this fluid, it spreads like wildfire because the fluid is circulated throughout the surrounding area of the brain, exposing the meninges to the bacteria. i would like to make a probably ignorant assumption (meaning- i realize that i am greatly oversimplifying the human body) that cells in the bacteria ridden area "know" that something is amiss, which starts the ball rolling, starting at the neocortex. the neurons here might be stimulated, and so on. the result: a high fever, etc. and other symptoms. is the communication between areas that well understood? let me know how off-track i am. thanks.
Not badly off track at all (though a little scatter gunned). Sure, article helps to understand how neurons get connected. Glad you found it. Yes, some diseases might have to do with failures of sodium inactivation (careful, this doesn't prevent "current" from flowing backwards; what it prevents is the resulting increased sodium permeability which would cause action potentials to propagate backwards). Seizures, though, probably have more to do with uncontrolled spontaneous action potential generation than they do with which direction the action potentials go. Yes, bacteria (and other things) may lead to conditions which initiate action potentials by interneurons. But remember that such action potentials might also be initiated with no "cause" external to the neuron itself (i.e. simply because the neuron is built with regions of high sodium permeability). PG
Neurons have regions that cause them to generate an action potential without the input signal from a sensory neuron. A region of the neuron is made with a high permeability and generates an action potential by itself. This explains how signals can begin in the middle of the nervous system. If a signal can be started by a neuron, then a behavior can occur without being triggered from outside the nervous system. This makes sense because there is no signal coming from outside the nervous system telling the body to breath, yet the behavior occurs. Genetics determines that the neurons are built with the region of high permeability. If genetics controls some neurons that initiate behavior like breathing, could our genes control other behaviors too? For instance, the varying degrees of permeability of neurons, determined by genes, could be responsible for varying reactions people have to the same stimulus. The development of action potentials by neurons that are made according to genetic information gives strength to the argument that behavior is controled or at least influenced by genes and not solely environment.
Yep, some behavior is initiated within nervous system. And yep, tends to support idea that genome can influence behavior. Good extensions with specifics. No new questions? PG
I wrote last week that the notion of 10^12 little boxes enhances my perception of nervous system and behavior as being the same thing, because it is not the case that one box is on for a particular behavior while the other boxes are off, but it is more likely how large number of boxes are interacting with each other and their pattern of activities. Now, this notion seems more likely after learning about action potential. I can extend the notion of patterns of activities of boxes to the patterns of activities of action potentials. I can begin to see how you can get behavior from patterns of action potentials (activities).
Clear statement of importance of pattern of activity as opposed to what on, what off, and of how action potentials help to see this better. Better though with some more concrete examples of what exactly you are beginning "to see", and what new questions this raises in your mind. PG
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