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An ongoing conversation on brain and behavior, associated with Biology 202, spring, 2000, at Bryn Mawr College. Student responses to weekly lecture/discussions and topics.
The nervous system is an input-output box consisting of interconnected input-output boxes themselves consisting of .... its boxes all the way down ... lots and lots of boxes ... and they're pretty much the same boxes everywhere". Is that a useful way to think about the nervous system? Does it help to make better sense of behavior? Of any particular behaviors?
Well here goes. We learned today that we have 10^12 neurons in the central nervous system, 99.9999% of which are interneurons, each of which typically is connected to 10^3 other neurons. It would be easy to 'lose track' of an input's relation to a later output with such an unconceivably complex cloud of neurons. Thoughts and ideas could be bouncing around from neuron to neuron for weeks before a signal ends as an observable output.
And another thought: do these truly astronomical numbers make it any easier to accept the implications that the statement "there is only the brain" has for the concepts of "self" or "soul"?
"The nervous system is an input-output box consisting of interconnected input-output boxes themselves consisting of .... its boxes all the way down ... lots and lots of boxes ... and they're pretty much the same boxes everywhere". Is that a useful way to think about the nervous system? Does it help to make better sense of behavior? Of any particular behaviors?
The estimate that 99.999% of the neurons are inside the nervous system was surprising; I thought that motor and sensory neurons accounted for more than that. This means that very little of our brain power is used on anything exterior to the nervous system. Under the assertion that the brain is behavior (which I still have my reservations about), this means that pretty much all of our behavior is inside of our nervous system. Perhaps the most amazing part of all of this is that if our nervous system only uses 0.001% of itself to comprise all external “behavior,” imagine the complexity of the behavior that is being performed by the other 99.999% of our nervous system. To me this just shows how complex behavior really is- it actually augments the problem of understanding behavior. If a majority of it is hidden within the nervous system and it is being dictated by a system almost a hundred times larger than our external behavior- How could we possibly understand behavior completely?
If the brain equals behavior and if 99.9999% of the boxes in the brain are composed of interneurons (and thus do not “talk” to the outside world), what does this mean about behavior? My first reaction is to say that most of behavior (99.9999%) DOES equal the brain. It appears that receiving input from the outside world is a very small part of what the brain does. Therefore, perhaps the outside world has very little to do with our behavior. I don’t agree with this last statement, in spite of the numbers.
I am reminded that we, as a class, have not defined “behavior.” In my previous essay, I defined behavior as observable actions/reactions. Using this definition, I don’t think we can say that what happens in 99.9999% of the boxes counts as “behavior”. We can’t see it! We can observe the inputs and outputs of sensory and motor neurons. But how can we talk about the input and output of interneurons? (I know we said that the inputs of interneurons are the outputs of other neurons, but this doesn’t explain what that input/output is.) I guess I’m saying that, while close to 100% of the neurons in the body do not communicate with the outside world, I’m not sure if we can call what these neurons are doing “behavior”.
Maybe I’m getting lost in the semantics here. But I do believe that the relative significance of the <<0.0001 % of neurons that are sensory and motor neurons is much greater than their numbers would suggest. They are the “bookends” of the system; they depend on the interneurons to translate inputs into outputs. But it is what comes in and goes out that counts (as behavior). What I want to know is how do the interneurons translate the inputs to outputs? Can interneurons themselves generate a chemical signal that results in an output to a motor neuron? Can they change a signal received from a sensory neuron? If so, does this count as behavior (even though it can’t be observed)?
for the behavior of learning, however, the model does give some logic to my understanding. learning is such a complex interweaving of various connections that endless sub-boxes acually begin to make sense. yet, the questions arise of where the input for learning comes in and in what ways it manifests itself. why do we use 99.9999% of our resources within ourselves/brain? what is the purpose, if there is one? i agree with stephanie that much gets confused in the semantics of this discussion. is there a way to lessen this confusion or will i (we?) continue to lose sight of the goal because of wording?
It seems an oversimplification to claim something to the effect of "the nervous system is turtles all the way down." We must account for questions like, what colors are the turtles? How old are they? Are they of the same species? Do they behave the same ways? Who do they associate with? What postion does each assume in relation to the others? It is important that we probe further into the neurons themselves--we have already learned that there are sensory neurons, motor neurons, and interneurons--there must be other such distinctions that might deter us form dismissing them all as one and the same. Just as different atoms combine to form a vast array of molecules, and just as they have different interactions and properties, so too must the different neurons be capable of forming various functional systems, engaging in different interactions and exhibiting different properties.
It is not my primary objective to try to complicate everything, but I do think that we might run into problems if we ignore the inconsistencies that may make our basic buliding blocks significantly different from one another. I just don't want us to be mixing apples with oranges, that's all. But if we acknowledge these differences explicitly and also recognize the great(er) simililarities, then we can probably use the units as useful building blocks of our known to be imperfect models.
To what stephanie was asking before about whether the interneurons can change an input or generate one, I think they can. I mean, as messages are being passed, I don't think that it can remain totally intact. We talked about in class how we did not think that one input led to one output. Well, I think that sometimes, many inputs can result in one output. This would change that preliminary input because it is not being affected by others. As to the question of whether the passage of signals from one neuron to another is behavior, well, that is rather vague. I mean, your defination of behavior was "observable actions/reactions". And at a microscopic level, the neuron is reacting to the message given to it by the neurotransmitters that it receives from it's dendrites. The depolarization wave, the charge developed, all these are reactions to the message being received and sent. So by that defination, this is a form of behavior for the neuron.
I, as hillary, would like to know if there is an end to this boxes theory. Would it be the molecules that make up the every piece of the cell? Where does it end? They can't all be the same boxes because messages need to reach different places, therefore, there must be different boxes that set them on the correct pathway.
These are just some quick thoughts I had. Although the input-output box theory explains behavior rather well on the physiological sense, I just feel that it is rather cold. To describe behavior as pathlike and logical.
I see differences in function at this smaller box leve as possibly stemming from two things. The first is the way in which one neuron communicates with other neurons. Although we have not talked about them, neurotransmitters and receptors are for me smaller boxes in boxes. A neuron that is releasing dopamine into its synapse cannot relay a message that serotonin must transmit to the neuron across the synaptic cleft, no matter how often it fires or how strong the input from the signal is in the nervous system. Thus different neurons could be specialized by the kind of small, neurotransmitter- production boxes that they contain. Accordingly, even if the first neuron was able to release the serotonin needed for the message, if the neuron across the cleft didn't have the receptors to receive the message, the message would not continue on along the path. Thus receptors seem also important for function. If a whole bunch of one type of neurotransmitter production neuron or specific receptor neuron made up one of the larger boxes, then it seems to follow that that larger box would only be able to perform the functions that its individual cells could do.
Another possibility regarding differences in funtion could be the actual messages that each part receives. Although we learned in class that each neuron communicates with 10^3 other neurons thus resulting in an unbelievable web of neurons in the brain, some signals may be not received or not as strong in some of the boxes as in others. For instance, maybe the way that the neurons are connected from the retinas, the visual cortex is "wired" to receive the signal, and gets it strongly. Maybe the auditory cortex gets this messgae as well, but it is much weaker than the information that it is receiving from the ears. If the function of boxes is related to the strenghth of the messages that they receive, then differences in function could be explained by this difference in strength.
On the same note as chemicals or environment, I can not conceive of a working nervous system without an action potential, which has to begin somewhere. The action potential is maintained by receptors and chemicals at the synapse, thus this chemical environment is imperative for nervous system function. Without it, we would have a bunch of useless boxes , or perhaps no boxes at all. Certain neurons contain growth factors for other neurons in nervous system development, and without these neurons, entire organizations of tissue and organs would not exist.
Maybe some of this sounds like a boring to review to some of you, but I say it to remind everyone that even though we are approaching the nervous system from a very theoretical level, we shouldn’t forget some of the basic biological principles that still have to apply in our theory. It’s like trying to play a game without remembering what the rules are. For instance, one person made the comment at the end of last Thursday’s class that if the organization of the nervous system really were interconnected boxes, then one box that didn’t work would screw up the whole system. Someone else responded that since there were so many other neurons/nerves in the system, it wouldn’t be that big of a deal because that neuron could get “bypassed”. I’m not exactly sure what “bypassed” meant in this context, but it is my hope that others in the class remind themselves of another basic biological principles before they start thinking about the exact implications of structure-homeostasis. One of the most fascinating things about living organisms is their ability to heal themselves, which is largely due to homeostasis. Homeostasis, just like our theoretical model, also occurs at the smallest possible box in the form of receptor regulation. People with Parkinson’s disease don’t manifest symptoms until 80% of the structure responsible is gone because of homeostasis at the level of dopamine receptors.
Another important effect of these chemicals on the nervous system is that through receptors and receptor regulation, they can change cyclic amp cycles, get into the membrane of the nucleus of the cell,change mrna transcription, and alter gene expression, all in a matter of seconds. These chemicals have a powerful effect- so how does this effect behavior? Psychotherapy has been shown to change receptor regulation at the level of the synapse. Therefore, this is an instance of the outputs of your nervous system being changed as a result of environment. What about the fact that somatosensory neurons may as well not exist statistically in comparison to interneurons? Does this change their importance in the way our behavior is effected? Does this change the way they are connected to neurons, or the importance of their role? It does not make sense to me that we should dismiss the role of the function of the nerves that are not interneurons simply because interneurons are so much more abundant. The point is, somatosesory neurons still exist. They are still important as a bridge between our external and internal environments. For this reason, and because of the role of the internal chemical environment in the nervous system, I am not comfortable with the conclusion that just because more interneurons exist, and they are located in the CNS, this serves as more evidence that the brain is behavior. There are still strong environmental forces(internally and externally) that exist.
The idea and definition of behavior that I have formulated is that behavior is the way human beings and other organisms, (Lets not forget are friends the frogs) act. There is an entire science dedicated to behavior, psychology. Psychologists regard behavior as any activity of a person or other living thing. Human behavior includes a person’s emotions and thoughts, and the responses of glands and muscles. Behavior itself can be broken down into two different parts: voluntary and involuntary. For example speaking up in class is a voluntary behavior, and breathing heavily after running is involuntary behavior. Both types of behavior may occur as a response to environmental stimuli. On the other hand, some voluntary behavior is self-determined. It takes place simply because a person chooses to act in a certain way, with no apparent outside stimulus. I think human behavior is determined partly by hereditary and partly by environment. But, most importantly it can be modified through learning.
Hereditary, determined by our genes. Environment, consists of those conditions and forces that surround and influence an organism. Learning, which I consider to be the most important, is the process by which behavior changes as a result of experience or practice. A person learns many behaviors through experience in situations that involve some type of motivation, such as a reward or punishment. The motivating factor stimulates the individual to behave in a certain way.
At one point my skepticism was fading, and the idea of brain and behavior being the same thing was beginning to become clear. This new approach that we have been discussing has halted my thinking. I don’t seem to understand the relationship we are making with behavior being less dependent on the outside world. The following paragraph has just explained how I view behavior and how behavior is impacted by other external factors, I know we are not disregarding these factors but where exactly do these ideas fight in our puzzle?
I don't really know if it helps us understand the nervous system or our behavior by saying that its boxes all the way down and they're pretty much the same boxes anywhere. I feel this way because you could really say that about anything. If you brake things down to a certain extent all things will be the same. But it really does not help us understand the why, and how it works etc. And the how and the whys are the key to understanding behavior and the nervous system (or at least I think so).
About the turtles..... Well well the ultimate question is what does the last turtle stand on???? The thing is for this analogy it is possible to say it is turtles all the way down. But for neurons? after a while the boxes are no longer boxes. If you go down too far they will no longer be neurons, or be something with a specific function. Right? or can you say it really is boxes all the way down?
When we learned that most neurons are also interneurons, this didn't seem to affect my opinion on if the brain equates, or rather is the primary influence on behavior. I agree with what Ann said earlier- our bodies are capable of maintaining homeostasis and so if one neuron malfunctions, our whole body does not falter. Along those lines, regardless if most neurons are interneurons, this just proves that our bodies are constructed of several intricate systems, some of which might not have been uncovered by scientists. But to say on the most basic level that these interneurons are so similar would be like saying that my foot has the same function as my eye. Some kind of distinction must be made. It might be more safe to say, something along the lines of.. the structure and physical function of these boxes are similar, but the ultimate operation and goal of these interneurons differs a great deal.
So, since there are what seems like an infinite number of interneurons in our system, how can we ever be sure that we have successfully found the necessary pathways of the inputs and outputs through these boxes? Have we just uncovered the shortest, but not necessarily the most effective pathway? This though leads me to my next point, because there are so many different available pathways, to say that behavior is generated somewhere WITHIN these routes would force me to doubt God and the outside world..which is frankly why this speculation (brain = behavior) seems too simple. If I think about the outside world purely in terms of its physical aspects, I would say this has a profound effect on me. Just think of a beautiful spring day where the birds are chirping and the sun is beaming on your face. I have not had any "emotional or spiritual" contact with the birds or the sun, yet they only help my mood. Now, if I walked out of my dorm and it was dark as night at 10 am, I don't think I would be able to smile so readily. The physical world has too much of an effect to assume that our behavior comes solely from within us.
My guess is that the inputs can be transmitted through only certain neurons. Some postsynaptic cells might have receptors which do not correspond to the input (neurotransmitters) sent from the presynaptic cell. So, I believe that the boxes are different although they all have similar basic structures.
My another point. As Maria, I also think that the behaviors are pretty much independent from outside inputs because of the tiny percentage of sensory neurons. Like the cricket's song, the foundations of behaviors are already set in the brain early in the embryonic development stage. I have mentioned before that brains consist of a network of input-output cables with some alarm clocks attached within a box. What I mean by alarm clocks is that some information of animal behaviors are set and "wake up" as the time comes - like the cricket which already has the information of its singing pattern early in its life but can only sing after the final molt.
Just think of things like codons which are comprised of 3 bases each -- just 4 different bases in different combinations has the ability to encode for 64 a.a.'s.
Now think of how many neurons ("boxes") we have -- I think Dr. Grobstein said 10^12. I can't even begin to comprehend all the different combinations that can be made with that massive number especially since a typical neuron receives inputs from 10^3 other neurons and also transmits outputs to 10^3 other different neurons. And that's not the end of it.
There are all those different neurotransmitters that can bring about different outputs. In one of our readings, Neuropeptides, Bloom gives an example of how injecting different species with angiotensin II brought about a drinking behavior despite a salt/water balance. Also, injecting rats with LHRH (luteinizing hormone releasing hormone) evokes the posture required for copulation.
I find it unbelievably amazing how the combo of the innumerable amounts of neurons and the different hormones/neurotransmitters can bring about such outputs. The individual "boxes" themselves may seem simple but the interactions between the whole lot them are anything but simple and I like to think that, that is the beauty of nature.
People seem uncomfortable with the idea (and implications) that somatosensory and motor neurons only account for .001% of our total neurons...the statistic surprised me as well, but I do not think that it necessitates a change in our view of everything we had come to believe about people and the importance of the exterior world ( Grobstein and others may well challenge me on this!) First of all .001 multiplied by 10^12 neurons is still a whole heck of a lot of neurons which allows for a very real neural connection with the outside world. I feel like one key thing to remember is that while interneurons are connected to lots of other interneurons, eventually, this string of interneurons is connected to an interneuron that is connected to either a sensory neuron (which connects with the outside world) or a motor neuron (which connects with the outside world....so although the connection may not be direct, it is nonetheless there and plays a central role in both the overall input and output (behavior) pathways...as far as I understand the neuroanatomy of the system this is true of all interneurons...so it is not as if there is this isolated system of interneurons within the central nervous system which is not affected and does not effect the outside world. Chrissy concludes her posting by saying that "The physical world has too much of an effect to assume that our behavior comes solely from within us" and I agree with her that I think that the physical world (environment) has a major impact on us. However, I don't think that the fact that 99.999% of our neurons are interneurons means that "our behavior comes solely from within us"...instead I would argue that it is precisely because of the complex interworkings of the nervous system that the outside world can have such a, as Chrissy writes, "profound effect on [us]"....
I realize that the following writing is very theoretical (and does not use the biological lingo]...If Ann is reading this, she is probably going to cringe...but my thinking is that the "profound effect" that the outside world has on our behavior and the amazing complexity with which our behavior unfolds arises out of the interworkings of the interneurons link the external ( to the body) input and internal output (behavior)...why should it make us feel that the importance of the environmental input in dictating person/situation specific behavior is diminished by the fact that it is processed by millions upon millions of neurons...if space aliens were told about our nervous systems, wouldn't it appear that info that got that much of attention before a motor output was spit out was incredibly important information.
I did find the notion that every neuron receives input and gives output to a thousand other neurons really surprising. But considering the consequences of neurons misfiring (seizures, etc.) it makes sense that there would be a web of neurons as opposed to a chain of neurons for every action. That way if one neuron does get damaged, the being may not necessarily be affected.
I think that the external environment has a greater effect on behavior than the .0001% would have us believe. There are probably internal factors that will predisposition us to behave in a certain manner; however, whether these behaviors manifest themselves is dependent upon the external environment.
The numbers discussed in class opened my eyes to the fact that internal processes make up a greater portion of our brains' functions. Currently I don't believe that I am fully aware of the implications of this. I am interested to see how this topic will progress in class discussions
The interneuronal line of thought goes along nicely with a piece of trivia I heard somewhere— that we humans use only a fraction of our brains during our lives…something like 1/9. If that’s true, think of all the untapped intelligence and power to control our lives we possess! That’s probably enough to will ourselves to fly over the mountaintops if we wanted to, which incidentally is a childhood dream of mine. But is it possible to learn to use the other 8/9? Maybe the geniuses and prodigies among us have already learned or possess the innate ability to tap into that reserve. For the rest of us, I wonder what’s happening in the unused portion. Does it constitute our subconscious? Or is it lazy brain mass that lies around waiting to be discovered?
I agree with what many people wrote in the forum this week about the implications of the interneurons accounting for 99.999%. I do not think that the relatively small number of sensory and motor neurons should effect the relationship of the nervous system = behavior. That 0.0001% is still a very large number. It just illustrates how complex behavior really is and how much of an effect the outside world has on it- especially if the 99.999% of neurons are needed to process the effects of the outside world. What else do interneurons do besides process information from the outside? Chrissy mentioned mood. I was wondering what actually accounts for mood? You would have different reactions to the same inputs depending on your mood. Do the interneurons have to do with the development of mood?
As for the idea that the nervous system is made up of many interconnected boxes, that sounds like a reasonable way of describing it (since the nervous system is made up of neurons and each one has inputs and outputs). Another thing I had never learned before was that each neuron receives input from and gives output to 10^3 other neurons. I mean, I'd figured it was a lot but I had never thought about just how many. The picture that comes to mind of 10^12 points with many branches coming out of each one seems very complicated and a bit disorderly but the boxes idea certainly fits that picture. Still, I agree with those who said that this model is oversimplified and ignores a lot of other issues.
As far as the ongoing "Is the brain equal to behavior" question, I still don't feel able to agree with it completely. It is sounding more reasonable but I guess I need more proof.
One reaction I had at the very end of class when we were discussing the shear numbers of neurons involved in every process great or small was that there is no room for spontaneity. The neurons have to be so coordinated and so in charge of every transmission that the interconnection leaves no room for chance. There therefore has to be a predefined set of purposes and pathways that are already known and then just traveled at the right time. Its like all the dancers know the dances ahead of time and just follow the right steps when the number is called. In that case is there really such things as spontineity within humans? Its interesting to thing that behavior might not be as spontaneous as it seems to us sometimes if brain is behavior. Maybe the other part of our brain is just storing the dance steps in a box marked spontaneity.
From the day a person is born, his or her ideas, values, beliefs and outlook on life are strongly influenced by outside factors. Parents are strong influential factors in molding the behavior of their small children. In observing small children it is interesting to note how they pattern their behavior after their parents. It has also been shown that many adults inadvertently exhibit behavior similar to that of their parents.
Peers and society in general also have an effect on an individual's behavior. "Everyone else does it" is a common explanation cited by many teens to explain their choices. The outbursts of school violence in the past few years has been blamed on the excessive violence portrayed in the media.
I find it hard to believe that of the 10^12 neurons found in the nervous system less than 0.0001% of the neurons are responsible for input from the outside. Although 0.0001% of the 10^12 neurons is still a very large number, I find it difficult to accept that there is less input from the outside world than from within the brain itself.
From different sources i have heard widely varing sayings as to how much of the human brain is used and how much wasted. I wonder how much of that is made up, if it is at all possible to say "well gee this part doesnt seem to be doing anything". Even if a part were removed and personality did not seem to change and organ function did not seem to change the internal personality could have changed and since it changed teh internal person not being the same might not be able to tell other people this.
i know it's boxes all the way down. all of my forum comments have been tainted with my pre-exposure. i'm afraid that this makes my comments dull. i am interested in knowing how the trail betwen boxes and beginning in boxes, etc. affects behavior. i want to know the neurological process behind my mood swings, muscle aches that emerge from nowhere, and why my torn rotator cuff - though supposedly recovered - hurts like the sun when i laugh. i want my neurological map! and i want to be the one charting it! i want to find out why the undiscovered territories are undiscovered. maybe i won't get that out of this course, but i and my measely gpa will go down trying. for now, i know it's all boxes. what starts the charge? those whims that we cannot explain? how does each box start a pathway of its own?
on a very different note, would any one like to meet up to brainstorm about paper topics and web sources, and whatnot? as most can probably tell, i just like to hear myself 'storm and thought maybe some one else would like to collaborate. i ifnd such taks help to refine paper topic ideas and provide a little more direction. extra input into the paper output box. ha ha ha. sorry.
has anyone seen animaniacs? the mindy and buttons sketches? why. why why? does any one else hope these boxes will answer?
