Neurobiology and Behavior, Week 4

Paul Grobstein's picture

Welcome to the on-line forum associated with the Biology 202 at Bryn Mawr College. Its a way to keep conversations going between course meetings, and to do so in a way that makes our conversations available to other who may in turn have interesting thoughts to contribute to them. Leave whatever thoughts in progress you think might be useful to others, see what other people are thinking, and add thoughts that that in turn generates in you.

You're free to write about whatever came into your mind this week, but if you need something to get you started ...

Our abbreviated week focused largely on the idea that the nervous system can generate outputs even when there is no perturbation in its surroundings (no "input" that "causes" the output).  What aspects of behavior might be more easily made sense of in this rather than in a more traditional a stimlus/response framework?  What "adaptive value" might there be in the nervous system being able to generate outputs by itself rather than in response to inputs?  What could such a nervous system do that it couldn't do without the ability to generate outputs by itself?    

Hannah Silverblank's picture

In Suzanne Nalbatian's Memory

In Suzanne Nalbatian's Memory in Literature: From Rousseau to Neuroscience, Nalbatian explores associative memory as portrayed in the narratives of Joyce, Woolf, and Faulkner. Nalbation suggests that "memory controls the workings of [the characters'] minds in a variety of ways that create a conscious interchange with the past" (78). Present engages Past in a dialogue, in which each character seems to be equally vocal, "real," and reliable. Nalbatian adds that "Woolf analyzed her own memory process, specifying that her recollection of scenes of the past was 'not altogether a literary device.' She vividly explained how the significant moments of the past survive 'undamaged' and enter her present consciousness" (78). If Woolf's understanding of her consciousness - as a quilt of present and past -  can be understood as more than just "poetic," does the stream-of-consciousness narrative model hold any resonance in neurobiological structure or activity? Or is Woolf's philosophy of memory a product of her effort to immortalize her mother - whose death consumed Woolf - and retain her in the present, as Nalbatian suggests? What I'm beginning to understand from Nalbatian is the idea that perhaps our experiences of memory are a product of some kind of personalization of neural patterns, and that our "personal memories" receive inputs generated by an abstraction, i.e. Woolf's mother's death (event) -> desire to immortalize and preserve her in present experience (reaction; self-generated output) -> experience of memory.

Congwen Wang's picture

After some clarifications of

After some clarifications of "input", now I can better appreciate the idea that brain can generate outputs without inputs. Like Raven, I also find it interesting that after several weeks of discussion, we seem to regard brain as a seperate entity more often. However, this relatively new perspective of the brain may cause some medical or bioethical questions. For example, how should we deal with people in vegetative state? Since the brain can generate outputs on its own, will it be hard to distinguish the outputs generated on the will of the patient and those generated randomly?

skim's picture

Finding force/stimuli/inputs everywhere

I have a hard time grappling with the idea that Newton is wrong. Though I'm no physicist, I can't help  this loyal feeling to Newton and his law - that a body in motion remains in motion (&a body in rest remains in rest) unless acted on by an outside force.

In class, the example of thermal motion was brought up. If an object - the table - feels cold/warm, is there a force causing the object to be at a certain temperature?

I was always taught that an object is composed of particles - molecules that are tightly packed together.  These molecules are in constant motion and held together by a variety of forces. Chemistry teaches us that certain molecules/atoms have charges, dipole moments, van der Waals forces, etc that keep solids/liquids/objects together.  Isn't temperature the amount of heat released by reactions between these forces, reactions that are dictated by these very forces?

Maybe if we redefine "force," this law could hold true in the context of this class and in Neurobiology. We said in class that the brain can just generate thoughts without any force causing this response.  I'm assuming that this statement refers to the process of generating new thoughts, something that existed from nothing, etc.

But I have to disagree. I think our thoughts are generated because of stimuli. We think because our minds are stimulated, in one way or another. This can be a thought that comes as a response to a given environment. Or a thought that comes as a response to a posed question, reading, argument, etc.  Thoughts originate from somewhere because of something.  Even our most esoteric, seemingly random thoughts have origins - according to psychology and Freud.

Maybe I'm too firm of a believer of causality.

meroberts's picture

No flirtation without instigation


18 pt
18 pt


/* Style Definitions */
{mso-style-name:"Table Normal";
mso-padding-alt:0in 5.4pt 0in 5.4pt;
font-family:"Times New Roman";

Humans, and animals in general, are unique (from computers and less-evolved organisms) in their ability to create outputs without inputs. This ability gives credit to the Harvard Law of Animal Behavior, which we discussed in class previously. This law implies that animals are able to create never-before-seen behavioral patterns regardless of input. When I was thinking of examples of this behavior, I remembered talking in class about flirting. I don't know if I believe that flirting is an output without an input. I think people flirt because they are attracted to other people. Attraction is based on pheromones and neurochemical processes that I don't quite understand. So isn't attraction the (internal) input and flirting the output? I think it could be argued that every behavior/output is caused by at least one stimulus, sometimes multiple stimuli, whether they be endogenous or exogenous. After thinking about it, I don't know if I totally accept the idea of outputs without inputs. I also don't think that inputs can only be external. I would bet that most of human behavior could be explained by internal stimuli, or a mix of both internal and external stimuli. Although the concept of outputs without inputs does make humans seem more evolved, I think that there is a lot more to the stimulus story. When we rule out internal stimuli from the equation, we can't fully understand the process.


Colette's picture

  Like Lauren, I was very


Like Lauren, I was very suspicious of a narrow definition of an input as something generated outside the nervous system.   Although I understand that most input into the brain comes from outside the nervous system, I am skeptical of a definition of input that excludes input from one part of the brain to another part of the brain especially since the various parts of the brain are massively interconnected.  I also am skeptical as to how activities such as stomach growling, seizures, dreams, etc., which are considered to be “pure outputs” - outputs without inputs.   Although not directly generated by outside events – inputs, there is still an out of body event that indirectly contributes to the generation of these “pure outputs.” For instance, a stomach growl may be triggered by absence of food and dreams are influenced by what happened outside the nervous system sometimes in the distant past.  Therefore, I think one or both of the terms, input and/or output, should be broadened to somehow include what are considered “in body effects,” outputs that are produced by inputs from the body.”


The human brain is an example of a non-traditional stimulus/response system.  It does not always require external inputs to generate outputs. This allows for creativity and advantageous adaptations.   For example, when Galileo was reaching the end of his life, he lamented that his world was getting smaller because he was diminished to his shrinking five senses. Nevertheless he could reflect and powerfully express his situation.  Another example is Beethoven.  At a young age, he went deaf, but could generate powerful sensory outputs - some of the world’s greatest music!

cschoonover's picture

Outputs, Signals, and Neurons

 Class this week did help me to understand some of the questions I had as to how an output can exist without an input. But there is a point of clarification that must be made in this analysis of the nervous system: that outputs can occur without inputs, but only if those inputs come from outside the nervous system. When we started talking about how a signal is transmitted from inside the nervous system to outside, I began to wonder how signals are able start in the middle of an axon when it seems like there is such a systematic method of translating these signals. We may have briefly touched on this at the end of class, but I would love to know more about it. And what causes them to stop midway through this process? I know that with Multiple Sclerosis, spasticity is the result of an interruption of the nerve conduction. Are these interruptions in the signal transduction responsible for other diseases? I guess what I am interested at this point in the class is how changes to these signals affect the nervous system as a whole, and if there are certain instances when a change yields no significant result.


I was fascinated by the fact that 99.99999999% of our neurons are interneurons. However, I have a similar question to Emily’s in that I wonder if, and to what degree, these interneurons rely on the sensory and motor neurons, which receive and transmit information from the outside world. It seems to me that communication between neurons would only be possible if there was some knowledge of the environment.

kdilliplan's picture

Simplicity and the Nervous System

 After our conversation last week, I feel like I have a better understanding of inputs and outputs, of interactions between neurons, of interactions between the environment and the nervous system. However, I am still interested in how these interactions come into being. We talked about neurons that connect the outside world to the nervous system, neurons that connect the nervous system to the outside world, and neurons that connect to other neurons. We talked about how there are orders of magnitude more neurons in one person’s nervous system than there are people on the planet and how the vast majority of those neurons connect to other neurons. I doubt that this was always the case. I wonder which of the three types of connections the original ones were. That is, can a nervous system be simplified so much that it only has one or two types of connections and still be a nervous system? Did all of the types of connections exist in the original, ancestral nervous system, or are some of them derived? Is the ability of the human nervous system to generate outputs without inputs common to all nervous systems, or is that, too, a derived trait? My question from the other week still remains: which came first, inputs or outputs?

natmackow's picture

Where do outputs come from?

Class this week did clarify for me the idea that outputs can be generated without inputs, but only if one considers inputs as belonging to an environment outside the nervous system. I find it hard to believe that outputs can be generated without any sort of stimulation and think that there must be an internal stimulus involved in the creation of outputs. Where do these outputs come from and how can they generate so many different inputs and outputs? What are the signals that pass through the neurons and what generates them (Inputs? Outputs?)? What causes neurons in the brain to stop transmitting signals?


I’ve been thinking about individuals whose brains have been severely damaged in accidents and are considered brain dead. Individuals who are declared brain dead do not show evidence of response to pain, reflexes, or spontaneous respirations.  An EEG will be flat and brain electrical activity is undetectable. Does brain damage prevent these “signals”, whatever they are, from being generated? Or does it prevent these signals from being transmitted? Perhaps some combination of the two? I think it will be interesting to learn about how the interactions between neurons lead to the transmissions of signals, how these signals lead to outputs, or behavior, and what exactly causes this whole process to start up or stop completely.   

yml's picture


Ok, so last week when I tried to come up with my own examples to understand how outputs can happen without inputs, I did think about autism and other cognitive disorders, but I wasn’t really sure if I could say those outputs are without inputs, or even what are the inputs in those examples. But now that it is clarified that the inputs are stimuli outside of the nervous system, it makes more sense. Yes, outputs can happen without inputs. This is what makes us to say, “we can think in our own”, whereas computers or robots cannot (at least, so far, they can’t). Between people, on the other hand, it’s the assembly that makes each individual different, from the same ‘contents’. As it seems like most people were, I was also surprised to learn that 99.9999% of neurons are interneurons. A question I have about this is that is outside world demanding very little or is it capable of affecting out brain with very little amount of neurons. All these topics brought me to think about nature vs. nurture, which has been a question I had for long time. I have believed that both have effect on humans, although nature seems to have greater effect. I feel like this talk about large portion of neurons being interneurons and how the structure makes each individual different support my argument, nature has bigger role in human development. Or maybe, these topics are not appropriate to apply to nature vs. nurture issue?


Raven's picture

brain: new ways of the thinking

 It seems the reason we have a difficult time investigating the brain is that the brain is the only structure in the human body which is structurally similar but does not behave uniformly from one healthy person to another. After writing this sentence I realized I wrote the ‘brain behaves’ as if it were it’s own entity separate from the body.

Although the concept seems strange that our nervous system not only computes inputs to outputs, but creates out puts on its own, it makes sense. It seems that these automatic inputs received from the brain itself function as an auto mode. Certain things to keep us running without the brain having to “think” hard to keep our heart pumping. But this definitely contradicts most scientific thought, including that of Newton and the era of biology which preceded this one. Things such as the lock and key fit theory of enzyme-substrate interaction are being replaced with the more contemporary theory that an induced fit model is more likely. People stop thinking of molecular signalling pathways as linear and now the current thought accepts that these biological molecules actually function as networks and various highway systems that all interact with each other. So it seems that as time progresses we may be more accepting of new thoughts on brain and behavior. 

Schmeltz's picture

Unidentified inputs??

I was talking to a friend about the ouput without an input phenomenon and she suggested I check out this New York Times post, Patient Voices: Tourette's Syndrome:  She thought that this post suggested that Tourette's Syndrome, a disease characterized by involuntary movements and vocalizations (outputs), did have associated inputs.  For example, one individual commented that specific people and locations prompted particular inappropraite tics or outbursts.  He said that when he encountered certain races he felt the urge to vocalize racial slurs.  Further, he felt the urge to say degrading things to his girlfriends such as "you're fat".  Also, in public locations he would shout "bomb" or something else he knew would elicit a startled response.  This would suggest that the environment, particular locations and people, provide particular inputs that generate related (and unfortunately oftentimes inappropriate) outputs.  Sometimes, however, it is a fortunate output.  One patient spoke of how acting and performing caused the involuntary movements to stop.  I have witnessed this.  I knew a guy who twitched uncontrollably and then he would sit at a piano bench, start playing, and then the tics would instanteously stop.  How is music, an input, inteferring with the neuronal connections?  It must be interferring with something, with some input.  Additionally, another Tourette's Syndrome patient expressed that stress and excitement definitely factored into the prevalence and severity of the tics.  However, despite these environmental factors, there are clearly still outputs that cannot be accounted for or that do not have an associated identified input.  We do not yet know from where these outputs stem, but I think it completely probable to say that perhaps there are inputs engendering these responses that we have not been able to pinpoint.  We learned in class that our nervous system is comprised of 99.999999% interneurons.  This is amazing and daunting because think of the limitless amount of things these interneurons are doing.  I think it is entirely possible that in the case of Tourette's Syndrome and other disorders of the nervous system, we have yet to discover the inputs that cause these oftentimes visible and mysterious behaviors.  Why did I just blink, or wiggle my toes, or bite my lip?  I have no idea.  Maybe environmental factors or restlessness or boredom.  Something though, I think, elicted that response whether I know what that something is or not.  The featured Tourette's patients do not fully know where their responses are coming from either.  Many experience frustruation with the lack of control or lack of free will.  Some admitted that they did have control over urges, but that to supress these urges caused physical pain and mental anguish.  I also found it interesting that obsessive compulsive disorder is a common partner with Tourette's syndrome.  It almost seems like compensation for the fact that since they have no control over parts of themselves, they try to control other situations.  Is Tourette's syndrome the input for the obsessive compulsive output?  Further, a point of interest was the fact that two twins had the disorder - one experienced tics that diminished with age, while the other experienced an increase in the severity of tics.  Does this suggest environmental inputs?  Lastly, one patient said that the one thing that helped the tics was marijuana.  I find this interesting.  Marijuana must be targetting or reacting with something to generate the improvement.  What is the something? I think it is just easier to say that there are outputs without inputs because we really have no way (at least now and i doubt if ever) of accounting for all the possible inputs.  By the way, have we even defined inputs?  I think in some cases it might be hard to differentiate between output and input and I think at some point it is just easier to say it must be a more circular network.  Right now our model seems pretty linear and I would argue that the whole call and response or response without a call models we have been working with are much too simple.  Yet, I am sure further discussion will produce a new, less wrong, model.  

JJLopez's picture

Learning More

I think last weeks conversation was very helpful in clearing up some of the confusions we had about the "boxes" we talked about two weeks ago, only because it gave it more familiar titles.  I did look at two of the websites he suggested in class.  However, all those names just made it a little more complicated for me to remember, so I think that now that I know these "boxes" have names like medulla and such names I have heard before, the idea of boxes was a lot more easier for me to understand in terms of how the boxes connect and interact with one another.  Also, the idea of inputs and outputs was cleared up in my mind with the examples given like the thermal example and how things can have outputs without any input.  

AndyMittelman's picture

Benefits of an output-generating nervous system

       In evaluating our evolving view of the nervous system, I imagine that there are several major benefits of a system that can generate outputs without the need for inputs. I am specifically approaching this issue with an evolutionary perspective. Firstly, I would think that the need for internal generation of stimuli is critical to maintaining a daily rhythm. Suppose, for example, that our nervous system only reacted when prompted with an input. If we were sleeping in a dark silent cave, could we sleep indefinitely until awoken by some stimulus (a bear entering the cave, or someone attacking us)? Clearly we cannot sleep indefinitely, and this daily cycle must be tied to internal stimuli. Devoid of any external stimuli, we still wake up (albeit after perhaps more sleep than we might normally get). These rhythms—Circadian rhythms—keep us functioning even without external stimuli. (Check out this cartoon). This cyclic rhythm presents evolutionary benefits in that we can meet our body’s needs in a timely and efficient manner. What if we had no idea when we would be hungry or tired? It would be impossible to plan anything. If you just became overwhelmingly hungry at random times that were not governed by some internal stimuli, it would be very difficult to survive as a hunter/gatherer (or pretty much anyone for that matter, aside from perhaps someone who lives in a supermarket).

       So what other benefits does this “spontaneously generating” nervous system present? It offers us the ability to adapt to new situations and environments. If we could only output based on input, we would be greatly troubled by a new situation. If an input came along that was totally foreign to us, what would we do? While some pathways of response are heavily-traveled highways of the nervous system, (eg- the fight or flight mechanism, or rest and digest), we will certainly be presented with new challenges and the outputs they will demand.

       One other evolutionary benefit would be that it allows us to avoid predation that might normally capitalize on routine. Consider the case of an unlucky mouse who was born with a very primitive nervous system. Whenever cheese was dropped on the floor, he immediately (and always) responded by running out to get the cheese. Furthermore, assume he only ran out of his hole when the cheese was dropped. A cat might notice this pattern and capitalize on his prey’s primitive ability to process inputs and outputs. The next time the cheese dropped on the ground, that cat might be waiting for the mouse. My point is that our ability to generate internal stimuli and operate in a non-prescribed manner is a critical element of defense from predators.

Kwarlizzle's picture

Just happy

I'm just glad we can finally put names to the 'inputs' and 'outputs' the nervous system uses. It makes a lot more sense. I understand 'grey matter' 'medulla oblongata' and words like that in the context of the brain better than 'boxes'. So yeah. i'm happy.

aeraeber's picture

Outputs in Evolution

Though the idea that the nervous system generates outputs without inputs seemed strange at first, it actually made a lot of sense to me once I thought about it.  Many of the behaviors that puzzle us, including many of the things that we define as mental illness, like depression, schizophrenia, OCD, mania, and panic attacks, can't be explained by a traditional stimulus/response explanation of the nervous system. They happen without any external cause, and the pharmacological treatments we have for them are based on changes within in the nervous system.

The fact that the nervous system can generate outputs without inputs from the surrounding environment is interesting from an evolutionary perspective. The nervous system is capable of changing how it reacts, because any one output is not linked to a specific action. As result it can adapt to a new environment more quickly and easily than a system that is based on linked inputs and outputs. It also introduces an element of the unexpected, because outputs that occur without inputs cannot be reliably predicted. Variation drives evolution, so in evolutionary terms the nervous system is highly valuable. It also begs the question of how such a system evolved. What was the starting point for outputs without inputs? Did it start as a stimulus/response system? Or as something else entirely?





MEL's picture

Input/Output Model and Neurons


Our conversation this week clarified some of my confusion from last week. I think now that I fully understand what an input is (a stimulus from outside the nervous system) I understand how the nervous system can generate an output even when there is no input. I think that the leech example is very powerful and really helps support this idea.  At first it was hard to believe that observations in the isolated nervous system of actually corresponded to the leech's swimming behavior. I found our discussion about neurons very interesting I was very surprised to find out that  99.99% of neurons are interneurons.  This shows that our nervous system’s main purpose is to deal with stimuli from within the body not from outside the body.  I also found it interesting how we actually assigned the boxes and arrows connecting the boxes to places in the brain. The central gray region acts as the “boxes” and the white regions act as the “arrows connecting the boxes”. It’s nice to finally see how our input/output model fits in the brain.


Saba Ashraf's picture



At first, I was also confused about how the brain could generate outputs without inputs; however, I found the example with the thermal motion to be helpful. Initially, I had believed that a cause is needed for an effect, but since particles (in the table) can move with absolutely no outside force to cause this to happen, there must be other instances as well which result from no cause. Because there is now an example to illustrate that an effect can occur without a cause, the brain must also be able to do the same, especially since the brain is capable of so much.  Also, in class I found it interesting when we said that about 20% of our neurons are motor neurons.  This is because when I think of neurons, I automatically assume their function is primarily movement. Basically, when I found out that 99.99…% of neurons are interneurons, it was very surprising.   This brings up the idea that even though we actually assume the nervous system mostly deals with the outside world, it is quite the opposite. We have a lot more going on inside of the body than we think. 


mcurrie's picture

Still questions and confusions

 So I'm trying really hard to understand the whole outputs without inputs and seeing Michelle's article emotions make sense but I'm still trying to figure the leech. I know that they isolated a nerve but I am wondering if they had to put any kind of electricity through it or if the nerve was just twitching because it was being cut out and in shock or how they knew that the same pulse given from the nerve was the same as when the leech swims away. Because when the topic was introduced the leech twitched when startled which is an input but when taking out the nerve and it twitches the twitch then becomes an output with input. I'm still confused and trying to get my head around it, or ignore the knowledge that was placed in my mind that all outputs had an input. I guess I just need to get more observations and information to truly make my own conclusion about outputs without inputs.

molivares's picture

neuron anatomy

While most of our discussion revolved around outputs and inputs and neural circuits, the very light neural anatomy that we did go into inspired me to look into basic neuron anatomy even more.  I found this neuron anatomy website  which I thought was particularly good at presenting neuron structure and basic function. What is amazing to me is not this notion of a generation of outputs with any input, but the fact that the cells in our body have the ability to do exactly that.  We see how outputs are generated without any inputs in every day life whether it be through dreams, desires, wants, creative thoughts, or through experiences or encounters with epilepsy or autism.

But what it comes down to is the basic anatomy or our brains and nervous systems. The overall structure and function of the neuron is basically the same across the human race.  Impulses, inputs, and outputs are the result of electrochemical gradients, sodium and calcium channels, and much more. Although scientists study neurons and how they function at the biochemical level, we still have been unable to build a neuron artificially.  We attempt to build robots and computer systems that function parallel to our own brain, but none have come close. None of these systems have had a mind of their own – they can’t produce outputs without any inputs.  And the way I see it, it is all because they don’t have the same building blocks that comprise our brains and nervous systems. It just gets me how we take these things called neurons for granted at times. Sometimes we just don’t realize how these neurons. so intricately architectured that we can’t even fully conceive how they work and function, allow us to do so much.


Jeanette Bates's picture


         It makes sense that the brain can generate its own outputs without receiving inputs. After all, people with epilepsy generate outputs without ever receiving a stimulus. Personally, I think that this is a very important trait. If we could only give outputs after we receive inputs, then that means we wouldn’t be able to think on our own-we would act like robots or computers. I don’t think that all of our responses are reactions-sometimes we talk or act because we want to, not because something on the outside inspired us to do so. We can contemplate, muse, and worry over things; I don't think these emotions are created by specific external inputs. We think on our own. Personally, I think that if we only reacted to things, we wouldn’t be able to dream up things on our own. In other words, I’m wondering if there would be any creativity without self-generated outputs. It might be true that having an absence of something could stimulate us to create new things, but I think that the ability to invent and mold completely new, sometimes strange, and often inspiringly original creations is something that comes from within. I think that the ability to create and to contemplate are all both results of outputs that lack a stimulus, and if this is the case, then it is something for which I am very thankful.

Lauren McD's picture


Even though I was slightly suspicious of our discussion of outputs being generated without the influence of inputs, I think one main point in class greatly cleared up my confusion. An input is defined as a stimuli OUTSIDE of the nervous system. Thus the many instances I was thinking of contradicting the 'output without input' statement were cleared up. A significant amount of our behavior can have stimuli within the nervous system, and yet these do not count as external stimuli. Therefore if a stimuli was generated within the nervous system, any action in response would be deemed an output without an input. Also, the many examples given in class showed that there really are many everyday examples supporting this statement that hadn't previously crossed my mind. Such examples of radioactive decay, seizures, and other topics discussed allowed me to realize that maybe our interactions in the world aren't as clear-cut as they are imagined in the introductory science levels of education. After Tuesday's class, I am much more open to the initially contradictory ideas that our behavior is not necessarily always linked to an input. The advantages of this are endless, but in short, the main point is that the body can act with a sort of 'free-will' without stimuli. While not all outputs without inputs are beneficial to the organism, a body that requires less input for everyday needs is much more independent.

As mentioned in previous posts, the percentage of interneurons compared to sensory and motor neurons is overwhelming. However, I don't think that necessarily supports the idea that the majority of our behavior is directly due to interneuron interactions. One sensory neuron can pick up on a signal, sending it through countless interneurons before it reaches a motor neuron. Less neurons are required for interacting with the outer world than forming the connections between the two. Also, I feel like one sensory neuron can trigger many other interneurons, suggesting a much greater need of interneurons as well. Although I don't have enough background to make any of these claims, we must remember that other factors can take away from this effect.

lfrontino's picture


I was certainly surprised this week to learn about the high percentage of our neurons that merely communicate with other neurons. I think when we tend to think of neurons sending signals, we automatically think about motor and sensory neurons as being important. These, after all, are the outputs that we can really experience and feel. It is interesting then to learn that 99.9999999% of our neuron activity occurs between two neurons rather than to an external source. This brings up how little we really know about our own brains and how our bodies function. The fact that so many signals are necessary without our even knowing about them or sensing any sort of reaction from them shows the true intricacies of the nervous system. 

gloudon's picture


After reading Michelle and Emily's comments about outputs with no physical stimuli and interneurons, a few things started to click.  During class we used Autism and seizure disorders as examples of outputs without inputs.  By creating outputs without inputs, it makes sense that seizures and autistic characteristics come from confusion within the interneurons, almost as if there was a traffic jam or a glitch in the system.  Further, if 99.99999% of our neurons are interneurons, it would explain how easy it would be for these problems to occur (with so many interneurons for them to occur at)  and therefore validate how prevalent these disorders are in society.  


As far as interneurons go, it seems to make sense to me why we would need 99.9999% of our neurons to be interneurons.  I can't even begin to imagine the complexity of regulating the entire human body.  From helping the body talk to itself about regulating temperature, blood pressure, breathing and heart rate, the demand on interneurons seems infinite.  If the job of these interneurons is to communicate with each other to achieve homeostasis, then I can justify how our communication with the external world demands only 0.000001% of our neurons.


emily's picture

Outputs and Interneurons

I agree with you, Michelle. Thinking about thoughts and emotions as outputs with no outside stimulus makes more sense than the more traditional stimulus/response framework. Sure, often there must be an external stimuli, such as a word a question to give one inspiration or to spur on something; but, the act of physically forming a thought, emotion, or even a dream being independent of an external stimulus makes sense to me. I often think in tangents, so knowing we have an infinite number of neuronal connections within our brains models my thinking patterns: as one neuron leads to the next, one thought leads to the next. An "adaptive value" for the NS to be able to generate outputs by itself is that the NS can act on its own, and can allow for individuality among creatures of the same species. The NS is not just a one dimensional responsive machine, but is more like a dynamic shape-shifter! If there was only one response for one stimulus, our lives would be much more boring because certain things could be predicted and people would be more similar. But because each person has their own set of neuronal connections and because the brain can create its own outputs based on these distinct connections, past experiences, evolution, and learned patterns, we can each be our own self!

One thing I was a little confused about in lecture this week was when Professor Grobstein mentioned that our brains are 99.9999999% interneurons, which implies that we are less constrained by the outside world than we think we are. I understand that sensory and motor neurons are responsible for our interactions with the world, and since they only make up an extremely small percent of our neurons, it can be said that our interactions with the outside world are actually very limited. But, most of what we do and think is based on past experiences and learned patterns which we acquire by means of our motor and sensory neurons. So, don't our interneurons rely deeply on the information we receive from the outside world?

Schmeltz's picture

last question

The last question you posed is interesting and hope we can discuss that during class. 

mcchen's picture


 While reading an article on emotions, I came across an explanation on the emotion sympathy.  Damasio described it as "[ing] that person's pain to a certain degree internally" and the recreation of the pain does not come from an external stimuli but from a change that is stimulated by the brain itself ("Feeling our emotions"  What he said about sympathy really intrigued me and definitely reminded me of our discussion this week about the brain generating its own stimuli.  I am interpreting this article as saying that thoughts, while not external stimuli but internal stimuli, can bring about physical changes in our bodies which we can interpret as the emotion of sympathy.  This brings new meaning to the phrase "I feel your pain" because maybe if you thought hard enough, you could! I wonder if this has anything to do with people being able to make themselves cry by thinking of a really sad thought and then actually being sad so they really did need to cry.