Finishing up neurons and their forms of communication

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. You're welcome to post here any thoughts that have arisen during the course this week (and to respond to thoughts others have posted).

Some issues worth further exploring this week are the what we can make sense of from thinking about things at the level of cells and the communication among them, and what we can't yet make sense of.  Is this helping us build a "translation" between neurons and behavior?  How does it help and what does it not yet help with?  Is the brain a "machine," a "computer," or ... ?


Jessica Krueger's picture

I know it's early

...and I'm not sure it's where Professor Grobstein intended to go, but when he began disucssion central pattern generators my mind went immediately to fixed action patterns. A fixed action pattern is an innate "pattern of action potentials across motor neurons" produced by an internal releasing mechanism upon seeing a key stimulus. Tinbergen showed such fixed behavior in male red bellied stickleback threat displays towards passing red trucks, and Lorenz showed it in egg rolling behavior in waterfowl after an experimenter had removed the egg. These behaviors were thought to be very unmodifiable; once triggered they had to be completed and they were insensitive to their consequences (another way of saying they are insensitive to the reafferent loop) (1). But they're not reflexes, like the patellar-stretch reflex discussed in class.

True these behaviors are readily discernable, but instead of being a single instance (like a kick) FAPs represent more of a "pattern" of behaviors (like grabbing a cup and bringing it to your mouth). The relationship between the illiciting stimulus and subsequent behavior isn't as tight as in a reflex loop: FAPs tend to be difficult to interrupt, but other FAPs can interrupt them. The key stimulus, or input, is very specific and often narrowed to a feature of the organism's environment - say the shape of a parent's head in seagulls. The last feature that distinguishes FAPs from a simple reflex is that they are modifiable by learning -- their form isn't as fixed as previously thought. (2)

Could FAPs, which may even exert their control over behavior genetically (3) and are commonly accepted to have at least neural substrates (4), be an example of Grobstein's "motor score"? Could investigating FAPs further illuminate any of the previous issues raised when considering the motor score? Are FAPs related in anyway to "muscle memory," a related concept brought up in class?

I would like to end with a caveat introduced in the "Kurze Mitteilung" portion of the Journal of Ornithology by authors Peter H. Klopfer and Norman Budnitz --

"Wir meinen, daß diese Formulierung eher einer modernen Form des Homunculus des 17. Jh. als einer echten Erklärung entspricht, weil sie nicht erklären kann, wie das exakt reproduzierbare Nervennetz entsteht. Außerdem ist bekannt, daß dasselbe Verhalten auch bei enormen Unterschieden in der Neuralanatomie auftreten kann; stereotype Bewegungen brauchen keine spezifischen Nervennetze."

"We believe that this interpretation is more a modern form of the 17th century homonculous than an actual explanation, because it cannot explain how the eact neural network is formed. Anyway, it is known that the same behaviors can be reached with extremely different neuroanatomy; stereotyped movements need no specific neural network." (My very poory translation)

Have we resurrected the homonculous? Does this reintroduce the mind-body dichotomy?






EB Ver Hoeve's picture

Do we have the foundation for this discussion?

Although I find our gender discussion interesting and worth pursuing, it is important to realize that it is just one of the possible distinctions in the larger argument of biological differences. Like several people have alluded to on the forum, evolution and selection seem to play an important role in creating these biological differences. And if we are going to get down to talking on the level of proteins, than we should probably also discuss genes. Recent studies are discussing the potential biological component of homosexuality and the possibility of a “gay gene. While I believe scientists remain unconvinced of the existence of a gay gene, we can once again (like in our gender discussion) try and connect how behavior is connected to biological differences. But I think at this point, in both our gender discussion and other potential discussions, we do not have enough knowledge to make any solid observations. I think we still lack a true understanding of proteins and the translation to behavior. We should figure that out so that we can start talking at a more scientific level.
Jen Benson's picture

more about boys and girls

I agree with those of you who have said that it is really valuable to consider the influence of social constructs on gender differences in behavior. In a similar vein other situational variables must significantly influence behavior, such as the constraints of the environment that determine the most adaptive behaviors for males and females.

For example, evolutionary psychologist (I'm sorry I don't have a citation but Ben Le teaches it in his Intro Social Psych course at Haverford) have argued that females having a lower number of sexual partners could possibly be more adventageous for their survival since sexual acts could potentially result in a 9-month investment and incapacitation, while the physical investment of males ends right after the act has been finished. Thus males and females have evolved to behave differently sexually. Women are naturally less promiscuous because adaptively they should only want to mate with males who will provide for them in their period of vulnerability (pregnancy), while males will be more so because it helps them spread their seeds. (Of course such a position has been challenged by feminists as merely providing justification for double standards in expectations of sexual conduct for males and females.)

Caitlin Jeschke brought brought up the point of plasticity of the nervous system as it responds to different inputs and new structures. While evolution leads to changes on the level of populations rather than individuals, perhaps environments can cause certain behaviors to be more likely in subsequent generations by favoring certain kinds of nervous systems in survival capacities.
Sophie F's picture

In some ways, there is a

In some ways, there is a disconnect between viewing the brain as capable of generating outputs without inputs, the effects of leaky membranes and the net effect on behavior. It feels unsettling to relegate the realm of “free will” and “consciousness” to the random movement of ions and the cascade of effects neurons propagate within the brain. On the other hand, that neurons are adaptive leads one to conclude that learning can and does take place and that the nervous system is dynamic and, yes, predictable its unpredictability.

There is some cultural drive to explain behavior and categorize behaviors based upon observable and easily categorized morsels, whether or not there is "truth" or merit to these categorizations. It is, therefore, particularly interesting that depression, for example, can manifest similarly in two people (i.e. insomnia, loss of appetite, feelings of isolation), but because neurons are arranged differently, the input leading to the output might be vastly different between the two people. Furthermore, one may respond to psychopharmacological treatment while the other might not. Of particular interest to me is that if neurons are adaptive, then must behavior too be adaptive? If, over time, one who is “depressed” rearranges her neurons such that the certain inputs generate the “depressed” output and even “depressed” outputs occur without inputs, is there a way to “re-train” the neurons to rearrange, so the loop of inputs and outputs is altered? Is that the potential of therapy? Is depression an “illness” or is the category or label of depression useful as an explanation? If outputs generate their own inputs, does behavior reinforce itself?

cheffernan's picture

Salt water

After looking at Madina’s comment, I thought: “salt water running through channels”. We left class undecided on the subject of whether males and females behaved differently, but in when thinking about it, if all nervous systems are made up of “salt water running through channels,” how can human nervous systems make us act so differently from dogs? The answer lies in the receptor proteins and how every cell responds to the binding of a chemical to a receptor.

Many hormones that are found in other mammals are also found within humans, but the cellular response accounts for the different outputs of behavior. For example, when a dog feels threatened, their hair stands up and the dog begins to growl; however, when a human feels threatened, there are various responses that can occur: challenge the stimulus or retreat. The difference between the outputs lies in the connections of the brain. Every individual has distinct connections in the brain, which account for the varying responses among species as well as within a species. The connections that are established during development and through maturation determine whether the organism will growl, challenge or retreat.

So yes, there are the differing levels of hormones in males and in females, and yet it is these varying intensities of estrogen and testosterone that produce the differences in behaviors, whether you perceive them to be vast or minute differences, among men and women because in reality they have the same “salt water running through channels.”
Jackie Marano's picture

Chicken or the Egg...Or not?

At the end of class last Thursday we were beginning a discussion of how the nervous system does not only involve the generation of outputs from inputs (whether it occurs at sensory or motor neurons) , but also the generation of inputs as a result of already-generated outputs. I realize that we are only in the beginning stages of our discussion of this matter, but I have already begun to wonder: what comes first in this sort-of feedback loop, the input or the output?

I can physically take notes in class, which would be a motor output. I can watch my physical output, I can feel the pen in my hand, and I can make note of the characters on the page, all written in blue ink. These would all be sensory inputs based on my output. But this output of mine also required an input...some sort of stimulus to take notes in the first place. It almost appears that the input-output loop inevitably links the two together. We decided, however, that inputs and outputs can BOTH happen in the nervous system without the existence of each other...maybe they're just the result of leaky membranes or channels.

The issue of the leaky membrane seems like it doesn't exactly fit into this potential 'loop' that I was pondering....which would negate the 'chicken or the egg' analogy. Could we begin to think, then, that leaky channels are not necessary PART of these loops...but just 'loop intiators'? Maybe a leaky membrane in my mind causes me to think of neuroscience question in class...and THEN I generate my motor output (writing down the question), which allows me to have visual and tactile input (my written characters themselves). This was a fictitious scenario...but maybe that is where the leaky channels could fit in? I hope to discover whether the input-output system is actually a loop, if it is a consistent loop, and how each type of input or output could or could not fit into this loop/system!

Madina G.'s picture

hormone levels

I think Jean brings up a really interesting point about the neurons being the same yet exposed to different "bathing waters" between the two sexes. This implies that neuron activity is identical in all humans yet the difference in hormonal levels between males and females results in different interactions between neurons and their environment and consequently in different observable behavior. This reminds me of our class discussion on neurons, cabling and synapses only I'm having some difficulty accepting this idea of behavioral dependency on chemical composition. If this is the case, and each individual has their own distinct endocrine system that secretes varying levels of hormones, then based on this assumption how are we able to attribute certain qualities to one particular gender? How do hormonal levels dictate the "nurturing mother" quality in women who have given birth? Suppose the father exhibits this quality moreso; would this imply he has higher levels of estrogen and progesterone than normal? Since these are hormones present in males as well, what is the horomone level threshold that makes the interaction between neuron and hormone distinguished as to result in a difference in behavior?
anonstudent01's picture

Behavior, Unpredictability and the Brain

The discussion about gender differences in behavior and adaptive behavior has been really interesting, thanks for the links! On tuesday we decided that free will = unpredictability. We also discussed whether or not the nervous system has free will. I think that because behavioral response is dependant upon perception by the I function (because neurons don't account for everything) , then the I function must have free will. If it didn't then we couldn't be selective when choosing mates or when developing character. On the other hand, I don't believe that unpredictibility in the brain is unpredictable in the least. Regardless of how many times the input has resulted in a specific output, any output is ordered even if for the very first time and seemingly at random or formed as a result of growth or experimentation. So does the I function have free will if the Nervous System is indeed an input-output machine and ordered/predictable? We discussed that neurons can generate inputs without outputs which I also do not think is random but purposeful, computers do not do this but because they are strictly input-output machines. So then the NS can't be an input-out machine?
nasabere's picture

More on unpredictability in the brain

Interesting thoughts. I feel like I've harped on this point so much, but here it goes again.

I completely agree with you when you say that you "don't think that unpredictability in the brain is unpredictable in the least." I believe that they brain is in fact highly ordered (or perhaps I'm just really uncomfortable with the notion of disorder), and that there is a predictablity that we don't have the means to understand as of yet. As I've stated before in a previous blog post "it seems to me that order is tied to the language with which we speak about such phenomena. That is, as science evolves, so will our understanding of "orderliness" and in this way orders and complexities can thus be created...Perhaps an order, unobservable to the human eye or any human sense exists." This would then imply that we do not have free will...this is unsettling to me as it would seem that if the brain were in fact so predictable then we should share more similarities in our behaviors than are actually manifested. But perhaps this is already the case???

Caitlin Jeschke's picture

More About Behavior and Nervous System Plasticity

I found an interesting article this morning about an experiment done on fiddler crabs:

Caitlin Jeschke's picture



In this experiment, developing feeding claws from female crabs were transplanted onto male crabs in place of their defense claws.  These transplanted claws apparently allowed the male crabs to sense chemical input that receptors on a defense claw would have been unable to detect, leading to behaviors that were more typical of female crabs.  What is very interesting is that the transplanted claws grew and formed connections with parts of the central nervous system which, in normal males, process pressure and vibration inputs rather than chemical ones.


I think that these findings are relevant to our class discussions of behavior because they illustrate the fact that different types/numbers of membrane proteins play a large part in observed behavior differences between sexes or between individuals, while also demonstrating the nervous system’s plasticity, and ability to adapt to unique structures and inputs. 


Margaux Kearney's picture

Hormones and Behavior

What a fascinating experiment! It reminded of a text we read in biology class concerning the physiology and genetics of animal behavior. Male zebra finches are the only ones to produce courtship songs. Very early in a male songbird's life, for example, certain cells in its brain produces estrogen, a hormone which affects target neurons in an area of the developing brain called the higher vocal center. The presence of this hormone leads to a complex series of biochemical changes which result in the production of more neurons in areas of the brain that control singing. With female zebra finches, their brains do not produce estrogen and, as a result, the number of neurons in the higher vocal center declines over time. Experiments have shown that when these female birds are given estrogen, they produce more neurons in the HVC. However, they do not sing later on in life unless they were also treated with androgens. I found this example very ironic as male zebra finches had higher estrogen levels than the females and the females could only sing with the addition of androgens (a male hormone). As Caitlin stated above, different numbers of neurons (in my case) play a large part in observed behavior differences between sexes.

heather's picture


the songbird example certainly is a good one, and the crab article really is fascinating...

so, essentially (at least in these examples), conspecifics of different genders can be manipulated to respond to each others' 'parts'. but this is not the case with heterospecifics - at least as far as i can tell.

extending the songbird example, for instance, heterospecifics do not (cannot?) learn each others' songs, even if they are exposed to them during the critical learning period in their development.

also, take this article from 2002 as an example. apparently, "If an unmodified pig heart were given to a human, the reaction would be so violent that the heart would turn black in 15 minutes and be virtually destroyed in 30."

so, why can't heterospecifics (in general) share quite so intimately? Obviously the answer is genetics, but i'm curious about the mechanisms...

is there also a neurobiological answer to this question?

Angel Desai's picture

More on computers etc.

I found this article just today


Interestingly enough, it describes a new invention which simulates what the author of the article calls the brain. However, upon reading the article there seems to be a distinction which is lacking (and which we have touched on in class). Apparently this device is operated by stimulating a molecule in the center which then sends weak impulses or "shifts" surrounding molecules. This sounds suspiciously like a neuron (and what we called a computer!) rather than the brain! This article actually reminds me of a conversation I had with a lawyer who specializes in technological patents on the plane ride home! We wondered if technology as it is proceeding now has a cap. The last 20 years have brought so many innovations and at such a rapid pace that there must be some point at which we cannot move any further. This made me wonder if, like a computer, the brain has some sort of "cap" as well. We have exercised it to the point where we can now mimic the activities of neurons...but I wonder if the innovations of the brain are really limitless...

As to the discussion above concerning gender, while I agree that there seems to be a societal persistance in distinguishing between the sexes, there is something to be said about (maybe) actual differences! The problem here is that people often get caught up in semantics-saying a difference exists doesnt mean that one is wholly unequal with the other. I watched a news clip today about a study conducted in which a man appeared to be verbally abusing his girlfriend in a park. The researchers observed how many people stopped the man from hurting the girl and the overwhelming majority of people that did so were women. What does that mean in terms of the brain and behavior along gender lines?

mcrepeau's picture

Gender, Sex, and the Peacock's tail

Believe it or not this discourse on gender roles and gender perscriptions v. descriptions is particularly pertinent to one of my art history courses this semseter which focuses on the theme of gender in Medieval art. One of the core tenants of this course is to try and define (or at least explore the possiblity of) the line between sex (i.e. biological dimorphism) and gender performance (i.e. societal norms for the behavior of man v. woman in a gregarious culture). It is clear to me that both aspects are pertinent to this discussion as many have already pointed out and that what we define as "gender" and "sex" are equally important in what goes into how we think of the distinct male organism versus the distinct female organism. There are differences between male and female organism in their biology and thus in their behavior; however, this does not mean that these differences are absolute, after all, we have had several examples of hermaphroditic organisms (worms. bacteria (everyone remember the little "conjugation" demonstration we were fortunate enough to witness), slugs and leeches) that are capable of "performing" both male and female roles in terms of reproductive acts as well as certain species of fish and frogs that can change sex if contained in a single sex environment...which means "behaving" like a male organism or a female organism (i.e. becoming more or less aggressive, even altering phenotype to match the other sex). Thus, the gender discussion cannot be delineated by specifcally black and white borders (or confined to the realm of the human organism alone...for we are still animals even if our behavioral makeup, especially in terms of gender and sex, is particularly plastic---however, we must also be aware that the definitions of male and female roles are human constructs superimposed upon other organisms. Yet, the fact that we are aware of some fundamental difference existing, even on a purely operational level, is important in and of itself) but is more accurately described as a spectrum in which a given individual's postion upon the spectrum is potentially subject to change given the extenuating circumstances and the organisms biological capabilities (including, as is our case, the higher levels of organization that contribute to the very intricate, and very mutable, nuances of gender play, such as those seen in social organisms). However, just because gender play and "sex" can be potentially mutable does not mean that distinctions do not exist (or at least within the realm between sexually reproductive organisms). If one looks outside of our species these gender distinct behaviors are perhaps more obvious, especially in cases where gender dimorphism is very obvious, and is a major part in sexual reprodcution (peacocks and peahens). Organisms where reproductive success is dependent upon sexual dimorphism, where the male is extremely different in appearance (loud, flashy, and ultimately a walking sign post for a meal for hungry predators) and behavior (i.e. mating/courtship rituals, especially were the behavior is potentialy risky--but hey nature rewards risk in many cases) have very clear distinctions in gender behavior, which cannot be so easily explained by "cultural" perscriptions since in many cases these organisms do not have the type of social hierarchy that could dictate such gendered behavior (it must therefore be a more biological and thus neurological distinction).

In the not so distant past of humans as well biological differences were used to describe what was seen as very clear-cut differences between what was male and what was female (and this goes back to Aristotle (grrrrr...) Plutarch and Gelatian) which the female was at times viewed as a completely different organism from the male human...or else seen as some kind of failed/flawed male (i.e. something went wrong in the reproductive process and the mutant thing created was a female)--and as such the behavior of the female organism was a gray area, a thing entirely dependent on what she lacked in contrast to the male (she doesn't have this, or it looks like that instead of this and thus she acts like this kind of mentality of providing rational in differing behavior---which would seem to indicate that beyond soicietal perscriptions something fundamentally different was observed in genderal between the two genders), for instance "hysteria" was an intricacy of female behavior arising from that wilely, roaming organ (or parasitic animal as described it as) known as the uterus which was often viewed as an underdeveloped and inverted set of male reproductive organs (also Gelatian had the idea that both males and females secreted two different types of semens which were both necessary and contrary to one another in order to produce a baby). The point is that despite the obvious fact that the dominant discourse back in the day discussed the female gender in terms of the male this sense of difference, and a difference that connected biological/phenotyical dimorphism with large scale social behavior/gender constructs at that, did exist. Why does this persistance for determining a difference between gender exist if there is not some basis for it?

Mahvish Qureshi's picture


On the topic of defining behavior, a definition that may be pausible is "anything that an organism does involving action and response to stimulation" given by merriam webster dictionary. Basically it is saying that behavior is the output to any given input. Which means that not only do girls act differently than boys but each individual behaves differently than the next.

However if it is looked at from a more general persepctive than overall I think it can be said boys and girls act differently because the general response for girls to certain inputs is portrayed as the same as is the case with the general response for boys to a certain input. This genralization however may be outdated, because there is starting to be more variation in responses boys are maybe more able to show emotion and girls are less squimish. So maybe intodays world it is becoming more of a mix in how girls and boys respond to inputs or behave.

nasabere's picture


I too am struggling with this notion of behavior and the Merriam Webster definition is disconcerting to me. In thinking about it, I keep hitting a wall in which the question at hand seems to be this: can behavior transcend that which we can't immediately observe? My immediate response is…sure, why not? But then that would mean behavior is essentially everything and that’s just too complex and intangible. So in an attempt for a more concrete understanding I was thinking about non-neuronal related inputs/ouputs. Let’s look at an enzyme processing a given substrate; the substrate, in this situation is the input that yields the output—the products of the reaction. This situation hones in on the notion of inputs/outputs on a really basic level and at this microscopic level “input” and “output” are not readily observable. My issue with Merriam Webster’s definition is that I feel that they have taken the easy way out. Ok…so let’s play with this idea of behavior as a bunch of “inputs” and “ouputs;” a complete attempt at defining “behavior” would answer these questions: 1) is “behavior” limited to that which we can readily observe? 2) are we talking about input/output in purely a neuronal (and perhaps hormonal) level? and 3) what is the scale with which we consider inputs and outputs? If the answer to the first question is yes, then I believe Merriam Webster ought to clean up their answer a bit; clearly not all inputs and outputs are observable to us and not all inputs yield an ouput (hmm...on another not, is lack of output in response to an input considered be “behavior?”)'s picture


Emily has a good point about defining exactly what behavior is.  However, I think that the beauty of it is that there are no boundaries and that everything can be neither teased or clumped together.  Where do we draw the lines?  How do we define things?  There are surely extremes but I don't know how to form boundaries.

 But I think that the building blocks of neurons are not different for males and females; it is more like the bathing waters are slightly different for each sex. 

This controls our differences? or tendency to be different but similar by sexes?


Emily Alspector's picture

Gender Behaviors?

One thing that has been bothering me about our class discussions is that I don't think we have collectively defined "Behavior". We attempted to on the first or second day, but never actually came to any sort of understanding. When Professor Grobstein was talking about the behavioral differences between boys and girls, I really had no answer because biologically boys and girls behave differently, but social behaviors are much more questionable. Obviously boys don't menstruate, so there are clear biological differences.

Jean (I think) brought up a possible Venn Diagram, but even this I don't think covers the entire population. The diagram that Professor Grobstein drew on the chalkboard (two overlapping arches) still doesn't, i don't think, accurately represent social behaviors. Behaviors are controlled by emotions, which are controlled by the endocrine system, which we all share. If I were to take every behavior (laughter, crying, rage, sexual behavior, etc, etc) I don't think I could find a context in which a male and a female wouldn't behave similarly. If a person thinks something is funny, they laugh, regardless of gender. Perhaps males tend to agree on what they consider to be funny, but for every male who disagrees there will be a female who agrees, for every male who agrees there will be a female who also agrees, etc. The population is too large to make such outlandish generalizations. The social constructs of gender roles instilled in young boys and girls make us want to think that boys and girls behave differently, but I would argue that, overall, we don't. Or, at least it's too difficult to measure. Also hormones that regualte behaviors (testosterone, estradiol, etc) have varying levels among all individuals. I would like to further discuss how the levels of such hormones are socially influenced (perhaps cross-culturally?)

Molly Pieri's picture

An article from my Anthropology course...

I just read an article ("Talk in the Intimate Relationship: His and Hers" by Deborah Tannen) for my cultural anthropology class that reminded me of this conversation. It was about differences in communication styles between men and women, claiming that typically, men tend to pay value conversation for its content, while women look for what the author called "meta-content", or the messages that are carried in the tones and implications made during content. What seemed particularly pertinent to our class though was the observation made by the article's author that women and men would remember different aspects of a conversation. For instance, while men were more prone to remember the facts and figures explained in a conversation, women were more apt to remember the relationships between the individuals mentioned in the conversation.
I'm not trying to imply that there is some "natural", "innate" or genetic difference which accounts for this discrepancy in memory abilities between men and women, but it seems probable that in the process of socialization, the emphasis placed on what is "important" for a little girl or a little boy to remember would influence the development of certain neural pathways over others. I wonder what this process might entail, and what the results of a study exploring the difference between the brains of men and women during conversation recollection might look like.
evanstiegel's picture

I agree that it is tough to

I agree that it is tough to make generalizations about behavioral differences between males and females.  Granted we are different biologically and there many overlaps between social behavior.  But, couldn't we also make the argument for humans and dogs?  Again, humans and dogs are different biologically.  But, I bet some (mostly dog-lovers) would argue that we share many social behaviors with dogs.  I know this is a pretty crazy comparison, and it echoes Jean's point  below that defining boundaries is often difficult. But, I really think drawing lines sometimes is important.  Although there will always be exceptions when lines are drawn, I think it helps simplify things for many circumstances. 

I find it slightly demeaning to compare my behavior to a dog's.  Therefore, if we get rid of certain boundaries (like that for gender behavior), we may be crossing into a dangerous territory.

Paul Grobstein's picture

Mahvish got here first