Biology 202
1998 First Web Reports
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Stimulus/Response Versus Input/Output Theory: An Orientation to the Syntax of Scientific Literature

Jeremy Hirst

There appears to be a steady desire within the scientific and lay community to explain events which occur in the universe in a concrete absolute fashion. This most likely extends from an unconscious (or conscious) need to control the world around us. Such control can give a sense of security regarding our future. If we can explain why events happen, we can attempt to predict when and for what reason events will precipitate sometime in the future. Being able to predict the future leads to a greater feeling of security and control.

However, it has been shown through decades of research that behavioral events are not predictable. Researchers tend to conclude that if they are to truly understand behavior then they must be able to develop a system which allows them to forecast the occurrence of certain behavior patterns. Conversely, if they are unable to state consecutively when and why a pattern is presented then they have failed to understand the event. In order to retain a sense that the universe is orderly the unpredictable results are often explained through the fault of the experimenter, that adequate control was not kept over the experimental situation. Through the Harvard Law of Animal Behavior ("under carefully controlled experimental circumstances, an animal will behave as it damned well pleases.") these "failed" experiments are incorporated into a succinct postulate which allows for the exploration of reason and desirability of such unpredictability (1).

Through lectures, reading, and World Wide Web research done during the current semester I am moving from a stimulus/response theory to an input/output theory. The stimulus/response theory let experimenters believe that the unpredictable behaviors (responses) they had observed were due to inadequately controlled stimuli. An input/output theory allows for, and seems to rest on, the fact that many behaviors originate from the internal (spontaneous) generation of outputs. Internal origination is fundamental to many aspects of commonly observed behavior (biological clocks, innate endogenous rhythm, and other innate behaviors) and the presence of these behaviors seems to rest on something other then concrete stimuli from the external world. The syntax of many of the studies found on the Web leads me to conclude that these scientists are searching for an input/output behavioral system yet are unable to adequately document such a clear relationship. This inability most likely stems from the recently discussed phenomena of bidirectionality within and outside the most broad input/output box (Lecture, Bio 202).

The scientists do not generally discuss the behaviors they observe in relation to the most fundamental input/output box: the neuron. Instead, they rely on the apparent truth that every behavior can be explained by some concrete stimulus. Many of the studies were very interesting in their approach and observations yet disappointing in their inability to carryout the final synthesis to explain how the organisms behavior can be explained by the function of the neuron.

The Web held information on experiments regarding orientation of a variety of organisms in space and time. A humorous starting point is the following story: "Forel (1910) observed that bees from a nearby hive would come to sample his marmalade as he ate breakfast on his patio. They would present themselves at the same time every morning in increasing numbers. Eventually, he was forced to eat inside, but he observed that the bees would present themselves at breakfast time even in the absence of the marmalade! Based on this observation, Forel postulated that bees possessed a memory of time." (2) Similar time dependent behaviors include the process of copulation and reproduction in springtime, Drosophila pupae emergence, increased mosquito activity at dusk, and running behavior of cockroaches shortly after sunset. (3)

"Insect Clocks" described several of these events in greater detail. It has been found through cockroach brain surgery that the area responsible for rhythms (neurons) is located in the insect's optic lobe region of the brain. When this lobe was removed from the brain, arythm resulted, and when transplanted to another cockroach the new cockroach had acquired the circadian rhythms attributed to the donating insect. A similar experiment done with silkmoths also showed that circadian rhythms may originate from the neurons within the brain. When a silkmoth was de-brained they lost the ability to carryout rhythmic behavior, yet when the brain was reconnected the rhythm was reinstated.

There appears to be a drastic hole in this argument, namely, would you carry out any type of rhythmic behavior if your brain had been removed?! However this argument does allow one to think of behaviors originating from neurons rather then from stimuli external to the animal. Light is often described as having the ability to cause behaviors in animals (3,4). Drosophila pupae emergence is a phenomenon which can be timed to occur twenty four hours after exposure to light. This exact twenty four hour clock is said to be innate to the pupa. So, here is an example of scientists merging an external stimulus with an internal, self-perpetuating series of events which lead to the hatching of an insect. In reference to the input/output theory, the light could be said to be an input which generates conditions for a series of input/output events that eventually lead (twenty four hours later) to a final "output" of the pupae. This timing event is satisfactory because it could rely on the action of the neuron. That is, it seems possible to keep time on the neuronal clock.

The page, Turning Strategies in the Walking Fly, Drosophila melanogaster (, describes "visually induced turns" of flies. The behavioral process is systematically broken down to a series of steps (pardon the pun): "(turning) is achieved by concomitant changes in step length and stepping frequency. For legs on the outside of a curve, step length depends on stepping frequency, just like during straight walking. Turning is achieved exclusively by diminishing the step lengths on the inner side." A one-two-three set of instructions on how to turn a fly is indicative of the constant desire to have pure if/then (stimulus/response) statements, for an ideal understanding of behavior. Yet, it was observed that the "orientation of the body relative to the direction of progression is astonishingly variable and may differ by up to forty degrees." In other words, these flies do not always walk straight, instead they may wonder and stagger about the experiment!

Another page, Positive phototaxis in Fabrea salina ( groups/fabrea/photo.html) also discussed the behavior of movement. This time it was found that the simple cellular organism moved toward a light source. While the information on this page was not extensive it gave the possibility that there is an internal system of processes, smaller than a neuron, which allow for outputs to be made such that the cell may locomote toward light. This random behavior correlates with the internally originating output theory. It gives autonomy to the insect and allows the insect to behave in a fashion beyond the concrete grasp of the scientific community. While not anthropormisizing Drosophila, this observation of autonomous behavior leads down a path to the neuron, which is capable of spontaneous depolarization (Lecture, Bio 202). Spontaneous depolarization could lead to spontaneous behavior, such as not walking in a predictable straight line to a light source.

The goal of developing a method for explaining behavior patterns may not ever be met. This failure will likely be a result of the very wording of the goal statement, behavior does not always occur in a predictable pattern. Examples of behavior, those above as well as many others, show that the stimulus/response theory is incapable of reliably predicting the future orientating movements of an animal. The language used by many of the authors I reviewed confines them to using the stimulus/response theory, thus their experiments cannot succeed with unpredictability. A bi-directional, spontaneous, neuron based, input/output theory seems more appropriate. As spontaneous variability is an attribute of many neurons, it follows that behavior originating from neurons would mirror these fundamental characteristics.

WWW References

1) Variability in Brain Function and Behavior.

2) Insect Clocks.

3) Light Related Behavior.

4) Gravitaxis and Phototaxis in the Flagellate Euflena studied on TEXUS Missions.

5) Turning Strategies in the Walking Fly, Drosophila melanogaster.

6) Positive phototaxis in Fabrea salina.

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This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.

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