Organization for the Advancement of   
Interdisciplinary Learning
Essay 1: 11/10/03 Behavioral Neuroscience, Biology, Psychology

An Example of Stimulus Response

One morning several weeks ago I was lying in bed as the sun began to rise. The sunlight that
reached my eyes created signals that traveled down my optic nerve, through a certain
neurological pathway to my pineal gland which is located in the base of my brain. The
electrical signals that were created by the light effectively caused a reduction in the melatonin
production in my pineal gland. Decreased melatonin levels in the blood stream cause people
to wake up from sleep and feel wakeful and vigilant. Before I knew it I was awake, and the first
thing that I wanted to do was get some breakfast.

In the kitchen I noticed that someone had thrown out a piece of meat and that the meat had
small white animals in it. They were maggots and they were writhing and squirming in the
meat inside of the plastic bag. Naturally I took the bag down to the dumpster and I hoped to
myself that I had seen the last of them.

Fly eggs had been laid in the meat some where on its trip to the supermarket. This is not an
uncommon occurrence because insecticides cannot be used on meat or animal byproducts.
When the meat was allowed to sit for a few days at room temperature the eggs that happened
to be laid on it hatched and the resulting maggots ate the meat to increase their mass. They
got big enough to reach a certain “critical mass” before they exhausted the food source and
were able to turn into flies. Insect eggs seem to “mysteriously” get into all types of food, partly
because many can become airborne.

Until a few dozen years ago no one really understood how these microscopic eggs (and other
forms of multicellular and unicellular life) got into seemingly clean pieces of meat. Bug eggs
and bacterial colonies created an anomaly that scientists could not rationally explain until
Louis Pasteur disproved the theory of spontaneous generation in 1959. Actually, in science
nothing mysteriously appears anywhere (until you consider things like thermal fluctuations in
terms of quantum mechanics).

The next morning I was very surprised to wake up to a kitchen full of flies. I walked around and
swatted them until I had to leave for work. By the time I got home from school I noticed that
they were much less active. They were weak due to the lack of available food. This made
them easier to hit but soon I realized that I was only making a big fly-gut mess. I needed an
alternative mode of action.

It was already very dark outside and I got an idea. I turned off all of the lights except for a
single light in the kitchen. After a few seconds, all of the flies were circling near the single light.
So I turned that one off and the light nearest to the back door on. Once again they all followed.
Next I turned that light off and an outside light on. After every fly flew out I quickly shut the door.
I had completely solved my problem. Flies become sexually active about 2 days following
pupation so I was very glad that I was able to get rid of them on the first day.

Flies, moths and many other types of nocturnal and diurnal flying insects are attracted to light.
This behavior is no doubt adaptive, meaning that it has become hardwired into their brains
after years of natural selection. A predilection for flying towards light sources gives them a
definite evolutionary advantage because it is easier for them to locate food when they are out
of the dark. It is as if evolution dictates their actions. Many insects will fly into a light even if it
means their death.

Flies have bundles of nerves within their small heads which are not complex enough to be
referred to as brains. Because of the way these simple bundles can interact with their nervous
system, flies are capable of some fantastic aerial acrobatics, they have some uncanny
abilities related to their sense of smell and sight and flies have actually exhibited the ability to
learn on a very simple level. When it comes to conscious volition though, they do not seem to
exhibit much.

Every healthy member of a group of flies in a dark room will be attracted to the closest salient
light source. This behavior is not learned by watching other flies, the behavior is instinctual,
they are born with it. The action of flying towards light is not initiated by a conscious decision
on their part, it is a physiological reaction that they cannot inhibit. Once they see the light they
will quickly dust off their wings and fly towards it.

…Well, I knew about this instinctual behavioral response to light and I used it to rid the place
of flies. Afterwards I felt pretty good about myself especially because I was able to contrive a
nonviolent method of insect removal. By this time it had gotten later, although it was still not
quite my bedtime. Because I had turned out all of the lights though, my pineal gland began to
up the production of melatonin. Very soon I began to feel sleepy. This reaction to the absence
of light is a physiological reaction that I was born with and have no control over. It was only
about 9:00 pm but pretty soon the physiological reaction induced a behavioral reaction and I
quickly brushed my teeth and got into bed.

Behavior: noun
The actions or reactions of a person or animal in response to external or internal

Inhibition: noun/verb
Conscious or unconscious restraint of a behavioral process, a desire, or an

Instinct: noun
An inborn pattern of behavior that is characteristic of a species and is often a
response to specific environmental stimuli: the spawning instinct in salmon; altruistic instincts
in social animals.

Louis Pasteur: noun
He solved the mysteries of rabies, anthrax, chicken cholera, and silkworm
diseases, and contributed to the development of the first vaccines. He debunked the widely
accepted myth of spontaneous generation, thereby setting the stage for modern biology and
biochemistry. He described the scientific basis for fermentation, wine-making, and the
brewing of beer.

Melatonin: noun
A hormone produced by the pineal gland that stimulates color change in the
epidermis of amphibians and reptiles and plays a role in sleep, aging, and reproduction in

Multicellular: adj
Describes an organism that has more than one cell, such as animals and

Optic Nerve: noun
A cranial nerve that arise from the retina and carries visual information to the
thalamus and other parts of the brain.

Physiology: noun
Being in accord with or characteristic of the normal functioning of a living

Pineal Gland:  noun
The pineal gland is a tiny structure located at the base of the brain. Its
principal hormone is melatonin, a derivative of the amino acid tryptophan.

Spontaneous Generation: noun/verb
In ancient Rome, the Middle Ages and up until the late
nineteenth century, it was generally accepted that some life forms arose spontaneously from
non-living matter.

Unicellular: adj
Describes an organism that has only one cell, such as bacteria, archaea,
protists, and certain algae and fungi.