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Biology 202, Spring 2005 First Web Papers On Serendip

Relooking at the Two Opposing Dream Theories in a Different Light

Elizabeth Madresh

The first time I learned about the major theories for why dreaming occurs, I remember feeling intrigued but perplexed. Theories that account for why dreaming occurs can be placed into two basic categories: psychology or physiological (1). My high school psychology teacher obviously had no intentions of flushing out why physiological theories were the most acceptable, but at the time I was forced to accept this, albeit with many doubts.

Revisiting the topic of dreaming after having almost half of a semester of Neurobiology and Behavior has helped to shed new light on these two competing theories. I have learned that one way of thinking about the nervous system is as equal to behavior, which is broadly defined to include human experience. Thus, a change in one causes a change in the other. Also, it is important to note that the organization or pattern of activity is critical for causing changes in behavior. This means that when neurons fire in certain patterns, one may walk, but if it changes the firing pattern, one may dance. It is the same neurons that are firing, but the patterning is different. However, what happens when the person is sleeping and they cannot display any changes in behavior? Is that why dreams occur? And if the firing patterns are different, could this explain different dreams? Furthermore, how does this tie into environmental influences during wakefulness? Aristotle explains dreaming as a perceptionless state where our senses of our outside stimulus are shut off. If this is the case, our human experience is momentarily "shut off". (2). Thus, there should be no change in the brain. However, how do dreams occur if this is the case? To answer some of these questions, it is important to look at two major opposing theories that have been created in an effort to explain why dreaming occurs.

Freud was the first to theorize about why people have dreams. Like most of his ideas, he believed that dreams were a result of underlying desires tied to the Id. During Freud's time period, the nervous system was thought to be a system of excitatory neurons. Based on this assumption, Freud believed that when a person was worried or preoccupied with something, an excited neuron causing a dream would be the only way to release this nervous energy. Now it is known that this is actually not true; the nervous system is made up of both excitatory and inhibitory neurons. However, based on what was known at the time, this was a logical theory. (3). Furthermore, this theory supports the idea that it is the pattern of firing and not the type of neuron that is critical in the production of behavior. Although Freud never delves into the details of how the excitatory neurons are firing, he does not explain dreaming by specific neurons but rather, their activity. However, one question that his theory does not answer is why repressed feelings have to be carried out in the form of a dream and during sleep? Why can't the person instead express their desires during wakefulness in some other disguised way? Perhaps moving to the next important theory of dreaming, we can develop a less wrong theory of dreaming.

In 1977, two influential men, Hobson and McCarley, developed yet another dream theory called the Activation Synthesis Model of dreaming. This model was meant to outright refute Freud's earlier psychoanalytic model. In laymen's terms, this model explains that the brain stem blocks motor and sensory neurons causing a flood of firings to the forebrain. Dreaming occurs because the forebrain tries to make sense of random firing of the brain stem. Furthermore, they suggest that dreams have nothing to do with emotion since they are merely triggered by sensory and motor aspects of bodily activity. (1). Most dreams are thought to occur when the pons sends signals to the thalamus, which then relays these signals to the cerebral cortex. (4). The function of the thalamus is to recognize sensory stimuli and relay sensory impulses to the cerebral cortex. The cerebral cortex is responsible for intelligence, memory, and the detection and interpretation of sensation. The thalamus and cerebral cortex are located in the forebrain, which is viewed as a more advanced structure (5). . Therefore, if these advanced structures are deciding how to interpret these random signals, doesn't this make the consequential dream not random? After all, just like we learned that the pattern of firing neurons are crucial to behavior, perhaps it is the structure or pattern of the story that is crucial to the dream.

Recently, there has been some evidence that dreams also occur during non-REM sleep, as well. (6). However, dreaming differs greatly depending upon the sleep stage the person is in. Specifically, a study by McNamara found that dreams where one is angry or emotionally aggressive towards another person were common in REM sleep but never occurred in non-REM sleep. (7). These differences may be key to understanding that dreams are not simply a result of random firing. Furthermore, it has been found that many dreams are linked to the ventro-medial frontal quadrant, which is the part of the brain that is responsible for wanting and seeking. This could possibly support Freud's theory, in that dreams are linked and perhaps motivated to our inner desires.

Furthermore, it is evident that sometimes the changes in brain (the dream) can later cause changes in behavior. For example, a mother has a bad dream about her children needing help and she wakes up and checks on her kids. Therefore, is it so far off to believe behavior can cause changes in the brain (i.e. the dream)? Perhaps Hobson and McCarley did not prove Freud wrong but rather made Freud's theory less wrong by explaining the actual physiological processes that lead up to dreaming as a breakthrough to the Id. After all, dreams have been shown to have coherence and have many similarities to people and events that occur in wakefulness and Hobson and McCarley's theory alone only offers the explanation that this is due to chance. However, if chance is the only reason for dreams, why is it that we dream of ourselves so often, if it is purely an unemotional stimulus coming from motor and sensory impulses. (8).


1) Dreaming: Function and Meaning , An essay of the two major dream theories and finding a middle ground.

2) On Dreams , an essay written by Aristotle about dreams.

3)The World of Dreams Reexamined , a helpful website on the Serendip web site.

4) Brain Basics: Understanding Sleep , a basic guide to what occurs during sleep

5) Online Learning Center: Health Psychology a>, a glossary of brain functions

6) American Psychoanalytic Association, A helpful article on the current scientific stance on REM sleep and dreams.

7) Metareligion: "Study Disputes Randomness of Dreams" , an interesting write-up of a study done on REM and non-REM dreams.

8) Dream The purpose of Dreams, , a site that talks about why dreams happen.

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