Serendip is an independent site partnering with faculty at multiple colleges and universities around the world. Happy exploring!

The Nature and Function of Dreams

SerendipUpdate's picture

Biology 202
1999 Final Web Reports
On Serendip

The Nature and Function of Dreams

Rachel Berman

There is a state of consciousness in which one could be or experience anything imaginable. This state encompasses the ability to dream (1). The dream state is quite remarkable and incorporates infinite possibilities for the dreamer within each of us. Nietzsche (1844-1900), a German philosopher, points out that dreams were a puzzle since “the ages of rude beginning of culture” when “man believed that he was discovering a second real world in a dream... (2).” The question that human beings were wrestling with since then is: why do we have dreams and what, if anything, do they mean. On the one hand, there are a number of prominent scientists, such as Drs. Allan Hobson and Robert McCarley of Harvard University, who argue that we dream for physiological reasons only and that dreams are nothing more than “meaningless biology” lacking any psychological content. The opposing view comes from a large number of psychoanalysts that follow Freudian thought. They believe that we dream for psychological reasons and that any dream can and should be interpreted because it is a road to our unconsciousness. Following Sir Richard Burton’s observation that “truth is the shattered mirror strown in myriad bits; while each believes his little bit the whole to own,” I will take a middle ground position in regards to current dream theories. This position recognizes that dreams might have physiological determinants, as well as psychological ones (3). Such an approach lets one explore the problem from more that one angle, thereby allowing a more “truthful” synthesis of the various pieces of our current knowledge of dreams. Before examining any dream theories, we must have some knowledge of the nature of dreams and of the stage of the sleep cycle during which dreams occur.

Dreaming is defined as “a sequence of sensations, images, emotions, and thoughts passing through a sleeping person’s mind” (4).The two important constituents of dreams are the sequence of perceptions and the presence of hallucinatory imagery, that is visual or auditory in nature. Dreams occur in the stage of the sleep cycle called REM sleep or paradoxical sleep. The subjects who awake from another stage of sleep called NREM sleep (occurs before REM sleep) do not describe their prior experience as dreaming (4).

According to biologists, consciousness is “an ability to react to the environment.” This ability is temporarily suspended during sleep and thus dreaming can be thought of as an unconscious process (5). Brain waves, eye movements, and muscle tone, are the three major measures of sleep that are used in its study. From the polygraph records of the two major stages of sleep, NREM and REM sleep, it is apparent that eye movement is much more intense during REM sleep (in fact, the letters stand for rapid eye movement). During wake periods, muscle tone is high relative to NREM muscle tone, which can be considered to be moderate. However, during REM sleep there is no significant muscle tone and the sleeper can be considered virtually paralyzed (6). The central paradox of REM sleep is that there is an increased responsiveness to sensory stimuli in the thalamocortical region of the brain (much like in the awakened state) despite the fact that there is a lack of cognitive responsiveness to sensory stimuli (7). Basically, our body is intensely responding, we are having all these emotions and images which seem so real....all while we are paralyzed from the neck down (8). Also, it should be stressed that everyone dreams; the people who claim that they do not, simply never wake up during their REM sleep to remember it (9). Now that we know what is meant by dreaming and when it occurs, we can turn to the question of what it signifies.

The oldest comprehensive theory of dreams was formulated by Sigmund Freud (1856-1939), an Austrian neurologist. In order to understand Freud’s view of dreams we must first look at his conception of how the brain works. Today, it is a known fact that two types of neurons are present in the nervous system - excitatory and inhibitory. Both types of neurons communicate through transmission of electrical signals. The neurons can either do so spontaneously or by receiving excitatory signals from other neurons. The difference is that excitatory neurons transmit signals which cause increased activity in other neurons, while inhibitory neurons send signals which decrease or inhibit the activity of other neurons. The nervous system is made of an extraordinarily complex network of intricate interconnections between billions of excitatory and inhibitory neurons (3).

During Freud’s time, only process of excitation has been discovered while the process of inhibition was not even hypothesized. Drawing from the model of a completely excitatory system, Freud concluded that “nervous energy” (caused by excitation due to, say a, thought) could only be discharged by some sort of motor action. An outcome of this theory is that once you got a notion in the brain, it would be passed around the nervous system until you decided to face it and do something about it, or until it found a way to manifest itself, either in an unintended action, such as the famous “Freudian slip,” or in form of visual imagery, such as a dream (3).

Of course, today we know that the nervous system which generates “blasts of energy” could not exist since it would produce persistent, uncontrolled seizure activity! However, from the excitatory model of nervous system, Freud’s theory about the nature of dreams can logically follow (3).

According to Freud, every dream has meaning and carries a message manifested by unconscious processes. The content of the dream is a metaphor for some disguised, or rather repressed, wish of the consciousness. In order to interpret a dream, one has to reason backwards in a process of interpretation known as “free association” (this method is still practiced in modern psychoanalysis). For example, if a person dreamt of a key, Freud would ask what was the first thing which came to mind in connection with a key. A person would likely answer that what came to mind is a lock. Freud would then reason about the connection of the two and about the symbolism involved. He would likely conclude that the “lock and key” imagery expressed the person’s wish to have sex! (3).

Freud thought that the function of dreams was to allow the release of repressed thoughts and impulses which cause excitation in neural activity. The force which causes dreams to occur was, in all cases, an unconscious and instinctual wish. The only way that the wish could be subdued is by the release of the “nervous energy” that was caused by it. Also, Freud noted that “though the number of symbols is large, the number of subjects symbolized is not large. In dreams those pertaining to sexual life are the overwhelming majority...They represent the most primitive ideas and interests imaginable (10).” Therefore, the same dream that is dreamt by two different people (or the same “dream symbol”) meant that they both had the same repressed wish. This wish, whether sexual or otherwise, was the force behind every dream and therefore all dreams must contain a necessarily meaningful message (3).

Today we know that dreams are not triggered by psychological factors, such as repressed desires or wishes, but rather by a purely biological process - REM sleep. We can no longer infer that wishes play a role in dreams because they do not spur dreams. If taken further, we can no longer assume that every, or any dream for that matter, has any significant meaning (3).

The latest neurophysiological theory of dreams, which is in direct opposition with Freudian concepts, was developed by two Harvard University scientists - Drs. Allan Hobson and Robert McCarley. According to their Activation-Synthesis Model, dreaming is caused physiologically by a “dream state generator,” which is located in the brain stem. It is “on” during REM sleep, while all sensory input and motor output are blocked, and the neurons in the cerebral cortex are activated by random impulses that generate sensory information within the nervous system. As Hobson and McCarley put it: “the activated forebrain then synthesizes the dream out of internally generated information, trying its best to make sense out of the nonsense it is being presented with (3).”

The logic used in the development of the Activation-Synthesis Model stems from the predictable regularity that is observed in the triggering of a dream state. Hobson and McCarley stress that “the motivating force for dreaming is not psychological but physiological since the time of occurrence and duration of dreaming sleep are quite constant, suggesting a preprogrammed, neurally determined genesis (3).”

Hobson’s and McCartey’s treatment of symbol formation is also in direct opposition with Freudian conception. They believe that “bizarre features” of a dream world are simply a reflection of the bizarre state (the bombardment with internal excitory signals, etc.) of the dreaming brain. That is, in the construction of a dream “the forebrain may be making the best of a bad job in producing even a partially coherent dream imagery from the relatively noisy signals sent up to it from the brain stem.” This implies that dreams have no emotional content since they are triggered only by sensory and motor aspects of bodily activity (3).

Hobson’s and McCarley’s notion that “dreams were after all merely senseless, random accompaniment of the autonomous electrical activity of the sleeping Central Nervous System” does not provide all the pieces of the broken mirror puzzle. Based on our knowledge of brain physiology, there is no doubt that the Activation-Synthesis Model is right by dismissing the Freudian notion that dreams are instigated by a wish. However, before regarding dreams as meaningless productions, the function of dreams and the factors that influence their synthesis must be further examined (3).

Hobson hypothesis that the likely function of dreams has to do with “the sign of genetically determined, functionally dynamic blueprint of the brain designed to construct and to test the brain circuits that underlie our behavior - including cognition and meaning attribution.” Another words, dreaming is a mechanism intended to stimulate the neural circuits and this stimulation must in some way be critical to normal brain functioning during the awake state (11).

Various evidence certainly suggests that dreaming is more than “genetically determined.” The fact that we, at some times, have dreams with an eloquently constructed story lines, as well as the fact that dreams do influence behavior in many instances, point to the idea that higher order mental functioning has the ability to influence a lower order functioning of the “dream state generator” of the brain stem (3).

Dreams very often have a profound effect on how one relates to the outside world. One dreamer recalls: “when my children were about nine and four I had a dream that they were crossing the street at a crosswalk with friend of theirs. All three got hit by a car and were killed. I recall waking up and being absolutely terrified. I jumped out of bed and went to check on them. They were both sound asleep and in good health. None the less the fear would not leave me so I did something that I ready do, I knelt be my bed with tears running down my face and prayed to God that this dream never come true.” In fact, this mother’s entire outlook on life was changed by her dream; she restored her belief in God and became a more protective mother who appreciated each day with her children (12). Stories like this are numerous and it is apparent that many dreams give people a profusion of various information about themselves and their relation to the outside world that they can not know from the genome alone (13).

Another point to consider is that the synthesis of dreams, while influenced by the genome, is also influenced by a particular person’s experiences. Perceptions gained through these experiences play a role in the type of a dream world that the brain makes up. The genome is there to establish the particular types, amounts, and various neural connections present in the brain. In what ways and which of these connections are used is determined by each person’s unique experiences which effect behavior by producing a permanent change in the brain (after the experience is detected by sensory nerves). This change may alter neural connections in the brain or alter how they work and thus it will influence how one dreams. However, in any discussion of dreams, it is equally important not to forget the genetic factors that are stressed by the Activation-Synthesis Model. It has been long apparent that the genome does influence what and how quickly and easily one learns. It must also influence how one dreams by providing the nervous system with the tools (neural connections, etc.) from which to create dreams (13). The point to note is that the phenomenon of the brain making things up for itself, which is evident during dreaming, has to do with both the genome and experience.

The case of lucid dreaming, which is the state of dreaming while knowing that you are dreaming (14), also shows that there is more to the story than what the Activation-Synthesis Model can offer. Lucid dreaming has been proven to occur due to technology which lets people signal through electrodes attached to corners of their eyes (by prearranged eye movements) when they realize that they are dreaming (15). If dreams were simply a result of the forebrain ”making the best of a bad job in producing even partially coherent dream imagery from the relatively noisy signals sent up to it” from the brain stem, then how could a person know that they are dreaming, be able to exercise volatile choice in a lucid dream, or carry out a previously planned course of action in a dream? Also, studies of lucid dreams indicate that dreamers are at times able to have their own intentions, ideas, and feelings. These feelings can not simply be attributed to random brain stem stimulus, but rather they might be a response of some higher order perceptions (3).

As is evidenced, dreaming has both physiological determinants as expressed by Activation-Synthesis Model, as well as psychological determinants. These two factors are played out in astonishingly unique ways in each individual. Therefor, it is hard to believe that the same symbol that appears in the dreams of two different people actually means the same thing, if anything at all. The brains of two people are extremely different, not only due to genetic differences but also due to their relation to the external world (the experiences of each person are very unique). The other fact that adds to this uniqueness is how each of their brains uses the input of genes and experience to synthesize the dream world (13). Taking all these factors into account, with the added knowledge of the complexity of the nervous system, it becomes apparent that the notion of universal dream symbols is quite shaky.

Dreams embody a synthesis of our being that is manifested at both the physiological and the psychological levels. All these give us a glimpse into what we are like. We have inside us, through the power of dreaming and imagining, a unique ability to experience the world like no one else has and to use ourselves as a subject of exploration (13). The important thing is to keep dreaming and questioning for the mystery of our unconsciousness may unravel itself through its own process of discovery.

WWW Sources

1) Lucidity Research, Past and Future

2) Dreaming, Illusion, and Reality

3)Dreaming: Function and Meaning

4)Dreaming: A Neurocognitive Approach

5)A Biophysical Model for Altered States of Consciousness

6)Brain/Body Activity During Sleep and Dreams

7)Conscious and pre-conscious processes

8)Function of REM and NREM

9)REM sleep

10)Freud: “Introductory lectures on psycho-analysis” , Reference #2 within Dreaming: Function and Meaning

11)Dream Dialogue , Reference #7 within Dreaming: Function and Meaning

12)Why is Dream Forgetting Common?

13)From Genomes to Dreams

14)What is a Lucid Dream?

15)Lucid Dreaming Proof



Continuing conversation
(to contribute your own observations/thoughts, post a comment below)

10/02/2005, from a Reader on the Web

i liked this arcticle a lot i t helped me do my paper fo rmy 8th grade language class thank you ~helen


Additional comments made prior to 2007
Dreams perform various functions: they quickly help us find our sense of orientation when we wake up; they salvage data gathered during the day prior to sleeping and they upload all programmes related to behaviour and thought. Should we awake abruptly without dreaming we would encounter great difficulties moving around or coordinating simple movements. This is the central issue reported in an article written by Elia Tropeano which recently appeared on Internet. The article however does not mention the case of a school teacher who relates that one night, while she was studying for a state exam with a friend it got very late and she fell asleep on her books. She suddenly woke up and started screaming out in terror because she was unable to understand why the other woman was at her house. It took her a while before she was able to get a hold of herself and recognize the woman as her friend who was bewildered by the episode. Nor does the article mention the case of a woman who, having read the article, felt reassured about what had happened to her fifteen year old son. One night she heard a noise. She turned on the lights and saw her son walking around the room with great difficulty. He was unable to speak and explain what he was doing. At first she thought he had been hit by a stroke and did not know what to do. Her husband quickly intervened and they tried to assist him. Later on the son recovered completely and explained that his problems, including a paralysed arm, all began when he woke up. What had happened was that he woke up accidentally without experiencing a dream.

The physiology of Dreams
The transition from a state of wakefulness to one of sleep comes about gradually and coincides with reduced bodily functions. Once a physiological loss reaches the critical level, the left hemisphere (dominant hemisphere of our brain) is activated and starts building upon images, sounds and sensations: dreams, with the aim of restoring those chemical-physical values which belong to a state of wakefulness. Once restored a new loss occurs and the cycle repeats itself for the entire period that we are asleep.
Dreams can raise the chemical-physical parameters but need to be continuously interrupted in order to avoid high levels thus the risk of waking us up. Continuous interruptions induce a deeper state of amnesia proportional to the interruptions. When we dream, lacking total access to our right hemisphere, we are without identity, nor do we remember anything rather, our mnemonic function is restricted to those events which have occurred during the day. We cannot conceive time, distance or residence.
The sole mnemonic function which remains concerns space-time which is activated by rapid access connections to the right hemisphere. Both hemispheres must be activated when we awake and more so when rapid access connections to the right hemisphere become more frequent. In this case the greater number of space-time coordinates are achieved, the more dreams are linked to real life ... Elia Tropeano, 11 June 2006


Preethika S (Serendip Visitor)'s picture

Can u please clear me

I am dreaming every night. Even if I sleep for ten minutes I will dream. This really stressing me because I feel like I can't sleep peacefully. Also, within five minutes after i slept, I dream like falling from a building, maximum relating to accidents. It feels like real, I just dream I am falling but with in a second I start falling , I woke up with a sudden jerk and I can't sleep again easily. What's the reason behind this

Serendip Visitor's picture

can you interpret this for me please

i often dream about my siblings and theres always something bad happening to them. on dream was about my older brother, i woke up in my dream and saw that my brother was missing so i asked my sister where he was and she told me he was dead and buried outside in front. another dream i had was about my older sister wanting to skip school on her birthday to see her boyfriend and she got caught. the weird thing is that later that day i asked her if she was thinking about skipping with her boyfriend and she said yes so i told her not to cause of my dream. the next dream was about my younger half sister.i was in the car with my mom and sister. we stopped in front of my old elementary school and my mom told my sister to get out so she just stood their out in the rain and we drove off without her. why do i have dreams about my siblings a lot? and why do bad things happen to them?

Anonymous's picture

thank you so much for this

thank you so much for this article it covers exactly what I need for my project. It is so interesting!

Emma's picture

Addition to article...

The tribe that live in the Malaysian rainforest believe that we are taken to another world when we dream, and that everything we experience during our dreams has some kind of purpose. The tribe called the Senoi view the dream world as the extension of the spirit... I personally find this so interesting. Thanks for a great article.

Anonymous's picture

from the article: ' .

from the article: ' . Nietzsche (1844-1900), a German philosopher, points out that dreams were a puzzle since “the ages of rude beginning of culture” when “man believed that he was discovering a second real world in a dream . . '

How did Nietzsche know exactly what people believed about dreams, especially when they existed eons before he did? Was he there?