Dreaming is the subjective conscious experiences we have during sleep; but what purpose does it have? There are many conflicting theories as to the purpose of dreaming. Testing these theories is next to impossible, but the few studies that have been done have hypothesized that dreaming has been selected for in order to teach us what to do in certain situations when we are awake.

There are two kinds of sleep; one is REM sleep or rapid eye movement and the other is SWS or slow wave sleep. REM is associated with a low level of brain activity, the inhibition of muscle tone, waves of excitation from the pontine brain stem, and rapid eye movement. The waves of excitation are the reason that we dream. The pons, or brain stem, send signals to the eyes, the midbrain, and thalamus. The thalamus is where the visual, auditory, and tactile are located. This stimulates the cortex and the cortex receives a valid sensory signal and reads it as if it were coming from the eyes. This is what actually creates the dream. When dreaming, the spinal cord is paralyzed and the senses are disconnected. REM sleep will occur four to five times a night in 90-minute intervals that last for about 20 minutes. SWS sleep is the sleep we experience the rest of the night when not in the deep sleep of REM ( Scaruffi, 2001).

The brain does pretty much the same thing whether we are awake or not. When dreaming the brain employs the same processes and systems as the awake brain. However, these processes are not activated by outside stimulation. Because of this, there is no significant movement and memory and self-awareness are dormant (Scaruffi, 2001).

One ultimate hypothesis for the purpose of dreams is to help us learn. Dreaming of hypothetical situations helps us prepare for them when we are faced with the same kind of situations. When a real-life situation occurs, we probably have already dreamed of it once or twice before, and we will know what to expect. Dreaming is like a mental exercise we receive for our brains (Scaruffi, 2001). The dream elements often appear to arise from memories of waking events (Strickgold, 2001).

Fred Synder was the first psychiatrist to look at dreaming from an evolutionary perspective, proposing that REM sleep came first and dreams came later. First, the brain developed the state of REM sleep and then dreams were engrafted upon REM sleep. In other words, REM sleep was available and was used to host dreams. Synder believes that dreaming evolved after a physical feature made it possible, just like language was evolved after an anatomical apparatus that was born for whatever reason (Scaruffi, 2001).

Since there is no way to actually test this hypothesis, there are several theories from different people about dreaming. However, scientists believe that dreaming has survived because there are no maladaptive consequences. The first theory is the activation-synthesis theory by Hobson. This theory states that there is a randomness of dream imagery and the randomness synthesizes dream-generated images to fit the patterns of internally generated stimulations (Revonsuo, 2000). In other words, Hobson believes that sleep has the function to reinforce and reorganize memory from short-term to long-term memory (Scaruffi, 2001).

The second theory is by Crick and Mitchinson which greatly reflects the topics of Hobson’s theory, but contains some new ideas. In this theory, memory in the brain is compared to simple models of associative nets. The net gets overloaded and a random output is produced of combinations of simple models already stored in the memory

(Revonsuo, 2000). When dreaming the brain is disconnected from its usual inputs and outputs, and is replaced with a more random input. In other words, dream images merely reflects the function of a memory-cleaning process (Revonsuo, 2001).

The third theory was created by David Foulkes. It is known as the cognitive theory of dreaming. The theory states that dreaming originates in diffuse, more or less random activation of semantic and episodic memory during sleep. Foulkes believes that dreams are so random that they serve no real adaptive functions. However, the theory distinguishes between the content of dreams and dreaming as a process (Revonsuo, 2000).

Solms defended the view proposed by Freud as the fourth theory. Freud’s view was that the function of dreaming is to protect sleep. Solms then regarded dreams as simply bizarre hallucinations that the weakened frontal reflective systems mistake for real perception (Revonsuo, 2000). In addition, Solms suggested that dreams may occur without REM sleep as when the brain is activated by a brain seizure (Cartwright, 2000).

It is difficult to test these theories. However, some studies have investigated intellectual problem-solving in dreams. The first study was administered to 500 undergraduate students who were given a copy of a problem and were told to spend 15 minutes before going to bed working on that problem. The problem was attempted to be solved 1,148 times and in those attempts the problem was only solved seven times through dreaming. This means that less than one percent of the dreams were successful in solving the problem. Another study was also done that involved six subjects. Four of them were given a formal problem to solve and the other two were given a problem about their careers. Although, elements of the problems appeared in their dreams, the subjects did not report finding a solution to their problem through the dreams. Instead, they were able to find the answer with relative ease during the first few waking hours. Even with these studies it still remains unclear as to whether or not dreaming solves waking life problems ( Revonsuo, 2000).

Nonetheless, there are three types of problem-solving dreams. There are dreams that create a new and useful solution to current problems in waking life. Second, there are dreams that contain problem-solving activity that is internal to problems encountered in the dream world, but not to problems in real life. The last type are the dreams that reflect solutions to problems in waking life, but it merely reflects the solution once it was already found while awake. There is only some evidence that any of these types of dreams really exist. Whatever the function of the dreaming experience is, it does not appear to be finding new and useful solutions to the problems in waking life (Revonsuo, 2000).

There is also a hypothesis as to whether or not dreams can solve emotional problems. This theory states that dreaming solves our emotion problems by helping us to adjust psychologically to, and maintain our mental health in, the real-life situations that trouble us emotionally and psychologically. There is evidence that shows that dreams do reflect the current emotional problems of the dreamer. However, the question still remains as to whether or not dreaming actually reduces the negative affect that is caused by our real-life problems (Renvonsuo, 2000).

Other theories also exist about the emotions in our dreams. Kramer argues that when in REM sleep there is a burst of emotion and that dreaming is a way to contain the surge. He also says that if the dream successfully fulfills this emotion, then the dream will not enter awareness. The dream is then said to have protected sleep. This theory was also known as the selective mood regulatory theory of dreaming (Revonsuo, 2000).

Another theory suggests a more general hypothesis about the function of dreaming. It states that dreaming is necessary in order to provide the mind with material or emotions to process during sleep. This keeps the mind active during the night so that the conscious reflection developed does not turn into external stimuli or to the current problems facing the dreamer. This would then disturb sleep and is another reason why dreaming is said to protect sleep. Looking at it from this point of view, dreaming serves the biological function of letting us get a full night’s rest (Montangero, 2000).

In opposition to this theory, if dreaming was to protect sleep and turn a stressful emotional experience into something better, then why does this function not exist when we need it the most? For example, recurrent dreams that occur during a time of stress have a negative content. This does not help the emotional state of the dreamer. Another example disproving this theory would be that fact that when people have a traumatic experience, they will often relive the trauma in their dreams. This causes the dreamer to feel powerful negative emotions. In theory, if dreaming was to help us heal emotionally, then the dreams should be completely opposite of what really occurs (Revonsuo, 2000).

One possible counter-argument is that the dreaming function has just simply failed. Nightmares are then treated as failures, but the failures occur too regularly for this statement to be completely true. When emotions are experienced or expressed in dreams it is more likely that they will be negative instead of positive. If the view was that dreams solve our emotional problems and increase happiness, then that would lead people to believe that normal life is free of emotional pain and trauma. It is believed that the feelings of pain and fear are there not to increase our happiness, but to increase our reproductive chances. In other words, natural selection cares only about our fitness (Revonsuo, 2000).

These negative emotions are mainly caused by the aggression in social interaction of the most dreams. People have strong tendencies to dream of aggression, friendliness, and sexual interaction. With the aggression, the dreamer is involved and more than likely they are the victim. These finding support the fact the dreams are specialized towards simulating threatening events (Revonsuo, 2000).

When the brain in not functioning properly during dreams of aggression, sleepwalkers have been able to commit murder. In several cases sleepwalkers did not recognize their victims. For example, one man drove 15 kilometers to his mother-in-law’s house, which means that his motor skills were intact. Then he stabbed her with a knife and did not respond to her screams. He acted as if he was under threat and initiated a fatal attack. This man had a genetic and personal history of awakening abruptly from the first cycle of sleep into a confused state and never entered REM sleep (Cartwright, 2000). The REM sleep is necessary to prevent waking hallucinations and mental illness (Siegel, 2001).

Since aggression is prominent in most dreams, it is likely that our enemies cause this aggression. In a study by Hall and Van de Castle, animals and male strangers are the primary enemies in both male and female dreams. When a animal enters a dream it is almost always going to pose some threat or danger to the dreamer. The reason for this was thought to be because in ancestral times humans lived in an environment full of dangerous animals. There was also a constant threat from other humans. These ever-present dangers made behavioral strategies to avoid contact with these things and was of a high survival value. Dreaming simulates these strategies in order to maintain efficiency; otherwise, one failure to respond to these threats in waking life could mean death. Dreams are biased towards simulating threats that were common in our ancestral environment ( Revonsuo, 2000).

Children also have a strong tendency to dream of animals. The animals in these dreams are often ones that the child had never encountered before in their waking life. As we get older the wild animals become domestic animals in the dreams. However, this is only occur if the child’s real environment does not have any of the wild animals. It is thought that children dream of animals because in the ancestral environment there was many encounters with dangerous animals. In the dreams, the children would learn the flight or fight response needed for their survival ( Revonsuo, 2000).

Real experiences of actual dangers or life-threatening events are very likely to be incorporated into dreams. This can be clearly seen in cases of post-traumatic nightmares. It appears that the greater the sense of threat created by the experience, the more likely it is that nightmares will follow. Experiencing a severe trauma can cause nightmares in almost anyone (Revonsuo, 2000).

There seems to be a pattern in which these post-traumatic dreams are created. The first stage, right after a traumatic event is experienced, the person will have more nightmares and will review the traumatic events in their dreams over and over. This could last a few days or several weeks, but if the trauma was severe enough, it could last for years. In the second stage, the nightmares change into modified versions of the event. This is because the original experience is now connected with other similar contents in the memory. After a few weeks, or even months, the nightmares will return to almost normal (Revonsuo, 2000).

Persistent post-traumatic nightmares are produced by the threat-simulation mechanisms when a set of memory traces is associated with an overwhelming charge of threatening emotional content. The memory traces become a large part of the dream production mechanisms and thus is selected for over and over. With time the memory traces should slowly wear off, but sometimes the nightmares remain for extended periods of time (Manquet, 2001).

The threat-simulation mechanisms can be compared to other biological defense mechanisms. For example, when a pathogen enters a host, the immune system triggers a response until the pathogen has been removed. Certain parts of the immune system will remember the pathogen and will be better prepared to fight it off next time. This is similar to what happens when we dream. The evolved biological function of the dream-production system is to construct appropriate threat simulations when triggered by real threats. Even if no threat-related experiences are encountered during regular dream production, a dream of some sort will still occur (Revonsuo 2000).

Although, the immune system is needed to protect and provoke the survival of humans, sometimes there are negative side effects. The threat simulation also sometimes had negative effects. For example, someone suffering from consistent nightmares often fear going to sleep, awakening from sleep, restless sleep, insomnia, and daytime fatigue. This means that the dream production system can be seen as an ancestral defense mechanism comparable to other biological defense mechanisms whose function is to automatically elicit efficient protective responses (Revonsuo, 2000).

In conclusion, dreaming has occurred since our ancestral times and will continue to occur as long as there is trauma and pain in our lives. The dreaming processes was selected for to increase our survival chances and these dreams are almost always negative. The theory as to why we dream of such negative things or why we even dream at all are many, but there is no way to prove for sure which ones are true.

Cartwright, Rosalind. (2000). How and why the brain makes dreams: A report card on current research on dreaming. Behavioral and Brain Sciences, 23, 914-916.

Maquet, Pierre. (2001). The Role of Sleep in Learning and Memory. Science, 294, 1048-1051.

Montangero, Jacques. (2000). A more general evolutionary hypothesis about dream function. Behavioral and Brain Sciences, 23, 972-973.

Revonsuo, Antti. (2000). The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming. Behavioral and Brain Sciences, 23, 877-901.

Scaruffi, P.(2001). The Interpretation of Dreams. Retrieved November 16, 2001 from the World Wide Web: http://www.thymos.com/science/dreaming.html