Dreams are successions of imagess, ideas, emotions, and sensations that occur involuntarily in the mind during certain stages of sleep.The content and purpose of dreams are not definitively understood, though they have been a topic of scientific speculation, as well as a subject of philosophical and religious interest, throughout recorded history. The scientific study of dreams is called oneirology.
Dreams mainly occur in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable. Dreams can last for a few seconds, or as long as twenty minutes. People are more likely to remember the dream if they are awakened during the REM phase.
Dreams have been seen as a connection to the unconscious. They range from normal and ordinary to overly surreal and bizarre. Dreams can have varying natures, such as frightening, exciting, magical, melancholic, adventurous, or sexual. The events in dreams are generally outside the control of the dreamer, with the exception of lucid dreaming, where the dreamer is self-aware. Dreams can at times make a creative thought occur to the person or give a sense of inspiration.
Opinions about the meaning of dreams have varied and shifted through time and culture. Dream interpretations date back to 5000-4000 BC. The earliest recorded dreams were acquired from materials dating back approximately 5000 years, in Mesopotamia, where they were documented on clay tablets. In the Greek and Roman periods, the people believed that dreams were direct messages from the gods, or from the dead and that they predicted the future. Some cultures practiced dream incubation with the intention of cultivating dreams that are prophetic.
The Austrian neurologist Sigmund Freud, who developed the discipline of psychoanalysis, wrote extensively about dream theories and interpretations. He explained dreams as manifestations of our deepest desires and anxieties, often relating to repressed childhood memories or obsessions. In The Interpretation of Dreams, Freud developed a psychological technique to interpret dreams and devised a series of guidelines to understand the symbols and motifs that appear in our dreams.
There is no universally accepted biological definition of dreaming. In 1952, Eugene Aserinsky identified and defined rapid eye movement (REM) sleep while working in the surgery of his PhD adviser. He noticed that the sleepers' eyes fluttered beneath their closed eyelids. Later he used a polygraph machine to record the sleepers' brainwaves during the periods of this activity of their eyes. In one session, he awakened a subject who was wailing and crying out during REM and confirmed his suspicion that dreaming was occurring. In 1953, Aserinsky and his advisor published the ground-breaking study in Science.
Accumulated observation has shown that dreams are strongly associated with rapid eye movement sleep, during which an electroencephalogram (EEG) shows brain activity that, among sleep states, is most like wakefulness. Participant-remembered dreams during NREM sleep are normally more mundane in comparison. During a typical lifespan, a person spends a total of about six years dreaming (which is about two hours each night). Most dreams only last 5 to 20 minutes. It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind.
During REM sleep, the release of the neurotransmitters norepinephrine, serotonin and histamine is completely suppressed. As a result, motor neurons are not stimulated, a condition known as REM atnia. This prevents dreams from resulting in dangerous movements of the body.
According to a report in the journal Neuron, rat brains show evidence of complex activity during sleep, including the activation in memory of long sequences of activity. Studies show that various species of mammals and birds experience REM during sleep, and follow the same series of sleeping states as humans.
Despite their power to bewilder, arouse, frighten or amuse, dreams can often be ignored in mainstream models of cognitive psychology. As methods of introspection were replaced with more self-consciously objective methods in the social sciences in 1930s and 1940s, dream studies dropped out of the scientific literature. Dreams were neither directly observable by an experimenter nor were subjects' dream reports reliable, being prey to the familiar problems of distortion due to delayed recall, if they were recalled at all. According to Sigmund Freud, dreams are more often forgotten entirely, perhaps due to their prohibited character. Altogether, these problems seemed to put them beyond the realm of science.
The discovery that dreams take place primarily during a distinctive electrophysiological state of sleep, rapid eye movement (REM) sleep, which can be identified by objective criteria, led to the rebirth of interest in this phenomenon. When REM sleep episodes were timed for their duration and subjects woken to make reports before major editing or forgetting could take place, it was determined that subjects accurately matched the length of time they judged the dream narrative to be ongoing to the length of REM sleep that preceded the awakening. There is no "time dilation" effect; a five-minute dream takes roughly five minutes of real time to play out. This close correlation of REM sleep and dream experience was the basis of the first series of reports describing the nature of dreaming: that it is a regular nightly, rather than occasional, phenomenon, and a high-frequency activity within each sleep period occurring at predictable intervals of approximately every 60–90 minutes in all humans throughout the life span.
REM sleep episodes and the dreams that accompany them lengthen progressively across the night, with the first episode being shortest, of approximately 10–12 minutes duration, and the second and third episodes increasing to 15–20 minutes. Dreams at the end of the night may last as long as 15 minutes, although these may be experienced as several distinct stories due to momentary arousals interrupting sleep as the night ends. Dream reports can be reported from normal subjects on 50% of the occasion when an awakening is made prior to the end of the first REM period. This rate of retrieval is increased to about 99% when awakenings are made from the last REM period of the night. This increase in the ability to recall appears related to intensification across the night in the vividness of dream imagery, colors, and emotions.
REM sleep and the ability to dream seem to be embedded in the biology of many organisms that live on Earth. All mammals experience REM. The range of REM can be seen across species: dolphins experience minimum REM, while humans remain in the middle and the opossum and the armadillo are among the most prolific dreamers.
Studies have observed dreaming in monkeys, dogs, cats, rats, elephants and shrews. There have also been signs of dreaming in certain birds and reptiles.Sleeping and dreaming are intertwined. Scientific research results regarding the function of dreaming in animals remain disputable; however, the function of sleeping in living organisms is increasingly clear. For example, recent sleep deprivation experiments conducted on rats and other animals have resulted in the deterioration of physiological functioning and actual tissue damage of the animals.
In 1954 the theta rhythm was discovered by two scientists at the University of California at Los Angeles when experimenting with rabbits, shrews, moles and rats. The theta rhythm is the oscillatory pattern of electric activity in the brain. This discovery lead to a commentary published in 1972 that explained differences in Theta Rhythm where defined by respective animal behaviors. Awake animals showed high Theta Rhythm when behaving in ways that were crucial to their survival, for example: eating and reproducing. This apparently was a response to a changing environment. The theta rhythm occurs during REM and studies suggest it "reflected a neural process whereby information that is essential to the survival of the species" is gathered throughout the day and is "reprocessed into memory during REM sleep". In conclusion: "dreams may reflect a memory-processing mechanism inherited from lower species".
Some scientists argue that humans dream for the same reason other mammals do. From a Darwinian perspective dreams would have to fulfill some kind of biological requirement or provide some benefit for natural selection to take place. Antti Revonsuo, a professor at the University of Turku in Finland, claims that centuries ago dreams would prepare humans for recognizing and avoiding danger by presenting a simulation of threatening events. This threat-simulation theory was presented in 2000.
Dreams mainly occur in the rapid-eye movement (REM) stage of sleep—when brain activity is high and resembles that of being awake. REM sleep is revealed by continuous movements of the eyes during sleep. At times, dreams may occur during other stages of sleep. However, these dreams tend to be much less vivid or memorable. Dreams can last for a few seconds, or as long as twenty minutes. People are more likely to remember the dream if they are awakened during the REM phase.
Dreams have been seen as a connection to the unconscious. They range from normal and ordinary to overly surreal and bizarre. Dreams can have varying natures, such as frightening, exciting, magical, melancholic, adventurous, or sexual. The events in dreams are generally outside the control of the dreamer, with the exception of lucid dreaming, where the dreamer is self-aware. Dreams can at times make a creative thought occur to the person or give a sense of inspiration.
Opinions about the meaning of dreams have varied and shifted through time and culture. Dream interpretations date back to 5000-4000 BC. The earliest recorded dreams were acquired from materials dating back approximately 5000 years, in Mesopotamia, where they were documented on clay tablets. In the Greek and Roman periods, the people believed that dreams were direct messages from the gods, or from the dead and that they predicted the future. Some cultures practiced dream incubation with the intention of cultivating dreams that are prophetic.
The Austrian neurologist Sigmund Freud, who developed the discipline of psychoanalysis, wrote extensively about dream theories and interpretations. He explained dreams as manifestations of our deepest desires and anxieties, often relating to repressed childhood memories or obsessions. In The Interpretation of Dreams, Freud developed a psychological technique to interpret dreams and devised a series of guidelines to understand the symbols and motifs that appear in our dreams.
There is no universally accepted biological definition of dreaming. In 1952, Eugene Aserinsky identified and defined rapid eye movement (REM) sleep while working in the surgery of his PhD adviser. He noticed that the sleepers' eyes fluttered beneath their closed eyelids. Later he used a polygraph machine to record the sleepers' brainwaves during the periods of this activity of their eyes. In one session, he awakened a subject who was wailing and crying out during REM and confirmed his suspicion that dreaming was occurring. In 1953, Aserinsky and his advisor published the ground-breaking study in Science.
Accumulated observation has shown that dreams are strongly associated with rapid eye movement sleep, during which an electroencephalogram (EEG) shows brain activity that, among sleep states, is most like wakefulness. Participant-remembered dreams during NREM sleep are normally more mundane in comparison. During a typical lifespan, a person spends a total of about six years dreaming (which is about two hours each night). Most dreams only last 5 to 20 minutes. It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind.
During REM sleep, the release of the neurotransmitters norepinephrine, serotonin and histamine is completely suppressed. As a result, motor neurons are not stimulated, a condition known as REM atnia. This prevents dreams from resulting in dangerous movements of the body.
According to a report in the journal Neuron, rat brains show evidence of complex activity during sleep, including the activation in memory of long sequences of activity. Studies show that various species of mammals and birds experience REM during sleep, and follow the same series of sleeping states as humans.
Despite their power to bewilder, arouse, frighten or amuse, dreams can often be ignored in mainstream models of cognitive psychology. As methods of introspection were replaced with more self-consciously objective methods in the social sciences in 1930s and 1940s, dream studies dropped out of the scientific literature. Dreams were neither directly observable by an experimenter nor were subjects' dream reports reliable, being prey to the familiar problems of distortion due to delayed recall, if they were recalled at all. According to Sigmund Freud, dreams are more often forgotten entirely, perhaps due to their prohibited character. Altogether, these problems seemed to put them beyond the realm of science.
The discovery that dreams take place primarily during a distinctive electrophysiological state of sleep, rapid eye movement (REM) sleep, which can be identified by objective criteria, led to the rebirth of interest in this phenomenon. When REM sleep episodes were timed for their duration and subjects woken to make reports before major editing or forgetting could take place, it was determined that subjects accurately matched the length of time they judged the dream narrative to be ongoing to the length of REM sleep that preceded the awakening. There is no "time dilation" effect; a five-minute dream takes roughly five minutes of real time to play out. This close correlation of REM sleep and dream experience was the basis of the first series of reports describing the nature of dreaming: that it is a regular nightly, rather than occasional, phenomenon, and a high-frequency activity within each sleep period occurring at predictable intervals of approximately every 60–90 minutes in all humans throughout the life span.
REM sleep episodes and the dreams that accompany them lengthen progressively across the night, with the first episode being shortest, of approximately 10–12 minutes duration, and the second and third episodes increasing to 15–20 minutes. Dreams at the end of the night may last as long as 15 minutes, although these may be experienced as several distinct stories due to momentary arousals interrupting sleep as the night ends. Dream reports can be reported from normal subjects on 50% of the occasion when an awakening is made prior to the end of the first REM period. This rate of retrieval is increased to about 99% when awakenings are made from the last REM period of the night. This increase in the ability to recall appears related to intensification across the night in the vividness of dream imagery, colors, and emotions.
REM sleep and the ability to dream seem to be embedded in the biology of many organisms that live on Earth. All mammals experience REM. The range of REM can be seen across species: dolphins experience minimum REM, while humans remain in the middle and the opossum and the armadillo are among the most prolific dreamers.
Studies have observed dreaming in monkeys, dogs, cats, rats, elephants and shrews. There have also been signs of dreaming in certain birds and reptiles.Sleeping and dreaming are intertwined. Scientific research results regarding the function of dreaming in animals remain disputable; however, the function of sleeping in living organisms is increasingly clear. For example, recent sleep deprivation experiments conducted on rats and other animals have resulted in the deterioration of physiological functioning and actual tissue damage of the animals.
In 1954 the theta rhythm was discovered by two scientists at the University of California at Los Angeles when experimenting with rabbits, shrews, moles and rats. The theta rhythm is the oscillatory pattern of electric activity in the brain. This discovery lead to a commentary published in 1972 that explained differences in Theta Rhythm where defined by respective animal behaviors. Awake animals showed high Theta Rhythm when behaving in ways that were crucial to their survival, for example: eating and reproducing. This apparently was a response to a changing environment. The theta rhythm occurs during REM and studies suggest it "reflected a neural process whereby information that is essential to the survival of the species" is gathered throughout the day and is "reprocessed into memory during REM sleep". In conclusion: "dreams may reflect a memory-processing mechanism inherited from lower species".
Some scientists argue that humans dream for the same reason other mammals do. From a Darwinian perspective dreams would have to fulfill some kind of biological requirement or provide some benefit for natural selection to take place. Antti Revonsuo, a professor at the University of Turku in Finland, claims that centuries ago dreams would prepare humans for recognizing and avoiding danger by presenting a simulation of threatening events. This threat-simulation theory was presented in 2000.
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