Why do dreams occur? What causes them? Can we control them? What do they mean?
You will see introductions at the end of some sections to any developments that have been covered by Medical News Today's news stories. Also look out for links to information about related conditions.
The second part of this article, discussing how we dream and why we have nightmares is available here.
Here are some key points about dreams. More detail and supporting information is in the main article.
- Though a few people may not remember dreaming, it is thought that everyone dreams between 3 to 6 times per night.
- It is thought that each dream lasts between 5 to 20 minutes.
- Around 95% of dreams are forgotten by the time a person gets out of bed.
- Dreaming can help you learn and develop long-term memories.
- Women dream more about family, children and indoor settings when compared with men.
- Recalling something from last week that has appeared in your dream is called the "dream-lag effect."
- There is a difference in the quality and quantity of dreams experienced in rapid eye movement and non-rapid eye movement sleep.
- 48% of people that feature in a dream are recognized by the person dreaming.
- Blind people dream more with other sensory components compared with sighted people.
- Both sleep and dream quality are affected by alcohol.
Experts still do not completely understand why we dream or the causes behind dreams.
There are several hypotheses and concepts as to why we dream. Are dreams merely part of the sleep cycle or do they serve some other purpose?
Possible explanations for why we dream include:
- To represent unconscious desires and wishes
- To interpret random signals from the brain and body during sleep
- To consolidate and process information gathered during the day
- To work as a form of psychotherapy.
From converging evidence and new research methodologies, researchers have speculated that dreaming:
- Is offline memory reprocessing - consolidates learning and memory tasks.79,90,91
- Is a subsystem of the waking default network, which is active during mind wandering and daydreaming. Dreaming could be seen as cognitive simulation of real life experiences.24
- Participates in the development of cognitive capabilities.17
- Is psychoanalytic; dreams are highly meaningful reflections of unconscious mental functioning.79
- Is a unique state of consciousness that incorporates three temporal dimensions: experience of the present, processing of the past, and preparation for the future.56
- Provides a psychological space where overwhelming, contradictory, or highly complex notions can be brought together by the dreaming ego that would be unsettling while awake. This process serves the need for psychological balance and equilibrium.67
As with many things concerning the brain and unconscious thought, there is so much that remains unknown about dreaming. Dreams are difficult to study in a laboratory. As technology and new research techniques are developed, the understanding of dreams will continue to grow.
Phases of sleep
There are five phases of sleep in a sleep cycle:
- Stage 1 - light sleep, eyes move slowly, and muscle activity slows. This stage forms 4-5% of total sleep
- Stage 2 - eye movement stops and brain waves (fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional bursts of rapid waves called sleep spindles. This stage forms 45-55% of total sleep
- Stage 3 - extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves. 4-6% of total sleep
- Stage 4 - the brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called "deep sleep." There is no eye movement or muscle activity. People awakened while in deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. This forms 12-15% of total sleep
- Stage 5 - REM - breathing becomes more rapid, irregular and shallow, eyes jerk rapidly in various directions, and limb muscles become temporarily paralyzed. Heart rate increases, blood pressure rises, and males develop penile erections. When people awaken during REM sleep, they often describe bizarre and illogical tales - dreams. Forms 20-25% of total sleep time.
Slow-wave sleep refers to stages 3 and 4 of non-rapid eye movement (NREM) sleep.
What are dreams?
Dreams are a universal human experience that can be described as a state of consciousness characterized by sensory, cognitive and emotional occurrences during sleep.27 The dreamer has reduced control over the content, visual images and activation of the memory.42
There is no cognitive state that has been as extensively studied and yet as misunderstood as much as dreaming.40,42
Dreams are full of experiences that have lifelike connections but with vivid and bizarre twists.
There are significant differences between the neuroscientific and psychoanalytic approaches to dream analysis. A neuroscientist is interested in the structures involved in dream production and dream organization and narratability. However, psychoanalysis concentrates on the meaning of dreams and on placing them in the context of relationships in the history of the dreamer.96
Reports of dreams tend to be full of emotional and vivid experiences that contain themes, concerns, dream figures, objects, etc. that correspond closely to waking life.27,28 These elements create a novel "reality" out of seemingly nothing, producing an experience with a lifelike timeframe and lifelike connections.28
Neuroscience offers explanations linked to the rapid eye movement (REM) phase of sleep as a pinpoint for where dreaming occurs.28
Nightmares are distressing dreams that cause the dreamer to feel a number of disturbing emotions. Common feelings include fear and anxiety.
Nightmares or bad dreams occur in both adults and children and can be caused by:
- Emotional problems
- Use of certain medications or drugs
Lucid dreaming is a state of sleep where the dreamer knows they are dreaming. As a result, the dreamer may have some measure of control over their dream.
The measure of control a dreamer has can vary from lucid dream to lucid dream. They often occur in the middle of a regular dream when the sleeping person realizes suddenly that they are dreaming.
Some people experience lucid dreaming at random while other people are able to increase their capacity to affect how their dreams unfold.
What goes through our minds just before we fall asleep could affect the content of our dreams. For example, during exam time, students may dream about course content; those in relationships may dream of their partner; web developers may see programming code. These circumstantial observations suggest that during the transition from wakefulness to sleep, elements from the everyday re-emerge in dream-like imagery.58
Studies have examined the "characters" that appear in dream reports and how they are identified by the dreamer.
Most characters that appear in a person's dream are known and can be named by the dreamer.
A study of 320 adult dream reports found:1
- 48% of characters represented a named person known to the dreamer
- 35% of characters were identified by their social role (e.g., policeman) or relationship to dreamer (e.g., a friend)
- 16% were not recognized.
Among named characters:
- 32% were identified by appearance
- 21% identified by behavior
- 45% by face
- 44% by "just knowing."
Elements of bizarreness were reported in 14% of named and generic characters.
Another study investigated the relationship between dream emotion and dream character identification. Affection and joy were commonly associated with known characters and were used to identify them even when these emotional attributes were inconsistent with those of the waking state.
The findings suggest that the dorsolateral prefrontal cortex, associated with short-term memory, is less active in the dreaming brain compared to the awake brain, while the paleocortical and subcortical limbic areas are more active. Also proposed was that limbic areas have minimal input from the dorsolateral prefrontal cortex in the dreaming brain.25
The concept of 'repression' dates back to Freud, whereby undesirable memories can become suppressed in the mind. Dreams ease repression by permitting these memories to be reinstated.
A study showed that sleep does not benefit the forgetting of unwanted memories. Instead, REM sleep might even counteract the voluntary suppression of memories, making them more accessible for retrieval.15
Two types of temporal effects characterize the incorporation of memories into dreams:
- The day-residue effect, involving immediate incorporations of events from the preceding day
- The dream-lag effect, involving incorporations delayed by about a week.
The findings of one study are consistent with the possibility that processing memories into dream incorporation takes a cycle of around 7 days, and that these processes help to further the functions of socio-emotional adaptation and memory consolidation.5
A recent study aiming to explore autobiographical memories (long-lasting memories about the self) and episodic memories (memories about discrete episodes or events) within dream content amongst 32 participants found that:
- One dream (0.5%) contained an episodic memory
- The majority (80%) was found to contain low to moderate incorporations of autobiographical memory features.
Researchers suggest that memories for personal experiences are experienced fragmentarily and selectively during dreaming, perhaps in order to integrate these memories into the long-lasting autobiographical memory.22
A hypothesis stating that dreams reflect waking-life experiences is supported by studies investigating the dreams of psychiatric patients and patients with sleep disorders, i.e., their daytime symptoms and problems are reflected in their dreams.53
In 1900, Freud described a category of dreams - "biographical dreams" - that reflect historical infantile experience without the typical defensive function. Many authors agree that some traumatic dreams perform a function of recovery.
One paper hypothesizes that the predominant aspect of such traumatic dreams is the communication of an experience that the dreamer has in the dream, but does not understand.60
The themes of dreams can be linked to the suppression of unwanted thoughts and, as a result, an increased occurrence of the suppressed thought in dreams.
Fifteen good sleepers were asked to suppress an unwanted thought 5 minutes prior to sleep. The results demonstrated increased dreams about the unwanted thought and a tendency to have more distressing dreams. Moreover, the data imply that thought suppression may lead to significantly increased mental disorder symptoms.9
Research has indicated that external stimuli presented during sleep can affect the emotional content of dreams. For example, the positively-toned stimulus of roses in one study yielded more positively themed dreams, whereas the negative stimulus of rotten eggs was followed by more negatively themed dreams.10
Typical dreams are defined as dreams with similar contents reported by a high percentage of dreamers. Up to now, the frequencies of typical dream themes have been studied with questionnaires and these have indicated that a rank order of 55 typical dream themes has been stable over different sample populations.82 The 55 dreams themes are:
Flying or soaring through the air is included in the top 10 themes most dreamt about.
- School, teachers, studying
- Being chased or pursued
- Sexual experiences
- Arriving too late
- A person now alive being dead
- Flying or soaring through the air
- Failing an examination
- Being on the verge of falling
- Being frozen with fright
- A person now dead being alive
- Being physically attacked
- Being nude
- Eating delicious food
- Being locked up
- Insects or spiders
- Being killed
- Your teeth falling out/losing your teeth
- Being tied, unable to move
- Being inappropriately dressed
- Being a child again
- Trying again and again to do something
- Being unable to find, or embarrassed about using a toilet
- Discovering a new room at home
- Having superior knowledge or mental ability
- Losing control of a vehicle
- Wild, violent beasts
- Seeing a face very close to you
- Having magical powers
- Vividly sensing, but not necessarily seeing or hearing, a presence in the room
- Finding money
- Floods or tidal waves
- Killing someone
- Seeing yourself as dead
- Being half awake and paralyzed in bed
- Lunatics or insane people
- Seeing yourself in a mirror
- Being a member of the opposite sex
- Being smothered, unable to breathe
- Encountering god in some form
- Seeing a flying object crash
- Seeing an angel
- Creatures: part animal, part human
- Tornadoes or strong winds
- Being at a movie
- Seeing extra-terrestrials
- Traveling to another planet
- Being an animal
- Seeing a UFO
- Someone having an abortion
- Being an object.
Authors have hypothesized that one cluster of typical dreams (object endangered, falling, being chased or pursued) is related to interpersonal conflicts; another cluster (flying, sexual experiences, finding money, eating delicious food) is associated with libidinal motivations; and a third group (being nude, failing an examination, arriving too late, losing teeth, being inappropriately dressed) is associated with superego concerns.
Musical dreams frequency is related to the age of beginning to learn music and not to how much music is listened to throughout the day.
This may suggest that the role of some cerebral structures, such as amygdala and hypothalamus, are involved in migraine mechanisms as well as in the biology of sleep and dreaming.19
Music in dreams is rarely reported in scientific literature. However, in a study of 35 professional musicians and 30 non-musicians, the musicians experienced twice as many dreams featuring music compared with non-musicians. Musical dream frequency was related to the age of commencement of musical instruction but not to the daily load of musical activity. Nearly half of the recalled music was non-standard, suggesting that original music can be created in dreams.77
Although it has been shown that realistic, localized painful sensations can be experienced in dreams - either through direct incorporation or from memories of pain - the frequency of pain dreams in healthy subjects is low.
Twenty-eight non-ventilated burn victims were interviewed for five consecutive mornings during their first week of hospitalization. Results found:
- 39% of patients reported pain dreams.
- Of those experiencing pain dreams, 30% of their total dreams were pain related.
- Patients with pain dreams showed evidence of worse sleep, more nightmares, higher intake of anxiolytic medication, and higher scores on the Impact of Event Scale.
- Patients with pain dreams also had a tendency to report more intense pain during therapeutic procedures.
More than half of the sample did not report pain dreams, but these results could suggest that pain dreams occur at a greater frequency in suffering populations than in normal volunteers.87
Recent findings link frontotemporal gamma EEG activity to conscious awareness in dreams. The study found that current stimulation in the lower gamma band during REM sleep influences ongoing brain activity and induces self-reflective awareness in dreams. Researchers concluded that higher order consciousness is related to synchronous oscillations around 25 and 40 Hz.20
Recent research has demonstrated parallels between romantic attachment styles and general dream content.
Assessment results from 61 student participants in committed dating relationships of six months duration or longer revealed a significant association between relationship-specific attachment security and the degree to which dreams about romantic partners followed. The findings illuminate our understanding of mental representations with regards to specific attachment figures.41
There has been an increase in the percentage of people who report flying in dreams from 1956 to 2000; investigators have proposed this increase may reflect the increasing amount of air travel.68
The dream content of psychiatric inpatients who had been admitted because of suicidal attempts was compared with three inpatient control groups who had been admitted for:
- Depression and suicidal ideation without attempt
- Depression with no suicidal ideation
- Commission of a violent act without suicide.
Results confirmed that both suicidal and violent patients have more death content and destructive violence in their dreams, but also that this was a function of the severity of depression and certain character traits such as impulsivity, rather than being specific to the behavior itself.100
A study investigating anxiety dreams in 103 children aged 9-11 years observed:86
Girls dream more often than boys about the loss of another person, of falling, of socially disturbing situations and small animals.
- Girls reported a higher frequency of anxiety dreams than boys, although they could not remember their dreams more often.
- Girls dreamt more often than boys about the loss of another person, of falling, of socially disturbing situations and small animals, of animals as aggressors, of family members (mainly siblings) and other female persons of known identity.
A study of older children and adolescents aged 10-17 years, comparing those with neurotic disorders with healthy subjects, found in left-handers:
- Subjects expressed less novelty factor and frequent appearance of rare phenomena, such as "déjà vu in wakefulness," reality, "mixed" (overlapped) dreams, prolonged dreams in repeat sleep, frequent changes of personages and scenes of action.
- Dream peculiarities detected only in neurotic patients but not in healthy subjects emerged as lucid phenomena deficit, "dream in dreams" and "dream reminiscence in dream" syndrome, only found in left-handers.
Right and left hemispheres seem to contribute in different ways to a dream formation. Authors from the study believe that the left hemisphere seems to provide dream origin while the right hemisphere provides dream vividness, figurativeness and affective activation level.88
During studies comparing the dreams of pregnant and non-pregnant women:34,92
- Baby and child representations were less specific in the late third trimester than in the early third trimester and than in non-pregnant women.
- Pregnant groups also had more pregnancy, childbirth and fetus themes.
- Childbirth content was higher in late than in early third trimester.
- Pregnant groups had more morbid elements than the non-pregnant group.
Those that give care to family or patients often have dreams related to the person or care given. A study following the dreams of adults that worked for at least a year with patients at US hospice centers noted:36
- Patients were generally manifestly present in participants' dreams, and dreams were typically realistic.
- In the dream, the dreamer typically interacted with the patient as a caretaker but was also typically frustrated by the inability to help as fully as desired.
It is widely believed that oppressive dreams are frequent in bereavement. A study analyzing dream quality, as well as the linking of oppressive dreams in bereavement, discovered:38
- Oppressive dreams occurred at a significantly higher frequency in the first year of bereavement
- Oppressive dreams were significantly associated with anxiety and depressive symptoms.
In another study of 278 bereaved persons:37
- 58% of respondents reported dreams of their deceased loved ones, with varying levels of frequency
- Most participants reported that their dreams were either pleasant or both pleasant and disturbing, and few reported purely disturbing dreams
- Prevalent dream themes included pleasant past memories or experiences, the deceased free of illness, memories of the deceased's illness or time of death, the deceased in the afterlife appearing comfortable and at peace, and the deceased communicating a message
- 60% of participants felt that their dreams impacted upon their bereavement process.
Can dreams predict the future?
Some dreams may seem to predict future events. Experts suggest that when this happens, it is usually due to coincidence, a false memory, or the unconscious connecting together known information.
Dreams may help people to learn more about their feelings, beliefs, and values. Images and symbols that appear in dreams will have meanings and connections that are specific to each person.
People looking to make sense of their dreams should think about what each part of the dreams mean to them. Books or guides that give specific, universal meanings to images and symbols may not be useful.
Does everyone dream in color?
Researchers discovered in a study that about 80% of participants younger than 30 years old dreamed in color. At 60 years old, 20% said they dreamed in color. The number of people aged in their 20s, 30s and 40s dreaming in color increased through 1993 to 2009. Researchers speculated that color television might play a role in the generational difference.114
Another study using both questionnaires and dream diaries found older adults also had more black and white dreams than the younger participants. Older people reported that both their color dreams and black and white dreams were equally as vivid. However, younger participants said that their black and white dreams were of poorer quality.115
Mistakes and misidentification
During neuroimaging studies looking at brain activity in REM sleep, scientists found that the distribution of brain activity during REM sleep might also be linked to specific dream features. Several bizarre features of normal dreams have similarities with well-known neuropsychological syndromes after brain damage, such as delusional misidentifications for faces and places.26
A study following the dream content of crack cocaine abusers in Trinidad and Tobago during abstinence detailed:89
- 41 patients reported drug dreams during the first month, mainly of using the drug (89.1%).
- 28 had drug dreams at six months follow-up, mainly of using or refusing the drug (60.9%).
Researchers estimate that 5 minutes after a dream, people have forgotten 50 percent of its content, increasing to 90 percent another 5 minutes later. Most dreams are entirely forgotten by the time someone wakes up.
It is not known precisely why dreams are so hard to remember. However, there are several steps that people can take to improve their dream recall. These include:
- Waking up naturally and not with an alarm
- Focusing on the dream as much as possible upon waking
- Writing down as much about the dream as possible upon waking
- Making recording dreams a routine
Evidence from laboratory studies indicates that everyone dreams. Although a small percentage may not remember dreaming at all or claim that they do not, it is thought that most people dream between 3 to 6 times a night, with each dream lasting between 5 to 20 minutes.
There are factors that can potentially influence who can remember their dreams, how much of the dream remains intact and how vivid it is.
Ageing is often associated with changes in sleep timing, structure and electroencephalographic (EEG) activity.
Scientific literature agrees that dream recall progressively decreases from the beginning of adulthood - not in old age - and that dream reports become less intense. This evolution occurs faster in men than women, with gender differences in the content of dreams.55
According to a small number of research papers, patients suffering degenerative dementia dream less than healthy older people. In Alzheimer's disease, this could be linked to the decrease of REM sleep and wasting of associative sensory areas of the brain's outer layer.
A study of 108 male and 110 female dreams found no differences between the amount of aggression, friendliness, sexuality, male characters, weapons, or clothes that feature in the dream's content. However, women's dreams featured a higher number of family members, babies, children, and indoor settings than men.98,99
In another study, men reported more instances of dreaming about aggression than women. Women had marginally longer dreams with more characters than men. The men in the study dreamt about other men twice as often as they did about women while women dreamt about both sexes equally.
Dream recall is heightened in patients with insomnia and their dreams reflect the stress associated with their condition. The stressor of breathing-related dreams in sleep apnea patients is rare, whereas those with narcolepsy have more bizarre and negatively toned dreams.62
One study tested the hypothesis that dream recall and dream content would imitate the dreamer's social relationship status. College student volunteers were assessed on measures of attachment, dream recall, dream content and other psychological measures. Participants who were classified as "high" on an "insecure attachment" scale were significantly more likely (when compared with participants who scored low on the insecure attachment scale) to:
- Report a dream
- Dream "frequently"
- Have more intense images that contextualize strong emotions in their dreams.
Older volunteers whose attachment style was classed as "preoccupied," were significantly more likely (when compared with participants classified as "securely" attached, as "avoidant" or as "dismissing") to:
- Report a dream
- Report dreams with a higher mean number of words per dream.
Dream recall was lowest for the "avoidant" subjects and highest for the "preoccupied" subjects.2
Have you ever noticed that often the images, experiences or people that emerge in dreams are images, experiences or people you have seen recently?
People you have seen or experiences you have had a day or a week ago can crop up in dreams. This recalling of a memory within a dream is referred to as dream-lag.
Frequently, details from a dream have been seen before, perhaps the previous day or a week prior to the dream. Recalling something from a week ago is known as the "dream-lag effect." The idea is that certain types of experiences take a week to be encoded into long-term memory, and some of the images from the consolidation process will appear in a dream.
Memory theorists suggest that the hippocampus (an area deep in the forebrain that helps regulate emotion, learning, and memory) takes events from the previous day, selects some to be consolidated into long-term memory and then begins to transfer these over to the neocortex (the top layer of the brain that is divided into four major lobes: frontal, parietal, temporal and occipital) for permanent storage.
The transfer process takes about a week. Dreaming may participate in the relocation of memory storage from hippocampus to neocortex over time.
Events experienced while we are awake are said to feature in 1-2% of dream reports, although 65% of dream reports reflect aspects of recent waking life experiences.
Authors of one study found a significantly higher rate of correspondence between waking life experiences and dream reports when the experiences occurred 1-2, or 5-7 days before the dream, in comparison with when the experiences occurred 3-4 days before the dream.44,55
The dream-lag effect has been reported in REM but not NREM stage 2 dreams (sleep stages are explained in the next section). These results may provide evidence for a 7-day sleep-dependent memory consolidation process that is specific to REM sleep, and would highlight the importance of REM sleep for emotional memory consolidation.44,84
What do blind people dream about?
Studies have shown that blind participants have fewer visual dream impressions compared with sighted participants. Congenitally blind participants reported more auditory, tactile, gustatory, and olfactory dream components compared with sighted participants. Blind and sighted participants did not differ with respect to emotional and thematic dream content.21
Paraplegic and those unable to hear or speak
One study explored the dream diaries of 14 people with impairments; four were born with paraplegia and 10 were born deaf and unable to speak. When compared with 36 able-bodied individuals, findings showed that around 80% of the dream reports of the deaf participants gave no indication of their impairment.
Many spoke in their dreams, while others could hear and understand spoken language. The dream reports of the people born paralyzed revealed something similar; they often walked, ran or swam, none of which they had ever done in their waking lives. 112
There was no difference between the number of bodily movements in the dream reports of the people with paraplegia and those of the deaf and able-bodied subjects.
A second study found similar results. Researchers looked at the dream reports of 15 people who were either born with paraplegia or had it later in life due to a spinal-cord injury. Their reports revealed that 14 of the participants with paraplegia had dreams in which they were physically active, and they dreamed about walking just as often as the 15 able-bodied control participants.113
Recent dream studies suggest that our brain has the genetically determined ability to generate experiences that mimic life, including fully functioning limbs and senses, and that people who are born deaf or paralyzed are likely tapping into these parts of the brain when they dream about things they cannot do while awake.
The strongest predictor of whether a man is developing dementia with Lewy bodies - the second most common form of dementia in the elderly - is whether he acts out his dreams while sleeping, Mayo Clinic researchers have discovered. Patients are five times more likely to have dementia with Lewy bodies if they experience a condition known as rapid eye movement (REM) sleep behavior disorder than if they have one of the risk factors now used to make a diagnosis, such as fluctuating cognition or hallucinations, the study found.