Dreams are stories and images that our minds create while we sleep. They can be entertaining, fun, romantic, disturbing, frightening and sometimes bizarre.
Why do dreams occur? Can we control them? What do they mean? Medical News Today investigates the current research on dreams and looks at possible explanations and theories as to why our minds invent these nightly musings.
You will see introductions at the end of some sections to any recent developments that have been covered by MNT'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.
Fast facts on dreams
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.
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
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 rapider, 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.
Why do we dream?
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
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
On the next page we take a look at what dreams mean, looking specifically at characters, memories, themes, senses, pain, relationships, flying and more.