Dreams are stories and images that our minds create while we sleep. They can be entertaining, fun, romantic, disturbing, frightening and sometimes bizarre. This article specifically focuses on how we dream, what nightmares are, lucid dreams and why some dreams are difficult to remember where others are more memorable. It follows on from a previous article: Dreams: why do we dream?
How do we dream?
Until REM sleep is completed, the body is essentially paralyzed. This paralysis is caused by the release of glycine - an amino acid - from the brain stem onto the motor neurons (neurons that conduct impulses outward from the brain or spinal cord). REM sleep is the sleep stage at which most dreaming occurs and this paralysis could be nature's way of making sure we do not act out our dreams.
Each complete sleep cycle takes about 90-110 minutes. The first REM sleep period usually occurs around 70 to 90 minutes after we fall asleep. The first sleep cycles each night contain relatively short REM periods and long periods of deep sleep. As the night progresses, REM sleep periods increase in length while deep sleep decreases. By morning, people spend nearly all their sleep time in stages 1, 2, and REM.107
The relationship between dreaming and strictly REM sleep has been one of controversy amongst researchers with varying hypotheses. Does REM-sleep physiology explain the dream experience, or is REM sleep neither a necessary nor a sufficient condition for dreaming to occur?14
One study hypothesized that different physiological processes underlie dreaming during REM and non-REM (NREM) sleep. Researchers concluded that although "dreaming" may occur during both REM and NREM periods, as previous researchers have suggested, the dreams obtained from these periods differ significantly in both quality and quantity and are likely to be produced by different processes.8
Paralysis during the REM stage of sleep could ensure we do not act out our dreams.
Visual imagery, in a separate study, was reported more often after awakenings from REM compared with stage 2 sleep. These results are consistent with previous researchers who have described REM sleep as a state of high visual hallucinatory quantity, and quality compared with NREM sleep. 83% of REM awakenings compared with only 34% stage 2 awakenings resulted in imagery reports.11
A study proposed that the hormone cortisol plays an important role in controlling the state of memory systems during sleep. High levels of cortisol, as are observed late at night and in the context of REM sleep, disrupt normal hippocampal to neocortical communication, which interferes with the form of memory consolidation that is dependent upon this communication. At the same time, the content of dreams is also affected.83
In slow-wave sleep, dream content reflects the normal interaction between hippocampal and neocortical circuits, allowing typical episodic memories to emerge. Normal episodic memories are only retrieved during slow-wave sleep when hippocampal to neocortical communication is functional.
In REM sleep, however, dream content reflects only neocortical activation, which we assume accounts for the fragmented, often bizarre, nature of these dreams.
fMRI scans can reveal the visual images we have in our brains while we are dreaming, researchers from Japan reported in the journal Science. Put simply, they have found a way of seeing our dreams.
What if dreams could be turned on or off with the flick of a switch? This possibility may be not be too far off, after researchers from the University of California-Berkeley say they may have uncovered a way to do just that.
What are bad dreams and nightmares?
A nightmare is a distressing dream that usually forces at least partial awakening. The dreamer may feel any number of disturbing emotions in a nightmare, such as anger, guilt, sadness or depression, but the most common feelings are fear and anxiety.
Nightmares can cause distressing emotions and can be especially disturbing for children.
Bad dreams, or nightmares are common in both adults and children. They can be caused by:
- Emotional issues
- Medication or drug use
How do you decide if a dream is considered to be a "bad dream" or a "nightmare"? The content of 9,796 dream reports was collected, which exposed:32,75
- 253 nightmares - frequently contained physical aggression, situations that were more bizarre and more emotionally intense, containing more failures and unfortunate endings. 35% of nightmares contained primary emotions other than fear.
- 431 bad dreams - frequently contained interpersonal conflicts. 55% of bad dreams contained primary emotions other than fear.
In a study of 840 German athletes from various sports, discussing distressing dreams on the nights before an important competition or game:46
- About 15% of the athletes stated that they experienced at least one distressing dream before an important competition or game during the preceding 12 months
- An almost equal number of athletes reported at least one distressing dream in their sports career
- In about 3% of the events, a distressing dream occurred
- Reported dream content referred mainly to athletic failure.
A survey examining the dreams, nightmares, and sleep patterns of 30 women who were dealing with relationship violence found:69
- 50% of the sample experienced nightmares on a weekly basis
- Some of the dream images included drowning, being chased, being killed or killing others
- 56% experienced a recurring dream
- Most women had trouble falling asleep and, on average, slept for 6.1 hours per night.
The threat simulation theory of dreaming (TST) states that dream consciousness is essentially an ancient biological defense mechanism, evolutionarily selected for its capacity to repeatedly simulate threatening events.
Children who live in an environment in which their physical and psychological well-being is constantly threatened should then have a highly activated dream production and threat simulation system, whereas children living in a safe environment that is relatively free of such threat cues should have a weakly activated system.
Results of a study with dream reports from severely traumatized and less traumatized Kurdish children and ordinary, non-traumatized Finnish children showed that severely traumatized children reported a significantly greater number of dreams, with their dreams including a higher number of threatening dream events. The dream threats of traumatized children were also more severe in nature than the threats of less traumatized or non-traumatized children.80
A study of 190 normal school children aged 4 to 12 years reported the following forms of anxiety symptoms:
- Fears - 75.8%
- Worries - 67.4%
- Scary dreams - 80.5%.
Fears of scary dreams were common among children aged 4-6 years old, becoming even more prominent in 7- to 9-year-olds and then decreasing in frequency for 10- to 12-year-olds.
Types of fears, worries, and dreams were found to change across age groups, with fears and scary dreams relating to imaginary creatures decreasing with age. In contrast, worries about test performance increased with age.95
Findings from dream reports of 610 boys and girls recalling disturbing and normal dreams at both 13 and 16 years of age highlights how a prevalence of disturbing dreams is especially marked for adolescent girls. Frequent recall of disturbing dreams is associated with pathological symptoms of trait anxiety, even in girls as young as 13 years of age.93
Certain conditions appear to increase the frequency of nightmares in individuals such as:
- Migraine: recurrent dreams featuring complex visual imagery, often terrifying nightmares, can occur as migraine aura symptoms.94 The brain of migraineurs seems to dream with some peculiar features, all with a negative connotation, as fear and anguish.18
- Sleep apnea: patients with sleep apnea have more emotionally negative dreams than sleepy snorers.50
- Depression: frequent nightmares are associated with suicidal tendency in patients with major depression.98
What are night terrors/sleep terrors?
Night terrors are very different from nightmares. The behavior of a child experiencing night terrors may feature:
- Thrashing around
- Jumping out of bed
- Inability to recognize parents trying to comfort them.
Night terrors occur on waking abruptly from deep NREM sleep, whereas nightmares are thought to occur during REM sleep.
It is estimated that approximately 1-6% of children in the US experience sleep terror at some point in their childhood. It is common in children aged between 3-12 years. Children are not fully awake in these episodes, even if their eyes are open, and usually have no memory of the event the next day.
The episodes usually occur in the early part of the night and can continue for several minutes (up to 15 minutes).
Night terrors are more common in children with a family history of night terrors or sleepwalking behavior.
A night terror attack may be triggered by anything that:
- Increases how much deep sleep the child has, such as tiredness, fever or certain types of medication.
- Makes the child more likely to wake from deep sleep, such as excitement, anxiety or sudden noise.
Most children will eventually grow out of night terrors.
Studies of twin cohorts and families with sleep terror and sleepwalking suggest genetic involvement of parasomnias (a category of sleep disorders that involve abnormal movements, behaviors, emotions, perceptions, and dreams that occur while falling asleep, sleeping, between sleep stages, or during arousal from sleep).
Restless leg syndrome and sleep-disordered breathing have been shown to have familial recurrence. Restless leg syndrome has been shown to have genetic involvement.117
Night terrors have also been linked to enlarged tonsils and adenoids.
What are recurring dreams?
A recurring dream is a type of dream that occurs on a regular basis when we sleep.
A study of 212 recurrent dreams that were scored using a slightly expanded version of the Dream Threat rating scale showed:74
- 66% of the recurrent dream reports contained one or more threats. The threats tended to be dangerous and aimed at the dreamer. When facing a threat, the dreamer tended to take defensive or evasive actions that were possible and reasonable.
- Less than 15% of the recurrent dreams depicted realistic and probable situations that were critical for physical survival or reproductive success. During these dreams, the dreamer rarely succeeded in fleeing the threat despite important and appropriate efforts.
These findings provide mixed support for the threat simulation theory.74
Research indicates that recurrent dreams in adults are associated with poor psychological well-being. Authors of a study hypothesized that children reporting recurrent dreams would also show poorer psychosocial adjustment than children without recurrent dreams.
In an examination of dream reports and measures of psychosocial adjustment in 168 children aged 11:61
- 35% of children reported having experienced a recurrent dream during the past year.
- Boys reporting recurrent dreams reported significantly higher scores for reactive aggression than those who did not.
What are lucid dreams?
Lucid dreaming is a rare state of sleep in which the dreamer gains insight into their state of mind during dreaming; a dream in which the dreamer knows they are dreaming is deemed to be a lucid dream.
Research has shown that lucid dreaming is accompanied by an increased activation of parts of the brain that are normally suppressed during sleep.
A German study revealed significantly increased brain activity during lucid dreams. An EEG machine recorded frequencies in the 40 Hz (or GAMMA) range in lucid dreamers. This is far higher than the normal dream state (THETA range, or 4-7 Hz).
The researchers also saw heightened activity in the frontal and frontolateral areas of the brain - the seat of linguistic thought as well as other higher mental functions linked to self-awareness. This supports the theory that lucid dreaming is a unique state of consciousness separate from any other mental state.111
Recent EEG and functional magnetic resonance imaging (fMRI) data found that cortical areas activated during lucid dreaming show striking overlap with brain regions that are impaired in psychotic patients lacking insight into their pathological state.103
Lucid dreams usually occur while a person is in the middle of a regular dream and suddenly realizes that they are dreaming.
Results of a study focusing on the distribution of lucid dreams in school children and young adults found:6
- Lucid dreaming is quite pronounced in young children
- Incidence rate of lucid dreaming drops at about age 16 years
- Increased lucidity was found in those attending higher level compared with lower level schools.
The study authors proposed a link between the natural occurrence of lucid dreaming and brain maturation.
What are wet dreams?
A wet dream is ejaculation during sleep. Usually, a wet dream happens while a person is having a sexual dream. The person may not even remember the dream.
A person does not have to masturbate to have a wet dream; they ejaculate without touching their penis.
Wet dreams are a normal part of growing up and cannot be prevented. Some people may experience wet dreams a few times a week; others may only have the experience a couple of times ever.
Not every teenage boy has wet dreams. If boys do not experience wet dreams, there is nothing wrong with them. Although girls cannot ejaculate, they can have an orgasm during a dream. This is less common than with boys.116
Clinical knowledge and a small number of published studies have reported that selective serotonin reuptake inhibitors (SSRIs) intensify dreaming.
A total of 21 clinical studies and 25 case reports were reviewed on the effect of antidepressants on dreaming. Findings of the review include:104
- In both depressed patients and healthy volunteers, there was a decrease of dream recall frequency with antidepressant use.
- Tricyclic antidepressants induced more positive dream emotions.
- Withdrawal from tricyclic antidepressants and monoamine oxidase inhibitors phenelzine and tranylcypromine caused nightmares.
- Intake and even more withdrawal of SSRIs/SNRIs seem to intensify dreaming.
Dreams and hallucinations under sedation or anesthesia have been a well-known phenomena since the introduction of anesthesia. Sexual hallucinations may lead to allegations of sexual molestation or assault by medical doctors or professional nursing staff.43
Since the introduction of anesthesia, hallucinations and dreams that are blurred with reality have been frequently reported.
There have been cases of propofol-induced hallucinations and dreams in patients described as pleasant, with a frequent "sexual connotation," uninhibited behavior or a verbal expression of patient's intimate thoughts.65
Thirty healthy volunteers completed questionnaires about retrospective home dream recall and were then given either ketamine or placebo. The study found:63
- Ketamine resulted in significantly more dream unpleasantness relative to placebo.
- The number of dreams reported over the three nights did not differ between the groups.
A study aiming to investigate sleep quality and the subjective dream experience in alcohol-dependent patients during withdrawal and abstinence compared with healthy controls found:
- Sleep quality was impaired in alcohol-dependent patients during detoxification, and the subjective dream experience was more negatively toned compared with healthy controls.
- Both sleep quality and dream experience improved slightly after four weeks of abstinence.
- Patients with alcohol dependency during withdrawal and abstinence dreamt significantly more often about alcohol.
Subjective sleep and dream quality is strongly impaired in patients with alcohol dependency.51
Smoked marijuana and oral tetrahydrocannabinol (THC):105
- Reduce REM sleep
- Increase stage 4 sleep
- Cause strange dreams among acute and subacute cannabis withdrawal
- Increase sleep onset latency, reduce slow-wave sleep, and a REM rebound can be observed.
Psychotic major depression
Cognitive bizarreness has been shown to be equally elevated in the dream and waking mentation of acutely symptomatic inpatients diagnosed with affective and non-affective psychoses. A study of patients hospitalized for psychotic major depression (PMD) had similar levels of cognitive bizarreness in their dream and waking mentation.30
Narcolepsy with cataplexy (NC) is a neurological disorder characterized by excessive daytime sleepiness and an altered architecture of sleep.
Dream reports were analyzed in NC patients and control participants. While dream recall (about 85%) was comparable in NC patients and controls, first-REM dream reports were longer in NC patients.
Statistical analyses on the NC patients and their matched controls who reported dreams after both REM periods showed that dream experiences occurring in first-REM reports of NC patients were longer and had a more complex organization than those of controls.
These findings suggest that the cognitive processes underlying dream generation reach their optimal functioning earlier in the night in NC patients than in normal subjects.64
- All PD patients with clinical RBD experienced violent dreams, but none of the 19 non-RBD patients reported violent dreams.
- While dream content appears to be more aggressive in PD patients with clinical RBD, the presence of violent dreams or clinical RBD is not associated with testosterone levels in men with PD.
Another study examined the dream characteristics of PD patients to determine whether dream content differed between patients with RBD and without RBD, men and women with RBD, and men and women with PD.72
- RBD patients had a higher percentage of violent dreams compared to non-RBD patients.
- There were no significant sex differences in the dream content of RBD patients.
- Men with PD had more aggressive dreams compared to females with PD.
- Aggressive dream content was characteristic of RBD patients and sex differences exist in the dream content of the PD population.
Post-traumatic stress disorder
Disturbed sleep patterns, nightmares, and anxiety-filled dreams form a cluster of symptoms belonging to the DSM- IV diagnosis of post-traumatic stress disorder.73
Researchers at the University of Toronto say a sleep disorder that causes people to act out their dreams is the best current predictor of brain diseases like Parkinson's and many other forms of dementia.
Why are dreams difficult to remember? How do we remember dreams?
It is thought that five minutes after the end of a dream, we have forgotten 50% of its content, and 10 minutes later, we have forgotten 90%. Dream researchers estimate that approximately 95% of all dreams are forgotten entirely upon awakening.
There is something about the phenomenon of sleep that makes it difficult to remember what has occurred. Most dreams are forgotten unless they are written down.
Some people have no difficulty in remembering several dreams nightly, whereas others recall dreams only occasionally or not at all.
Some aspect of the phenomenon of sleep makes it difficult for dreamers to remember what has occurred, and most dreams are forgotten unless they are written down.
Sometimes a dream is suddenly remembered later in the day or on another day, suggesting that the memory is not totally lost but for some reason is very hard to retrieve.109
Brain lesion and neuroimaging studies converge in indicating that the temporo-parieto-occipital junction and ventromesial prefrontal cortex play crucial roles in dream recall.
Surface EEG studies showed that sleep cortical oscillations associated with successful dream recall are the same as those involved in encoding and recall of episodic memories during wakefulness.45
Cortical brain oscillations of human sleep are predictive of successful dream recall. After waking up from REM sleep in the morning, higher frontal 5-7 Hz (theta) activity was associated with successful dream recall. This finding mirrors the increase in frontal theta activity during successful encoding of episodic memories in wakefulness.
A different predictive relationship was found after awakening from stage 2 NREM sleep. Specifically, a lower 8-12 Hz (alpha) oscillatory activity of the right temporal area was associated with a successful dream recall.
These findings provide the first evidence of univocal cortical electroencephalographic correlates of dream recall, suggesting that the neurophysiological mechanisms underlying the encoding and recall of episodic memories may remain the same across different states of consciousness.48
In French research, investigators conducted brain scans on 41 people while they were awake and while they slept. Of the participants, 21 remembered dreams about five mornings per week and were labeled "high dream recallers," while the other 20 remembered dreams only two mornings per month. These participants were labeled as "low dream recallers."
When asleep and awake, the high dream recallers showed higher levels of activity in the brain's medial prefrontal cortex and temporo-parietal junction - an information-processing hub.
An Italian research team used technology to measure participants' brain waves during various sleep-stages.
While previous studies have already indicated that people are more likely to remember their dreams when woken directly after REM sleep, this current study explains why. Participants exhibiting more low-frequency theta waves in the frontal lobes were also more likely to remember their dreams.
Increased frontal theta activity is like the successful encoding and retrieval of autobiographical memories seen while we are awake - the same electrical oscillations in the frontal cortex that make the recollection of episodic memories (e.g., things that happened to you) possible. These findings suggest that the neurophysiological mechanisms that we employ while dreaming (and recalling dreams) are the same as when we construct and retrieve memories while we are awake.
In another recent study conducted by the same research team, the authors used the latest MRI techniques to investigate the relation between dreaming and the role of deep-brain structures.
The researchers found that vivid, bizarre and emotionally intense dreams (the dreams that people usually remember) are linked to parts of the amygdala and hippocampus. While the amygdala plays a primary role in the processing and memory of emotional reactions, the hippocampus has been implicated in important memory functions, such as the consolidation of information from short-term to long-term memory.
Scientists have also identified where dreaming is likely to occur in the brain. A very rare clinical condition known as "Charcot-Wilbrand Syndrome," has been known to cause (among other neurological symptoms), loss of the ability to dream. However, recently a patient reported having lost the ability to dream while having virtually no other permanent neurological symptoms.
The patient suffered a lesion in a part of the brain known as the right inferior lingual gyrus (located in the visual cortex), which could suggest that dreams are generated in, or transmitted through, this particular area of the brain, associated with visual processing, emotion and visual memories.There is a huge amount concerning the brain and how it operates while awake or asleep that remains a mystery. Scientists may never pinpoint the exact nature of dreams and why humans need them, but that does not discourage continued research and studies at research facilities looking for an answer.
Why we dream is still a mystery to science. But differences in brain activity may give a clue as to why some people frequently remember their dreams while others rarely do, according to neuroscientists in France.
Dreaming remains one of the great mysteries of human cognition. It is still not fully known when dreams occur and which mechanisms in the brain produce them.