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.
On the next page we look at lucid dreams, wet dreams, medications and drugs, conditions and why some dreams are difficult to remember whist others are more memorable.