Dream Series: Part III – Why and how we dream remains something of a mystery. To understand our dreams, we need to discover how we dream, what nightmares are, and why some dreams are difficult to remember where others are more memorable.
Sleep happens in cycles. Each complete sleep cycle takes about 90 to 110 minutes. Most dreams happen during a phase known as rapid eye movement (REM) sleep. The first REM sleep period usually occurs around 70 to 90 minutes after we fall asleep. During this phase, an amino acid known as glycine is released from the brain stem onto the motor neurons. These motor neurons conduct impulses outward from the brain or spinal cord. This release of glycine effectively causes the body to become paralyzed. This paralysis is believed to be nature’s way of making sure we do not act out our dreams and thus prevents injury.
The first sleep cycles each night contain relatively short periods of REM and long periods of deep sleep. As the night progresses, REM sleep periods increase in length, while deep sleep decreases. Researchers have different theories about the relationship between dreaming and REM sleep. Does REM-sleep physiology explain the dream experience? Or is it not necessary to be in REM sleep for dreaming to occur?
One study has suggested that dreaming can happen during both REM and non-REM (NREM) sleep, but that different physiological processes underlie the dreaming at each stage. The dreams that occur during these periods may differ significantly in both quality and quantity and probably result from different processes.
Visual imagery appears to be more common after waking from REM sleep, compared with NREM sleep. People reported visual images after 83 percent of REM awakenings, compared with only 34 percent after Stage 2 sleep.
One study has proposed that the hormone cortisol plays an important role in controlling memory systems during sleep. High cortisol levels have been observed late at night and during REM sleep. Cortisol affects the interaction between the hippocampus and the neocortex. This interaction appears to have an impact on a specific type of memory consolidation. These could affect the content of dreams.
In NREM sleep, the interaction between the neocortex and the hippocampus is not disrupted, and typical episodic memories occur. However, in REM sleep, dream content reflects only neocortical activation. Dreams are more likely to be fragmented and bizarre.
Both adults and children can experience bad dreams and nightmares.
During a nightmare, the dreamer may experience a range of disturbing emotions, such as anger, guilt, sadness or depression. However, the most common feelings are fear and anxiety. The person usually wakes up at least once during the dream.
Causes of bad dreams include:
- emotional issues
- medication or drug use
A study that looked at 253 episodes described as “nightmares” found they frequently contained:
- physical aggression
- bizarre and emotionally intense situations
- failures and unfortunate endings
One in three of these nightmares contained primary emotions other than fear. In a further 431 bad dreams, as opposed to nightmares, interpersonal conflicts were common. Just over half contained primary emotions other than fear.
In another study, 840 German athletes discussed distressing dreams that occurred on the nights before an important competition or game. About 15 percent of the athletes reported having had at least one distressing dream before an important competition in the last 12 months. Most of these related to athletic failure.
Elsewhere, a survey in which 30 women who were dealing with relationship violence described their dream experiences, half reported having weekly nightmares, and just over half had recurring dreams.
Dream events included:
- being chased
- bring killed
- killing someone else
One theory about recurrent dreams is the threat simulation theory. According to this theory, dreams are an ancient biological defense mechanism that aims to repeatedly simulate threatening events, presumably to prepare people for threats they might face in their waking life. Researchers have proposed that children who live in a threatening environment would dream more actively than those who do not, and at least one study has confirmed this.
In one investigation, children who had undergone severe trauma experienced a significantly greater number of dreams and a higher number of threatening dream events, featuring more severe threats, compared with children who had not experienced trauma. However, in a study that looked at the dreams of 190 school children aged 4 to 12 years who had not undergone any trauma, the following was noted:
- Fear featured in 75.8 percent of dreams.
- Worries featured in 67.4 percent.
- Scary dreams represented 80.5 percent.
Fears relating to scary dreams were common among children aged 4 to 6 years old, and more so among those aged 7 to 9 years. These fears became less frequent between the ages of 10 and 12 years.
Types of fears, worries, and dreams changed across age groups. Fears and scary dreams relating to imaginary creatures reduced with age, while worries about test performance increased with age. In one study, dream reports from 610 teenagers showed that disturbing and normal dreams occur at both 13 and 16 years of age. However, disturbing dreams are especially common among adolescent girls. They often had disturbing dreams that showed signs of trait anxiety, even at 13 years of age.
Certain conditions appear to increase the frequency of nightmares in some people. These include:
Migraine: Recurrent dreams featuring complex visual imagery, often terrifying nightmares, can occur as migraine aura symptoms. These dreams often involve the emotions of fear and anguish.
Sleep apnea: People with sleep apnea have more emotionally negative dreams than those who simply snore while asleep.
Depression: Frequent nightmares are associated with suicidal tendency in individuals with major depression.
Night terrors are different from nightmares. A child who is experiencing night terrors may:
- thrash around
- jump out of bed
- fail to recognize parents trying to comfort them
Night terrors occur on waking abruptly from deep NREM sleep, while nightmares are thought to happen during REM sleep. Around one to six percent of children are thought to experience sleep terrors at some point in their childhood. It is common in children aged between 3 to 12 years. Children are not fully awake in these episodes, even if their eyes are open, and they 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 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 the amount of 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. Research has suggested that parasomnias and other sleep conditions — such as restless leg syndrome (RLS) and sleep-disordered breathing — may run in families. There could be a genetic link. Night terrors have also been linked to enlarged tonsils and adenoids.
A recurring dream is a type of dream that occurs on a regular basis when we sleep. A study of 212 reports of recurring dreams found that:
- Two in three dreams contained one or more threats, which 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.
- Fewer than 15 percent of the recurrent dreams depicted realistic and probable situations. In these, the dreamer rarely succeeded in fleeing the threat, despite efforts.
A wet dream is when an ejaculation occurs during sleep, usually during a sexual dream. The person may not remember the dream, and it can happen without touching the sexual organ. They may or may not wake up.
They usually affect boys during puberty, when the body starts to produce the male hormone testosterone. Once the body can produce testosterone. Wet dreams are a normal part of growing up and cannot be prevented. Some boys may have several dreams a week, while other never experience one. This, too, is normal.
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. It is often said that five minutes after the end of a dream, we have forgotten 50 percent of its content, and 10 minutes later, we have forgotten 90 percent. Dream researchers estimate that around 95 percent of all dreams are forgotten entirely upon awakening.
Some people have no difficulty remembering several dreams nightly, while others rarely or never recall dreams. Some aspect of sleep appears to make it difficult for dreamers to remember what happened. Most dreams are forgotten, but sometimes a dream is suddenly remembered later in the day or on another day. Writing down or recording dreams may help you remember them. This suggests that the memory is not totally lost, but for some reason it is hard to retrieve.
The Mind Affects Dream Memories
Brain lesion and neuroimaging studies have indicated that portions of the mind 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 forming and recalling episodic memories while awake. These findings suggest that mechanisms underlying the encoding and recall of episodic memories may remain the same across different states of consciousness, in other words, whether awake or asleep.
Another study using MRI techniques found that vivid, bizarre, and emotionally intense dreams — the dreams people usually remember — are linked to parts of brain areas known as the amygdala and hippocampus. 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 consolidating information from short-term to long-term memory.
Scientists have also identified where dreaming is likely to occur in the brain. People who have a clinical condition known as Charcot-Wilbrand syndrome lose the ability to dream. A loss of the ability to dream was also noted in one person who experienced a lesion in a part of the brain known as the right inferior lingual gyrus. This is located in the visual cortex. It may be that this area of the brain, which is associated with visual processing, emotion and visual memories, plays a role in either generating or transmitting dreams.
People have speculated about dreams for thousands of years, but only recently have advances in technology make it possible to study brain activity in ways that may help us understand what really happens when we dream. However, much about the life of dreams remains a mystery.