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Why We Dream What We Dream

An expert guide to what goes on behind the wall of sleep.


Not all dreaming is the same. It runs the gamut of human experience (and sometimes beyond), incorporating a dizzying range of emotions and events, often with elements of the bizarre. Dreams can be funny, frightening, sad or strange. Flying dreams can be euphoric, chasing dreams can be terrifying, forgot-to-study-for-my-exam dreams can be stressful.

There are several dream classifications, including nightmares, recurring dreams, and lucid dreams. Let’s look briefly at some distinct forms:

Nightmares are broadly defined as frightening dreams that result in some degree of awakening from sleep. "Bad dreams" are considered a less severe form of nightmare. Most people experience nightmares throughout life, usually very rarely and, less commonly, with more regularity. A small percentage of the population—studies suggest around 5%—have nightmares as often as once a week.

Nightmares can result from different triggers, including stress, emotional upheaval, and traumatic experiences. They can occur as side effects of some medications, use and abuse of drugs and alcohol, and illness. Nightmares themselves disrupt sleep by not only by waking the sleeper, but also leading to a fear of falling asleep and returning to a disturbing dream.

Nightmares can have other negative sleep-related health consequences, as well. According to research, they may contribute to insomnia, daytime fatigue, depression, and anxiety.

Studies indicate that people with certain conditions may be more likely to experience nightmares, including:

  • Migraine
  • Obstructive sleep apnea
  • Clinical depression

(The relationship of nightmares to depression is complex. Depression is linked to a greater incidence of nightmares, and nightmares themselves may contribute to worsening depression.)

Night terrors, or sleep terrors, create another frightening dream-like experience. While they are frightening and disruptive to sleep, night terrors are not the same as nightmares. Night terrors are very intense episodes of fright during dreams. These frightening episodes are often accompanied by screaming or yelling, as well as by physical movement such as leaping out of bed or flailing in panic. Research suggests that sleep terrors occur during non-REM sleep dreaming, while nightmares tend to happen during REM sleep.

Adults do experience night terrors, but they are somewhat more common in children. Estimates suggest that as many as 6% of children experience night terrors, most often between the ages of 3-12. Night terrors sometimes run in families. There may be a genetic predisposition to night terrors (as well as to sleep walking and other parasomnias). There is also evidence of a relationship among night terrors, sleep apnea, and enlarged tonsils and adenoids in children.

Recurring dreams are ones that reappear with some pattern of regularity. Studies suggest that recurring dreams may contain more threatening content than regular dreams. Research suggests links between recurring dreams and psychological distress in both adults and children.

Lucid dreams are an especially fascinating form of dream. In lucid dreams, the dreamer is aware of the fact that he or she is dreaming, and often can manipulate or control the dream as it unfolds.

Research links lucid dreaming to unusually elevated levels of brain activity. Studies have found that lucid dreamers displayed significantly higher brain wave frequencies than non-lucid dreamers, as well as increased activity in parts of the frontal lobe. This area of the brain is deeply involved with conscious awareness, a sense of self, as well as language and memory. Studies of lucid dreams are not only shedding light on the mechanics of dreaming, but also on the neural underpinnings of consciousness itself.

Dreams appear to be influenced by our waking lives in many ways. Theories about why we dream include those that suggest dreaming is a means by which the brain processes emotions, stimuli, memories, and information that’s been absorbed throughout the waking day.

According to research, a significant percentage of the people who appear in dreams are known to the dreamer. One study found more than 48% of dream characters were recognizable by name to dreamers. Another 35% of characters were identifiable to dreamers by their generic social role or relationship—as a friend, doctor, or police officer, for example. Fewer than one fifth of dream characters—16%—were unrecognizable to dreamers.

Other research indicates that a majority of dreams contain content related to autobiographical memories—memories about the self—as opposed to episodic memories, which deal with events and details, such as locations and times.

There’s a body of study that suggests our waking lives have great influence over the content of our dreams. Pregnant women dream more about pregnancy and childbirth. Hospice workers who act as caregivers to others (whether patients or family members) dream about the experiences of caregiving and the people for whom they care. Musicians dream twice as often about music as non-musicians do.

There’s also fascinating research that shows our capacity to dream beyond our waking experiences, in profound ways. Dream reports of people born paralyzed reveal that they walk, swim, and run in their dreams as often as people without paralysis. Dream reports of people born deaf indicate they often hear in their dreams. These reports may lend credence to the theory that dreams serve as a broad, virtual-reality model of waking life—a proto-consciousness—that instructs and supports survival and growth.

Daily life experiences don’t always present themselves in dreams immediately. Sometimes an experience from life will filter through to a dream after several days, or even a week. This delay is what’s known as dream lag. Scientists studying the relationship of memory to dreams have identified different types of memory that can be incorporated into dreams. Both very short-term memories (known as day-residue), and slightly longer-term memories (from a period of about a week), often present themselves in dreams. Dreaming of these events—and the timing by which memories appear in dreams—may actually be an important part of the memory consolidation process. The incorporation of memories into dreams isn’t seamless or even realistic. Rather, memories from waking life often appear in dreams in incomplete pieces, like shards of glass from a broken mirror.

As much as dreams may contain aspects of everyday, routine life, dreaming is also a state in which we contend with extraordinary experiences. Another likely function of dreaming appears to be processing and coming to terms with traumatic events. Grief, fear, loss, abandonment, even physical pain are all emotions and experiences that often replay themselves in dreams. Studies of people who’ve experienced loss of loved ones indicate that most of them dream about the deceased. Grieving people report several similar themes to these dreams, including:

  • Recalling past experiences when loved ones were alive
  • Seeing loved ones happy and at peace
  • Receiving messages from loved ones

The same study found that 60% of bereaved dreamers said their dreams exerted influence over their grieving process. Dreams during periods of grief can be difficult as well as helpful. One study found that dreamers during the first year of bereavement had a significantly higher frequency of oppressive dreams, and found a link between these dreams and symptoms of depression and anxiety. Dreams, and especially nightmares, are deeply associated with depression as well as other conditions such as post-traumatic stress disorder, which we’ll look at more closely in part three.

Examining and interpreting the content of dreams has fascinated people since ancient times. In ancient cultures, dream interpreters were sought-after and revered experts. Modern science has, to some degree, shifted its focus away from the study of dream content to investigations—both psychological and cognitive—of the mechanics of dreaming, and its purpose. But there are scientists who have continued to explore the content of dreams, and new technologies have given us the ability to observe dream content as never before.

Most data on dream content has been gathered using dream reports and questionnaires. Dream experiences vary widely, but there are well-established themes that occur among many dreamers. Some of the most common dream subjects include:

  • School dreams (studying, taking tests)
  • Being chased
  • Sexual dreams
  • Falling
  • Being late
  • Flying
  • Being attacked physically
  • Dreaming of someone dead being alive, or someone alive being dead

A recent study of the content of nightmares found the most common themes included:

  • Physical aggression
  • Interpersonal conflicts
  • Experiences of failure and helplessness

Researchers found fear to be the most common emotion in nightmares and bad dreams, though it’s often accompanied by other emotions as well.

Recently, scientists in Japan made a breakthrough in decoding the content of dreams. They used a technique called neural decoding—which involves brain scans and repeated questioning of study subjects—in order to identify visual content in dreams. The researchers were ultimately able to predict dreams' visual content based on brain activity with 75-80% accuracy.

Will neural decoding be the future of dream content studies? Perhaps. Examining the content of dreams is one way to seek answers about the most fundamental question we still must answer: Why do we dream at all?

More from Michael J. Breus Ph.D.
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