Dream

A dream is an involuntary sequence of mental activity during sleep, composed of images, shifting scenes, ideas, emotions, and sensations. Each night, humans dream for over two hours, with individual episodes lasting between five and twenty minutes. Throughout recorded history, the nature and purpose of dreams have drawn scrutiny from science, philosophy, and religion.

Dream interpretation dates back to the Babylonians in the third millennium BCE and even earlier to the ancient Sumerians, appearing prominently in various religious texts and later playing a key role in psychotherapy. A related practice, dreamwork, avoids assigning fixed meanings. The scientific field dedicated to dreams is called oneirology, with most contemporary research concentrating on the neurophysiology of dreaming and testing hypotheses about its function. It remains unknown where in the brain dreams originate, whether a single region or multiple areas are involved, or what purpose dreaming serves for the body, brain, or mind.

How humans experience and interpret dreams has shifted considerably over time. In ancient Mesopotamia and Egypt, writings show that dreams strongly dictated behavior after waking, a influence that diminished in later eras. These early records often describe visitation dreams, in which a deity or ancestor commands the dreamer to act or foretells future events. The framing of dream experience varies across cultures and historical periods.

Dreaming is closely tied to sleep. It occurs mainly during rapid-eye movement (REM) sleep, when brain activity is high and resembles wakefulness. Since REM sleep is detectable in many species and all mammals appear to experience it, this link has led to speculation that animals dream. However, humans also dream during non-REM sleep, and not all awakenings from REM produce dream reports. To study a dream, it must first be turned into a verbal report—a memory of the dream, not the experience itself. Consequently, dreaming in non-humans, as well as in human fetuses and pre-verbal infants, cannot currently be proven.

**Etymology**

In Old English, the word *drēam* meant "noise," "joy," or "music," unrelated to sleep-induced mental activity. Only in the 13th century did *dream* come to mean "a series of thoughts, images or emotions occurring during sleep." Etymologists attribute this shift to influence from the Old Norse *draumr*, which carried the modern sense of the word.

**Subjective experience and content**

Preserved writings from early Mediterranean civilizations suggest a relatively abrupt change in subjective dream experience between the Bronze Age and the classical era. In ancient visitation dreams, dreamers were largely passive, with visual content mainly framing authoritative auditory messages. For instance, Gudea, king of the Sumerian city-state of Lagash (reigned c. 2144–2124 BCE), rebuilt the temple of Ningirsu after a dream commanded him to do so. After antiquity, passive hearing of visitation dreams gave way to visualized narratives where the dreamer actively participates as a character.

From the 1940s to 1985, Calvin S. Hall collected over 50,000 dream reports at Western Reserve University. In 1966, Hall and Robert Van de Castle published *The Content Analysis of Dreams*, outlining a coding system for 1,000 reports from college students. Results showed that participants from different parts of the world had similar dream content. The only remnant of antiquity's authoritative dream figure in their listing of dream characters is God, included under prominent persons. Hall's complete reports were made publicly available in the mid-1990s by his protégé William Domhoff. More recent studies, while more detailed, continue to cite Hall's work favorably.

In Hall's study, the most common emotion in dreams was anxiety, followed by abandonment, anger, fear, joy, and happiness. Negative emotions were far more common than positive ones. Sexual dreams occurred no more than 10% of the time, most often in young to mid-teens. Another study found that 8% of both men's and women's dreams have sexual content, which can sometimes lead to orgasms or nocturnal emissions, colloquially known as "wet dreams." Dreams are generally highly phantasmagoric, with locations and objects blending into one another. Visuals typically reflect a person's memories and experiences, but conversations can become exaggerated and bizarre. Some dreams tell elaborate stories, introducing entirely new worlds and leaving the dreamer with novel ideas, thoughts, and feelings. People blind from birth do not have visual dreams; their dream content involves other senses—hearing, touch, smell, and taste—that were present from birth.

**Effects of regional or global catastrophes**

The COVID-19 pandemic influenced dream content, according to a scientific study of over 15,000 dream reports by Deirdre Barrett. Themes of fear, illness, and death were two to four times more common in dreams after the pandemic began than before.

**Neurophysiology**

Dream study is popular with researchers.