Dreams are a succession of images, thoughts, sounds, or emotions passing through the mind during sleep. The content and purpose of dreams are not fully understood, though they have been a topic of speculation and interest throughout recorded history.
The scientific study of dreams is known as oneirology.
Dreams have a long history. They have been a subject of controversy and disagreement. Throughout history, people have sought meaning in dreams or divination through dreams.
Dreams have been described physiologically as a response to neural processes during sleep, psychologically as reflections of the subconscious, and spiritually as messages from gods or predictions of the future.
Many cultures had practiced dream incubation, with the intention of cultivating dreams that were prophetic or contained messages from the divine.
Judaism has a traditional ceremony called hatavat halom literally meaning making the dream a good one.
Through this rite disturbing dreams can be transformed to give a positive interpretation by a rabbi or a rabbinic court.
There is no universally agreed biological definition of dreaming. In 1952, Eugene Aserinsky discovered REM sleep while working in the surgery of his PhD advisor. Aserinsky noticed that the sleepers eyes fluttered beneath their closed eyelids. In one session, he awakened a subject who was wailing and crying out during REM and confirmed his suspicion that dreaming was occurring.
Accumulated observation shows that dreams are strongly associated with rapid eye movement REM sleep, during which an electroencephalogram shows brain activity to be most like wakefulness.
Participant nonremembered dreams during non REM sleep are normally more mundane in comparison. During a typical lifespan, a human spends a total of about six years dreaming.
Most dreams last only 5 to 20 minutes. It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind.
During REM sleep, the release of certain neurotransmitters is completely suppressed.
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