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There is no universally agreed biological definition of dreaming. General 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-remembered dreams during non-REM sleep are normally more mundane in comparison.[1] During a typical lifespan, a human spends a total of about six years dreaming[2] (which is about 2 hours each night[3]). 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 the purpose of dreaming is for the body or mind.
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When the body decides that it is time to sleep, neurons near the eyes begin to send signals throughout the body. According to J. Allan Hobson, these neurons are located in such close proximity to neurons that control eyelid muscles that the eyelids begin to grow heavy.[4] Glands begin to secrete a hormone that helps induce sleep and neurons send signals to the spinal cord which cause the body to relax.
During sleep the body passes through five different stages, each differing in length and degree of sleep. REM (Rapid-Eye-Movement) sleep is when the majority of dreams takes place. Dreams tend to last for the entire REM cycle, ranging from about ten to twenty-five minutes.
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