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No one had ever tried timing a dream before, but many people had long subscribed to the opinion of French psycologist Alfred Maury, who postulated in 1861 that dreams were infinitesimally brief. It is also known as the popular 7-second-theory, but latest researches say that REM sleep periods, and therefore dreams, can even take 5 to 45 minutes. Anyway, time is one ot the perceptions that are heavily distorted in dreams.
But a scientist called Dement established how long people linger in REM state, thereby providing an estimate of the duration of dreams. For a newborn, he determined, REM sleep constitutes 50% of sleep. This level gradually decreases to a stabilization level fo 20 to 25% at adolescence. It reaches a low of 18% during old age. The severely mentally retarded and those with extremely low IQ spend less time in REM sleep than normal subjects. Variations in REM sleep also occur with some kinds of mental disorders.
With approximately five dreams a night, humans will have about 136,000 dreams in a lifetime, spending the equivalent of six years in a REM dream state.
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