Sleep is the time when the brain imposes rest upon itself and the body. The Earth rotates every 24 hours and humans, like all creatures, have through evolution, incorporated a 24-hour activity-rest cicle into their genetic material.

As we fall asleep the body becomes inert and the flow of saliva decreases so we do not drown. Heart rate, oxygen consumption, breathing and temperature all diminish and the electrical brainwaves take on changed appearances.

In dreams we are not passive observers of pictures. People blind from birth do not see in dreams, but like all of us, they live in a fantasy world whilst asleep.

Everybody experiences two states of sleep, which alternate four or five times a night. Rapid eye movement (REM) occupies about 20% of the time ,and if sleepers are deliberately awakened from REM sleep they are especially likely to describe a dream.

In REM sleep, periods which last 5-30 minutes, there are intermittent flurries of jerky eye movements accompanied by finger, toe and facial twichings,erection of the penis or increased vaginal blood flow, and generalbodily paralysis. Mental life goes on all night: dreams are very common when we are merely drowsy at the start of the night, and the most vivid of all dreams, night terrors, occurin non-REM sleep. REM sleep itself is in fact most proeminent in infancy (and before birth) when memories and knowledge for the creation of dreams are not available.

Throughout history it has been believed that dreams foretell the futureand that they contain symbols. Sigmund Freud and Carl Gustav Jung hoped that by understanding symbols in dreams it would be possible to help people with psychological difficulties. Their writings influenced imagery of creative artists such as the Surrealists but their hopes have not been realized.

We don't know yet what our dreams really mean or if they mean something at all (they probably do). But between the scientific studies and our ancestors ways to interpret dreams there's still a gap.