Science

The study of dreams started with the discovery of rapid eye movements, or REM, when people are dreaming.

Two American researchers, Eugene Aserinsky and Nathaliel Kleitman, discovered REM in 1953.

This demonstrated that, instead of being in a resting state, the brain is indeed active when we are sleeping.

But the research on dreaming did not end with the discovery of REM.

Alan Hobson and Robert McCarley suggested that cortical synthesis of neural signals and their interpretation lead to dreams. They concluded that dreams were meaningless and random.

However, a few years later Hobson put forward the converse hypothesis that dreams were important to the dreamer because there was evidence of self-knowledge.

Prof. Chan refers the REM discovery as the most significant development in the studies of sleeping and dreaming.

"Dreams are based on biological needs, but we cannot preclude the possibility that they may be coupled with psychological factors," Prof. Chan said.

Nowadays, some people propose that dreams are meaningful mental products that express important wishes, fears, concerns and worries of the dreamer.

People can figure out various mental functions through the analysis of dreams.

The whole sleeping period is made up of 20 percent of REM sleep and 80 percent of non-REM sleep.

There are five stages in one sleeping period. They are characterized by particular brainwaves.

Stage 1 is a 7-minute transitional stage between wakefulness and the sleep made up of alpha and theta activities. Alpha, theta and delta are merely references to the kinds of brainwaves emitted during various mental states.

After Stage 1, sleeping subjects go into theta activity, or Stage 2. Sensory awareness of sleeping subjects is then decreased.

Dreaming does not start at this stage, but vague thoughts are driven into the subjects' minds.

Stages 3 and 4 are related to delta activity. Nightmares may occur during these stages of sleep.

But even if a sleeping subject wakes up at this point, no dreams can be reported. The sleepers only have an emotional change.

After that, the sleep cycle returns from the deepest sleep to Stage 2.

The sleepers then enter REM sleep, in which dreaming take place.

In view of the timing of the sleep-wake cycle, Prof. Chan said that the time for each new non-REM sleep was shorter than the previous one during sleeping. The cycle is controlled by the biological clock located in brain.

REM sleep has a developmental cycle. REM sleep shortens slightly with increasing age among mammals.

In the same context, mammals with developed brains have shorter REM sleeps than those with less developed brains.

There are some physiological mechanisms responsible for dreaming.

For instance, some portions of the brain emit certain brainwaves that trigger REM sleep.

Rapid eye movements, muscular paralysis and increased genital activity also occur when people are dreaming.

According to an experiment on the relationship between the length of REM sleep and learning, more REM sleep will occur after learning.

The experiment showed as well that deprivation of sleep after learning would result in impaired performance.

It is obvious that REM sleep is conducive to learning.

Prof. Chan describes dreams as discontinuous. They consist of fragments of unrealistic and incredible stories.

However, dreams usually have a story line.

Researcher discovered that most of the dreams are with colours and are mainly composed of visual images.

Taste, smell and touch may sometimes be involved in dreams.

It is rare for dreams to be made up solely of static pictures.

People may think daydreaming should be regarded as dreaming.

Said Prof. Chan: "They are the same in producing images, but daydreaming is not based on physiological needs.

"Besides, our muscular movements are partly suppressed when we are dreaming, but they are under control during daydreaming."