There are two theories on sleep function; the conservation theory and the restoration theory. The conservation theory proposes that we basically need to sleep in order to preserve our energy for our daytime use. When our use of energy amount is considered in terms of the rate of metabolism, slow wave sleep especially the first four stages spends merely 5 to 25 % of the amount we use during day, and slow wave sleep is strongly “associated with conservation of energy”. Another theory, the restoration theory, holds two hypotheses, the whole body restoration and the neurological restoration. The whole body restoration hypothesis suggests that sleep functions as a process of “anabolism” with respect to protein as well as a release of more hormones. The neurological restoration hypothesizes that brain is the one that needs to sleep. In addition, each stage is responsible for the partial brain restoration and that is why people need to repeat several non REM and REM sleep cycles throughout the night. Some researchers even hypothesize that these two theories might be both correct, and the sleep function is still a myth.

Why do we sleep in the first place? What triggers to fall asleep is not a single source. For example, it has been said that the hypothalamus, located in the center of the brain, collects messages from certain cells and carry the signal to the pineal gland in the brain. This process causes to produce the “hormone melatonin” which helps the body temperature to go down. Also, another example is raphe nuclei, located in the part of the brain which is in charge of “unconscious activity” such as walking and eating, sends an order to nerve impulses to shut down the brain system. Therefore, falling asleep is not merely a single process but a collective event

Many researchers have been trying to find out the functions and symbols of dreams. Though there are many theories, researchers have not exactly found out the reasons we dream and whether the contents of dreams have directly something to do with our everyday life. The first theory came up by a psychologist, Sigmund Freud. Freud explained that what is in our dream is the “repressed longing”: the suppressed thoughts and desires that we are usually unable to express socially. Carl Jung also supports Freudian ideas especially the origin of dreams, but except for one important principle. What Jung sees different is that dreams enable us to see ourselves as well as solve our problems. The third theory, “activation-synthesis hypothesis”, proposed by Allan Hobson and Robert McCarley in 1970’s takes a very different view compared to Freud and Jung. They claim that dream consists of random images which are stored as a memory in our head. These random images, dreams, are created by “nerve signals sent out during REM sleep from a small area called the pons” .Though there are many theories to solve the representation of dreams, the recently study in 1997 by Mark Solms using fMRI and PET seem to lean toward Freudian theory. Solms studied people with a brain damage, and concluded that the most active place during sleep was the part which controls emotion regardless of the differences in brain damages. Though many researchers including Solm do not necessarily see Freudian ideas as completely valid, they do believe that unconscious thoughts may be projected on our dreams.

REM sleep and dreams are related, but what is important about them? In the study by William Dement at Stanford University School of Medicine, participants were awaken when they were about to go to REM sleep stage, and Dement concluded that many participants had a psychological problem such as anxiety and irritability. According to this theory, REM seems like an essential sleep stage for humans. Jerry Siegel, director of UCLA’s center for sleep research explains that “REM sleep may have evolved for physiological reasons” considering that Non REM and REM behave like the automatic temperature change which a lot of animals do. Siegel also see dreams as a kind of “epiphenomenon” of a sleep product. The importance and function of sleep and dreams are controversial; some researchers claim that sleep and dreams are essential for health whereas some claim that they were a necessary development for human.
Although there has been many researches and theories on sleep and dreams, we still have not found why we actually sleep and what exactly the importance of this activity. After all, sleeping can be accepted as a fact that we all have to do everyday in our life regardless of the puzzles in reasoning. Because of the technological advancement, our scientific discovery has been much more rapid. Someday, some research might be able to find out the definite answers for sleep and dreams, but until then, the myth of sleep and dreams remains with us.