The dreams we have during our sleep have always fascinated humanity, the earliest evidence of this being the first dream interpretation guide by Artemidorus (100 AD), based on the stories of people from Greece, Italy and Ancient Asia.
Studies in this field began in 1950-1960, when William Dement discovered that during a night, a person goes through 5 stages of sleep, of which the best know is the REM phase. During this phase rapid eye movements and brain waves are recorded similar to those observed in the waking state. REM sleep occurs 4-5 times a night, and its duration increase from 10 (at sleep onset) to 20 minutes (in the morning).
The human brain can go into REM sleep as early as the intrauterine period (week 26 of pregnancy), a newborn spending almost half of his sleep in REM phase, whereas an elderly person spends up to 15% of his sleep in this phase. In humans, deprivation of REM for one night makes the person enter REM faster the next night and it takes longer. 74% of dreams occur in REM sleep.
The brain structures involved in producing REM sleep and dreams are areas from the brainstem, the limbic system (responsable for emotion processing) and areas from the parietal cortex, areas of association and areas for facial recognition. Areas involved in long-term memory are inactive, therefore we remember only a few elements of the dream and, as the time passes, we are left with fewer details. Also, the motor cortext is inactive, so we can not make the movements we have in the dream. The prefrontal cortex is the fist one that becomes inactive during sleep and the last to activate on waking. As a result there is no spatial orientation, reasoning and decision making are impaired (when we dream on flying or meeting a deceased person).
Regarding the content of dreams, in proportion of 70% there are emotions (anger, anxiety, euphoria, sadness, stress, confusion, helplessness) caused by the activation of the amygdala by the brainstem. A study of the dreams of 20 000 respondents, analysed using a computer algorithms, indicate that there are more similarities than intracultural differences. Women tend to dream other women and men, in equal proportions, while men dream predominantly dream of men, usualy in a context loaded with physical aggression. Children often dream of animals. Generally, dreams contain more negative emotions than positive ones, more aggression than friendship.
Given the bizzare elements that frequently appear in dreams attributed to the brain’s ability to work with metaphors, it is considered that one of dreaming’s role is the figurative processing of information. If we would consider the human brain a computer and sleep the stand-by state, the dream would be a sort of offline information processing, which favors memory. Otherwise, the prefrontal cortex should have been overdeveloped, beyond the capacity of the skull.
Other researchers consider dream as a simulation of a threat that favors learning, adaptation, repetition and practice of skills. This is possible despite the fact that during REM sleep the motor cortex is inactive- the brain beliefs that the motor commands have been actually fulfilled (the action from the dream is “real”, from a neuropsychological point of view).
Another role of dreams is to regulate affect. Dreams at the begining of sleep are more emotionally charged, and those in the morning contain more autobiographical elements.
Another clue in this regard are the nighmares, specially those that occur after a traumatic event. Sigmund Freud once said that „the dream is the royal path to the unconscious”. Thus, the elements that cannot be processed in the waking statet because of their intensity and their emotional load appear in a dream, in a symbolic form. Therefore, the dream is an important tool in psychotherapy, its interpretation through free association being a technique frecquently used in many psychotherapeutic approaches.