The first recorded use of the word was in 1653. An advocate of this discipline was the French sinologist Marquis d'Hervey de Saint Denys. The field gained momentum when Nathaniel Kleitman and his student Eugene Aserinsky discovered regular cycles. A further experiment by Kleitman and William C. Dement, then another medical student, demonstrated the particular period of sleep in which electrical brain activity as measured by an electroencephalograph (EEG) closely resembled that of waking as the eyes darted about actively. This kind of sleep became known as REM sleep, and Kleitman and Dement's experiment found a correlation of .80 between REM sleep and dreaming.
Current research seeks correlations in dreaming to current knowledge about the functions of the brain and how the understanding how the brain works during dreaming pertains to memory formation and mental disorders. The study of oneirology can be distinguished from dream analysis in that the aim is to quantitatively study the process of dreams instead of analyzing the meaning behind them.
Research into dreams include researching the mechanisms of dreaming, the influences on dreaming, and the disorders linked to dreaming. Work in oneirology overlaps into neurology and can vary from quantifying dreams, analyzing brain waves during dreaming, and studying the effects of drugs and neurotransmitters on sleeping or dreaming. Though much debate still exists about the purpose or origins of dreams, many significant correlations can be found in studying dreams as a function of brain activity. In addition, the data found could have correlation to treating certain types of mental diseases.
Dreaming occurs mainly during REM sleep and brain scans recording brain activity have witnessed heavy activity in limbic system and the amygdala. Though current research has reversed the myth that dreaming only occurs during REM sleep, it has also shown that the dreams reported in NREM and REM differ qualitatively and quantitatively, suggesting that the mechanisms that control both are different. 
During REM sleep, researchers theorize that the brain goes through a process known as synaptic efficacy refreshment. This is observed as brain waves self firing during sleep in slow cycles at a rate of around 14Hz and is believed to serve a purpose of consolidating recent memories and reinforcing old memories. This brain stimulation that occurs has dreaming that occurs as a by-product. 
During normal sleep cycles humans alternate between Non-Rapid Eye Movement (NREM or NonREM) sleep and Rapid Eye Movement sleep. Dreaming type waves observed from the brain during REM sleep is the type most commonly studied in dream research because the most dreaming occurs during the deep sleep signaled by REM. 
In 1952, Eugene Aserinsky discovered REM sleep while working in the surgery of his PhD advisor. Aserinsky noticed that the sleepers' eyes fluttered beneath their closed eyelids, later using a polygraph machine to record their brain waves during these periods. In one session, he awakened a subject who was wailing and crying out during REM and confirmed his suspicion that dreaming was occurring. In 1953, Aserinsky and his advisor published the ground-breaking study in Science.
Accumulated observation shows that dreams are strongly associated with rapid eye movement (REM) sleep, during which an electroencephalogram shows brain activity to be most like wakefulness. Participant-nonremembered dreams during non-REM sleep are normally more mundane in comparison. During a typical lifespan, a human spends a total of about six years dreaming (which is about two hours each night). Most dreams last only 5 to 20 minutes. It is unknown where in the brain dreams originate, if there is a single origin for dreams or if multiple portions of the brain are involved, or what the purpose of dreaming is for the body or mind.
During REM sleep, the release of certain neurotransmitters is completely suppressed. As a result, motor neurons are not stimulated, a condition known as REM atonia. This prevents dreams from resulting in dangerous movements of the body.
Animals have complex dreams and are able to retain and recall long sequences of events while they are asleep. Studies show that various species of mammals and birds experience REM during sleep, and follow the same series of sleeping states as humans.
The discovery that dreams take place primarily during a distinctive electrophysiological state of sleep, rapid eye movement (REM) sleep, which can be identified by objective criteria, led to rebirth of interest in this phenomenon. When REM sleep episodes were timed for their duration and subjects woken to make reports before major editing or forgetting could take place, it was determined that subjects accurately matched the length of time they judged the sleep the dream narrative to be ongoing to the length of REM sleep that preceded the awakening. This close correlation of REM sleep and dream experience was the basis of first series of reports describing the nature of dreaming: that it is regular nightly, rather than occasional, phenomenon, and a high-frequency activity within each sleep period occurring at predictable intervals of approximately every 60–90 minutes in all humans throughout the life span. REM sleep episodes and the dreams that accompany them lengthen progressively across the night, with the first episode being shortest, of approximately 10–12 minutes duration, and the second and third episodes increasing to 15–20 minutes. Dreams at the end of the night may last as long as 15 minutes, although these may be experienced as several distinct stories due to momentary arousals interrupting sleep as the night ends. Dream reports can be reported from normal subjects on 50% of the occasion when an awakening is made prior to the end of the first REM period. This rate of retrieval is increased to about 99% when awakenings are made from the last REM period of the night. This increase in the ability to recall appears to be related to intensification across the night in the vividness of dream imagery, colors and emotions. The dream story itself in the last REM period is farthest from reality, containing more bizarre elements, and it is these properties, coupled with the increased likelihood of spontaneous arousals allowing waking review to take place, that heighten the chance of recall of the last dream.
The definition of dream used in quantitative research is defined through four base components: 1) a form of thinking that occurs under minimal brain direction, external stimuli are blocked, and the part of the brain that recognizes self shuts down. 2) a form of experience that we believed we experience through our senses. 3) something memorable. 4) have some interpretation of experience by self. In summary, a dream, as defined by Bill Domhoff and Adam Schneider, "a report of a memory of a cognitive experience that happens under the kinds of conditions that are most frequently produced in a state called 'sleep.'" [10 ]
Authentic dreams are defined by their tendency to occur "within the realm of experience" and reflect actual memories or experiences the dreamer can relate to. Authentic dreams are believed to be the side effect of synaptic efficacy refreshment that occurs without errors.  Research suggests that the brain stimulation that occurs during dreaming authentic dreams is significant in reinforcing neurological pathways, serving as a method for the mind to "rehearse" certain things during sleep.
Defined as dreams that contain impossible, incongruent, or bizarre content as the types of dreams hypothesized to stem from memory circuits accumulating efficacy errors. In theory, old memories having undergone synaptic efficacy refreshment multiple times throughout one's lifetime result in accumulating errors that manifest as illusory dreams when stimulated. Qualities of illusory dreaming have been linked to delusions observed in mental disorders.  Illusory dreams are believed to most likely stem from older memories that experience this accumulation of errors in contrast to authentic dreams that stem from more recent experiences.
One aspect of dreaming studied is the capability to externally influence the contents of dreams with various stimulus. One such successful connection was made to the olfactory, influencing the emotions of dreams through a smell stimulus. Their research has shown that the introduction of a positive smelling stimulus induced positive dreams (roses) while negative smelling stimulus (rotten eggs) induced negative dreams. 
Though there is much debate within the field about the purpose of dreaming, a leading theory involves the consolidation of memories and experiences that occurs during REM sleep. The electric involuntary stimulus the brain undergoes during sleep is believed to be a basis for a majority of dreaming.
The link between memory, sleep, and dreams become more significant in studies analyzing memory consolidation during sleep. Research has shown that NREM sleep is responsible for the consolidation of facts and episodes in contrast to REM sleep that consolidates more emotionally related aspects of memory. The correlation between REM and emotional consolidation could be interpreted as the reason why dreams are of such an emotional nature and produce strong reactions from humans.
In addition to the conscious role people are aware of memory and experience playing a role in dreaming unconscious effects such as health of relationships factor into the types of dreams the brain produces. Of the people analyzed, those suffering from "insecure attachments" were found to dream with more frequency and more vividly than those who we evaluated to have "secure attachments."
Correlations between the usage of drugs and dreaming have been documented particularly the use of drugs, such as sedatives, and the suppression of dreaming because of drugging effects on the cycles and stages of sleep while not allowing the user to reach REM. Drugs used for their stimulating properties (cocaine, marijuana, and ecstasy) have shown to also decrease the restorative properties of REM sleep and its duration. 
Dreaming disorders are difficult to quantify due to ambiguous nature of dreaming. However, dreaming disorders can be linked to psychological disorders such as Post Traumatic Stress Disorder expressed as nightmares. Research into dreaming also suggests similarity and links in illusory dreaming and delusions. 
Diagnostic symptoms include re-experiencing original trauma(s), by means of flashbacks or nightmares; avoidance of stimuli associated with the trauma; and increased arousal, such as difficulty falling or staying asleep, anger, and hypervigilance.
Links to post traumatic stress disorder (PTSD) and dreaming have been made in studying the flashbacks or nightmares the victims would suffer. Measurement of the brain waves exhibited by the subjects experiencing these episodes showed great similarity between those of dreaming. The drugs used to treat those suffering from these symptoms of flashbacks and nightmares would suppress not only these traumatic episodes but also any other sort of dreaming function. 
The delusions experienced by those with schizophrenia have been likened to the experience of illusory dreams that have come to be interpreted by the subject as actual experiences.  Additional research into medication to suppress symptoms of schizophrenia have also shown to influence the REM cycle of those taking the medication and as a result influence the patterns of sleep and dreaming in the subjects.