Somniloquy or sleep-talking is a parasomnia that refers to talking aloud while asleep. It can be quite loud, ranging from simple mumbling sounds to loud shouts and long, frequently inarticulate speeches, and can occur many times during a sleep cycle. As with sleepwalking and night terrors, sleeptalking usually occurs during delta-wave NREM sleep stages or during temporary arousals therefrom.
It can also occur during the REM sleep stage, at which time it represents what sleep therapists call a motor breakthrough (see sleep paralysis) of dream speech: words spoken in a dream are spoken out loud. Depending on its frequency, this may or may not be considered pathological. All motor functions are typically disabled during REM sleep thus, motoric, i.e., verbal elaboration of dream content, could be considered an REM behavior disorder (see below).
Sleep-talking can occur by itself (i.e., idiopathic) or as a feature of another sleep disorder such as:
- Rapid eye movement behavior disorder (RBD) – loud, emotional or profane sleep talking
- Night terrors – intense fear, screaming, shouting
- Sleep-related eating disorder (SRED)
In 1966, researchers worked to find links between heredity and somniloquy. Their research suggests the following:
- Sleep-talking parents are more likely to have children who sleep-talk
- Sleep talking can still occur, though much less commonly, when neither parent has a history of sleep talking
- A large portion of parents begin to sleep-talk later in life without any prior history of sleep-talking during childhood or adolescence
Sleep-talking by itself is typically harmless; however, it can wake others and cause them consternation—especially when misinterpreted as conscious speech by an observer. If the sleep-talking is dramatic, emotional, or profane it may be a sign of another sleep disorder (see above). Sleep-talking can be monitored by a partner or by using an audio recording device; devices which remain idle until detecting a sound wave are ideal for this purpose. Polysomnography (sleep recording) shows episodes of sleep talking that can occur in any stage of sleep.
Stress can also cause sleep talking. Researchers have found than 30.7% of people who suffered from PTSD (post-traumatic stress disorder) talk in their sleep. Another study shows that Vietnam War veterans having PTSD report talking more in their sleep than non-PTSD patients. 
Somniloquy can also be caused by depression, sleep deprivation, day-time drowsiness, alcohol, and fever. It often occurs in association with other sleep disorders such as confusional arousals, sleep apnea, and REM sleep behavior disorder. In rare cases, adult-onset somniloquy is linked with a psychiatric disorder or nocturnal seizure.
Sleep-talking is very common and is reported in 50% of young children at least once a year. A large percentage of people progressively sleep-talk less often after the age of 25 while lot of people continue to talk in their sleep. And a sizable proportion of people without any episode during their childhood begin to sleep-talk in adult life. Somniloquy appears to run in families.
In a study reporting the prevalence of somniloquy in childhood, the authors reported that the frequency of somniloquy differs between children. About half of the children have sleep-talking episodes at least once a year but less than 10% of children present somniloquy every night whereas 20%-25% talk in their sleep at least once a week. In addition, they didn’t find any difference between gender or socioeconomic class.
However, valid estimation of the prevalence of this phenomenon is difficult as the sleep-talker do not remember or are not aware of their sleep-talking. The same uncertainty exist concerning the age of onset because early occurrences may have escaped notice. Thus, we find disparate results regarding its prevalence in the literature.
Usually, treatment is not required for somniloquy because it generally does not disturb sleep or cause other problems. But a behavioral treatment has already shown results in the past. Le Boeuf (1979) used an automated auditory signal to treat chronic sleep-talking in a patient suffering from sleep talking for 6 years. An aversive sound was produced for 5 seconds when the patient started talking in his sleep. Somniloquy was rapidly eliminated and the patient demonstrated no adverse effects of treatment.
Although extremely rare, people who experience somniloquy may sometimes speak in another language. This phenomenon known only as "different-language sleep-talk", is currently under extensive research in numerous locations, though many are unknown, some are known to be located in New York City and San Diego inside the United States. This occurrence will most times be in a language that the person has obtained earlier on in one's life, although it is also possible to different-language sleep-talk a second language that one has learned later in one's childhood or pre-adulthood. It is impossible for someone experiencing different-language sleep-talk to speak in a language that he or she does not know or has not learned. The most common cases of people who experience different-language sleep-talk occur in teen to adulthood and will usually range anywhere between the ages of 17 to 26. Friends and family members of the one experiencing different-language sleep-talk should not awaken the person; they should instead consult him or her after they have awoken from their sleep and approach them on the issue. Much studying has yet to be completed on different-language sleep-talk, but for now, scientists can conclude that this case is non-harmful and is usually a byproduct of someone that regularly sleep-talks on a regular basis.
Sleep-talking appears in Shakespeare's Macbeth, the famous sleepwalking scene. Lady Macbeth, in a "slumbery agitation," is observed by a gentlewoman and doctor to walk in her sleep and wash her hands, and utter the famous line, "Out, damned spot! out, I say!" (Act 5, Scene 1)
Sleep-talking also appears in The Childhood of King Erik Menved, a 19th-century historical romance by Danish author Bernhard Severin Ingemann. In the story, a young girl named Aasé has the prophetic power of speaking the truth in her sleep. In an 1846 English translation, Aasé is described thus:
She is somewhat palefaced; and, however blithe and sprightly she may be, she is, nevertheless, now and then troubled with a kind of dreaming fit. But that will wear off as she gets older. Her mother was so troubled before her; and I believe it runs in the family as I am not entirely free from it myself. I do not give much heed to such dreaming now; but she has never yet said anything, while in this state, that has not proved in a manner true; though she can discern nothing, by night or day, more than others may do when they are in their senses.
- Dion McGregor, noted 20th-century somniloquist
- http://www.webmd.com/sleep-disorders/talking-in-your-sleep Talking in Your Sleep
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