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 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. 
Sleep-talking is very common and is reported in 50% of young children, with most of them outgrowing it by puberty, although in rare cases it may persist into adulthood (about 4% of adults are reported to talk in their sleep). It appears to run in families.
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
- American Academy of Sleep Medicine (2014) International classification of sleep disorders, 3rd edn. American Academy of Sleep Medicine, Darien
- Ohayon, M. M., & Shapiro, C. M. (2000). Posttraumatic Stress Disorder in the General Population. Comprehensive psychiatry, 41(6), 469–478.
- Inman, D. J., Silver, S. M., & Doghramji, K. (1990). Sleep disturbance in post-traumatic stress disorder: A comparison with non-PTSD insomnia. Journal of Traumatic Stress, 3(3), 429‑437. https://doi.org/10.1002/jts.2490030311
- Arkin, Arthur M. (1981). Sleep Talking Psychology and Psychophysiology. L. Erlbaum Associates. pp. 40–41. ISBN 0-89859-031-0.
- Shakespeare, William. "Macbeth". Shakespeare Online. Amanda Mabillard. Retrieved 21 February 2017.
- Ingemann, Bernhard Severin (1846). The Childhood of King Erik Menved: An Historical Romance. London: Bruce and Wyld. p. 11. Retrieved 21 February 2017.
- White, William (March 1963). "Whitman's First "Literary" Letter". American Literature. 35 (1): 83–85. JSTOR 2923025.
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