Talking to Yourself in your Sleep

Over the years, more often than not, I have shared a room with my younger sister, whether it be in a hotel room or at home. No big deal, but for as long as I remember, my sister has talked in her sleep (how weird). She often replays the day's events in her mind, talking to her best friends or her teammates on the soccer field. It turns out that sleep-talking, or somniloquy, is more common than I originally thought. According to my parents, my sister has talked in her sleep since she was a baby. About 50% of children between the ages of 3 and 10 talk in their sleep. Also, most occurrences are 30 second bursts. Most children who sleep-talk, grow out of it during puberty, so why does my 15 year old sister regularly have long conversations with herself throughout the night?

There are several stages of sleep, each differentiated by the level of electrical activity. When asleep, the brain's neural structures are temporarily paralyzed. REM sleep, or Rapid Eye Movement, is when all body muscles, except the eyes, are paralyzed. 
In this case, things like sleep-talking, sleep-walking, or any kind of parasomnia, most often occurs outside of this stage of sleep. Even so, it is possible for sleep-talking to occur during the REM stage. The brain fails to inactivate some motor functions, allowing one to speak. In other words, parts of the brain remain "asleep" while another is "awake." Sleep-talking during REM sleep, called "motor breakthrough" , usually consists of short utterances, but also multiple people to whom the person talks to. With that said, sleep-talking is usually seen in momentary lapses of consciousness when the individual is not in a deep sleep, also known as NREM or non-rapid eye sleep. This is why sleep-talking is common in the early stages of sleep. Contrary to what many may think, one does not dream during NREM sleep, meaning that the sleeper usually doesn't even "see" the people who they are talking to. The real question is what do we say when we sleep-talk?  NREM sleep-talking is usually more complex than REM in that the sentences are more complete and are presented as single thoughts. What's said is less likely to be connected to one another. In both REM and NREM sleep, it is common for the sleeper to go through the past day's events and encounters. Whether the sleeper has long conversations or a few incoherent bursts, in the morning the individual has no recollection of what was said. Additionally, sleep-talking usually isn't treated, as it does not negatively affect one's health. Maybe the best treatment plan is just to get some earplugs for a good night's sleep.