A reader asked, after reading my last post on 11 reasons a good night's sleep is so important:
What is happening in the brain when kids talk while sound asleep? (I am usually asleep when this happens, but it's loud enough to arouse me to check on my child).
Sleep talking is one of a number of unusual sleep behaviors known as non-rapid eye movement sleep (NREM) parasomnias. Other forms of NREM parasomnias include sleep eating, sleep walking, confusional arousals, night terrors. In order to better understand parasomnias, it is important to understand what happens while we sleep. We start out awake when we lie down, close our eyes, and fall asleep, entering into light sleep, which then quickly gives way to deep (or slow wave sleep). After a period of slow wave sleep, we enter into a period of light sleep, often followed by a brief period of REM (rapid eye movement) sleep. This is referred to as a sleep cycle, and generally lasts between 90-120 minutes. Sleep cycles again several more times during the night, though as the night progresses, the amount of deep sleep decreases, and light sleep and REM increase. Most slow wave sleep is found in the first third of the night, and most REM in the last third.
The different stages of sleep are characterized by distinct brain wave patterns, as well as by differences in other physiologic parameters, such as muscle tone, eye movement, heart rate, breathing rate and patterns, and blood pressure. In REM sleep, dreams are most vivid and memorable. Men also experience erections in REM, which is why doing a sleep study to look for nocturnal penile tumescence (as these REM sleep erections are referred to in medical jargon) can be helpful in evaluating men with complaints of erectile dysfunction, in order to distinguish between organic and non organic causes of this.
As one transitions between the different stages of sleep, there can be brief awakenings, either partial or full, following which most people immediately return to sleep. Sometimes, however, there are strong pulls both to wakefulness and to deep sleep, and the result is that part of the brain continues to be in slow wave sleep, while another part is simultaneously in a state of wakefulness. The behavioral consequence is one of the NREM parasomnias: sleep walking, sleep talking, sleep eating, confusional arousals, night terrors. The person going through one of these is not aware of what she or he is doing and is often incoherent while it is happening, and has no recollection of it afterwards (though the episode can be quite dramatic, and even traumatic, for those witnessing it).
Most NREM parasomnias occur in the first third of the night, which is when most of the slow wave sleep occurs. They seem to be more frequent when the drive to maintain either wakefulness or slow wave sleep is especially strong. For example, they are more frequent when a person is sleep deprived, and in need of slow wave sleep (which is thought to be the most restorative for the brain). They are also more frequent when one is sleeping in a strange location (such as a hotel room), or in children who fall asleep in one location and are moved to another location once asleep (from the sofa to the bed). These circumstances evoke a need for vigilance that translates into a need to stay awake so as to protect oneself from harm, which often collides with the drive for sleep. NREM parasomnias are also seen when people are sick, especially with fever, likely for the same reason.
When one comes across a person who is sleep talking, sleep walking, or having a night terror, there is no benefit to be gained by waking her up, and that in fact can often wind up being quite traumatic for her. Instead, it is better to guide that person back to bed and make sure she is safe. If one identifies specific triggers, such as those listed above, they can be eliminated so as to reduce the occurrences (making sure a child gets enough sleep, for example, and falls asleep in her own bed). While medications are sometimes used, most of the time there is no need for them, and reassurance and guidance are all that is necessary to minimize their frequency and help the family deal with them.
Dennis Rosen, M.D.
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