The Mysteries of the Brain: Are Sleep Talks Live Commentaries of Dreams? The Regularity of Words Revealed Through Research

The Mysteries of the Brain: Are Sleep Talks Live Commentaries of Dreams? The Regularity of Words Revealed Through Research

The Night When a Sleeping Person Suddenly Starts Talking

The person sleeping next to me suddenly said "No" clearly. After a brief pause, they answered something no one had asked. The next morning, when I told them about it, they had no memory of it at all.

Sleep talking is a familiar yet mysterious phenomenon. It can end with a short grunt or laugh, or become a long utterance like a question, command, insult, or conversation. While the listener might find it amusing, they might also feel anxious, wondering, "Who were they talking to?" "Is this their true feelings?" or "Did they reveal a secret?"

However, the image of sleep talking that emerges from sleep research is not so much a phenomenon of confessing hidden truths from the depths of consciousness, but rather a phenomenon indicating that the brain is not a monolith during sleep. The entire brain does not shut down at once; even during sleep, the level of activity varies by region. It is from these momentary discrepancies that voices spill out.


Sleep is not a single state that continues until morning

When a person falls asleep, they progress from light NREM sleep to deep NREM sleep, and then move into REM sleep. This cycle is repeated several times throughout the night. Generally, NREM sleep is more prevalent in the first half of the night, while vivid dreams are more likely to occur during REM sleep, which becomes longer towards morning.

During REM sleep, brain activity increases, and the eyes move rapidly. Meanwhile, a mechanism suppresses muscle movement in the body, making it difficult to physically act out the actions in dreams. In NREM sleep, especially in its deeper stages, the brain and body are in a more relaxed state.

However, real sleep is not as neatly divided as textbooks suggest. Sometimes, only parts of the brain increase activity at the boundary between sleep and wakefulness, leading to phenomena such as turning over, teeth grinding, sleepwalking, night terrors, and sleep talking. These behaviors and experiences during sleep are broadly referred to as "parasomnias."

Sleep talking can occur in any stage of sleep, including both REM and NREM sleep. Therefore, just because someone talks in their sleep does not necessarily mean they were dreaming. Conversely, even if they were dreaming, it does not mean it will be vocalized.


Why do words come out while sleeping?

The current leading explanation is that the circuits for constructing language and the motor system involved in vocalization temporarily activate, disrupting the balance with the mechanism that usually suppresses speech. In other words, not all parts of the brain are asleep to the same depth.

A brainwave study published in 2022 showed that brain activity just before meaningful sleep talking shares characteristics with speech preparation during wakefulness. This supports the possibility that some language processing is running within the sleeping brain, rather than the mouth moving randomly to produce sounds.

However, most sleep talking is not composed of coherent long sentences. In reality, it often consists of unintelligible murmurs, laughter, whispers, or single sounds. Even when words can be understood, studies have found that negative words, questions, commands, and confrontational expressions are prominent.

In a study by a French research team analyzing nighttime speech of healthy individuals and parasomnia patients, negative words equivalent to "no" accounted for about 5% of all words. Grammar and the order of conversation were surprisingly maintained, with pauses as if waiting for a response. However, the content tended to be more aggressive and negative than conversations during wakefulness.

This does not mean the personality of the sleeping person becomes worse. Scenes of threat, conflict, and escape easily infiltrate dreams and mental experiences during sleep. Additionally, the functions related to social consideration and self-censorship are not in the same state as during wakefulness, making short rejections or warnings more likely to be voiced than polite expressions.


Is sleep talking a "live broadcast" of dreams?

There is a relationship between sleep talking and dreams. In studies observing sleep in laboratories, many examples have been reported where speech during REM sleep corresponded to the content of dreams when the person was awakened immediately after speaking. The original article mentions that the rate of sleep talking during REM sleep matching the content of dreams is about 80%.

However, reading this number as "sleep talking is a complete live broadcast of dreams" is an overstatement. Sleep talking studies are small in scale and often conducted in sleep laboratories, which differ from everyday bedrooms. There is also no method to confirm that the dreams remembered after waking are exactly the same as the mental experiences that occurred during sleep.

Nevertheless, sleep talking is valuable for researchers. Dream research usually relies on memories after waking. With sleep talking, fragments of language generated during sleep can be observed on the spot. It serves as a "window" to explore how well the sleeping brain can maintain grammar, meaning, and the order of conversation.


Sometimes they respond when spoken to

When someone talking in their sleep is spoken to, they may respond as if answering a question. A study introduced in the original article found that about half of the people who were sleep talking responded to external prompts.

Recent lucid dream research has also reported instances where participants in REM sleep understood simple math problems or questions and responded with eye movements or facial muscles. Sleep is not a state completely cut off from the outside world; under certain conditions, information can reach inside, and responses can be sent out.

However, there is no guarantee that the response will be accurate. The voice heard may be incorporated into the dream's storyline, resulting in responses unrelated to reality. Sleep talking cannot be used for interrogation or fact-checking.


Does sleep talking reveal "secrets" or "true feelings"?

This is likely the biggest concern for many people. In conclusion, there is no scientific basis for treating sleep talking as the person's true feelings, memories, or confessions.

Memory reprocessing occurs during sleep, and experiences from the day, such as work, school, and relationships, can mix into dreams and sleep talking. However, old memories, imaginary scenes, heard sounds, emotions, and word associations are also combined. Even if a real name is mentioned, it does not directly prove the current feelings or real actions towards that person.

Rather, sleep talking is grammatically natural but has low contextual reliability. The brain can construct sentences but is not in a wakeful state to verify facts and make responsible statements. Judging "it's true because it was said in sleep talking" is as precarious as using events seen in dreams as evidence in reality.

If hurt by a partner's sleep talking, there's no need to deny the feelings. However, rather than pursuing the sleep talking itself, it's more constructive to share the feelings of anxiety heard and discuss using real-life relationships and actions as materials.


Three prominent reactions on social media

Posts about sleep talking repeatedly become a topic on social media and forums. There are largely three types of reactions.

 

The first is a reaction of pure amusement. Partners or family members serve non-existent guests, give nonsensical instructions, or rave about food in their dreams. Some people create "sleep talk memos" and laugh with the person the next morning. This group sees it as a small amusement of communal living.

The second is curiosity about whether it has meaning or if secrets are leaked. On the overseas forum Reddit, questions are posted about why the content is strange even though they can speak in complete sentences, and why there are few examples of passwords or secrets being leaked. Comments include experiences where sleep talking seemed to recreate daytime work or reports of getting responses when asked questions.

The third is anxiety or fear. Posts express worry after hearing abusive language, another person's name, or violent words, wondering if that's what the person truly thinks. Some even report that suspicion of infidelity or hostility based solely on sleep talking has worsened relationships.

These are personal experiences and not medical evidence. However, it is clear that sleep talking often has a stronger impact on the "listener" than the person themselves. While sleep talking itself is harmless, if it disrupts a cohabitant's sleep or causes misunderstandings and distrust, it can become a problem in daily life.

More people are using recording apps to collect sleep talking, but caution is needed when sharing. Publishing a voice unconsciously uttered by the person on social media without permission can be a privacy violation that cannot be dismissed as a joke. If recording, the purpose should be communicated, and consent for sharing should always be obtained from the person.


More common in children, tends to decrease in adults

Sleep talking is a very common phenomenon. Surveys targeting the general population show that about 66% have experienced it at least once in their lifetime, about 17% in the past three months, and about 6% in the past week. However, since the person does not remember, the numbers vary depending on the presence of cohabitants or how questions are asked.

It is particularly common in children and tends to decrease with growth. One reason is that children have more deep slow-wave sleep than adults, making transitions between sleep and wakefulness more unstable. Genetic factors are also suggested, with examples of sleep talking and sleepwalking overlapping within families.

Additionally, it is said to be more likely to occur when there are factors that disrupt sleep, such as lack of sleep, severe fatigue, stress, irregular sleep, fever, and alcohol consumption. There is no specific remedy to completely stop sleep talking, but basic measures such as ensuring sufficient sleep time, regulating bedtime and wake-up time, and refraining from drinking at night are meaningful.


"Common sleep talking" and signs to consider seeing a doctor

If short sleep talking occurs occasionally and neither the person nor the cohabitant is troubled, treatment is often not necessary. There is no need to consider it a disease based solely on sleep talking.

On the other hand, in the following cases, it may be worth considering consulting a sleep specialist or medical institution.

  • Frequent and intense sleep talking suddenly started in adulthood

  • Actions such as shouting, hitting, kicking, or jumping up occur simultaneously

  • There is a risk of injury to the person or cohabitant

  • Accompanied by loud snoring, breathing pauses, or choking sounds

  • Frequent nighttime behaviors and strong daytime sleepiness or decreased concentration

  • Repetitive movements, rigidity, or confusion suggesting seizures

  • Sleep talking and related behaviors significantly impair the lives of the person or family

Sleep talking can be associated with obstructive sleep apnea, arousal disorders, REM sleep behavior disorder, and nocturnal seizures. Especially if the body moves violently in accordance with dream content, it should not be dismissed as mere sleep talking.

When consulting, it is helpful to record the time of occurrence, frequency, relationship with alcohol or medication, snoring, movements, and next-day sleepiness. Showing short audio or video clips to the doctor can also aid in diagnosis. However, ensuring the safety of the bedroom should be prioritized first.


What sleep talking teaches us is the boundary between "sleep" and "wakefulness"

The fascination with sleep talking is not just in its odd content. It shows that whether a person is asleep or awake cannot be simply divided into two choices.

The body is lying down, conscious memories are not formed, and the person remembers nothing the next morning. Yet, language circuits construct grammar, maintain the order of conversation with an unseen interlocutor, and move the muscles of the mouth and throat. Parts of the brain receive external voices and sometimes even formulate responses.

The sleeping brain is not a halted machine. It continues complex work every night, organizing memories, processing emotions, and keeping the door to the outside world half-closed. Sleep talking may be a fragment of that work accidentally reaching our ears as a voice.

Therefore, the next time someone utters an inexplicable word while asleep, there is no need to assume it is a secret confession. If it can be laughed off, it can become a small topic of conversation the next morning. And if the frequency or intensity increases, it is wise to take it as a sign to adjust sleep, rather than as a "true intention" from the brain.


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