Stress and Sleep Talking

Bo-Rin Kim's picture


My roommate last year told me one day that she heard me talking in my sleep. I was a little disconcerted by this because I never knew that I talked in my sleep or that talked loudly enough to wake up my roommate, who was a heavy sleeper. However, I just thought that I may have had a bad dream and had talked aloud in the context of this lucid dream. I thought this case of sleep talking was an exceptional occasion that resulted from an unusually vivid dream. However, my roommate this year also told me that she heard me talking in my sleep. This made me question if I was a regular sleep talker and whether it was something that I developed in college. I had gone on overnight retreats and slept over my friends’ houses before, and I was never told I talked in my sleep until my roommate brought it up the year before. Moreover, my parents never said anything about me talking in my sleep as a baby or a child, even though I have heard of numerous stories of how I would roll around a lot, disturbing whoever slept next to me. This made me wonder what the causes of sleep talking are and what triggers bring about the sudden onset of sleep talking in someone who never sleep-talked before.

Sleep talking, formally known as somniloquy, is a type of parasomnia, or sleep disorder, that involves talking during sleep without being aware of it. Sleep talking can occur during any stage of sleep, but it has been found that the lighter the sleep, the more understandable the speech. People in the earliest stages of sleep have been reported to engage in more conversational speech, while those in the deeper sleep stages are only able to produce nonsensical sounds (1). The severity of sleep talking can range from occasional instances to talking every night.

While most people, like myself, assume that sleep talking occurs during lucid dreaming, research studies that have analyzed brain activity during sleep have found that most sleep talking occurs during the lighter non-rapid eye movement stage of sleeping (2). Sleep is divided into rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep. REM sleep consists of faster, more frequent brain waves and heart rate, and this is the sleep stage where dreaming occurs. Moreover, muscles are made immobile in a temporary state of paralysis during REM sleep, which prevents people from acting out their dreams. NREM sleep is characterized by slower, infrequent brain waves. Dreaming does not occur during NREM sleep, and the body is not under paralysis. NREM sleep is further split into four stages, where stages 1 and 2 are lighter stages of sleep and stages 3 and 4 are deeper stages of sleep (3). Thus, most sleep talking has been found to occur in stage 2 of NREM sleep when the body can still move and the brain is not yet in the stages of deep sleep.

However, sleep talking can also occur during REM sleep in a condition called REM Behavior Disorder (RBD). In this condition, body movements occur during REM sleep, which is supposed to be characterized by immobility. Parasomnias like sleepwalking or sleep talking can result from RBD. Although the exact cause of RBD is unknown, researchers speculate that one possible explanation is damage to the brain stem, which is involved in controlling motor activity. Moreover, the temporary paralysis of REM sleep occurs when neurotransmitters like acetylcholine, are not released and do not stimulate the motor neurons. Hence, damage to the systems that regulate the synthesis and release of these motor neurotransmitters may also be responsible for RBD (4).

While sleep talking is normal and fairly commonplace, it seems to be most common among young children. 50% of children aged 3 to 10 have been found to talk in their sleep while only 5% of adults sleep-talk (1). The tendency to sleep talk seems to decrease with age. The sleep stages also change and stabilize through infancy and childhood. Infants spend twice as much time in REM sleep than adults, which may be due to the ability of REM sleep to help in early brain development. While infants spend more time in REM sleep, the paralysis mechanism that inhibits bodily movements during REM sleep is not fully developed early in life. Thus, babies and young children are seen engaging in more dramatic twitches and movements while asleep (5). Hence, children may sleep talk more than adults because their brains have not fully developed the mechanism that temporarily paralyzes body movement during REM sleep.

The exact mechanisms involved in sleep paralysis are unknown. However, scientists do know that the brain stem and neurotransmitters that stimulate motor neurons are involved. I speculate that the lack of this ability to paralyze the body in infants is not a result of the underdevelopment of the brain stem, as the brain stem is the least complex part of the brain and is the area to develop first (6). Infants must already have a developed brain stem. I hypothesize that infants and young children are not able to properly induce sleep paralysis because they have a harder time suppressing the activity of neurotransmitters involved in motor activity. The sleep stages of young children are known to last only 50 minutes while they last 90 minutes in adults (5). Thus, children experience more frequent transitions between the sleep stages. Perhaps this frequent switching of sleep stages makes it more difficult for the body to effectively suppress the release of neurotransmitters as the brain frequently goes in and out of REM sleep.

However, according to my parents, I did not sleep-talk growing up. Thus, something in college must have reduced my brain’s ability to suppress the release of neurotransmitters responsible for motor activity, making this ability infant-like. Or, something must have affected my sleep cycle as to increase the time I spent in NREM sleep, the stage where sleep talking frequently occurs. There are many known triggers of sudden sleep talking, such as substance use, fever, medication use, mental health disorders and stress (1). As I was not on medication, did not use substances, was physically and mentally healthy, the only sleep-talking trigger that applied to my life was stress.

Upon further investigation of the effects of stress, I found that stress is capable of putting my brain in state that is more likely to trigger sleep talking. As part of the stress response, the hypothalamus produces higher levels of corticotrophin-releasing hormone (CRH), which stimulates the pituitary gland to release additional hormones in response to stress. CRH is known to disrupt sleep by stimulating the brain. High CRH levels are correlated with greater difficulty falling asleep and greater time spent in the light stages of NREM sleep, which are the stages where sleep talking occurs (7). Cortisol is another hormone that is released in response to heightened levels of stress. Cortisol has been found to reduce REM sleep, which means that NREM sleep is also extended by this hormone (8). In addition, this hormone has a stimulating effect on the brain, as it increases fast brainwave activity during NREM sleep. Corisol is found in abnormally high levels in insomniacs, which gives it the nickname “the anti-sleep hormone” (9). Adrenaline, which is also released in response to stress, increases the supply of glucose and fatty acids to the blood stream and moves more oxygen-rich blood to the brain (10). By adding more energy supply to the blood and rushing this blood to the brain, adrenaline encourages activity in the brain. This rush of energy may be what stimulates the brain to produce speech.

In addition to increasing light NREM sleep and stimulating the brain, stress may also play a role in reducing the brain’s ability to suppress the release of neurotransmitters involved in motor activity. As the brain is stimulated by cortisol and CRH and energized by adrenaline, perhaps these stimulating effects reduce the brain’s inhibitory abilities. In studies with rats, it has been found that higher levels of acetylcholine, a neurotransmitter that stimulates motor activity, are released from the prefrontal cortex in response to increased stress (11). Thus, while there is not much work in this area, such findings indicate that stress can decrease the brain’s ability to inhibit the release of neurotransmitters responsible for body movements, including the movements of the mouth and tongue involved in producing speech.

Hence, I may have started talking in my sleep in college due to the increased levels of stress I was experiencing. Moreover, both of my roommates told me about my sleep talking during finals week. I first heard about it during the finals week of sophomore spring semester and then again during the finals week of junior fall semester. During other times of the semester, they did not mention my sleep talking, and they told me that I did not talk in my sleep regularly. Thus, the increased stress of finals week may have been what disrupted my sleep cycles and over-stimulated my brain, resulting in sleep talking. Therefore, while sleep talking is more prevalent among young children, it can be triggered in adults by factors that increase later in life, such as stress.









References
1. Talking in Your Sleep, WebMD, http://www.webmd.com/sleep-disorders/talking-in-your-sleep; accessed May 4, 2009

2. Sleep, Encyclopedia Britannica, http://www.britannica.com/EBchecked/topic/548545/sleep/38766/Behavioral-variables#ref=ref423157; accessed May 4, 2009

3. Sleep Stages, Sleep Disorder Channel, http://www.sleepdisorderchannel.com/stages/index.shtml; accessed May 4, 2009

4. REM Behavior Disorder, Sleep Disorder Channel, http://www.sleepdisorderchannel.com/rem/index.shtml; accessed May 4, 2009

5. Changes in Sleep with Age, Healthy Sleep, http://healthysleep.med.harvard.edu/healthy/science/variations/changes-in-sleep-with-age; accessed May 4, 2009

6. Understanding Brain Development in Young Children, North Dakota State University site, http://74.125.47.132/search?q=cache:xLttCx1pOIsJ:www.ag.ndsu.edu/pubs/yf/famsci/fs609w.htm+brain+stem+development+in+children&cd=3&hl=en&ct=clnk&gl=us&client=firefox-a; accessed May 4, 2009

7. Sleep and Stress, The Human Brain by the Franklin Institute, http://www.fi.edu/learn/brain/sleep.html#top; accessed May 4, 2009

8. Lee-Chiong, Teofilo L. Sleep: A Comprehensive Handbook. John Wiley & Sons, Inc, 2006.
http://books.google.com/books?id=aNhAk4knmukC&pg=PA410&lpg=PA410&dq=crh+cortisol+rem&source=bl&ots=fQWbVlZdgI&sig=zYsMhOBUBcY0Y5JE6T1aFM61-Gg&hl=en&ei=JHP_SfL7E4qcMtvouLEE&sa=X&oi=book_result&ct=result&resnum=2#PPA412,M1; accessed May 4, 2009

9. Cortisol: the Anti-Sleep Hormone, Vaxa, http://www.vaxa.com/sleep-cortisol.cfm; accessed May 4, 2009

10. Distress Signals From Your Brain, The Human Brain by the Franklin Institute, http://www.fi.edu/learn/brain/stress.html; accessed May 4, 2009

11. Sex Differences in the Stress-Induced Release of Acetylcholine in the Hippocampus and Corticosterone from the Adrenal Cortex in Rats, Neuroendocrinology, http://content.karger.com/produktedb/produkte.asp?typ=fulltext&file=NEN2003078004234; accessed May 4, 2009

Comments

Paul Grobstein's picture

sleep talking

is interesting in another context as well.  If there is an inactive I-function during non-REM sleep then speech production clearly doesn't depend on the I-function.  

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