Dream-enacting behaviors in REM sleep behavior disorder
It is generally believed that the virtual behaviors we feel ourselves engaging in during dreaming are prevented from any expression in the real world by the inhibitory mechanisms of REM sleep. Without REM sleep muscle atonia, dreamers would disrupt their own sleep by acting out the scenarios in which they seem to speak, act and express their emotions. However, for some REM sleep parasomnias, and for REM sleep behavior disorder (RBD) in particular(Mahowald & Schenck, 2005; Oudiette et al., 2009) (see(Nielsen, 2005) for review), the emotional, verbal and motor components of dreaming are, in fact, acted out on a regular basis and form part of the symptomatology of the disorder. RBD behaviors are distinct from other types of behaviors that have been recorded during REM sleep and that are less obviously associated with dream content, e.g., phasic muscle twitches recordable only from the EMG and gross body movements that are recordable from video or EMG channels. They are also distinct from somnambulistic behaviors that are observed during NREM sleep; the latter may be associated with brief dreams, but these are not typically neither long nor particularly vivid in nature.
Dream-enacting behaviors in popular culture
Dream enacting behaviors are frequently represented in movie depictions of individuals suffering nightmares or other disturbing dreams. Bolting awake from a terrifying dream is a particularly common theme. In fact, among healthy individuals dream-enacting behaviors are usually reported for transitions from dreaming to wakefulness, probably because the behaviors and the dream imagery are most easily recalled right after they occur.
Cinematic representations of dream-enacting behaviors may be rooted in some degree of fact. The behaviors have been reported by healthy individuals in numerous autobiographical accounts and by parents asked to evaluate their children’s sleep.(Fisher et al., 1994) The following dream recorded by U.S. President Barack Obama in his Dreams from my father (1995; p. 372) nicely illustrates an intense nightmare ending with a vigorous dream-enactment (part in bold):
I finally fell asleep, and dreamed I was walking along a village road. Children dressed only in strings of beads played in front of the round huts, and several old men waved to me as I passed. But as I went farther along, I began to notice that people were looking behind me fearfully, rushing into their huts as I passed. I heard the growl of a leopard, and started to run into the forest, tripping over roots and stumps and vines, until at last I couldn't run any longer, and I fell to my knees in the middle of a bright clearing. Panting for breath, I turned around to see the day turned to night, and a giant figure, looming as tall as the trees, wearing only a loincloth and a ghostly mask. The lifeless eyes bored into me, and I heard a thunderous voice saying only that it was time. And my entire body began to shake violently with the sound, as if I were breaking apart...I jerked up in a sweat, hitting my head against the wall lamp that stuck out above the bunk. In the darkness, my heart slowly evened itself, but I couldn't get back to sleep again.(Obama, 1995)
Dream-enacting behaviors in new mothers
We recently discovered (Nielsen & Paquette, 2007) that as many as 63% of new mothers report some form of dream enactment in the first 12 postpartum weeks. We measured body and limb movements, emotional expression (e.g., weeping during a sad dream), and speaking out loud parts of what was spoken in the dream. Behaviors were also found for pregnant women (56%) and controls who had never had children (40%) (see Figure 1).
The following dreams illustrate some of the dream-enactments reported by these women:
First-time mother, 3 weeks postpartum:
Dream: The baby was in my bed and I was looking for him everywhere, but couldn’t find him. I thought he was in my husband’s arms and woke up touching him, looking for the baby. That has happened a dozen times in the last 20 days.
Behaviors: I was looking for my baby in the bed; I touched my husband.
First-time mother, 3 weeks postpartum:
Dream: I dream…I look for the baby and that wakes me up…I realize that he is in his room. I have the pillows in my arms thinking it’s him.
Behaviors: I'm feeling around the sheets.
Second-time mother, 3 weeks postpartum:
Dream: The baby is sleeping with me in my bed. I turn on my side to pick him up but cannot find him. I look under the sheets, begin to wake up and start to realize that it is a dream.
Behaviors: I turned on my side and I felt around in the sheets.
Dream-enacting behaviors in university students
In a subsequent study (Nielsen et al., 2009), we investigated in more detail the prevalence of dream-enacting behaviors in a university student population. We found that dream-enacting behaviors are very prevalent in healthy subjects—over 90% reported at least one—(see Figure 2) and are sensitive to how detailed of a question is used. That is, if examples of dream-enacting behaviors are given, subjects are much more likely to recognize the phenomenon and therefore indicate that they have experienced them.
Figure 2. Prevalence of 7 subtypes of dream-enacting behavior, i.e., % subjects reporting speaking, motor activity, 4 types of emotions and sexual arousal at least rarely in the last year. Somnambulism and somniloquy estimates are presented at right for comparison (from Nielsen, et al., 2009).
Prevalence of dream-enacting behaviours differs with gender (see Figure 3), being more prevalent for all types except sexual arousal dreams, and is independent of other parasomnias like nightmares and sleepwalking. The behaviors resemble those seen routinely in RBD but are much less frequent and severe. However, in some severe nightmares, the associated dream behaviours might be more extreme or cause injuries (see Obama’s nightmare cited earlier).
Figure 3. Gender differences in %subjects reporting dream speaking, motor activity, emotions and sexual arousal “sometimes” or “often.” Females more frequently reported behaviors on all items except sexual arousal, which was characteristic of males (‡P < 0.06; **P < 0.005; ***P < 0.000001; ****P < 0.0000001). Somnambulism and somniloquy did not differentiate the sexes (from Nielsen, et al., 2009).
Dream-enacting behaviors are correlated moderately with the personality trait absorption, which is a disposition to experience focused attention, fantasy, and altered states of consciousness.
Fisher, B. E., McGuire, K., & Honeyman, K. (1994). Relationships between nocturnal activity, parental ratings of daytime activity and measures from the Children's Sleep Behaviour Scale. Canadian Journal of Behavioural Science, 26, 477-483.
Mahowald, M. W. & Schenck, C. H. (2005). REM sleep parasomnias. In M.H.Kryger, T. Roth, & W. C. Dement (Eds.), Principles and practice of sleep medicine (4th ed., pp. 897-916). Philadelphia: Elsevier Saunders.
Nielsen, T. A. (2005). Disturbed dreaming in medical conditions. In M.Kryger, N. Roth, & W. C. Dement (Eds.), Principles and practice of sleep medicine (4th ed., pp. 936-945). Philadelphia: Elsevier Saunders.
Obama, B. (1995). Dreams from my father. A story of race and inheritance. New York: Three Rivers Press.
Oudiette, D., De, C., V, Lavault, S., Leu, S., Vidailhet, M., & Arnulf, I. (2009). Nonviolent elaborate behaviors may also occur in REM sleep behavior disorder. Neurology, 72, 551-557.