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Incorporation of External Stimuli into Dream Content

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Elizaveta Solomonova at McGill University
Elizaveta Solomonova
Michelle Carr at University of Rochester
Michelle Carr
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External stimuli dream content Solomonova & Carr
1
Incorporation of External Stimuli Into Dream Content
Elizaveta Solomonova1 & Michelle Carr2
1Dream and Nightmare Laboratory, Center for Advanced Research in Sleep Medicine; and
Psychiatry Department, McGill University, Montreal, Quebec, Canada
2Sleep Laboratory, Swansea University, Swansea, United Kingdom
To appear in: Dreams: Biology, Psychology and Culture. Valli, K., and Hoss, R. editors.
Greenwood Publishing Group.
Many positions exist about the relationship between the sleeping body and the dreaming
body, and about the extent to which the dreamer is responsive to the outside world.
Phenomenology and recent theories of embodied mind (Varela et al., 1992) suggest that the body
constantly contributes to dream experience, and that being, at the very least implicitly, aware of
the body is crucial for the sense of self.
Sleep is a state of a particular kind of balancing act. On the one hand, it is important to
protect sleep and not to be awakened by every noise, light or touch. On the other hand, the
sleeping individual needs to be responsive enough to the outside world in order to react to
important stimuli, such as sensations that are related to possible danger. Studies using
polysomnography (see chapter 2) show that the sleeping brain reacts to outside stimuli even if
the sleeper does not wake up. Similarly, experimental dream research shows that the sleeper is
responsive to the external world (albeit in an attenuated way), processes environmental and
bodily information during sleep, and that dream content reacts in many ways to somatosensory,
auditory, olfactory and visual stimuli.
External stimuli incorporations
Early dream scholars, such as Alfred Maury and Hervey de Saint-Denys, experimented
with the notion that sensory stimulation during sleep, especially of the somatosensory nature,
incorporates into and changes the dream scenario. One of the most famous examples of that
phenomenon comes from Alfred Maury:
“He dreamed of the Reign of Terror during the [French] Revolution. (…). Finally he himself was
summoned before the Tribunal (….) and was sentenced to death. Accompanied by an enormous crowd, he was led
to the place of execution. He mounted the scaffold; the executioner tied him to the plank, it tipped over, and the
knife of the guillotine fell. He felt his head severed from his trunk, and awakened in terrible anxiety, only to find
that the head-board of the bed had fallen, and had actually struck the cervical vertebrae just where the knife of the
guillotine would have fallen.” (Cited in Freud 1900/2010, pp. 58-59)
External stimuli dream content Solomonova & Carr
2
This dream illustrates vividly the strong effect of a somatosensory sensation (head-board
of the bed falling on his neck) on the dream content. The interesting point here is that the
external stimulus (head-board) gets incorporated into and is contextualized by the dream
(guillotine), rather than appearing as a direct incorporation of a real external object. In another
vivid example, Maury writes of being tickled with a feather in his sleep on his face. This
sensation produced a dream of being tortured: Maury had a mask applied on his face, which was
being peeled off, together with his skin.
Experimental studies of sensory incorporation into dream content are relatively rare. The
typical procedure for stimulus incorporation research is to have a participant sleep in the
laboratory and monitor their brain activity with scalp electrodes. In most studies, a target
stimulus is presented during REM sleep, and the dreamer is then awakened and asked questions
about their experience. Dream reports are subsequently analyzed by researchers for dream
elements that appear to have a relationship to the stimulus. The success rate of stimuli
incorporation ranges from 9% to 87%. This wide range is likely due to differences in the nature
and intensity of a stimulus, and to individual studies’ definition of what counts as stimulus
incorporation. Additionally, sensory incorporation into sleep onset (stage 1 NREM sleep) has
been studied, both with experimental stimulation and as case studies of napping and recording
the relationship between physical sensations/posture and dream content.
Somatosensory incorporations
The most widely studied form of sensory incorporation into dream content is
somatosensory stimulation. This includes putting pressure on body parts, spraying water on the
sleeper, electric stimulation, tensors on skin, rocking in sleep, and manipulation of limb position
in sleep, among other methods. In Tore Nielsen’s laboratory, a method of putting pressure on leg
(above the knee or on an ankle) using a blood-pressure cuff was used in a number of studies
(Nielsen, 1993; Nielsen et al., 1993; Solomonova, 2017). Using this approach, the experimenter
can monitor the sleeper from the control room, and inflate the cuff remotely and gradually, while
monitoring the EEG, so as not to awaken the sleeper. This method produced a variety of creative
ways in which the sleeping mind reacts to somatosensory stimuli. Pressure stimulation
sometimes produces direct and intrusive imagery of either the blood pressure cuff or unpleasant
sensations in the stimulated leg. Sometimes it triggers intensified bodily imagery (such as
paralyzed leg), bizarre and unusual bodily experiences (such as flying or swimming), and, most
intriguingly, projection of bodily imagery onto other dream characters (see Table 1 for
examples). The most striking quality of the incorporation of the somatosensory stimuli is the
variety of ways in which they may change the ongoing dream scenario. Further, these examples
demonstrate that the sleeping body is actively contributing to the dreaming body, albeit in subtle
ways, as opposed to being ‘disconnected’ or inert in sleep.
External stimuli dream content Solomonova & Carr
3
Table 1. Some examples of sensory incorporation
Stimulation type/Sleep
stage and reference
Dream content
Incorporation
quality
Electric stimulation to
the wrist. /REM sleep.
(Koulack, 1969)
"The thought was I felt a pinch in my hand. Electrical impulse.”
Direct incorporation
of the sensation
Somatosensory
stimulation. Inflated
blood pressure cuff on
ankle. /Stage 1 NREM
sleep.
(Solomonova,2017)
“I felt the pressure from the cuff, and all of a sudden I thought about
my cat jumping, because my cat sleeps all the time on my legs.”
A direct
incorporation + an
associative image of
the cat
Somatosensory
stimulation. Inflated
blood pressure cuff on
ankle. /REM sleep.
(Solomonova. 2017)
“Liza was there to wake me up. She turned on the lights and asked me
about my dreams. I was answering her. I could feel the pressure pump
on my leg. She asked me what does it feel like, I said it feels like a hug.
She said: “Doesn’t it feel like someone pulling on your leg?”
A direct
incorporation of the
pressure cuff + a false
awakening and
incorporation of
laboratory personnel
and of a dream
interview
Somatosensory
stimulation. Inflated
blood pressure cuff on
ankle. /REM sleep.
(Solomonova, 2017)
“At first I was flying… there were mountain tops everywhere, there
was snow (…) then I found myself on a boat, it was stormy. I was
holding on to a prow when the boat was tilting, I could touch the water
(…). Suddenly, a dolphin took me and I was swimming on its back.”
An indirect
incorporation:
intensified movement
(boat, tilting, being
carried away)
Somatosensory
stimulation. Inflated
blood pressure cuff on a
leg. / REM sleep.
(Nielsen et al., 1993)
“…the farmer (…) is trying to put a saddle on the horse. (…) At one
point the horse was rolling right across his body. I heard this ‘unnffl’
sound as if it hurt him when it rolled across his legs. (…) He got up and
turned his back on the horse. The horse stood up too. He put the horse's
right hind foot in this suitcase-like thing with a metal box so he
wouldn't stray. (…) I looked … and saw it was not hurting the horse,
just trapping his foot. The horse tried to pull his foot out and follow the
farmer, but he couldn't…”
Projection of the
feeling of pressure on
the leg onto two other
dream characters: the
farmer and the horse
Somatosensory
stimulation. Tensors on
foot. / sleep stage
unknown. (Cubberley,
1923)
“People are dancing on a verandah, which also resembles a lighted
stage. I am watching from B little way off, as if I were a spectator in a
theatre.”
Feeling of something
on the foot
transformed into
dancing imagery
Auditory stimulation.
Name “Richard”. /REM
sleep. (Berger. 1963)
“Had been to a sale in at a big shot at the center of Edinburgh.”
“Richard” – the name
of the shop in
Edinburgh
Dozing while sitting on a
couch near an IKEA cash
register, which abruptly
sounds with a loud
clatter. Auditory. /Stage
1 NREM sleep. (Nielsen,
2017)
“A bright, multi-colored clown/jester suddenly somersaults with a
snapping, elastic motion. His black suit had patches of red, yellow,
green, blue, and other colors.”
A sound triggers a
sudden awakening/
movement in the
dream character
Olfactory stimulation.
/REM sleep. (Schredl et
al., 2009)
“Cleaning a toilet that was full of yellow liquid.”
Strong smell –
imagery that likely
has a strong olfactory
component
External stimuli dream content Solomonova & Carr
4
Auditory stimuli and olfactory stimuli
Even in sleep the mind is continuously monitoring the environment. We get used to loud
noises that we know are not relevant to our sleep (for example, sounds of busy streets), but may
wake up abruptly when we hear our children call us. In other words, personal relevance of the
stimulus appears to matter more than just its intensity. The same holds true for the success rate of
incorporation of sound stimuli into dream content. For example, in one of the earliest laboratory-
based studies, Berger (1963) presented his participants with personally significant names during
REM sleep, and found a high rate of incorporation of these stimuli into dreams. These
incorporations, however, were not necessarily representations of the named individuals (which
also happened on some occasions), rather they were often processed in an associative manner.
For example, the name “Peter” was incorporated as a title of a firm that sounded like
“Portobello”, or hearing a name of a mathematician girlfriend, triggered a mathematics-related
dream content. Hoelscher and colleagues (1981) found that words that have personal importance
for the dreamer have a higher chance of being incorporated into a dream than words that are not
particularly important for that person.
Olfactory stimuli have also been used to study how the sleeping mind reacts to the
outside world. Early dream scholar Hervey de Saint-Denys, for instance, noted that sense of
smell is relatively rare in dreams and in waking memories. However, he noticed that just as
smells often trigger associations with memories and emotions in wake, so in dreams, when one is
exposed to a smell, for example of fireplace smoke, they may dream about a fire station, but not
about the smell itself (Hervey de Saint-Denys, 1867). Experimental studies confirmed his
intuition, for example, Michael Schredl and colleagues (2009) presented their participants with
either a pleasant smell (roses), an unpleasant smell (rotten eggs), or a neutral smell during REM
sleep. These smells did not appear explicitly in the dreams, rather, pleasant smells were
associated with more emotionally positive dreams, and unpleasant smells with more negative
dream experiences. It is unclear why olfactory stimulation in sleep produces almost exclusively
associative changes in dream content (changes in visual and auditory modalities and in emotional
tone), and almost never activates the sense of smell. Research on home dream reports shows that
olfactory sensations are rarely mentioned in dreams: in one study only 1% of over three thousand
dream reports contained smells and tastes (Zadra et al., 1998). It is possible that smells are
processed differently than other sensory modalities in both wake and in sleep: sense of smell has
been linked to memory, emotion, mood, recognition of objects and foods as pleasurable or
repulsive, and so on. Thus, smells may not have independent information, and are rather always
attached to an object or a context, and that quality of odor perception is then manifested in the
effects of olfactory stimulation on dreams.
Visual stimuli
Incorporation of visual stimuli during sleep is harder to study due to the obvious fact that
the dreamer’s eyes are usually closed. In one study, visual stimuli were presented to participants
during REM sleep while their eyes were taped open (Rechtschaffen & Foulkes, 1965). No direct
correspondence was found between the images presented to the sleepers and reported dream
content. It was suggested that the sleeper is “functionally blind” to the external stimulation, and
External stimuli dream content Solomonova & Carr
5
the vivid perception of the dream world effectively overrides the real world’s visual information.
In another study, flashing light stimuli paired with tones were presented in stage 2 NREM sleep
and in REM sleep. Only in NREM sleep did these stimuli produce more visual imagery in the
dream report (Conduit et al., 1997), further suggesting that REM sleep mentation is not sensitive
to visual stimulation.
One profitable avenue for visual stimulation, however, is induction of lucid dreams via
presentation of flashing light stimuli (see chapter 9). LaBerge and Levitan (1995), for example,
report that wearing a LED light-fitted mask, designed to detect rapid eye movements and to send
visual stimuli, alerts the dreamer to the fact that they are currently in the REM sleep state, and
increases incidence of lucid dreaming. In this case, the visual stimuli are strongly incorporated
into the dream, for example, with the whole environment being illuminated by a flashing red
light, or with lightning or a street lamp appearing in a dream.
Why do external stimuli incorporate into dreams?
One explanation for the stimuli incorporation into dreams is that stimulation produces a
micro-arousal, i.e., slightly awakens the dreamer so that they perceive it, but not enough to wake
them up. Thus, the dream continues, but the mind has already registered a stimulus that does not
quite “fit” with the dream. In order to maintain the dream, the stimulus is re-contextualized and
now becomes part of the ongoing narrative. This process is known as multisensory integration
and refers to the mind’s preference for unified perception of the world. When two stimuli of
different modalities coincide, we tend to think they are related. For example, when a sound
appears at the same time as a visual stimulus, we tend to think that the image produced the
sound. Accordingly, when a blood pressure cuff puts pressure on the leg, the dreamer may feel
“stuck”, and that feeling might be translated into seeing a horse trapped by its leg, for example.
The multisensory integration explanation is consistent with recent research, showing that
dreams integrate new memories in an associative manner (Carr & Nielsen, 2015; Horton &
Malinowski, 2015) by activating the larger contextual semantic and episodic networks. This
process may be important for making sense of new experiences. The disruption produced by the
external stimulus thus triggers a variety of memories and the dreaming mind attempts to make
sense of this new event. Thus, a smell may produce a dream with someone grimacing (associated
memories of seeing someone smell something unpleasant) (Schredl et al., 2009), or a feeling of
pressure on an ankle may temporarily transport the dreamer back into her bed and conjure the
image of their cat, who often sleeps on their legs (Solomonova, 2017).
To the best of our knowledge, hypnopedia (sleep learning), at least as presented in
Aldous Huxley’s Brave New World, is not likely to be an efficient way to acquire knowledge.
Still, the relationship between sensations of the sleeping body, dream content and dreamer’s
behaviour can illuminate some of the fundamental aspects concerning dream formation,
contribution of sensory experiences to dream narrative, and information processing in sleep.
External stimuli dream content Solomonova & Carr
6
Summary
Experimental evidence from studies of stimuli incorporation into dream content show
that the sleeping mind is sensitive to the external world. Dreams react in a variety of ways to
sensory stimulation, ranging from direct incorporation of the stimulus into the dream scenario to
indirect effects, such as changes in the emotional tone or in stimulus modality (e.g.
somatosensory into visual). Somatosensory and auditory stimulation seem to be the most
effective in producing different kinds of incorporation, and visual stimulation seems not to have
as much effect on dream content, except for induction of lucid dreams.
References
Berger, R. J. 1963. "Experimental Modification of Dream Content by Meaningful Verbal
Stimuli." Br J Psychiatry 109:722-40.
Carr, M., and T. Nielsen. 2015. "Morning rapid eye movement sleep naps facilitate broad access
to emotional semantic networks." Sleep 38 (3):433-43. doi: 10.5665/sleep.4504.
Conduit, R., D. Bruck, and G. Coleman. 1997. "Induction of visual imagery during NREM
sleep." Sleep 20 (11):948-56.
Cubberley, AJ. 1923. "The effects of tensions of the body surface upon the normal dream."
British Journal of Psychology. General Section 13 (3):243-265.
Hervey de Saint-Denys, L. 1867. Les rêves et les moyens de les diriger. Paris: Amyot.
Hoelscher, T. J., E. Klinger, and S.G. Barta. 1981. "Incorporation of concern-and nonconcern
related verbal stimuli into dream content." Journal of Abnormal Psychology 90 (1):88-
91.
Horton, C. L., and J. E. Malinowski. 2015. "Autobiographical memory and hyperassociativity in
the dreaming brain: implications for memory consolidation in sleep." Front Psychol
6:874. doi: 10.3389/fpsyg.2015.00874.
Koulack, D. 1969. "Effects of somatosensory stimulation on dream content." Arch Gen
Psychiatry 20 (6):718-25.
LaBerge, S., and L. Levitan. 1995. "Validity established of DreamLight cues for eliciting lucid
dreaming." Dreaming 5 (3):159-168.
Nielsen, T. 1993. "Changes in the kinesthetic content of dreams following somatosensory
stimulation of leg muscles during REM sleep." Dreaming 3 (2):99-113.
External stimuli dream content Solomonova & Carr
7
Nielsen, T. 2017. "Microdream neurophenomenology." Neuroscience of Consciousness 3 (1):1-
17. doi: https://doi.org/10.1093/nc/nix001.
Nielsen, T., D. L. McGregor, A. Zadra, D. Ilnicki, and L. Ouellet. 1993. "Pain in dreams." Sleep
16 (5):490-8.
Rechtschaffen, A., and D. Foulkes. 1965. "Effect of Visual Stimuli on Dream Content." Percept
Mot Skills 20:SUPPL:1149-60. doi: 10.2466/pms.1965.20.3c.1149.
Schredl, M., D. Atanasova, K. Hormann, J. T. Maurer, T. Hummel, and B. A. Stuck. 2009.
"Information processing during sleep: the effect of olfactory stimuli on dream content
and dream emotions." J Sleep Res 18 (3):285-90. doi: 10.1111/j.1365-
2869.2009.00737.x.
Solomonova, E. 2017. "Embodied mind in sleep and dreaming: a theoretical framework and an
empirical stidy of sleep, dreams and memory in meditators and controls." PhD,
Biomedical Sciences/Individualized Program, Université de Montréal.
Varela, Francisco J., Evan Thompson, and Eleanor Rosch. 1992. The Embodied Mind: Cognitive
Science and Human Experience. Cambridge: MIT Press.
Zadra, A. L., T. Nielsen, and D. C. Donderi. 1998. "Prevalence of auditory, olfactory, and
gustatory experiences in home dreams." Percept Mot Skills 87 (3 Pt 1):819-26.
... Among the available dream engineering techniques, sensory stimulation protocols seem particularly promising. In fact, while sleep is known to involve some degree of sensory disconnection from the external environment [10], dream modifications caused by sensory perceptions have been documented and even sought after by philosophers, artists, and scientists alike for centuries [11] (see Supplementary Text S1). Nonetheless, a consensus has yet to be reached regarding the underlying mechanisms and functional significance of stimulus-dependent dream changes (SDDCs), defined here as any change in dream features induced by an external stimulus. ...
... Alpha activity Neural oscillations in the frequency range of [8][9][10][11][12] predominantly occipital, typically observed during closed-eye resting wakefulness Arousal threshold The intensity of a stimulus necessary to induce a behavioural response or awakening from sleep. Bottom-up Cognitive or perceptual mechanism in which information is processed starting from sensory input and gradually building up to more complex, higher-level cognitive representations Chemosensory Detection and interpretation of environmental chemical stimuli, namely taste and smell Dream engineering Methods and technologies aimed at influencing and arbitrarily modifying dream experiences to improve sleep, mental well-being, or cognitive processes Exposure therapy Therapeutical technique for the psychological treatment of fear-related issues, based on exposure to the fearinducing stimulus in a safe environment K-complex EEG waveform (0.5-2 Hz) comprising an initial positive bump, followed by a giant negative deflection and a large positive one. ...
Influencing dreams through sensory stimulation: A systematic review
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Full-text available
  • Feb 2024
Sleep is typically considered a state of disconnection from the environment, yet instances of external sensory stimuli influencing dreams have been reported for centuries. Explaining this phenomenon could provide valuable insight into dreams' generative and functional mechanisms, the factors that promote sleep continuity, and the processes that underlie conscious awareness. Moreover, harnessing sensory stimuli for dream engineering could benefit individuals suffering from dream-related alterations. This PRISMA-compliant systematic review assessed the current evidence concerning the influence of sensory stimulation on sleep mentation. We included 51 publications, of which 21 focused on auditory stimulation, ten on somatosensory stimulation, eight on olfactory stimulation, four on visual stimulation, two on vestibular stimulation, and one on multimodal stimulation. Furthermore, nine references explored conditioned associative stimulation: six focused on targeted memory reactivation protocols and three on targeted lucid reactivation protocols. The reported frequency of stimulus-dependent dream changes across studies ranged from 0 to ∼80%, likely reflecting a considerable heterogeneity of definitions and methodological approaches. Our findings highlight a lack of comprehensive understanding of the mechanisms, functions, and neurophysiological correlates of stimulus-dependent dream changes. We suggest that a paradigm shift is required for meaningful progress in this field.
View
... Among the available dream engineering techniques, sensory stimulation protocols seem particularly promising. Indeed, while sleep is known to involve some degree of sensory 'disconnection' from the external environment Koroma et al., 2020;Siclari, 2020), dream modification caused by sensory stimuli appears to be fairly common in physiological conditions (Solomonova & Carr, 2019). Dali's famous painting 'One Second Before Awakening from a Dream Caused by the Flight of a Bee Around a Pomegranate' (1944) is a good example of how the influence of sensory perceptions on the dream world has been documented and even sought after for centuries by artists and scientists (see Appendix A for a brief historical overview of early studies and preliminary findings about this topic). ...
... Furthermore, all bibliographic references from the selected papers were recursively checked for potential inclusion. Previously published non-systematic review papers on the topic of sensory stimulation and dreams (e.g., Arkin & Antrobus, 1991;Schredl & Stuck, 2009;Solomonova & Carr, 2019) were screened for further relevant citations. ...
Influencing dreams through sensory stimulation: a systematic review
Preprint
  • Feb 2023
Sleep is commonly regarded as a state of disconnection from the environment. Yet, instances of external sensory stimuli affecting the course of dreams have been reported for centuries. Importantly, understanding the impact of external stimuli on dreams could shed light on the origin and generation of dreams, the functional mechanisms that preserve sleep continuity, and the processes that underlie conscious awareness. Moreover, the possibility of using sensory stimuli for dream engineering could potentially benefit patients suffering from alterations in the intensity or content of sleep conscious experiences. Here, we performed a systematic review following PRISMA guidelines to evaluate the robustness of the current evidence regarding the influence of external sensory stimulation during sleep on dreams experiences. In a literature search using PsycNET, PubMed, ScienceDirect, and Scopus, we selected any experimental work presenting dream data obtained from a confirmed sleep episode during which visual, auditory, olfactory, gustatory, or somatosensory stimulation was administered. A methodological assessment of the included studies was performed using an adapted version of the Downs and Black’s (1998) checklist. Fifty-one publications met the inclusion criteria, of which 21 reported data related to auditory stimulation, 10 to somatosensory stimulation, 8 to olfactory stimulation, 4 to visual stimulation, 2 to vestibular stimulation, and 1 to multi-modal stimulation (audio-visual). Furthermore, 9 references involved pre-conditioned associative stimulation procedures: 6 relied on targeted memory reactivation protocols and 3 on targeted lucid reactivation protocols. The reported frequency of stimulus-dependent dream changes across studies ranged from 0% to ~90%. Such a variability likely reflects the considerable heterogeneity of experimental and methodological approaches. Overall, the literature analysis identified a lack of substantial understanding of the key mechanisms, functions, and correlates of stimulus-dependent dream changes. We believe that a paradigm shift is required for meaningful and significant advancement in the field. We hope that this review will serve as a starting point for such a shift.
View
... Among the available dream engineering techniques, sensory stimulation protocols seem particularly promising. Indeed, while sleep is known to involve some degree of sensory 'disconnection' from the external environment Koroma et al., 2020;Siclari, 2020), dream modification caused by sensory stimuli appears to be fairly common in physiological conditions (Solomonova & Carr, 2019). Dali's famous painting 'One Second Before Awakening from a Dream Caused by the Flight of a Bee Around a Pomegranate' (1944) is a good example of how the influence of sensory perceptions on the dream world has been documented and even sought after for centuries by artists and scientists (see Appendix A for a brief historical overview of early studies and preliminary findings about this topic). ...
... Furthermore, all bibliographic references from the selected papers were recursively checked for potential inclusion. Previously published non-systematic review papers on the topic of sensory stimulation and dreams (e.g., Arkin & Antrobus, 1991;Schredl & Stuck, 2009;Solomonova & Carr, 2019) were screened for further relevant citations. ...
Influencing dreams through sensory stimulation: a systematic review
Preprint
Full-text available
  • Feb 2023
Sleep is commonly regarded as a state of disconnection from the environment. Yet, instances of external sensory stimuli affecting the course of dreams have been reported for centuries. Importantly, understanding the impact of external stimuli on dreams could shed light on the origin and generation of dreams, the functional mechanisms that preserve sleep continuity, and the processes that underlie conscious awareness. Moreover, the possibility of using sensory stimuli for dream engineering could potentially benefit patients suffering from alterations in the intensity or content of sleep conscious experiences. Here, we performed a systematic review following PRISMA guidelines to evaluate the robustness of the current evidence regarding the influence of external sensory stimulation during sleep on dreams experiences. In a literature search using PsycNET, PubMed, ScienceDirect, and Scopus, we selected any experimental work presenting dream data obtained from a confirmed sleep episode during which visual, auditory, olfactory, gustatory, or somatosensory stimulation was administered. A methodological assessment of the included studies was performed using an adapted version of the Downs and Black's (1998) checklist. Fifty-one publications met the inclusion criteria, of which 21 reported data related to auditory stimulation, 10 to somatosensory stimulation, 8 to olfactory stimulation, 4 to visual stimulation, 2 to vestibular stimulation, and 1 to multi-modal stimulation (audio-visual). Furthermore, 9 references involved pre-conditioned associative stimulation procedures: 6 relied on targeted memory reactivation protocols and 3 on targeted lucid reactivation protocols. The reported frequency of stimulus-dependent dream changes across studies ranged from 0% to ~90%. Such a variability likely reflects the considerable heterogeneity of experimental and methodological approaches. Overall, the literature analysis identified a lack of substantial understanding of the key mechanisms, functions, and correlates of stimulus-dependent dream changes. We believe that a paradigm shift is required for meaningful and significant advancement in the field. We hope that this review will serve as a starting point for such a shift.
View
... We can only speculate whether these incorporations reflect episodic memories of events that had already taken place before unresponsiveness ensued, similar to how dreams collected in an experimental setting frequently reflect sleep laboratory elements, 36 or whether in some cases the incorporations could signify connected consciousness, similar to how dreams can, directly or in an associative manner, reflect stimulus incorporation into contents of consciousness during sleep. 37 Although we have conceptualised memory incorporation as disconnected contents of consciousness, it is possible that these experiences mark continuing integration of stimuli from both external and internal sources, from wakefulness into unresponsiveness. Our evidence suggests that the line between sensory connectedness and disconnectedness is not absolute but gradual, including a grey zone where internally and externally generated experiences become entangled with each other and Table 5 Complexity and modality of experiences in reports from anaesthetic-induced unresponsiveness (Experiment 1) and non-rapid eye movement (NREM) sleep (Experiment 2). ...
Subjective experiences during dexmedetomidine- or propofol-induced unresponsiveness and non-rapid eye movement sleep in healthy male subjects
Article
  • May 2023
  • BRIT J ANAESTH
Background: Anaesthetic-induced unresponsiveness and non-rapid eye movement (NREM) sleep share common neural pathways and neurophysiological features. We hypothesised that these states bear resemblance also at the experiential level. Methods: We compared, in a within-subject design, the prevalence and content of experiences in reports obtained after anaesthetic-induced unresponsiveness and NREM sleep. Healthy males (N=39) received dexmedetomidine (n=20) or propofol (n=19) in stepwise doses to induce unresponsiveness. Those rousable were interviewed and left unstimulated, and the procedure was repeated. Finally, the anaesthetic dose was increased 50%, and the participants were interviewed after recovery. The same participants (N=37) were also later interviewed after NREM sleep awakenings. Results: Most subjects were rousable, with no difference between anaesthetic agents (P=0.480). Lower drug plasma concentrations were associated with being rousable for both dexmedetomidine (P=0.007) and propofol (P=0.002) but not with recall of experiences in either drug group (dexmedetomidine: P=0.543; propofol: P=0.460). Of the 76 and 73 interviews performed after anaesthetic-induced unresponsiveness and NREM sleep, 69.7% and 64.4% included experiences, respectively. Recall did not differ between anaesthetic-induced unresponsiveness and NREM sleep (P=0.581), or between dexmedetomidine and propofol in any of the three awakening rounds (P>0.05). Disconnected dream-like experiences (62.3% vs 51.1%; P=0.418) and memory incorporation of the research setting (88.7% vs 78.7%; P=0.204) were equally often present in anaesthesia and sleep interviews, respectively, whereas awareness, signifying connected consciousness, was rarely reported in either state. Conclusions: Anaesthetic-induced unresponsiveness and NREM sleep are characterised by disconnected conscious experiences with corresponding recall frequencies and content. Clinical trial registration: Clinical trial registration. This study was part of a larger study registered at ClinicalTrials.gov (NCT01889004).
View
... External auditory and somatosensory stimuli are still in fact often heard and felt respectively when dreaming under normal conditions, and can even affect the dream content (Bloxham & Durrant, 2014;Nielsen, 1993;Solomonova & Carr, 2019). For example, recently I was dreaming that I walked near a major street and I then suddenly started to hear the persistent honking of a car horn only to then be awakened by the continual barking of our neighbor's dog while clearly noticing the transition from the dream sound of the honking to the accurately synchronized external sound of the barking. ...
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Full-text available
  • Apr 2023
The NDE OBE Research Project has so far consisted of two phases, and has now examined 252 perceived out-of-body experiences (OBEs) reported by 240 participants. Phase II of the NDE OBE Research Project officially began on October 16, 2020 and ended on December 31, 2021. Its objectives were the same as Phase I: to (1) identify and define differing types of perceived out-of-body experiences (OBEs), and (2) discover the differences and commonalities among them, focusing on any possible catalysts, the event itself, and the process from beginning to end. This retrospective research has been exploratory in nature. This second phase based the primary categorization of perceived OBEs on the experient's condition or state, which included physiologically near-death perceived OBEs (NDOBEs), life-danger perceived OBEs (LDOBEs), life-danger-to-near-death perceived OBEs (LD-NDOBEs), altered-mind perceived OBEs (AMOBEs), and other spontaneous perceived OBEs (OSOBEs). Although the report for the first phase of this research (King, 2021) did not make any conclusions about the possible triggers, catalysts, and/or contributory factors for perceived OBEs that were specifically examined (lack of oxygen, pain/trauma, and substance intake), this second report now suggests that reduction, disruption, or cessation to the body's oxygen supply may be associated in some way with many perceived OBEs. It also acknowledges that this may also be the case with intense pain and/or physical trauma, as well as with substance intake under certain variable conditions for some experients. This second phase of the research also reiterates (as in Phase I) the hypothesis that the primary catalyst for perceived NDOBEs, perceived LDOBEs, and perceived LD-NDOBEs may be an unconscious, adaptive, reactionary process triggered by various psychological and/or physiological stimuli initiating the onset of a nonpathological dissociation or detachment. Furthermore, this second phase has expanded this hypothesis to include some perceived OSOBEs and possibly even some perceived AMOBEs, Additionally, another hypothesis has been offered suggesting that this dissociation in these types of cases is purposeful as either an orienting response to threat/stress and/or to allow for a beneficial absorption, depending on the conditions and circumstances. This research so far has found that there are both commonalities and differences among different types and subtypes of perceived OBEs. This includes the finding that most of the features reported in perceived OBEs that took place during real physiological conditions of near-death were also found in some perceived OBEs in which individuals were not actually near death. In particular, this has included features such as perceptions of seeing one's own physical body, experiencing a lack of pain, feeling a sense of peace, experiencing different perceptions of time, having a visual life review experience (VLRE), seeing perceived-OBE personages, observing a bright light, encountering tunnels, and experiencing a transcendental otherworldly type of environment. In this second phase new dilemmas were also explored and discussed, such as the high report of missing facial features on perceived-OBE personages and incorrect perceptions of the immediate environment during non-transcendental perceived OBEs across all types and subtypes. (This is the final quotable report for Phase II; there are no further forthcoming changes)
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... -Spectral measures: we computed the normalized power spectral densities (PSD) in delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), and gamma (30-45) frequency bands. -Connectivity measures: we computed the weighted symbolic mutual information (wSMI), a functional connectivity measure capturing linear and non-linear coupling between sensors, which relies on the symbolic transformation of the EEG signal. ...
Behavioral and brain responses to verbal stimuli reveal transient periods of cognitive integration of external world in all sleep stages
Preprint
Full-text available
  • May 2022
Sleep has long been considered as a state of disconnection from the environment, with absent reactivity to external stimuli. Here, we questioned this sleep disconnection dogma by directly investigating behavioral responsiveness in 49 napping subjects (27 with narcolepsy and 22 healthy volunteers) engaged in a lexical decision task. Participants were instructed to frown or smile depending on the stimulus type (words vs pseudo-words). We found accurate behavioral responses, visible via contractions of the corrugator or zygomatic muscles, in all sleep stages in both groups (except slow-wave sleep for healthy volunteers). Stimuli presented during states with high (vs. low) values of neural markers indexing rich cognitive states more often yielded responses. Our findings suggest that transient windows of reactivity to external stimuli exist in all sleep stages, even in healthy individuals. Such windows of reactivity could be used to probe sleep-related mental and cognitive processes in real-time across all sleep stages.
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... Another way in which the dreamer's attention may be hijacked or reoriented in the dream, is through incorporation of outside stimuli into dreams. Studies of sensory incorporation into dreams show that the dreaming mind reacts to the physical world in a variety of ways (Nielsen, 1993(Nielsen, , 2017Sauvageau et al., 1998;Schredl et al., 2009;Solomonova & Carr, 2019). Interestingly, stimuli only rarely appear directly in the dream, rather, this new intruding information is often transformed by the dream into something else, which may more or less fit within the ongoing dream scenario. ...
Chapter 7 The Role of Attention and Intention in Dreams
Chapter
Full-text available
  • Feb 2022
In this chapter, we review the different ways that attention works in relation to dreams and how it may function in dreams, and apply the framework of attention, proposed in this volume - as a means of accessing and mediating interactions with the world - to the dreaming world. We first review prior work on the role of attention as 1) access to dreams, e.g., how practices of recording and sharing dreams act as enabling factors for improving dream recall and enhancing richness of dream experience; and as 2) a mediator of dreams, e.g., how incubation, imagery rehearsal, and ultimately lucidity can be cultivated as cognitive skills enabling agency in the dream experience. We propose that attention functions as a constitutive factor in dream experience and that it is a trainable, developmental cognitive skill. We argue that dreams are not simply experiences that happen to the dreamer, rather, through employing attentional techniques in various ways, the dreamer may cultivate different degrees of agency in the dream.
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... External stimuli presented during sleep can infiltrate dream content 1) in non-obvious associative ways (e.g., the smell of roses incites a countryside scene) or 2) in direct ways (e.g., hearing an actual sound) (Schredl et al., 2014;Solomonova & Carr, 2018). ...
Whole-body procedural learning benefits from targeted memory reactivation in REM sleep and task-related dreaming
Article
  • May 2021
  • NEUROBIOL LEARN MEM
Sleep facilitates memory consolidation through offline reactivations of memory traces. Dreaming may play a role in memory improvement and may reflect these memory reactivations. To experimentally address this question, we used targeted memory reactivation (TMR), i.e., application, during sleep, of a stimulus that was previously associated with learning, to assess whether it influences task-related dream imagery. Specifically, we asked if TMR-induced or task-dream reactivations in either slow-wave (SWS) or rapid eye movement (REM) sleep benefit whole-body procedural learning. Healthy participants completed a virtual reality (VR) flying task prior to and following a morning nap or rest period during which task-associated tones were readministered in either SWS, REM sleep, wake or not at all. Findings indicate that learning benefits most from TMR when applied in REM sleep compared to a Control-sleep group. REM dreams that reactivated kinesthetic elements of the VR task (e.g., flying, driving) were also associated with higher improvement on the task than were dreams that reactivated visual elements (e.g., landscapes) or that had no reactivations. TMR did not itself influence dream content but its effects on performance were greater when coexisting with task-dream reactivations in REM sleep. Findings may help explain the mechanistic relationships between dream and memory reactivations and may contribute to the development of sleep-based methods to optimize complex skill learning.
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Perdons-nous vraiment conscience lorsque nous dormons ? Exploration de l’expérience du dormeur dans des modèles d'hypersomnies centrales
Thesis
Full-text available
  • Nov 2020
Les expériences de notre nuit sont souvent décrites comme des îlots d'activité mentale, internement générées dans un océan d'inconscience. En sous-texte de cette vision se cachent deux pré-supposés que le sommeil lent est un modèle d'inconscience et que le traitement sensoriel du monde extérieur en sommeil paradoxal ne peut être qu'inconscient. Dans cette thèse, nous avons voulu tester ces pré-supposés avec une approche empruntant à trois littératures complémentaires : celle de la conscience, celle du sommeil sain et pathologique et celle de la philosophie de l'esprit. Dans une première étude nous avons mis en évidence l'existence de "blackout' de nuit : une absence total de rappel de contenu du couche au lever dans l'hypersomnie Idiopathique. Nous pensons que notre démonstration de l'existence du phénomène de blackout est intéressante car elle permet, par contraste, de mettre en évidence l'existence d'une expérience minimale de la nuit, comme les philosophes l'avaient suggéré. Dans deux autres études nous avons montré la capacité de patients narcoleptiques (lucides ou non) à traiter l'extérieur pendant des siestes en utilisant comme réponses les muscles de leurs visages. Cela suggère qu'un traitement conscient dans le sommeil peut avoir lieu en sommeil paradoxal chez ces patients. L'ensemble de ce travail de thèse invite à penser que l'idée selon laquelle on perd conscience pendant que l'on dort serait à réévaluer. En effet, une réelle perte de conscience dans le sommeil, si elle existe, pourrait être plutôt transitoire et négligeable face à la fabuleuse pluralité des processus qui se déroulent en son sein.
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Autobiographical memory and hyperassociativity in the dreaming brain: implications for memory consolidation in sleep
Article
Full-text available
  • Jul 2015
In this paper we argue that autobiographical memory (AM) activity across sleep and wake can provide insight into the nature of dreaming, and vice versa. Activated memories within the sleeping brain reflect one’s personal life history (autobiography). They can appear in largely fragmentary forms and differ from conventional manifestations of episodic memory. Autobiographical memories in dreams can be sampled from non-REM as well as REM periods, which contain fewer episodic references and become more bizarre across the night. Salient fragmented memory features are activated in sleep and re-bound with fragments not necessarily emerging from the same memory, thus de-contextualizing those memories and manifesting as experiences that differ from waking conceptions. The constructive nature of autobiographical recall further encourages synthesis of these hyper-associated images into an episode via recalling and reporting dreams. We use a model of AM to account for the activation of memories in dreams as a reflection of sleep-dependent memory consolidation processes. We focus in particular on the hyperassociative nature of AM during sleep.
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Validity Established of DreamLight Cues for Eliciting Lucid Dreaming
Article
Full-text available
  • Sep 1995
Lucid dreaming is a learnable, but difficult skill. Consequently, we have sought methods for helping dreamers to realize that they are dreaming by means of external cues applied during REM sleep, which if incorporated into dreams, can remind dreamers that they are dreaming. Here we report on an experiment testing the validity and effectiveness of a portable computerized biofeedback device (DreamLight®) designed to deliver light cues during REM sleep. The 14 subjects used DreamLights on 4 to 24 nights. They were unaware that the DreamLights were specially programmed to deliver cues only on alternate nights. Eleven subjects reported 32 lucid dreams, 22 from nights with light cues, 10 from nights without cues. All lucid dreams scored (by judges blind to DreamLight condition) as being "cued" by the DreamLight’s stimuli occurred on nights when the DreamLight was actually delivering cues. Subjects reported seeing in their dreams what they believed to be DreamLight cues significantly more often on light cue nights (73 total) compared to nights without light cues (9). The conclusion is that cueing with sensory stimuli by the DreamLight appears to increase a subject’s probability of having lucid dreams, and that most of the resulting lucid dreams are due to the specific effect of light cues rather than general "placebo" factors.
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Changes in the Kinesthetic Content of Dreams Following Somatosensory Stimulation of Leg Muscles During REM Sleep
Article
Full-text available
  • Jun 1993
The notion that dreaming is isolated from sensory activity is challenged by demonstrations that somatosensory stimuli are frequently incorporated into dream content. To further study such effects, four volunteers were administered pressure stimulation to either the left or the right leg during REM sleep and awakened to report their dreams. These dreams were rated and compared to non-stimulated dreams. Stimulated dreams more frequently contained leg sensations and references to the pressure stimulus than did non-stimulated dreams; dreamed leg activity, but not dreamed arm activity, was also rated as more intense. Incorporations of the stimulus were typically simple, direct kinesthetic sensations of pressure or squeezing but were also sometimes embedded in more extended ‘problem-solving’ sequences. Stimulation also increased bodily bizarreness. The latter included changes in kinesthetic quality of movement, instabilities of posture and the environment, as well as visual-kinesthetic synthesias. Although micro-arousals may be an explanatory factor, the results suggest that somatosensory stimulation influences ‘kinesthetic fantasy’, a dimension of dreaming associated with both central and peripheral sources of kinesthetic activity.
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Information processing during sleep: The effect of olfactory stimuli on dream content and dream emotions
Article
Full-text available
  • Jul 2009
  • J SLEEP RES
Research has shown that external stimuli presented during sleep can affect dream content, thus reflecting information processing of the sleeping brain. Olfactory stimuli should have a stronger effect on dream emotions because their processing is linked directly to the limbic system. Because selective olfactory stimulation does not increase arousal activity, intense olfactory stimulation is therefore a prime paradigm for studying information processing during sleep. Fifteen healthy, normosmic volunteers were studied by intranasal chemosensory stimulation during rapid eye movement sleep based on air-dilution olfactometry. For olfactory stimulation, hydrogen sulphide (smell of rotten eggs) and phenyl ethyl alcohol (smell of roses) was used and compared with a control condition without stimulation. The olfactory stimuli affected significantly the emotional content of dreams: the positively toned stimulus yielded more positively toned dreams, whereas the negative stimulus was followed by more negatively toned dreams. Direct incorporations, i.e. the dreamer is smelling something, were not found. The findings indicate that information processing of olfactory stimuli is present in sleep and that the emotional tone of dreams can be influenced significantly depending upon the hedonic characteristic of the stimulus used. It would be interesting to conduct learning experiments (associating specific odours with declarative material) to study whether this declarative material is incorporated into subsequent dreams if the corresponding odour cue is presented during sleep. It would also be interesting to study the effect of positively toned olfactory stimuli on nightmares.
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Microdream neurophenomenology
Article
  • Mar 2017
Nightly transitions into sleep are usually uneventful and transpire in the blink of an eye. But in the laboratory these transitions afford a unique view of how experience is transformed from the perceptually grounded consciousness of wakefulness to the hallucinatory simulations of dreaming. The present review considers imagery in the sleep-onset transition—“microdreams” in particular—as an alternative object of study to dreaming as traditionally studied in the sleep lab. A focus on microdream phenomenology has thus far proven fruitful in preliminary efforts to (i) develop a classification for dreaming’s core phenomenology (the “oneiragogic spectrum”), (ii) establish a structure for assessing dreaming’s multiple memory inputs (“multi-temporal memory sources”), (iii) further Silberer’s project for classifying sleep-onset images in relation to waking cognition by revealing two new imagery types (“autosensory imagery,” “exosensory imagery”), and (iv) embed a potential understanding of microdreaming processes in a larger explanatory framework (“multisensory integration approach”). Such efforts may help resolve outstanding questions about dream neurophysiology and dreaming’s role in memory consolidation during sleep but may also advance discovery in the neuroscience of consciousness more broadly.
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Morning REM Sleep Naps Facilitate Broad Access to Emotional Semantic Networks
Article
  • Nov 2014
The goal of the study was to assess semantic priming to emotion and nonemotion cue words using a novel measure of associational breadth for participants who either took rapid eye movement (REM) or nonrapid eye movement (NREM) naps or who remained awake; assess relation of priming to REM sleep consolidation and REM sleep inertia effects. The associational breadth task was applied in both a priming condition, where cue-words were signaled to be memorized prior to sleep (primed), and a nonpriming condition, where cue words were not memorized (nonprimed). Cue words were either emotional (positive, negative) or nonemotional. Participants were randomly assigned to either an awake (WAKE) or a sleep condition, which was subsequently split into NREM or REM groups depending on stage at awakening. Hospital-based sleep laboratory. Fifty-eight healthy participants (22 male) ages 18 to 35 y (Mage = 23.3 ± 4.08 y). The REM group scored higher than the NREM or WAKE groups on primed, but not nonprimed emotional cue words; the effect was stronger for positive than for negative cue words. However, REM time and percent correlated negatively with degree of emotional priming. Priming occurred for REM awakenings but not for NREM awakenings, even when the latter sleep episodes contained some REM sleep. Associational breadth may be selectively consolidated during REM sleep for stimuli that have been tagged as important for future memory retrieval. That priming decreased with REM time and was higher only for REM sleep awakenings is consistent with two explanatory REM sleep processes: REM sleep consolidation serving emotional downregulation and REM sleep inertia. © 2014 Associated Professional Sleep Societies, LLC.
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