Olfaction modulates cortical arousal independent of perceived odor intensity and pleasantness

Throughout history, various odors have been harnessed to invigorate or relax the mind. The mechanisms underlying odors' diverse arousal effects remain poorly understood. We conducted five experiments (184 participants) to investigate this issue, using pupillometry, electroencephalography, and the attentional blink paradigm, which exemplifies the limit in attentional capacity. Results demonstrated that exposure to citral, compared to vanillin, enlarged pupil size, reduced resting-state alpha oscillations and alpha network efficiency, augmented beta-gamma oscillations, and enhanced the coordination between parietal alpha and frontal beta-gamma activities. In parallel, it attenuated the attentional blink effect. These effects were observed despite citral and vanillin being comparable in perceived odor intensity, pleasantness, and nasal pungency, and were unlikely driven by semantic biases. Our findings reveal that odors differentially alter the small-worldness of brain network architecture, and thereby brain state and arousal. Furthermore, they establish arousal as a unique dimension in olfactory space, distinct from intensity and pleasantness.

Enhancing and advancing the understanding and study of dreaming and memory consolidation: Reflections, challenges, theoretical clarity, and methodological considerations

Empirical investigations that search for a link between dreaming and sleep-dependent memory consolidation have focused on testing for an association between dreaming of what was learned, and improved memory performance for learned material. Empirical support for this is mixed, perhaps owing to the inherent challenges presented by the nature of dreams, and methodological inconsistencies. The purpose of this paper is to address critically prevalent assumptions and practices, with the aim of clarifying and enhancing research on this topic, chiefly by providing a theoretical synthesis of existing models and evidence. Also, it recommends the method of Targeted Memory Reactivation (TMR) as a means for investigating if dream content can be linked to specific cued activations. Other recommendations to enhance research practice and enquiry on this subject are also provided, focusing on the HOW and WHY we search for memory sources in dreams, and what purpose (if any) they might serve.

Impact of Pre-Sleep Visual Media Exposure on Dreams: A Scoping Review

A body of experimental research has aimed to investigate processes underlying dream formation by examining the effects of a range of pre-sleep stimuli and events on subsequent dream content. Given its ever-growing presence and salience in people's everyday lives, pre-sleep media consumption stands out as a key variable that could influence people's dreams. We conducted a scoping review to evaluate the experimental evidence of the effects of pre-sleep exposure to visual media on dream content. A systematic search on PubMed, PsycInfo, and Web of Science using terms related to moving visual media and dreams yielded 29 studies meeting the inclusion criteria. Overall, we found modest yet varied effects of pre-sleep exposure to visual media on dream content, with rates of stimulus-related incorporation ranging from 3% to 43% for REM dream reports, 4% to 30% for NREM sleep mentation reports, and between 11% and 35% for home dream reports. Our review highlights the large methodological heterogeneity and gaps across studies, the general difficulty in influencing dream content using pre-sleep exposure to visual media, and suggests promising venues for future research to advance our understanding of how and why digital media may impact people's dreams.

Nocturnal exposure to a preferred ambient scent does not affect dream emotionality or post-sleep core affect valence in young adults

Emotions experienced within sleep mentation (dreaming) affect mental functioning in waking life. There have been attempts at enhancing dream emotions using olfactory stimulation. Odors readily acquire affective value, but to profoundly influence emotional processing, they should bear personal significance for the perceiver rather than be generally pleasant. The main objective of the present sleep laboratory study was to examine whether prolonged nocturnal exposure to self-selected, preferred ambient room odor while asleep influences emotional aspects of sleep mentation and valence of post-sleep core affect. We asked twenty healthy participants (12 males, mean age 25 ± 4 years) to pick a commercially available scented room diffuser cartridge that most readily evoked positively valenced mental associations. In weekly intervals, the participants attended three sessions. After the adaptation visit, they were administered the odor exposure and odorless control condition in a balanced order. Participants were awakened five minutes into the first rapid eye movement (REM) stage that took place after 2:30 a.m. and, if they had been dreaming, they were asked to rate their mental sleep experience for pleasantness, emotional charge, and magnitude of positive and negative emotions and also to evaluate their post-sleep core affect valence. With rs < 0.20, no practically or statistically significant differences existed between exposure and control in any outcome measures. We conclude that in young, healthy participants, the practical value of olfactory stimulation with self-selected preferred scents for enhancement of dream emotions and post-sleep core affect valence is very limited.

Influencing dreams through sensory stimulation: A systematic review

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.

Study protocol: Cerebral characterization of sensory gating in disconnected dreaming states during propofol anesthesia using fMRI

Background

Disconnected consciousness describes a state in which subjective experience (i.e., consciousness) becomes isolated from the external world. It appears frequently during sleep or sedation, when subjective experiences remain vivid but are unaffected by external stimuli. Traditional methods of differentiating connected and disconnected consciousness, such as relying on behavioral responsiveness or on post-anesthesia reports, have demonstrated limited accuracy: unresponsiveness has been shown to not necessarily equate to unconsciousness and amnesic effects of anesthesia and sleep can impair explicit recollection of events occurred during sleep/sedation. Due to these methodological challenges, our understanding of the neural mechanisms underlying sensory disconnection remains limited.

Methods

To overcome these methodological challenges, we employ a distinctive strategy by combining a serial awakening paradigm with auditory stimulation during mild propofol sedation. While under sedation, participants are systematically exposed to auditory stimuli and questioned about their subjective experience (to assess consciousness) and their awareness of the sounds (to evaluate connectedness/disconnectedness from the environment). The data collected through interviews are used to categorize participants into connected and disconnected consciousness states. This method circumvents the requirement for responsiveness in assessing consciousness and mitigates amnesic effects of anesthesia as participants are questioned while still under sedation. Functional MRI data are concurrently collected to investigate cerebral activity patterns during connected and disconnected states, to elucidate sensory disconnection neural gating mechanisms. We examine whether this gating mechanism resides at the thalamic level or results from disruptions in information propagation to higher cortices. Furthermore, we explore the potential role of slow-wave activity (SWA) in inducing disconnected consciousness by quantifying high-frequency BOLD oscillations, a known correlate of slow-wave activity.

Discussion

This study represents a notable advancement in the investigation of sensory disconnection. The serial awakening paradigm effectively mitigates amnesic effects by collecting reports immediately after regaining responsiveness, while still under sedation. Ultimately, this research holds the potential to understand how sensory gating is achieved at the neural level. These biomarkers might be relevant for the development of sensitive anesthesia monitoring to avoid intraoperative connected consciousness and for the assessment of patients suffering from pathologically reduced consciousness.

Clinical trial registration

European Union Drug Regulating Authorities Clinical Trials Database (EudraCT), identifier 2020-003524-17.

What is sleep exactly? Global and local modulations of sleep oscillations all around the clock

Wakefulness, non-rapid eye-movement (NREM) and rapid eye-movement (REM) sleep differ from each other along three dimensions: behavioral, phenomenological, physiological. Although these dimensions often fluctuate in step, they can also dissociate. The current paradigm that views sleep as made of global NREM and REM states fail to account for these dissociations. This conundrum can be dissolved by stressing the existence and significance of the local regulation of sleep. We will review the evidence in animals and humans, healthy and pathological brains, showing different forms of local sleep and the consequences on behavior, cognition, and subjective experience. Altogether, we argue that the notion of local sleep provides a unified account for a host of phenomena: dreaming in REM and NREM sleep, NREM and REM parasomnias, intrasleep responsiveness, inattention and mind wandering in wakefulness. Yet, the physiological origins of local sleep or its putative functions remain unclear. Exploring further local sleep could provide a unique and novel perspective on how and why we sleep.

Subjectively intense odor does not affect dream emotions during rapid eye movement sleep

Dreams experienced during rapid eye movement (REM) sleep have emotional features. Intervention methods for dream affectivity have recently garnered interest; we previously demonstrated that negative dreams were induced during REM sleep by exposure to favorable or familiar odors. However, the underlying mechanisms behind this phenomenon remain unclear. Thus, to address this gap, we investigated whether more intense odors could induce negative dreams, as odors tend to be perceived as more intense when they are preferred or familiar. Contrary to our hypothesis, the results of our study indicated that subjective intense odors did not induce negative dreams. We initially anticipated stronger odors to have a greater impact on dream emotionality, as they stimulate the brain more intensely. Notably, during arousal, weak odors tended to evoke a more potent olfactory response, while strong odors tended to produce a weaker response. To investigate whether this difference influenced the effects on dreams, we compared the respiratory activities of the strongly and weakly perceived odor groups; however, no significant differences were observed. Our findings suggest that subjectively perceived strong odors are unlikely to affect dream emotionality and may be processed differently than favorable or familiar odors.

Sleep and dreaming in the light of reactive and predictive homeostasis

Dreams are often viewed as fascinating but irrelevant mental epihenomena of the sleeping mind with questionable functional relevance. Despite long hours of oneiric activity, and high individual differences in dream recall, dreams are lost into oblivion. Here, we conceptualize dreaming and dream amnesia as inherent aspects of the reactive and predictive homeostatic functions of sleep. Mental activity during sleep conforms to the interplay of restorative processes and future anticipation, and particularly during the second half of the night, it unfolds as a special form of non-constrained, self-referent, and future-oriented cognitive process. Awakening facilitates constrained, goal-directed prospection that competes for shared neural resources with dream production and dream recall, and contributes to dream amnesia. We present the neurophysiological aspects of reactive and predictive homeostasis during sleep, highlighting the putative role of cortisol in predictive homeostasis and forgetting dreams. The theoretical and methodological aspects of our proposal are discussed in relation to the study of dreaming, dream recall, and sleep-related cognitive processes.

Reciprocal relationships between sleep and smell

Despite major anatomical differences with other mammalian sensory systems, olfaction shares with those systems a modulation by sleep/wake states. Sleep modulates odor sensitivity and serves as an important regulator of both perceptual and associative odor memory. In addition, however, olfaction also has an important modulatory impact on sleep. Odors can affect the latency to sleep onset, as well as the quality and duration of sleep. Olfactory modulation of sleep may be mediated by direct synaptic interaction between the olfactory system and sleep control nuclei, and/or indirectly through odor modulation of arousal and respiration. This reciprocal interaction between sleep and olfaction presents novel opportunities for sleep related modulation of memory and perception, as well as development of non-pharmacological olfactory treatments of simple sleep disorders.

Effects of odors on sleep quality in 139 healthy participants

The present study aimed to systematically examine whether laurinal, orange odor, and a specifically designed "perfume" influence sleep quality. During sleep, healthy participants (n = 139) were presented with odor or no odor through nose clips for fourteen consecutive nights (phase one). We collected physiological parameters together with subjective reports. Later on, longer lasting effects of this manipulation were examined for the following fourteen nights (phase two) without exposition to odors. Additionally, olfactory, cognitive and non-cognitive measures were conducted before phase one, between both phases and after phase two. One-way analyses of variance for repeated measures with nights and condition (1 vs 2) as the within-subject factor and odor condition (0, 1, 2 or 3) together with odor pleasantness rating as between-subject factor, was employed to analyse data. Overall, the present results demonstrated that the odor condition in comparison to control had no consistent effect on sleep in healthy participants which can be possibly explained by exposure to odors via nose clips. However, the analyses indicated that the individual pleasantness of odors enhanced the positive assessment of sleep quality. Altogether, the present results indicate that the subjective perception of an odor's hedonic value appears to be crucial for sleep quality, not the odors themselves.

Do you remember if you have olfactory dreams? A content analysis of LOFTER and a questionnaire survey conducted in China

OBJECTIVES

Dreams often involve visual and auditory sensations, but olfactory experiences have not received the same amount of attention. This study explores the prevalence and content of olfactory dreams in China and investigates the relationship between olfactory imagery, olfactory significance, and olfactory dreamers.

METHODS

In the first part of the study, 4302 dream records from LOFTER were screened and classified to preliminarily identify the prevalence and content of olfactory dreams. In the second part, 718 participants completed an online questionnaire about olfactory dreams, imagery, and significance.

RESULTS

The prevalence of olfactory dreams in the diary dream entries and questionnaire survey participants were 3.95% and 18.70%, respectively. Instances in which odors appeared in dreams were more positive than negative and were mainly related to food, burning and smoke, body odor, nature, and certain environments and objects. Moreover, individuals with olfactory dreams showed better olfactory imagery, and stronger olfactory significance.

CONCLUSIONS

Olfactory sensations occurred in the dreams of Chinese individuals, but their prevalence was very low. Most of the odors that emerged in these dreams were ones that the dreamers were familiar with in their daily lives.

The vision of dreams: from ontogeny to dream engineering in blindness

The mechanisms involved in the origin of dreams remain one of the great unknowns in science. In the 21st century, studies in the field have focused on 3 main topics: functional networks that underlie dreaming, neural correlates of dream contents, and signal propagation. We review neuroscientific studies about dreaming processes, focusing on their cortical correlations. The involvement of frontoparietal regions in the dream-retrieval process allows us to discuss it in light of the Global Workspace theory of consciousness. However, dreaming in distinct sleep stages maintains relevant differences, suggesting that multiple generators are implicated. Then, given the strong influence of light perception on sleep regulation and the mostly visual content of dreams, we investigate the effect of blindness on the organization of dreams. Blind individuals represent a worthwhile population to clarify the role of perceptual systems in dream generation, and to make inferences about their top-down and/or bottom-up origin. Indeed, congenitally blind people maintain the ability to produce visual dreams, suggesting that bottom-up mechanisms could be associated with innate body schemes or multisensory integration processes. Finally, we propose the new dream-engineering technique as a tool to clarify the mechanisms of multisensory integration during sleep and related mental activity, presenting possible implications for rehabilitation in sensory-impaired individuals. The Theory of Proto-consciousness suggests that the interaction of brain states underlying waking and dreaming ensures the optimal functioning of both. Therefore, understanding the origin of dreams and capabilities of our brain during a dreamlike state, we could introduce it as a rehabilitative tool.

CITATION

Vitali H, Campus C, De Giorgis V, Signorini S, Gori M. The vision of dreams: from ontogeny to dream engineering in blindness. J Clin Sleep Med. 2022;18(8):2051-2062.

Essential Oils, Phytoncides, Aromachology, and Aromatherapy—A Review

Chemical compounds from plants have been used as a medicinal source for various diseases. Aromachology is a unique field that studies the olfactory effects after inhaling aromatic compounds. Aromatherapy is a complementary treatment methodology involving the use of essential oils containing phytoncides and other volatile organic compounds for various physical and mental illnesses. Phytoncides possess an inherent medicinal property. Their health benefits range from treating stress, immunosuppression, blood pressure, respiratory diseases, anxiety, and pain to anti-microbial, anti-larvicidal, anti-septic, anti-cancer effects, etc. Recent advancements in aromatherapy include forest bathing or forest therapy. The inhalation of phytoncide-rich forest air has been proven to reduce stress-induced immunosuppression, normalize immune function and neuroendocrine hormone levels, and, thus, restore physiological and psychological health. The intricate mechanisms related to how aroma converts into olfactory signals and how the olfactory signals relieve physical and mental illness still pose enormous questions and are the subject of ongoing research. Aromatherapy using the aroma of essential oils/phytoncides could be more innovative and attractive to patients. Moreover, with fewer side effects, this field might be recognized as a new field of complementary medicine in alleviating some forms of physical and mental distress. Essential oils are important assets in aromatherapy, cosmetics, and food preservatives. The use of essential oils as an aromatherapeutic agent is widespread. Detailed reports on the effects of EOs in aromatherapy and their pharmacological effects are required to uncover its complete biological mechanism. This review is about the evolution of research related to phytoncides containing EOs in treating various ailments and provides comprehensive details from complementary medicine.

What about dreams? State of the art and open questions

Several studies have tried to identify the neurobiological bases of dream experiences, nevertheless some questions are still at the centre of the debate. Here, we summarise the main open issues concerning the neuroscientific study of dreaming. After overcoming the rapid eye movement (REM) ‐ non‐REM (NREM) sleep dichotomy, investigations have focussed on the specific functional or structural brain features predicting dream experience. On the one hand, some results underlined that specific trait‐like factors are associated with higher dream recall frequency. On the other hand, the electrophysiological milieu preceding dream report upon awakening is a crucial state‐like factor influencing the subsequent recall. Furthermore, dreaming is strictly related to waking experiences. Based on the continuity hypothesis, some findings reveal that dreaming could be modulated through visual, olfactory, or somatosensory stimulations. Also, it should be considered that the indirect access to dreaming remains an intrinsic limitation. Recent findings have revealed a greater concordance between parasomnia‐like events and dream contents. This means that parasomnia episodes might be an expression of the ongoing mental sleep activity and could represent a viable direct access to dream experience. Finally, we provide a picture on nightmares and emphasise the possible role of oneiric activity in psychotherapy. Overall, further efforts in dream science are needed (a) to develop a uniform protocol to study dream experience, (b) to introduce and integrate advanced techniques to better understand whether dreaming can be manipulated, (c) to clarify the relationship between parasomnia events and dreaming, and (d) to determine the clinical valence of dreams.

Olfaction-Related Factors Affecting Chemosensory Dream Content in a Sleep Laboratory

Mental activity in sleep often involves visual and auditory content. Chemosensory (olfactory and gustatory) experiences are less common and underexplored. The aim of the study was to identify olfaction-related factors that may affect the occurrence of chemosensory dream content. Specifically, we investigated the effects of all-night exposure to an ambient odour, participants' appraisal of their current olfactory environment, their general propensity to notice odours and act on them (i.e., odour awareness), and their olfactory acuity. Sixty pre-screened healthy young adults underwent olfactory assessment, completed a measure of odour awareness, and spent three nights in weekly intervals in a sleep laboratory. The purpose of the first visit was to adapt to the experimental setting. On the second visit, half of them were exposed to the smell of vanillin or thioglycolic acid and the other half to an odourless control condition. On the third visit, they received control or stimulation in a balanced order. On each visit, data were collected twice: once from the first rapid eye movement (REM) stage that occurred after 3 a.m., and then shortly before getting up, usually from a non-REM stage. Participants were asked to report the presence of sensory dream content and to assess their current olfactory environment. Neither exposure, nor participants' assessments of the ambient odour, or olfactory acuity affected reports of chemosensory dream content but they were more frequent in individuals with greater odour awareness. This finding may have implications for treatment when such experiences become unwanted or bothersome.

Effect of Rosa damascena on improvement of adults' sleep quality: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Recent studies have reported inconclusive results regarding the potential effects of Rosa damascena on sleep quality. Therefore, this review aimed to summarize the findings of parallel-group and cross-over randomized controlled trials (RCTs) on the effects of aromatherapy and oral intake of Rosa damascena on adults' sleep quality.

METHODS

The electronic data sources of PubMed, Scopus, Web of Science Core Collection, Embase, CENTRAL, ProQuest, CINAHL, SID, and MagIran were searched from inception to June 30, 2021. Out of 1341 publications found in the initial search, 10 RCTs were considered eligible for this review. The Cochrane risk-of-bias assessment tool was used to evaluate the risk of bias. Sufficient data were statistically pooled by a random-effects model using Stata software (version 11.2); otherwise, a narrative summary was presented.

RESULTS

Based on the systematic review, the inhalation and oral intake of Rosa damascena could improve some sleep-related outcomes. The pooled analysis of seven effect sizes revealed that inhalation aromatherapy with Rosa damascena significantly improved sleep quality (standardized mean difference: 2.24; 95% confidence interval: 1.01-3.48; P < 0.001). Most RCTs had fair methodological quality, and two RCTs reported the adverse effects of treatment, including headache, nausea, vomiting, and frequent sneezing.

CONCLUSIONS

The administration of Rosa damascena seems to be a promising approach in complementary and alternative medicine for the improvement of adults' sleep quality. However, considering the fair methodological quality of most RCTs and reported adverse effects, it is required to perform further high-quality RCTs to draw an evidence-based conclusion on the use of Rosa damascena for the improvement of adults' sleep quality.

PROSPERO NO

CRD42020211778.

Whole-body procedural learning benefits from targeted memory reactivation in REM sleep and task-related dreaming

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 (or task-dream reactivations). Specifically, we asked if TMR 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, accelerating) 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.

Investigation on Neurobiological Mechanisms of Dreaming in the New Decade

Dream research has advanced significantly over the last twenty years, thanks to the new applications of neuroimaging and electrophysiological techniques. Many findings pointed out that mental activity during sleep and wakefulness shared similar neural bases. On the other side, recent studies have highlighted that dream experience is promoted by significant brain activation, characterized by reduced low frequencies and increased rapid frequencies. Additionally, several studies confirmed that the posterior parietal area and prefrontal cortex are responsible for dream experience. Further, early results revealed that dreaming might be manipulated by sensory stimulations that would provoke the incorporation of specific cues into the dream scenario. Recently, transcranial stimulation techniques have been applied to modulate the level of consciousness during sleep, supporting previous findings and adding new information about neural correlates of dream recall. Overall, although multiple studies suggest that both the continuity and activation hypotheses provide a growing understanding of neural processes underlying dreaming, several issues are still unsolved. The impact of state-/trait-like variables, the influence of circadian and homeostatic factors, and the examination of parasomnia-like events to access dream contents are all opened issues deserving further deepening in future research.

A pilot study on essential oil aroma stimulation for enhancing slow-wave EEG in sleeping brain

Sleep quality is important to health and life quality. Lack of sleep can lead to a variety of health issues and reduce in daytime function. Recent study by Fultz et al. also indicated that sleep is crucial to brain metabolism. Delta power in sleep EEG often indicates good sleep quality while alpha power usually indicates sleep interruptions and poor sleep quality. Essential oil has been speculated to improve sleep quality. Previous studies also suggest essential oil aroma may affect human brain activity when applied awake. However, those studies were often not blinded, which makes the effectiveness and mechanism of aroma a heavily debated topic. In this study, we aim to explore the effect of essential oil aroma on human sleep quality and sleep EEG in a single-blinded setup. The aroma was released when the participants are asleep, which kept the influence of psychological expectation to the minimum. We recruited nine young, healthy participants with regular lifestyle and no sleep problem. All participants reported better sleep quality and more daytime vigorous after exposing to lavender aroma in sleep. We also observed that upon lavender aroma releases, alpha wave in wake stage was reduced while delta wave in slow-wave sleep (SWS) was increased. Lastly, we found that lavender oil promote occurrence of SWS. Overall, our study results show that essential oil aroma can be used to promote both subjective and objective sleep quality in healthy human subjects. This makes aroma intervention a potential solution for poor sleep quality and insomnia.

Effects of all-night exposure to ambient odour on dreams and affective state upon waking

Previous laboratory research has shown that exposure to odours of contrasting pleasantness during sleep differentially affects the emotional tone of dreams. In the present study, we sought to investigate how a generally pleasant (vanillin) and unpleasant (thioglycolic acid [TGA]) smell influenced various dream characteristics, dream emotions, and post-sleep core affect during all-night exposure, controlling for appraisal of the olfactory environment during the assessments and sleep stage from which the participants woke up. We expected that exposure to vanillin would result in more pleasant dreams, more positive and less negative dream emotions, and a more positive post-sleep core affect compared to the control condition, whereas exposure to TGA would have the opposite effect. Sixty healthy volunteers (36 males, mean age 24 ± 4 years) were invited to visit the sleep laboratory three times in weekly intervals. The first visit served to adapt the participants to the laboratory environment. On the second visit, half the participants were exposed to an odour (vanillin or TGA, 1:1) and the other half to the odourless control condition. On the third visit, they received control or exposure in a balanced order. On each visit, the participants woke up twice, first from the rapid eye movement (REM) sleep stage and then in the morning, usually from a non-REM sleep stage. Repeated measures were taken upon each awakening. Dream pleasantness, emotional charge of the dream, positive and negative emotions experienced in the dream, and four dimensions of post-sleep core affect (valence, activation, pleasant activation - unpleasant deactivation, and unpleasant activation - pleasant deactivation) were assessed. We found a small effect of condition (exposure vs. control) in interaction with appraisal of the ambient olfactory environment on dream pleasantness. Specifically, false alarms (i.e., perceiving odour in the absence of the target stimulus) were associated with lower dream pleasantness than correct rejections. Although exposure had a statistically significant positive influence on post-sleep core affect (namely, valence, activation, and pleasant activation - unpleasant deactivation), the size of the effect was small and lacked practical significance. The hypothesised differential effects of vanillin and TGA were only modelled for dream ratings because they decreased the fit of the other models. Neither dream pleasantness nor emotionality differed according to the odour used for stimulation. The results of the present study suggest that all-night exposure to odours is unlikely to produce practically significant positive effects on dreams and post-sleep core affect.

Methodological Recommendations to Control for Factors Influencing Dream and Nightmare Recall in Clinical and Experimental Studies of Dreaming

In order to ensure robust relationships between the dependent and independent variables in clinical dream/nightmare studies, the major factors which influence the frequency of reported dreams must be controlled. This article sets out methodological recommendations to both researchers seeking to ensure the equivalence of experimental groups of participants in group-matching designs, and to clinicians who wish to check that any change in frequency of reported nightmares over the course of a psychological or a pharmacological intervention is not caused by factors other than the experimental treatment itself. The main factors influencing the frequency of dream recall are presented: demographic variables, psychological characteristics, pathological dimensions, and substance consumption. A series of questionnaires is proposed for easily measuring these control variables.

Dream engineering: Simulating worlds through sensory stimulation

We explore the application of a wide range of sensory stimulation technologies to the area of sleep and dream engineering. We begin by emphasizing the causal role of the body in dream generation, and describe a circuitry between the sleeping body and the dreaming mind. We suggest that nearly any sensory stimuli has potential for modulating experience in sleep. Considering other areas that might afford tools for engineering sensory content in simulated worlds, we turn to Virtual Reality (VR). We outline a collection of relevant VR technologies, including devices engineered to stimulate haptic, temperature, vestibular, olfactory, and auditory sensations. We believe these technologies, which have been developed for high mobility and low cost, can be translated to the field of dream engineering. We close by discussing possible future directions in this field and the ethics of a world in which targeted dream direction and sleep manipulation are feasible.

Olfaction scaffolds the developing human from neonate to adolescent and beyond

The impact of the olfactory sense is regularly apparent across development. The fetus is bathed in amniotic fluid (AF) that conveys the mother's chemical ecology. Transnatal olfactory continuity between the odours of AF and milk assists in the transition to nursing. At the same time, odours emanating from the mammary areas provoke appetitive responses in newborns. Odours experienced from the mother's diet during breastfeeding, and from practices such as pre-mastication, may assist in the dietary transition at weaning. In parallel, infants are attracted to and recognize their mother's odours; later, children are able to recognize other kin and peers based on their odours. Familiar odours, such as those of the mother, regulate the child's emotions, and scaffold perception and learning through non-olfactory senses. During juvenility and adolescence, individuals become more sensitive to some bodily odours, while the timing of adolescence itself has been speculated to draw from the chemical ecology of the family unit. Odours learnt early in life and within the family niche continue to influence preferences as mate choice becomes relevant. Olfaction thus appears significant in turning on, sustaining and, in cases when mother odour is altered, disturbing adaptive reciprocity between offspring and carer during the multiple transitions of development between birth and adolescence. This article is part of the Theo Murphy meeting issue 'Olfactory communication in humans'.

Modulating dream experience: Noninvasive brain stimulation over the sensorimotor cortex reduces dream movement

Recently, cortical correlates of specific dream contents have been reported, such as the activation of the sensorimotor cortex during dreamed hand clenching. Yet, despite a close resemblance of such activation patterns to those seen during the corresponding wakeful behaviour, the causal mechanisms underlying specific dream contents remain largely elusive. Here, we aimed to investigate the causal role of the sensorimotor cortex in generating movement and bodily sensations during REM sleep dreaming. Following bihemispheric transcranial direct current stimulation (tDCS) or sham stimulation, guided by functional mapping of the primary motor cortex, naive participants were awakened from REM sleep and responded to a questionnaire on bodily sensations in dreams. Electromyographic (EMG) and electroencephalographic (EEG) recordings were used to quantify physiological changes during the preceding REM period. We found that tDCS, compared to sham stimulation, significantly decreased reports of dream movement, especially of repetitive actions. Other types of bodily experiences, such as tactile or vestibular sensations, were not affected by tDCS, confirming the specificity of stimulation effects to movement sensations. In addition, tDCS reduced EEG interhemispheric coherence in parietal areas and affected the phasic EMG correlation between both arms. These findings show that a complex temporal reorganization of the motor network co-occurred with the reduction of dream movement, revealing a link between central and peripheral motor processes and movement sensations of the dream self. tDCS over the sensorimotor cortex interferes with dream movement during REM sleep, which is consistent with a causal contribution to dream experience and has broader implications for understanding the neural basis of self-experience in dreams.

Presentation of familiar odor induces negative dream emotions during rapid eye movement (REM) sleep in healthy adolescents

OBJECTIVE

Odor presentation is a crucial tool in the experimental investigation of dreaming since odors rarely cause arousal, and are processed in the brain during sleep. Our previous study demonstrated that the presentation of a preferred odor during rapid eye movement (REM) sleep-induced negative dream emotions. However, preference and familiarity of an odor are known to be strongly related to each other in olfactory perception. Consequently, the above result might have been due to the confounding effects of familiarity. Therefore, the present study was designed to clarify the effects of an individual's degree of familiarity with an odor on negative emotions experienced when dreaming.

METHODS

The airflow with phenylethyl alcohol (PEA: rose-like smell) was presented as a stimulus of experimental condition, and odorless airflow was presented as the control. Participants who were familiar (n = 7) and unfamiliar (n = 7) with the odor of PEA experienced both conditions during REM sleep in the second and later sleep cycle. Then, they were awakened, and they rated the characteristics of their dream using a questionnaire.

RESULTS AND CONCLUSIONS

Participants who were familiar with the odor of PEA rated their dreams more negatively in the experimental condition relative to the control condition. It is concluded based on these results that a familiar odor may induce negative emotion in dreams, possibly because familiar odors tend to be perceived more strongly, and the olfactory pathway has direct connections to the amygdala, which is primarily involved in processing negative emotions.

An Exploration of Form Factors for Sleep-Olfactory Interfaces

Releasing scent during sleep has been shown to influence the emotional valence of dreams, reduce cigarette smoking behavior, strengthen memories as well as enhance restorative slow-wave activity. Nevertheless, current scent technologies used in sleep laboratories are not portable and require the use of nasal masks and large olfactometers. In this paper we investigated the preferred form factor and acceptance of a set of biometric wearables that can release scent based on the user's physiological state. We conducted an online survey with 163 participants and evaluated 8 different form factors. The results showed that 73.5% of the subjects preferred the designs that are not wearable during the night but that can be worn during the day. We provide insights to take into account for the design of next generation sleep-olfactory technologies. We provide a literature review of sleep and scent studies and discuss the opportunities for well-being and memory applications.

Dreams and Nightmares in Patients With Obstructive Sleep Apnea: A Review

Obstructive sleep apnea (OSA) can present with or provoke various psychological symptoms. In this article, we critically review studies that have examined dreams, dream recall, and dream content in patients with OSA. Obstructive events induce recurrent sleep fragmentation and intermittent desaturations in patients with OSA, which may trigger different parasomnias, including nightmares. Contradictory results have been reported concerning dreams in patients with OSA; while some investigators have reported less dreams in OSA patients, others have described that patients with OSA have increased dreams with emotional content, mainly violent and hostile content. Although there are reports of respiratory-related dream content in patients with OSA, most studies that have assessed the dream content of patients with OSA revealed that respiratory-related dream content was unusual. A clear association between post-traumatic stress disorders, comorbid OSA, and nightmares has been reported in several studies. Furthermore, an improvement in nightmare frequency with continuous positive airway pressure (CPAP) treatment has been shown. An inverse relationship between the severity of OSA reflected by the apnea-hypopnea index and dream recall has been demonstrated in several studies. Future studies should differentiate between patients with non-stage specific OSA and patients with rapid eye movement (REM) predominant OSA.

BioEssence: A Wearable Olfactory Display that Monitors Cardio-respiratory Information to Support Mental Wellbeing

This work introduces a novel wearable olfactory display that provides just-in-time release of scents based on the physiological state of the wearer. The device can release up to three scents and passively captures subtle chest vibrations associated with the beating of the heart and respiration through clothes.BioEssenceiscontrolledviaacustom-madesmartphone app that allows the creation of physiological rules to trigger different scents (e.g., when the heart rate is above 80 beats per minute, release lavender scent). The device is wireless and lightweight, and it is designed to be used during daily life, clipped on clothes around the sternum area or used as a necklace. We provide a description of the design and implementation of the prototype and potential use cases in the context of mental wellbeing.

Nocturnal Olfactory Stimulation for Improvement of Sleep Quality in Patients With Posttraumatic Stress Disorder: A Randomized Exploratory Intervention Trial

Posttraumatic stress disorder (PTSD) is characterized by sleep impairment and nightmares. As pleasant odors presented during sleep affect the emotional tone of dreams without inducing arousal, we investigated whether sleep patterns in PTSD can be improved via nocturnal olfactory stimulation. Participants were 40 inpatients with PTSD (n = 35 women; age range: 20-59 years) who completed a randomized, patient-blind, placebo-controlled trial. Baseline measurement for 5 consecutive nights was followed by a 5-night experimental intervention or placebo trial. During the intervention, patients received nocturnal stimulation with a pleasant odor (odor condition) or clean air (placebo condition) via an olfactometer that delivered inspiration-triggered stimuli in a nasal tube or via an odorized nasal clip. After each night, the patients completed standardized questionnaires that assessed sleep parameters and dream content. Each night, sleep efficiency, sleep onset latency, and wakefulness after sleep onset were monitored with a motion biosensor. Baseline assessment revealed that PTSD severity was associated with poorer sleep outcomes. An interaction effect showed that nocturnal odorization affected dream intensity. Post hoc tests revealed an improvement in the group that used the nasal clip as compared to baseline, d = 0.68. No negative effects were observed after odorization with the nasal clip. Considering the limited sample size, the study indicates that nocturnal olfactory stimulation may serve as a low-cost concomitant intervention to improve sleep quality in PTSD.

Neurophysiological Response to Olfactory Stimuli in Combat Veterans With Posttraumatic Stress Disorder

There is a need for a better understanding of underlying pathology in posttraumatic stress disorder (PTSD) to develop more effective treatments. The late positive potential (LPP) amplitude from electroencephalogram has been used to assess individual differences in emotional reactivity. There is evidence that olfaction is particularly important in emotional processing in PTSD. The current study examined LPP amplitudes in response to olfactory stimuli in 24 combat veterans with PTSD and 24 nonmilitary/non-PTSD controls. An olfactometer delivered three negatively valenced odorants, with 12 trials of each delivered in a random order. The groups did not differ in LPP amplitude across odorants. However, within the PTSD group, higher Clinician-Administered PTSD Scale scores related to an increased LPP amplitude after diesel fuel and rotten egg, but not n_butanol, odorants. Results provide specific targets and theory for further research into clinical applications such as selection of idiographic odorants for use in virtual-reality exposure therapy.

Linking psychological need experiences to daily and recurring dreams

The satisfaction of individuals’ psychological needs for autonomy, competence, and relatedness, as conceived from a self-determination theory perspective, is said to be conducive to personal growth and well-being. What has been unexamined is whether psychological need-based experiences, either their satisfaction or frustration, manifests in people’s self-reported dream themes as well as their emotional interpretation of their dreams. A cross-sectional study (N = 200; M age = 21.09) focusing on individuals’ recurrent dreams and a three-day diary study (N = 110; M age = 25.09) focusing on daily dreams indicated that individuals experiencing psychological need frustration, either more enduringly or on a day-to-day basis, reported more negative dream themes and interpreted their dreams more negatively. The contribution of psychological need satisfaction was more modest, although it related to more positive interpretation of dreams. The discussion focuses on the role of dreams in the processing and integration of psychological need-frustrating experiences.

Dream Content in Patients With Sleep Apnea: A Prospective Sleep Laboratory Study

STUDY OBJECTIVES

Few studies have addressed dreaming in patients with sleep apnea. We hypothesized that respiratory events and subsequent oxygen desaturation act as an important physiological trigger and may thus influence dream content in patients with a sleep-related breathing disorder.

METHODS

Seventy-six patients (28 women, mean age 54 years, range 20-82) who underwent polysomnography because of suspected sleep apnea participated in this study. Dream reports and dream questionnaires were collected immediately after first morning awakening, at 5:30 AM, at the sleep laboratory. Dream content analysis with respect to possible respiratory-related content was performed. Patients were stratified into primary snoring, mild, moderate, and severe sleep apnea groups.

RESULTS

In 63 patients sleep apnea was diagnosed (mild n = 31, 49.2%, moderate n = 13, 20.6%, severe n = 19, 30.2%), and 13 subjects in whom a sleep-related breathing disorder was not confirmed were included as a control group with primary snoring. There was no significant difference in respiratory-related dream topics between patients and controls. Also, no influence of respiratory parameters measured during polysomnography on dream content was detectable.

CONCLUSIONS

We failed to detect a difference in dream content between patients with sleep apnea and controls. Further studies are required to determine whether these results indicate that the incorporation of respiratory events into dreams is absent in patients with sleep apnea or represents a bias due to the collection of dream content in the early morning hours.

Pain Dreams and Dream Emotions in Patients with Chronic Back Pain and Healthy Controls

Background:

Although some theorists have suggested that pain sensations cannot be part of the dreaming world, research has shown that pain sensations occur in about 1% of the dreams in healthy persons and in about 30% of patients with acute, severe pain.

Objective:

The present study is the first to study pain dreams in patients with chronic pain.

Method:

A questionnaire was administered to 100 patients with chronic lower back pain and 270 controls.

Results:

The patients reported more pain dreams and more negatively toned dreams compared to healthy controls. In addition, patients reported more often that the dreamed pain persisted into waking state.

Conclusion:

In patients, pain dreams might be instigated by actual pain whereas for healthy persons pain dreams might be pain memories (self-experienced pain and/or seeing persons in pain). Future research should clarify how pain is processed during sleep. As patients with chronic pain experience negatively toned dreams, it will be beneficial to ask chronic pain patients about their dreams and, if necessary, offer specific treatment options like imagery rehearsal treatment.

A new view of "dream enactment" in REM sleep behavior disorder

Patients with REM sleep behavior disorder (RBD) exhibit increased muscle tone and exaggerated myoclonic twitching during REM sleep. In addition, violent movements of the limbs, and complex behaviors that can sometimes appear to involve the enactment of dreams, are associated with RBD. These behaviors are widely thought to result from a dysfunction involving atonia-producing neural circuitry in the brainstem, thereby unmasking cortically generated dreams. Here we scrutinize the assumptions that led to this interpretation of RBD. In particular, we challenge the assumption that motor cortex produces twitches during REM sleep, thus calling into question the related assumption that motor cortex is primarily responsible for all of the pathological movements of RBD. Moreover, motor cortex is not even necessary to produce complex behavior; for example, stimulation of some brainstem structures can produce defensive and aggressive behaviors in rats and monkeys that are strikingly similar to those reported in human patients with RBD. Accordingly, we suggest an interpretation of RBD that focuses increased attention on the brainstem as a source of the pathological movements and that considers sensory feedback from moving limbs as an important influence on the content of dream mentation.

The Yin and Yang of Sleep and Attention

Sleep is not a single state, but a complex set of brain processes that supports several physiological needs. Sleep deprivation is known to affect attention in many animals, suggesting that a key function of sleep is to regulate attention. Conversely, tasks that require more attention drive sleep need and sleep intensity. Attention involves the ability to filter incoming stimuli based on their relative salience, and this is likely to require coordinated synaptic activity across the brain. This capacity may have only become possible with the evolution of related neural mechanisms that support two key sleep functions: stimulus suppression and synaptic plasticity. We argue here that sleep and attention may have coevolved as brain states that regulate each other.

Olfactory drug effects approached from human-derived data

The complexity of the sense of smell makes adverse olfactory effects of drugs highly likely, which can impact a patient's quality of life. Here, we present a bioinformatics approach that identifies drugs with potential olfactory effects by connecting drug target expression patterns in human olfactory tissue with drug-related information and the underlying molecular drug targets taken from publically available databases. We identified 71 drugs with listed olfactory effects and 147 different targets. Taking the target-based approach further, we found additional drugs with potential olfactory effects, including 152 different substances interacting with genes expressed in the human olfactory bulb. Our proposed bioinformatics approach provides plausible hypotheses about mechanistic drug effects for drug discovery and repurposing and, thus, would be appropriate for use during drug development.

Developing Sensorimotor Systems in Our Sleep

Every animal must learn how to use its limbs within the developmental context of an ever-changing body. Typically, investigations of sensorimotor development focus on waking movements. Here I consider another class of behavior: Twitching movements that occur exclusively during active (REM) sleep. Twitches are particularly abundant in early infancy when critical sensorimotor networks are established. In light of behavioral, electrophysiological, neurophysiological, and computational investigations of this unique behavior, twitches may prove critical for the development and maintenance of the sensorimotor system, as well as its repair after injury or disease.

Trigeminal induced arousals during human sleep

BACKGROUND

Arousals caused by external stimuli during human sleep have been studied for most of the sensorial systems. It could be shown that a pure nasal trigeminal stimulus leads to arousals during sleep. The frequency of arousals increases dependent on the stimulus concentration. The aim of the study was to evaluate the influence of different stimulus durations on arousal frequency during different sleep stages.

METHODS

Ten young healthy volunteers with 20 nights of polysomnography were included in the study. Pure trigeminal stimulation with both different concentrations of CO2 (0, 10, 20, 40% v/v) and different stimulus durations (1, 3, 5, and 10 s) were applied during different sleep stages to the volunteers using an olfactometer. The application was performed during different sleep stages (light sleep, deep sleep, REM sleep).

RESULTS

The number of arousals increased with rising stimulus duration and stimulus concentration during each sleep stage.

CONCLUSION

Trigeminal stimuli during sleep led to arousals in dose- and time-dependent manner.