The American Journal of Psychology
August 21, 2017
Pilleriin Sikka, Diana Feilhauer, Katja Valli et al.
63 citations
How emotions in dreams are measured can lead to opposite conclusions about whether dreams are mostly positive or negative. Over three weeks, 44 participants reported their dreams each morning and rated their own emotional experiences using a standard emotion scale. Two external judges rated the same 552 dream reports using the same scale. Self-ratings showed dreams as more emotional and more positive, with most dreams rated positively. External ratings showed most dreams as negatively valenced. The two methods partially agreed on negative emotions but diverged sharply on positive emotions. This suggests negative emotional experiences may be measured more reliably than positive ones, and the two methods may capture different phenomena and should be used together.
May 16, 2023
William Wong, Kátia C. Andrade, Thomas Andrillon et al.
21 citations
preprint
A new open-access database, DREAM, combines sleep magneto/electroencephalography (M/EEG) recordings with standardized dream reports to enable large-scale neurocognitive research on dreaming. The initial release includes 20 datasets from 561 participants and 2649 awakenings, each with at least 20 seconds of high-frequency M/EEG data and a classification of the subject's experience. Analyses demonstrate that features extracted from EEG can predict whether a person reports having had a conscious experience during both REM and NREM sleep. The database aims to overcome the limitations of small sample sizes and methodological variability in dream research, allowing new questions to be addressed at a scale unattainable by individual labs.
Nature Communications
August 13, 2025
William Wong, Rubén Herzog, Kátia Cristine Andrade et al.
10 citations
A new open database, the DREAM database, combines standardized sleep magneto/electroencephalography (M/EEG) recordings with dream reports from 505 participants across 20 datasets, totaling 2,643 awakenings. Each awakening includes at least 20 seconds of high-resolution sleep EEG (≥100 Hz, ≥2 electrodes) and a classification of the sleeper's reported experience. Analyses showed that reports of conscious experiences during sleep can be predicted from objective EEG features in both REM and NREM sleep. The database aims to overcome limitations of small sample sizes and methodological variability in dream research, enabling larger-scale investigations of the neurocognitive basis of dreaming.
Sci Rep
October 16, 2024
Andreas Krabbe, Pilleriin Sikka, Jussi Jylkkä
9 citations
Psychological flexibility—the ability to adapt thoughts and behaviors to changing circumstances—may explain why psychedelic experiences can improve mental well-being. In a cross-sectional internet survey of 629 people who had used classical psychedelics, network analysis showed that the depth of psychological insight during a single psychedelic experience, rather than how often someone had used psychedelics, was linked to the psychological flexibility component of Acceptance. Mediation analyses indicated that psychological flexibility mediated the relationship between past psychedelic use and both well-being and ill-being. The findings suggest that the quality of the psychedelic experience, especially fostering acceptance, is more important than frequency of use for long-term mental health benefits.
Conscious Cogn
July 7, 2025
Jussi Jylkkä, Hilla Väyrynen, Enyu Lin et al.
3 citations
Meditation and psychedelics both foster mystical, psychological, and philosophical-existential insights that predict wellbeing. A qualitative-quantitative study found that these insights, whether from meditation or controlled psychedelic use, are associated with positive shifts in personal wellbeing. The authors suggest that the types of insights from both practices overlap and can profoundly benefit individuals, leading to enhanced wellbeing and personal transformation.
April 9, 2021
Pilleriin Sikka, Katja Valli, Antti Revonsuo et al.
2 citations
preprint
Across the wake-sleep cycle, the positivity bias typical of waking experiences diminishes. Mind-wandering episodes are more positively valenced than dreams, and both are more negatively valenced than active wakefulness. When participants rated their own affect, all episodes were predominantly positive. However, analysis of verbal reports describing the same experiences showed a shift from positively valenced waking reports to affectively balanced mind-wandering reports to negatively valenced dream reports. These findings indicate that the nature of affective experiences depends on the measurement method and the state of consciousness, calling for integration across emotion, mind-wandering, and dream research.
JAMA Psychiatry
June 1, 2026
Ben Deverett, Duan Li, Theresa R. Lii et al.
1 citation
Ketamine produces distinct brain-wave patterns that may be linked to its therapeutic effects. General anesthesia selectively blocks one of these patterns—theta oscillations—while leaving another pattern, beta-gamma oscillations, intact. In 52 participants, ketamine given during anesthesia preserved beta-gamma power increases but eliminated the characteristic theta augmentation seen during awake administration. This suggests that different neurophysiologic effects of ketamine can be separated, offering a way to investigate which brain-wave changes underlie its antidepressant, analgesic, or dissociative properties.
Anesthesiology
February 3, 2026
Pilleriin Sikka, May Ching Ngo, Sherry Hu et al.
1 citation
A standardized propofol-based anesthesia protocol with EEG monitoring and verbal priming about dreaming led 69% of 452 surgical patients to report dreaming, and 93% of those who received all protocol elements did so. Most dreams were positive (86%), and dreamers reported higher subjective sleep quality than nondreamers. The protocol was safe, with no intraoperative awareness, and recovery times and medication use did not differ between groups. Adherence was high for most elements but low for the no-stimulation emergence period. The approach is feasible in routine clinical care and aligns with Enhanced Recovery After Surgery principles.
Consciousness and Cognition
December 15, 2025
Andreas Krabbe, Pilleriin Sikka, Jussi Jylkkä
Meditation practice may enhance the benefits of psychedelic experiences and can confound associations between psychedelic use and well-being. In two cross-sectional online surveys, when examined separately, both cumulative psychedelic use and meditation practice were associated with greater well-being and psychological flexibility. However, when considered jointly, the associations for psychedelics were reduced or became nonsignificant, while meditation remained consistently associated with outcomes. In a second study, participants who experienced a personally meaningful event through meditation alone or combined with psychedelics reported significantly greater improvements in well-being compared with those who used psychedelics alone, though all groups showed positive change on average. Weak evidence suggested a potential synergy between the two practices.
medRxiv
August 7, 2025
Ben Deverett, Duan Li, Theresa R. Lii et al.
preprint
Ketamine produces dissociative, analgesic, and antidepressant effects, but it is unclear whether its underlying neurophysiological signatures can be separated. In this observational cohort study, 52 participants (healthy volunteers, elective surgery patients, and patients with depression) received a subanesthetic infusion of ketamine or placebo, with or without general anesthesia. When ketamine was given under general anesthesia, its characteristic low-frequency brain wave augmentation was absent, while high-frequency power modulation was preserved. This selective modulation suggests a method for investigating the distinct roles of high- and low-frequency neural activity in ketamine's behavioral effects.
British Journal of Anaesthesia
August 1, 2026
Pilleriin Sikka, Sherry Hu, Boris D. Heifets
Dreaming during anaesthesia is common and has been documented for over a century, but remains poorly understood. This review of 157 studies from 1921 to 2024 involving 87,866 participants found that dream recall rates vary widely, from 3% to 8% in large clinical trials to 40% to 80% in experimental settings. Ketamine and propofol are most consistently associated with recall. Dreams are predominantly pleasant and feature everyday autobiographical content. Dream recall is not linked to intraoperative awareness, challenging the idea that dreams indicate inadequate anaesthetic depth. Higher home dream recall, preoperative suggestion, and immediate post-emergence assessment increase recall rates. Unpleasant dreams reduce willingness to undergo the same anaesthetic again. The positive nature and suggestibility of anaesthesia dreams suggest potential therapeutic uses.
The Journal of neuroscience : the official journal of the Society for Neuroscience
June 12, 2019
Pilleriin Sikka, Antti Revonsuo, Valdas Noreika et al.
Frontal alpha asymmetry (FAA) during REM sleep and evening wakefulness predicts ratings of anger in dreams. Individuals with greater alpha power in the right frontal hemisphere may be less able to regulate strong affective states, such as anger, in dreams. FAA was positively correlated across wakefulness and REM sleep. These findings imply that FAA may serve as a neural correlate of affect regulation in both waking and dreaming states.
Journal of Sleep Research
April 1, 2018
Pilleriin Sikka, Antti Revonsuo, Nils Sandman et al.
Dreams collected at home upon morning awakening are more emotional and more negative than those collected in the lab after early REM sleep awakenings, but not more emotional than those after late REM awakenings. Home dreams also contain a higher density of emotions than lab dreams from either early or late REM sleep. The differences in overall emotionality may be due to the time of night, while the causes of differences in emotion density and negativity—whether from the sleep environment, reporting procedures, or time spent in a sleep stage—remain unclear.
Consciousness and Cognition
April 1, 2014
Pilleriin Sikka, Katja Valli, Tiina Virta et al.
Emotional experiences in dreams may appear inconsistent across studies because of whether dream emotions are self-rated or judged by external raters. In a sleep-laboratory study, 17 participants were awakened from REM sleep and provided oral dream reports, then rated their own emotions using a modified scale. External judges rated the same reports with the same scale. Self-ratings yielded higher estimates of emotional dreams, positively valenced dreams, the number of positive and negative emotions per dream, and various discrete emotions compared to external ratings. The discrepancy appears largely due to underrepresentation of positive emotions in dream reports when judged externally.