The American Journal of Psychology
April 1, 2009
Katja Valli, Antti Revonsuo
132 citations
The threat simulation theory (TST) proposes that dreaming about threatening events serves a biological function. This review examines studies that tested TST using the Dream Threat Scale (DTS), a system for identifying and classifying threats in dreams. The reviewed research includes dreams from Finnish and Swedish university students, traumatized and nontraumatized Kurdish, Palestinian, and Finnish children, and recurrent dreams and nightmares from Canadian participants. The authors conclude that new evidence and direct tests yield strong support for TST, and its strengths outweigh its weaknesses.
The Journal of neuroscience : the official journal of the Society for Neuroscience
February 24, 2021
Annalotta Scheinin, Oskari Kantonen, Michael Alkire et al.
92 citations
Consciousness often persists even when unresponsiveness occurs. In two experiments involving 76 healthy males, brain activity was measured during varying states of consciousness induced by propofol and dexmedetomidine (n = 39) and during sleep-deprived wakefulness and non-REM sleep (n = 37). Most participants reported internally generated experiences while unresponsive. Key brain regions, including the thalamus and cingulate cortices, were found critical for consciousness, showing consistent activity patterns regardless of anesthetic type or sleep state, highlighting a core network essential for conscious awareness.
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.
Brain and Cognition
December 1, 2011
Valdas Noreika, Leila Jylhänkangas, Levente Móró et al.
62 citations
Subjective experiences can occur even when a person appears unresponsive under sedation. In a nonsurgical setting, participants given dexmedetomidine, propofol, sevoflurane, or xenon recalled having subjective experiences in almost 60% of sessions after regaining responsiveness. During dexmedetomidine sessions, such experiences were linked to shallower sedation depth as measured by an EEG-based monitor. The findings indicate that unresponsiveness does not guarantee absence of consciousness, and studies on phenomenal consciousness under anesthetics should assess subjective states through post-recovery interviews.
Neuroscience of Consciousness
January 1, 2020
William Wong, Valdas Noreika, Levente Móró et al.
35 citations
In a test of whether brain activity alone can reveal when someone is dreaming, researchers used an unsupervised machine learning classifier to distinguish dreamful from dreamless sleep based on EEG spectral power and electrode location. Nine participants contributed 54 one-minute polysomnograms from non-rapid eye movement sleep—27 with dreams and 27 without. A blinded Analysis Team attempted to classify each recording over five iterations with gradually reduced blindness. At no stage did the classifier perform significantly better than chance, indicating that EEG spectral power features could not reliably detect signatures of phenomenal consciousness in this dataset.
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.
Epilepsy & behavior : E&B
August 1, 2008
Mirja Johanson, Katja Valli, Antti Revonsuo et al.
19 citations
People with partial epilepsy experience widespread distortions in their subjective experience during seizures, yet the pattern of those distortions remains consistent from one seizure to the next. A standardized questionnaire called the Phenomenology of Consciousness Inventory (PCI) proved suitable for capturing these changes in consciousness. The findings suggest that the PCI could help researchers and clinicians better understand the nature of phenomenal consciousness in epilepsy.
Translational Psychiatry
February 27, 2024
Hanna M. Ollila, Nasa Sinnott-Armstrong, Katri Kantojärvi et al.
18 citations
Nightmares are vivid, negative dreams that awaken the dreamer. While occasional nightmares are common, frequent ones often indicate underlying emotional regulation problems. A genome-wide association study of 45,255 individuals found no single genetic variants linked to nightmare frequency, but estimated heritability at 5%. Genetic correlation analysis revealed strong correlations between nightmares and anxiety, depressive disorders, posttraumatic stress disorder, and the personality trait neuroticism. Mendelian randomization suggested that insomnia may causally increase the likelihood of frequent nightmares. These findings indicate that nightmares share genetic factors with psychiatric conditions and that insomnia may heighten susceptibility to nightmares, highlighting the need for systematic nightmare assessment in clinical settings.
Psychology of Consciousness Theory Research and Practice
June 12, 2025
Etzel Cardeña, Aviva Berkovich-Ohana, Katja Valli et al.
11 citations
A multidisciplinary, international group used taxonomic principles and a modified Delphi method to create a taxonomy of altered states of consciousness based on central phenomenological features. They identified eight distinct states, some with subcategories: proto and transitional, delirium, minimal to no awareness, experiential detachment, enhanced physicality, altered identity, imaginary/fantasy/visionary, and unity/mystical. The authors hope this taxonomy will foster conceptual clarity and stimulate research across specializations, helping reveal what is common and different across triggers and antecedents of altered states, and encouraging phenomenological, psychological, cultural, and neuroscientific understanding.
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.
bioRxiv (Cold Spring Harbor Laboratory)
November 9, 2019
Hanna M. Ollila, Nasa Sinnott-Armstrong, Katri Kantojärvi et al.
5 citations
preprint
Nightmares are vivid, disturbing dreams that wake the dreamer. Twin studies show nightmare frequency is 36–51% heritable. A genome-wide association study of 28,596 individuals from Finland and the United States identified genetic variants near MYOF and PTPRJ (a gene previously linked to sleep duration) that predispose to nightmares. Strong genetic correlations were found between nightmare frequency and neuroticism, post-traumatic stress disorder, major depressive disorder, daytime sleepiness, and insomnia. Mendelian randomization indicated that feelings of being fed-up, nervous, and miserable cause nightmares, with no evidence that nightmares cause psychological problems. The findings suggest nightmares arise from unique genetic risk factors and are substantially caused by underlying psychological and sleep problems.
Consciousness and Cognition
February 8, 2024
Ville Loukola, Jarno Tuominen, Santeri Kirsilä et al.
4 citations
During the COVID-19 pandemic, dreams did not become more threatening or nightmarish overall compared to before the pandemic. Analysis of 1,132 pandemic-era dreams and 166 pre-pandemic dreams found no differences in the number of threatening events, disease-related threats, or severity of threats between the two periods. However, the minority of dreams that directly referenced the pandemic did contain more threats, disease-related threats, and severe threats. The findings suggest the pandemic's impact on dream content was limited to a subset of dreams rather than causing a general increase in threatening dream content.
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.
Journal of Sleep Research
April 2, 2026
Ville Loukola, J T Tuominen, Eveliina Malinen et al.
Individual factors, such as low life satisfaction and fewer positive emotions, are better predictors of threatening dream content during the COVID-19 pandemic than daily situational factors like worry or media consumption. In a large Finnish sample of prospective dream diaries, lower life satisfaction was the only statistically significant predictor of threatening events in dreams, while experiencing fewer positive emotions in the past two weeks was the only significant predictor of pandemic-related threatening events. The findings suggest that the tendency to have threatening dreams is more a stable trait than a daily fluctuating feature, supporting the threat simulation theory's idea that individual differences in simulating threats interact with daily experiences.
September 11, 2025
Ville Loukola, Jarno Tuominen, Eveliina Malinen et al.
preprint
During the COVID-19 pandemic, individual factors such as life satisfaction and positive emotions were better predictors of threatening dream content than daily situational factors like worry about the virus or media consumption. In a large Finnish sample using prospective dream diaries, lower life satisfaction was the only statistically significant predictor for threatening events in dreams, and fewer positive emotions in the past two weeks was the only significant predictor for pandemic-related threatening events. These findings suggest that the tendency to experience threatening dreams is more of a stable trait than a daily fluctuating feature, consistent with the threat simulation theory of dreaming.
British Journal of Anaesthesia
August 1, 2023
Katja Valli, Linda Radek, Roosa E Kallionpää et al.
Anaesthetic-induced unresponsiveness and non-rapid eye movement (NREM) sleep share similar conscious experiences. In a within-subject study, 39 healthy males received either dexmedetomidine or propofol to induce unresponsiveness, and 37 were later awakened from NREM sleep. Most participants were rousable, with no difference between the two drugs. Lower drug concentrations were linked to being rousable but not to recall of experiences. Of interviews after anaesthesia and sleep, 69.7% and 64.4% included experiences, respectively, with no significant difference in recall. Disconnected dream-like experiences and memory incorporation of the research setting occurred equally often in both states, while awareness was rare. The findings suggest that both states involve disconnected conscious experiences with similar recall frequencies and content.
The Journal of neuroscience : the official journal of the Society for Neuroscience
June 28, 2023
Oskari Kantonen, Lauri Laaksonen, Michael Alkire et al.
Anesthesia-induced disconnectedness—unresponsiveness and unawareness of external events—is linked to reduced activity in the thalamus, but not to widespread cortical suppression, which instead reflects drug exposure itself. In a study of 160 healthy men, four anesthetics (propofol, dexmedetomidine, sevoflurane, S-ketamine) or saline placebo were administered at doses designed to make half of subjects unresponsive. Positron emission tomography showed that, for all anesthetics except S-ketamine, lower thalamic metabolic activity distinguished disconnected from connected states. Widespread cortical metabolic suppression occurred in both connected and disconnected subjects compared with placebo, indicating it is necessary but insufficient for loss of consciousness.
Consciousness and Cognition
November 1, 2021
Linda Radek, Lauri Koskinen, Nils Sandman et al.
Subjective experiences, most often dreaming or incorporating elements of the setting, are common during sedation with anesthetics that act through different molecular mechanisms. In healthy male participants given equisedative doses of dexmedetomidine, propofol, sevoflurane, or S-ketamine for one hour, 46.9% of those who were arousable reported experiences. Dexmedetomidine was associated with the most frequent reports, while S-ketamine produced the most multimodal experiences. Whether participants were responsive at the end of administration did not affect the prevalence or content of the experiences. The differences between drugs were small in this sample.
Lancet Neurology
October 1, 2020
F. Siclari, Katja Valli, I. Arnulf
Dreaming is now linked to specific brain activity patterns thanks to advances in neuroimaging. Neurological conditions such as lucid dreams and parasomnias reveal that dreaming is reflected in physiological signals, behaviors, and brain activity, with the body sometimes enacting dream content. However, the dream body can differ from the real body: patients with congenital paraplegia can walk in dreams, those with sleep apnoea rarely suffocate, and phantom limb pain can disappear. These conditions offer valuable models for studying the mechanisms underlying dream experiences.
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.
bioRxiv Preprint Server
May 27, 2019
William Wong, Valdas Noreika, Levente Móró et al.
preprint
A test called the Dream Catcher test was conducted for the first time in a simplified form to see if brain activity alone can reveal whether someone is dreaming. Data Team collected brain measurements (polysomnograms) during NREM sleep from 9 participants, producing 54 one-minute recordings—27 from dreamful sleep and 27 from dreamless sleep. A blinded Analysis Team tried to classify each recording as dreamful or dreamless using an unsupervised machine learning classifier based on EEG spectral power and electrode location. Over five iterations with gradually reduced blindness, the team never performed significantly better than chance. The results suggest that EEG spectral power does not carry signatures of phenomenal consciousness, and the study also failed to replicate key findings from earlier reports on dreaming consciousness.
bioRxiv Preprint Server
April 12, 2019
Valdas Noreika, Jennifer Windt, Markus Kern et al.
preprint
Applying transcranial direct current stimulation (tDCS) over the sensorimotor cortex during REM sleep reduces reported dream movement, particularly repetitive actions, without affecting other bodily sensations like touch or balance. This effect coincides with reduced interhemispheric coherence in parietal areas and altered muscle activity correlation between arms. The findings indicate that tDCS causally interferes with the neural mechanisms underlying dream movement, confirming the spatial specificity of the stimulation site and suggesting a reorganization of the motor network during dreaming.
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.
Advances in Consciousness Research
October 28, 2010
Antti Revonsuo, Katja Valli
Dreaming is a pure form of phenomenality—conscious experience—and the dreaming brain can serve as a model system for studying consciousness. The dreaming brain preserves all essential features of consciousness, making it a challenging but necessary object for any theory aiming to explain consciousness. The argument is grounded in biological realism, the assumption that consciousness is a real natural biological phenomenon in the brain.