Pilleriin Sikka is a postdoctoral scholar at the Stanford School of Medicine. She is also affiliated with the Stanford Psychophysiology Laboratory in the Department of Psychology at Stanford as well as with the Department of Psychology at the University of Turku (Finland). Pilleriin is also a senior lecturer in cognitive neuroscience in the Department of Cognitive Neuroscience and Philosophy at the University of Skövde (Sweden). She holds a PhD degree in psychology (University of Turku, Finland), MSc degree in neuroscience (University of Oxford, UK), as well as MSc and BSc degrees in psychology (University of Tallinn, Estonia). Previously, she worked in the Department of Psychiatry at the University of Oxford (UK) in the field of molecular neuroscience. Pilleriin has received several prestigious research (e.g., Postdoctoral Reseach Award from the Finnish Foundations' Post Doc Pool) and teaching (The Golden Apple Award for Excellence in Teaching) awards as well as research grants (as a PI) from international and national foundations. She has more than ten years of teaching experience (courses in neuroscience, psychology, and well-being) and supervised as well as served as a mentor to many undergraduate and graduate students in the fields of psychology and cognitive neuroscience.

Honors & Awards

  • Merited Lecturer (awarded for excellence in research-based teaching), University of Skövde, Sweden (2022)
  • First Prize for PhD dissertation, Skaraborg’s Academy, Sweden (2021)
  • PhD Dissertation Award, The Finnish Sleep Research Society, Finland (2021)
  • Postdoctoral Fellowship, The Finnish Foundations' Post Doc Pool and the Emil Aaltonen Foundation (2020)
  • The Golden Apple Award for Excellence in Teaching, University of Skövde, Sweden (2020)
  • Best Poster Award, The Finnish Sleep Research Society, Finland (2018)
  • The Golden Apple Award for Excellence in Teaching, University of Skövde, Sweden (2015)
  • The Golden Apple Award for Excellence in Teaching, University of Skövde, Sweden (2010)
  • Winner of the Main Prize at the National Contest for University Students, Estonian Research Council (2005)
  • Winner of the Main Prize at the Contest of Students’ Research Papers, Tallinn University, Estonia (2005)
  • Harald Raudsep Scholarship, Estonian-Revelia Academic Fund, Maryland, USA (2005)
  • Kristjan Jaak Scholarship, Archimedes Foundation, Estonia (2005)
  • Kristjan Jaak Scholarship, Archimedes Foundation, Estonia (2004)
  • National Scholarship, Estonian Ministry of Education and Research, Estonia (2000)

Boards, Advisory Committees, Professional Organizations

  • Member, Society for Affective Science (SAS)
  • Member, International Society for Research on Emotion (ISRE)
  • Member, Association for the Scientific Study of Consciousness (ASSC)
  • Member, European Sleep Research Society (ESRS)
  • Member, Finnish Sleep Research Society (SUS)
  • Member, International Association for the Scientific Study of Dreams (IASD)

Professional Education

  • Master of Science, Tallinn University (2005)
  • Doctor of Philosophy, University Of Turku (2020)
  • Master of Science, University of Oxford (2008)
  • Bachelor of Science, Tallinn University (2003)
  • Ph.D., University of Turku (Finland), Psychology (2020)

Stanford Advisors

Current Research and Scholarly Interests

I strive to understand the phenomenology, dynamics, mechanisms, and impact of subjective experiences that occur across different states of consciousness—from wakefulness to normal sleep and dreaming, to anesthesia dreaming, and to psychedelic experiences. As part of my doctoral research, conducted under the mentorship of Prof. Antti Revonsuo, I investigated the conceptual and methodological challenges in the study of dream experiences, the neural correlates of these experiences, and how dreaming is associated with waking well-being. In 2021, I joined Stanford University as a Postdoctoral Scholar, initially working at the Stanford Psychophysiology Laboratory under the mentorship of James J. Gross. In this role, I expanded my research to explore emotions and emotion regulation across the wake-sleep cycle and to study an oft-overlooked aspect of well-being--peace of mind. Since November 2023, I have been a Postdoctoral Scholar in the Department of Anesthesiology, Perioperative and Pain Medicine, where, under the mentorship of Dr. Boris Heifets, I am investigating transformative experiences, specifically, the mechanisms and therapeutic potential of anesthesia-induced dream states and psychedelic experiences.

Leveraging my unique multidisciplinary background, my goal is to bridge the fields of consciousness research, sleep and dream research, emotion research, and well-being research and draw upon the concepts, theories, and methods from psychology, neuroscience, and (molecular) biology. To this end, I have experience in using diverse methods, including self-reports (development, validation, and use of questionnaires), interviews, ecological momentary assessment (EMA/ESM; diaries), behavioural experiments, natural language processing, sleep monitoring techniques, and electrophysiological (EEG/ERP) recordings, combined with qualitative and quantitative data analysis.

With an overarching goal of conducting research with societal impact, I aspire to: (1) develop innovative diagnostic and prognostic markers of mental health and well-being, and (2) to devise and test interventions scalable for enhancing the mental and physical well-being of communities.

All Publications

  • The role of objective sleep in implicit and explicit affect regulation: A comprehensive review NEUROBIOLOGY OF STRESS Straus, L. D., ten Brink, M., Sikka, P., Srivastava, R., Gross, J. J., Colvonen, P. J. 2024; 31
  • Reduction in Trauma-Related Symptoms After Anesthetic-Induced Intra-Operative Dreaming. The American journal of psychiatry Hack, L. M., Sikka, P., Zhou, K., Kawai, M., Chow, H. S., Heifets, B. 2024: appiajp20230698

    View details for DOI 10.1176/appi.ajp.20230698

    View details for PubMedID 38476046

  • Alexithymia profiles and depression, anxiety, and stress. Journal of affective disorders Preece, D. A., Mehta, A., Petrova, K., Sikka, P., Pemberton, E., Gross, J. J. 2024


    BACKGROUND: Alexithymia is a multidimensional trait comprised of difficulties identifying feelings, difficulties describing feelings, and externally orientated thinking. It is regarded as an important risk factor for emotional disorders, but there are presently limited data on each specific facet of alexithymia, or the extent to which deficits in processing negative emotions, positive emotions, or both, are important. In this study, we address these gaps by using the Perth Alexithymia Questionnaire (PAQ) to comprehensively examine the relationships between alexithymia and depression, anxiety, and stress symptoms.METHODS: University students (N = 1250) completed the PAQ and the Depression Anxiety Stress Scales-21. Pearson correlations, hierarchical regressions, and latent profile analysis were conducted.RESULTS: All facets of alexithymia, across both valence domains, were significantly correlated with depression, anxiety, and stress symptoms (r = 0.27-0.40). Regression analyses indicated that the alexithymia facets, together, could account for a significant 14.6 %-16.4 % of the variance in depression, anxiety, and stress. Difficulties identifying negative feelings and difficulties identifying positive feelings were the strongest unique predictors across all symptom categories. Our latent profile analysis extracted eight profiles, comprising different combinations of alexithymia facets and psychopathology symptoms, collectively highlighting the transdiagnostic relevance of alexithymia facets.LIMITATIONS: Our study involved a student sample, and further work in clinical samples will be beneficial.CONCLUSIONS: Our data indicate that all facets of alexithymia, across both valence domains, are relevant for understanding depression, anxiety, and stress. These findings demonstrate the value of facet-level and valence-specific alexithymia assessments, informing more comprehensive understanding and more targeted treatments of emotional disorder symptoms.

    View details for DOI 10.1016/j.jad.2024.02.071

    View details for PubMedID 38387670

  • Alexithymia or general psychological distress? Discriminant validity of the Toronto Alexithymia Scale and the Perth Alexithymia Questionnaire. Journal of affective disorders Preece, D. A., Petrova, K., Mehta, A., Sikka, P., Gross, J. J. 2024


    BACKGROUND: Alexithymia is an important transdiagnostic risk factor for emotion-based psychopathologies. However, it remains unclear whether alexithymia questionnaires actually measure alexithymia, or whether they measure emotional distress. Our aim here was to address this discriminant validity concern via exploratory factor analysis (EFA) of the 20-item Toronto Alexithymia Scale (TAS-20) and the Perth Alexithymia Questionnaire (PAQ).METHOD: United States general community adults (N = 508) completed the TAS-20, PAQ, and the Depression Anxiety Stress Scales-21 (DASS-21). EFA was used to examine the latent dimensions underlying these measures' scores.RESULTS: Our EFA extracted two higher-order factors, an "alexithymia" factor and a "general distress" factor (i.e., depression, anxiety, stress). All PAQ scores loaded cleanly on the alexithymia factor, with no cross-loadings on the distress factor. However, for the TAS-20, Difficulty Identifying Feelings (DIF) facet scores cross-loaded highly on the distress factor.LIMITATIONS: Our sample consisted of general community adults; future work in clinical settings will be useful.CONCLUSIONS: Our data indicate that the PAQ has good discriminant validity. However, the TAS-20 appears to have significant discriminant validity problems, in that much of the variance in its DIF facet reflects people's current levels of distress, rather than alexithymia. The TAS-20, which has traditionally been the most widely used alexithymia questionnaire, may therefore not be the optimal alexithymia tool. Our findings add to the body of evidence supporting the validity and utility of the PAQ and suggest that, moving forward, it is a superior option to the TAS-20 for alexithymia assessments.

    View details for DOI 10.1016/j.jad.2024.01.271

    View details for PubMedID 38320659

  • Affect Across the Wake-Sleep Cycle. Affective science Sikka, P., Gross, J. J. 2023; 4 (3): 563-569


    Affective scientists traditionally have focused on periods of active wakefulness when people are responding to external stimuli or engaging in specific tasks. However, we live much of our lives immersed in experiences not related to the current environment or tasks at hand-mind-wandering (or daydreaming) during wakefulness and dreaming during sleep. Despite being disconnected from the immediate environment, our brains still generate affect during such periods. Yet, research on stimulus-independent affect has remained largely separate from affective science. Here, we suggest that one key future direction for affective science will be to expand our field of view by integrating the wealth of findings from research on mind-wandering, sleep, and dreaming to provide a more comprehensive account of affect across the wake-sleep cycle. In developing our argument, we address two key issues: affect variation across the wake-sleep cycle, and the benefits of expanding the study of affect across the full wake-sleep cycle. In considering these issues, we highlight the methodological and clinical implications for affective science.

    View details for DOI 10.1007/s42761-023-00204-2

    View details for PubMedID 37744973

    View details for PubMedCentralID PMC10514005

  • Individual differences in peace of mind reflect adaptive emotion regulation PERSONALITY AND INDIVIDUAL DIFFERENCES Sikka, P., Revonsuo, A., Gross, J. J. 2023; 215
  • COVID-19 on mind: Daily worry about the coronavirus is linked to negative affect experienced during mind-wandering and dreaming. Emotion (Washington, D.C.) Sikka, P., Tuominen, J., Ezquerro Nassar, A., Kirberg, M., Loukola, V., Revonsuo, A., Valli, K., Windt, J., Bekinschtein, T. A., Noreika, V. 2023


    Despite a surge of studies on the effects of COVID-19 on our well-being, we know little about how the pandemic is reflected in people's spontaneous thoughts and experiences, such as mind-wandering (or daydreaming) during wakefulness and dreaming during sleep. We investigated whether and how COVID-19-related general concern, anxiety, and daily worry are associated with the daily fluctuation of the affective quality of mind-wandering and dreaming, and to what extent these associations can be explained by poor sleep quality. We used ecological momentary assessment by asking participants to rate the affect they experienced during mind-wandering and dreaming in daily logs over a 2-week period. Our preregistered analyses based on 1,755 dream logs from 172 individuals and 1,496 mind-wandering logs from 152 individuals showed that, on days when people reported higher levels of negative affect and lower levels of positive affect during mind-wandering, they experienced more worry. Only daily sleep quality was associated with affect experienced during dreaming at the within-person level: on nights with poorer sleep quality people reported experiencing more negative and less positive affect in dreams and were more likely to experience nightmares. However, at the between-person level, individuals who experienced more daily COVID-19 worry during the study period also reported experiencing more negative affect during mind-wandering and during dreaming. As such, the continuity between daily and nightly experiences seems to rely more on stable trait-like individual differences in affective processing. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

    View details for DOI 10.1037/emo0001255

    View details for PubMedID 37347885

  • Mediation Analysis of Conspiratorial Thinking and Anti-Expert Sentiments on Vaccine Willingness HEALTH PSYCHOLOGY Blackburn, A. M., Han, H. A., Gelpi, R. A., Stockli, S., Jeftic, A., Ch'ng, B., Koszalkowska, K., Lacko, D., Milfont, T., Lee, Y., Vestergren, S., COVIDISTRESS II Consortium 2023; 42 (4): 235-246


    Vaccines are an effective means to reduce the spread of diseases, but they are sometimes met with hesitancy that needs to be understood.In this study, we analyzed data from a large, cross-country survey conducted between June and August 2021 in 43 countries (N = 15,740) to investigate the roles of trust in government and science in shaping vaccine attitudes and willingness to be vaccinated.Despite significant variability between countries, we found that both forms of institutional trust were associated with a higher willingness to receive a COVID-19 vaccine. Furthermore, we found that conspiratorial thinking and anti-expert sentiments predicted reduced trust in government and science, respectively, and that trust mediated the relationship between these two constructs and ultimate vaccine attitudes. Although most countries displayed similar relationships between conspiratorial thinking and anti-expert sentiments, trust in government and science, and vaccine attitudes, we identified three countries (Brazil, Honduras, and Russia) that demonstrated significantly altered associations between the examined variables in terms of significant random slopes.Cross-country differences suggest that local governments' support for COVID-19 prevention policies can influence populations' vaccine attitudes. These findings provide insight for policymakers to develop interventions aiming to increase trust in the institutions involved in the vaccination process. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

    View details for DOI 10.1037/hea0001268

    View details for Web of Science ID 000964769600002

    View details for PubMedID 37023325

  • Alexithymia and Emotion Regulation AFFECTIVE SCIENCE Preece, D. A., Mehta, A., Petrova, K., Sikka, P., Bjureberg, J., Becerra, R., Gross, J. J. 2023; 4 (1)
  • The Perth Alexithymia Questionnaire-Short Form (PAQ-S): A 6-item measure of alexithymia. Journal of affective disorders Preece, D. A., Mehta, A., Petrova, K., Sikka, P., Bjureberg, J., Chen, W., Becerra, R., Allan, A., Robinson, K., Gross, J. J. 2023


    BACKGROUND: Alexithymia is a trait characterized by difficulties identifying feelings, difficulties describing feelings, and externally orientated thinking. It is widely regarded as an important transdiagnostic risk factor for a range of psychopathologies, including depressive and anxiety disorders. Whilst several well-validated psychometric measures of alexithymia exist, these are relatively lengthy, thus limiting their utility in time-pressured settings. In this paper, we address this gap by introducing and validating a brief 6-item version of the Perth Alexithymia Questionnaire, called the Perth Alexithymia Questionnaire-Short Form (PAQ-S).METHOD: Across two studies with adult samples (Study 1 N = 508 United States community; Study 2378 Australian college students), we examined the psychometric properties of the PAQ-S in terms of its factor structure, reliability, and concurrent/criterion validity.RESULTS: In exploratory and confirmatory factor analyses, all PAQ-S items loaded well on a single general alexithymia factor. The PAQ-S total score had high reliability, and correlated as expected with the long-form of the PAQ, as well as other established markers of alexithymia, emotion regulation, and affective disorder symptoms.LIMITATIONS: Our samples were general community or college student samples from two Western countries; future validation work in clinical samples and more diverse cultural groups is thus needed.CONCLUSIONS: The PAQ-S retains the psychometric strengths of the PAQ. As such, the PAQ-S can be used as a quick, robust measure of overall alexithymia levels. The introduction of the PAQ-S hence enables valid assessments of alexithymia in a more diverse range of settings and research designs.

    View details for DOI 10.1016/j.jad.2023.01.036

    View details for PubMedID 36642314

  • COVIDiSTRESS diverse dataset on psychological and behavioural outcomes one year into the COVID-19 pandemic (vol 9, 331, 2021) SCIENTIFIC DATA Blackburn, A. M., Vestergren, S., Tran, T. P., Stockli, S., Griffin, S. M., Ntontis, E., Jeftic, A., Chrona, S., Ikizer, G., Han, H., Milfont, T. L., Parry, D., Byrne, G., Gomez-Lopez, M., Acosta, A., Kowal, M., De Leon, G., Gallegos, A., Perez, M., Abdelrahman, M., Ahern, E., Yar, A., Ahmed, O., Alami, N. H., Amin, R., Andersen, L. E., Araujo, B., Asongu, N., Bartsch, F., Bavolar, J., Bhatta, K., Bircan, T., Bita, S., Bombuwala, H., Brik, T., Cakal, H., Caniels, M., Carballo, M., Carvalho, N. M., Cely, L., Chang, S., Chayinska, M., Chen, F., Ch'ng, B., Chukwuorji, J., Costa, A., Dalizu, V., Deschrijver, E., Aldemir, I., Doherty, A. M., Doller, R., Dubrov, D., Elegbede, S., Elizalde, J., Ermagan-Caglar, E., Fernandez-Morales, R., Garcia-Castro, J., Gelpi, R., Ghafori, S., Goldberg, X., Gonzalez-Uribe, C., Alpizar-Rojas, H., Haugestad, C., Higuera, D., Hoorelbeke, K., Hristova, E., Hubena, B., Huq, H., Ihaya, K., Jayathilake, G., Jen, E., Jinadasa, A., Joksimovic, J., Kacmar, P., Kadreva, V., Kalinova, K., Kandeel, H., Kellezi, B., Khan, S., Kontogianni, M., Koszalkowska, K., Hanusz, K., Lacko, D., Landa-Blanco, M., Lee, Y., Lieberoth, A., Lins, S., Liutsko, L., Londero-Santos, A., Mauritsen, A., Maegli, M., Magidie, P., Maharjan, R., Makaveeva, T., Makhubela, M., Malagon, M., Malykh, S., Mamede, S., Mandillah, S., Mansoor, M., Mari, S., Marin-Lopez, I., Marot, T. A., Martinez, S., Mauka, J., Moss, S., Mushtaq, A., Musliu, A., Mususa, D., Najmussaqib, A., Nasheeda, A., Nasr, R., Machado, N., Natividade, J., Ngowi, H., Nyarangi, C., Ogunbode, C., Onyutha, C., Padmakumar, K., Paniagua, W., Pena, M., Pirko, M., Portela, M., Pouretemad, H., Rachev, N., Ratodi, M., Reifler, J., Sadeghi, S., Sahayanathan, H., Sanchez, E., Sandbakken, E., Sandesh, D., Sanjesh, S., Schrotter, J., Shanthakumar, S., Sikka, P., Slaveykova, K., Studzinska, A., Subandi, F., Subedi, N., Sullivan, G., Tag, B., Delphine, T., Tamayo-Agudelo, W., Travaglino, G. A., Tuominen, J., Turk-Kurtca, T., Vakai, M., Volkodav, T., Wang, A., Williams, A., Wu, C., Yamada, Y., Yaneva, T., Yanez, N., Yeh, Y., Zoletic, E. 2023; 10 (1): 12

    View details for DOI 10.1038/s41597-022-01896-0

    View details for Web of Science ID 000923009600001

    View details for PubMedID 36599849

    View details for PubMedCentralID PMC9812347

  • Alexithymia and emotion regulation. Journal of affective disorders Preece, D. A., Mehta, A., Petrova, K., Sikka, P., Bjureberg, J., Becerra, R., Gross, J. J. 2022


    Alexithymia is a key transdiagnostic risk factor for emotion-based psychopathologies. Conceptual models specify that this is because alexithymia impairs emotion regulation. However, the extent of these putative emotion regulation impairments remains underexplored. Our aim in this study was to begin to address this gap by examining whether people with high, average, or low levels of alexithymia differ in the types of emotion regulation strategies they typically use.General community adults from the United States (N = 501) completed a battery of alexithymia and emotion regulation measures. Participants were grouped into high, average, and low alexithymia quantiles.After controlling for demographics and current levels of distress, the high, average, and low alexithymia groups differed in their use of cognitive and behavioral emotion regulation strategies. Compared to the other groups, the high alexithymia group reported lesser use of generally adaptive regulation strategies (cognitive reappraisal, approaching problems, and seeking social support) and greater use of generally maladaptive regulation strategies (expressive suppression, behavioral withdrawal, ignoring).Our data were cross-sectional and from self-report questionnaires. Future work in other cultural groups would be beneficial.Our results support the view that alexithymia is associated with impaired emotion regulation. In particular, people with high alexithymia seem to exhibit a less adaptive profile of emotion regulation strategies. Direct targeting of these emotion regulation patterns in psychotherapy may therefore be a useful pathway for the treatment of emotional disorder symptoms in people with high alexithymia.

    View details for DOI 10.1016/j.jad.2022.12.065

    View details for PubMedID 36566943

  • Event-Related Potential Correlates of Learning to Produce Novel Foreign Phonemes. Neurobiology of language (Cambridge, Mass.) Railo, H., Varjonen, A., Lehtonen, M., Sikka, P. 2022; 3 (4): 599-614


    Learning to pronounce a foreign phoneme requires an individual to acquire a motor program that enables the reproduction of the new acoustic target sound. This process is largely based on the use of auditory feedback to detect pronunciation errors to adjust vocalization. While early auditory evoked neural activity underlies automatic detection and adaptation to vocalization errors, little is known about the neural correlates of acquiring novel speech targets. To investigate the neural processes that mediate the learning of foreign phoneme pronunciation, we recorded event-related potentials when participants (N = 19) pronounced native or foreign phonemes. Behavioral results indicated that the participants' pronunciation of the foreign phoneme improved during the experiment. Early auditory responses (N1 and P2 waves, approximately 85-290 ms after the sound onset) revealed no differences between foreign and native phonemes. In contrast, the amplitude of the frontocentrally distributed late slow wave (LSW, 320-440 ms) was modulated by the pronunciation of the foreign phonemes, and the effect changed during the experiment, paralleling the improvement in pronunciation. These results suggest that the LSW may reflect higher-order monitoring processes that signal successful pronunciation and help learn novel phonemes.

    View details for DOI 10.1162/nol_a_00080

    View details for PubMedID 37215343

    View details for PubMedCentralID PMC10158638

  • The Neural Bases of Expressive Suppression: A Systematic Review of Functional Neuroimaging Studies. Neuroscience and biobehavioral reviews Sikka, P., Stenberg, J., Vorobyev, V., Gross, J. J. 2022: 104708


    Expressive suppression refers to the inhibition of emotion-expressive behavior (e.g., facial expressions of emotion). Although it is a commonly used emotion regulation strategy with well-documented consequences for well-being, little is known about its underlying mechanisms. In this systematic review, we for the first time synthesize functional neuroimaging studies on the neural bases of expressive suppression in non-clinical populations. The 12 studies included in this review contrasted the use of expressive suppression to simply watching emotional stimuli. Results showed that expressive suppression consistently increased activation of frontoparietal regions, especially the dorsolateral and ventrolateral prefrontal cortices and inferior parietal cortex, but decreased activation in temporo-occipital areas. Results regarding the involvement of the insula and amygdala were inconsistent with studies showing increased, decreased, or no changes in activation. These mixed findings underscore the importance of distinguishing expressive suppression from other forms of suppression and highlight the need to pay more attention to experimental design and neuroimaging data analysis procedures. We discuss these conceptual and methodological issues and provide suggestions for future research.

    View details for DOI 10.1016/j.neubiorev.2022.104708

    View details for PubMedID 35636561

  • Negative dream affect is associated with next-day affect level, but not with affect reactivity or affect regulation. Frontiers in behavioral neuroscience Sikka, P., Engelbrektsson, H., Zhang, J., Gross, J. J. 2022; 16: 981289


    There is increasing evidence that sleep plays an important role in affective processing. However, it is unclear whether dreaming-the subjective experiences we have during sleep-also serves an affect regulation function. Here, we investigated the within-person relationship between negative affect experienced in dreams and next-day waking affect level, affect reactivity, and affect regulation. For 5 days, 40 participants reported their dreams and rated their dream affect and post-sleep waking affect level upon morning awakening. Thereafter, they performed an affect reactivity and regulation task which involved viewing neutral and negative pictures with the instruction either to simply view the pictures or to down-regulate the affect evoked by these pictures. Multilevel regression analyses showed that the more negative affect people experienced in their dreams at night, the more negative affect and the less positive affect they reported the next morning. However, negative dream affect was associated neither with affect reactivity to the pictures nor with the ability to down-regulate negative affect in response to these pictures. In fact, Bayesian analyses favored the null hypotheses. These findings fail to provide support for the affect regulation function of dreaming and, instead, speak for affective continuity between dreaming and post-sleep wakefulness.

    View details for DOI 10.3389/fnbeh.2022.981289

    View details for PubMedID 36338877

  • Event-Related Potential Correlates of Learning to Produce Novel Foreign Phonemes NEUROBIOLOGY OF LANGUAGE Railo, H., Varjonen, A., Lehtonen, M., Sikka, P. 2022; 3 (4): 599-614
  • The dynamics of affect across the wake-sleep cycle: From waking mind-wandering to night-time dreaming. Consciousness and cognition Sikka, P., Valli, K., Revonsuo, A., Tuominen, J. 2021; 94: 103189


    Affective experiences occur across the wake-sleep cycle-from active wakefulness to resting wakefulness (i.e., mind-wandering) to sleep (i.e., dreaming). Yet, we know little about the dynamics of affect across these states. We compared the affective ratings of waking, mind-wandering, and dream episodes. Results showed that mind-wandering was more positively valenced than dreaming, and that both mind-wandering and dreaming were more negatively valenced than active wakefulness. We also compared participants' self-ratings of affect with external ratings of affect (i.e., analysis of affect in verbal reports). With self-ratings all episodes were predominated by positive affect. However, the affective valence of reports changed from positively valenced waking reports to affectively balanced mind-wandering reports to negatively valenced dream reports. These findings show that (1) the positivity bias characteristic to waking experiences decreases across the wake-sleep continuum, and (2) conclusions regarding affective experiences depend on whether self-ratings or verbal reports describing these experiences are analysed.

    View details for DOI 10.1016/j.concog.2021.103189

    View details for PubMedID 34419707

  • Tears evoke the intention to offer social support: A systematic investigation of the interpersonal effects of emotional crying across 41 countries* JOURNAL OF EXPERIMENTAL SOCIAL PSYCHOLOGY Zickfeld, J. H., Ven, N., Pich, O., Schubert, T. W., Berkessel, J. B., Bhushan, B., Mateo, N., Barbosa, S., Sharman, L., Kokonyei, G., Schrover, E., Kardum, I., Aruta, J., Lazarevic, L. B., Escobar, M., Stadel, M., Arriaga, P., Dodaj, A., Shankland, R., Majeed, N. M., Li, Y., Lekkou, E., Hartanto, A., Ozdogru, A. A., Vaughn, L., Espinoza, M., Caballero, A., Kolen, A., Karsten, J., Manley, H., Maeura, N., Eskisu, M., Shani, Y., Chittham, P., Ferreira, D., Bavolar, J., Konova, I., Sato, W., Morvinski, C., Carrera, P., Villar, S., Ibanez, A., Hareli, S., Garcia, A. M., Kremer, I., Gotz, F. M., Schwerdtfeger, A., Estrada-Mejia, C., Nakayama, M., Ng, W., Sesar, K., Orjiakor, C. T., Dumont, K., Allred, T., Gracanin, A., Rentfrow, P. J., Schonefeld, V., Vally, Z., Barzykowski, K., Peltola, H., Tcherkassof, A., Haque, S., Smieja, M., Su-May, T., IJzerman, H., Vatakis, A., Ong, C., Choi, E., Schorch, S. L., Paez, D., Malik, S., Kacmar, P., Bobowik, M., Jose, P., Vuoskoski, J. K., Basabe, N., Dogan, U., Ebert, T., Uchida, Y., Zheng, M., Mefoh, P., Sebena, R., Stanke, F. A., Ballada, C., Blaut, A., Wu, Y., Daniels, J. K., Kocsel, N., Burak, E., Balt, N. F., Vanman, E., Stewart, S. K., Verschuere, B., Sikka, P., Boudesseul, J., Martins, D., Nussinson, R., Ito, K., Mentser, S., Colak, T., Martinez-Zelaya, G., Vingerhoets, A. 2021; 95
  • Stress and worry in the 2020 coronavirus pandemic: relationships to trust and compliance with preventive measures across 48 countries in the COVIDiSTRESS global survey ROYAL SOCIETY OPEN SCIENCE Lieberoth, A., Lin, S., Stockli, S., Han, H., Kowal, M., Gelpi, R., Chrona, S., Tran, T., Jeftic, A., Rasmussen, J., Cakal, H., Milfont, T. L., Yamada, Y., Amin, R., Debove, S., Flis, I., Sahin, H., Turk, F., Yeh, Y., Ho, Y., Sikka, P., Delgado-Garcia, G., Lacko, D., Mamede, S., Zerhouni, O., Tuominen, J., Bircan, T., Wang, A., Ikizer, G., Lins, S., Studzinska, A., Uddin, M., Juarez, F., Chen, F., Sanli, A., Lys, A. E., Reynoso-Alcantara, V., Flores Gonzalez, R., Griffin, A. M., Lopez, C., Nezkusilova, J., Cepulic, D., Aquino, S., Marot, T. A., Blackburn, A. M., Boullu, L., Bavolar, J., Kacmar, P., Wu, C. S., Areias, J., Natividade, J. C., Mari, S., Ahmed, O., Dranseika, V., Cristofori, I., Coll-Martin, T., Eichel, K., Kumaga, R., Ermagan-Caglar, E., Bamwesigye, D., Tag, B., Contreras-Ibanez, C. C., Aruta, J. R., Naidu, P. A., Tran, T. P., Dilekler, I., Cenek, J., Islam, M., Ch'ng, B., Sechi, C., Nebel, S., Sayilan, G., Jha, S., Vestergren, S., Ihaya, K., Guillaume, G., Travaglino, G. A., Rachev, N. R., Hanusz, K., Pirko, M., West, J., Cyrus-Lai, W., Najmussaqib, A., Romano, E., Noreika, V., Musliu, A., Sungailaite, E., Kosa, M., Lentoor, A. G., Sinha, N., Bender, A. R., Meshi, D., Bhandari, P., Byrne, G., Kalinova, K., Hubena, B., Ninaus, M., Diaz, C., Scarpaci, A., Koszalkowska, K., Pankowski, D., Yaneva, T., Morales-Izquierdo, S., Uzelac, E., Lee, Y., Hristova, D., Hakim, M., Deschrijver, E., Kavanagh, P. S., Shata, A., Reyna, C., De Leon, G. A., Tisocco, F., Mola, D., Shani, M., Mahlungulu, S., Ozery, D., Caniels, M. J., Correa, P., Ortiz, M., Vilar, R., Makaveeva, T., Pummerer, L., Nikolova, I., Bujic, M., Szebeni, Z., Pennato, T., Taranu, M., Martinez, L., Capelos, T., Belaus, A., Dubrov, D. 2021; 8 (2): 200589


    The COVIDiSTRESS global survey collects data on early human responses to the 2020 COVID-19 pandemic from 173 429 respondents in 48 countries. The open science study was co-designed by an international consortium of researchers to investigate how psychological responses differ across countries and cultures, and how this has impacted behaviour, coping and trust in government efforts to slow the spread of the virus. Starting in March 2020, COVIDiSTRESS leveraged the convenience of unpaid online recruitment to generate public data. The objective of the present analysis is to understand relationships between psychological responses in the early months of global coronavirus restrictions and help understand how different government measures succeed or fail in changing public behaviour. There were variations between and within countries. Although Western Europeans registered as more concerned over COVID-19, more stressed, and having slightly more trust in the governments' efforts, there was no clear geographical pattern in compliance with behavioural measures. Detailed plots illustrating between-countries differences are provided. Using both traditional and Bayesian analyses, we found that individuals who worried about getting sick worked harder to protect themselves and others. However, concern about the coronavirus itself did not account for all of the variances in experienced stress during the early months of COVID-19 restrictions. More alarmingly, such stress was associated with less compliance. Further, those most concerned over the coronavirus trusted in government measures primarily where policies were strict. While concern over a disease is a source of mental distress, other factors including strictness of protective measures, social support and personal lockdown conditions must also be taken into consideration to fully appreciate the psychological impact of COVID-19 and to understand why some people fail to follow behavioural guidelines intended to protect themselves and others from infection. The Stage 1 manuscript associated with this submission received in-principle acceptance (IPA) on 18 May 2020. Following IPA, the accepted Stage 1 version of the manuscript was preregistered on the Open Science Framework at This preregistration was performed prior to data analysis.

    View details for DOI 10.1098/rsos.200589

    View details for Web of Science ID 000672607700001

    View details for PubMedID 33972837

    View details for PubMedCentralID PMC8074580

  • COVIDiSTRESS Global Survey dataset on psychological and behavioural consequences of the COVID-19 outbreak SCIENTIFIC DATA Yamada, Y., Cepulic, D., Coll-Martin, T., Debove, S., Gautreau, G., Han, H., Rasmussen, J., Tran, T. P., Travaglino, G. A., Lieberoth, A., Blackburn, A. M., Boullu, L., Bujic, M., Byrne, G., Caniels, M. J., Flis, I., Kowal, M., Rachev, N. R., Reynoso-Alcantara, V., Zerhouni, O., Ahmed, O., Amin, R., Aquino, S., Areias, J., Aruta, J. R., Bamwesigye, D., Bavolar, J., Bender, A. R., Bhandari, P., Bircan, T., Cakal, H., Capelos, T., Cenek, J., Ch'ng, B., Chen, F., Chrona, S., Contreras-Ibanez, C. C., Sebastian Correa, P., Cristofori, I., Cyrus-Lai, W., Delgado-Garcia, G., Deschrijver, E., Diaz, C., Dilekler, I., Dranseika, V., Dubrov, D., Eichel, K., Ermagan-Caglar, E., Gelpi, R., Flores Gonzalez, R., Griffin, A., Hakim, M., Hanusz, K., Ho, Y., Hristova, D., Hubena, B., Ihaya, K., Ikizer, G., Islam, M., Jeftic, A., Jha, S., Juarez, F., Kacmar, P., Kalinova, K., Kavanagh, P. S., Kosa, M., Koszalkowska, K., Kumaga, R., Lacko, D., Lee, Y., Lentoor, A. G., De Leon, G. A., Lin, S., Lins, S., Castro Lopez, C., Lys, A. E., Mahlungulu, S., Makaveeva, T., Mamede, S., Mari, S., Marot, T. A., Martinez, L., Meshi, D., Jeanette Mola, D., Morales-Izquierdo, S., Musliu, A., Naidu, P. A., Najmussaqib, A., Natividade, J. C., Nebel, S., Nezkusilova, J., Nikolova, I., Ninaus, M., Noreika, V., Victoria Ortiz, M., Ozery, D., Pankowski, D., Pennato, T., Pirko, M., Pummerer, L., Reyna, C., Romano, E., Sahin, H., Sanli, A., Sayilan, G., Scarpaci, A., Sechi, C., Shani, M., Shata, A., Sikka, P., Sinha, N., Stockli, S., Studzinska, A., Sungailaite, E., Szebeni, Z., Tag, B., Taranu, M., Tisocco, F., Tuominen, J., Turk, F., Uddin, M., Uzelac, E., Vestergren, S., Vilar, R., Wang, A., West, J., Wu, C. S., Yaneva, T., Yeh, Y., COVIDiSTRESS Global Survey 2021; 8 (1): 3


    This N = 173,426 social science dataset was collected through the collaborative COVIDiSTRESS Global Survey - an open science effort to improve understanding of the human experiences of the 2020 COVID-19 pandemic between 30th March and 30th May, 2020. The dataset allows a cross-cultural study of psychological and behavioural responses to the Coronavirus pandemic and associated government measures like cancellation of public functions and stay at home orders implemented in many countries. The dataset contains demographic background variables as well as measures of Asian Disease Problem, perceived stress (PSS-10), availability of social provisions (SPS-10), trust in various authorities, trust in governmental measures to contain the virus (OECD trust), personality traits (BFF-15), information behaviours, agreement with the level of government intervention, and compliance with preventive measures, along with a rich pool of exploratory variables and written experiences. A global consortium from 39 countries and regions worked together to build and translate a survey with variables of shared interests, and recruited participants in 47 languages and dialects. Raw plus cleaned data and dynamic visualizations are available.

    View details for DOI 10.1038/s41597-020-00784-9

    View details for Web of Science ID 000604956300001

    View details for PubMedID 33398078

    View details for PubMedCentralID PMC7782539

  • Subjective ratings of fear are associated with frontal late positive potential asymmetry, but not with early brain activity over the occipital and centro-parietal cortices PSYCHOPHYSIOLOGY Grassini, S., Sikka, P., Revonsuo, A., Koivisto, M. 2020; 57 (12): e13665


    The human frontal cortex is asymmetrically involved in motivational and affective processing. Several studies have shown that the left-frontal hemisphere is related to positive and approach-related affect, whereas the right-frontal hemisphere is related to negative and withdrawal-related affect. The present study aimed to investigate whether evolutionarily threatening stimuli modulate asymmetrical frontal activity. We examined hemispheric differences in frontal late positive potentials (f-LPP asymmetry) and frontal alpha power activation (frontal alpha asymmetry, FAA) in response to images depicting snakes, spiders, butterflies, and birds. Results showed that the late component of f-LPP asymmetry, but not FAA, was modulated by the category of stimuli. Specifically, threatening stimuli (snakes and spiders) evoked a relatively large late f-LPP over the right-frontal hemisphere than non-threatening stimuli (birds and butterflies). Moreover, this relatively great right-frontal activity was positively associated with the subjective ratings of fear. Importantly, the subjective ratings of fear were not associated with early brain activity over the occipital or centro-parietal cortices. These results suggest that late f-LPP asymmetry may reflect higher order affective processes, specifically the subjective appraisal of threatening stimuli and the subjective experience of fear, that are independent of the fast and automatic processing of evolutionarily significant and affectively arousing stimuli.

    View details for DOI 10.1111/psyp.13665

    View details for Web of Science ID 000558906400001

    View details for PubMedID 32790915

  • Dream affect: Conceptual and Methodological Issues in the Study of Emotions and Moods Experienced in Dreams PhD Dissertation Sikka, P. University of Turku. 2020
  • EEG Frontal Alpha Asymmetry and Dream Affect: Alpha Oscillations over the Right Frontal Cortex during REM Sleep and Presleep Wakefulness Predict Anger in REM Sleep Dreams The Journal of Neuroscience Sikka, P., Revonsuo, A., Noreika, V., Valli, K. 2019; 39 (24): 4775-4784
  • How to Study Dream Experiences DREAMS Understanding Biology, Psychology, and Culture Sikka, P. Greenwood, an Imprint of ABC-CLIO LLC. 2019; 1: 153-166
  • Peace of mind and anxiety in the waking state are related to the affective content of dreams SCIENTIFIC REPORTS Sikka, P., Pesonen, H., Revonsuo, A. 2018; 8: 12762


    Waking mental well-being is assumed to be tightly linked to sleep and the affective content of dreams. However, empirical research is scant and has mostly focused on ill-being by studying the dreams of people with psychopathology. We explored the relationship between waking well-being and dream affect by measuring not only symptoms of ill-being but also different types and components of well-being. Importantly, this is the first time peace of mind was investigated as a distinct aspect of well-being in a Western sample and in relation to dream content. Healthy participants completed a well-being questionnaire, followed by a three-week daily dream diary and ratings of dream affect. Multilevel analyses showed that peace of mind was related to positive dream affect, whereas symptoms of anxiety were related to negative dream affect. Moreover, waking measures were better related to affect expressed in dream reports rather than participants' self-ratings of dream affect. We propose that whereas anxiety may reflect affect dysregulation in waking and dreaming, peace of mind reflects enhanced affect regulation in both states of consciousness. Therefore, dream reports may possibly serve as markers of mental health. Finally, our study shows that peace of mind complements existing conceptualizations and measures of well-being.

    View details for DOI 10.1038/s41598-018-30721-1

    View details for Web of Science ID 000442606800008

    View details for PubMedID 30143673

    View details for PubMedCentralID PMC6109051

  • Dream emotions: a comparison of home dream reports with laboratory early and late REM dream reports JOURNAL OF SLEEP RESEARCH Sikka, P., Revonsuo, A., Sandman, N., Tuominen, J., Valli, K. 2018; 27 (2): 206-214


    The aim of this study was to compare the emotional content of dream reports collected at home upon morning awakenings with those collected in the laboratory upon early and late rapid eye movement (REM) sleep awakenings. Eighteen adults (11 women, seven men; mean age = 25.89 ± 4.85) wrote down their home dreams every morning immediately upon awakening during a 7-day period. Participants also spent two non-consecutive nights in the sleep laboratory where they were awoken 5 min into each continuous REM sleep stage, upon which they gave a verbal dream report. The content of a total of 151 home and 120 laboratory dream reports was analysed by two blind judges using the modified Differential Emotions Scale. It was found that: (1) home dream reports were more emotional than laboratory early REM dream reports, but not more emotional than laboratory late REM dream reports; (2) home dream reports contained a higher density of emotions than laboratory (early or late REM) dream reports; and (3) home dream reports were more negative than laboratory dream reports, but differences between home and early REM reports were larger than those between home and late REM reports. The results suggest that differences between home and laboratory dream reports in overall emotionality may be due to the time of night effect. Whether differences in the density of emotions and negative emotionality are due to sleep environment or due to different reporting procedures and time spent in a sleep stage, respectively, remains to be determined in future studies.

    View details for DOI 10.1111/jsr.12555

    View details for Web of Science ID 000426866500008

    View details for PubMedID 28568911

  • How You Measure Is What You Get: Differences in Self- and External Ratings of Emotional Experiences in Home Dreams AMERICAN JOURNAL OF PSYCHOLOGY Sikka, P., Feilhauer, D., Valli, K., Revonsuo, A. 2017; 130 (3): 367-384
  • I know how you felt last night, or do I? Self- and external ratings of emotions in REM sleep dreams CONSCIOUSNESS AND COGNITION Sikka, P., Valli, K., Virta, T., Revonsuo, A. 2014; 25: 51-66


    We investigated whether inconsistencies in previous studies regarding emotional experiences in dreams derive from whether dream emotions are self-rated or externally evaluated. Seventeen subjects were monitored with polysomnography in the sleep laboratory and awakened from every rapid eye movement (REM) sleep stage 5 min after the onset of the stage. Upon awakening, participants gave an oral dream report and rated their dream emotions using the modified Differential Emotions Scale, whereas external judges rated the participants' emotions expressed in the dream reports, using the same scale. The two approaches produced diverging results. Self-ratings, as compared to external ratings, resulted in greater estimates of (a) emotional dreams; (b) positively valenced dreams; (c) positive and negative emotions per dream; and (d) various discrete emotions represented in dreams. The results suggest that this is mostly due to the underrepresentation of positive emotions in dream reports. Possible reasons for this discrepancy are discussed.

    View details for DOI 10.1016/j.concog.2014.01.011

    View details for Web of Science ID 000333228100007

    View details for PubMedID 24565868

  • The Existence of a Hypnotic State Revealed by Eye Movements PLOS ONE Kallio, S., Hyona, J., Revonsuo, A., Sikka, P., Nummenmaa, L. 2011; 6 (10): e26374


    Hypnosis has had a long and controversial history in psychology, psychiatry and neurology, but the basic nature of hypnotic phenomena still remains unclear. Different theoretical approaches disagree as to whether or not hypnosis may involve an altered mental state. So far, a hypnotic state has never been convincingly demonstrated, if the criteria for the state are that it involves some objectively measurable and replicable behavioural or physiological phenomena that cannot be faked or simulated by non-hypnotized control subjects. We present a detailed case study of a highly hypnotizable subject who reliably shows a range of changes in both automatic and volitional eye movements when given a hypnotic induction. These changes correspond well with the phenomenon referred to as the "trance stare" in the hypnosis literature. Our results show that this 'trance stare' is associated with large and objective changes in the optokinetic reflex, the pupillary reflex and programming a saccade to a single target. Control subjects could not imitate these changes voluntarily. For the majority of people, hypnotic induction brings about states resembling normal focused attention or mental imagery. Our data nevertheless highlight that in some cases hypnosis may involve a special state, which qualitatively differs from the normal state of consciousness.

    View details for DOI 10.1371/journal.pone.0026374

    View details for Web of Science ID 000296515200016

    View details for PubMedID 22039474

    View details for PubMedCentralID PMC3200339

  • D-Serine Metabolism in C6 Glioma Cells: Involvement of Alanine-Serine-Cysteine Transporter (ASCT2) and Serine Racemase (SRR) but Not D-Amino Acid Oxidase (DAO) JOURNAL OF NEUROSCIENCE RESEARCH Sikka, P., Walker, R., Cockayne, R., Wood, M. A., Harrison, P. J., Burnet, P. J. 2010; 88 (8): 1829-1840


    D-serine is an endogenous N-methyl-D-aspartate (NMDA) receptor coagonist. It is synthesized from L-serine by serine racemase (SRR), but many aspects of its metabolism remain unclear, especially in the forebrain, which lacks active D-amino acid oxidase (DAO), the major D-serine degradative enzyme. Candidate mechanisms include SRR operating in alpha,beta-eliminase mode (converting D-serine to pyruvate) and regulation by serine transport, in which the alanine-serine-cysteine transporter ASCT2 is implicated. Here we report studies in C6 glioma cells, which "simulate" the forebrain, in that the cells express SRR and ASCT2 but lack DAO activity. We measured D-serine, ASCT2, SRR, and DAO expression and DAO activity in two situations: after incubation of cells for 48 hr with serine isomers and after increased or decreased SRR expression by transfection and RNA interference, respectively. Incubation with serine enantiomers decreased [(3)H]D-serine uptake and ASCT2 mRNA and increased SRR immunoreactivity but did not alter DAO immunoreactivity, and DAO activity remained undetectable. SRR overexpression increased D-serine and pyruvate and decreased [(3)H]D-serine uptake and ASCT2 mRNA but did not affect DAO. SRR knockdown did not alter any of the parameters. Our data suggest that D-serine transport mediated by ASCT2 contributes prominently to D-serine homeostasis when DAO activity is absent. The factors regulating D-serine are important for understanding normal NMDA receptor function and because D-serine, along with DAO and SRR, is implicated in the pathogenesis and treatment of schizophrenia.

    View details for DOI 10.1002/jnr.22332

    View details for Web of Science ID 000277245500021

    View details for PubMedID 20091774

    View details for PubMedCentralID PMC2883191

  • What is an altered state of consciousness? PHILOSOPHICAL PSYCHOLOGY Revonsuo, A., Kallio, S., Sikka, P. 2009; 22 (2): 187-204
  • D-amino acid oxidase activity and expression are increased in schizophrenia MOLECULAR PSYCHIATRY Burnet, P. J., Eastwood, S. L., Bristow, G. C., Godlewska, B. R., Sikka, P., Walker, M., Harrison, P. J. 2008; 13 (7): 658-660

    View details for DOI 10.1038/mp.2008.47

    View details for Web of Science ID 000256832700004

    View details for PubMedID 18560437

    View details for PubMedCentralID PMC2629619

  • Perception of successive targets presented in invariant-item streams ACTA PSYCHOLOGICA Bachmann, T., Sikka, P. 2005; 120 (1): 19-34


    When two successive, spatially overlapping, targets (S1 and S2) are presented on a blank background, S2 typically dominates in explicit perception. We tested whether S2 dominance is also found for the conditions of presenting S1 and S2 in a stream of irrelevant objects. Successive target letters were presented within a stream of invariant stimulus items (capital Is). The stream items were presented either as a perceptually continuous object where both type and token appeared invariant (60-Hz stream) or as a flickering stream of successive replicas of the invariant stationary object where the type appeared invariant but the token appearance seemed intermittent (20-Hz condition). Compared to the control condition where targets were presented on a blank background we found that (1) recognition rate was lower for targets embedded in a perceptually continuous type-and-token object (60 Hz), but was unchanged for targets in a perceptually flickering sequence of the invariant-object tokens (20 Hz); (2) S1 recognition rate was higher compared to S2 recognition rate within the first epoch of stream (0-150 ms) while within the later stream-epochs S2 dominated over S1 as usual; (3) the overall difference in recognition rates between S1 and S2 was decreased. The results are discussed in the theoretical context of visual masking and attentional blink.

    View details for DOI 10.1016/j.actpsy.2005.02.007

    View details for Web of Science ID 000231644900002

    View details for PubMedID 15876418