Abstract

Consciousness never fades during waking. However, when awakened from sleep, we sometimes recall dreams and sometimes recall no experiences. Traditionally, dreaming has been identified with rapid eye-movement (REM) sleep, characterized by wake-like, globally 'activated', high-frequency electroencephalographic activity. However, dreaming also occurs in non-REM (NREM) sleep, characterized by prominent low-frequency activity. This challenges our understanding of the neural correlates of conscious experiences in sleep. Using high-density electroencephalography, we contrasted the presence and absence of dreaming in NREM and REM sleep. In both NREM and REM sleep, reports of dream experience were associated with local decreases in low-frequency activity in posterior cortical regions. High-frequency activity in these regions correlated with specific dream contents. Monitoring this posterior 'hot zone' in real time predicted whether an individual reported dreaming or the absence of dream experiences during NREM sleep, suggesting that it may constitute a core correlate of conscious experiences in sleep.

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Acknowledgements

The authors thank D. Bachhuber, L. Barbosa, R. Benca, E. Carrera, A. Castelnovo, A. Cayo, C. Cirelli, R. Davidson, C. Funk, M. Gevelinger, J. Harris, A. Mensen, P. Nori, R. Smith, L. Vuillaume, S. Yu, C. Zennig and our undergraduate research assistants for help with data collection, sleep scoring, technical assistance and discussions. This work was supported by NIH/NCCAM P01AT004952 (to G.T.), NIH/NIMH 5P20MH077967 (to G.T.), Tiny Blue Dot Inc. grant MSN196438/AAC1335 (to G.T.), Swiss National Science Foundation Grants 139778 (to F.S.), 145571 (to F.S.) and 155120 (to L.P.), Swiss Foundation for Medical Biological Grants 151743 and 145763 (to F.S.), NIH/NINDS F32NS089348 (to B.B.), UW Medical Scientist Training Program Grant T32 GM008692 (to J.J.L.), NIH Grants MH064498 and MH095984 (to B.R.P.).

Author information

Author notes

    • Francesca Siclari
    • , Benjamin Baird
    •  & Lampros Perogamvros

    These authors contributed equally to this work.

Affiliations

  1. Department of Psychiatry, University of Wisconsin–Madison, Madison, Wisconsin, USA.

    • Francesca Siclari
    • , Benjamin Baird
    • , Lampros Perogamvros
    • , Giulio Bernardi
    • , Brady Riedner
    • , Melanie Boly
    • , Bradley R Postle
    •  & Giulio Tononi
  2. Center for Research and Investigation in Sleep (CIRS), Lausanne University Hospital (CHUV) and University of Lausanne, Lausanne, Switzerland.

    • Francesca Siclari
    •  & Giulio Bernardi
  3. Sleep Laboratory, Division of Pneumology, Geneva University Hospitals (HUG), Geneva, Switzerland.

    • Lampros Perogamvros
  4. Department of Neuroscience, University of Geneva, Geneva, Switzerland.

    • Lampros Perogamvros
  5. IMT School for Advanced Studies, Lucca, Italy.

    • Giulio Bernardi
  6. Medical Scientist Training Program and Neuroscience Training Program, University of Wisconsin, Madison, Wisconsin, USA.

    • Joshua J LaRocque
  7. Department of Neurology, University of Wisconsin–Madison, Madison, Wisconsin, USA.

    • Melanie Boly
  8. Department of Psychology, University of Wisconsin–Madison, Madison, Wisconsin, USA.

    • Bradley R Postle

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Contributions

F.S., L.P., B.B., J.J.L., M.B., B.R., B.R.P. and G.T. designed the experiments; F.S., L.P., B.B. and J.J.L. conducted the experiments; F.S., L.P., B.B. and G.B. analyzed the data; and F.S., L.P., B.B. and G.T. wrote the paper.

Competing interests

G.T. and B.R. are involved in a research study in humans supported by Philips Respironics. This study is not related to the work presented in the current manuscript.

Corresponding author

Correspondence to Giulio Tononi.

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