The neural correlates of dreaming

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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Figure 1: Dreaming experience vs. no experience in NREM sleep (low-frequency power).
Figure 2: Dreaming experience vs. no experience in REM sleep (low-frequency power).
Figure 3: Dreaming experience vs. no experience in NREM and REM sleep (high-frequency power).
Figure 4: The content of dream experiences in REM sleep.
Figure 5: Real-time prediction of dream experience.

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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.).

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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.

Corresponding author

Correspondence to Giulio Tononi.

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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.

Integrated supplementary information

Supplementary Figure 1 Dreaming experience vs. no experience (experiment 2)

Cortical distribution of t-values for the contrast between DEs and NEs at the source level for low-frequency power (1-4 Hz) in NREM sleep (20s before awakening). p<0.05 after correction for multiple comparisons (two-tailed, paired t-tests, 7 subjects, t(6) ≥ 2.45). B. Same as A for high- frequency power (25-50 Hz) in NREM sleep (two-tailed, paired t-tests, 7 subjects, t(6) ≥ 2.45).

Supplementary Figure 2 Conjunction between DE–NE and DEWR–NE contrasts (experiment 1)

Conjunction maps: differences and overlaps between the two contrasts (DE/NE and DEWR/NE) for low-frequency power in NREM sleep. DE/NE contrast: 32 subjects, DEWR/NE contrast 20 subjects.

Supplementary Figure 3 Dreaming experience vs. no experience (experiment 1)

Cortical distribution of t-values for the contrast between DEs and NEs at the source level for high-frequency power (25-50 Hz) in NREM sleep (20s before awakening) for experiment 1. p<0.05 after correction for multiple comparisons (two-tailed, paired t-tests, 32 subjects, t(31) > 2.04).

Supplementary Figure 4 Dreaming experience without recall vs. no experience (experiment 1)

A. Cortical distribution of t-values for the contrast between DEWRs and NEs at the source level for high-frequency power (20-50 Hz) in NREM sleep (20s before awakening). p<0.05 after correction for multiple comparisons (two-tailed, paired t-tests, 20 subjects, t(19) > 2.09). B. Cortical distribution of unthresholded t-values for the same comparison.

Supplementary Figure 5 Absolute power values for DE and NE (experiments 1 and 2)

Power spectral density for DE and NE, averaged over the posterior hot zone, (determined by the overlap between the DE/NE contrast in REM and NREM sleep, as shown in Figure 2B), for high- and low-frequency bands in NREM (n=32) and REM sleep (n=10). Two-tailed paired t-tests (NREM LF: t(31)= -2.98; NREM HF: t(31)= 3.46; REM LF: t(9)= -3.59; REM HF: t(9)= 3.10). Whiskers correspond to 3 standard deviations from the mean, crosses indicate values above this limit.

Supplementary Figure 6 Dreaming experience vs. no experience (experiment 3)

High-frequency power (20-50 Hz) for dream experiences (DE) and no experiences (NE) in NREM, averaged over the ROI used for prediction in experiment 3.7 subjects, paired t-test, t(6)=4.41, p=0.005, two-tailed). The asterisk indicates a significant difference (p=0.005) between DE and NE trials.

Supplementary Figure 7 Dreaming experience vs. no experience (experiment 3)

Cortical distribution of t-values for the contrast between DEs and NEs for the HF/LF power ratio in NREM sleep (20s before awakening), p<0.05 SnPM corrected (two-tailed, paired t-tests, 7 subjects). All vertices displayed a significant effect for DE>NE.

Supplementary Figure 8 Dreaming experience vs. no experience (experiments 1 and 2)

Cortical distribution of unthresholded t-values for the contrast between DEs and NEs for delta power in NREM sleep (20s before awakening) for experiments 1 (32 subjects) and 2 (7 subjects). Paired two-tailed t-tests.

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Siclari, F., Baird, B., Perogamvros, L. et al. The neural correlates of dreaming. Nat Neurosci 20, 872–878 (2017). https://doi.org/10.1038/nn.4545

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