1 Submitted: 9 March, 2019; Revised: 23 July, 2019 © Sleep Research Society 2019. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail journals.permissions@oup.com. Original Article Cortical hyperarousal in NREM sleep normalizes from pre- to post- REM periods in individuals with frequent nightmares Borbála Blaskovich 1,2 , Richárd Reichardt 2 , Ferenc Gombos 3,4 , Victor I. Spoormaker 1 and Péter Simor 5,6, * , 1 Department of Translational Research in Psychiatry, Max Planck Institute of Psychiatry, Munich, Germany, 2 Department of Cognitive Science, Budapest University of Technology and Economics, Budapest, Hungary, 3 Department of General Psychology, Pázmány Péter Catholic University, 1088, Budapest, Hungary, 4 MTA-PPKE Adolescent Development Research Group, 1088, Budapest, Hungary, 5 Institute of Psychology, ELTE Eötvös Loránd University, 1064, Budapest, Hungary and 6 Institute of Behavioural Sciences, Semmelweis University, 1089, Budapest, Hungary *Corresponding author. Péter Simor, Institute of Psychology, ELTE Eötvös Loránd University, 1064 Budapest, Izabella utca 46., Hungary. Email: simor. peter@ppk.elte.hu. Abstract Study Objectives: Frequent nightmares have a high prevalence and constitute a risk factor for psychiatric conditions, but their pathophysiology is poorly understood. Our aim was to examine sleep architecture and electroencephalographic markers—with a specifc focus on state transitions—related to sleep regulation and hyperarousal in participants with frequent nightmares (NM participants) versus healthy controls. Methods: Healthy controls and NM participants spent two consecutive nights in the sleep laboratory. Second night spectral power during NREM to REM sleep (pre- REM) and REM to NREM (post-REM) transitions as well as during NREM and REM periods were evaluated for 22 NM participants compared to 22 healthy controls with a similar distribution of age, gender, and dream recall frequency. Results: We found signifcant differences between the groups in the pre-REM to post-REM changes in low- and high-frequency domains. NM participants experienced a lower amount of slow-wave sleep and showed increased beta and gamma power during NREM and pre-REM periods. No difference was present during REM and post-REM phases. Furthermore, while increased pre-REM high-frequency power seems to be mainly driven by post-traumatic stress disorder (PTSD) symptom intensity, decreased low-frequency activity occurred regardless of PTSD symptom severity. Conclusion: Our fndings indicate that NM participants had increased high-frequency spectral power during NREM and pre-REM periods, as well as relatively reduced slow frequency and increased fast frequency spectral power across pre-and post-REM periods. This combination of reduced sleep-protective activity and increased hyperarousal suggests an imbalance between sleep regulatory and wake-promoting systems in NM participants. Key words: nightmare; PTSD; sleep; pathophysiology; EEG Statement of Signifcance The prevalence of frequent nightmares is high in the general population and in psychiatric samples, but their pathophysiology remains poorly understood. Our results show reduced low frequency and increased high-frequency electroencephalogram (EEG) activity in pre-REM periods that normalizes to post-REM periods. Increased power in the higher frequencies during pre-REM sleep correlated to subjective post-traumatic stress disorder (PTSD) symptom severity, whereas reduced low-frequency activity occurred regardless of PTSD severity. Understanding the pathophysiology of frequent nightmares is highly relevant for the identifcation of treatment targets for nightmares, and could lead to a better understanding of the sleep pathophysiology of PTSD. Finally, our analyses show that it is methodologically bene- fcial to focus sleep analyses on sleep state transitions, such as the highly active pre-REM and the more quiescent post-REM sleep stages. SLEEPJ, 2020, 1–11 doi: 10.1093/sleep/zsz201 Advance Access Publication Date: 26 September 2019 Original Article Downloaded from https://academic.oup.com/sleep/article/43/1/zsz201/5574411 by guest on 08 September 2021