Vol.:(0123456789) 1 3 Brain Topogr DOI 10.1007/s10548-017-0563-1 ORIGINAL PAPER Predicting Dream Recall: EEG Activation During NREM Sleep or Shared Mechanisms with Wakefulness? Serena Scarpelli 1  · Aurora D’Atri 1  · Anastasia Mangiaruga 1  · Cristina Marzano 1  · Maurizio Gorgoni 1  · Cinzia Schiappa 1  · Michele Ferrara 2  · Luigi De Gennaro 1   Received: 5 December 2016 / Accepted: 18 April 2017 © Springer Science+Business Media New York 2017 in confict with the hypothesis of common wake-sleep mechanisms. We also confrmed that EEG correlates of DR depend on a state-like relationship. Keywords Dream recall · EEG correlates · NREM sleep · Nap · Activation model · Delta activity Introduction Although in the last years many studies have tried to explain how we remember dreams, there are still no une- quivocal empirical data about EEG correlates of dream recall (DR). It is well-known that we cannot have directly access on dream experience, so several works investigated the EEG pattern related to the subsequent dream reports, which are—intrinsically—retrospective (Chellappa et al. 2011; Esposito et al. 2004; Marzano et al. 2011a; Scarpelli et al. 2015a; Siclari et al. 2014; Takeuchi et al. 2003). For decades, the history of dream research has been strongly infuenced by the dichotomy REM sleep = dream- ing versus NREM sleep = non-dreaming (Scarpelli et al. 2015b). More complex designs and interview techniques highlighted the fallacy of this postulate (Cipolli et al. 2016). Indeed, a DR rate of about 50% is obtained after awakening from NREM sleep, especially from stage 2 (Foulkes 1962; Pivik and Foulkes 1968) and also naptime (Foulkes 1962; Taub 1971). Despite it is well-known that the dreaming is not just an epiphenomenon of REM sleep and the dichot- omy is now outdated, very few explanations on the encod- ing and retrieval of dream contents from NREM sleep have been proposed. Under the assumption that dream recall is the only (and viable) object of study, some evidence showed that the mechanisms responsible for DR are substantially the same Abstract The common knowledge of a uniqueness of REM sleep as a privileged scenario of dreaming still per- sists, although consolidated empirical evidence shows that the assumption that dreaming is just an epiphenomenon of REM sleep is no longer tenable. However, the brain mechanisms underlying dream generation and its encoding in memory during NREM sleep are still mostly unknown. In fact, only few studies have investigated on the mecha- nisms of dream phenomenology related to NREM sleep. For this reason, our study is specifcally aimed to elucidate the electrophysiological (EEG) correlates of dream recall (DR) upon NREM sleep awakenings. Under the assump- tion that EEG activity predicts the presence/absence of DR also during NREM sleep, we have investigated whether DR from stage 2 NREM sleep shares similar brain mechanisms to those involved in the encoding of episodic memory during wakefulness, or it depends on the specifc electro- physiological milieu of the sleep period along the desyn- chronized/synchronized EEG continuum. We collected DR from a multiple nap protocol in a within-subjects design. We found that DR is predicted by an extensive reduction of delta activity during the last segment of sleep, encom- passing left frontal and temporo-parietal areas. The results could represent an update on the mechanisms underlying the sleep mentation during NREM sleep. In particular, they support the hypothesis that an increased cortical EEG acti- vation is a prerequisite for DR, and they are not necessarily * Luigi De Gennaro luigi.degennaro@uniroma1.it 1 Department of Psychology, Sapienza University of Rome, Via dei Marsi, 78, 00185 Rome, Italy 2 Department of Biotechnological and Applied Clinical Sciences, University of L’Aquila, Coppito, L’Aquila, Italy