Rapid eye movement sleep does not seem to unbind memories from their emotional context GA  ETANE DELIENS 1,2 , DANIEL NEU 2,3 and PHILIPPE PEIGNEUX 1 1 Neuropsychology and Functional Neuroimaging Research Group at Center for Research in Cognition and ULB Neurosciences Institute, Universit e Libre de Bruxelles (ULB), Brussels, Belgium, 2 Sleep Laboratory and Unit for Chronobiology U78, Brugmann University Hospital, Universit e Libre de Bruxelles (ULB) and Vrije Universiteit Brussel (VUB), Brussels, Belgium and 3 Laboratory of Medical Psychology ULB312, Faculty of Medicine, Neuroscience Institute U.L.B., Brussels, Belgium Keywords interference, memory consolidation, mood induction, partial sleep deprivation Correspondence Philippe Peigneux, UR2NF, Neuropsychology and Functional Neuroimaging Research Unit, Universit e Libre de Bruxelles, CP191, Avenue F.D. Roosevelt 50, B-1050 Brussels, Belgium Tel: +32-(0)2-650-26-39; fax: +32-(0)2-650-22-09; e-mail: Philippe.Peigneux@ulb.ac.be Accepted in revised form 12 May 2013; received 19 February 2013 DOI: 10.1111/jsr.12065 SUMMARY Sleep unbinds memories from their emotional learning context, protect- ing them from emotional interference due to a change of mood between learning and recall. According to the ‘sleep to forget and sleep to remember’ model, emotional unbinding takes place during rapid eye movement sleep. To test this hypothesis, we investigated emotional contextual interference effects after early versus late post-learning sleep periods, in which slow wave and rapid eye movement sleep, respectively, predominate. Participants learned a list of neutral word pairs after induction of a happy or a sad mood, then slept immediately afterwards for 3 h of early or late sleep under polysomnographic recording, in a within- subject counterbalanced design. They slept for 3 h before learning in the late sleep condition. Polysomnographic data confirmed more rapid eye movement sleep in the late than in the early sleep condition. After awakening, half the list was recalled after induction of a similar mood than during the encoding session (non-interference condition), and the other half of the list was recalled after induction of a different mood (interference condition). The results disclosed an emotional interference effect on recall both in the early and late sleep conditions, which does not corroborate the hypothesis of a rapid eye movement sleep-related protection of recent memories from emotional contextual interference. Alternatively, the contextual demodulation process initiated during the first post-learning night might need several consecutive nights of sleep to be achieved. INTRODUCTION Recollection of personally experienced events involves the retrieval of two main aspects of episodic memory, namely the retrieval of what events happened (item memory) and the retrieval of the context in which these events have been encoded (context memory) (Graham and Cabeza, 2001). Context memory stores various information including, for instance, details of the physical environment in which the events occurred, the voice in which information was pre- sented or the learner’s emotional state. Context memory allows distinguishing one stored event from similar events co-existing in memory, and provides cues for item retrieval. Consequently, recollection of memorized items is enhanced when recall of the learned information occurs in the same context than at learning. This ‘context-dependent memory’ phenomenon was observed for multiple dimensions of the contextual background of learning, including physical envi- ronment (Godden and Baddeley, 1975; Smith, 1979), room size, odours and background music (Parker et al., 2007) and mood state (Bartlett and Santrock, 1979; Kenealy, 1997). It is known that sleep contributes to the offline consolida- tion of item memories (Peigneux and Smith, 2010). However, its role in the processing of contextual information has received less attention, with inconsistent results. In one study (van der Helm et al., 2011), participants had to create an association between a poster on the wall (context) and a list of words (item). Two lists were learned, each associated with a different context. Although item memory was similar, context memory was enhanced selectively after the nap, suggesting sleep-dependent consolidation of the context. Conversely, in another study (Cairney et al., 2011) partici- pants learned two lists of words, each list in a room differing in size, odour and background music. Here, recall was better ª 2013 European Sleep Research Society 656 J Sleep Res. (2013) 22, 656–662 Unbinding memories