The Role of Sleep in the Consolidation and Processing of Emotional Memory

Abstract

Spontaneous reactivation of memory traces during sleep enables long-term consolidation and integration of memories with prior knowledge. Emotion can enhance the consolida-tion of memories during sleep and during wakefulness. However, at the same time, emo-tion may disrupt consolidation of contextual information. Furthermore, sleep not only consolidates emotional memories, but may also influence emotional salience in terms of valence and arousal. The work presented in this thesis utilises behavioural declarative and procedural memory testing; subjective arousal, valence, and likeability testing; targeted memory reactivation (TMR); polysomnography (PSG); electroencephalography (EEG); and functional magnetic resonance imaging (fMRI), to investigate sleep-related processing and memory consolidation of emotional and neutral stimuli. In Chapter 2, we investigate sleep-dependent object-location memory and processing of valence and arousal. We use negative and neutral pictures paired with matching sounds as the stimuli. During slow-wave-sleep (SWS) or wakefulness, we replay half of the stimuli. TMR during SWS results in memory stabilization of the cued stimuli regardless of stimuli's emotionality. Furthermore, TMR enhances arousal habituation of the negative cued stimuli. TMR during wake has no effects in memory or emotional ratings. In Chapter 3, we use fMRI to further investigate the effects of TMR during SWS on emotional associative memory and arousal processing. At the behavioural level, our results indicate that the effects of TMR on arousal depend on whether the stimuli are negative or neutral and the duration of SWS. The neuroimaging results suggest that TMR has different effects on the neural correlates of arousal for negative and neutral stimuli. Furthermore, there is an interaction of TMR, emotion, and rapid-eye-movement sleep (REM) duration on the neural correlates of location memory. In Chapter 4, we investigate whether the neural traces of negative and neutral memories differ when they are reactivated during SWS. We trained an EEG classifier on wake data while participants imagined performing a motor sequence task they had previously practiced. Subsequently, we classified SWS data while auditory cues of the task were replayed. We find that the classification is above chance for both sequences, having either negative or neutral items. The classification rate of the negative sequence is positively correlated with pre-sleep performance and negatively correlated with overnight improvement. The classification rate of the neutral sequence is positively correlated with REM duration. Lastly, in Chapter 5, we investigate how implicit and explicit associative memory and emotional ratings change across periods of sleep or wakefulness. We use happy, peaceful, scary, and sad musical excerpts as stimuli. Our findings suggest that sleep stabilizes valence and arousal ratings and may stabilize explicit memory too. Conversely, wake makes valence more positive, increases arousal ratings and deteriorates explicit memory. Furthermore, emotions influence how ratings of valence and arousal and explicit memory change. These results shed light on the role of sleep in emotional processing and memory con-solidation. We provide evidence that TMR modulates emotional salience and associated memories differently for negative and neutral stimuli, both at the behavioural and at the neural level. Further work needs to be done to elucidate the different networks associated in the processing and consolidation of emotional and neutral stimuli, and the roles of SWS and REM.

Date of Award	1 Aug 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Ian Anderson (Supervisor) & Rebecca Elliott (Supervisor)