MECHANISMS OF MEMORY CONSOLIDATION Justyna Maria Sobczak PhD University of York Psychology October 2017 ABSTRACT Extensive research has shown that sleep supports memory. Newer work suggests that wakefulness can also benefit retention of new information. However, the exact mechanisms which govern memory consolidation in sleep and wake are largely unknown. The implementation of new technologies, which draw on these natural memory processes, allows some insight into their characteristics. This work aims at elucidating some aspects of memory consolidation processes in the realm of sleep and wake. Firstly, we train novel non-words, a material previously indicated to benefit from sleep-associated consolidation, with explicit and implicit methods to determine whether the implicit learning (via the Hebb repetition task) would facilitate lexical integration independently of sleep. The results reveal that lexical integration of novel words is contingent on a good level of explicit training, followed by a consolidation delay with sleep. We speculate that sleep-associated consolidation may be mediated by the degree of overlap between new and already known material. To further capitalise on these findings, we test whether applying non-verbal cues during sleep can improve learning of novel words and their integration within the lexicon using Targeted Memory Reactivation (TMR) paradigm. Our results indicate that reactivating novel lexical representations in sleep improves their consolidation and facilitates their recall. However, the lack of lexical integration observed suggests the need for future research. Finally, based on recent evidence that quiet wakeful rest can result in comparable memory increases to sleep, we explore the consolidation during awake state using transcranial direct current stimulation (tDCS). We found that applying tDCS to the right occipital-parietal site enhances memory for a list of words as compared to no stimulation. The findings imply that memory consolidation during quiet wakefulness can be manipulated externally, which may direct future research. Nevertheless, the exact neuro- correlates of memory consolidation in quiet wake are yet to be fully investigated. 2 TABLE OF CONTENTS ABSTRACT ................................................................................................................................................................ 2 TABLE OF CONTENTS…………………………………………………………………………………………………… 3 LIST OF FIGURES ................................................................................................................................................... 7 LIST OF TABLES ..................................................................................................................................................... 9 ACKNOWLEDGEMENTS ................................................................................................................................... 10 DECLARATION ..................................................................................................................................................... 11 CHAPTER 1 GENERAL INTRODUCTION AND LITERATURE REVIEW .......................................... 12 1.1 Models of Memory Consolidation .............................................................................................. 13 1.1.1 Complementary Learning Systems (CLS) Account ......................................................... 14 1.1.2 Multiple Trace Theory (MTT) .................................................................................................. 16 1.2 Sleep and Memory Consolidation ............................................................................................. 18 1.2.1 Sleep and its cycle ................................................................................................................. 19 1.2.2 Sleep-dependent memory consolidation ..................................................................... 20 1.2.3 Summary ................................................................................................................................... 26 1.3 Role of Memory Consolidation in Novel Word Learning ................................................. 27 1.3.1 Sleep and word learning ..................................................................................................... 28 1.3.2 Fast and slow consolidation of novel words .............................................................. 31 1.3.3 Neural correlates of word learning ................................................................................ 34 1.3.4 Summary ................................................................................................................................... 35 1.4 Memory Manipulations during Sleep ...................................................................................... 36 1.4.1 Spontaneous mnemonic reactivations ......................................................................... 36 1.4.2 Reactivating memories in sleep -Targeted Memory Reactivation paradigm 38 1.4.3 Manipulating brain activity in sleep .............................................................................. 39 1.4.4 Summary ................................................................................................................................... 42 1.5 Memory Consolidation during Quiet Wakefulness ............................................................ 43 1.5.1 Quiet wakefulness and memory improvement ......................................................... 44 1.5.2 Physiological underpinnings of memory consolidation in quiet wakefulness ................................................................................................................................................ 46 3 1.5.3 Reduced interference and inhibition hypothesis ..................................................... 47 1.5.4 Oscillatory basis for memory consolidation in quiet wake .................................. 49 1.5.5 Summary ................................................................................................................................... 50 1.6 Conclusions ........................................................................................................................................ 50 1.7 Aims and Outline of the Thesis .................................................................................................. 51 CHAPTER 2 IMPLICIT VERSUS EXPLICIT MECHANISMS OF VOCABULARY LEARNING AND CONSOLIDATION ................................................................................................................................................ 52 2.1 Introduction ............................................................................................................................................. 52 2.2 Experiment 1 ........................................................................................................................................... 59 2.2.1 Method .............................................................................................................................................. 59 2.2.2 Results ............................................................................................................................................... 65 2.2.3 Discussion ........................................................................................................................................ 69 2.3 Experiment 2 ........................................................................................................................................... 71 2.3.1 Method .............................................................................................................................................. 71 2.3.2 Results ............................................................................................................................................... 71 2.3.3 Discussion ........................................................................................................................................ 73 2.4 Experiment 3 ..................................................................................................................................... 74 2.4.1 Method ............................................................................................................................................. 74 2.4.2 Results .............................................................................................................................................. 75 2.4.3 Discussion ....................................................................................................................................... 79 2.5 General Discussion ............................................................................................................................... 80 2.6 Conclusions ............................................................................................................................................. 84 CHAPTER 3 TARGETED MEMORY REACTIVATION IN LANGUAGE LEARNING ....................... 86 3.1 Introduction ............................................................................................................................................ 86 3.1.1 Memory reactivation in sleep ................................................................................................. 87 3.1.2 Sleep dependent consolidation of novel words .............................................................. 89 3.1.3 Neural correlates