MECHANISMS OF MEMORY CONSOLIDATION

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.