Consolidation of Implicit Auditorily-Cued Motor Sequence Learning During SleepPublic
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An important tenet in memory research is the dissociation between explicit and implicit memory systems in the brain. Whereas a robust literature exists on the consolidation of memories in the explicit domain, research on implicit memory consolidation is relatively understudied, particularly questions about what is being consolidated and the mechanisms supporting implicit memory change. The key question guiding the investigation described in this dissertation is whether memory reactivation during sleep facilitates the consolidation of implicit memories. Sleep has been shown to be relevant for explicit memory reactivation, particularly through studies making use of targeted memory reactivation (TMR), a technique whereby sleep-dependent consolidation can be manipulated. We assumed that TMR could provide relevant information for understanding the basic mechanisms underlying the acquisition of implicit memories. Specifically, we hypothesized that TMR during slow-wave sleep might influence subsequent performance of an auditorily cued motor sequence that was implicitly learned prior to sleep. We also investigated the generalization of implicit sequence learning. The sequence learning task we used was developed to examine implicit memories independent of explicit knowledge. In one experiment, we found that implicit sequence knowledge did not readily generalize to minor changes in perceptual information along changes in the pitch interval of sound-key mapping (Chapter 3). We also found that sequence performance in the trained condition and generalization along the tone frequency perceptual dimension did not relate to the amount of explicit sequence knowledge participants had. In a further experiment, TMR during slow-wave sleep improved sequence performance, suggesting that it biased consolidation toward a stabilized representation (Chapter 4). The effects of TMR were transient, dissipating after a week, presumably due to the recovery of performance and greater performance improvements in the control group compared to the experimental cuing group. That is, spontaneous reactivation over a week of overnight sleep may contribute to long-term stabilization. Furthermore, we speculate that sleep between training sessions increased memory generalization. In general, sleep-induced neural reorganization may allow for more generalizable representations. However, future work would be needed to directly test the relationship between N3 sleep reactivation and sequence performance generalization. A dissociation found between sequence performance and explicit knowledge of the sequence also suggests that TMR during sleep influenced the consolidation of the implicit performance of the sequence memory independently of the explicit memory components. These findings contribute to our current understanding of implicit memory consolidation during sleep and suggest that reactivation mechanisms play a crucial role. Overall, sleep effects on implicit sequence performance highlight mechanisms of reorganization and stabilization of memories outside of active practice.
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