Unraveling the effects of memory reactivation on emotional memory

Abstract

While emotional memory is evolutionarily adaptive to threatening life events, excessive emotional memories contribute to mental health disorders and impair daily functioning. In Chapter 1, we introduced the consolidation and reconsolidation of emotional memory, and how the emotional memory could be potentially attenuated by memory reactivation. In Chapter 2, we conducted a meta-analysis to compare memory reactivation during wakefulness and sleep. Consolidated emotional memories can be potentially intervened by memory reactivation during wakefulness with the reconsolidation-based approaches and during sleep with targeted memory reactivation (TMR). Our meta-analysis compiled 26 studies with 119 effect sizes (N = 1594) for memory reconsolidation studies and 14 studies with 24 effect sizes (N = 583) for TMR studies. Based on the three-level modeling, the reconsolidation studies with memory reactivation showed a significant moderating effect of memory reactivation in modulating fear responses in the overall sample. In contrast, the overall sleep TMR had no effect on modulating emotional memory. This meta-analysis suggested that memory reactivation followed by a behavioural intervention during wakefulness had a stronger effect than memory reactivation followed by TMR during sleep in modulating memory. In Chapter 3, we performed two behavioral experiments on the interplay of the reactivation of fear memory and eye movement. In the two independent experiments, we investigated whether post-reactivation extinction learning with eye movement reduced the return of fear in a 3-day classical conditioning paradigm. Experiment 1 examined extinction learning with eye movement at standard speed (1.0 Hz) in interfering with non-reactivated fear memories. Experiment 2 examined extinction learning with eye movement of standard speed and fast speed (1.2 Hz) in interfering with the reactivated fear memories. Results showed that extinction learning with standard eye movement elicited significantly larger pupil responses than standard extinction (no eye movement) in the test of reinstatement in both experiments. However, extinction learning with faster eye movement did not elicit greater pupil size responses in the test of reinstatement in Experiment 2. Taken together, our two behavioral experiments did not support the efficacy of eye movements on reducing the return of fear , but extinction learning with faster eye movement may induce greater cognitive load and reduce fear responses to a greater extent. In Chapter 4, we summarized the key findings and discussed the potential implication of memory reactivation in modulating emotional memories in humans and its potential clinical applications.