Reactivating aversive memories in humans: An EEG and Microstates study of post-retrieval processes

Although fear conditioning is one of the most widely used models to study anxiety in humans, much remains to be explored regarding its underlying neural correlates. In this study, we employed a three-day threat-conditioning protocol in which an angry face (conditioned stimulus, CS+) was paired with an aversive sound (unconditioned stimulus, US). Our main objective was to identify neural markers of post-retrieval processes triggered by the presentation of the CS+ alone, 24 hours after acquisition. We recorded resting-state electroencephalographic (EEG) activity before and after memory reactivation in two groups of participants (females and males counterbalanced): a Reactivation group previously exposed to threat conditioning on Day 1 (n=26) and a Control group (n=26) with no prior conditioning, focusing on memory-related patterns in the frequency domain and microstate dynamics. Our results confirmed successful conditioning and memory retention 48 hours later, as evidenced by implicit, declarative, and emotional responses. Regarding neural activity, we found lower beta-band activity (25-30 Hz) in central brain regions after reactivation, which may reflect enhanced post-reactivation processing of the threat conditioning memory, in contrast to participants who viewed the stimulus for the first time. We observed changes in microstates and a potential link between microstate C and conditioned threat memory. These findings provide initial evidence for neural correlates of post-retrieval processes of an implicit threat memory offering potential relevance for understanding mechanisms implicated in anxiety and related disorders.