An Insightful Trio: Stress, Imagination and the Angular Gyrus Shape Mnemonic Integration

Abstract

Updating memory is essential for maintaining an accurate model of the world. Yet, our understanding of how we integrate new information into existing memory has remained limited. Therefore, this work aims to delineate the factors that shape mnemonic integration. Building upon prior research emphasizing the anterior hippocampus's role in mnemonic integration and the impact of stress on hippocampal function, Study 1 leveraged fMRI to explore how acute stress affects mnemonic integration. Although stress boosted recognition, it disrupted a representational change in the anterior hippocampus, likely by decreasing hippocampal activity during insight. Inspired by the anterior hippocampus’s role in mnemonic integration and imagination, Study 2 utilized fMRI to investigate the behavioral and neural consequences of imagination-based insight. While improving overall memory, imagination resulted in lower immediate insight and abolished a representational change in the anterior hippocampus, possibly due to heightened hippocampal activity during imagination. To explore the role of the angular gyrus in mnemonic integration, given its implications in memory and imagination, we combined inhibitory continuous theta burst stimulation (cTBS) at the angular gyrus with electroencephalography (EEG) in Study 3. Angular gyrus inhibition reduced the memory boost for integrated narratives and eliminated representational changes for linked events in the theta band. These findings converge in a comprehensive model, positing the angular gyrus as a buffer and proposing an inverted U-shaped relationship between hippocampal activity and mnemonic reconfiguration when integrating previously separate events. Altogether, these insights enhance our comprehension of mnemonic integration and may aid in developing a better understanding of the etiology of conditions such as posttraumatic stress disorder (PTSD).