On the Trail of Memory Traces: How Stress Affects Initial Memory Formation and Updating Processes

Abstract

Forming and updating memories are central aspects of human cognition, which are strongly affected by stressful encounters. Due to the large variety in study designs and lack of neural correlates, our understanding of how stress affects encoding and post-retrieval memory processes is limited. To uncover the underlying mechanisms, three multi-day neuroimaging studies were conducted as part of this thesis. Using Magnetoencephalography (MEG), study I investigated the role of theta oscillations in emotional encoding under stress. Studies II and III aimed to further delineate the interaction between stress and memory updating processes by employing functional Magnetic Resonance Imaging (fMRI) in a three-day associative memory task. While studies I and II employed a behavioral stress induction, study III leveraged a pharmacological intervention to increase either noradrenergic activity or cortisol levels. Despite differing methodologies, results of all three studies consistently highlight the critical role of the hippocampus and connected occipito parietal areas in memory formation and updating under stress. While study I revealed that increased theta oscillations in this cortico-hippocampal network during the encoding of emotionally negative images were linked to memory enhancements, results from studies II and III showed that stress, and especially noradrenaline, following a strong activation of a similar network during reactivation, significantly impaired subsequent memory. These findings suggest the cortico-hippocampal network to reflect a critical yet vulnerable target to stress across the whole memory formation process, yielding major relevance for (i) understanding the pathogenesis of stress-related disorders and (ii) developing targeted interventions to alleviate symptoms emerging from maladaptive memories.