Episodic integration under stress

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The integration of separate events to episodes is a fundamental process for episodic-autobiographical memory. Recent research shows that this integration is critically mediated by the medial prefrontal cortex (mPFC) and hippocampus, with different subregions of the hippocampus representing episodes at a different degree of abstraction. Both the mPFC and the hippocampus are highly sensitive to stressful events and the hormones and neurotransmitters that are released in response to stressful encounters; stress is thought to reduce the activity in those areas. Whether stress affects the integration of events to episodes and which neural mechanisms are involved in the putative stress effect is completely unknown, despite the considerable implications of this issue, also for applied contexts. We hypothesize that stress impairs the integration of events to episodes and the neural processes supporting this integration, mainly in the mPFC and hippocampus. More specifically, we predict that stress will reduce the hippocampal mismatch-reaction and the hippocampal-prefrontal reorganization after insight into the relationship of previously unrelated episodes. Furthermore, we assume a stress-induced decrease in the hierarchical representation of episodic relationships along the hippocampal long axis. These stress-induced changes should result in impaired memory for the encoded episodes and their relationships after one week. In order to test these hypotheses, healthy volunteers will be exposed to a stressor or a control manipulation before they complete, in a MRI scanner, a task that probes episodic integration processes. The successful integration is tested immediately after the task as well as one week later. Beyond their crucial relevance for our understanding of episodic-autobiographical memory in general, the findings of this project might have important implications for stress-related mental disorders, such as post-traumatic stress disorder, in which disintegrated and fragmented memories for events encoded under high stress conditions are very common.