Characterization of long-term memory formation for experimental, real-life-like stressful events on the behavioral and neural level - from encoding, over early to ling-term consolidation

• Applicant: Dr. Tobias Sommer-Blöchl
• Subject Area: Human Cognitive and Systems Neuroscience
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443416333

The memories for the episodes of our lives are initially vivid and detailed but most of them are transformed to more gist-like or even schematic representations. Our long-term memories for stressful experiences however, seem to stay particularly accurate and detailed. But human retrospective studies on traumatic memories suggest that those are only perceived as more detailed but not objectively better remembered. Consolidation theory propose that the transformation from detailed to gist-like and schematic memories is reflected in a shift along the hippocampal axis and to cortical memory retrieval. Longitudinal studies in humans over sufficiently long time periods to rigorously test these theories are currently missing. With respect to long-term memory for stressful events the only animal study suggests that they stay longer detailed and hippocampus dependent, contrary to the retrospective studies in humans. The goal of the first funding period was therefore to characterize long-term memory formation for neutral and stressful episodes, from encoding, over early- to long-term consolidation on the behavioural and neural level. Memory for a 2.5 hours long series of standardized real-life stressful and neutral episodes was tracked in 92 participants (46 controls) from time of encoding and over the 8 months following using behavioural measures, eye-tracking, biometrics, sleep polygraphy, and fMRI. The preliminary results show a transformation to less detailed and more false memories. This goes along with a shift towards prefrontal and temporal cortical retrieval indicating that systems consolidation clearly has begun. Memory formation for stressful episodes shows the hypothesized particularities starting with attentional narrowing during encoding, prolonged slow wave sleep – implicated in early-consolidation – in the subsequent night, greater amygdala activity during recall the next day and stronger precuneal involvement also after 8 months. On the next day, stressed participants recall more central and introspective details. Even after 8 months, the difference in introspective details still exists – consistent with higher subjective detailedness. Taken together, our preliminary results show clearly that long-term consolidation and transformation of the memories have begun but at the same time that these processes are not yet completed. It would be of great interest for current consolidation theories and for the understanding of the complex characteristics of our memories for stressful events to characterize the consolidation trajectories of these memories for an even longer time. The goal of the proposed project is therefore to build on this unique data set and follow-up the participants’ memories for up to 3 years after encoding. We propose not only to characterize the memories on the behavioural and neural level but also explore whether systems consolidation can be reversed and to what degree by then inaccessible details can be restored using fil.

• DFG Programme: Research Grants