How the reconstruction of simple event memories dynamically unfolds in human brain and behaviour

Abstract: Memories are not exact replicas of the events we originally experience. How does the brain, step-by-step, reconstruct information about past events? What features are preferentially recalled? The talk will give an overview of our work investigating how memory reconstruction dynamically unfolds over time, using pattern analysis of electrophysiological and fMRI data as well as behavioural reaction time analyses. The results highlight two prominent characteristics of memory recall. First, when the hippocampus reactivates a previously stored visual memory, the information flow in neocortex tends to follow a reverse feature processing hierarchy compared to initial perception, starting with the reconstruction of high-level conceptual image features and ending with low-level perceptual detail. We also find consistent evidence for a representational shift towards conceptual features (“semanticisation”) over longer consolidation periods and with repeated, active recall. Second, memory reactivation is rhythmic, as visible in brain and behaviour. This observation is in line with models suggesting that the hippocampal theta rhythm orchestrates the timing of memory reactivation relative to incoming sensory input, and can help segregate overlapping, potentially competing memories. Together, these findings emphasise the dynamic and reconstructive nature of our memories.