The Developing Engram – Imaging Memory Consolidation in Wakefulness and Sleep

• Applicant: Professorin Dr. Monika Schönauer
• Subject Area: Biological Psychology and Cognitive Neuroscience
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426865207

A question that has motivated research for decades is how continuous perception is transformed into lasting memories. New experiences leave lasting imprints in our brain, so-called “memory engrams.” But what determines whether an event will engender a neural engram and how long this physical record of the past will endure? Only if we can observe and manipulate the formation and development of memory traces in the brain can these questions be satisfactorily answered.After encoding, new memories have to be transformed to be stored for long term usage. During the course of this consolidation, the neural substrate supporting new memories is supposed to gradually shift from highly plastic hippocampal to slower-learning neocortical regions, a process that has been termed systems memory consolidation. This transformation is thought to be achieved by repeated training of neocortical memory networks, either by active rehearsal or by offline reactivation during sleep.Until recently, it has been difficult to study the covert processes that support memory consolidation. The advent of novel imaging methods and analysis approaches has now made it possible to locate and track memory engrams in both animals and humans. Contrary to the long-held belief that the neocortex is a slow learner, studies applying these tools have found that independent neocortical memory engrams are formed rapidly from the outset of learning.The overall goal of this proposal is to explore three factors that we think contribute to an accelerated redistribution of physical memory traces from the hippocampus to neocortex –retrieval, distributed practice, and sleep. We will apply novel diffusion-weighted imaging of learning induced plasticity in the human brain to test how and where memories are stored in the brain and to observe their redistribution over time. In particular, we will (1) assess how fast neocortical engrams emerge over repeated rehearsal, and whether they are formed at a temporal delay with respect to the hippocampal engram, (2) test whether rapidly formed neocortical engrams already carry specific information about the previous learning experience, (3) determine whether memory reactivation during sleep facilitates plasticity in the neocortex, and (4) whether beneficial effects of learning strategies such as learning by testing and distributed practice can be attributed to an acceleration of systems consolidation.Our results can help to critically revise model of memory consolidation, such that they make more accurate predictions about how the neocortex contributes to memory processing. Neocortical storage is critical for the long-term retention of new memories. Elucidating the factors that facilitate systems consolidation and neocortical plasticity is thus of the greatest relevance, not only for basic research, but also for clinical and educational settings.

• DFG Programme: Independent Junior Research Groups