Characterizing rapid rehearsal-induced memory consolidation and its modulation by sleep by combining fMRI and intracranial EEG

• Applicants: Dr. Jonas Bause; Dr. Svenja Brodt
• Subject Area: Human Cognitive and Systems Neuroscience ; Biological Psychology and Cognitive Neuroscience
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545540192

Memory rehearsal is a powerful tool to facilitate long-term memoryformation, however the underlying neural mechanisms are still largely unknown. Recent research has revealed a remarkable resemblance between rapid changes in functional brain activity in the neocortex (NEO) and hippocampus (HC) after rehearsal and time-dependent memory reorganization. This has sparked the idea that rehearsal might provide a means to speed up systems memory consolidation by effecting the necessary reactivation otherwise generated during off-task periods like sleep. However, it remains unknown whether rehearsal and sleep induce similar kinds of memory representations. Here we aim to characterize rehearsal-induced consolidation by systematically investigating similarities and differences with sleep-dependent consolidation. We hypothesize that rehearsal also rapidly engenders stable memories integrated into NEO networks, but that these memories will be more precise, remain context-specific and rely more on posterior parietal networks compared to sleep-dependent consolidation. Assuming complementarity of rehearsal- and sleep-dependent consolidation, we predict that sleep after rehearsal will further transform memory traces. To this end, participants will learn object-place associations either once or by repeated encoding and retrieval. Memory quality will be tested at multiple delays. To assess the effect of sleep, the retention phase will start with a day of wakefulness, a night of sleep or sleep deprivation. This paradigm will be applied in three different studies, each using a different neuroimaging technique tailored to assess one aspect of the declarative memory system. In Tübingen, we will leverage the whole-brain coverage of 3T fMRI to study distributed NEO networks and the higher signal-to-noise ratio of 9.4T fMRI to zoom in on the role of HC subunits at submillimeter resolution. In Lyon, intracranial EEG (iEEG) in patients with epilepsy will enable us to investigate HC-NEO communication at high temporal resolution. Multivariate pattern analyses will allow us to precisely characterize how represented information is shaped by rehearsal, sleep and their combination. Furthermore, the previously reported changes of a rapid shift from HC to NEO networks across rehearsal suggest that rehearsal might even serve as a compensation strategy for memory deficits caused by HC dysfunction by providing a shortcut to NEO networks. Investigating memory impaired patients with medial temporal lobe epilepsy with iEEG offers the unique opportunity to explore the underlying dysfunctional and potential compensative mechanisms of rehearsal. Beyond the crucial relevance for our general understanding of memory consolidation, investigating the nature and neural underpinnings of rehearsal-consolidated memory can inform us about the optimal conditions for applying rehearsal as a mnemonic technique in educational as well as pathological contexts.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partners: Professorin Laure Peter-Derex, Ph.D.; Dr. Nadine Ravel