New memories are initially labile and have to be consolidated into stable long-term representations. Current theories assume that this is supported by a shift in the neural substrate that supports the memory, away from rapidly plastic hippocampal networks towards more stable representations in the neocortex. Rehearsal, i.e. repeated activation of the neural circuits that store a memory, is thought to crucially contribute to the formation of neocortical long-term memory representations. This may either be achieved by repeated study during wakefulness or by a covert reactivation of memory traces during offline periods, such as quiet rest or sleep.
My research investigates memory consolidation in the human brain with multivariate decoding of neural processing and non-invasive in-vivo imaging of microstructural plasticity. We demonstrate that active rehearsal of learning material during wakefulness can facilitate rapid systems consolidation, leading to an immediate formation of lasting memory engrams in the neocortex. These representations satisfy general mnemonic criteria and cannot only be imaged with fMRI while memories are actively processed but can also be observed with diffusion-weighted imaging when the traces lie dormant. Importantly, also offline periods, such as sleep, hold a crucial role in stabilizing memories. Using multivariate pattern analysis on brain imaging data, we show that we spontaneously reprocess memories during sleep and in dreaming, and that this reactivation benefits memory retention. Online and offline reactivation may thus jointly contribute to forming lasting memories.
Characterizing the covert processes that decide whether, and in which ways, our brains store new information is crucial to our understanding of memory formation. In my talk, I will discuss how the potential to image memory consolidation in the human brain provides new opportunities for memory research.
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