Awake Memory Consolidation Can Bias the Way New Information Is Perceived

Post by Flora Moujaes 

What's the science?

Our brains consist of an estimated 100 billion neurons, which are connected to each other by over 100 trillion synapses. Whenever you experience an event, a specific set of neurons and a pattern of connections is activated. Memories are thought to be stored in these patterns of connections. However, we still don’t fully understand the process through which representations of experiences are consolidated into long-term memory. This week in Trends in cognitive sciences, Tambini and Davachi review new evidence from recent human fMRI studies showing that memory consolidation occurs through reactivations that happen outside of conscious awareness during awake periods, and that memory consolidation can bias on-going cognition.

What do we already know? 

The infamous patient H.M. had his hippocampus and surrounding medial temporal lobe (MTL) surgically removed in 1953, in an attempt to cure his epilepsy. However, the surgery left him unable to form new memories. This indicates that while the hippocampus and MTL are vital for the formation of new memories, long-term memory involves additional storage in cortical networks outside the MTL. Studies across multiple species have since confirmed that the hippocampus is vital for acquiring new memories and that these memories can then be transformed across hippocampal-cortical networks for storage in long-term memory. This transformation is widely believed to involve repeated memory reactivation, both during sleep and ‘offline’ during awake periods.

What’s new? 

The authors propose that repeated memory reactivation in the hippocampus during awake periods is related to memory strengthening. This memory reactivation happens offline, outside of conscious awareness. While more restful states promote memory reactivation, studies have shown it can occur alongside cognitively intensive tasks. Memory reactivation is closely related to the salience of the initial event, as it’s more advantageous to strengthen memories that may provide a greater learning potential. Memory reactivation is also associated with long-term memory storage, as studies have shown reactivation promotes memory integration across hippocampal-cortical networks. What’s also 'new' is that these processes have been studied mostly in animals, however, in this review, the authors summarize evidence that similar mechanisms can be studied in humans using non-invasive measures like fMRI. 

The authors propose that spontaneous reactivation can shape the way in which we experience and interact with the world. For example, emotional arousal is known to increase memory, and so if an emotional memory is consolidated offline while a memory task is being performed, performance on the task might improve. However, it is important to note that the mechanisms underlying the reactivation of memories may be similar to the mechanisms underlying the retrieval of memories, and so future work is needed to help disentangle human reactivation that supports ‘online’ cognition versus consolidation.

What's the bottom line? 

Human neuroimaging studies have shown that memory consolidation through reactivation occurs during awake periods. Tambini and Davachi emphasise memory consolidation is a complex process as: (1) it is related to memory strengthening, (2) it can be used to track the salience of information and thus whether information will get stored in long-term memory, and (3) it can bias the ways in which new information is encountered and processed. Overall, this review furthers our understanding of the process through which experiences are consolidated into long-term memory and highlights many new and exciting avenues for future research. 

Tambini and Davachi. Awake Reactivation of Prior Experiences Consolidates Memories and Biases Cognition. Trends in cognitive sciences (2019). Access the original scientific publication here.