Memories replayed: reactivating past successes and new dilemmas

Abstract

Our experiences continue to be processed ‘offline’ in the ensuing hours of both wakefulness and sleep. During these different brain states, the memory formed during our experience is replayed or reactivated. Here, we discuss the unique challenges in studying offline reactivation, the growth in both the experimental and analytical techniques available across different animals from rodents to humans to capture these offline events, the important challenges this innovation has brought, our still modest understanding of how reactivation drives diverse synaptic changes across circuits, and how these changes differ (if at all), and perhaps complement, those at memory formation. Together, these discussions highlight critical emerging issues vital for identifying how reactivation affects circuits, and, in turn, behaviour, and provides a broader context for the contributions in this special issue. This article is part of the Theo Murphy meeting issue ‘Memory reactivation: replaying events past, present and future’.

Early excitatory and inhibitory modifications in the motor cortex following skill learning support motor memory consolidation and cortical plasticity overnight

“…One of these processes may be the offline reactivation/replay of recently acquired motor memories. Offline memory reactivation/replay is currently thought to play a vital role in the consolidation of explicit and implicit new memories 14 , even during wakefulness 80 . While offline memory reactivation has been investigated mainly in the hippocampus and in the context of episodic memory, recent evidence suggest a similar process occurs in the motor cortex in both animals 15 and humans 3 .…”

“…In addition, changes in the functional communication between M1 and related brain regions have been shown following the acquisition of new skills 9–12 , highlighting the importance of early post-learning functional modifications to the learning outcomes 9 . Moreover, offline motor memory reactivation, a putative mechanism of memory consolidation 13,14 , has been demonstrated in M1 in animals 15 , and evidence for motor memory reactivation has also been demonstrated in humans 3 , by demonstrating a resemblance of neural activity patterns during rest following learning to those observed during the learning experience itself 16 . However, while significant progress has been made regarding the offline macroscopic and systems-level modifications, the microscale mechanisms which may underlie motor consolidation and skill learning-induced plasticity in the human brain remain unclear.…”

Clustering and temporal organization of sleep spindles underlie motor memory consolidation

“…The repeated practice of a motor skill is crucial for its initial acquisition 1 . Yet, ample evidence from both animal and human studies indicate that following this early learning phase, the resulting motor memory trace is thought to be dynamically maintained during wakefulness and actively reprocessed (reactivated) during a subsequent sleep period [2][3][4] .…”

Memory reactivations during sleep: a neural basis of dream experiences?

“…Nonetheless, a few recent investigations in both humans and non-human mammals have extended evidence of reactivation for other types of experiences, such as motor learning (e.g., [32,33,51]), visual memory [31], associative memory [34], declarative memory [35,36], and social memory [52]. However, which information of the encoded memory is reactivated remains unclear [53]. The content of reactivation may not only reflect past learned experiences but also anticipated experiences.…”