The Roles of Cortical Slow Waves in Synaptic Plasticity and Memory Consolidation.

Daisuke Miyamoto,Masanori Murayama,Daichi Hirai

doi:10.3389/fncir.2017.00092

Abstract

Sleep plays important roles in sensory and motor memory consolidation. Sleep oscillations, reflecting neural population activity, involve the reactivation of learning-related neurons and regulate synaptic strength and, thereby affect memory consolidation. Among sleep oscillations, slow waves (0.5–4 Hz) are closely associated with memory consolidation. For example, slow-wave power is regulated in an experience-dependent manner and correlates with acquired memory. Furthermore, manipulating slow waves can enhance or impair memory consolidation. During slow wave sleep, inter-areal interactions between the cortex and hippocampus (HC) have been proposed to consolidate declarative memory; however, interactions for non-declarative (HC-independent) memory remain largely uninvestigated. We recently showed that the directional influence in a slow-wave range through a top-down cortical long-range circuit is involved in the consolidation of non-declarative memory. At the synaptic level, the average cortical synaptic strength is known to be potentiated during wakefulness and depressed during sleep. Moreover, learning causes plasticity in a subset of synapses, allocating memory to them. Sleep may help to differentiate synaptic strength between allocated and non-allocated synapses (i.e., improving the signal-to-noise ratio, which may facilitate memory consolidation). Herein, we offer perspectives on inter-areal interactions and synaptic plasticity for memory consolidation during sleep.

Highlights

Neural oscillations during sleep support memory consolidation, which refers to post-learning processes whereby new memory transitions from a fragile to a stable form
In rodents, visually acquired declarative memory is dependent on slow waves (Binder et al, 2013, 2014) and ripples (Girardeau et al, 2009; Ego-Stengel and Wilson, 2010; Maingret et al, 2016); the causal relation between slow waves and non-declarative memory remain unclear
Our optogenetic study in mice demonstrated that slow waves are causally related to non-declarative memory of tactile-perceptual information (Miyamoto et al, 2016)

Summary

INTRODUCTION

Neural oscillations during sleep support memory consolidation, which refers to post-learning processes whereby new memory transitions from a fragile to a stable form. Was negligible, and spontaneous slow waves are rare and not repetitive during active wakefulness (Vyazovskiy and Harris, 2013; Fisher et al, 2016), neural activity in slow-wave rhythm in the NREM periods, when we applied optogenetic stimulation to sleep-deprived awake mice, would be important for memory consolidation. If sleep suppresses non-potentiated, but not potentiated, synapses during learning, the signal-to-noise ratio will increase, which may be good for memory consolidation These hypotheses have not been tested directly, recent studies (Diering et al, 2017; de Vivo et al, 2017) have shown cortical synaptic depression during sleep, at single-synapse resolution. While recent studies have reported sleep-related synaptic depression at a single-synapse resolution, how potentiated synapses with learning are processed during sleep remains a significant question

CONCLUSION

Findings

ETHICS STATEMENT