Optical imaging and manipulation of sleeping-brain dynamics in memory processing

During sleep, the brain undergoes transitions of activity states and reorganization of neural circuits. Recent in vivo optical imaging and manipulation techniques are revealing spatiotemporal and multiscale brain dynamics during sleep and their functional roles in awake state cognition, including learning and memory. First, along with electrophysiological recordings, Ca2+ imaging is becoming the gold standard for tracking the activity of large neural ensembles to analyze memory replay during the sleep/wake cycle in freely moving and head-fixed animals. Comparable to the speed of electrophysiological recordings, voltage indicators can monitor neural activity at millisecond resolution. While one-photon systems have advantages in temporal resolution, two-photon lasers can image microstructures such as dendritic spines and axonal terminals in vivo. Also, optogenetic manipulation is used to perform loss- or gain-of-function experiments with temporal precision, cell-type, and pathway specificity without the artifacts observed with electrophysiological stimulation. In particular, closed-loop optogenetic manipulation is well suited to reveal the functional roles of neural activity and synaptic plasticity in each sleep/ wake state. Here, I describe the recent advances in optical imaging and manipulation approaches for sleepingbrain dynamics in memory processing.