TY - JOUR T1 - Low activity microstates during sleep JF - bioRxiv DO - 10.1101/067892 SP - 067892 AU - Hiroyuki Miyawaki AU - Yazan N. Billeh AU - Kamran Diba Y1 - 2016/01/01 UR - http://biorxiv.org/content/early/2016/08/05/067892.abstract N2 - A better understanding of sleep requires evaluating the distinct activity patterns of the brain during sleep. We performed extracellular recordings of large populations of hippocampal region CA1 neurons in freely moving rats across sleep and waking states. Throughout non-REM (non-rapid eye movement) sleep, we observed periods of diminished oscillatory and population spiking activity lasting on the order of seconds, distinct from characterized DOWN states, which we refer to as “LOW” activity sleep states. LOW states lasted longer than characterized DOWN states and were distinguished by a subset of “LOW-active” cells. LOW activity sleep was preceded and followed by increased sharp-wave ripple (SWR) activity. We also observed decreased slow-wave activity (SWA) and sleep spindles in the hippocampus local-field potential (LFP) and neocortical electroencephalogram (EEG) upon LOW onset, but only a partial rebound immediately after LOW. LOW states demonstrated LFP, EEG, and electromyogram (EMG) patterns consistent with sleep, but otherwise resembled previously described small-amplitude irregular activity (SIA) during quiet waking. Their likelihood increased over the course of sleep, particularly following REM sleep. To confirm that LOW is a brain-wide phenomenon, we analyzed data from the entorhinal cortex of rats, medial prefrontal cortex, and anterior thalamus of mice, obtained from crcns.org and confirmed that LOW states corresponded to markedly diminished activity simultaneously in all of these regions. We propose that LOW states are an important microstate within non-REM sleep that provide respite from high-activity sleep, and may serve a restorative function.Significance Statement In large-population neural recordings from sleeping rats, we observed long-lasting LOW activity epochs during which neuronal spiking and oscillatory activities were suppressed. By incorporating data from multiple brain regions, we observed that LOW states are a far-reaching phenomenon and not restricted to the hippocampus. The likelihood of occurrence of LOW activity states varied inversely with sleep pressure, increasing with time asleep, particularly after REM, and decreasing following time awake. These LOW activity states may allow neurons to rest and repair and provide windows for potential transitions to waking. ER -