Sleep stage dynamics in neocortex and hippocampus

Abstract

Mammalian sleep comprises the stages of slow-wave sleep (SWS) and rapid eye movement (REM) sleep. Additionally, a transition state is often discriminated which in rodents is termed intermediate stage (IS). Although these sleep stages are thought of as unitary phenomena affecting the whole brain in a congruent fashion, recent findings have suggested that sleep stages can also appear locally restricted to specific networks and regions. Here, we compared in rats sleep stages and their transitions between neocortex and hippocampus. We simultaneously recorded the electroencephalogram (EEG) from skull electrodes over frontal and parietal cortex and the local field potential (LFP) from the medial prefrontal cortex and dorsal hippocampus. Results indicate a high congruence in the occurrence of sleep and SWS (>96.5%) at the different recording sites. Congruence was lower for REM sleep (>87%) and lowest for IS (<36.5%). Incongruences occurring at sleep stage transitions were most pronounced for REM sleep which in 36.6 per cent of all epochs started earlier in hippocampal LFP recordings than in the other recordings, with an average interval of 17.2 ± 1.1 s between REM onset in the hippocampal LFP and the parietal EEG (p < 0.001). Earlier REM onset in the hippocampus was paralleled by a decrease in muscle tone, another hallmark of REM sleep. These findings indicate a region-specific regulation of REM sleep which has clear implications not only for our understanding of the organization of sleep, but possibly also for the functions, e.g. in memory formation, that have been associated with REM sleep.

Heterogeneous profiles of coupled sleep oscillations in human hippocampus

“…Also noteworthy is that while fast spindle peaks were absent during REM at the scalp (in line with sleep scoring criteria), such peaks were sometimes observed in HPC ( Fig. 1DG), possibly related to asynchronous sleep stage transitions between brain structures (60,61). In contrast, REM beta power frequently showed a peak at the scalp, but generally not in HPC.…”

Local Aspects of Avian Non-REM and REM Sleep

“…However, such local sleep is not restricted to these animals. As new technology allows more brain regions to be examined simultaneously, it is becoming evident that even in conventional mammalian models for studying sleep, such as rodents and humans, traits used to define different states can occur at the same time in different brain regions (Nir et al, 2011, 2017; Vyazovskiy et al, 2011b; Emrick et al, 2016; Funk et al, 2016; Tamaki et al, 2016; Durán et al, 2018). Herein, we review the various types of local sleep found in birds, including those not known to occur in mammals.…”

The Transition Between Slow-Wave Sleep and REM Sleep Constitutes an Independent Sleep Stage Organized by Cholinergic Mechanisms in the Rostrodorsal Pontine Tegmentum

“…Transition states are difficult to analyze because of their short duration and complexity. However, these periods are critical since they involve changes in multiple brain areas that are essential for the proper establishment of each sleep stage (Durán et al, 2018; Sánchez-López et al, 2018). One of these critical transition states is the slow-wave sleep (SWS) to rapid eye movement (REM) sleep transition.…”