Researchers have published research results on REM sleep staging and cortical regulation

On November 18, Liu Danqian's research group of the Center for Excellence in Brain Science and Intelligent Technology (Institute of Neuroscience) of the Chinese Academy of Sciences published a research paper
entitled Cortical Regulation of Two-stage Rapid Eye Movement Sleep online in Nature Neuroscience 。 The study revealed and defined for the first time two phases of rapid eye movement sleep (REM sleep) in mice—quiet and active—corresponding to significantly different facial expressions, autonomic activity, and EEG spectrum
, respectively.
Using large-scale widefield fluorescence calcium imaging, it was found that the mouse postcompression cortex (RSC) was selectively activated during REM sleep and specifically initiated calcium waves propagating across brain regions
.
Combining two-photon imaging, machine learning algorithms and optogenetics, the important role
of RSC in the coding and regulation of REM sleep staging was clarified.
This work has achieved important progress in the understanding of REM sleep staging and regulatory mechanism, and laid a solid foundation
for exploring the complexity of dream sleep.

REM sleep was first discovered and defined
by American scientist Eugene Aserinsky.
When recording his son's sleep, he found a recurring sleep state - the eye muscles were highly active, and subsequently confirmed that this is a special sleep state, that is, accompanied by low frequency and high amplitude of brain electrical activity, obvious stiffness of trunk muscles, defined as REM sleep, often accompanied by rich and vivid dreams, also known as dream sleep
。 However, years after REM sleep was discovered, why did a state of high activity in the cerebral cortex shield external stimuli to maintain sleep? Why dream? Is the highly active cerebral cortex activity associated with dreams biologically significant? How are they involved in higher cognitive activities (e.
g.
, memory, emotional processing, etc.
)? These questions are not yet clearly answered
.
Evolutionarily speaking, REM sleep exists in birds, mammals and other higher animals with brain-like or cerebral cortex, so exploring the activity and regulation mechanism of the cerebral cortex in REM sleep is of great significance
for analyzing the evolutionary evolution of the nervous system.
However, existing studies have focused on a single cortical region, which has limitations
.
In this study, the calcium activity of the entire dorsal cortex of mice was detected with high spatiotemporal resolution on a large scale, and the relationship between
REM sleep regulation and cerebral cortical activity was analyzed from a global perspective.

In order to explore the cerebral cortex activity of REM sleep, the research team installed a transparent glass window covering the entire dorsal cortex in Thy1-GCaMP6s transgenic mice to observe the calcium signal of the global cerebral cortex, and simultaneously monitor the EEG, myoelectric, facial behavior and blood oxygen of the mice (Figure A).

The study first found that the activity pattern of the cerebral cortex during REM sleep was significantly different from that during the awake phase, and that the RSC brain region was specifically highly active in REM sleep among the eleven cortical functional modules obtained by spatially independent component analysis (Figure A).

Combining Granger causality and spatiotemporal "motif"), it was found that the cerebral cortex during REM sleep is rich in calcium waves that propagate across brain regions, and these calcium waves specifically start at RSC (Figure B).

Using two-photon microscopy for single-cell resolution calcium imaging, it was found that pyramidal neurons in the second/third layer of RSC (rather than the fifth layer) were significantly activated during REM sleep, indicating that selective activation of RSCs is also cell layer specific (Figure C).

When the researchers observed facial videos during the REM phase of mice, they found that in addition to intermittent rapid eye movements, there was a continuous abundance of facial movements, including those of the masticatory muscles and beards of the face (Figure D).

Through feature analysis and unsupervised clustering of facial expressions or facial EMG, REM sleep consists of two distinct phases, the "quiet" phase (qREM) without any facial movement and the "active" phase with facial movement (aREM, Figure D).

In both REM phases, there were significant differences in facial movement, EEG spectrum, and autonomic nervous system activity, and REM sleep always transitioned from qREM to aREM
.
During REM sleep, the population activity of RSC second/third layer neurons showed two distinct modes of timing (Figure C), and the switching of activity modes coincided with the transition of qREM →aREM (Figure E).

The specific inhibition of RSC activity during REM sleep by the closed-loop system showed that the fragmentation of REM sleep, the conversion of qREM → aREM and the maintenance of aREM were significantly reduced in mice, thereby clarifying the key role of RSC in REM sleep substage transition (Figure F).

This study revealed and defined the staging and switching rules of REM sleep for the first time, and systematically interpreted the characteristic transcerebral cortex calcium waves
in REM sleep.
RSC neurons play an important role
in mediating cortical calcium waves and regulating REM sleep staging.
In recent years, the observation and regulation of specific neural activity based on different stages of non-REM sleep have made rapid progress in the study of the function of non-REM
.
The REM sleep staging revealed in this study will promote the accurate analysis of REM sleep function and propose new ideas
for understanding the complexity of dream sleep.

The research work is supported
by the Chinese Academy of Sciences, the Ministry of Science and Technology, the National Natural Science Foundation of China, Shanghai Municipality and Lingang Laboratory.

(A) Schematic diagram of dual-channel widefield fluorescence imaging (top); Eleven functional modules REM sleep and wakefulness state activity differences (below).

(B) the three main calcium waves of REM sleep (left); Schematic diagram of calcium wave activity starting from RSC in REM sleep, where the thickness of the arrow represents the Granger causal value
of calcium activity between RSC and the target region.
(C) RSC L2/3 neuronal activity was obtained by two-photon imaging and divided into two types by k-means clustering, and the figure shows the calcium activity of
two types of RSC neurons during a period of REM sleep.
(D) Facial video of mice in REM sleep (upper left) acquired by infrared camera, where the mouse's eyes, beards, and cheeks at the masticatory muscle position have abundant movement in the late REM sleep period (upper right).

Next: Use the HOG algorithm to divide REM sleep substates - qREM and aREM
.
(E) Changes in calcium signaling in RSC L2/3 neurons during the REM sleep substate qREM to aREM (data processing normalizes qREM and aREM lengths to 1).

(F) Schematic diagram of closed-loop optogenetic experiments (top).

Specific inhibition of RSC excitatory neurons during REM sleep blocks the conversion of qREM to aREM and the maintenance of aREM (bottom).

Source: Center for Excellence in Brain Science and Intelligent Technology, Chinese Academy of Sciences