REM Sleep Loss Harms Brain Connectivity

In a recent study published in the journal Translational Psychiatry, researchers looked into the effects of full-night, early-night, and late-night sleep deprivation on whole-brain connectivity. They used connectome-based predictive modeling (CPM) to analyze data from the Somte polysomnographic (PSG) mobile recording system, which included electroencephalography (EEG), electrooculography (EOG), and electromyography (EMG) recordings from a cohort of 113 right-handed adult volunteers from Beijing universities.

The study on Brain connectivity found that the rapid eye movement (REM) sleep stage was strongly linked to connections within and between the default mode network (DMN), the cingulo-opercular network (CON), and the visual and auditory networks. They also discovered that the thalamus plays an important part in the REM connectome, serving as a relay station for sensory information during REM. While not the first to establish a link between REM sleep loss and DMN connectivity, this study indicated that late-night sleep loss had the greatest impact on the latter, potentially increasing the risk and severity of psychiatric diseases.

Background

Sleep deprivation is a hidden pandemic in today’s fast-paced world, with studies showing that more than 30% of Americans do not get enough sleep. Sleep deprivation has been shown to have a significant impact on people’s physical and emotional well-being, making it a major public health concern. Sleep deprivation as a result of psychosocial stress, shifts in work schedules, and, most importantly, excessive electronic media intake have previously been related to obesity, an increased risk of metabolic disorders, and emotional disruptions.

Unfortunately, a large amount of these findings are based on anecdotal or observational evidence, with no rigorous research into the effects of sleep disruptions on dynamic reorganizations of important brain components. Recent studies have attempted to elucidate how the two distinct sleep phases – rapid eye movement (REM) and non-REM (NREM; also known as slow-wave sleep [SWS]) are related to sleep duration and time, with the latter predominating in early-night periods and the former occurring later in the night. While science has established the relevance of REM sleep in maintaining the brain’s energy balance and removing active-state metabolic waste, the relationship between REM and brain function is still unclear.

About the study

In the current study, researchers employed the split-night paradigm. This study procedure divides rapid eye movement (REM) and non-rapid eye movement (NREM) sleep to answer two major questions:

What specific brain areas are connected with REM?
How can REM sleep interruptions (particularly late-night ones) affect REM-associated brain networks in comparison to normal sleep?

The study cohort consisted of right-handed adult volunteers recruited from six Beijing universities. Following screening, 113 volunteers were randomly assigned to one of three investigation cohorts: late-night sleep deprivation (n = 41; sleep duration from 23:00 to 03:30), full-night sleep (n = 36; sleep duration from 23:00 to 08:00), or early-night sleep deprivation (n = 36; sleep duration from 03:00 to 07:30). Participants were required to abstain from alcohol, drugs, and caffeine for two days before the study began. Following the sleep restriction intervention, all subjects underwent experimental investigations at 08:00 a.m. The participants’ usual sleep patterns were recorded using sleep actigraphy and a seven-day sleep diary.

Resting-State Functional MRI (rs-fMRI) scans were used in the experimental studies to discover regional brain connections after sleep restriction therapies. Somte polysomnographic (PSG) mobile recording equipment were utilized to measure and record electroencephalography (EEG) values (F3, F4, C3, C4, O1, O2), electrooculography (EOG), and electromyography (EMG). The American Academy of Sleep Medicine (AASM) criteria were used to measure and manually score participants’ sleep stages.

The above-mentioned data was utilized to divide participants’ brains into 227 regions, which included ten brain networks. These networks were the default mode network (DMN), the dorsal and ventral attention networks (DAN and VAN), the visual network (VIS), and the auditory network (AUD). Using rs-fMRI data, Connectome-based Predictive Modeling (CPM) was used to reveal neural network connection patterns.

Study findings

REM sleep pattern segment analysis found that late-night sleep had a considerably longer duration and proportion of REM sleep than early-night sleep. When the full-night sleep (FS) group data was divided into early-FS and late-FS groups, and late-FS data was compared to early- and late-night sleep cohorts, the findings revealed that the early-deprivation group showed significant decreases in both duration and proportion of REM sleep state, whereas the late-deprivation group only showed reductions in duration.

However, early deprivation patterns produced much better REM effects than late deprivation. These data suggest that, while both early and late deprivation have a deleterious impact on REM sleep states, the early deprivation pattern is preferred when lifestyles or vocations require sleep deprivation. A multi-level analysis of the REM sleep connectome indicated that the CPM is mostly located in the DMN-DMN and CON-CON networks, but it is also seen in subcortical (SUB)-VIS networks. Surprisingly, the thalamus and visual/auditory cortex were discovered to have critical roles in CPM predictions and, consequently, the REM connectome.

“…we observed that the thalamus exhibited the highest degree centrality and made a significant contribution to the REM connectome. Additionally, the subcortical networks, to which the thalamus belongs, displayed the third most prominent predictive edges. During REM sleep, the thalamus acts as a relay station for sensory information, transmitting signals from the environment to the cerebral cortex. It is involved in regulating the transition between different sleep stages, including the onset and termination of REM sleep cycles.”

The study does have a significant flaw in that it just measures brain activity and connection without looking into behavioral changes (such as cognition or memory). Despite this restriction, the study lays the framework for future investigations into both psychiatric and NREM evaluations.

Conclusions

The current study emphasizes the effects of early and late sleep deprivation on REM sleep patterns by identifying network connectivity and affected brain areas during these increasingly widespread suboptimal behaviors. The study’s findings show that sleep deprivation and disturbances have a deleterious influence on the DMN network and may impair thalamic function. In conclusion, this work adds to our understanding of how REM sleep phases sustain or adjust variability in normal brain functioning.

For more information: Di, T., Zhang, L., Meng, S. et al. The impact of REM sleep loss on human brain connectivity. Transl Psychiatry 14, 270 (2024), DOI – 10.1038/s41398-024-02985-x, https://www.nature.com/articles/s41398-024-02985-x