Preprint Human deep sleep facilitates faster cerebrospinal fluid dynamics linked to brain oscillations for sleep homeostasis and memory, 2025, Uji et al

Human deep sleep facilitates faster cerebrospinal fluid dynamics linked to brain oscillations for sleep homeostasis and memory

Makoto Uji, Xuemei Li, An Saotome, Ryosuke Katsumata, R. Allen Waggoner, Chisato Suzuki, Kenichi Ueno, Sayaka Aritake, Masako Tamaki

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Abstract
How sleep maintains our healthy brain function has remained one of the biggest mysteries in neuroscience, medical settings, and daily lives. While cerebrospinal fluid (CSF) during sleep have been implicated in metabolic waste reduction in animals, how CSF dynamics are driven in the healthy human brain during deep sleep remains elusive. A myriad of research has shown that crucial cognitive processing manifests in slow wave and rapid-eye movement (REM) sleep, suggesting that a key to maintaining brain functions lies in deep sleep.

By leveraging a simultaneous sparse-fMRI and polysomnography method, we demonstrate that deep sleep-specific faster CSF dynamics are associated with spontaneous brain oscillations in healthy young human participants.

Slow waves and sleep spindles during slow-wave sleep and rapid eye movements and sawtooth waves during rapid eye movement (REM) sleep are tightly linked to low-amplitude faster CSF fluctuations. In contrast, slow waves during light sleep and arousals produced large but slower CSF signal changes. Furthermore, CSF signals are significantly faster in frequency during deep than light sleep.

These brain oscillations during light and deep sleep recruited essentially different brain networks, with deep sleep involving memory and homeostatic circuits. Thus, human deep sleep has a unique way of enabling faster CSF dynamics that are distinctive from arousal mechanisms.

Link | PDF (Preprint: BioRxiv) [Open Access]

 

It’s funny, a while ago I started using an app that tracks sleep movement so it could wake me up at the “optimal point” within a 45 minute time frame. The only mornings that I felt anything approaching well rested, my sleep tracker showed that I spent nearly the entire night in deep sleep. My entire head felt so much clearer.

 

I experienced that once a long time before I got sick, at an altitude of ~4000 meters. It was a striking difference, but I never got around to fixing my sleep. Now I do everything right and sleep terribly

 

It seemed like this only happened when I was active enough during the day to “tire myself out” in the same way that healthy people describe from good exercise, but not active enough to trigger PEM and insomnia. Very rare balance to strike, I truly don’t think any amount of sleep hygiene discipline would make it happen more often.

 

Agreed as long as you’ve got ME/CFS. If healhy, sleep hygiene probably can get you a lot closer to «good sleep».

 

I'd say good sleep hygiene can still move anyone in the right direction at least. I stopped looking at my phone after midnight every night which made the biggest difference, and now falling asleep is fairly quick. I added more bright light during the day (which I understand would be an issue for many with ME/CFS) and now I sleep about an hour longer on average. Unfortunately, on many days I still only sleep about 6 hours and don't feel as rested, but it's better than it was.

 

I stay off all my devices after 4pm and don't turn them back on until the next day after 8am. I was surprised how I drifted off to sleep when I didn't even feel tired and thought I wouldn't fall asleep.

 

Looks from a quick glance at the pdf that there were only 25 people being studied.