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Wide-spread brain activation and reduced CSF flow during avian REM sleep
Gianina Ungurean1, Mehdi Behroozi2, Leonard Böger3,4
1Avian Sleep Group, Max Planck Institute for Biological Intelligence, Seewiesen, Germany. gianina.ungurean@bi.mpg.de.
Nature Communications
|June 5, 2023
Summary
Brain waste clearance via cerebrospinal fluid (CSF) flow during sleep differs between bird and mammal sleep stages. In pigeons, CSF flow increases during non-rapid eye movement (NREM) sleep but drops during REM sleep, unlike in mammals.
Area of Science:
- Neuroscience
- Comparative Physiology
- Sleep Research
Background:
- Mammalian sleep facilitates brain waste clearance via the glymphatic system and cerebrospinal fluid (CSF) flow.
- This process is crucial for removing toxic proteins accumulated during wakefulness.
- Previous studies linked CSF flow to non-rapid eye movement (NREM) sleep in mice and humans.
Purpose of the Study:
- To investigate the relationship between sleep stages and CSF flow in birds, a group not previously studied.
- To compare avian sleep-related CSF dynamics with those observed in mammals.
Main Methods:
- Utilized functional magnetic resonance imaging (fMRI) to image naturally sleeping pigeons.
- Monitored brain activity and ventricular CSF flow during different sleep stages (wakefulness, NREM, REM).
Main Results:
- REM sleep in pigeons showed activation in visual processing areas, similar to wakefulness.
- Ventricular CSF flow increased during NREM sleep compared to wakefulness.
- CSF flow significantly decreased during REM sleep in pigeons.
Conclusions:
- Avian REM sleep, characterized by high brain activity, may compromise waste clearance functions.
- Sleep-dependent CSF flow dynamics in birds differ from mammals, suggesting divergent evolutionary paths for brain maintenance.
- The trade-off between brain activation and waste clearance during REM sleep may be a conserved, yet differently implemented, feature across vertebrates.
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