Wide-spread brain activation and reduced CSF flow during avian REM sleep.
Level 5 - mechanism / opinion, no new human data
Animal neuroimaging study (CEBM Level 5).
PubMed 37277328 · doi:10.1038/s41467-023-38669-1
What was done
Functional magnetic resonance imaging (fMRI) was used to measure regional brain activation and ventricular cerebrospinal fluid (CSF) flow in naturally sleeping pigeons across wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep.
What was found
The abstract reports no numerical values. Directionally, REM sleep was characterized by activation in brain regions involved in visual processing (such as optic flow during flight). Ventricular CSF flow increased during NREM sleep relative to wakefulness, but decreased sharply during REM sleep.
Why it matters
This establishes that sleep-dependent CSF dynamics exist in birds, showing that NREM-associated CSF influx is evolutionarily conserved beyond mammals while demonstrating an apparent trade-off between REM brain activation and fluid clearance.
Limits
The study was conducted in pigeons, so findings cannot be directly assumed for humans or other non-avian species. The abstract does not report sample sizes, specific flow rates, effect sizes, or direct measures of parenchymal metabolic waste clearance.
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- contradicts Alcohol consumption reduces REM sleep, which consequently reduces glymphatic clearance.