Research has shown that sleep is essential for cognition and healthy brain function. Slow waves in neural activity contribute to memory consolidation and cerebrospinal fluid can clear metabolic waste products. However, the relationship between these two processes had yet to be seen. Cerebrospinal fluid is a translucent liquid that flows around the brain and helps cushion the brain and spinal cord from injury, as well as providing nutrients.
Yet, this study revealed an additional function. The researchers used accelerated neuroimaging to measure the physiological and neural dynamics in the human brain, and unveiled a pattern that suggests a coherent connection between brain dynamics during non-rapid eye movement sleep.
The study participants were asked to lie down and fall asleep inside an MRI machine wearing an EEG cap. This allowed the researchers to observe the blood oxygen levels in their brains and how much cerebrospinal fluid flowed in and out of their brains via the MRI machine. And meanwhile, the EEG caps simultaneously measured the electrical currents flowing through their brains.
The researchers discovered that during non-REM sleep, the stage of sleep that occurs when a person is transitioning from being awake to falling asleep, large, slow waves of fluid were washing over the participants’ brains after an electrical wave when the neurons would stop firing. This meant that less blood would flow within the brain, yet cerebrospinal fluid would rush in to fill the space, clearing out metabolic byproducts as it moved.
This study shows that sleep has a very distinct function for the brain, and this could have exciting clinical applications for patients in need of cognitive support.
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