The cerebrospinal fluid flows in waves across the brain and seems to "cleanse" it during sleep

Cerebrospinal fluid (CSF) is a biological fluid contained in the meninges and in which the brain and spinal cord swim. It helps to absorb the physical shocks to which the brain can be subjected, and also to eliminate molecules and other physiological waste. For the first time, neurobiologists have seen how LCS flows in waves through the brain during sleep. Observations that could lead to a better understanding of certain neurological disorders.

This latest study shows waves of cerebrospinal fluid (CSF), pulsating rhythmically during sleep, while eliminating the toxins accumulated during the day. The team explains that these findings could help in the study of various neurological and psychological disorders, particularly those associated with sleep disorders. The study was published in the journal Science .

" We have known for a long time that there are electrical waves of activity in neurons. But so far, we have not realized that there are really waves in the LCS,  "says neuroscientist Laura Lewis of Boston University.

The pulsatile rhythm of the cerebrospinal fluid

Previous studies have suggested that LCS is important for the elimination of brain toxins, but so far neuroscientists have not known or been able to observe this pulsating action. Combined with slow-wave brain activity (which partly serves to fix our memories) and the decreased blood flow that occurs during sleep, these CSF waves seem to eliminate unnecessary protein.

Graph showing a rise in the frequency of CSF waves during sleep (blue zone) compared to the waking state (pink zone). The data was obtained by fMRI. Credits: Nina E. Fultz et al. 2019

As the slow frequency of brain waves declines as we get older, the new study may help research into normal age-related problems as well as specific disorders. The researchers' work also means that it is now possible to know if a person is sleeping or not, simply by analyzing the LCS patterns on a brain scan.

Better understand the synchronization of physiological processes during sleep

For the purpose of the study, 13 subjects aged 23 to 33 years were followed during their sleep during an MRI. Future research could also focus on older subjects - again to try to detect the deterioration of the process as we get older. The researchers suggest that another improvement in follow-up studies might be finding ways to eliminate MRI: the noise it generates is not very conducive to sleep.

It remains to be seen how the LCS, brain waves and blood flow synchronize so effectively. It may be that when neurons are inhibited for the night, they do not need a lot of blood - and as the blood flows, the pressure in the brain is maintained by the influx of LCS.

Video showing the pulsatile flow of the LCS:


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