What happens in deep sleep? Exciting new research!

In July 2018, we discussed recent research regarding how the flow of cerebrospinal fluid (CSF) in deep sleeps helps remove waste material from the brain.  This is important, because we believe that the accumulation of this waste, notably beta amyloid, is an important part of the Alzheimer's disease process.  One question we would like to answer is what causes the movement of CSF during deep sleep?

One thing we know is that the neurons shrink during deep sleep, increasing the volume of the space between them.  This allows CSF to move into the brain from the spine.  So that helps.  But the ALZForum recently reported on recent research at Boston University linking electrical activity in the brain -- brain waves -- with the movement of CSF during deep sleep.  The research suggests that electrophysiological waves drive slow pulses of CSF through the brain.

The linkage appears to be indirect.  The cyclic electrical activity causes changes in blood flow which then ... somehow ... causes movement of the CSF.  As we discussed before, the CSF picks up waste (hopefully including amyloid) and delivers it to the lymphatic system at the periphery of the brain.  (In Alzheimer's disease, a reduced presence of amyloid in the CSF may indicate that it is not being removed but is accumulating as plaques on neurons.)

So how did they do this?  They found 13 young volunteers willing to sleep overnight in an MRI machine with an EEG cap on their heads!  The EEG cap measured their brain waves, while the functional MRI (fMRI) measured both changes in blood oxygen levels (a proxy for blood flow) and the movement of CSF in the brain.  (In June of this year, we discussed how fMRIs can measure the activity of blood in the brain, activity that can be a proxy for neuronal activity.)   

The researchers then found a correlation between slow brain waves and changes in blood flow and changes in the flow of CSF.  The article describes a possible mode of linkage between these dynamics that begins with the reduced need for blood in the brain during deep sleep.  The reduced volume of blood in the brain increases the room for CSF which can be drawn up from the spine.  These movements are somehow synchronized with brain waves, although it wasn't clear to me what the mechanism for this might be.  I'm thinking that it wasn't (yet) clear to them either.

The subjects for this research were young.  The researchers noted that further studies should involve older people, perhaps including some with Alzheimer's disease.

I mentioned earlier that I had some scary cognition issue begin to appear last spring, although these seem to have subsided.  My neurologist attributed this to problems I was having sleeping, partly due to the long days and short nights we have here in the Pacific Northwest.  Sleep is so important to brain health!