Coupling brain cerebrovascular oscillations and CSF flow during wakefulness: An fMRI study
Cerebral spinal fluid (CSF) plays an important role in the clearance of metabolic waste products from the brain, yet the driving forces of CSF flow are not fully understood. It is commonly believed that CSF flow is facilitated by the blood vessel wall movements (i.e., hemodynamic oscillations) in the brain. A coherent pattern of low frequency hemodynamic oscillations and CSF flow was found recently during non-rapid eye movement sleep (NREM) sleep via functional MRI. However, questions remain regarding 1) the explanation of coupling between hemodynamic oscillations and CSF flow using fMRI signals; 2) the existence of the coupling during wakefulness; 3) the direction of CSF flow. In this resting state fMRI study, we proposed a mechanical model to explain the coupling between hemodynamics and CSF flow through the lens of fMRI. We found that the observed delays between these two signals match those predicted by the model. Moreover, by conducting separated fMRI scans of the brain and neck, we confirmed the low frequency CSF flow at the fourth ventricle is bidirectional. Our finding also demonstrates that CSF flow is facilitated by hemodynamic oscillations mainly in the low frequency range, even when the individual is awake.