Effect of brief rest on hemodynamics and CSF oscillations across age

Brief eyes-closed rest (e.g., 30 min) during the day promotes rejuvenation and enhances mental clarity. However, its effect on neurofluid dynamics-including cerebral hemodynamics and cerebrospinal fluid (CSF) oscillations-remains largely unexplored. These neurofluid dynamics, driven by low-frequency oscillations (LFOs), respiration, and cardiac pulsation, play a critical role in the brain's waste clearance and may serve as a key mechanism underlying the cognitive benefits of rest. This study used fast functional MRI (TR=363msec) to assess neurofluid dynamics across three frequency bands in five key regions of interest (ROI): cerebral arteries, superior sagittal sinus, grey matter, white matter, and fourth ventricle CSF. Measurements were taken before and after 30 min of eyes-closed rest in a cohort of 38 participants aged 35-82. After rest, we observed a significant increase in LFO power across all five ROIs, suggesting that enhanced LFO may promote neurofluid clearance and contribute to the rest's restorative effects. Concurrently, cardiac power significantly decreased across all ROIs, indicating cerebrovascular relaxation, consistent with reduced cardiovascular activity during drowsiness. Lastly, older participants exhibited significantly smaller LFO and cardiac power changes than younger individuals, reflecting an age-related decline in neurofluid modulation that may diminish the benefits of rest. By simultaneously examining arterial, venous, and parenchymal hemodynamics, this study offers a integrated view of how brief rest influences brain pulsations and how these effects change with aging.