Impact of Drowsiness on Low-Frequency, Respiratory, and Cardiac Oscillations across Neurofluid Compartments

Motivation: Low-frequency oscillations (LFOs) dominate grey matter and increase with drowsiness, but their variations across key neurofluid compartments (e.g., arteries and venous sinuses) remain poorly understood. Goal(s): To investigate how drowsiness influences physiological oscillations across neurofluid compartments. Approach: Power density in fMRI signals was analyzed across three frequency bands (LFOs, respiration, cardiac pulsation) in five compartments: cerebral arteries, superior sagittal sinus, fourth ventricle CSF, grey and white matter. Changes from alert to drowsiness states were analyzed. Results: LFO power was highest in grey and white matter, lowest in arteries. Drowsiness led to a global LFO power increase across all compartments, while cardiac power decreased. Impact: These findings demonstrate regional variability in LFO across neurofluid compartments and reveal a consistent increase during drowsiness, suggesting its potential role in driving glymphatic movement, particularly in sleep.