EXPRESS: Distinct pressure- and flow-driven propagation pathways of low-frequency oscillations in the human brain

IntroductionLow-frequency oscillations (LFOs) are emerging as key drivers of brain fluid dynamics, and through functional MRI (fMRI) studies, systemic LFOs (sLFOs) have been identified as endogenous contrast agents that track cerebral blood flow. However, their cerebral propagation has largely been interpreted as reflecting slow blood flow, potentially overlooking a faster pressure transmission mechanism. In this work, we propose a comprehensive physiological framework for the propagation of cerebral vascular sLFOs, leveraging both blood-oxygen-level-dependent (BOLD) and non-BOLD fMRI signal components to capture flow- and velocity-driven dynamics.MethodsCerebral artery and superior sagittal sinus (SSS) sLFOs (0.01-0.15 Hz) were extracted from fMRI and time-locked to gray matter (GM) sLFOs to characterize their temporal coupling and transmission patterns.ResultsIn 605 subjects, artery-GM-SSS sLFOs exhibited strong temporal coupling, revealing two distinct pathways: a rapid, millisecond-scale pressure transmission route reflecting intracranial pulse transmission (~100 milliseconds), and a slower, second-scale route consistent with artery-to-capillary-to-venous blood flow transit (~5 seconds).DiscussionThese findings distinguish the pressure- and flow-driven components of sLFOs, revealing distinct propagation pathways with different timescales, providing a comprehensive characterization of their underlying physiology, enabling new approaches to investigate cerebrovascular health using fMRI.