Neural activity drives directional subarachnoid cerebrospinal fluid flow in the human brain.

Neural activity is a potential driver of cerebrospinal fluid (CSF) dynamics and brain waste clearance, yet how neural activity shapes localized CSF flow in the subarachnoid space remains poorly understood in humans. Here we introduce an MRI framework that enables concurrent mapping of ultra-slow subarachnoid CSF flow at velocity scales of tens of micrometers-per-second together with hemodynamic activity measured by simultaneous functional MRI in the human brain. Using this framework, we found that neural activity drives spatiotemporally coherent, directional CSF flow in the subarachnoid space near sites of neural activation in awake humans. These flow responses were highly spatially specific, shaped by local cortical and subarachnoid anatomy, while exhibiting oscillatory temporal dynamics modulated by the stimulus cycle and strongly coupled to hemodynamic responses. These findings establish a link between neural activity, vascular dynamics, and localized subarachnoid CSF flow, and provide a framework for investigating neural-activity-driven CSF transport in humans.