Temporal fluctuation in lateral ventricle volume and its coupling with CSF inflow and global BOLD signal

Recent studies have highlighted the intricate relationship between cerebrospinal fluid (CSF) dynamics and global brain activity, suggesting a role in neurovascular coupling and brain waste clearance. The lateral ventricles are believed to play a key role in linking global BOLD (gBOLD) signals to CSF inflow (CSF_in) to the fourth ventricle. In this study, we developed a method to reliably quantify lateral ventricle volume (LVV) in fMRI data. Using three independent datasets, including resting-state and task-based fMRI, we assessed dynamic changes in LVV and their associations with gBOLD and CSF_in. Our findings reveal a strong anti-correlation between LVV and gBOLD across all datasets, with an average gBOLD lag of approximately 1 s. The derivative of the LVV time series were positively correlated with CSF_in, with CSF_in lagging LVV changes by 1.4-2.4 s. A moderate negative correlation was also observed between CSF_in and gBOLD, consistent with prior research. These results support the hypothesis that LVV fluctuations, driven by global cerebral blood volume oscillations, regulate CSF movement into and out of the fourth ventricle. Our findings provide a foundation for further investigations into the role of LVV dynamics in aging and neurological disorders.