The coupling of global brain activity and cerebrospinal fluid inflow is correlated with Alzheimer's disease related pathology

The glymphatic system plays an important role in clearing the amyloid-{beta} and tau proteins that are closely linked to Alzheimers disease (AD) pathology. Glymphatic clearance, as well as amyloid-{beta} accumulation, is highly dependent on sleep, but the sleep-dependent driving forces behind cerebrospinal fluid (CSF) movements essential to the glymphatic flux remain largely unclear. Recent studies have reported that widespread, high-amplitude spontaneous brain activations in the drowsy state and during sleep, which are shown as large global signal peaks in resting-state fMRI, is coupled with the CSF movements, suggesting their potential link to the glymphatic flux and metabolite clearance. By analyzing multimodal data from the Alzheimers Disease Neuroimaging Initiative project, here we showed that the coupling between the global fMRI signal and CSF influx is correlated with AD-related pathology, including various risk factors for AD, the severity of AD-related diseases, the cortical amyloid-{beta} level, and the cognitive decline over a two-year follow-up. These results provide critical initial evidence for involvement of sleep-dependent global brain activity, as well as the associated physiological modulations, in the clearance of AD-related brain waste.