Brain self-cleaning during sleep observed in real time

Researchers at the University of Oulu used an ultrafast MRI sequence (MREG) alongside DC-EEG and near-infrared tracking to observe faster vasomotor and bidirectional cerebrospinal fluid pulses during sleep, and they reported increased movement of sodium and potassium ions in that fluid.

Researchers at the University of Oulu in Finland developed and used a suite of real-time imaging methods to track fluid movements and related signals in the human brain during wakefulness and sleep. The team combined an ultrafast MRI sequence called magnetic resonance encephalography (MREG) with direct-current electroencephalography (DC-EEG) and functional near-infrared spectroscopy to follow water molecules and concentration changes. Two short studies tested these methods in healthy volunteers and compared patterns during wake and various sleep states. The researchers reported shifts in the directionality and speed of slow fluid pulses and associated electrolyte movements during sleep. Key findings: - The imaging approach paired MREG with DC-EEG and near-infrared spectroscopy to trace pulsed water movement and related signals in real time. - One study tested 22 volunteers and a follow-up study reported measurements from 24 volunteers, with the second study published in the Proceedings of the National Academy of Sciences. - Each volunteer session included roughly 46 minutes of wakefulness recording and about an hour of assorted sleep states. - During sleep, researchers reported faster vasomotor pulses (about one wave every 10 seconds, or 0.1 Hz) and a loss of net directional flow, producing more bidirectional interactions in regions such as the posterior insula, thalamus, and upper cerebellum. - The team reported increased movement of sodium and potassium ions in cerebrospinal fluid during sleep and noted their methods avoid the need for injected contrast agents. Summary: The studies report measurable changes in brain fluid rhythms and electrolyte movement during sleep that the researchers describe as increased bidirectionality and faster vasomotor pulses, which are associated with fluid motion that can influence electrical activity. The group says the less invasive, real-time methods could help monitor age-related changes in brain fluid dynamics, and they plan to study volunteers for longer periods, ideally a full night of sleep.