Blood Flow Makes Waves Across Surface of Mouse Brain

Researchers have, for the first time, visualized the full network of blood vessels across the cortex of awake mice, finding that blood vessels rhythmically expand and contract leading to “waves” washing across the surface of the brain. These NIH-funded findings improve understanding of how the brain receives blood, though the function of the waves remains a mystery.

Blood flows in ripples across the brain. Red color shows blood vessels expanding as blood flow increases.

Photo:  NINDS

A network of elastic and actively pumping vessels carrying oxygenated blood span the surface of the brain before entering the cortex. There, they feed into a second network of capillaries that supply oxygen deeper into the tissue. In addition to the pulses of blood flow that occur with each heartbeat, there are slower waves of blood flow changes that sweep across the brain and occur about once every ten seconds. The change in blood flow that occurs with these slow waves was up to 20% of the entire brain blood supply. Surprisingly, this phenomenon was only weakly tied to changes in brain activity.

The waves produced visible bulges in the blood vessels, which will aid in mixing the fluid around the brain’s cells. This mixing activity could aid in removing misfolded proteins and other components from the brain into the cerebrospinal fluid that surrounds it. This process is considered an important protective mechanism for a variety of neurological disorders, such as Alzheimer’s disease and other related dementias, and is more active during sleep.  

Findings may also affect current approaches to interpreting fMRI scans, which measure changes in blood oxygenation within brain structures as they are activated. This research was funded by NIH’s Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative, NINDS, NIMH and NIBIB.