This is the first time that a team has been able to visualize the entire network of blood vessels across the cortex. The research, conducted on mice, reveals that blood vessels expand and contract rhythmically, forming “waves” that cross the surface of the brain. Despite these findings, the process that allows these waves to occur remains a mystery.
A network of elastic vessels that actively pump blood
The study uses experimental methods and physics analyses and reveals that:
- In addition to the pulses of blood flow that occur with each heartbeat, slower waves of blood flow pass through the brain and occur approximately every 10 seconds;
- the change in blood flow caused by these waves accounts for up to 20% of the total blood supply to the brain;
- this phenomenon appears to be only weakly linked to changes in brain activity;
- This network of vessels crosses the surface of the brain before entering the cortex;
- There it feeds a second network of capillaries which brings oxygen deeper into the tissues.
Waves that feed and eliminate: The waves produce visible bulges in the blood vessels, and these bulges help mix the fluid around brain cells. This has implications for how waste and other materials are removed from the fluid surrounding brain cells. These pulses of blood vessel expansion and contraction not only help mix the fluid around the cells, but also appear to help remove misfolded proteins and other components from the brain into the cerebrospinal fluid.
A major protection mechanism: theThe vessels and capillaries are therefore involved in this “natural” and “glymphatic” protection mechanism against various neurological disorders, such as Alzheimer’s disease and other types of dementia.
Finally, these results, which may seem very fundamental, have clinical implications for the interpretation of fMRI scanswhich measure changes in blood oxygenation in brain structures as they are activated. The fact that these waves of blood flow changes occur independently of brain activity suggests a new level of complexity that should now be taken into account when interpreting the link between fMRI data and brain activation.
