The findings confirm the existence of a glymphatic system that scientists first identified in mouse brains in 2012.
This system transports cerebrospinal fluid (CSF) from the outside of the brain to the inside, delivering nutrients and removing waste products - such as proteins that form clumps in Alzheimer's disease - from brain tissue.
Since 2012, several pioneering studies have shown that the glymphatic system also exists in the human brain. However, without seeing the movement of fluid from the outside of the brain into the space between neurons, this idea remained very controversial among scientists.
"I myself have always been skeptical about it, and there are still many skeptics who don't believe it. That's what makes this discovery so remarkable," said neuroscientist Juan Piantino of OHSU.
Piantino and his OHSU colleagues are the first to image the colorless fluid as it infuses into the tissue of a living human brain, and the results support previous research.
The study was made possible with the consent of five adults undergoing brain surgery who needed to have spinal fluid divertedfor the procedure.
Before the fluid was replaced, the scientists marked it with a dark contrast tracer. Later, a special kind of MRI mapped where in people's brains the fluid went.
The findings show that the human brain does not randomly absorb CSF as a sponge would. Instead, the fluid penetrates deeper into neurological tissue, following the trail of blood vessels.
These distinct channels of CSF are actually wrapped around the outside of the blood vessels. The borders of these "perivascular spaces" are formed by brain cells that adhere their ends to create a permeable barrier.
Some scientists suggest that it is this membrane that allows the CSF to mix with the fluid that houses and supports our brain cells, delivering nutrients and removing waste.
OHSU neurosurgeon Erin Yamamoto said that on the MRI images from their study, "you can actually see how the dark perivascular spaces in the brain become lighter" over time as the contrast tracer flows in deeper.
"This is quite similar to the imaging in mice," she added.
These CSF channels have been imaged before in human brains, but because the OHSU researchers took MRI scans 12, 24 and 48 hours after surgery, they were able to track the fluid dynamics in a way that had not been observed before.
The findings suggest that the CSF channels are not stagnant, fluid-filled structures, but "functional channels" that facilitate "the distribution of CSF in the brain." | BGNES
