The 'Garbage Truck' of the Human Brain: New Clues to Treating Alzheimer's

The brain works like a complex machine, sending electrical signals that allow us to perceive and understand the world around us. Now, scientists have discovered a new system in this brain that acts as a "garbage truck," removing waste that might affect the brain. The findings could have large implications for treating neurological disorders like Alzheimer's disease.

The body defends the brain like a fortress, ringing it with a complex system of gateways that control which molecules can enter and exit. This "blood-brain barrier" was known to exist for quite some time, but it's only now that researchers are beginning to understand how it functions. This latest system for waste removal, for example, is just part of the wider picture.

Waste removal is an essential biological function. The lymphatic system, a circulatory network of organs and vessels, performs this task in most of the body. Yet the lymphatic system doesn't extend to the brain. Because of this, scientists have never fully understood what the brain does with its own waste.

In order to better understand how the brain might remove waste, the researchers used a new imaging technology called two-photon microscopy. This allowed them to peer deep within the living brains of mice. The scientists found what amounts to an extensive plumbing system responsible for flushing waste from throughout the brain.

The brain itself is surrounded by a membrane called the arachnoid and bathed in cerebral spinal fluid (CSF). CSF flows into the interior of the brain through the same pathways as the arteries that carry blood and is drawn into brain tissue via a system of conduits that are controlled by a type of support cells in the brain, known as glia--in this case, astrocytes. The CSF is flushed through the brain tissue at high speeds, which sweeps away excess "garbage" that might be located in the brain. The scientists decided to coin this newly discovered system the "glymphatic system."

Yet this system doesn't just tell us a bit more about the brain. It also may have implications for diseases associated with it.

"The idea that 'dirty brain' diseases like Alzheimer's may result from a slowing down of the glymphatic system as we age is a completely new way to think about neurological disorders," said Maiken Nedergaard, one of the researchers, in a news release. "It also presents us with a new set of targets to potentially increase the efficiency of glymphatic clearance and, ultimately, change the course of these conditions."

The findings are published in the journal Science.