We have come to think of the brain as a computer. And it’s not. It’s a living organ.”

David Kohn reports in the Washington Post,

...every once in a while in science, you stumble on something really unexpected. You open a new door, to a whole new world.”

...The discovery is much more than a historical footnote. It has major implications for a wide variety of brain diseases, including Alzheimer’s, multiple sclerosis, stroke and traumatic brain injury.

...Researchers have identified two networks: the vessels that lead into and surround the brain, and those within the brain itself. The first is known as the lymphatic system for the brain, while the latter is called the glymphatic system. The “g” added to “lymphatic” refers to glia, the kind of neuron that makes up the lymphatic vessels in the brain. The glymphatic vessels carry cerebrospinal fluid and immune cells into the brain and remove cellular trash from it.

Alitalo, Nedergaard, Kipnis and others have found evidence that when the systems malfunction, the brain can become clogged with toxins and suffused with inflammatory immune cells. Over decades, this process may play a key rolein Alzheimer’s disease, Huntington’s disease, Parkinson’s disease and other neurodegenerative illnesses, research suggests. “This is a revolutionary finding,” Nedergaard says. “This system plays a huge role in the health of the brain.”

Nedergaard describes the glymphatic system as like a dishwasher for the brain. “The brain is very active,” she says, “and so it produces a lot of junk that needs to be cleaned out.”

In hindsight, she says, the system should have been noticed long ago. When the skull and head are dissected, the vessels are visible to the naked eye. But no one bothered to really look: “Usually the brain is seen only as a bunch of nerve cells. We have come to think of the brain as a computer. And it’s not. It’s a living organ.”

Nedergaard and Helene Benveniste, a scientist at Yale University, have found evidence linking problems in the lymphatic and glymphatic systems to Alzheimer’s. In a study on mice, they showed that glymphatic dysfunction contributes to the buildup in the brain of amyloid beta, a protein that plays a key role in the disease.

Last year, Jeff Iliff, a neuroscientist at Oregon Health & Science University, and several colleagues examined postmortem tissue from 79 human brains. They focused on aquaporin-4, a key protein in glymphatic vessels. In the brains of people with Alzheimer’s, this protein was jumbled; in those without the disease, the protein was well organized. This suggests that glymphatic breakdowns may play a role in the disease, Iliff says.

...One key to glymphatic performance seems to be sleep. Nedergaard has shown that at least in mice, the system processes twice as much fluid during sleep as it does during wakefulness. She and her colleagues focused on amyloid beta; they found that the lymphatic system removed much more of the protein when the animals were asleep than when they were awake. She suggests that over time, sleep dysfunction may contribute to Alzheimer’s and perhaps other brain illnesses. “You only clean your brain when you’re sleeping,” she says. “This is probably an important reason that we sleep. You need time off from consciousness to do the housekeeping.”

...Nedergaard and Benveniste have also found that sleep position is crucial. In an upright position — someone who is sitting or standing — waste is removed much less efficiently. Sleeping on your stomach is also not very effective; sleeping on your back is somewhat better, while lying on your side appears to produce the best results. The reason for these differences remains unclear, but Nedergaard suspects that it is probably related to the mechanical engineering of the lymphatic vessels and valves; she suggests that the healthiest approach may be to move periodically while you sleep.

Read more here.