In 2026, we are still trying to understand how the brain eliminates its waste. Scientists have just found a missing piece. : Science Alert

You read a sentence, remember a familiar face, then turn to another thought. Behind all this activity, your brain also has a maintenance problem: what to do with proteins that can become harmful when they build up.

These proteins need an exit. But tracing their journey outside the brain has proven surprisingly difficult.

Now, researchers at University College London have identified a previously undocumented network of tiny channels that could fill part of the map.

In mice, fluorescently labeled proteins entered these channels and traveled to the brain surface. Similar structures appeared in human brain tissue removed during surgery, suggesting that we share this clearance pathway.

The study is a preprint that has not been peer-reviewed, and the function of the channels in living humans remains to be established.

“The pathways by which toxic proteins are cleared from the brain are poorly understood,” neuroscientist David Attwell told ScienceAlert.

This lack of knowledge poses a problem for research into Alzheimer’s disease, which involves the accumulation of beta-amyloid and abnormal tau proteins. Understanding why they accumulate requires studying both their production and their elimination.

Scientists have proposed different exit routes. We follow the walls of the arterioles, small vessels supplying the brain tissue with blood. Another follows the spaces around the Venules, small vessels that carry blood, and appears in explanations of the glymphatic system.

Previous research has explored the movement of fluids along blood vessels in the brain. The new study identifies a specific cellular structure that could help explain how proteins travel through two proposed exit pathways.

“We have now shown that, in these two locations, proteins are actually removed through tiny tubes that appear similar to tubes found in lymph nodes outside the brain (for example in the armpit or neck),” Attwell explained.

The channels are approximately 2 micrometers in diameter and form an interconnected mesh. They extend along blood vessels to the membranes covering the brain and along the nerves that leave it.

The results suggest that they are formed by fibroblastic reticular cells. Related cells build networks that transport fluids and dissolved substances through the lymph nodes.

To track what was moving through the channels, the researchers made tau and amyloid beta visible using fluorescent markers.

In the mouse experiments, the labeled proteins accumulated inside the channels as they moved. In some experiments, the tracers reached the upper surface channels within 7.5 minutes of administration.

Tau passed through both the walls of the arterioles and the channels around the Venules. The measurements suggest that roughly similar quantities pass through each route, supporting the possibility that they belong to a shared network.

Other customs clearance mechanisms may operate in parallel. Some proteins can be broken down in brain tissue or pass through blood vessel cells to reach the bloodstream.

The researchers also investigated whether the network processed proteins produced inside the brain, rather than just substances introduced during experiments.

In mice modeling aspects of Alzheimer’s disease, they discovered the animals’ own beta-amyloid in the ducts. This confirms a role in the transport of naturally produced proteins, although it does not establish how much ends up passing through the network.

The human results come from five patients undergoing surgery for brain tumors. The team examined living tissue removed during their operations that otherwise would have been discarded.

When fluorescently labeled tau and beta-amyloid proteins were applied to human tissues, the proteins became concentrated in mouse-like channels. Their dimensions were also similar.

But tissues preserved outside the body cannot reveal the complete process of elimination inside a living person.

“In the future, it will be important to demonstrate that these tubes work the same way in living humans,” Attwell said.

Another mystery concerns what motivates the movement. Researchers don’t yet know precisely how proteins enter the channels or how fluid passes through them so quickly. Pulsing blood vessels could contribute, but the pumping mechanism remains unresolved.

Understanding this mechanism could help researchers determine whether impaired transport contributes to disease and whether altering flow would make a difference.

“We also need to know whether slowing this pumping contributes to the onset of Alzheimer’s disease and whether therapeutically speeding up the pumping could help treat the disease,” Attwell said.

The study did not test any treatment or demonstrate any improvement in memory. These possibilities require further research.

For now, scientists must study a newly identified structure. Tracking proteins through these tiny channels could help answer a much larger question: When potentially harmful substances accumulate in the brain, where does their journey go wrong?

A preprint of the study is available on bioRxiv.