Antoine Louveau was looking through his microscope at thin membranes that protect the brain, when he saw something that absolutely shouldn't be there: a lymphatic vessel.
The lymphatic system is like the circulatory system but, instead of blood, it carries lymph — a clear liquid that ferries immune cells and rids the body of toxins and waste. As a 2009 research review notes, it is "an undisputed anatomical fact" that the brain is the only major organ that lacks a direct connection to the lymphatic system.
"All the textbooks said there were not supposed to be any lymphatic vessels in that area," said Louveau, a post-doctoral researcher at the University of Virginia (UVA). But after he and UVA neuroscientist Jonathan Kipnis ran a battery of tests, they discovered Louveau had been right. "It was exactly what we thought it couldn't be," Louveau said.
"You know nothing Jon Snow" – the lymph system IS connected to the brain after all. What else don't we know? Or to be more accurate – what else do we think we know that we don't?