Hollow Tubes (IMAGE) Brown University Caption A cross-section under the electron microscope shows a big open space, confirming that the minibrain vessels are open for flow. Credit Hoffman-Kim Lab/Brown University Usage Restrictions with credit License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.