Brain images of old and young mice (IMAGE) University of Maryland School of Medicine Caption PDE11A memory enzyme (green) in the brains of young (left) and old (right) mice. Credit University of Maryland School of Medicine Usage Restrictions No restrictions. License Public Domain 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.