Is there an angel or a devil behind the mask? Scientists say it may not matter in terms of anonymous behavior. Joel Saget/AFP/Getty Images hide caption

itoggle caption Joel Saget/AFP/Getty Images

A rat neuron before (top) and after (bottom) ketamine treatment. The increased number of orange nodes are restored connections in the rat's brain. Ronald Duman/Yale University hide caption

itoggle caption Ronald Duman/Yale University