One of the hottest tickets at this year's Society for Neuroscience meeting in San Diego was a session on psychedelic drugs. About 1,000 brain scientists squeezed into an auditorium at the San Diego Convention Center for the symposium, called Psychedelics and Neural Plasticity. They'd come to hear talks on how drugs like psilocybin and MDMA can alter individual brain cells, can help rewire the brain, and may offer a new way to treat disorders ranging from depression to chronic pain. "I was pleasantly surprised at the number of people," says Alex Kwan, a biomedical engineer at Cornell University who spoke...