OAKLAND, Calif. — In a packed, cavernous space one weekend late in April, a crowd of thousands was becoming increasingly amped up. Rainbow hair was commonplace, purple silk pants were sighted, and the smell of marijuana drifted in from a designated smoking area nearby. Audience members watched the stage with avid interest, leaping to occasionally shoeless feet to applaud and cheer.

This wasn’t Coachella, taking place the same weekend some 500 miles south, or any other music festival, but a five-day convention of the Multidisciplinary Association for Psychedelic Studies (MAPS), its first in four years. Rather than rock stars, scientists from schools like Johns Hopkins and N.Y.U. were the main attraction, bringing evidence to the medical case for psychedelics like psilocybin (the active ingredient in magic mushrooms) to assuage end-of-life anxiety, to help deepen meditation practices, to search for the shared underpinnings of spiritual life, and — in a new study — to explore a possible treatment for severe depression.

Paul Austin, 26, of Grand Rapids, Mich., a so-called social entrepreneur who runs a website called The Third Wave devoted to getting out information on psychedelic substances, had come to meet other members of the pro-psychedelic community and share with them his vision for how the next generation must proceed. “A lot of the people who are leading the movement now are 60 or 70 years old, based in academia or research,” Mr. Austin said. “But to catalyze change, you have to speak to people, get to them on an emotional level.”

The conference was taking place just over the Bay Bridge from the city that introduced psychedelics to the American imagination in the early 1960s, when LSD was relatively new, legal and regarded by those who used it as a portal to expanded consciousness, a deeper life and an enlightened, humane society. (Cary Grant and other Hollywood stars were among those who experimented with it as part of their psychotherapeutic process.)