Ken Kesey was responsible for starting a lot of it after he took LSD and part of CIA experiments at the Menlo Park Veterans Hospital and started doing "acid tests" with music by what became the Grateful Dead. There's are some good documentaries on YouTube about this.
“Taking LSD was a profound experience, one of the most important things in my life. LSD shows you that there’s another side to the coin, and you can’t remember it when it wears off, but you know it. It reinforced my sense of what was important—creating great things instead of making money, putting things back into the stream of history and of human consciousness as much as I could.”
“Taking LSD was a profound experience, one of the most important things in my life. LSD shows you that there’s another side to the coin, and you can’t remember it when it wears off, but you know it. It reinforced my sense of what was important—creating great things instead of making money, putting things back into the stream of history and of human consciousness as much as I could.”
― Steve Jobs