Considering it was widely dismissed at the time as merely another momentary fad, and erroneously presumed to be pretty much dead in the water by the middle of 1968, the influence of psychedelic rock is strong today. If one is to broadly interpret the term as a catch-all synonym for expansion of the consciousness, psychedelia has been a significant (often drug-assisted) cultural pursuit since ancient times, whether conducted with the utmost ritualistic discipline and seriousness as a means of attaining spiritual enlightenment, or simply as a hedonistic derangement of the senses.
From Discover Music.com:
For entire swathes of the record-buying public, their first encounter with psychedelic music was provided by Revolver – the game-changing Beatles album, released in August 1966, that contained so many of the exotic elements that came to define the form. It beguiled, ensnared and, in some cases, disturbed the listener with its fresh, unorthodox textures: reality-shifting tape reversal techniques, tape loops, undulant sitars and opaque lyrics.
Of course, nothing simply materialises out of nowhere. The mind-remapping initiatives eagerly showcased on Revolver represented a flowering that couldn’t help but burst forth; in a beneficially reciprocal loop, contributors to The Beatles’ expanded worldview included musical peers such as the coolly enigmatic Byrds and the previously surfing-fixated Beach Boys. Bob Dylan, too, though musically far removed from the psychedelic sounds of The Beatles and co, exerted his influence as a conundrum-generating lyricist, and, crucially, as the genial host who allegedly turned John, Paul, George and Ringo on to marijuana in a room of New York’s Hotel Delmonico in August 1964. Furthermore, when George Harrison’s dentist irresponsibly spiked the coffees of Harrison, John Lennon and their wives with LSD at a dinner party in April 1965, his recklessness would have profound implications.
As is well known, the concluding (and most extreme) track on Revolver was actually the first to be tackled when sessions began in April 1966. ‘Tomorrow Never Knows’ drew its eerie lyric (“Lay down all thought, surrender to the void – it is shining”) from Timothy Leary and Richard Alpert’s book The Psychedelic Experience: A Manual Based On The Tibetan Book Of The Dead – a much-discussed tome of the day which Lennon had picked up in London’s Indica bookshop in Mason’s Yard. (The bookshop in question, a beacon for London’s arty inner set, was also supported by Paul McCartney.)