The origins of the Psychonauts came with the experimentation of hallucinogens on religious experiences. Unknown to the experimenters, the idea attracted a large number of people sensitive to the spirit world. The combination of the drugs and the sensitives tore open the barrier between the spirit realm and the physical one. Most of the victims were killed or driven mad in the ensuing chaos, which lead to a government cover-up.
A few, however, escaped and met up later to compare notes. They decided that, rather than take the experience as a warning, they had come close to touching some vast celestial Truth. They began experiments of their own, as well as recruiting new members to assist them with their ideas. By the early 1990s, members of the Psychonauts were spread over college campuses across the nation, handing out drugs to continue the experiments. Their continued experimentation brought them several more encounters with the supernatural; most of them took it as a sign that the Truth was at hand. And so, they continued on.
With the right combination of drugs and spiritual sensitivity, the Brotherhood hopes to one day attain the Truth behind the universe. The more encounters they have, the closer they feel they are. To most outsiders, however, the Brotherhood looks like a group of drug addicts who attract nothing but trouble.
The Brotherhood has little organization to speak of, mostly because members die so quickly. The Psychonauts are lovers, not fighters, and so many go into their spiritual encounters unaware and unprepared. Most cannot defend themselves against the spirits they encounter, and so quickly fall when they cross paths with the wrong one. The only defense most members have is not to get actively involved with what they see.
The Illuminated Brotherhood offers three main support groups: the Children of Leary focus more on expanding the mind more than encountering supernaturals, although they have their fair share of nightmares. The Spirit-Seekers are the opposite, actively tracking down and investigating spirit encounters. Finally, the Watching Eye looks for humans who have become spirit-possessed.