"The Neurochemistry of Psychedelic Experiences": One interesting tidbit from the article -- humans are "the only species that will voluntarily take a psychedelic drug again after having experienced the effects. Although laboratory animals such as rats or monkeys will readily self-admininister most other drugs abused by humans, including cocaine, heroin, amphetamine, nicotine and alcohol, they find psychedelic drugs highly aversive." (Via SciTech Daily.)