This Is Your Brain on Drugs; May / June 2012; Scientific American Mind; by Christof Koch; 2 Page(s)

In the 1954 foundational text of the Age of Aquarius, The Doors of Perception, Aldous Huxley describes his encounters with mescaline, a psychoactive substance derived from the peyote cactus and traditionally used by Native Americans for religious purposes. Huxley’s experiences include profound changes in the visual world, colors that induce sound, the telescoping of time and space, the loss of the notion of self, and feelings of oneness, peacefulness and bliss more commonly associated with religious visions or an exultant state: “A moment later a clump of Red Hot Pokers, in full bloom, had exploded into my field of vision. So passionately alive that they seemed to be standing on the very brink of utterance, the flowers strained upwards into the blue.... I looked down at the leaves and discovered a cavernous intricacy of the most delicate green lights and shadows, pulsing with undecipherable mystery.” Yet remarkably these enhanced percepts are not grounded in larger but in reduced brain activity, as a recent experiment reports. More on that in a moment.

Mescaline, together with psilocybin, another natural psychoactive compound produced by “magic” mushrooms, and lysergic acid diethylamide (LSD or, simply, acid), a potent synthetic psychedelic drug, became widely popular in the 1960s counterculture. The striking similarities between the reports of LSD users and symptoms of acute psychosis led researchers to postulate that serotonin, a chemical-signaling compound or neurotransmitter released by certain groups of neurons in the brain stem, helped to mediate both types of experiences. Indeed, it is now quite certain that the characteristic subjective and behavioral effects of psychedelics are initiated via stimulation of serotonin 2A receptors (known as 5-HT2A) on cortical neurons.