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in the brain and in animal behavior clinched its role as the first known neurotransmitter.” 24 + THE BUILDING BLOCKS mind and its brain chemistry, was the child of these two strange bedfel- lows: LSD and Thorazine. And serotonin was the matchmaker. In 1948 researchers discovered that serotonin carried in the blood- stream was responsible for contracting the muscles lining veins and arteries. This was vitally important in understanding how to control the bleeding process. The name for serotonin came from the Latin sew, "blood," and tonin, "tightening." A few years later, in the mid-1950s, investigators discovered seroto- nin in the brain of laboratory animals. Subsequent experiments demonstrated its precise localization and its effects on electrical and chemi- cal functions of individual nerve cells. Drugs or surgery that modified serotonin-containing areas of an animal's brain profoundly altered sexual and aggressive behavior as well as sleep, wakefulness, and a diverse ar- ray of basic biological functions. The presence and function of serotonin At the same time, scientists showed that LSD and serotonin molecules looked very much like each other. They then demonstrated that LSD and serotonin competed for many of the same brain sites. In some experimen- tal situations, LSD blocked the effects of serotonin; in others, the psychedelic drug mimicked serotonin's effects. These findings established LSD as the most powerful tool available for learning about brain-mind relationships. If LSD's extraordinary sen- sory and emotional properties resulted from changing the function of brain serotonin in specific and understandable ways, it might be possible to "chemically dissect" particular mental functions into their basic physi- ological components. Other mind-altering drugs with comparably well-characterized effects on different neurotransmitters could lead to a decoding of the varieties of conscious experience into their underlying chemical mechanisms. Dozens of investigators around the world administered a dizzying ar- ray of psychedelic drugs to thousands of healthy volunteers and psychiatric patients. For more than two decades, generous government and private