Why does LSD make you hallucinate?
The Secret Intelligence Service, MI6, has paid thousands of pounds in compensation to servicemen after feeding them LSD in mind control experiments in the 1950s, it emerged this week.
One of the men involved in the clandestine tests received the drug twice a week, and recalls lengthy hallucinations in which walls melted, cracks appeared in people's faces and eyes ran down cheeks. The hallucinations happen because the drug mimics a chemical messenger in the brain called serotonin. While serotonin is usually described as a "feelgood" chemical - it is the neurotransmitter released by the drug ecstasy - it also plays a number of other roles.
The brain has at least 14 different receptors for serotonin, all of which play a different part in regulating functions such as our mood and how we interpret what our senses tell us. "We think serotonin helps keep a handle on perception and actually stops us from hallucinating," says Clare Stanford, a psychopharmacologist at University College London.
A dose of LSD, or lysergic acid diethylamide, targets a specific serotonin receptor called 5-HT2A, and in doing so appears to throw our senses into a jumble. As a result, images we would never normally perceive become vivid and fool our brains into thinking they are real. "The drug can also cause synaesthesia, a condition which happens naturally in a small percentage of the population, where your senses get mixed up and you start smelling colours and tasting sounds," says Dr Stanford.
The MI6 experiments were carried out between 1953 and 1954 by scientists intent on developing a "truth drug" to extract confessions from prisoners. The CIA tested LSD for the same purpose, but both agencies eventually ditched the studies after concluding the drug could not be used to manipulate people.
The Guardian (UK)
Science behind the news feature by Ian Sample
25th February 2006