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.