Taking cocaine for science's sake

American scientists are giving drug addicts doses of cocaine and watching how their brains react on a scanner. By identifying the parts of the brain that react to the drug, and subsequently trigger craving for more, they hope to understand the chemistry of addiction.

All that could be seen of the addict were his socks sticking out of a brain scanner the size of a walk-in cupboard. He had been in there about an hour when a technician pushed a button and infused 40mg of cocaine into his bloodstream.

Two psychiatrists watched, along with a heart specialist, a drug counsellor and a nurse. For a minute and a half, nothing happened. Then the man's heart rate began to rise to 90 beats per minute ... 130 ... 135. His blood pressure lifted sharply. A number came up on a computer screen. "He's getting maximal rush," said Dr Hans Breiter.

The man inside the scanner signalled that he was enjoying himself. His head immobilised and his ears plugged, he rated the experience on a scale of one to four. Four meant really good.

In this unusual experiment at Massachusetts General Hospital, scientists were looking inside a man's head to see what cocaine does. A souped-up Magnetic Resonance Imaging scanner, programmed to run faster than the kind used to take pictures of strokes or tumours, rattled off an image a second of the man's brain.

Within minutes the rush fell to 2, then 1. Then came less pleasant feelings. Low 2, the man reported. Low 3. He felt jittery and out of sorts. Finally the numbers began to rise on another scale, his hunger for more. Craving 3.

Dr Breiter was relieved. There had been no need to yank the man out of the machine and jolt him with defibrillator paddles - something they had practised doing in 30 seconds in case the cocaine triggered a heart attack.

At about 10 pm, after promising he wouldn't go looking for more cocaine that night, the addict was sent home with a lecture about the dangers of drugs, an offer of drug rehabilitation and his payment, a $260 (pounds 160) credit at a supermarket.

The National Institute on Drug Abuse, headed by Dr. Alan Leshner, is paying for this and similar experiments around America. Scientists hope that by observing exactly how cocaine gets people high and keeps them coming back for more, they will find clues to making medicines that can blunt these effects.

"That state of feeling good, high, euphoria, buzz, whatever you call it, that's what we're after, and that's what users are after," said Dr Scott Lucas, who is doing some of the research at McLean Hospital in Belmont, Massachusetts.

The Massachusetts General doctors have counted 90 different parts of the brain that are turned on during cocaine's rush. But as the euphoria ebbs and the craving sets in, almost all of these fade out, leaving just a few distinct structuresstill working hard. "The picture emerging is that drugs take over structures that are involved in normal pleasure," said Dr Elliot Stein of the Medical College of Wisconsin.

The findings suggest that drug addiction is not just a failure of will but a brain disease - a lasting, perhaps permanent change in the brain's chemistry and physiology that produces compulsive craving. It also suggests possible approaches to making antidotes.