The rich may be different, as the saying goes, but the richly creative are different still. Just what goes on inside the head of an artist or a poet, however, is a mystery.

Now, however, researchers from the University of California at Berkeley have learned a little about what went on inside the heads of some of the more creative artists and poets the world has known.

The researchers have identified the mechanism by which absinthe, the liqueur of choice for the likes of van Gogh, Rimbaud, Baudelaire, Toulouse-Lautrec and others – indeed, for much of 19th century French society — affects the brain. It makes neurons fire like mad.

It has long been known that absinthe, a potent, emerald-green distillate of wormwood and other herbs, can cause convulsions, hallucinations, psychotic episodes and, with chronic use, permanent neurological damage. The liqueur has been blamed for the bizarre behavior of van Gogh and others, and it was eventually banned in many countries, including the United States, early in the 20th century.

The Berkeley research, done in collaboration with scientists at Northwestern University, is the first to show the pathway by which the toxic component of the liqueur (other than the alcohol) does its damage.

That component, alpha-thujone, has a sort of double-negative effect on the brain. It blocks a receptor, known as GABA-A, that has also been linked to a form of epilepsy. Under normal conditions, GABA-A inhibits the firing of brain cells by regulating the flux of chloride ions in them. By essentially blocking the blocker, thujone allows the brain cells to fire at will.

Exactly how thujone works ”had been a big question mark for a long time,” said Dr. Karin Hold, a postdoctoral researcher at Berkeley and a co-author of the study, which was published last week in The Proceedings of the National Academy of Sciences. ”No one had ever found out which receptor it was working on.” One theory had held that thujone affected the same receptor as THC, the active ingredient in marijuana, but the new research disproves that conclusively, Dr. Hold said.

”It’s very significant work,” said Dr. Wilfred Niels Arnold, a biochemist at the University of Kansas Medical Center in Kansas City and the author of ”Vincent Van Gogh: Chemicals, Crises and Creativity” (Springer-Verlag, 1992). ”It’s the sort of thing that many pharmacologists had guessed at, but this is the first time it’s been demonstrated.”
The work is of more than historical interest, particularly with the rise in popularity of herbal medicines. Wormwood oil, which contains thujone, is present in some herbal preparations used to treat stomach disorders and other ills. (In fact, wormwood, a relative of daisies, got its name from its use in ancient times as a remedy for intestinal worms.)
Though rare, incidents of wormwood oil poisoning have occurred in recent years, resulting in convulsions and, in at least one case, kidney failure. The National Toxicology Program of the National Institutes of Health plans to study thujone as part of a long-term investigation of the active ingredients in many herbal preparations.

Absinthe itself is still manufactured, in Spain and the Czech Republic, although European Union regulations limit the amount of thujone in it to less than 10 parts per million. Old absinthe contained up to 260 parts per million, Dr. Arnold said. In modern absinthe, alcohol, which makes up three-quarters of the liqueur, is by far the most toxic component.
It is still illegal to buy absinthe in the United States, though it can be obtained through the Internet and when traveling overseas. Some do-it-yourselfers soak wormwood and other herbs in grain alcohol or even port to make a poor imitation of absinthe, while the more adventurous try distilling the liqueur themselves.

Absinthe has something of a cult following among people lured by its history, and by the ritual associated with it. The liqueur, which is extremely bitter, is traditionally poured through a lump of sugar on a special slotted spoon, and mixed with five parts water. This creates what is known as the louche, a milky-white effect that occurs when compounds in the liqueur precipitate out of the absinthe-water solution. (Toulouse-Lautrec was said to have favored a drink called the Earthquake, in which the absinthe was diluted with cognac, and there was no louche effect.)