"And all the people perceived the thunderings, and the lightnings, and the voice of the horn, and the mountain smoking." Thus the book of Exodus describes the impressive moment of the giving of the Torah on Mount Sinai.

The "perceiving of the voices" has been interpreted endlessly since these words were first written. When Professor Benny Shanon, professor of cognitive psychology at the Hebrew University of Jerusalem, reads the verse, he recalls a powerful hallucinatory experience he had when he visited the Amazon and drank a potion made from a plant called ayahuasca.

"One of the things that happens when you drink the potion is a visual experience created via sounds," he says.

Shanon presents a provocative theory in an article published this week in the philosophy journal Time and Mind. The religious ceremonies of the Israelites included the use of psychotropic materials that can found in the Negev and Sinai, he says. "I have no direct proof of this interpretation," and such proof cannot be expected, he says. However, "it seems logical that something was altered in people's consciousness. There are other stories in the Bible that mention the use of plants: for example, the tree of the knowledge of good and evil in the Garden of Eden."

Shanon, former head of the Hebrew University psychology department, said his first experience with ayahuasca was in 1991 when he was invited to a religious ceremony in the northern Amazon in 1991 in Brazil. "I experienced visions that had spiritual-religious connotations," he says. Since that time, he has used it hundreds of times, and has published a book about the plant.

"Hypotheses have been around for 20 years connecting the beginning of religions with psychoactive materials," Shanon says. He believes the Israelites used two plants in Sinai and the Negev: one of them is wild rue, a hallucinogen used by the Bedoin to this day. However this plant is not identified with any plant mentioned in the Bible.

The acacia tree also has psychedelic properties, Shanon says, which the Israelites could have used. The acacia is mentioned frequently in the Bible, and was the type of wood of which the Ark of the Covenant was made. According to Shanon, he drank a potion prepared from a species of acacia while he was in South America, which caused similar experiences to those produced by the ayahuasca.

Shanon also sees signs of a hallucinogenic vision in the story of the burning bush.

"Moses 'looked, and, behold, the bush burned with fire, and the bush was not consumed,'" Shanon quotes from Exodus 3:2. Time passes differently when under the influence of the plant, he notes. "That's why Moses thought the bush was not consumed. It should have been burned in the time he thought had passed. And in that time, he heard God speaking to him."

"But not everyone who uses a plant like this brings the Torah," Shanon concedes. "For that, you have to be Moses."