Why do people experience religious visions? BBC Two's Horizon suggests that in some cases the cause may be a strange brain disorder.
By Liz Tucker
Controversial new research suggests that whether we believe in a God may not just be a matter of free will. Scientists now believe there may be physical differences in the brains of ardent believers.
Gwen Tighe thought her child was Jesus
Inspiration for this work has come from a group of patients who have a brain disorder called temporal lobe epilepsy. In a minority of patients, this condition induces bizarre religious hallucinations - something that patient Rudi Affolter has experienced vividly.
Despite the fact that he is a confirmed atheist, when he was 43, Rudi had a powerful religious vision which convinced him he had gone to hell.
"I was told that I had gone there because I had not been a devout Christian, a believer in God. I was very depressed at the thought that I was going to remain there forever."
Gwen Tighe also has the disorder. When she had a baby, she believed she had given birth to Jesus. It was something her husband Berny found very difficult to understand.
"She said, isn't it nice to be part of the holy family? I thought, holy family? It then turned out she thought I was Joseph, she was Mary and that little Charlie was Christ."
Professor VS Ramachandran, of the University of California in San Diego, believed that the temporal lobes of the brain were key in religious experience. He felt that patients like Rudi and Gwen could provide important evidence linking the temporal lobes to religious experience.
So he set up an experiment to compare the brains of people with and without temporal lobe epilepsy. He decided to measure his patients' changes in skin resistance, essentially measuring how much they sweated when they looked at different types of imagery.
What Professor Ramachandran discovered to his surprise was that when the temporal lobe patients were shown any type of religious imagery, their bodies produced a dramatic change in their skin resistance.
"We found to our amazement that every time they looked at religious words like God, they'd get a huge galvanic skin response."
This was the very first piece of clinical evidence revealing that the body's response to religious symbols was definitely linked to the temporal lobes of the brain.
"What we suggested was that there are certain circuits within the temporal lobes which have been selectively activated in these patients and somehow the activity of these specific neural circuits makes them more prone to religious belief."
Scientists now believe famous religious figures in the past could also have been sufferers from the condition. St Paul and Moses appear to be two of the most likely candidates.
But most convincing of all is the evidence from American neurologist Professor Gregory Holmes. He has studied the life of Ellen G White, who was the spiritual founder of the Seventh-day Adventist movement. Today, the movement is a thriving church with over 12 million members.
During her life, Ellen had hundreds of dramatic religious visions which were key in the establishment of the church, helping to convince her followers that she was indeed spiritually inspired. But Professor Holmes believes there may be another far more prosaic explanation for her visions.
He has discovered that at the age of nine, Ellen suffered a severe blow to her head. As a result, she was semi-conscious for several weeks and so ill she never returned to school.
Following the accident, Ellen's personality changed dramatically and she became highly religious and moralistic.
And for the first time in her life, she began to have powerful religious visions.
Professor Holmes is convinced that the blow to Ellen's head caused her to develop temporal lobe epilepsy.
"Her whole clinical course to me suggested the high probability that she had temporal lobe epilepsy. This would indicate to me that the spiritual visions she was having would not be genuine, but would be due to the seizures."
Professor Holmes' diagnosis is a shattering one for the Seventh-day Adventist movement. Their spokesman, Dr Daniel Giang, is a neurologist as well as a member of the church.
He dismisses the claims, insisting the visions started too long after the accident to have been caused by it. He goes on to say: "Ellen White's visions lasted from 15 minutes to three hours or more. She never apparently had any briefer visions - that's quite unusual for seizures."
We will never know for sure whether religious figures in the past definitely did have the disorder but scientists now believe the condition provides a powerful insight into revealing how religious experience may impact on the brain.
They believe what happens inside the minds of temporal lobe epileptic patients may just be an extreme case of what goes on inside all of our minds.
For everyone, whether they have the condition or not, it now appears the temporal lobes are key in experiencing religious and spiritual belief.
Horizon: God On The Brain was broadcast on 17 April 2003 on BBC Two.