Front temporal lobe is the key area, says a scientist

Both Stephen and Derek Paravicini, an autistic man who is a superb jazz pianist, are savants - people with profound intellectual disabilities who have a "fragment of genius" - of whom there are thought to be no more than 25 in the world.

Experts have been unable to explain why people have these talents.

But now two scientists have identified an area of the brain which they think may hold the key.

Dr Bruce Miller, a dementia specialist at the University of California in San Francisco, found some of his patients were developing artistic talents.

After scanning them, he found they had all had problems in the same part of the brain - the left arterial temporal lobe.

He found the same part of the brain was damaged in an American savant, Dane Bottino, an 11-year-old with artistic talents.

Allan Snyder, professor of science at the Australian National University, University of Sydney and director of Centre for the Mind, has also been looking at why savants have such amazing talents, when they are so severely disabled in other ways.

He says that everyone may be able to tap into the area of the brain that gives savants these abilities.

His theory is that because a specific part of the brain does not work properly, abilities in another area may be unlocked.

Brain malfunction

And he says the savants have their gifts, because of this "malfunction" of the brain, not in spite of it.

Snyder: Everyone has the potential to be an artistic genius

He said savants were able to access certain parts of the brain most people could not.

"They are exceptional in that they can tap in and somehow we can't. They have privileged access."

And he said if ordinary people could also find a way to get access: "Each of us could draw like a professional, do lightning fast arithmetic."

This malfunctioning may, he believes, enable them to access certain "primitive" parts of the brain which process sound, vision and numbers.

In the BBC programme, Stephen Wiltshire is taken up in a helicopter over London. Hours later, he produces a detailed and accurate drawing of a four-square mile area of the city.

The scientists believe this is possible because instead of his brain processing details of information, such as identifying a building or recognising it, he can tune in to all the complex mental processes that lie behind that recognition, and copy them.

A team from Flinders University in Adelaide, Australia, recently used the findings of Miller and Snyder to run their own tests which found "savant skills" - memory, maths and art - improved in five out of 17 volunteers, supporting Professor Snyder's theory.

The scientists used transcranial magnetic stimulation, a technique used in the treatment of depression.

It was used to switch off the frontal temporal lobe. The volunteers were tested before, during and after the treatment.

The five showed improvements in calendar calculating - naming what day of the week any date in recent history was on - and drawing abilities.

Fragments of Genius, BBC1, 11 March at 1940 GMT