It was a prodigious feat. Yet for Peek - the real-life 'savant' on whom Dustin Hoffman's character in the film Rain Man is based - such recall only gives a glimpse of his powers. He knows 9,000 books off by heart; he can direct people around US cities from maps he has memorised years ago; and he has total recall of the dates of all major world events.

Now studies of Peek's abilities are being used by scientists to shed intriguing light on the human mind, and to open the way for men and women to exploit far more of their intellectual potential, as the latest issue of Scientific American reveals.

'Kim's story tells us that the human brain is far more flexible than we had thought,' said Darold Treffert, a psychiatrist and co-author of the Scientific American paper told The Observer. 'Like many other savants, he has suffered disability in one area of his brain, but has compensated by acquiring remarkable new abilities in other areas. This shows we all have considerable hidden intellectual potential. By studying Kim and other savants, we can learn how to tap those powers.'

This potential has been of particular interest to Nasa - currently carrying out lengthy electronic scans of Kim's brain in its attempts to understand how astronauts are using their brains while on deep space missions.

Kim - now 54 - was born with a malformed cerebellum, at the base of his brain, and lacks a corpus callosum, the thick bundle of nerves that normally connects the brain's two hemispheres. As a child he was assumed to be suffering from severe mental retardation. Only later was his condition found to be more complex. He had superb abilities at arithmetic but could not deal with the abstractions of mathematics. In 1988 he was given an IQ rating of 87, well below average. Yet some of his subscores were in the genius bracket, while others plunged into the mentally retarded range.

Kim has poor physical co-ordination, cannot button his shirts but has remarkable memory power and has started to develop as an accomplished pianist in the last two years. This latest development - in a man in his 50s with large chunks of his brain missing - is particularly significant, added Treffert. 'His brain is still adapting to his condition, even in mid-life.'

One key to understanding Kim's condition is that his right and left brain hemispheres are not connected. Our left brain, in which our linguistic prowess has its centre, tends to dominate our right. That has not happened with Kim, however, suggesting the possibility that his right brain has been allowed to develop more freely and reach a greater potential than normal.

Kim displays little personal interest in people outside the arithmetical details of their lives. When I talked to him by phone in his home in Salt Lake City last week, he asked for my birthday. I told him. 'Ah, you were born on a Sunday, your next birthday will be a Sunday, and you are scheduled to retire on a Thursday,' he replied, correctly.

'He remembers 98 per cent of what he reads,' said his father Fran. 'It's like downloading data on to a hard disk - except his never crashes.'