Let's get the jokes out of the way from the beginning. When I told a friend that I was to review A Beautiful Mind, he asked me if I was "in two minds" about seeing it. When I groaned out loud he just thought that the tired old joke had worn thin. Like many - and if you watched the presentation of the Baftas you will know what I mean - he was simply unaware of the joke's inaccurate and prejudicial implications.

Schizophrenia is not the "split personality" portrayed up until now in the stereotypical films churned out by Hollywood over the years. You know how the plot goes: the psychiatrist falls in love with a beautiful blonde twin, with an evil sister, only to discover that they are one in the same person. That is Disassociative Identity Disorder and if you were a psychiatrist you would be very lucky to see a genuine case in your professional lifetime. Unlike schizophrenia.

This disorder is very prevalent, affecting around one in a hundred of us. The confusion comes from the Greek root of the name, schizo, which roughly translates as "to split away from" and phren meaning the mind. The term was coined in 1908 by a Swiss psychiatrist who was deeply influenced by Freudian psychoanalysis. The idea was that schizophrenia was a breaking away from the "associative" threads of purposeful thinking. Hence the common confusion with the idea of a "split" personality, which schizophrenia is not.

Our popular culture abounds with the feared archetype of the "split personality" - such as the werewolf or Dr Jekyll and Mr Hyde - and it is deeply unfortunate that schizophrenia has become confused with fairy tale and superstition.

Schizophrenia is a medical term for a collection of symptoms, both positive - hallucinations, delusions and bizarre behaviour - and negative - behavioural deficits such as blunted affect (emotion), poverty of speech, personal neglect and an inability to feel pleasure or experience intimacy. A person suffering with schizophrenia experiences a combination of all or some of the above symptoms - making them an extremely diverse group of people who need very individualised treatment.

One of the reasons why so many of us labour under the illusion that schizophrenia involves a split personality is because this unfashionable subject has been largely ignored by mainstream cinema. Until now.

This is what makes A Beautiful Mind an all the more remarkable film.

As you may know, this movie is based on the true-life story of the Nobel Prize winning American mathematician John Nash and his battle with Paranoid Schizophrenia. Without giving too much away the film makes clever use of a plot device similar to that of Sixth Sense. By doing this it is able to convincingly bring the viewer into the reality of Nash's internal universe.

When a psychiatrist tries to convey the "nightmare of schizophrenia" by asking John Nash's wife to imagine "if you discovered the people and places you knew were not there, imagine what hell that would be", we can do just that. We too have been in Nash's mind, we can empathise because we have seen the world as he perceives it. We understand his paranoia because we have engaged with his delusions. We share his heartache when it emerges that some of the people most pivotal to his life are simply not real, because we find ourselves wishing for friends as fun and kind as the ones existing in John Nash's internal world.

When Nash is forced to "betray" his illusory confidant - "you have been a very good friend but I can't talk to you any more" - we grieve with him.

The cognitive coping strategy which he employs is tragic and painful to watch, even though it also excludes some of the more aggressive and sinister characters which stalk him. "They are my past," he says once on the road to recovery, "every one is haunted by their past."

We watch as a witty and unique human being is reduced to "patient", not a person, subject to seizures resulting from horrific experimental therapy involving insulin-induced comas.

The de-personalisation is brutal. The brilliant mind of John Nash is now unable to solve mathematical hypotheses under the influence of his drugs. Watching him experience these side effects - including erectile dysfunction - we come to understand why, like others then and now, he is not compliant with his treatment. "Why did you stop your medication?" he is asked. "Because I couldn't do my work, couldn't help with the baby, couldn't respond to my wife," he replies.

And vitally, we learn that it is possible to recover from schizophrenia, as we watch Nash re-engage with the world, his wife and his students.

This movie still contains a fair degree of ham - his acceptance speech for the 1994 Nobel Prize in Economics being a prime example. And yes there is a degree of censorship - his divorce and alledged bisexuality are simply not mentioned. But then we have to ask whether these elements would have alienated the more conservative American movie-goers - this convincing portrayal of schizophrenia may never have found a mainstream audience.

My friend is going to see A Beautiful Mind next week and as a result, it won't just be his joke repertoire which will have been improved. There may be just one less person in the world unwittingly discriminating against an undeserving and vulnerable group of people.