Sometimes a reader's letter really hits home. It's not enough just to answer it in a single paragraph: it needs much more, and there are long odds against a one-paragraph reply helping. Yet if the reader really believes what I write, she will hugely improve her enjoyment of life.

She is 40, from Bradford, and has had schizophrenia for 20 years. She is on regular injections for the illness. She writes that she feels better than she has for years, and is coping with everyday life. She is on good terms with her daughter for the first time in years.

But this doesn't mean that she is cured completely. If she stops her three weekly injections she will probably return to her hell of delusions, hallucinations and suspicion. And her letter betrays that a little of that mental state survives.

She writes that she has severe body odour. She believes that everyone who meets her can smell it, and they talk about it behind her back. She washes and uses deodorants, but they don't work. Her doctor says she is imagining this, but she doesn't believe him.

And that is the crux. In fact, she doesn't smell. No one is talking about her behind her back. She could go out and enjoy life and holidays without fear of causing revulsion. The problem is how to convince her that this is so. One small part of her brain is still producing the wrong chemical and electrical messages, making her suspicious and paranoid. Somehow she has to stop believing what her brain tells her.

Her doctors can support her mental effort with drugs and advice, but one day, perhaps, they may be able to add new treatment techniques to cure her problem completely. She may be able to alter her thoughts just by passing a magnet over a spot just above her collarbone.

Sounds like science fiction? The method is already working in other brain disorders, such as epilepsy and Parkinson's disease, is being tried out in depression - and schizophrenia may well be next. The new science has been developed from heart pacemakers and is called neurocybernetics.

Pacemakers are small devices put just under the skin of the chest. They deliver tiny electrical currents along wires to the surface of the heart. The heart responds to each impulse by beating. Control the impulses delivered each minute and you control the heart rate.

If a pacemaker can control the heart, why not the brain, too?

The first brain problem to be tackled in this way has been epilepsy. Convulsions ('fits') happen because a part of the brain has been overwhelmed by a huge increase in electrical activity.

Neurocybernetic 'pacemakers' are fitted to the vagus nerve, which carries information between the brain and the lungs, heart, throat and stomach. It's been discovered that you can pass minute electrical currents along it into the part of the brain that is the control centre for the brain's normal electrical activity.

Trials so far show that it does halve the number of fits - and in some people can stop them. American doctors found the vagus pacemaker also helps with severe depression.

The vagus pacemaker is implanted in the upper chest. If the symptoms are getting the person down, they just pass a small magnet over the pacemaker. That starts the pulses in the wire and the brain responds.

No-one is yet using pacemaker technology for schizophrenia, because we can't yet precisely identify the area of brain involved. But we are getting closer, year by year, with the new types of brain scan. It may not be too long before the first trial of pacemakers in schizophrenia - and that may help to deal with those harmful thoughts.

Converted for the new archive on 30 June 2000. Some images and formatting may have been lost in the conversion.