Just imagine you are worried about developing Alzheimer's or having a heart attack and you go to your doctor for a check-up. But instead of asking about the usual suspects - weight, smoking, diet, exercise and so on - he makes a sudden loud noise and then asks you to fill in a personality questionnaire.
You might wonder whether he was having a breakdown - but in fact he'd be at the cutting edge of research. In recent months, a number of studies have given a hi-tech spin to the old idea that your personality can affect your risk of developing various disorders. What seems to be especially significant is how prone you are to negative thoughts and feelings - hence the testing of the strength of your startle reflex with a sudden noise. The stronger it is, the more susceptible to the damaging effects of stress you are likely to be.
That is certainly the case with rats who are "neophobic", or afraid of new things - a trait that goes with being anxious and fearful. A recent report found that such rats die sooner than their bolder relatives. But it's not just rats - similar trends appear in humans. A study at Rush University Medical Center in Chicago has just found that people who have negative emotions most often are twice as likely to develop Alzheimer's. And the connection has also shown up with Aids.
For years, it has been observed that shy and introverted Aids patients die sooner. Then, in December, researchers at the University of California Aids Institute reported that they had recorded a higher level of nervous- system activity in these patients, and this was what reduced their resistance to HIV. The effect was so strong that some standard drug treatments, which usually reduce viral load by a factor of 10, were ineffective.
The idea of a link between personality and disease goes back to the ancient Greeks with their doctrine of the four humours, which remained popular in Europe until at least the 17th century. In Victorian times, tuberculosis was believed to be the result of an overactive creative spirit consuming a frail body. However, once the tuberculosis bacterium was discovered and the disease could be treated with antibiotics, it became an example of how the theory that mind affects disease was simply a measure of our ignorance.
This highlights a split that runs through modern medicine, which explains why the idea of a link between personality and disease has always been a tricky concept. Scientific medicine developed in the shadow of the philosopher Descartes, who "solved" the mind/body problem by declaring the mind an ethereal thing, of a quite different substance to the body. At the time, it was a liberating idea, and medicine made huge strides by ignoring the mind and treating the body as a mechanical system. Antibiotics work, whatever your personality.
As a result doctors, by and large, have never been terribly keen on the links between psychological states and disease. They like to deal with what they can see and measure - a viral infection, a malignant tumour. This comes from an editorial in the New England Journal of Medicine a few years ago: "It is time to acknowledge that our belief in disease as a direct reflection of mental state is largely folklore."
Part of this suspicion has been fuelled by some of the wilder pronouncements of the psychotherapists. Freud, for instance, distinguished between real illnesses and hysterical ones brought on by unconscious emotional conflicts - asthma, for example, was explained as "the fear of losing parental love". As recently as the 1940s, the psychiatric explanation for Parkinson's disease was that it was the result of "conflict between an aggressive drive to action and an equally strong internal pressure to inhibit action". The specific conflict was the result of "the wish to masturbate in the ambitious moralistic man".
Despite these absurdities, …