HYPOTHESES

Depression is very depressing, not only for the victims, but for those who live with them. For depressives are totally negative and self- centred. They are victims in the sense that they have a frightening and disabling illness. It is an illness that affects as many as one in ten of the population; considering how widespread depression is, it is particularly unfortunate that it carries with it the additional burden of severe social stigma. It is one of those illnesses that people are ashamed of.

Clinical depression is not just feeling much lower than usual. It is a quite different state, a state that bears only a tangential resemblance to normal emotions. It is also associated with a variety of physical symptoms. One anthropologist has linkened it to "soul loss". There is a feeling of emptiness, as if the soul had left the body. William Styron in Darkness Visible claims that it deserves some new and special word that would somehow encapsulate both the tumult and the conviction that no remedy will ever come. But this may be merely a particularly Western view.

While there is undoubtedly a common biological basis for depression, there is a strong cultural influence on how it manifests itself. During the 18th century there was a change from viewing it as melancholy - known as the English Malady - with many physical ailments, to its association with guilt and self-accusation. Moreover, when the Chinese feel sick, Americans very often feel depressed. Patients in China suffering from chronic pain often meet the diagnostic criteria for major depressive disorder. Depression is so rare among the Kaluli of the New Guinea Highlands that they have no word for it. These variations reflect how different cultures relate to complex emotions.

Last year, after I had emerged from a very frightening and disabling clinical depression, mercifully of brief duration, I thanked my psychiatrist for all her help. I then asked her if I was correct in thinking that psychiatrists really understood nothing about depression. She agreed. Of course they have great skills at diagnosis and treatment; for example Prozac related anti-depressive drugs can bring about remarkable cures. But it was at a mechanistic level that virtually nothing seemed to be known.

It was even far from clear to me what it meant to understand a mental illness in the same way that one now understands cancer. For example even if low levels of serotonin - one of the signals between nerve cells - are linked to depression, this on its own would still be an inadequate explanation. Is the low level the cause or result of depression? What, too, is the relation of the levels to cognitive processes and emotions?

A major advance in the treatment and understanding of depression comes from the cognitive model of Beck. He maintained that negative thoughts not only characterise depression but are a key factor in maintaining the depressed state. Cognitive therapy aims to alter the patients thought processes and to teach them new ways of thinking. This approach has met with considerable success. However, it is still far from clear whether or not negative thoughts are the cause or consequence of depression or why some are more vulnerable than others.

A new cognitive approach to depression has been put forward by Teasdale and Barnard working at a Medical Research Council Unit in Cambridge. They propose a quite complex hierarchical scheme for thoughts and their links to emotion. It explains, for example, why we recall more easily those events that we experienced in a mood similar to our current one. They draw a clear distinction between two levels at which we understand thoughts and statements. At the Propositional level statements like "Try again" are taken at their face value and would simply mean try again. However at what they call the Implicational level the meaning of a statement is captured as a whole, and so the statement "Try again" is now closely linked with the context within which it is made. It could be a reprimand or an encouragement. Depression can result from self-regenerating processes between the two levels with the Implicational level having depression related schematic models. The complexity of the model makes intuitive understanding very difficult. But one should be extremely wary of simple models of how the brain works. It is, after all, the most complex object in the universe.

The facile and untested psychoanalytical approach has not illuminated depression, which is regarded as aggresion turned inwards. Never the less, in an important essay Freud described the similarities between depression and mourning. A key difference is that mourning is not associated with loss of self-esteem. The significance of the similarities is that there should be a major effort to understand mourning and grief, since the cause is not in dispute. Unless we can understand mourning we are most unlikely to understand depression. It is also necessary to understand depression within an evolutionary framework. Since it is so dysfunctional why has it not been selected out? Perhaps it is the inevitable pathology associated with the basic emotion of sadness, just as cancer is with cell multiplication.

There is currently a wonderful exhibition of Durer engravings in Paris. In one, titled "Melancolia" an angel sits, dishevelled and disconsolate, staring at the word emblazoned on the horizon. I am not surprised at her state. Depression is depressingly difficult to understand.

Lewis Wolpert, of University College London, is chairman of Copus (the Committee on the Public Understanding of Science). His book, 'The Unnatural Nature of Science', is published by Faber.