Through the Eighties and Nineties, psychotherapy has reigned supreme. Whatever your problem, therapy would take out those kinks left by childhood - eventually. Now, research suggests much mental illness may have physical origins. Will the shrink soon be out of a job? Jerome Burne reports
Parents of anorexic children across the country offered up a silent prayer of thanks last week when they heard about the latest research at Great Ormond Street Hospital. While scanning the brains of 19 teenagers suffering from this slimming disease, Dr Bryan Lask found nearly all of them had reduced blood flow to the part of their brain that controls vision. So that was why girls stared at their emaciated bodies in the mirror and declared, "I'm too fat". Damaged brain cells meant that their vision really was distorted.

The research begged all sorts of questions about the treatment of anorexia and other mental illnesses. Psychotherapy in all its forms has long been viewed by the public as the civilised alternative to the brutal physical interventions of the past. Nature went out of fashion; nurture was all. Whatever your problem, enough therapy of the right sort could take out the kinks left by childhood. It meant that we were perfectible beings, but also that, if we weren't happy, it was because we weren't making the effort, weren't "working through" our problems. Then along came Prozac and drugs like it. People who had spent thousands of pounds and hundreds of hours in therapy were suddenly released from their prison of depression. Perhaps the problem never had been their childhood; perhaps it had been physical, a chemical imbalance of some sort in the brain.

The backlash against therapy is understandable, but it is only half of a very interesting story. A new generation of sophisticated and sensitive equipment is letting us see ever more clearly exactly what is going on in the brain when behaviour goes awry. Lask's research is just one among dozens of brain-scan projects in Europe and America that are changing the way we think about mental illness in general. In our scientific culture, the physical (brain cell activity) seems somehow more "real" than the intangible (emotions and attitudes). It also has the added bonus of reducing blame.

For years, the psychological interpretation of conditions such as anorexia has put parents in the firing line. Controlling and aggressive mothers and distant but demanding fathers are among the usual suspects, along with sexual abuse and capitulating to the demands of a male-dominated society. But if the cause lies in the architecture of the brain then it's no longer anyone's fault.

At this point, we are peering once more into the great big chasm that runs through our theory about how the mind works. Is it the product of billions of brain cells, which in turn are defined by our genes, or is it shaped by more nebulous factors, such as upbringing, early experiences and culture? The hardware theory is certainly seductive. We can all experience what it is like to change our psychological state by physical means - just down a bottle of wine or smoke a joint. And, as neurologists know, the effects of messing about with brain cells can be a lot more specific and bizarre than feeling cheerful or morose.

Take people with Capgrass syndrome, for example. They appear perfectly normal and lucid except that they believe that their parents are impostors. The real ones have been removed and fake ones put in their place. Professor Vilayanur Ramachandran of the University of California, San Diego, is studying them and he has found that this ludicrous belief is due to a malfunctioning in a particular bit of the right brain.

If faulty neurons can produce such an obviously psychological effect - what hours of fun a psychoanalyst might have with that one - it doesn't seem such a big leap to say that anorexia, depression, anxiety, schizophrenia and the rest will all turn out to be the result of faulty wiring and treatable by physical methods like drugs or surgery. Combine that with our rapidly expanding understanding of the way genes control brain development, and biological psychiatry would seem set to sweep the field.

Someone you might expect to be gung-ho for biology is Professor Robin Murray of the Institute of Psychiatry in South London - a place where brain surgery and even a modern version of the lobotomy is regularly performed. "It's true that drugs have made an enormous difference," he says. "When I started in psychiatry 25 years ago the wards were full of long-term depressives. We gave them psychotherapy and electric shocks but it didn't do much good. Now, with a new range of drugs, most of those sorts of patients can lead a life outside."

But surprisingly, perhaps, he admits to a change of heart about how much can be done just by treating the body. "Biologists like me used to have a pretty crude idea about how the brain worked because we had pretty crude machines. Now we can see what is going on in more detail and we are realising that we have to take into account the working of the environment. We used to think that genes pretty much determined the way the brain developed, but now we can see that the interaction is much more subtle. For example, the quality of the mother's nutrition in pregnancy, together with the stimulation a child receives, can dramatically effect the way the infant's brain is wired up."

All the same, there has long been a tendency among biological psychiatrists to think that because you can see changes in the brain when a particular behaviour is going on, the brain must be causing that behaviour. But, ironically, the new brain-scan technology is showing the process to be far more of a two-way street.

Therapy that changes the way people feel about themselves also changes the way their brain cells fire. Take that inalienable right of all Americans - happiness. Professor Richard Davidson of Madison University has located the brain cells that control happiness in the left pre-frontal lobe of the brain, that is, just above the left eyebrow (he's found that new-born babies with greater activity in this sector cry or fuss less). But, and this is the interesting part, that doesn't mean you are doomed to misery if your lobe is sluggish. Brain scans of people who have gone through a psychological self-help programme of thinking positive thoughts, exercise, deliberate smiling and setting achievable goals, reveal that their happiness lobe is now firing on all cylinders.

A particularly revealing piece of work, reported only last month by Dr Donald Edwards at Georgia State University, involves dominant crayfish. Despite being further down the evolutionary ladder than ourselves, these creatures have well-established dominance hierarchies, with the leaders being more aggressive and the subordinates more depressive. The brain chemical involved in this behaviour is serotonin, the same one that is linked with human status and aggressive behaviour. If you give a dominant crayfish extra serotonin it will become more aggressive but, interestingly, if you boost the levels in a subordinate it will merely become more depressed. But, the real clincher comes if you change the status levels so that a previously dominant crayfish gets all the signals that tell him he is a subordinate. Can you boost his aggression by upping his serotonin? No, you can't. It simply makes him more depressed. Far from being the independent triggers of behaviour, brain chemicals have different effects depending on the animal's psychological state.

What all this means is that we could be on the edge of far more integrated treatment. "The new approach to anorexia is to treat it on three levels," says Lask. "There probably is an underlying biological factor, but there is also the psychological level - teenagers who are perfectionists with low self-esteem are much more at risk - and the social one - no one gets anorexia in cultures where being fat is thought attractive."

It was Plato who said, "A major mistake of the physician is to separate the body from the mind." We seem to have needed 2,500 years and some very clever computer hardware to appreciate the sense of that.