Anhedonia was largely ignored throughout the 20th Century in favour of more obvious symptoms of depression, which include 'low' mood, poor concentration, tiredness, disturbed appetite and sleep, feelings of guilt and suicidal thoughts. But since the late 1980s, anhedonia has been recognised as a core symptom of depression, and is also present in schizophrenia and other mental disorders.

It is best described by examples. An anhedonic mother gains no joy from playing with her baby, a footballer is no longer excited when his team wins, a teenager is left unmoved by passing their driving test.

Anhedonia and depression

Not everybody suffering from depression has anhedonia, according to Consultant Psychiatrist Dr Tonmoy Sharma of the Maudsley Hospital, London. Many people who go into mild depression can be cheered by 'tea and sympathy'. But in severe depression anhedonia becomes a serious problem.

'It's worse than not being able to get any joy from life,' says Dr Sharma. 'People in this state have an incredibly flat mood. They can't react properly or feel anything. There is no modulation of mood at all. They can't take things forward.'

Depression strikes one in every five people at some time in their lives and is a potentially fatal illness through suicide. Anhedonia places a great strain on relationships and is usually accompanied by a loss of sex drive. Anhedonia can continue after depression, but usually it goes away at the same time.

Depression is often called the 'invisible illness'. Victims hide their symptoms for fear of being seen as unable to cope or as miseries. It can be triggered by a sad event like a bereavement, by a physical illness or by imbalances in brain chemistry that come apparently out of the blue. The desire to remove the stigma from depression and to find better treatments prompted Dr Sharma and his team in the Section of Cognitive Psychopharmacology at the Institute of Psychiatry to research anhedonia.

Antidepressant drugs only partially deal with anhedonia symptoms. Dr Sharma hopes to identify specific areas of the brain involved with the problem. It might be that the limbic system, which has already been linked with pleasure, might be shown to work differently in people with anhedonia. Then it would be possible to target this area either with existing drugs, which can be shown to work, or with new drugs or psychological treatments.

Watching the brain in action

Dr Sharma's team is using a new imaging technique called functional magnetic resonance imaging - fMRI - that scans the brain at work. Some differences in the brains of depressives have already been observed. For example, in comparison with healthy volunteers, depressives have smaller hippocampi - the area which deals with emotion - larger white matter lesions and differences in brain metabolism.

A previous study found that when depressed people were shown film clips designed to cause passing sadness, they activated areas of the brain - the left medial prefrontal cortex and the right anterior cingulate gyrus - that were not involved in the reaction of a group of healthy controls. The investigators suggested that this might disconnect the limbic system from the normal prioritisation of emotional importance. In this new study the brains of people with anhedonia are being examined.

In an interview with NetDoctor, Dr Tonmoy Sharma explains his research methods by saying that as he is talking, he is using the brain cells at the front part of his brain. The increase in neural activity in this area means there is an increased need for oxygen. This is delivered by the haemoglobin, which carries oxygen in the blood to all the cells of the body. When this happens, there is a difference in the magnetic properties between oxygenated haemoglobin and deoxygenated hemoglobin as the oxygen is brought to the active area of the brain which is picked up by the MRI scan.

'We are treading new ground,' he says. 'Instead of just looking at the structures of the brain, we are examining its functioning. We are seeing the changes in the brain as they happen.'

Not only can the activity of the brain be recorded when the person moves or signals the answer to a question by pressing a button, it can also be observed when the brain is active during thinking or planning.

When a rose lover loses the ability to take pleasure even from the most luscious bloom, the researchers hope to be able to discover the normal reaction of the brain to the fragrance of a rose. They will be able to pinpoint the normal reaction, then observe when that's absent.

The search for treatments

The next step is to see what effects drugs and psychological therapy have on the brain. The brain can be scanned after the volunteer has been given antidepressive drugs to see what is happening. There are drugs that can treat depression successfully but it is not known which drugs react on which parts of the brain.

'This is something that will be exciting to discover,' says Dr Sharma. 'When we know the effects on the brain of pharmacological and psychological therapies for depression, it will help us predict who is going to get depressed and also who is going to respond to treatment and what kind of treatment and who is likely to relapse. We will also be able to monitor the effects of the drugs as we give them.'

In the research, volunteers are shown film clips such as the famous comic orgasm scene from the movie When Harry met Sally, and slides to invoke emotions in people while they are having fMRI scans. If patients with depression and anhedonia show patterns of activity different from those who respond positively to the images, it will provide information on the pleasure responses in the brain and identify abnormalities.

Dr Sharma believes that when it is clearly demonstrated that depressive illness is caused by physical changes in the brain, even if it is triggered by life events or illness, the stigma attached to it will be removed. 'These are important advances that do give new hope for people who have suffered from depression and change our understanding of the illness,' he says.

The results of the research will be published next year.

Sharing experiences

Lizzie Gardiner, a 36-year-old writer and single mother from South London, told how depression and anhedonia affected her life. After several short bouts of the illness in her teenage years, she was hit by a major depression five years ago. It was brought on by a series of shattering life events - the break-up of her marriage, a move from one end of the country to another, bad health, financial problems and the threat of eviction.

Driven by the need to keep the lives of her two children as normal as possible, Lizzie somehow managed to keep going with the help of antidepressants and psychological treatment. She didn't know about anhedonia then, but she has since taken part in Dr Sharma's research.

Her anhedonia took many forms and partly remains with her. She is still unable to gain pleasure from her own achievements and to see that her children are a credit to her as well as to themselves. She recalls the anhedonia of some of her darkest moments when she sat down to listen to Elgar's Enigma variations, and found to her horror that she was left completely unmoved by the hauntingly beautiful music she had always loved.

Lizzie, who has learned to live with her symptoms, spoke of how she was helped by being given information and reassurance when she was depressed. 'Up to now it has been an invisible illness,' she said. 'If this research can show physical evidence that depression is caused by changes in the brain, it will be immensely helpful in removing the stigma that is attached to it.'

Bravely, she now shares her own experiences to help other people understand the problem.