Can drilling electrodes into your brain cure depression?

Deep brain stimulation sounds like a form of fiendish torture. You're wide awake as your head is clamped in a metal cage and two holes are drilled into your skull. Fine wires attached to electrodes are then slid directly into the soft grey matter of your brain.

A local anaesthetic numbs the pain of drilling but you have to remain conscious so that you can help the neurosurgeon guide the wires to precisely the correct spot - to do this, you report your thoughts and emotions as the stimulating electricity is turned on.

As freakish as the operation may sound, it's painless - the brain itself has no pain nerves. Furthermore, it holds out the hope of relief from a range of conditions where conventional treatments have failed.

Until recently, treatments for brain disorders have largely concentrated on using drugs to change the levels of natural brain chemicals. This new approach focuses on the brain's constant electrical activity. Drugs are an imprecise tool, affecting the whole brain.

Electrical stimulation, however, enables neurosurgeons to target areas involved in specific feelings and actions, such as movement, and then turn them on or off.

Just as a pacemaker resets the electrical rhythm of the heart, deep brain stimulation acts like a pacemaker for various areas of the brain.

The technique has helped prevent the tics - the uncontrollable blinking, coughing, grimacing - of Tourette's syndrome as well as epileptic fits. There have been positive results with patients suffering from severe depression and anorexia, too.

Only last week, Canadian scientists reported that deep brain stimulation might also eventually help patients with Alzheimer's recover their memory.

They had been using the technique to stimulate the brain of a severely obese man in order to try to damp down his appetite when he suddenly began reporting intense memories from his 20s. Over the next year the man started getting much higher scores on memory and learning tests when the current was switched on.

"We can keep on changing brain chemistry with drugs," says Dr Helen Mayberg, a neurologist who has pioneered the use of deep brain stimulation for depression.

"But we will increasingly be able also to target specific brain pathways with electricity."

Deep brain stimulation is best known as a treatment for Parkinson's. It works by blocking out the bit of the brain that sends abnormal electrical signals, causing erratic movements and tremors.

In the 1950s, neurosurgeons found they could help patients by cutting out this area of the brain. They first started using deep brain stimulation to do this 20 years ago. So far, 130 Parkinson's patients have been treated with deep brain stimulation in the UK, and 30,000 worldwide.

The well-known chef Fergus Henderson, owner of the celebrated St John restaurant in London, had the treatment three years ago.

He developed Parkinson's at the early age of 32 - the average age of onset is 58. His arms began to jerk and flail, making cooking impossible. Electrodes were inserted into the basal ganglia, an area of the brain that controls movement.

These remain permanently in Fergus's head. (In another operation, surgeons placed a tiny battery pack in his chest to power the electrodes.) The whole procedure has been a great success and he is now able to cook again.

About 10 per cent of Parkinson's patients are thought to be suitable for this treatment, although the results are variable.

Dr Mayberg first started using the technique for depression three years ago. In a trial of 12 profoundly depressed patients at the University of Toronto, she found eight of them experienced dramatic improvements after being given deep brain stimulation.

One patient described what the operation had done for her: "All of a sudden, as the electrodes went in, I felt so calm and peaceful." Another, who had once been a keen gardener, reported feeling as if she were walking though a field of wild flowers. Two days later she was at work in her garden that had been abandoned for years.

Some have been hugely better for three years now, but it's far from a complete cure - the patients still have to take medication as well as receive psychiatric support.

There are also questions about whether the benefits will last - and if there will be long-term damaging effects. No one knows, and at £20,000 for the operation, it's not about to become the next Prozac.

However, deep brain stimulation is just one of several similar techniques which directly target the electrical activity in the brain. Another, called transcranial magnetic stimulation, can turn brain cells on and off using magnetic pulses from the outside.

Last month a large-scale study found it was an effective treatment for major depression. A third technique uses a pacemaker implanted in the chest to target the vagus nerve that runs from the gut to the brain. It's been used to treat epilepsy, depression and chronic headaches.

But the field of brain stimulation is controversial. Critics claim that use of such techniques is highly speculative and that invasive and experimental procedures are being driven by commercial interests.

It was recently revealed that all nine authors of a major article in favour of deep brain stimulation were in the pay of the manufacturers of the equipment.

"We must be extraordinarily careful that digging around in an organ as complex and fragile as the brain doesn't harm individuals," says a leading critic, Dr David Roy, of the Centre For Bioethics in Montreal.

"At this point, there is very little scientific evidence around the benefits and risks of electrical stimulation." There is also the risk of sideeffects.

With Parkinson's patients, for instance, there have been reports of bizarre side-effects such as aggression, excessive interest in sex, criminal behaviour and suicide. There is also the risk of infection and memory loss.

And then there is the instinctive opposition that many people feel towards the procedure.

"People still have the notion that surgery for psychiatric disorders is barbaric," says Dr Patricia Limousin, a clinical neurologist at University College London.

"So I don't think anyone is using deep brain stimulation for depression in the UK yet."

However, the neurologists involved are very positive about the benefits.

"People can get very emotional about brain surgery," says Professor Vincent Walsh, of the Institute For Cognitive Neuroscience, also at University College.

"It's highly complicated, of course, but it is just another organ, and if operating can help patients then we should do it.

"If you ask a Parkinson's patient if he is willing to risk the possible problems for the probable benefits, the answer is nearly always yes."

But while deep brain stimulation is likely to remain very specialised, the use of devices that work from the outside, such as transcranial magnetic stimulation, or a related form, transcranial direct current stimulation, may eventually become more widespread.

Instead of the brutal invasion of drilling into the brain, the equipment is put against the head and directs a magnetic field or weak electric current through the skull.

"They can turn nearby brain cells temporarily on or off without having to operate," explains Professor Walsh.

"At the moment we've more data on transcranial magnetic stimulation but transcranial direct current stimulation is a more compact form of equipment and so may eventually be more suitable for use in the home."

As well as treating depression, transcranial magnetic stimulation may be able to boost your memory while you sleep and speed up recovery from a sleepless night.

Every night, brain waves - another term for electrical activity - flicker across the surface of your sleeping brain. While you're dreaming they are at their fastest; during deep sleep they slow down.

Recently, scientists at the University of Wisconsin School of Medicine used transcranial magnetic stimulation on sleeping patients so that they produced slow waves.

This plays a role in strengthening memories during sleep, although how it works is still debated. Slow waves also indicate deep sleep. "This could be a way of helping people recover from insomnia," says one of the scientists, Marcello Massimini.

These electrical technologies are still in their infancy, but it's predicted that within ten years there might be all sorts of applications. One of the most exciting is the use of deep brain stimulation technology to help stroke victims who have lost the use of a limb.

"An implanted computer chip would monitor the region of the brain where the intention to move shows up," explains Dr Limousin.

"Then, using the knowledge gained with deep brain stimulation, the chip would send a signal to the area that tells the muscles to move."

This technology is already being worked on and offers the promise of transforming millions of lives.