Most people shudder at the mere thought of implanting electrodes in the brain. "Deep brain stimulation" sounds like a terrible science-fiction scenario. But for the patients Professor Veerle Visser-Vandevalle sees at the University Hospital in Cologne, the operation is often their only chance of living a normal life.
"The patients who come to me are usually seriously ill," she explains. "In my experience, they're weighing up the possible risks against their quality of life, which is often very low." These people's lives can be improved with deep brain stimulation (DBS).
The day before the operation an MRI (magnetic resonance imaging) is done of the patient's head. The surgeons can clearly see on the images where the electrodes should be implanted. They can also see where the blood vessels are; it's important not to damage them.
"First we fix a frame, known as a stereotactic framework, to the patient's head," says Visser-Vandevalle. "That's done around eight o'clock in the morning. This is followed by a CT (computerized tomography) scan of the head. This scan and the MRI imaging are placed over each other. There's an element of distortion on an MRI, but not on a CT scan. We're talking about precision of less than one millimeter."
Special software provides 3-D coordinates of the target point, where the team will affix the electrodes. The patient is conscious during this phase: They are lightly sedated and feel no pain. The preparations take until around eleven o'clock.
The serious part
For most of us, the thought of having a hole drilled into our brain is sheer horror. However, it's one of the most important steps when introducing a brain 'pacemaker'. It's through this hole that surgeons implant two or three delicate micro-electrodes into the brain, which are key to the whole procedure.
"With these electrodes we can measure electrical activity millimeter by millimeter. We look at where the greatest electrical disturbance is, and then we conduct a test stimulation," Professor Visser-Vandevalle explains. With this test, the doctors can check whether, for example, a patient who suffers from tremors is still shaking. Once the optimum target point has been found, the surgeons implant the final electrodes.
Not just Parkinson's
Most patients treated with DBS are suffering from Parkinson's disease. However, brain 'pacemakers' are also used to treat motor disturbances like dystonia.
This affects around 160,000 people in Germany alone. With dystonia, it's the brain that causes the disturbance. Patients suffer from sudden and prolonged muscle contractions they are unable to control. Even their eyelids may go into spasm. Dystonia can also impair vision and speech or make eating difficult.
Of the psychiatric illnesses that doctors treat with DBS, obsessive-compulsive disorder is the most common. "Did I really switch off the light? Is the oven still on?" – People who are constantly checking that everything is in order, not once or twice but 30 or 40 times, are suffering from OCD. They may also feel compelled to enact certain rituals over and over again, such as repeating specific phrases, moving in a certain way or opening and closing doors.
Professor Visser-Vandevalle gives an example. "A patient drives somewhere and worries that he's hit someone. So he drives back again to make sure that this isn't the case. But then he thinks, 'Maybe I hit someone the second time.' So he has to go back again, and he ends up constantly driving back and forth." The neurologist explains that this is prompted by an electrical disturbance in the brain.
A specific area of the brain is active when we ask ourselves whether we've switched off the light. In people with OCD, this area remains active. The electrodes inhibit this over-activity.
Constant electric current
The electrodes are connected to cables and attached to a generator. This generator is implanted below the collarbone and supplies a constant electric current, meaning that that area of the brain is permanently stimulated by high-frequency electricity of more than 100 Hertz.
Between 10 and 15 percent of all such operations are performed to treat very severe psychiatric disturbances. Doctors are keen to use DBS to treat depression, too, but in this field the procedure is still in its infancy. "We have yet to establish the optimum target point with 100 percent certainty," says Professor Visser-Vandevalle. "We're now going to apply a different technique: vagus nerve stimulation. For this, the electrodes are not implanted in the brain, but in the neck. A study of 400 patients has shown that this method can significantly reduce depression." Implanting the electrodes in the neck is less invasive, and most people find it more tolerable than the idea of drilling through the skull.
So far, Visser-Vandevalle has operated on three patients with depression. All three procedures went extremely well, then one patient suddenly deteriorated. "He was having negative thoughts and was even considering suicide. We examined him and established that his generator was empty. So we exchanged the generator, and the patient was fine again." This sounds simple – and from the neurologists' point of view, it is.
Treatment for dementia?
Scientists are also looking at the possibility of treating dementia with deep brain stimulation. They will soon be publishing a European study on the subject. "Dementia research is very important. We must use DBS as widely as possible here," says Visser-Vandevalle.
So far, researchers have been able to establish that DBS has improved memory and concentration. The method has also had a positive effect on dealing with everyday things like getting dressed.
Second lease of life
Many Parkinson's patients feel reborn after the operation – as if they've been given a second lease of life. Every day Visser-Vandevalle meets people who are dealing with very difficult life situations, but she also has many positive experiences.
"The greatest compliment I've ever received was from a child I operated on. It was a nine-year-old boy with dystonia. He'd already had to rely on a wheelchair for two years. Then I operated on him. A few months later he came running into my room. He had painted a picture for me; he'd written on it 'Thank you – I can run again', and had drawn a heart over the top. Of course that was very, very nice."
Professor Visser-Vandevalle and her team also want to inform a wider audience about their work and the different possibilities of brain surgery. They hope this will make people less afraid of such an intervention.Gudrun Heise