Deep brain stimulation — explained
Deep brain stimulation is the main surgical treatment for Parkinson’s, but how does it work and what’s on the horizon?
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Controlling and coordinating our movements is something we can take for granted. But even simple actions, like picking up a cup of tea and drinking from it, require an incredible interplay between families of cells inside our brains to get the movement just right and avoid spilling our drink.
In Parkinson’s, this delicate balance gets out of kilter because one of the key families of brain cells involved in this movement circuit stops working properly.
The circuit inside our brains responsible for controlling our movements is called the basal ganglia. It’s made up of several different groups of brain cells that connect and talk to each other to fine tune movement.
For decades researchers have been studying how these circuits function to help us understand how we move, and this has helped us piece together a picture of how these complex circuits function.
What goes wrong in Parkinson’s?
In Parkinson’s, dopamine-producing cells in the substantia nigra, slowly stop working properly and are lost over time. Without the injection of dopamine these cells provide, it becomes harder to get moving and to maintain movements — so, things like stride length can get shorter over time.
So if you imagine that our movement is controlled in a similar way to a car, then you can think of the substantia nigra playing the role of the accelerator pedal — and dopamine is the chemical needed push the accelerator down.
So when these brain cells start struggling to produce enough dopamine (the chemical they use to send these messages), it becomes harder and harder to push down on the accelerator and get moving. That’s where Parkinson’s medication can really help, by boosting dopamine levels, these drugs can make it easier to push down the accelerator again and help people to move.
However, medications that boost dopamine are not a perfect solution because as brain cells in substantia nigra continue to struggle and be lost over time, more drugs are needed and keeping dopamine levels in the ‘sweet spot’ to control symptoms becomes more and more difficult. The swings in dopamine levels in the brain mean that movement control becomes more erratic and unpredictable.
Going back to our car analogy, it’s like jabbing the accelerator pedal so the car moves in a stop/start fashion.
At this point, sometimes a type of surgery called deep brain stimulation (or DBS), can be a good option.
In DBS, very fine wires are carefully inserted into the brain to electrically stimulate particular groups of brain cells involved in controlling movement to adjust their activity. These wires are then connected to a battery pack which is usually placed under the skin in the chest.
Although we still do not fully understand how this electrical stimulation works to improve movement, scientists now believe that the stimulation may disrupt abnormal electrical activity in the basal ganglia and help to rebalance movement control.
The effect on symptoms is similar to taking levodopa, but the key advantage is that the effects of DBS are constant and stable. So, it helps avoid the problems due to the swings in dopamine levels in the brain by smoothly pressing on the accelerator pedal.
Around 300 people with Parkinson’s undergo deep brain stimulation every year in the UK. There are several different areas within the basal ganglia that can be targeted with DBS:
- the subthalamic nucleus (or STN) is the most commonly used target for Parkinson’s. It is very effective for people with stiffness and slowness of movement, and stimulation here usually allows a significant reduction in the amount of medication people need to take.
- the globus pallidus internus (GPi) is also effective for stiffness and slowness. GPi stimulation does not usually result in medication reduction but it is the best target if you have severe dyskinesias (uncontrollable movements) or dystonia (painful muscle cramps).
- the thalamus is a good target to stimulate if the main problem is a severe tremor.
- the pedunculopontine nucleus (PPN) is also being explored as a potential site to stimulate to improving freezing and falling problems, but this is still in the research stages.
One of the main advantages of deep brain stimulation is that it’s adjustable. The level of electrical stimulation can be tweaked to give the brain cells the right ‘dose’ to give the best movement control, and this can be reviewed and adjusted over time.
It is particularly effective for improving simple movements like walking, but it’s usually less effective for more complex movements like speech and freezing, and can occasionally even make these worse.
What’s next for DBS?
Dr James FitzGerald is a consultant neurosurgeon at the University of Oxford.
We picked his brains about the latest advances in deep brain stimulation, and how he sees the future for this important therapy developing:
“Even in the last few years there have been some important technical improvements in DBS.
“For example, the electrodes we implant into the brain are becoming more and more sophisticated. The wires now have more stimulation points located around the tips so that we can choose which brain cells to stimulate with greater precision than ever before to get the best possible control of symptoms.
“Another potential advance is the development of less invasive surgical techniques such as focused ultrasound — which hit the headlines this time last year. Unlike DBS, this approach does not require anything to be inserted into the brain. Instead very high frequency sound waves are used to burn away the specific brain cells that are causing movement problems — usually tremor.
“Focused ultrasound is definitely a potentially useful tool but has drawbacks. It is irreversible, so unlike DBS it cannot be fine-tuned over time. And it can only be used on one side of the brain. So it is effective for treating a severe tremor that only affects one side of the body, but won’t be so good if symptoms are troublesome on both sides.
“One thing I really hope to see in the next few years is more people with Parkinson’s being considered for surgery at an earlier stage of the condition.
“Recent research has shown that DBS is more beneficial than staying on medication alone for people at an earlier stage of Parkinson’s than previously thought. It is worth considering as soon as on/off fluctuations become troublesome. We shouldn’t be waiting until people are experiencing very severe problems with their movement and medication before we consider surgery.
“Looking further ahead, there are several exciting innovations on the horizon. DBS systems are becoming ‘smarter’, for example we are exploring whether short bursts of stimulation (which is more like how brain cells communicate) are more effective than continuous lower level stimulation. This has worked really well in stimulators we use in the spine to treat severe pain and we hope it might work well in the brain too.
“Researchers are also looking to see if we can listen to the brain cells in the basal ganglia and selectively intervene with the right type of stimulation when abnormal activity is identified. And within few years we will be able to adjust DBS systems remotely so patients no longer have to travel long distances to our clinics.
“Finally, although currently deep brain stimulation for Parkinson’s is almost exclusively used to manage movement-related issues, researchers are investigating the possibility of using stimulation to improve other aspects of the condition. For example, results published recently suggest low frequency stimulation could be helpful for improving thinking and memory.
“I believe that deep brain stimulation still has much more to offer for people with Parkinson’s and I’m excited to be part of developing and delivering this vital therapy to people with the condition.”
Special thanks to James FitzGerald for his help us with this blog.
This blog is not meant as health advice. You should always consult a qualified health professional or specialist before making any changes to your treatment or lifestyle.
