Currently, scientists are not entirely certain how deep brain stimulation causes similar effects as lesions in the same region of the brain. Somehow the electrode stimulations override pathological activity patterns, but the patterns induced are not necessarily normal. Here are the four dominant theories:
Through stimulation induced alterations in voltage activation of the neural membrane, neural outputs near the stimulating electrode are blocked. Although this theory accounts for the results of DBS being similar to ablation, it doesn't take into account the possible independent activation of the efferent axon of projection neurons. Thus, it does not explain why impulses are still being generated around the area of the electrode.
Neurons can not generate electrical impulses when electrically stimulated due to activation of axon terminals near the stimulating electrode. However, for the same reason as the depolarization blockade theory, it looses credibility because it does not explain the ability of efferent axons to fire impulses.
Synaptic transmission failure of the efferent output of stimulated neurons as a result of transmitter depletion caused by excessive stimulation by the electrode. This theory is discredited because several in vivo experimental studies have shown increases in transmitter release and sustained changes in firing of neurons in efferent nuclei when repeatedly stimulated by an electrode.
Stimulation induced modulation of pathological network activity
This is the only general theory that is consistent with the current available data. It accounts for the continuing of firing of impulses by efferent axons located in the electrode region. The alteration in the neural network could have the same results as ablation therapy induces. Thus, both results are accounted for. However, this theory does not explain much. It simply states that the neural network is altered by the electrodes stimulations. We still are not sure how or why the network is altered.
DBS is approved in the United States by the Food and Drug Administration for the treatment of Parkinson's. A systematic review of DBS for treatment resistant depression and obsessive–compulsive disorder identified 23 cases—nine for OCD, seven for treatment-resistant depression, and one for both. It found that "about half the patients did show dramatic improvement" and that adverse events were "generally trivial" given the younger psychiatric patient population than with movements disorders.
Deep brain stimulation has been used experimentally in treating a few patients with severe Tourette syndrome. Despite widely publicized early successes, DBS remains a highly experimental procedure for the treatment of Tourette's, and more study is needed to determine whether long-term benefits outweigh the risk. DBS has been used in the treatment of obsessive-compulsive disorder and phantom limb pain. The procedure is being tested for effectiveness in patients with severe epilepsy.
DBS has been tried for patients with Lesch-Nyhan syndrome in Japan, Switzerland and France.
DBS requires brain surgery. The head is shaved and then attached with screws to a sturdy frame that prevents the head from moving during the surgery. Scans of the head and brain using MRI are taken. The surgeon uses these images as guides during the surgery. Patients are awake during the procedure to provide the surgeon with feedback, but they feel no pain because the head is numbed with a local anesthetic.
Once ready for surgery, two holes are drilled into the head. From there, the surgeon threads a slender tube down into the brain to place electrodes on each side of a specific part of the brain. In the case of depression, the part of the brain targeted is called Area 25. This area has been found to be overactive in depression and other mood disorders. In the case of OCD, the electrodes are placed in a different part of the brain believed to be associated with the disorder.
After the electrodes are implanted and the patient provides feedback about the placement of the electrodes, the patient is put under general anesthesia. The electrodes are then attached to wires that are run inside the body from the head down to the chest, where a pair of battery-operated generators are implanted. From here, electrical pulses are continuously delivered over the wires to the electrodes in the brain. Although it is unclear exactly how the device works to reduce depression or OCD, scientists believe that the pulses help to "reset" the area of the brain that is malfunctioning so that it works normally again.
Pros for this therapy
- Improves quality of life for medication resistant Parkinson's disease
- Decreases side effects of Parkinson's medications
- Can allow for a reduction in medication regimen
- Effects are reversible
- Allows for non-permanent denervation in dystonia patients
Cons for this therapy
DBS carries risks associated with any type of brain surgery. For example, the procedure may lead to:
- Bleeding in the brain or stroke
- Disorientation or confusion
- Unwanted mood changes
- Movement disorders
- Trouble sleeping
Because the procedure is still experimental, other side effects that are not yet identified may be possible. Long-term benefits and side effects are unknown.
Deep brain stimulation was approved by the Food and Drug Administration for the treatment of essential tremor in 1997. It was later expanded to treat Parkinson's disease in 2002, and dystonia in 2003. It can be approved on a case by case basis to treat obsessive-compulsive disorder.
Up until the 1950s, the only treatment for Parkinson's disease was using surgery to lesion parts of the corticospinal pathway or the basal ganglia structures in the brain that were affected. By destroying the specific parts of the brain that were being affected by the disease, the symptoms often improved. However, this was not ideal, because the surgery was permanent, and while it treated the positive symptoms of Parkinson's disease (tremor and rigidity), the negative symptoms remained (difficulty with postural fixation and akinesia).
In the 1970's a drug called levodopa was discovered. In Parkinson's disease, the part of the brain called the substantia nigra is not producing the neurotransmitter dopamine. Levodopa can be taken by patients, and it is converted into dopamine in the brain, bringing relief. The drug brought relief to many patients, but it was not without side effects.
In the 1980's it was discovered that by stimulating with electricity the same regions of the brain that used to be lesioned, similar effects could be achieved. The procedure is now used to help patients whose symptoms cannot be treated with medications or patients who have had severe side effects to medication.
Deep brain stimulation (DBS) was first developed as a treatment for Parkinson's disease to reduce tremor, stiffness, walking problems and uncontrollable movements. In DBS, a pair of electrodes is implanted in the brain and controlled by a generator that is implanted in the chest. Stimulation is continuous and its frequency and level is customized to the individual.
DBS has only recently been studied as a treatment for depression or obsessive compulsive disorder (OCD). Currently, it is available on an experimental basis only. So far, very little research has been conducted to test DBS for depression treatment, but the few studies that have been conducted show that the treatment may be promising. One small trial involving people with severe, treatment-resistant depression found that four out of six participants showed marked improvement in their symptoms either immediately after the procedure, or soon after. Another study involving 10 people with OCD found continued improvement among the majority three years after the surgery.