Brain Stimulation

In this decade designated as the "Decade of the Brain" there have been astonishing developments in our understanding of brain function, and in our ability to successfully treat neurologic disorders.
The brain is the most complex entity known to mankind, composed of billions of nerve cells arranged in a complex network of interconnected circuits. Each mental/physical function (movement, cognition, emotion, sensations, etc.) requires the precise orchestration of these circuits and their components. Small perturbation in these precisely engineered electrical highways can completely disrupt normal functions, rendering a once normal individual completely debilitated and dependent.
One of the most exciting neurosurgical advances has been the use of electrical stimulation of the nervous system to treat a variety of disabling conditions. Neurosurgeons are now able to place tiny electrodes in the depths of a brain to detect the regions affected by disease as well as to treat the condition. The recent media attention to Parkinson’s disease and its surgical treatment is just one small example of the enormous therapeutic potential of this technique.
These brain stimulation procedures represent a revolutionary new frontier in neurosurgery. Most neurosurgical procedures employ the destruction or removal of brain tissue. Brain stimulation allows physicians to augment, modulate, and even improve brain function without destroying any area of the brain. Currently, the most commonly utilized use of brain stimulation is in patients with debilitating movement disorders. This includes essential tremor, Parkinson’s disease, multiple sclerosis, and dystonia.
Patients who have become totally debilitated by their Parkinson’s disease are now able to return to normal activities of daily living and get a second chance to enjoy the full quality of their lives. As a result of Parkinson’s disease, the normally coordinated wiring for body movement becomes chaotic. A combination of hyperactivity in some brain areas and underactivity in other areas renders patients shaking and rigid, prisoners in their own bodies. Brain stimulation allows the brain to return to a more organized and functioning state.
Another area of immediate application of brain stimulation is in patients with severe and debilitating chronic pain. This technique can benefit some of the millions of patients who are afflicted with chronic pain conditions emanating from stroke, head injury, spinal cord injury, facial pain, phantom limb, arm, back, and leg pain.
The use of brain stimulation for essential tremor, chronic pain, and Parkinson’s disease are just few of the applications of deep brain stimulation. We are yet to achieve the full potential of the diagnostic and therapeutic potential of these techniques.
These advances underlie the foundation for the next era in neurosurgery in the new millennium. In the near future, improvement in these technologies will allow physicians to correct aberrant circuitry in various diseases such as stroke, Parkinson’s disease, Alzheimer’s disease, chronic pain, psychiatric, cognitive, and developmental disorders.
In the next decade, further advances will revolutionize our view of the brain and the way in which numerous disabling conditions will be treated.

Traditionally, the surgical management of Parkinson’s disease has consisted of lesioning procedures such as pallidotomy and thalamotomy. These procedures are effective for the control of tremor, disabling dyskinesias, bradykinesia, and rigidity. However, they involve the destruction of brain tissue, thus being irreversible and offering a one-time benefit. Over time, with the progression of the disease, the beneficial effects of the surgery may decline. In addition, bilateral (both sided) procedures carry a high risk of complications consisting of speech difficulties, cognitive dysfunction, visual compromise, and motor weakness.
Deep Brain Stimulation (DBS) involves the precise electrical stimulation of specific deep brain structures using tiny implanted electrodes. The major advantage of DBS over the traditional lesioning procedures is that DBS is reversible and adjustable. DBS causes no destruction of brain tissue and the stimulator can be adjusted, minimized, turned off or even removed if there are untoward side effects. The other major advantage of DBS is that it is adjustable or programmable allowing the stimulation to be altered to achieve the optimal clinical outcome. For example, if a patient develops increasing rigidity, bradykinesia, or tremor some time after DBS surgery, the stimulation can be modified to achieve better clinical effects, which is not possible with lesioning procedures.
In short, deep brain stimulation technology allows for the optimal scenario in which we can maximize clinical outcome while minimizing complications.
The components of the DBS unit include a tiny multipolar electrode, a connecting wire going from the scalp to the chest wall below the collarbone, and finally a pulse generator similar to a heart pacemaker, which is implanted under the skin below the collarbone.
The FDA approved the use of DBS for Parkinson’s disease in August of 1997. Currently, DBS therapy is only FDA-approved for refractory tremor of the extremities. This procedure is similar to a pallidotomy, involving the use of a stereotactic frame, an MRI, computer guided targeting of the thalamus, followed by physiological localization of the movement and tremor areas of the thalamus. The results of multi-center studies with long-term outcome have shown >80% resolution or significant suppression of tremor with chronic deep brain stimulation. Possible complications of this include the risk of hemorrhage or infection, which occurs in approximately 2% of patients.
Perhaps the most exciting new development for Parkinson’s patients is surgical intervention in a new area of the brain called the subthalamic nucleus (STN). Recent studies in animal models of Parkinson’s and in patients with Parkinson’s have demonstrated that in Parkinson’s disease, the STN is hyperactive. Lesioning the STN, or subthalamotomy, carries a high risk of inducing abnormal movements known as hemiballismus. However, the reversible and adjustable features of DBS have permitted its use in the STN. Electrical stimulation can block the hyperactivity of the STN, and ameliorate many of the symptoms of Parkinson’s including rigidity, bradykinesia, postural instability, drug-induced dyskinesias, as well as tremor. The use of STN stimulation for Parkinson’s disease was developed in France and subsequently utilized in other centers in Europe and Canada.
High frequency electrical stimulation is believed to "jam" the signals, normal or abnormal, emanating from a brain site. Stimulation therefore has the same outward effect of a lesion but, unlike a permanent lesion, the effect is reversible. Turn the stimulator off and within minutes to days, the structure begins to function as it had prior to stimulation. Thus, if stimulation yields an unwanted side effect, the stimulator may be turned off or repositioned. With lesioning procedures, what's done is done.
DBS also allows stimulation parameters to be customized for each patient. The DBS lead, which is stereotactically implanted into the brain, is equipped with 4 electrodes, any of which, alone or in combination, can be used for stimulation. The lead is connected via subcutaneously tunneled wires to an implanted pulse generator (IPG), which is placed beneath the skin of the chest wall like a cardiac pacemaker. This device can be programmed to deliver stimulation of many different characteristics, providing a great deal of therapeutic flexibility. Because the DBS lead is left in place, physicians have on-going access to the site, allowing them to adjust stimulation parameters in response to changes in the patient's illness.
In addition to these features, which provide distinct advantages of DBS as compared to lesioning, DBS also allows surgeons to intervene at targets that simply cannot, or should not be lesioned. Bilateral pallidotomy, for example, carries a 20% or higher risk of speech and swallowing difficulty, even when performed perfectly. As PD is a bilateral disease, patients often have to choose which side, typically their worse side, they wish to be improved by surgery. Moreover, "midline symptoms" such as gait instability and freezing spells, symptoms that are typically the most disabling and medically resistant features of PD, are rarely improved even in those brave souls who do risk having bilateral lesions.
The current indications for the use of STN stimulation are bilateral advanced Parkinson’s disease, which has become severe and disabling despite optimization of medication therapy. This includes patients with increasingly problematic and disabling tremor, rigidity, bradykinesia, gait and postural instability, dyskinesias, as well as on-off motor fluctuations.
The results from centers abroad have been very encouraging and at times dramatic. In these studies using chronic high frequency bilateral STN stimulation, the patients had improvements in the total motor score of 60% with subscore improvements in bradykinesia, rigidity, tremor, gait and postural instability while off medications. Additionally, there was a reduction in dyskinesias of greater than 70% and reduction of dopaminergic drug dose by more than 50%.
These striking benefits of bilateral STN stimulation have prompted a great resurgence of interest in the surgical management of advanced Parkinson’s disease. While the STN stimulation is not currently FDA approved in the US, this procedure can be performed under an institutionally approved investigational protocol. There is such a protocol at the New York University School of Medicine Movement Disorder Program at the Department of Neurology and Neurosurgery where they have begun to perform bilateral Subthalamic nucleus DBS.