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Thalamotomy is also a destructive (ablative) procedure during which a part of the thalamus is destroyed. The thalamus is the area of the brain that helps process information from the senses and transmits it to other parts of the brain. Thalamotomy is most effective for tremors in younger patients and has some benefit for rigidity and peak-dose dyskinesia. The ablation can be unilateral or bilateral. There are two methods used to perform this procedure:

• Stereotactic Electrode Heat Coagulation - Using stereotactic techniques, a specific area of the thalamus is located and an electrode (probe) is inserted. The tip of the electrode is heated which destroys the tissue around it. A positive effect on tremors is seen immediately.

• Gamma Knife Radiosurgery - This is a new method and employs focused radiation. It is used primarily on older patients who cannot tolerate stereotactic surgery. Improvement is usually seen within 1-2 months.

The probe in thalamotomy may damage other major brain centers that are adjacent to the thalamus. Also, thalamotomy can cause worsening gait and speech problems. Patients who exhibit these symptoms prior to surgery are usually excluded from the procedure. Thalamotomy also carries the risk of hemorrhage or stroke.

Deep Brain Stimulation (DBS)

Deep brain stimulation is not a destructive procedure. It does not ablate any tissue. Rather, an electrode is placed in the brain and a battery is inserted into the chest wall with a wire connecting the electrode and the battery. Continuous high-frequency electrical stimulation is delivered to the GPi, the thalamus, or the subthalamic nucleus. High frequency stimulation stops the activity of cells in the target area and helps "reset" the control of movement.

Consideration of which brain structure is targeted for DBS is partially based on the following:

• GPi - for treatment of bradykinesia, tremors and drug induced dyskinesia. Some patients can reduce the dosage of levodopa following this surgery. This surgery is also effective on patients suffering from dystonia.
• Subthalamic nucleus - improves most motor features of Parkinson's disease, namely bradykinesia, tremor and rigidity. Some patients can reduce the dosage of levodopa. This is performed primarily on patient with advanced and disabling Parkinson's disease
• Thalamus - reduces disabling tremor when it is stronger on one side of the body than the other. This procedure is reported to significantly reduce tremor in approximately 2/3 of the patients undergoing the surgery.

Stimulation of the GPi and the subthalamic nucleus are performed primarily for restoration of movement.

The FDA has approved bilateral DBS of the GPi and subthalamic nucleus. A patient who already has undergone pallidotomy or thalamotomy is still considered eligible for DBS.

Possible complications include an electrode or wire leading to the battery becoming infected, or excessive bleeding may occur if a blood vessel is penetrated. Stroke is also recognized as a risk factor of DBS. Hemorrhage or stroke occurs in approximately 1-3% of patients who undergo this surgical procedure.

The advantages of DBS over pallidotomy or thalamotomy include:

• Brain tissue is not destroyed and can be continuously treated or the current can be turned off if necessary