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of the first human stereotactic atlas by Ernst Spiegel and Henry Wycis in 1947, precise coordinates for subcortical nuclei could be localized. Initially, electrical stimulation of these sites was employed to confirm accurate localization prior to lesions. It was soon realized that the electrical stimulation could also be used as a therapeutic method itself, not only as a neuromodulator, but also to restore normal neuronal activity. Consequently, the evolution from lesional to stimulating functional neurosurgery had occurred. Also, the major safety of DBS led to a gradual abandonment of lesional techniques.

DBS Surgical Procedure The DBS surgical procedure begins with MRI or CT imaging for stereotactic localization of stimulus sites in the thalamus, subthalamic nucleus (STN) or globus pallidus (GP) in the case of Parkinson’s disease (PD). The DBS System consists of electrodes, an extension cord, and an implantable pulse generator (IPG) including battery. The IPG is a programmable digital device the size of a stopwatch used to deliver electrical stimulation. The electrode component is a thin wire insulated along the shaft with some bare exposed wire at the tip for current propagation. The electrode is inserted into a stereotacticallymounted guide tube and lowered to the precise target site. In some instances a bipolar (two adjacent electrodes) stimulation procedure must be employed to restrict current spread. The distribution of the stimulus current field is crucial in controlling neuronal activation of minuscule fiber tracts or nuclei. The guide tube is then retracted leaving the electrode to be cemented to the cranium for attachment of the extension cord. In some instances, multiple electrodes are placed in the thalamus, subthalamic nucleus (STN) or the globus pallidus (GP) in the case of Parkinson’s disease (PD). The extension cord is composed of multiple insulated wires that are passed under the scalp, neck and shoulder and connected to the IPG.

The IPG is normally implanted under the skin near the clavicle. Sometimes there may be complications such as bleeding within the brain, brain edema, mild disorientation and sleepiness following surgery. Following implantation, the next step is selecting appropriate stimulation parameters to provide the maximum therapeutic benefit. Finding the optimal voltage, pulse width and frequency is a process of trial and error to assess the clinical benefit. In some instances, computer models have been employed to determine optimal stimulation parameters

September/October 2015

Insertion of electrode during surgery using a stereotactic frame.

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2015-Sep/Oct - SSV Medicine  

Sierra Sacramento Valley Medicine is the official journal of the Sierra Sacramento Valley Medical Society (SSVMS) and promotes the history,...

2015-Sep/Oct - SSV Medicine  

Sierra Sacramento Valley Medicine is the official journal of the Sierra Sacramento Valley Medical Society (SSVMS) and promotes the history,...