Título del libro: Epilepsy: Mechanisms, Models, And Translational Perspectives
Título del capítulo: Deep brain stimulation for epilepsy
FRANCISCO JESUS VELASCO CAMPOS; JOSE DAMIAN CARRILLO RUIZ; FIACRO JIMENEZ PONCE;
Autores externos:
Idioma:
Inglés
Año de publicación:
2010
Resumen:
Electrical stimulation of central nervous system structures for the treatment of chronic neurologic disorders started over 40 years ago (Velasco, 2000). Electric current is delivered through electrodes placed in specific areas and generated by internalized pulse generators (IPGs), powered by high-performance batteries and connected to electrodes by extension cables. There are two types of electrodes. One consists of 4 to 12 rounded or square platinum contacts and wires embedded in a plate of silicon used for cortical, cerebellar, and spinal cord stimulation. The other type is tetrapolar; 1.5-mm-length individual platinum rings mounted on silicon tubing and separated from each other by a distance of 0.5 to 1.5 mm. This type of electrode is stereotactically implanted into deep brain structures, and the process is referred to as deep brain stimulation (DBS). IPGs are usually implanted in a subcutaneous subclavicular or abdominal, surgically created pouch, and an extension cable is passed from this place through a subcutaneous tunnel to meet the proximal (or extracranial) end of the electrode. IPGs are programmed through an external device that uses radiofrequency to read and adjust an IPG program. Pulse frequency (Hz), amplitude (V or mA), and duration (µs) are readily adjusted within a range approved for safety. The possibility of using several combinations of contacts acting as cathodes or anodes in bipolar stimulation or cathodes in monopolar stimulation provides the clinician with multiple options of extending or restricting the stimulated area to optimize the effect on individual cases. Stimulation can be continuous or cycling. Cycling may be set to deliver current for fixed periods of time, or the patient can use a programmer to turn the current on or off as needed. Correct placement of electrodes is essential for successful treatment and to avoid undesirable side effects; therefore, implanting electrodes has become a multidisciplinary procedure where neurosurgeons share responsibilities with imaging specialists, neurophysiologists, neurologists, and biomedical engineers. The use of stereotaxis coupled with neuronavigation systems, where virtual trajectories for electrodes designed on the basis of magnetic resonance imaging (MRI) fusion, computed tomography (CT), functional MRI (fMRI), and stereotactic atlases of human brain, increases the precision and safety of surgical procedures. Transoperative confirmation of the correct placement using evoked responses, microelectrode recording, and deep brain stimulation mapping is used routinely in stereotactic procedures. Sometimes, a therapeutic trial of stimulation with temporarily externalized electrodes is necessary before deciding on internalization of the stimulation system. Of course, imaging confirmation of electrode location is also imperative and nowadays is often carried out with intraoperative MRI facilities. Although the mechanisms of action of electrical stimulation are still far from being fully understood, certain procedures have been adopted that have proven to work consistently. For example, low-frequency stimulation is performed to enhance the neuronal or fiber activity of stimulated structures, whereas high-frequency stimulation often mimics the effects of lesions of stimulated targets. This lesion-like effect is reversible, as it tends to disappear when stimulators are turned off. Recently, this dual effect of electric current on neurologic symptoms, related to the frequency of the delivered current, has been demonstrated for tremor amplitude (Birdno and Grill, 2008). Because electric current may enhance or inhibit neural activity depending on the parameters of stimulation and the stimulated site, there is a tendency to refer to the technique as neuromodulation, because stimulation may mistakenly be considered to be equivalent to excitation. © 2010 by Taylor and Francis Group, LLC.
Entidades citadas de la UNAM:
ISBN:
9781420085600
Editorial:
CRC Press Nombre de la publicación:
Deep brain stimulation for epilepsy
Página inicial:
345
Página final:
360
