Selective Activation of the Spinal Cord with Epidural Electrical Stimulation.

Spinal cord epidural electrical stimulation (EES) has been successfully employed to treat chronic pain and to restore lost functions after spinal cord injury. Yet, the efficacy of this approach is largely challenged by the suboptimal spatial distribution of the electrode contacts across anatomical targets, limiting the spatial selectivity of stimulation. In this study, we exploited different ESS paradigms, designed as either Spatial-Selective Stimulation (SSES) or Orientation-Selective Epidural Stimulation (OSES), and compared them to Conventional Monopolar Epidural Stimulation (CMES). SSES, OSES, and CMES were delivered with a 3- or 4-contact electrode array. Amplitudes and latencies of the Spinally Evoked Motor Potentials (SEMPs) were evaluated with different EES modalities. The results demonstrate that the amplitudes of SEMPs in hindlimb muscles depend on the orientation of the electrical field and vary between stimulation modalities. These findings show that the electric field applied with SSES or OSES provides more selective control of amplitudes of the SEMPs as compared to CMES. We demonstrate that spinal cord epidural stimulation applied with SSES or OSES paradigms in the rodent model could be tailored to the functional spinal cord neuroanatomy and can be tuned to specific target fibers and their orientation, optimizing the effect of neuromodulation.

Los potenciales pre-motores y el libre albedrío / Pre-motor potentials and free wil

En este trabajo se analizan las experiencias de Libet acerca de los potenciales motores "espontáneos", o potenciales pre-motores, y su relación con la noción filosófica de "libre albedrío". Libet no deduce de sus experiencias la inexistencia del libre albedrío, sino que afirma que éste puede ejercerse por intermedio del "veto" consciente de una acción intentada. Postula la existencia de un "campo mental consciente" que no puede ser estudiado por medios físicos. El planteamiento antropológico del problema continúa siendo el mismo de la época de Aristóteles, porque se trata de un planteo filosófico, y no de ciencia natural. En cuanto al libre albedrío y a su relación con el cuerpo, continuamos inmersos en el misterio. El libre albedrío no es "localizable", ni en la epifisis, como pensaba Descartes, ni en la corteza pre-motora, según las experiencias de Libet. Pero podemos coincidir con el filósofo Jaime Balmes cuando dice que "El sentido íntimo nos asegura que somos libres. El argumento que se funda en el testimonio del sentido íntimo es tan concluyente que no necesita para nada del auxilio de otro". Se trata del testimonio del sentido común, de la evidencia inmediata.

This paper analyzes Libet's studies on the "spontaneus" motor potentials, or pre-motor potentials, and their relationship with the philosophic concept of "free will". Libet does not conclude from his studies that free will does not exist. Rather, he affirms that it may be exercised through the conscious "veto" of an intended act. He posits the existence of a "conscious mental field" that cannot be studied trough physical study methods. The ongoing anthropological issue is -as was true in Aristotle's day- a philosophical issue, not an issue of the natural sciences. And the issue of freewill and its relationship with the body continues to be a mystery. Free will is not to be found in the epiphysis, as postulated by Descartes, not in the pre-motor cortex, as per the studies of Libet. But we can agree with Balmes, the philosopher, who states that "The intimate sense assures us that we are free. The reasoning that is based on the testimony of the intimate sense is so conclusive that it needs no other assistance". This is the testimony of common sense, of the readily available evidence.

Vigilancia neurofisiológica transoperatoria multimodal en cirugía de columna / Neurophysiological monitoring in spinal cord surgery

Introducción: La vigilancia neurofisiológica durante la cirugía de columna vertebral y de la médula espinal consiste en pruebas de potenciales evocados somatosensoriales, potenciales motores musculares, potenciales dermatomales y electromiografía. El riesgo de daño neurológico permanente después de una cirugía medular sin monitorización es significativo y el costo alto. El objetivo de la vigilancia neurofisiológica es identificar, prevenir y corregir de forma inmediata el daño neurológico que puede pasar inadvertido durante la cirugía de columna vertebral y médula espinal. Material y métodos: Estudio transversal, observacional y descriptivo de los pacientes sometidos a cirugía de columna entre 2007 y 2008 con vigilancia neurofisiológica transoperatoria. Resultados: La muestra estuvo integrada por 351 pacientes, 135 del sexo masculino (38.46 %) y 216 del femenino (61.54 %); 82 % correspondió a patología osteodiscal con o sin afectación medular, 12 % a etiología traumática, 4 % a corrección de escoliosis y 2 % a tumores medulares; por localización, 62.1 % a patología lumbar, 33 % a cervical, 4.3 % a nivel dorsal y 0.5 % a nivel sacro. El 12.4 % de los pacientes presentó mejoría de la respuesta basal de sus potenciales evocados somatosensoriales; 56.8 % los mantuvo similares a sus controles prequirúrgicos, 28.4 % requirió llamada de alerta al cirujano por riesgo de daño y 2.4 % caída severa de respuesta. En ningún caso hubo pérdida permanente. Conclusiones: La vigilancia neurofisiológica constituye una herramienta de gran valor que evita daños que pueden producirse durante esta cirugía.

BACKGROUND: Intraoperative neurophysiological monitoring (IOM) during spine surgery consists of several functional tests including somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), dermatomal potentials (DPs) and EMG (electromyography). Permanent neurological damage after spine surgery performed without intraoperative neurophysiological monitoring is frequent and often very costly. The main goal of IOM is the immediate detection, prevention and correction of neurological damage during surgery, which may go unnoticed without using these tests. METHODS: A total of 351 clinical files of patients with spinal surgery and continuous neurophysiological monitoring were transversally and descriptively reviewed from 2007 to 2008. RESULTS: There were 135 male patients (38.46%) and 216 female patients (61.54%); 82% of the cases were osteodiscal pathology with or without medullar involvement, 12% were patients with traumatic injuries, 4% with scoliosis and 2% had medullary tumors. Regarding localization, 62.1% were lumbar, 33% cervical, 4.3% thoracic and 0.5% sacral involvement; 12.4% of our cases showed significant improvement of the basal responses on SSEPs, and 56.8% showed no significant change during the procedure. In 28.4% of the cases, the surgical team had to be advised of potential neurological damage and in 2.4% there was absence of neurophysiological responses. No patient showed complete loss of any neurophysiological response. All patients reported clinical improvement after hospital discharge. CONCLUSIONS: Intraoperative neurophysiological monitoring may help avoid certain neurological risks during spine surgery, which may go unnoticed without the use of this technique.