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Nicolas Kon Kam King, Vibhor Krishna, Diellor Basha, Gavin Elias, Francesco Sammartino, Mojgan Hodaie, Andres M. Lozano and William D. Hutchison

motor cortex (primary motor and premotor cortex) is confirmed. The reproducibility and clinical application of this methodology was described previously. In this paper we analyzed the electrophysiological findings relative to T-VIM imaging, within the same patient cohort, to correlate the 2 methods of target localization and further evaluate the merit of imaging findings. The VIM has a distinct electrophysiological signature in humans. 20 Microelectrode recording (MER) studies have shown that VIM neurons fire within a frequency range of 10 to 15 Hz, 31 exhibit

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Ravikant S. Palur, Caglar Berk, Michael Schulzer and Christopher R. Honey

different methods of target localization and lesioning. Individual methods are often advanced as being superior without any supporting evidence. Perhaps the most polarizing argument is whether the procedure should be performed using microelectrode recording. No prospective randomized trial has been conducted that might answer this question. In an attempt to bring evidence-based medicine to this often dogmatic field, we performed a metaanalysis of data in reports of pallidotomy that were published between 1992 and 2000 to assess whether there was a statistically

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Helena Karlberg Hippard, Mehernoor Watcha, Amber J. Stocco and Daniel Curry

the stimulating electrode into the GPi. The neurophysiologist uses variations in spontaneous firing rates from single-unit microelectrode recordings (MERs) to identify the location of the electrode tip. Finally, macrostimulation permits confirmation of accurate placement of the permanent electrode and observation of any clinical improvements or side effects. 11 Unfortunately, many anesthetic drugs can affect neuronal firing frequency, resulting in the inability to use MERs to guide electrode placement. 16 Because the brain is free from pain fibers, the electrode

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Christopher S. Lozano, Manish Ranjan, Alexandre Boutet, David S. Xu, Walter Kucharczyk, Alfonso Fasano and Andres M. Lozano

S ubthalamic nucleus (STN) deep brain stimulation (DBS) surgery is commonly used to treat Parkinson’s disease (PD) throughout the world. With the passage of time, there have been a number of innovations in surgical technique. These include a shift away from electrophysiological confirmation of the STN target with microelectrode recordings (MERs) and a trend toward surgery with the patient awake or asleep, relying solely on MRI of the target for electrode placement in some centers. 2 , 3 , 6 , 8 The relative merits and limitations of the imaging-only methods are

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Patrick B. Senatus, David Teeple, Shearwood McClelland III, Seth L. Pullman, Qiping Yu, Blair Ford, Guy M. McKhann II and Robert R. Goodman

Object

Implantation of a subthalamic nucleus (STN) deep brain stimulation (DBS) electrode is increasingly recognized as an effective treatment for advanced Parkinson disease (PD). Despite widespread use of microelectrode recording (MER) to delineate the boundaries of the STN prior to stimulator implantation, it remains unclear to what extent MER improves the clinical efficacy of this procedure. In this report, the authors analyze a series of patients who were treated at one surgical center to determine to what degree final electrode placement was altered, based on readings obtained with MER, from the calculated anatomical target.

Methods

Subthalamic DBS devices were placed bilaterally in nine patients with advanced PD. Frame-based volumetric magnetic resonance images were acquired and then transferred to a stereotactic workstation to determine the anterior and posterior commissure coordinates and plane. The initial anatomical target was 4 mm anterior, 4 mm deep, and 12 mm lateral to the midcommissural point. The MERs defined the STN boundaries along one or more parallel tracks, refining the final electrode placement by comparison of results with illustrations in a stereotactic atlas.

In eight of 18 electrodes, the MER results did not prompt an alteration in the anatomically derived target. In another eight placements, MER altered the target by less than 1 mm and two of 18 electrode positions differed by less than 2 mm. The anterior–posterior difference was 0.53 ± 0.65 mm, whereas the medial–lateral direction differed by 0.25 ± 0.43 mm. The ventral boundary of the STN defined by MER was 2 ± 0.72 mm below the calculated target (all values are the means ± standard deviation). All patients attained clinical improvement, similar to previous reports.

Conclusions

In this series of patients, microelectrode mapping of the STN altered the anatomically based target only slightly. Because it is not clear whether such minor adjustments improve clinical efficacy, a prospective clinical comparison of MER-refined and anatomical targeting may be warranted.

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Shearwood McClelland III, Brian Kim, Linda M. Winfield, Blair Ford, Tresha A. Edwards, Seth L. Pullman, Qiping Yu, Guy M. McKhann II and Robert R. Goodman

Object

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become a popular treatment for patients with medically refractory Parkinson disease. Many surgeons believe that microelectrode recording (MER) during DBS electrode implantation is needed to optimize placement, whereas stimulation-induced side effects such as paresthesias, dystonic contractions, dyskinesias, and ocular motor signs that become apparent postoperatively may be an indicator of the proximity of the electrode to various boundaries of the STN. This study was performed to evaluate the relationship between mapping of the STN by using MER and postoperative stimulation-induced side effects.

Methods

Eighty-two electrodes implanted in 75 patients between March 1999 and March 2003 were retrospectively examined to evaluate the length of the STN defined by MER, and the number of and threshold for postoperative stimulation-induced side effects. Electrodes were typically tested with increasing stimulation amplitudes (maximum 6 V) by using a monopolar array.

The 82 electrodes were associated with 97 stimulation-induced side effects. The mean time between surgery and testing stimulation-induced side effects was 3.9 months. Statistical analysis (two-tailed t-test) revealed no significant difference in the number of stimulation-induced side effects (or the mean threshold for paresthesias, the most common side effect) for electrodes associated with an STN length less than 4.5 mm (13 electrodes) compared with those associated with an STN greater than or equal to 4.5 mm (69 electrodes, p = 0.616). For every electrode, the target adjustment based on MER results was within 2 mm of the image-planned target (usually 1 mm anterior). In the x axis (medial–lateral orientation), there was no systematic difference in adjustments made for the electrodes associated with the shorter compared with the longer STN lengths. In the y axis (anterior–posterior orientation), there was a very small statistically significant difference in the mean adjustment (0.4 mm) between the two groups.

Conclusions

Analysis of these results suggests that a shorter MER-determined STN length alone does not reliably predict the incidence of stimulation-induced side effects.

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Matthew A. Howard III, Igor O. Volkov, Mark A. Granner, Hanna M. Damasio, Michael C. Ollendieck and Hans E. Bakken

Human Subject Institutional Review Boards. Flexible Shaft HDE Each HDE (Radionics, Inc., Burlington, MA) has three low-impedance clinical EEG contacts, as well as multiple bipolar and tripolar microelectrode recording sites ( Fig. 1 ). The shaft is constructed of flexible, tecoflex-poly-urethane (1.25 mm outer diameter) through which tefloncoated platinum—iridium high-impedance electrode wires run (50 µm cross-section diameter, 15 Mohm DC resistance). A thin removable stainless steel stylet is used during electrode placement. The flexible HDE has been used for

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Shang-Yih Yan, Chia-Lin Tsai and Dueng-Yuan Hueng

T o T he E ditor : We are highly interested in the clinical article by Burchiel et al. 3 (Burchiel KJ, McCartney S, Lee A, et al: Accuracy of deep brain stimulation electrode placement using intraoperative computed tomography without microelectrode recording. Clinical article. J Neurosurg 119: 301–306, August 2013). The use of deep brain stimulation (DBS) is well established in functional neurosurgery for the treatment of Parkinson disease (PD), dystonia, and essential tremor. 1–4 Burchiel et al. 3 investigated the accuracy of DBS electrode

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Erwin B. Montgomery Jr.

T o T he E ditor : With regard to optimal targeting for deep brain stimulation (DBS) and the use of microelectrode recordings (MERs), Burchiel et al. 1 (Burchiel KJ, McCartney S, Lee A, et al: Accuracy of deep brain stimulation electrode placement using intraoperative computed tomography without microelectrode recording. Clinical article. J Neurosurg 119: 301–306, August 2013) and numerous other authors 3 have made important contributions to the debate, but unfortunately have made serious logical errors. First, with respect to the repeated use of the

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Sheng-Tzung Tsai, Hsiang-Yi Hung, Chien-Hui Lee and Shin-Yuan Chen

T o T he E ditor : We read with interest the recent publication by Burchiel et al. 1 (Burchiel KJ, McCartney S, Lee A, et al: Accuracy of deep brain stimulation electrode placement using intraoperative computed tomography without microelectrode recording. Clinical article. J Neurosurg 119: 301–306, August 2013). The authors suggest that performing subthalamic nucleus (STN) deep brain stimulation (DBS) with intraoperative CT and the NexFrame system (Medtronic, Inc.) can achieve a high level of accuracy (mean vector error 1.59 mm, trajectory deviation 1