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Intraoperative neuromonitoring encompasses a variety of different modalities in which different neuropathways are monitored either continuously or at defined time points throughout a neurosurgical procedure. Surgical morbidity can be mitigated with careful patient selection and thoughtful implementation of the appropriate neuromonitoring modalities through the identification of eloquent areas or early detection of iatrogenic pathway disruption. Modalities covered in this article include somatosensory and motor evoked potentials, electromyography, electroencephalography, brainstem auditory evoked responses, and direct cortical stimulation., (Copyright © 2022 Elsevier Inc. All rights reserved.)

During stereotactic procedures for treating medically refractory movement disorders, intraoperative neurophysiology shifts its focus from simply monitoring the effects of surgery to an integral part of the surgical procedure. The small size, poor visualization, and physiologic nature of these deep brain targets compel the surgeon to rely on some form of physiologic for confirmation of proper anatomic targeting. Even given the newer reliance on imaging and asleep deep brain stimulator electrode placement, it is still a physiologic target and thus some form of intraoperative physiology is necessary. This chapter reviews the neurophysiologic monitoring method of microelectrode recording that is commonly employed during these neurosurgical procedures today., (Copyright © 2022 Elsevier B.V. All rights reserved.)

While intra-operative neuro-physiologic assessment and monitoring improve the safety of patients, its use may also introduce new risks of injuries. This chapter looks at the electric safety of equipment and the potential hazards during the set-up of the monitoring. The physical and functional physiologic effects of electric shocks and stimulation currents, standards for safety limits, and conditions for tissue damage are described from basic physical principles. Considered are the electrode-tissue interface in relation to electrode dimensions and stimulation parameters as applied in various modalities of evoked sensory and motor potentials as to-date used in intra-operative monitoring, mapping of neuro-physiologic functions. A background is given on circumstances for electric tissue heating and heat drainage, thermal toxicity, protection against thermal injuries and side effects of unintended activation of neural and cardiac tissues, adverse effects of physiologic amplifiers from transcranial stimulation (TES) and excitotoxicity of direct cortical stimulation. Addressed are safety issues of TES and measures for prevention. Safety issues include bite and movement-induced injuries, seizures, and after discharges, interaction with implanted devices as cardiac pacemaker and deep brain stimulators. Further discussed are safety issues of equipment leakage currents, protection against electric shocks, and maintenance., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Introduction: Up to 27% of individuals undergoing subthalamic nucleus deep brain stimulation (STN-DBS) have a genetic form of Parkinson's disease (PD). G lucocerebrosidase ( GBA ) mutation carriers, compared to sporadic PD, present with a more aggressive disease, less asymmetry, and fare worse on cognitive outcomes with STN-DBS. Evaluating STN intra-operative local field potentials provide the opportunity to assess and compare symmetry between GBA and non- GBA mutation carriers with PD; thus, providing insight into genotype and STN physiology, and eligibility for and programming of STN-DBS. The purpose of this pilot study was to test differences in left and right STN resting state beta power in non- GBA and GBA mutation carriers with PD. Materials and Methods: STN (left and right) resting state local field potentials were recorded intraoperatively from 4 GBA and 5 non- GBA patients with PD while off medication. Peak beta power expressed as a ratio to total beta power (peak beta ratio) was compared between STN hemispheres and groups while co-varying for age, age of disease onset, and disease severity. Results: Peak beta ratio was significantly different between the left and the right STN for the GBA group ( p < 0.01) but not the non- GBA group ( p = 0.56) after co-varying for age, age of disease onset, and disease severity. Discussion: Peak beta ratio in GBA mutation carriers was more asymmetric compared with non-mutation carriers and this corresponded with the degree of clinical asymmetry as measured by rating scales. This finding suggests that GBA mutation carriers have a physiologic signature that is distinct from that found in sporadic PD., Competing Interests: FD and MM received grant support from NIH. JS receives consulting fees from Medtronic. SS received grant support from NIH, Medtronic, Abbott, and Boston Scientific. LV has research support from Michael J. Fox Foundation, Medtronic, Inc., US WorldMeds LLC, Pfizer Inc, Boston Scientific, Avanir Pharmaceuticals, Inc., and Adamas Pharmaceuticals, Inc.; is on the scientific advisory board of Britannia Pharmaceuticals Ltd.; and consults for Medtronic, Inc., and Boston Scientific. DC received grant support from NIH and Michael J. Fox and receives lecture and reviewer fees from NIH. GP received grant support from NIH and the Parkinson's Disease Foundation. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 David, Munoz, Shils, Pauciulo, Hale, Nichols, Afshari, Sani, Verhagen Metman, Corcos and Pal.)

The American Society of Neurophysiological Monitoring (ASNM) was founded in 1989 as the American Society of Evoked Potential Monitoring. From the beginning, the Society has been made up of physicians, doctoral degree holders, Technologists, and all those interested in furthering the profession. The Society changed its name to the ASNM and held its first Annual Meeting in 1990. It remains the largest worldwide organization dedicated solely to the scientifically-based advancement of intraoperative neurophysiology. The primary goal of the ASNM is to assure the quality of patient care during procedures monitoring the nervous system. This goal is accomplished primarily through programs in education, advocacy of basic and clinical research, and publication of guidelines, among other endeavors. The ASNM is committed to the development of medically sound and clinically relevant guidelines for the performance of intraoperative neurophysiology. Guidelines are formulated based on exhaustive literature review, recruitment of expert opinion, and broad consensus among ASNM membership. Input is likewise sought from sister societies and related constituencies. Adherence to a literature-based, formalized process characterizes the construction of all ASNM guidelines. The guidelines covering the Professional Practice of intraoperative neurophysiological monitoring were initially published January 24th, 2013, and subsequently that document has undergone review and revision to accommodate broad inter- and intra-societal feedback. This current version of the ASNM Professional Practice Guideline was fully approved for publication according to ASNM bylaws on February 22nd, 2018, and thus overwrites and supersedes the initial guideline.

Connectomes abound, but few for the human spinal cord. Using anatomical data in the literature, we constructed a draft connectivity map of the human spinal cord connectome, providing a template for the many calibrations of specialized behavior to be overlaid on it and the basis for an initial computational model. A thorough literature review gleaned cell types, connectivity, and connection strength indications. Where human data were not available, we selected species that have been studied. Cadaveric spinal cord measurements, cross-sectional histology images, and cytoarchitectural data regarding cell size and density served as the starting point for estimating numbers of neurons. Simulations were run using neural circuitry simulation software. The model contains the neural circuitry in all ten Rexed laminae with intralaminar, interlaminar, and intersegmental connections, as well as ascending and descending brain connections and estimated neuron counts for various cell types in every lamina of all 31 segments. We noted the presence of highly interconnected complex networks exhibiting several orders of recurrence. The model was used to perform a detailed study of spinal cord stimulation for analgesia. This model is a starting point for workers to develop and test hypotheses across an array of biomedical applications focused on the spinal cord. Each such model requires additional calibrations to constrain its output to verifiable predictions. Future work will include simulating additional segments and expanding the research uses of the model.

Spinal cord stimulation (SCS) is a common therapeutic technique for treating medically refractory neuropathic back and other limb pain syndromes. SCS has historically been performed using a sedative anesthetic technique where the patient is awakened at various times during a surgical procedure to evaluate the location of the stimulator lead. This technique has potential complications, and thus other methods that allow the use of a general anesthetic have been developed. There are two primary methods for placing leads under general anesthesia, based on 1) compound muscle action potentials and 2) collisions between somatosensory evoked potentials. Both techniques are discussed, and the literature on SCS lead placement under general anesthesia using intraoperative neurophysiological mapping is comprehensively reviewed., Competing Interests: The authors have no financial conflicts of interest., (Copyright © 2018 Korean Neurological Association.)

Background: Deep brain stimulation (DBS) has effects on axons that originate and terminate outside the DBS target area., Objective: We hypothesized that DBS generates action potentials (APs) in both directions in "axons of passage," altering their information content and that of all downstream cells and circuits, and sought to quantify the change in fiber information content., Methods: We incorporated DBS parameters (fiber firing frequency and refractory time, and AP initiation location along the fiber and propagation velocity) in a filtering function determining the AP frequency reaching the postsynaptic cell. Using neural circuitry simulation software, we investigated the ability of the filtering function to predict the firing frequency of APs reaching neurons targeted by axons of passage. We calculated their entropy with and without DBS, and with the electrode applied at various distances from the cell body., Results: The predictability of the filtering function exceeded 98%. Entropy calculations showed that the entropy ratio "without DBS" to "with DBS" was always >1.0, thus DBS reduces fiber entropy., Conclusions: (1) The results imply that DBS effects are due to entropy reduction within fibers, i.e., a reduction in their information. (2) Where fibers of passage do not terminate in target regions, DBS may have side effects on nontargeted circuitry., (© 2018 S. Karger AG, Basel.)

Objective: Spinal cord stimulation (SCS) treats neuropathic pain through retrograde stimulation of dorsal column axons and their inhibitory effects on wide dynamic range (WDR) neurons. Typical SCS uses frequencies from 50-100 Hz. Newer stimulation paradigms use high-frequency stimulation (HFS) up to 10 kHz and produce pain relief but without paresthesia. Our hypothesis is that HFS preferentially blocks larger diameter axons (12-15 µm) based on dynamics of ion channel gates and the electric potential gradient seen along the axon, resulting in inhibition of WDR cells without paresthesia., Methods: We input field potential values from a finite element model of SCS into an active axon model with ion channel subcomponents for fiber diameters 1-20 µm and simulated dynamics on a 0.001 msec time scale., Results: Assuming some degree of wave rectification seen at the axon, action potential (AP) blockade occurs as hypothesized, preferentially in larger over smaller diameters with blockade in most medium and large diameters occurring between 4.5 and 10 kHz. Simulations show both ion channel gate and virtual anode dynamics are necessary., Conclusion: At clinical HFS frequencies and pulse widths, HFS preferentially blocks larger-diameter fibers and concomitantly recruits medium and smaller fibers. These effects are a result of interaction between ion gate dynamics and the "activating function" (AF) deriving from current distribution over the axon. The larger fibers that cause paresthesia in low-frequency simulation are blocked, while medium and smaller fibers are recruited, leading to paresthesia-free neuropathic pain relief by inhibiting WDR cells., (© 2016 International Neuromodulation Society.)

Objective: Stimulation of axons within the dorsal columns of the human spinal cord has become a widely used therapy to treat refractory neuropathic pain. The mechanisms have yet to be fully elucidated and may even be contrary to standard "gate control theory." Our hypothesis is that a computational model provides a plausible description of the mechanism by which dorsal column stimulation (DCS) inhibits wide dynamic range (WDR) cell output in a neuropathic model but not in a nociceptive pain model., Materials and Methods: We created a computational model of the human spinal cord involving approximately 360,000 individual neurons and dendritic processing of some 60 million synapses--the most elaborate dynamic computational model of the human spinal cord to date. Neuropathic and nociceptive "pain" signals were created by activating topographically isolated regions of excitatory interneurons and high-threshold nociceptive fiber inputs, driving analogous regions of WDR neurons. Dorsal column fiber activity was then added at clinically relevant levels (e.g., Aβ firing rate between 0 and 110 Hz by using a 210-μsec pulse width, 50-150 Hz frequency, at 1-3 V amplitude)., Results: Analysis of the nociceptive pain, neuropathic pain, and modulated circuits shows that, in contradiction to gate control theory, 1) nociceptive and neuropathic pain signaling must be distinct, and 2) DCS neuromodulation predominantly affects the neuropathic signal only, inhibiting centrally sensitized pathological neuron groups and ultimately the WDR pain transmission cells., Conclusion: We offer a different set of necessary premises than gate control theory to explain neuropathic pain inhibition and the relative lack of nociceptive pain inhibition by using retrograde DCS. Hypotheses regarding not only the pain relief mechanisms of DCS were made but also regarding the circuitry of pain itself, both nociceptive and neuropathic. These hypotheses and further use of the model may lead to novel stimulation paradigms., (© 2014 International Neuromodulation Society.)

Objective: The purpose of this study was to examine how scar formation may affect electrical current distribution in the spinal cord when using paddle leads placed in the epidural space during treatment with spinal cord stimulation., Materials and Methods: A finite element model of the spinal cord was used to examine changes in stimulation using a guarded cathode configuration with and without scar. Additionally, two potential "compensatory" programming patterns were examined in order to understand how the three-dimensional electrical field may be affected by scar. Direct comparisons with prior studies in the literature and use of known anatomy of dorsal column fiber distributions also enabled a computational estimate of the number of fibers likely reaching threshold with each stimulus pattern., Results: Notable potential and current distribution changes were found related to the modeled scar. Compensatory stimulation patterns (both in spatial and in amplitude dimensions) affect the fiber activation patterns in complex ways that may not be easily predetermined by a programming specialist., Conclusions: This study is one of the first to examine the effects of scar tissue on dorsal column stimulation and the only one using a detailed computational approach toward that end. It appears that different thickness and location of scar between electrode contacts and the dura may likely lead to a significant number and location of complex changes in the activated fibers. It is likely that a more complete assessment of scarring and its effect on the electrical environment of any given paddle lead would allow more accurate and predictable reprogramming of patients with commercially available systems in place., (© 2013 International Neuromodulation Society.)

Objective: Transcranial electric stimulation elicited muscle motor evoked potentials (TESmMEPs) is one of the best methods for corticospinal tract's function monitoring during spine and spinal cord surgeries. A train of multipulse electric stimulation is required for eliciting TESmMEPs under general anaesthesia. Here, we investigated the best stimulation parameters for eliciting and recording tibialis anterior's TESmMEPs during paediatric scoliosis surgery., Patients and Methods: Numbers of pulses (NOP), inter-stimulus intervals (ISI) and current intensities allowing the best size tibialis anterior muscle's TESmMEPs under general anaesthesia, were tested and collected during 77 paediatric scoliosis surgery monitoring procedures in our hospital. Individual pulse duration was kept at 0.5 ms and stimulating electrodes were positioned at C1 and C2 (International 10-20-EEG-System) during all the tests., Results: The NOP used for eliciting the best tibialis anterior TESmMEPs response was 5, 6, and 7 respectively in 21 (27%), 47 (61%) and 9 (12%) out of the 77 patients. The ISI was 2, 3 and 4 ms respectively in 13 (17%), 55 (71%) and 9 (12%) of them. The current intensity used varied from 300 to 700 V (mean: 448±136 V)., Conclusion: Most patients had 6 as best NOP (61%) and 3 ms as best ISI (71%). These findings support that a NOP of 6 and an ISI of 3 ms should be preferentially used as optimal stimulation settings for intraoperative tibialis anterior muscle's TESmMEPs eliciting and recording during paediatric scoliosis surgery., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Objectives:   To demonstrate that spinal cord stimulators (SCSs) may be placed safely and accurately under general anesthesia (GA) and that the proposed evaluation method activates structures predominantly in the dorsal columns., Materials and Methods:   Data were retrospectively analyzed from 172 electrodes implanted with spinal cord SCSs at the Lahey Clinic between September 2008 and July 2011. All patients had their SCS placed under GA. Electromyography was recorded from upper or lower limb muscle groups related to the placement of the stimulator electrode. Lateralization was performed based on electromyographic responses and electrode pairs stimulated. In a select group of patients, standard neurophysiologic tests, paired pulse, and collision studies were performed to demonstrate that the pain stimuli were activating the dorsal columns., Results:   One hundred fifty-five patients had standard thoracic or cervical SCS placement. Preoperatively this cohort of patients had a visual analog score (VAS) of 7.51 ± 1.93, while postoperatively the VAS was 3.63 ± 2.43 (a reduction of 52.11%). Based on the electromyographic recording technique, the electrodes were repositioned intraoperatively in 15.9% of patients. The recovery time (initial approximately 70 msec and complete approximately 150-300 msec) in both the paired-pulse tests and the collision studies showed that the stimulation used to elicit the compound muscle action potentials came from antidromic activation of the dorsal columns and not from the corticospinal tract., Conclusion:   GA SCS is safe and appears to be at least as accurate and efficacious as using the awake SCS placement technique based on a 50% improvement in the VAS. In addition, the technique presented herein demonstrates that the test stimuli activate the same fiber tracts as that of the therapeutic stimulation., (© 2012 International Neuromodulation Society.)

The use of microelectrodes for both recording and stimulation of cortical tissue is a well-established technique in neuroscience. We demonstrate that the use of existing microelectrode arrays and instrumentation can be extended to studying the spinal cord. We show that microelectrode arrays can be used to perform stimulation and recording in the corticospinal tract of an animal model commonly used in spinal cord injury (SCI) research. This technique could not only provide fundamental insights into the structure and function of the spinal cord, but also ultimately serve as the basis of a therapeutic treatment for severe spinal cord injuries.

Objective: Considerable overlap exists in nerve root innervation of various muscles. Knowledge of myotomal innervation is essential for the interpretation of neurological examination findings and neurosurgical decision-making. Previous studies relied on cadaveric dissections, animal studies, and cases with anomalous anatomy. This study investigates the myotomal innervation patterns of cervical and lumbar nerve roots through in vivo stimulation during surgeries for spinal decompression., Methods: Patients undergoing cervical and lumbar surgeries in which nerve roots were exposed in the normal course of surgery were included in the study. Electromyography electrodes were placed in the muscle groups that are generally accepted to be innervated by the roots under study. These locations included levels above and below the spinal levels undergoing decompression. After decompression, a unipolar neural stimulator probe was placed directly on the nerve root sleeve and constant current stimulation in increments of 0.1 mA was performed. Current was raised until at least a 100 μV amplitude-triggered electromyographic response was noted in 1 or more muscles. All muscles that responded were recorded., Results: A total of 2295 nerve root locations in 129 patients (mean age 57 ± 15 years, 47 female [36%]) were stimulated, and 1589 stimulations met quality criteria and were analyzed. Four hundred ninety-five stimulations were performed on roots contributing to the cervical and brachial plexus from C-3 to T-1 (31.2%), and 1094 (68.8%) were roots in the lumbosacral plexus between L-1 and S-2. The authors were able to construct a statistical map of the contributions of each cervical and lumbosacral nerve root for the set of muscle groups monitored in the protocol. In many cases the range of muscles innervated by a specific root was broader than previously described in textbooks., Conclusions: This is the largest data set of direct intraoperative nerve root stimulations during decompressive surgery, demonstrating the relative contribution of root-level motor input to various muscle groups. Compared with classic neuroanatomy, a significant number of roots innervate a broader range of muscles than expected, which may account for the variability of presentation between patients with identical number and location of compressed roots.

Previous studies examining discrete movements of Parkinson's disease (PD) patients have found that in addition to performing movements that were slower than those of control participants, they exhibit specific deficits in movement coordination and in sensorimotor integration required to accurately guide movements. With medication, movement speed was normalized, but the coordinative aspects of movement were not. This led to the hypothesis that dopaminergic medication more readily compensates for intensive aspects of movement (such as speed), than for coordinative aspects (such as coordination of different limb segments) (Schettino et al., Exp Brain Res 168:186-202, 2006). We tested this hypothesis on rhythmic, continuous movements of the forearm. In our task, target peak speed and amplitude, availability of visual feedback, and medication state (on/off) were varied. We found, consistent with the discrete-movement results, that peak speed (intensive aspect) was normalized by medication, while accuracy, which required coordination of speed and amplitude modulation (coordinative aspect), was not normalized by dopaminergic treatment. However, our findings that amplitude, an intensive aspect of movement, was also not normalized by medication, suggests that a simple pathway gain increase does not act to remediate all intensive aspects of movement to the same extent. While it normalized movement peak speed, it did not normalize movement amplitude. Furthermore, we found that when visual feedback was not available, all participants (PD and controls) made faster movements. The effects of dopaminergic medication and availability of visual feedback on movement speed were additive. The finding that movement speed uniformly increased both in the PD and the control groups suggests that visual feedback may be necessary for calibration of peak speed, otherwise underestimated by the motor control system.

The authors report the cases of 2 young male patients (aged 16 and 26 years) with dystonic cerebral palsy of unknown origin, who developed status dystonicus, an acute and persistent combination of generalized dystonia and chorea. Both patients developed status dystonicus after undergoing general anesthesia, and in 1 case, after administration of metoclopramide. In attempting to control this acute hyperkinetic movement disorder, multiple medication trials failed in both cases and patients required prolonged intubation and sedation with propofol. Bilateral deep brain stimulation of the globus pallidus internus (4 and 2 months after the onset of symptoms in the first and second case, respectively) produced immediate resolution of the hyperkinetic movement disorder in each case. Deep brain stimulation provided persistent suppression of the dystonic movement potential after a follow-up of 30 and 34 months, respectively, as demonstrated by the reemergence of severe dystonia during the end of battery life of the implantable pulse generators that was readily controlled by exchange of the generators in each case.

Object: Since the initial 1991 report by Tsubokawa et al., stimulation of the M1 region of cortex has been used to treat chronic pain conditions and a variety of movement disorders., Methods: A Medline search of the literature published between 1991 and the beginning of 2007 revealed 459 cases in which motor cortex stimulation (MCS) was used. Of these, 72 were related to a movement disorder. More recently, up to 16 patients specifically with Parkinson disease were treated with MCS, and a variety of results were reported. In this report the authors describe 4 patients who were treated with extradural MCS., Results: Although there were benefits seen within the first 6 months in Unified Parkinson's Disease Rating Scale Part III scores (decreased by 60%), tremor was only modestly managed with MCS in this group, and most benefits seen initially were lost by the end of 12 months., Conclusions: Although there have been some positive findings using MCS for Parkinson disease, a larger study may be needed to better determine if it should be pursued as an alternative surgical treatment to DBS.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) for Parkinson's disease (PD) has become routine over the past decade, utilizing microelectrode recordings to ensure accurate placement of the stimulating electrodes. The clinical benefits of STN DBS for PD are well documented, but the mechanisms by which DBS achieves these results remain elusive. We have created a closed-form mathematical function of the potential field generated by a typical 4-contact DBS electrode and inserted this function into a computational model designed to simulate individual neurons and neural circuitry of significant portions of the basal ganglia. We present the mathematical function representing the potential field itself and the basis for the neural circuitry modeling in this paper., ((c) 2007 S. Karger AG, Basel.)

Since initial reports in the early 1990s, stimulation of the M1 region of the cortex (MCS) has been used to treat chronic refractory pain conditions and a variety of movement disorders. A Medline search of literature between 1991 and 2007 revealed 512 cases using MCS. Although most of these relate to the treatment of pain (422), 84 of them involve movement disorders. More recently, several studies have specifically looked at treating Parkinson's disease (PD) with MCS. We report here several of our own cases using MCS to treat poststroke and non-poststroke pain syndromes and movement disorders (n = 8), PD (n = 4), ET (n = 2), and cortico-basal degeneration (n = 1). We also cover the essential history of this procedure and our current research using computational modeling to understand further the underlying mechanisms of MCS.

Treatment with deep brain stimulation (DBS) for Parkinson's disease (PD) has become routine over the past decade, particularly using the subthalamic nucleus (STN) as a target and utilizing microelectrode recordings to ensure accurate placement of the stimulating electrodes. The clinical changes seen with DBS in the STN for PD are consistently beneficial, but there continues to be only marginal understanding of the mechanisms by which DBS achieves these results. Using an analytical model of the typical DBS 4-contact electrode and software developed to simulate individual neurons and neural circuitry of the basal ganglia we compare the results of the model to those of data obtained during DBS surgery of the STN. Firing rate, interspike intervals and regularity analyses were performed on the simulated data and compared to results in the literature., ((c) 2007 S. Karger AG, Basel.)

Intraoperative monitoring (IOM) adds new information to intraoperative surgical decision-making. When presented clearly and accurately, it can help guide decision processes during the procedure, but can be a detriment overall if the information is inaccurate or misleading. Troubleshooting abilities and vigilance of the IOM staff play a large role in bolstering the level of trust a surgeon develops in IOM. Additionally, a surgeon may impart his own interpretation and experience with this new information that can undermine or enhance its impact on the case. In this article, we explore these issues with IOM in general and as they relate to the special context of DBS for movement disorders.

Objective: To evaluate the safety and efficacy of 60 Hz deep brain stimulation (DBS) of the globus pallidus internus (GPi) in 15 consecutive patients with primary dystonia., Methods: We conducted a retrospective analysis of clinic charts relative to 15 consecutive patients with medically refractory primary dystonia who underwent stereotactic implantation of DBS leads within the GPi. Twelve had the DYT1 gene mutation. Frame-based MRI and intraoperative microelectrode recording were employed for targeting. All patients were treated exclusively with stimulation at 60 Hz from therapy outset. The Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS) served as the primary measure of symptom severity at baseline and 1, 3, 6, and 12 months after treatment., Results: All patients tolerated DBS treatment well and showed a progressive median improvement of their BFMDRS motor subscores from 38% at 1 month to 89% at 1 year (p < 0.001, Wilcoxon rank sum test). The disability subscores were similarly improved. The clinical response to DBS allowed seven patients to completely discontinue their medications; six additional patients had reduced their medications by at least 50%. Surgical complications were limited to two superficial infections, which were treated successfully., Conclusions: Stimulation of the internal globus pallidus at 60 Hz is safe and effective for treating medically refractory primary dystonia.

Repositioning of a subthalamic nucleus deep brain stimulation lead alleviated a parkinsonian patient's dyskinesias without the need for parkinsonian medication reduction. After the initial placement and programming, the patient was doing well. During repair of a skin erosion, the lead moved ventral and the patient developed severe dyskinesias and, when the deep brain stimulation system was on, diplopia. Multiple reprogramming attempts did not alleviate these problems. The electrode was moved dorsally by about 6 mm. Intraoperatively the patient's dyskinesias stopped with no diplopia with the stimulator on. Two years after the revision the patient is doing very well.

We report the case of a patient with medically refractory primary dystonia who was treated with bilateral pallidal deep brain stimulation. Stimulation at 130 Hz or higher, by means of the more ventral contacts generated capsular side effects, which made their use impractical. Consequently, the patient was treated for 9 months at 130 to 185 Hz, by means of the more dorsal contacts, achieving modest results. By reducing the stimulation frequency to 80 Hz, we were able to activate the ventral contacts without inducing side effects. Within days, the patient experienced a dramatic improvement in function that has persisted for 1 year. A further reduction in stimulation frequency to 60 Hz resulted in a worsening of his symptoms. We conclude that chronic stimulation at frequencies of <100 Hz may be efficacious in dystonia and may enhance the tolerability of stimulation by means of contacts that are positioned posteroventrally within the internal globus pallidus, nearer the internal capsule.

The authors demonstrate that high-frequency electrical stimulation dorsal to the subthalamic nucleus (STN) can directly suppress levodopa-induced dyskinesias. This 63-year-old woman with idiopathic Parkinson disease underwent surgery for placement of bilateral subthalamic deep brain stimulation (DBS) electrodes to control progressive rigidity, motor fluctuations, and levodopa-induced dyskinesias. The model 3389 DBS leads were implanted with microelectrode guidance. Magnetic resonance imaging confirmed proper placement of the leads. Postoperatively the patient exhibited improvement in all of her parkinsonian symptoms; however, her right leg dyskinesias had not improved. Based on their previous experiences treating levodopa-induced dyskinesias with subthalamic stimulation through the more dorsally located contacts of the model 3387 lead, the authors withdrew the implanted 3389 lead 3 mm. Following relocation of the lead they were able to suppress the right leg dyskinesias by using the most dorsal contacts. The patient's dopaminergic medication intake increased slightly. These findings indicate that electrical stimulation dorsal to the STN can directly suppress levodopa-induced dyskinesias independent of dopaminergic medication changes. The 3389 lead may provide inadequate coverage of the subthalamic region for some patients.

Intraoperative neurophysiologic methods for localizing targets deep in the brain require the use of specialized monitoring and recording equipment, including stimulators, neurophysiologic recording devices, and image manipulation tools. When using microelectrode recording devices there are some specifications that are more important than others, such as signal-to-noise ratios and amplifier impedance. As more companies develop tools to be used in the operating room, the end users have more choices. Some of the more important specifications are discussed and a comparison is made of the five major brands on the market today., (Copyright 2002 S. Karger AG, Basel)

Previous electrophysiological studies have demonstrated interactions between dichoptic visual stimuli presented to the same location in visual space. In this study, we used non-liner spectral analysis, in particular the bispectrum, to study interactions between the electrocerebral activity resulting from stimulation of the left and right visual fields. The stimulus consisted of two squares, one in each visual field, flickering at different frequencies. Bispectra, bichoherence and biphase were calculated for 8 subjects monocularly observing a visual stimulus. Both phase vs. frequency and biphase vs. frequency plots were made to determine weighted time delays from stimulus application to signal appearance in the EEG electrodes. Bispectral analysis reveals non-liner interactions between visual fields occurring with weighted delay times of 410 + / - 58 msec while non-interactive components propagated with weighted time delays of 202 + / - 39 msec. Evaluating these results in light of the predictions of various models, we were able to conclude that this interaction does not occur in the retina. These results illustrate how bispectral analysis can be a powerful tool in analyzing the connectivity of neural networks in complex systems. It allows different neuronal systems to be labeled with stimuli at specific frequencies, whose connections can be traced using frequency analysis of the scalp EEG.