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Objective To compare directional monopolar, bipolar, and directional bipolar thalamic deep brain stimulation (DBS) in tremor patients. Methods Fourteen tremor patients (7 Essential Tremor and 7 Parkinson's Disease) implanted with directional DBS electrodes in the ventral intermediate nucleus (VIM) were enrolled. Side-effect thresholds of monopolar directional stimulation (DIRECT) were compared to circular DBS as well as, in a randomized design, to those of two different bipolar stimulation settings (BIPOLAR = circular anode; BI-DIRECT = directional anode). Tremor suppression (Tremor Rating Scale, TRS) right below the side-effect threshold was also assessed. Results Directional DBS in the individually best direction showed higher side-effect thresholds than circular DBS (p = 0.0063). The thresholds were raised further using either one of the bipolar stimulation paradigms (BIPOLAR p = 0.0029, BI-DIRECT p = 0.0022). The side-effect thresholds did not differ between both bipolar settings, but side-effects were less frequent with BI-DIRECT. No difference in TRS scores with stimulation just below the side-effect threshold was found between all stimulation conditions. Conclusions Side-effect thresholds of monopolar directional and bipolar stimulation with both circular and directional anodes were higher compared to traditional monopolar circular stimulation in the VIM. Bipolar DBS with directional anodes evoked side-effect less frequently than bipolar and monopolar directional stimulation. All stimulation settings had comparable effects on tremor suppression just below their side-effect thresholds. Thus, directional and different bipolar settings should be explored in patients with bothersome side-effects of thalamic stimulation when monopolar stimulation settings are not satisfying. Further studies are needed to explore the efficiency of the different bipolar stimulation paradigms.

I read with interest the article by Dionigi et al . “Monitored transoral endoscopic thyroidectomy via long monopolar stimulation probe”, published on Journal of Visualized Surgery (1). The article is very interesting, well written and innovative, introducing the use of neuromonitoring in the new technique of transoral thyroidectomy (1).

International audience; PURPOSE: To assess the validity and utility of monopolar stimulation (between a peridural needle and a large adhesive anode placed in the sternal area) for intraoperative monitoring in scoliosis surgery. METHODS: This procedure was assessed during 41 operations involving either arthrodesis with posterior instrumentation or a Vertical Expandable Prosthetic Titanium Rib (VEPTR). Responses evoked by monopolar stimulation were compared with those evoked by bipolar stimulation between two epidural needle electrodes. Potentials evoked by monopolar stimulation in the upper limbs were compared with those evoked in the lower limbs during the same stimulation procedure. RESULTS: Monopolar stimulation yielded equivalent and, if anything, more stable responses in the lower limbs. Recording in the upper limbs was satisfactory and allowed a decrease in responses to be detected in two patients. Acceptable thresholds for changes in amplitude relative to baseline were 40 % for upper limbs and 30 % for lower limbs. CONCLUSIONS: Monopolar stimulation can be used to monitor the spinal cord during surgery for scoliosis correction. This procedure is more convenient for the surgeon and allows for the combined recording of responses in all four limbs, which can be useful in the case of surgical techniques such as those involving a VEPTR

Detection of a target tone in a simultaneous multi-tone masker can be improved by preceding the stimulus with the masker alone. The mechanisms underlying this auditory enhancement effect may enable the efficient detection of new acoustic events and may help to produce perceptual constancy under varying acoustic conditions. Previous work in cochlear-implant (CI) users has suggested reduced or absent enhancement, due perhaps to poor spatial resolution in the cochlea. This study used a supra-threshold enhancement paradigm that in normal-hearing listeners results in large enhancement effects, exceeding 20 dB. Results from vocoder simulations using normal-hearing listeners showed that near-normal enhancement was observed if the simulated spread of excitation was limited to spectral slopes no shallower than 24 dB/oct. No significant enhancement was observed on average in CI users with their clinical monopolar stimulation strategy. The variability in enhancement between CI users, and between electrodes in a single CI user, could not be explained by the spread of excitation, as estimated from auditory nerve evoked potentials. Enhancement remained small, but did reach statistical significance, under the narrower partial-tripolar stimulation strategy. The results suggest that enhancement may be at least partially restored by improvements in the spatial resolution of current CIs.

This video aimed to describe the role of intraoperative neuromonitoring (IONM) during transoral endoscopic thyroidectomy vestibular approach (TOETVA) with emphasis given to IONM technical and technological notes, the identification of recurrent laryngeal nerve (RLN). Standardized technique of IONM consist in identifying and monitoring both the vagus nerve and the RLNs before and after resection (V1, V2, R1, R2). According to this report, IONM during TOETVA is feasible and safe in providing identification and function of laryngeal nerves. IONM enable surgeons to feel more comfortable with their initial approach to TOETVA or extended indications. Larger series are needed for appropriated evaluation of IONM in reduction of the rates for RLN complications.

OBJECTIVES: Auditory brainstem potentials can be elicited by electrical stimulation of the round window (RW). In this technique, extracochlear stimulation is objectively used in the selection of cochlear implant (CI) candidates to avoid cochlear damage. However, until now, its use is limited due to the large artifacts generated by electrical stimulation. Our objective was to obtain reliable and reproducible electrically evoked auditory brainstem responses (eFARRs) using a new method of stimulation MATERIALS and METHODS: This was a prospective study including subjects who under went electrical stimulation on RW during CI surgery between 2013 and 2016. A "Stimulator Box;" which produces electric stimuli identical to those provided by a CI, and an evoked potential recording equipment were used. The results obtained with monopolar and bipolar electrodes were compared. RESULTS: RW eEABR recordings of 49 subjects (mean age, 34 years) were characterized by their stability and by having wave V between 3 and 5.5 ms. A higher percentage of responses wee obtained on increasing the phase duration instead of the pulse amplitude. A significantly greater percentage of positive responses were obtained using bipolar stimulation than using monopolar stimulation (p

Highlights • Monopolar mapping is effective for cortical and subcortical language areas. • 250–500 Hz stimulation parameters are adequate and safe for speech testing. • It may improve resection rate of infiltrating tumor areas involving the speech area., Objectives To determine whether high-frequency 250–500 Hz monopolar stimulation is effective for mapping cortical and subcortical language structures during brain tumor resection. Methods Using high-frequency monopolar stimulation, we mapped the speech areas of 41 awake patients undergoing brain tumor resection in the dominant hemisphere, subject to risk of lesions in the cortical and subcortical speech tracts. Patients were tested for object naming, semantic and other language tasks. Results Mapping was positive in 22 out of 41 patients. Nine patients presented clinical worsening immediately after surgery. Only one patient did not recover after the 30-day follow-up. Nineteen patients showed negative mapping for language tracts, none of whom exhibited worsening of symptoms at the final evaluation. The applied method showed 89% sensitivity and 56% specificity rates. Conclusions The applied method was effective in identifying cortical and subcortical speech areas during the surgical resection of brain tumors. Significance Determining whether monopolar high-frequency stimulation is effective for language mapping is important, since it may be very effective in infiltrating tumor areas and nearby edema region.

This personal reflection outlines the discoveries at the University of Melbourne leading to the multi-channel cochlear implant, and its development industrially by Cochlear Limited. My earlier experimental electrophysiological research demonstrated temporal coding occurred for only low frequencies, i.e. below 200-500 pulses/second. I was able to confirm these findings perceptually in behaviourally conditioned animals. In addition, these studies showed that temporal discrimination occurred across spatial coding channels. These experimental results correlated with the later conscious experience for electrical stimulation in my implant patients. In addition, the mid-to-high frequencies were coded in part by place of stimulation using bipolar and monopolar stimulation to restrict current spread. Furthermore, place of stimulation had the qualities of sharpness and dullness, and was also experienced as vowels. Owing to the limitation in coding speech with a physiological model due to the overlap of electrical current leading to unpredictable variations in loudness, a speech coding strategy that extracted the most important speech features for transmission through an electro-neural 'bottle-neck' to the brain was explored. Our inaugural strategy, discovered in 1978, extracted the second formant for place of stimulation, voicing for rate of stimulation, and sound pressure for current level. This was the first coding strategy to provide open-set speech understanding, as shown by standard audiological tests, and it became the first clinically successful interface between the world and human consciousness. This strategy was improved with place coding for the third formant or high-frequency spectrum, and then the spectral maxima. In 1989, I operated on our first patient to receive a bilateral implant, and in 1990, the first with a bimodal processor. The psychophysics and speech perception for these showed that the stimuli from each side could be fused into a single image, and localized according to differences in intensity and time of arrival of the stimuli. There were significant improvements for speech perception in noise. In 1985, I implanted our first children with the multi-channel prosthesis and found that speech understanding and spoken language were greatly improved the younger the child at surgery, and especially when younger than 12 months. Speech understanding was strongly related to the development of place coding. In 1990, the US Food and Drug Administration approved the implant for deaf children, the first by any world health regulatory body making it the first major advance in helping deaf children to communicate.

Background and Purpose: The aim of the study was to analyse the lifetime of Soletra implantable pulse generators (IPG) in deep brain stimulation (DBS) of the globus pallidus internus (GPi) for dystonia, depending on stimulation parameters and the total electrical energy delivered (TEED) by the IPG. Methods: In a prospective series of 20 patients with GPi DBS for dystonia, we recorded IPG longevity and stimulation parameters over time. An evaluation of the TEED was performed using the previously suggested equation [(voltage2 × pulse width × frequency)/impedance] × 1 s. Results: During median follow-up of 57 months (range 23–79 months), 64 IPGs were replaced because of battery depletion or end of life signal. We found a mean IPG longevity of 25.1 ± 10.1 (range 16–60) months, which was inversely correlated with the TEED (r = −0.72; P

BACKGROUND Intraoperative identification and preservation of the corticospinal tract is often necessary for glioma resection. OBJECTIVE To make a proposal for intraoperative management with the high-frequency monopolar stimulation technique for monitoring the corticospinal tract. METHODS Ninety-two patients operated on with the assistance of the high-frequency monopolar stimulation. Clinical and neurophysiological data have been related with the motor status at 3 months to establish prognostic factors of motor deterioration. RESULTS Twenty-one patients (22.8%) presented intraoperative alterations in motor-evoked potentials (MEPs). Twelve (13%) presented an increment in the MEP threshold ≥5 mA (no deficit at 3 months). Two (2.2%) presented an MEP amplitude reduction >50% (100% deficit at 3 months). Seven (7.6%) had an intraoperative MEP loss (80% deficit at 3 months). Subcortical stimulation was positive in 75 patients (81.5%). Eighty-five patients were available for the analysis at 3 months. Fourteen presented new deficits (16.5%). Among them, 5 presented a deficit in nonmonitored muscles (5.9%) and 1 presented a new deficit not detected intraoperatively. The combination of patients with preoperative motor deficits, MEP deterioration, or loss and intensity of subcortical stimulation ≤3 mA showed the highest sensitivity and specificity in the prediction of new deficits. CONCLUSIONS Persistent MEP loss or deterioration is associated with a high probability of new deficits. It seems recommendable to stop the subcortical resection before obtaining a subcortical MEP threshold at 3 mA especially in patients with preoperative motor deficits. A careful selection of muscles for the registration of MEPs is mandatory to avoid deficits in nonmonitored muscles.

Neurophysiological studies in animals and humans suggest that severe hearing loss during early development impairs the maturation of the auditory brainstem. To date, studies in humans have mainly focused on the neural activation of the auditory brainstem in children treated with a cochlear implant (CI), but little is known about the pattern of activation in adult CI users with early onset of deafness (prelingual, before the age of 2 years). In this study, we compare auditory brainstem activation in prelingually deaf and late-implanted adult CI users to that in postlingually deaf CI users. Electrically evoked auditory brainstem responses (eABRs) were recorded by monopolar stimulation, separately using a middle and an apical electrode of the CI. Comparison of the eABR latencies revealed that wave V was significantly delayed in the prelingually deaf CI users on both electrode locations. Accordingly, when the apical electrode was stimulated, the III-V interwave interval was significantly longer in the prelingually deaf group. These findings suggest a slower neural conduction in the auditory brainstem, probably caused by impairment of maturation during the long duration of severe hearing loss in infancy. Shorter wave V latencies, reflecting a more mature brainstem, appeared to be a predictor for better speech perception.

Objective Pilot study to evaluate computer-guided deep brain stimulation (DBS) programming designed to optimize stimulation settings using objective motion sensor-based motor assessments. Materials and Methods Seven subjects (five males; 54–71 years) with Parkinson's disease (PD) and recently implanted DBS systems participated in this pilot study. Within two months of lead implantation, the subject returned to the clinic to undergo computer-guided programming and parameter selection. A motion sensor was placed on the index finger of the more affected hand. Software guided a monopolar survey during which monopolar stimulation on each contact was iteratively increased followed by an automated assessment of tremor and bradykinesia. After completing assessments at each setting, a software algorithm determined stimulation settings designed to minimize symptom severities, side effects, and battery usage. Results Optimal DBS settings were chosen based on average severity of motor symptoms measured by the motion sensor. Settings chosen by the software algorithm identified a therapeutic window and improved tremor and bradykinesia by an average of 35.7% compared with baseline in the “off” state (p < 0.01). Conclusions Motion sensor-based computer-guided DBS programming identified stimulation parameters that significantly improved tremor and bradykinesia with minimal clinician involvement. Automated motion sensor-based mapping is worthy of further investigation and may one day serve to extend programming to populations without access to specialized DBS centers.

Adult non-dysraphic intradural spinal lipomas are rare entities. Here we report two cases of adult non-dysraphic intradural lumbar lipoma. Case 1: A 66-year-old man experienced gradual progression of sensory disturbance and numbness in the lower extremities bilaterally over the course of 2 years. Magnetic resonance imaging (MRI) suggested an intradural lipoma at T12 with no evidence of dysraphism. Adequate decompression and duraplasty were performed with intraoperative monopolar stimulation to elicit evoked electromyography responses. Case 2: A 54-year-old man with a 10-year history of lower back pain and gradual progression of weakness of the right lower extremity over the course of 2 years was referred to our hospital, where he presented with urinary disturbance. An MRI suggested intradural lipoma at L2 without evidence of dysraphism. Roentgenograms revealed L5 isthmic spondylolisthesis. Adequate resection, duraplasty, and L4-S posterior lumbar interbody fusion were performed with intraoperative monopolar stimulation monitoring. Both patients received pathological diagnoses of lipomas, and neurological symptoms improved postsurgically in both cases. Adequate resection is recommended for adult lumbar lipomas without dysraphism in order to achieve a good clinical outcome. The evoked electromyography response was a simple and useful intraoperative tool to demonstrate adequate decompression of adult non-dysraphic intradural spinal lipomas in both of these cases.

Human behavioral thresholds for trains of biphasic pulses applied to a single channel of Nucleus CI24 and LAURA cochlear implants were measured as a function of inter-phase gap (IPG). Experiment 1 used bipolar stimulation, a 100-pps pulse rate, and a 400-ms stimulus duration. In one condition, the two phases of each pulse had opposite polarity. Thresholds continued to drop by 9-10 dB as IPG was increased from near zero to the longest value tested (2900 micros for CI24, 4900 micros for LAURA). This time course is much longer than reported for single-cell recordings from animals. In a second condition, the two phases of each pulse had the same polarity, which alternated from pulse to pulse. Thresholds were independent of IPG, and similar to those in condition 1 at IPG=4900 micros. Experiment 2 used monopolar stimulation. One condition was similar to condition 1 of experiment 1, and thresholds also dropped up to the longest IPG studied (2900 micros). This also happened when the pulse rate was reduced to 20 pps, and when only a single pulse was presented on each trial. Keeping IPG constant at 8 micros and adding an extra biphasic pulse x ms into each period produced thresholds that were roughly independent of x, indicating that the effect of IPG in the other conditions was not due to a release from refractoriness at sites central to the auditory nerve. Experiment 3 measured thresholds at three IPGs, which were less than, equal to, and more than one half of the interval between successive pulses. Thresholds were lowest at the intermediate IPG. The results of all experiments could be fit by a linear model consisting of a lowpass filter based on the function relating threshold to the frequency of sinusoidal electrical stimulation. The data and model have implications for reducing the power consumption of cochlear implants.

Objective The primary purpose of this study was to evaluate the diagnostic accuracy of averaged electrode voltages (AEVs) for identifying malfunctioning electrodes in cochlear implant users. Design AEVs were measured using common ground (N = 33 ears) and monopolar stimulation modes (N = 40 ears) in adult subjects implanted with the Nucleus 24M or Nucleus 24R(CS) cochlear implant. AEV measures were then compared with common ground electrode impedance measures as well as to subjective judgments of electrode sound quality to determine the sensitivity and specificity of AEVs. Results Results showed excellent specificity for both modes of AEV testing: 97.9% for common ground and 99.8% for monopolar. Sensitivity for common ground AEV testing was 91.7%; however the sensitivity of monopolar AEVs was very poor, at 7.7%. Monopolar AEVs accurately identified open circuits but missed all short circuits. These results are consistent with the sensitivity of impedance measures made with each of the two stimulation modes. Conclusions Common ground AEVs are more reliable than monopolar AEVs for identifying malfunctioning electrodes.

In this short communication, we evaluate the place-pitch relation of a newly designed, deeply inserted, cochlear implant electrode. The insertion depths ranged from 471 degrees to 662 degrees. Pitch perception was measured in eight subjects with monopolar stimulation on each electrode contact at intensities of 50% and 80% of the dynamic range. We observed a monotonic reduction of pitch estimate with insertion depth. For about half of the subjects, a flattening of the pitch estimate at the basal end of the electrode was seen, while for the other half, pitch continued to decrease monotonically up to the most apical part of the array. We conclude that deeper insertion could increase pitch range for at least some cochlear implant recipients, and could hence potentially increase group performance.

Cochlear implants are highly successful neural prostheses that restore hearing in the deaf, often resulting in high levels of speech understanding in quiet listening conditions. In more challenging conditions, however, cochlear implant subjects often score much lower than their normal-hearing peers, possibly reflecting limits of the electrode-neural interface. In this study, we compare monopolar stimulation versus focused stimulation, using multipolar channels, to test if current focusing can increase spectral resolution. Psychophysical results show that current focusing significantly improves subjects' ability to discriminate spectral features and detect dynamic modulations in sound stimuli. These results suggest that focused stimulation can successfully increase the number of effective channels with a cochlear implant and may lead to improved hearing in noisy conditions.

It has been argued that a main limitation of the cochlear implant is the spread of current induced by each electrode, which activates an inappropriately large range of sensory neurons. To reduce this spread, an alternative stimulation mode, the all-polar mode, was tested with five participants. It was designed to activate all the electrodes simultaneously with appropriate current levels and polarities to recruit narrower regions of auditory nerves at specific intracochlear electrode positions (denoted all-polar electrodes). In this study, the all-polar mode was compared with the current commercial stimulation mode: the monopolar mode. The participants were asked to judge the sound dissimilarity between pairs of two-electrode pulse-train stimuli that differed in the electrode positions and were presented in either monopolar or all-polar mode with pulses on the two electrodes presented either sequentially or simultaneously. The dissimilarity ratings were analyzed using a multidimensional scaling technique and three-dimensional stimulus perceptual spaces were produced. For all the conditions (mode and simultaneity), the first perceptual dimension was highly correlated with the position of the most apical activated electrode of the electrical stimulation and the second dimension with the position of the most basal electrode. In both sequential and simultaneous conditions, the monopolar and all-polar stimuli were significantly separated by a third dimension, which may indicate that all-polar stimuli have a perceptual quality that differs from monopolar stimuli. Overall, the results suggest that both modes might successfully represent spectral information in a sound processing strategy.

Sharp spatial selectivity is critical to auditory performance, particularly in pitch-related tasks. Most contemporary cochlear implants have employed monopolar stimulation that produces broad electric fields, which presumably contribute to poor pitch and pitch-related performance by implant users. Bipolar or tripolar stimulation can generate focused electric fields but requires higher current to reach threshold and, more interestingly, has not produced any apparent improvement in cochlear-implant performance. The present study addressed this dilemma by measuring psychophysical and physiological spatial selectivity with both broad and focused stimulations in the same cohort of subjects. Different current levels were adjusted by systematically measuring loudness growth for each stimulus, each stimulation mode, and in each subject. Both psychophysical and physiological measures showed that, although focused stimulation produced significantly sharper spatial tuning than monopolar stimulation, it could shift the tuning position or even split the tuning tips. The altered tuning with focused stimulation is interpreted as a result of poor electrode-to-neuron interface in the cochlea, and is suggested to be mainly responsible for the lack of consistent improvement in implant performance. A linear model could satisfactorily quantify the psychophysical and physiological data and derive the tuning width. Significant correlation was found between the individual physiological and psychophysical tuning widths, and the correlation was improved by log-linearly transforming the physiological data to predict the psychophysical data. Because the physiological measure took only one-tenth of the time of the psychophysical measure, the present model is of high clinical significance in terms of predicting and improving cochlear-implant performance.

In normal subjects, electrical stimulation of the labyrinth with surface electrodes located on the mastoid process induced illusions of shifting of a fixed point of light in darkness similar to the oculogyral illusion induced by rotatory vestibular stimulation. Monoaural anodal stimulation of the right labyrinth induced apparent shift of the target to the left; with cathodal stimulation, it shifted to the right; threshold current was 0.35–0.6 mA. When the current strength increased, the amplitude and rate of apparent movement of the target increased approximately linearly. With binaural, bipolar stimulation, the illusory movement of the target was toward the site of the cathode and the threshold decreased by 1.5–2.5 times. With binaural, monopolar stimulation, the target seemed to shift along the vertical and the threshold current was 1.4–3.0 mA. Eye movement appeared at substantially higher currents than those resulting in apparent movement of the target. It is suggested that visual illusions are linked not to vestibular eye-movement reactions, but to the effect vestibular signals have on the spatial perception system.

Direct cortical stimulation in commonly used for the accurate localization of the motor cortex but the electrical threshold stimulation parameters with this technique had not been fully established.A retrospective review of 15 cases of pediatric surgical cases were performed. The patients consisted of nine male patients and six female patients with age range from 2 to 18 years (mean: 10.8 years; median: 14 years). The most common pathology was cortical dysplasia (nine cases). Stimulation was performed with a train of five stimulations (range five-seven stimulations;5% of stimulations required more than five stimulations) applied, each train of 50 micros pulse duration, with an interstimulus interval of 1.1 msec. Stimulation intensity commenced at 25 V and this was increased at 5-10 V increments until motor evoked potentials waveforms of sufficient duration and morphology were consistently generated.Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were found to be more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate (83.7%) and required the lowest stimulation voltage (36.0 V). The stimulation voltage was found to be statistically significant compared to threshold values for abductor hallucis, tibialis anterior, deltoid, and orbicularis oris with respective p values of 0.006, 0.021, 0,027, and 0.015. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds when compared to other pathology (p = 0.067).Monopolar electrical stimulation threshold for intraoperative motor cortical mapping were more consistent in the upper limb compared to lower limb and facial muscles. Evoked responses from the extensor digitorium communis had the highest recorded rate and required the lowest stimulation voltage. There was also a distinct trend that patients with cortical dysplasia/tuberous sclerosis have higher stimulation thresholds.

The patient was 3 years 5 months at the implantation with the Clarion device. The patient had normal otoacoustic emission but no auditory brainstem responses. Speech perception scores were not obtained due to the short length of implant use for the patient. Stimuli were presented through a laptop computer connected to a clinician’s programming interface (CPI) unit, a speech processor and the subject’s headpiece. A radio frequency (RF) filter was positioned between the recording electrodes and the amplifier to reduce stimulus artefact. Stimuli were 75 μs biphasic current pulses delivered to the internal electrodes with medial monopolar stimulation. Electrically evoked potential responses were recorded with a Nicolet Compact 4 electrodiagnostic system externally triggered by the stimulus output of the SCLIN for window software and the interface unit. For the evoked potential testing, stimulus rates of 20.03 Hz were used.

International audience; ObjectIn deep brain stimulation, the anatomic positions of electrode contact centers are used as the basis for analysis. We propose a new semi-quantitative approach (contact membership concept) considering patient’s individual anatomy, contact size , and extent of involvement of STN and neighboring structures. Materials and methodsIn ten bilaterally operated and improved Parkinsonian patients, effective contact positions (contacts used for monopolar stimulation) were analyzed. The position of the contact center (classical binary approach: each center assigned, 1, or not, 0, to a given structure) and of the contact in its dimension (contact membership concept: membership degree, ordinal values from 0 to 1, assigned to each anatomic structure according to extent of involvement) were compared for the whole patient group and, individually, for each patient.ResultsThe membership concept revealed that for 13 out of 20 contacts, more than one structure was involved, where the classical binary approach assigned only one structure. For both approaches lateral STN, zona incerta and H1 (Forel’s Field) were the main structures involved, but their frequencies of appearance differed.ConclusionThe membership concept allows detailed analysis of the anatomic contact position. In the future this approach could assist in correlating anatomy and clinical results for all electrode contacts (effective ones and clinically less efficient ones).

The design of the placement of the Clarion cochlear implant's intracochlear electrode array has undergone 2 revisions since its introduction, each to improve modiolar proximity. Stimulation with modiolar proximity may reduce current requirements for threshold levels and most comfortable levels of stimulation. This study analyzed the effects of electrode design on programming levels for deaf children implanted with the 3 cochlear implant designs and followed at The Children's Hospital of Philadelphia. Psychophysical data were reported if measurements were taken approximately 3 months after initial activation, and programming parameters included nonsequential monopolar stimulation of 75-μs-per-phase biphasic pulses presented at 813 Hz per electrode. The threshold level and most comfortable programming level were measured by standard clinical techniques appropriate for children. The results indicate that the 2 electrode placement revisions have each significantly reduced threshold levels and most comfortable stimulation levels. These results are discussed in the context of device aesthetics, safety, and function.

Object. The repetitive application of high-frequency anodal monopolar stimulation during surgery in or near the motor cortex allows a qualitative and quantitative evaluation of motor evoked potentials (MEPs). Using this method, motor pathways and motor function can be continuously monitored during surgery. Methods. In this prospective study, 70 patients underwent MEP monitoring during surgery performed in the central region. All procedures were performed after general anesthesia had been induced without the aid of muscle relaxants. The motor pathways were monitored during the entire surgical procedure by repetitive high-frequency anodal monopolar stimulation (frequency 400–500 Hz; train 7–10 pulses; impulse duration 0.2–0.7 msec; and stimulation intensity 16.9 ± 7.76 mA). The MEPs were continuously evaluated to assess their latency, potential duration, and amplitude. Recorded alterations in these parameters were subsequently correlated with surgical maneuvers and with postoperative neurological deterioration. The monitoring parameters (latency, potential duration, and amplitude) had a broad interindividual range of variation. A correlation between individual intraoperative changes in the potentials and surgical maneuvers or postoperative neurological deterioration was observed in eight cases. A spontaneous shift in latency greater than 15% or a sudden reduction in the amplitude of the potential greater than 80% was considered a warning criterion. In all cases in which there was an irreversible change in latency or a complete loss of potentials were observed, there was postoperative neurological deterioration. Conclusions. Improved surgical safety can be achieved using intraoperative neurophysiological monitoring procedures. Repetitive stimulation of the motor cortex proved to be a reliable method for monitoring subcortical motor pathways. Changes in MEP latency and MEP amplitude served as warning criteria during surgery and possessed prognostic value.

Intraoperative cranial motor nerve monitoring has improved the preservation of cranial nerve function during cerebellopontine angle and skull base surgery. Further improvements are needed to provide greater selectivity and sensitivity during intraoperative motor nerve stimulation. Use of bipolar stimulator probes has been recommended by previous investigators. The authors hypothesized that a coaxial bipolar stimulator design might provide important advantages over existing designs. This study compared the results of bipolar and monopolar stimulation using a coaxial stimulator probe in a rat model and during neurotologic procedures. The coaxial bipolar probe was superior in selectivity, thereby permitting useful multichannel monitoring. The coaxial design may also offer advantages over previous bipolar stimulator designs.

44 patients underwent intraoperative stimulation with a monopolar electrode prior to computed tomography (CT)-guided stereotactic biopsy. Stimulation at 2–100 Hz resulted in functional responses in 6/21 patients with subcortical or callosal lesions, 4/6 with basal ganglion lesions, 8/10 with thalamic and 4/4 with brainstem lesions. In all but 2 patients with mesencephalic lesions, where limited biopsy sites were available, an alternative biopsy site was used if a functional response was obtained. No morbidity was seen among these patients, although postbiopsy CT scans demonstrated small 3- to 7-mm hematomas in 5/11 patients. Retrospective review of 79 patients who underwent biopsies without stimulation demonstrated hematomas in 6/10 patients and a 3.3% transient surgical morbidity. These data indicate that postbiopsy hematomas are a relatively common occurrence, that intraoperative electrical stimulation within abnormal lesions can identify functional potential, and that avoidance of biopsies within these functional areas may be associated with reduced morbidity.

This study investigated the possibility of using electrically evoked auditory brainstem response (EABR) for predicting surviving spiral ganglion cell populations. EABR recordings were made from six kanamycin induced deaf cats by the round window monopolar stimulation (RW) and the scala tympani bipolar stimulation (ST). On completing the electrical stimulation, each animal was sacrificed and prepared for histological examination. The spiral ganglion cell populations were estimated by classifying them into four groups (0-25%, 25-50%, 50-75%, 75-100%) as a percentage of survival cells under magnification. EABR thresholds and input-output function of amplitude were compared with microscopic findings of surviving spiral ganglion cell populations. The results were as follows: 1) The rate of amplitude growth in response to increased stimulus intensity of electrically evoked potentials from ST was gradual, but that of RW was steep. 2) The vestibular potentials were elicited by RW, and at a lower stimulus intensity the RW waveform began to become distorted by the myogenic potentials. 3) EABR threshold was a poor predictor of surviving spiral ganglion cell populations. 4) There was a correlation between surviving spiral ganglion cell populations and the slope of the input-output functions of ST EABR. However, there was no correlation between that of RW EABR and the slope.

Intracranial self-stimulation experiments in the dog using a two-wire electrode, with each wire used as a monopolar electrode and the combination as a bipolar electrode, show that monopolar stimulation may produce either a higher or a lower rate of response than that produced by bipolar stimulation. A theoretical consideration of the changes in current density around the electrode when it is changed from a monopolar to a bipolar electrode shows that such differences are to be expected. The exact location of the structure being stimulated with reference to the two electrode tips will determine whether the structure is subjected to a higher current density on monopolar or on bipolar stimulation.