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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.

Direct electrical motor cortex stimulation with short-train high-frequency stimulation (HFS) for motor evoked potentials (MEPs) has been used intraoperatively during supratentorial surgeries, but the safety threshold is poorly defined. The goal of this study is to establish a rat model for the investigation of neural damage in the cerebral cortex caused by high current HFS to aid in defining safety thresholds. We performed bilateral craniotomy on 12 rats. Cerebral sensory-motor cortex was stimulated with a high-frequency current for 100 times. The rats were sacrificed and the brains were sliced for Nissl, DAPI, and IBA-1 staining. Severe neural damage of the cerebral cortex was found in all cases, including markedly shrunken and pyknotic cells. IBA-1 staining revealed reactive microglia morphology in the lesion area. DAPI staining showed nucleus degeneration and deformation. The cell density were significantly lower within the lesion area compared to the contralateral side. This study has established a brain lesion model caused by HFS on rats. These results suggest HFS may carry a risk of serious neural damage if repeatedly applied to the same brain site. More experiments are needed to fully understand the safety threshold of direct cortical stimulation with HFS for clinical use.

Motor cortex stimulation, either non-invasively or with implanted electrodes, has been applied worldwide as a treatment for intractable neuropathic pain syndromes. Although computer simulations of non-invasive brain stimulation have been investigated largely to optimize protocols and improve our understanding of underlying mechanisms using a realistic head model, computational studies of invasive cortical stimulation are rare and limited to very simplified cortical models. In this paper, we present an anatomically realistic head model for epidural cortical stimulation that includes the most sophisticated epidural electrodes with an insulating paddle. The head model predicted the stimulus-induced field strengths according to two different stimulation techniques, bipolar and monopolar stimulations. We found that the stimulus-induced field focused on the precentral and postcentral gyri because of the epidural lead's invasiveness. Different stimulation configurations influenced the shape of the field markedly, and complex patterns of inward and outward directions of the radial field were observed in bipolar stimulation compared to those in monopolar stimulation. The spatial distributions of field strength showed that the optimal stimulation varied according to the target areas. In conclusion, we proposed an anatomically realistic head model and a sophisticated epidural lead to simulate epidural cortical stimulation-induced field strengths and identified the importance of such detailed modeling for epidural cortical stimulation because of the current's shunting through the cerebrospinal fluid.

Intraoperative cortical and subcortical bipolar or monopolar mapping is the gold standard for neurosurgical procedures that involve lesions near functional or "eloquent" cortex. However, the classic Penfield stimulation has a higher intraoperative seizure rate than high-frequency short-train stimulation. As a result, high-frequency monopolar stimulation is now the most widely practiced technique. However, seizure-free mapping cannot be guaranteed even with high-frequency stimulation particularly at high current thresholds. We encountered a case of severe generalized tonic-clonic seizure and consequent severe brain bulge in an 8-year-old child during cortical mapping with the high-frequency protocol.

ObjectiveIntracranial electrical stimulation of subcortical axonal tracts is particularly useful during brain surgery, where mapping helps identify and excise dysfunctional tissue while avoiding damage to functional structures. Stimulation parameters are generally set empirically and consequences for the spatial recruitment of axons within subcortical tracts are not well identified.ApproachComputational modeling is employed to study the effects of stimulation parameters on the recruitment of axons: monophasic versus biphasic stimuli induced with monopolar versus bipolar electrodes, oriented orthogonal or parallel to the tract, for isotropic and anisotropic tracts.Main resultsThe area and depth of axonal activation strongly depend on tissue conductivity and electrode parameters. The largest activation area results from biphasic stimulation with bipolar electrodes oriented orthogonal to axonal fasciculi, for anisotropic and especially isotropic tracts. For anisotropic tracts, the maximal activation depth is similar regardless of whether a monopolar or bipolar electrode is employed. For isotropic tracts, bipolar parallel and monopolar stimulation activate axons deeper than orthogonal bipolar stimulation. Attention is warranted during monophasic stimulation: a blockade of action potentials immediately under cathodes and a propagation of action potentials under anodes are found.SignificanceConsidering the spatial patterns of blockade and activation present during monophasic stimulation with both monopolar and bipolar electrodes, biphasic stimulation is recommended to explore subcortical axon responses during intraoperative mapping. Finally, the precise effect of electrical stimulation depends on conductivity profiles of tracts, and as such, should be explicitly considered for each individual subject and tract undergoing intracranial mapping.

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.

Objective Bipolar stimulation (BS) used in intraoperative mapping is said to have less influence of leakage current. Its characteristics were actually verified while comparing with monopolar stimulation (MS). Methods A stimulating probe was brought into contact with agar with a comb-shaped detection electrode (platinum) placed at intervals of 2 mm. The stimulation current was kept constant, and resistance and voltage between the electrodes were measured while changing the distance between the electrode and the stimulation probe. Results The calculated current decreased exponentially with the distance between the stimulation portion and the electrode. When the stimulation portion was 2 mm away from the detecting electrode in BS, the current became 1/3 or less of the set current and almost no detectable at 1 cm or more. The current by MS was same as that of BS at the stimulation-detection distance of 1 mm. The current by MS is less than 1/10 of the set current at 5 mm, which is higher than BS. In MS, slight current was observed even when the stimulation-detection distance was 2 cm or more away. Conclusion In MS, the spread of the current at the stimulation portion is larger than the BS. Clinically it was considered that current leakage was negligible for both stimulations.

This chapter explores various aspects of that interface by examining the principles and methods used in both recording from and stimulation of neural tissue. It also reviews the principles and techniques required to record neural activity. The chapter further discusses functional imaging techniques, the current trend in examining the activity within neural tissue of the central nervous system (CNS). Neural stimulators employ different electrode configurations in order to excite neural tissue. Two popular clinical stimulation modes are monopolar and bipolar stimulation. In monopolar stimulation, a current is passed between an electrode in close proximity to the tissue being stimulated and a large remote ground, reference or return electrode. In bipolar stimulation, a current is passed between two electrodes, both located near the neural tissue being targeted. More advanced stimulation mode is known as multipolar or phased array mode. Finally, the chapter provides the processes of metabolic and electrochemical stress.

This chapter addresses stimulation techniques, the issue of the stimulation electrode positioning, motor unit (MU) activation order, and spinal involvement in electrically elicited contractions. Two stimulation techniques are commonly used: bipolar, and monopolar stimulation. The differences between these two methods concern the geometry and relative position of the stimulation electrodes. Surface electromyography (sEMG) signals can be detected during selective electrical stimulation of a nerve branch or of a motor point of a muscle. The resultant sEMG signal is a compound motor action potential (CMAP), also termed as M-wave. Since the M-wave represents the sum of the potentials of the concurrently activated MUs, its change is generally assumed to reflect changes either in the number or in the sarcolemmal properties of activated MUs. Neuromuscular electrical stimulation (NMES) combined with sEMG isolates the contributions of peripheral fatigue because it gives the experimenter control of MU firing frequency and recruitment.

Cochlear implantation is carried out to recover the sense of hearing. However, its functional outcome varies highly between patients. In the current work, we present a study to assess the functional outcomes of cochlear implants considering the inter-variability found among a population of patients. In order to capture the cochlear anatomical details, a statistical shape model is created from high-resolution human \(\mu \)CT data. A population of virtual patients is automatically generated by sampling new anatomical instances from the statistical shape model. For each virtual patient, an implant insertion is simulated and a finite element model is generated to estimate the electrical field created into the cochlea. These simulations are defined according to the monopolar stimulation protocol of a cochlear implant and a prediction of the voltage spread over the population of virtual patients is evaluated.

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.

For intra-operative subcortical electrical stimulation of the corticospinal tract, two techniques - originally described for cortical stimulation - have evolved: the 50-Hz-stimulation first described by Penfield in 1937 and the high-frequency multipulse train stimulation technique first described by Taniguchi in 1993. Motor thresholds of both methods in combination with a bipolar and monopolar stimulation technique and their reliability for eliciting motor evoked potentials (MEPs) were studied.Data were obtained in 20 patients (50±17 years; 10 females) undergoing tumour resection under general anaesthesia. Both 50-Hz-stimulation of 1-s duration and a multipulse stimulation (5 pulses interstimulus interval 4 ms, 0.5-Hz repetition rate) were applied with a bipolar probe (1.5-mm ball tip, 8-mm interelectrode distance) and a monopolar probe (1.5-mm-diameter tip). MEPs were recorded in muscles contralateral to the stimulated hemisphere. Comparison of different stimulation modalities was performed at the site where monopolar multipulse stimulation technique elicited MEPs with the lowest stimulation intensity (constant current monophasic cathodal stimulation, individual pulse width 0.5 ms, max. 25 mA).MEPs were elicited by monopolar multipulse stimulation with an intensity of 8±3.9 mA (21/21 stimulation sites); monopolar 50-Hz stimulation with 12±5.4 mA (18/21 stimulation sites); bipolar multipulse stimulation with 14±8.1 mA (12/21 stimulation sites) and bipolar 50-Hz stimulation with 15±6.3 mA (11/21 stimulation sites).Stimulation intensities for eliciting MEPs are significantly lowest for the monopolar multipulse stimulation (p0.025). Monopolar compared to bipolar stimulation resulted in eliciting MEPs in a higher number of tested patients (Fisher's p0.0001).Subcortical stimulation with a monopolar probe and a multipulse stimulation is most efficient for the purpose of identifying the corticospinal tract. This is explained by the more radiant electric field properties of the monopolar probe compared to the bipolar probe.

Forward-masked psychophysical spatial tuning curves (fmSTCs) were measured in 15 cochlear-implant subjects, 10 using monopolar stimulation and 5 using bipolar stimulation. In each subject, fmSTCs were measured at several probe levels on an apical, middle, and basal electrode using a fixed-level probe stimulus and variable-level maskers. Tuning curve slopes and bandwidths did not change significantly with probe level for electrodes located in the apical, middle, or basal region although a few subjects exhibited dramatic changes in tuning at the extremes of the probe level range. Average tuning curve slopes and bandwidths did not vary significantly across electrode regions. Spatial tuning curves were symmetrical and similar in width across the three electrode regions. However, several subjects demonstrated large changes in slope and/or bandwidth across the three electrode regions, indicating poorer tuning in localized regions of the array. Cochlear-implant users exhibited bandwidths that were approximately five times wider than normal-hearing acoustic listeners but were in the same range as acoustic listeners with moderate cochlear hearing loss. No significant correlations were found between spatial tuning parameters and speech recognition; although a weak relation was seen between middle electrode tuning and transmitted information for vowel second formant frequency.

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

Neural excitation profile widths at the neural level, for monopolar stimulation with Nucleus straight and contour arrays respectively, were simulated using a combined volume-conduction-neural model. The electrically evoked compound action potential profile widths at the electrode array level were calculated with a simple approximation method employing stimulus attenuation inside the cochlear duct, and the results compared to profile width data from literature. The objective of the article is to develop a simple method to estimate stimulus attenuation values by calculating the values that best fit the modelled excitation profile widths to the measured evoked compound action potential profile widths. Results indicate that the modelled excitation profile widths decrease with increasing stimulus attenuation. However, fitting of modelled excitation profile widths to measured evoked compound action potential profile widths show that different stimulus attenuation values are needed for different stimulation levels. It is suggested that the proposed simple model can provide an estimate of stimulus attenuation by calculating the value of the parameter that produces the best fit to experimental data in specific human subjects.

This paper presents the results of the first investigations into the use of bipolar electrical stimulation of the retina with a suprachoroidal vision prosthesis, and the effects of different electrode configurations on localization of responses on the primary visual cortex. Cats were implanted with electrodes in the suprachoroidal space, and electrically evoked potentials were recorded on the visual cortex. Responses were elicited to bipolar and monopolar stimuli, with each stimulating electrode coupled with either six-return electrodes, two-return electrodes, or a single-return electrode. The average charge threshold to elicit a response with bipolar stimulation and six-return electrodes was 76.47 ± 8.76 nC. Bipolar stimulation using six-return electrodes evoked responses half the magnitude of those elicited with a single or two-return electrodes. Monopolar stimulation evoked a greater magnitude, and area of cortical activation than bipolar stimulation. This study showed that suprachoroidal, bipolar stimulation can elicit localized activity in the primary visual cortex, with the extent of localization and magnitude of response dependent on the electrode configuration.

A model was developed to simulate acoustically the effects of excitation spread in cochlear implants (CI). Based on neurophysiologic data, the proposed model simulates the electrical-current decay rate associated with broad and narrow types of excitation, such as those produced by monopolar and bipolar electrode configurations. The effect of excitation spread on speech intelligibility was simulated in normal hearing subjects by varying the slopes of the synthesis bands in the noise vocoder. Sentences and monosyllabic words processed via 4–16 channels of stimulation with varying degrees of excitation spread were presented to normal-hearing listeners for identification. Results showed significant interaction between spectral resolution (number of channels) and spread of excitation. The effect of narrowing the excitation spread was minimal when the spectral resolution was sufficiently good (> 8 channels) but it was significant when the spectral resolution was poor (4 channels). A significant decrement in performance was observed for extremely narrow excitation spread. This outcome is partly consistent with behavioral data obtained with cochlear implant studies in that CI users tend to do as well or better with monopolar stimulation than with bipolar stimulation.

Objective Intraoperative monitoring of the motor-evoked potential has been widely used in patients undergoing neurosurgery. Direct stimulation of the brain with high-frequency monopolar stimulation (HFMS) is one of the most common methods to produce motor-evoked potential. We studied the influence of HFMS on the rat cerebral cortex. Methods We applied 1.5, 15, 30, 40, or 50 mA of HFMS to the rat sensorimotor cortex by a short sequence of five monopolar, monophasic, anodal rectangular 500-Hz pulses. We delivered one short five-pulse train 100 times every 5 seconds and examined pre- and post-stimulation electroencephalograms and histological changes at the stimulation site. Results We observed no spike waves after HFMS in any of the rats. There was no change in the power spectrum or frequency content in any of the rats exposed to HFMS. Histologically, there was significant swelling of the dendrites in rats sacrificed immediately after exposure to 40- and 50-mA stimulation; the 50-mA stimulation group also exhibited slight swelling of the mitochondria. These findings were not obtained in any of the rats sacrificed 30 days after stimulation. Conclusion In rats exposed to a stimulation intensity of 30-mA or less, no morphological or electrophysiological changes were observed. However, the possibility that HFMS may affect neural tissue cannot be ruled out.

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.