Somatosensory Evoked Potentials Waveforms Research Articles

Application of Machine Learning Strategies to Model the Effects of Sevoflurane on Somatosensory-Evoked Potentials during Spine Surgery

In this study, a small sample of patients’ neuromonitoring data was analyzed using machine learning (ML) tools to provide proof of concept for quantifying complex signals. Intraoperative neurophysiological monitoring (IONM) is a valuable asset for monitoring the neurological status of a patient during spine surgery. Notably, this technology, when operated by neurophysiologists and surgeons familiar with proper alarm criteria, is capable of detecting neurological deficits. However, non-surgical factors, such as volatile anesthetics like sevoflurane, can negatively influence robust IONM signal generation. While sevoflurane has been shown to affect the latency and amplitude of somatosensory evoked potential (SSEP), a more complex and nuanced analysis of the SSEP waveform has not been performed. In this study, signal processing and machine learning techniques were used to more intricately characterize and predict SSEP waveform changes as a function of varying end-tidal sevoflurane concentration. With data from ten patients who underwent spinal procedures, features describing the SSEP waveforms were generated using principal component analysis (PCA), phase space curves (PSC), and time-frequency analysis (TFA). A minimum redundancy maximum relevance (MRMR) feature selection technique was then used to identify the most important SSEP features associated with changing sevoflurane concentrations. Once the features carrying the maximum amount of information about the majority of signal waveform variability were identified, ML models were used to predict future changes in SSEP waveforms. Linear regression, regression trees, support vector machines, and neural network ML models were then selected for testing. Using SSEP data from eight patients, the models were trained using a range of features selected during MRMR calculations. During the training phase of model development, the highest performing models were identified as support vector machines and regression trees. After identifying the highest performing models for each nerve group, we tested these models using the remaining two patients’ data. We compared the models’ performance metrics using the root mean square error values (RMSEs). The feasibility of the methodology described provides a general framework for the applications of machine learning strategies to further delineate the effects of surgical and non-surgical factors affecting IONM signals.

Value of multi-channel somatosensory evoked potentials recording in patients undergoing scoliosis correction surgery.

We aimed to investigate the value of intraoperative multi-channel recording of somatosensory evoked potentials (SSEPs) in patients undergoing posterior instrumentation surgery with fusion. This study included 176 patients with scoliosis who underwent posterior correction surgery from January 2019 to June 2020. Among them, 88 patients underwent routine SSEPs monitoring via single-channel (Cz'-Fpz) cortical recording (control group), while the remaining 88 patients underwent multi-channel (Cz'-Fpz and C3'-C4') SSEPs monitoring in the cortex. Chi-square and Fisher's exact tests were used to analyze the influence of age, spinal deformity classification, and Cobb angle on waveform differentiation and the success rate of SSEPs monitoring. Univariate analysis revealed that age, type of scoliosis, and Cobb angle exerted significant effects on the success rate of intraoperative SSEPs monitoring, and the SSEPs waveform differentiation rate was poorest among patients with congenital scoliosis. Intraoperative monitoring results indicated that the success rate of single-channel SSEPs monitoring was 90.9%, while that of multi-channel monitoring was 98.9% (P < 0.05). Among the intraoperative alarm cases, the incidence of adverse events after single-channel SSEPs monitoring was 66.7%, while the incidence of adverse events after multi-channel SSEPs monitoring was only 28.6%. Multi-channel cortical SSEPs monitoring can effectively and accurately evaluate the function of the posterior column of the spinal cord. Use of multi-channel SSEP monitoring may help to improve the success rate of monitoring and reduce the incidence of postoperative adverse events in patients with congenital scoliosis.

NIMG-99. REAL-TIME DELINEATION OF THE CENTRAL SULCUS WITH THE SPATIAL PROFILE OF SSEPS CAPTURED WITH HIGH-DENSITY ECOG GRID

Abstract OBJECTIVE Cortical mapping during tumor resection is critical to reducing the risk of neurological complications. While the somatosensory evoked potential (SSEPs) is widely employed to delineate the central sulcus, the evoked response can be misconstrued from the manual peak interpretation. This is due to the poor spatial resolution of the strip electrode as well as a result of edema or tumor infiltration of the overlying cortex. We present a real-time computer-based visualization system that uses recorded SSEPs with a subdural grid to aid in cortical mapping. Method: The neural data during electrical stimulation of the median nerve at 0.6Hz are picked up with a bio-amplifier. The stimulation artifact recorded from the bipolar electromyogram (EMG) is used as the stimulation onset. The ECoG data are assessed online with MATLAB Simulink to process and visualize the SSEPs waveform. The visualization system is programmed to display the SSEP's peak activation as a heat map on a 2D grid and projected onto a screen, showcasing the nature of the cortical activities over the contact surface area in real-time. RESULTS SSEPs were recorded from 3 patients during their awake craniotomies. The ECoG grid occupied a large cortical surface where the heatmap delineated the central sulcus. The color-coding of the heatmap revealed the anterior and posterior channels, providing a consistently high separation accuracy in each patient (accuracy = 98%). The map could be viewed at any time point along the SSEP trace without peak interpretation. CONCLUSION We believe that this visualization system will aid in the rapid definition of the sensorimotor area during surgical planning to provide additional information during cortical mapping and facilitate interpreting ECoG grid data.

Application of multimodal neuroelectrophysiological monitoring technology in surgical treatment of thoracic tuberculosis

To explore the value of multimodal neuroelectrophysiological monitoring technology in the evaluation of spinal cord and nerve root function for the treatment of thoracic tuberculosis with debridement and bone grafting and posterior internal fixation by transcostal transverse process approach. The clinical data of 25 patients with thoracic tuberculosis underwent debridement and bone grafting and posterior vertebral arch internal fixation by transcostal transverse process approach from December 2018 to September 2019 was retrospectively analyzed. Among these 25 patients, including 14 males and 11 females;aged from 20 to 83 years old, with a mean of (63.45±9.65) years;there were 3 cases of single vertebral body destruction, 13 cases of 2 vertebral bodies destruction, and 9 cases of 3 or more vertebral bodies destruction. All surgical patients underwent intraoperative detection of somatosensory evoked potential(SEP) and transcranial electric stimulation-motor evoked potential(TES-MEP);and electromyography (EMG) was used to monitor the pedicle screw placement and lesion removal. The erythrocyte sedimentation rate(ESR) was used to evaluate the decline of inflammatory indexes, the visual analogue scale (VAS) was used to evaluate the thoracic spine pain, and the Cobb angle and Oswestry Disability Index(ODI) were used to evaluate the improvement of function. All 25 patients were successfully monitored. Five patients had abnormal SEP waveforms during operation, 3 cases were caused by intraoperative clearing of lesions and spinal cord compression during irrigation, timely replacement of instruments and gestures, and adjustment of irrigation water flow rate returned the waveform to normal; one case was caused by a decrease in systolic blood pressure, and the waveform returned to normal after timely treatment of increased blood pressure;after 1 case of SEP waveform abnormality, the operation was suspended for 10 minutes and recovered spontaneously, and the waveform abnormality did not reappear until the end of the operation. Seven patients had abnormal TES-MEP waveforms, 5 cases occurred when the pedicle screw was inserted, the nail path was adjusted in time, and the waveform recovered after nail repositioning;one case was caused by tilting the operation bed during operation, and the waveform gradually recovered after adjusting the tilt angle of operation bed; one case occurred during the correction of the pedicle screw and rod system, and the waveform gradually returned to normal after the contralateral screw and rod correction were completed during operation. In 5 cases, the EMG burst potential was detected at the same time when the TES-MEP waveform was abnormal. After adjustment, the EMG burst potential disappeared. There was no abnormality in the TES-MEP and SEP waveforms at the same time. Postoperative VAS, ESR, Cobb angle, and ODI were improved compared with preoperatively (P<0.05). In patients with thoracic tuberculosis, the use of debridement and bone grafting and posterior internal fixation by transcostal transverse process approach combined with intraoperative SEP, TES-MEP and EMG monitoring can timely reflect the spinal cord and nerve root function, avoid intraoperative injuries while achieving good fixation and lesion removal.

Multi-modal Neuroelectrophysiological Monitoring in the Treatment of Thoracic Tuberculosis with Debridement and Bone Grafting and Posterior Pedicle Screw Fixation via Costal Transverse Process Approach.

ObjectiveTo explore the value of multi‐mode neuroelectrophysiological monitoring (MIOM) in evaluating spinal cord and nerve root function in the treatment of thoracic tuberculosis via costal transverse process approach.MethodsFrom December 2017 to September 2019, a retrospective study of thoracic tuberculosis patients in our hospital was conducted. This study included 25 patients (14 men and 11 women). The average age of patients at the time of surgery was 63.3 years (range, 20–83 years). All patients (three cases with the destruction of a single vertebral body, 13 cases with the destruction of two vertebral bodies, and nine cases with the destruction of three or more vertebral bodies) underwent costal transverse process approach with debridement and bone grafting and internal fixation combined with intraoperative multimodal neuroelectrophysiological monitoring. During the operation, somatosensory evoked potential (SEP), transcranial electrical stimulation motor evoked potential (TES‐MEP), and spontaneous electromyography (EMG) were used to monitor progress. ESR, visual analogue scale (VAS), Cobb angle, and Oswestry disability index (ODI) were statistically analyzed to evaluate the treatment effects and patient satisfaction.ResultsAll 25 patients were successfully monitored. The follow‐up time ranged from 12 to 21 months, with an average of 15.3 months. SEP waveform abnormalities occurred in five patients during the operation, the incidence rate was 28%. Of these five patients, three patients changed their instruments and postures, and adjusted the flushing water flow in time; one patient received pressure therapy in time; the operation was suspended for 10 min for one patient. There were seven cases with abnormal TES‐MEP waveform, the incidence rate was 28%. Among these seven cases, five cases adjusted the nail path during the operation and adjusted the nail position in time. One case adjusted the inclination angle of the operating table in time; one case completed the contralateral nail stick correction in time; five of them had abnormal TES‐MEP waveforms, and EMG burst potential was also detected, the incidence rate was 20%. After prompt treatment, the abnormal waveforms of all patients returned to normal; no abnormal waveforms, recurrence of tuberculosis, loosening of internal fixation, nerve and spinal cord dysfunction, etc. The VAS score, erythrocyte sedimentation rate (ESR), Cobb angle, and ODI scores of the patients 1 year after operation were significantly improved compared with 1 week after operation (P < 0.05).ConclusionMulti‐mode intraoperative electrophysiological detection combined with costal transverse process approach for the treatment of thoracic tuberculosis could avoid intraoperative nerve and blood vessel damage, reduce surgical risk, improve surgical efficiency, and ensure curative effect.

Unsupervised machine learning can delineate central sulcus by using the spatiotemporal characteristic of somatosensory evoked potentials

Objective. Somatosensory evoked potentials (SSEPs) recorded with electrocorticography (ECoG) for central sulcus (CS) identification is a widely accepted procedure in routine intraoperative neurophysiological monitoring. Clinical practices test the short-latency SSEPs for the phase reversal over strip electrodes. However, assessments based on waveform morphology are susceptible to variations in interpretations due to the hand area’s localized nature and usually require multiple electrode placements or electrode relocation. We investigated the feasibility of unsupervised delineation of the CS by using the spatiotemporal patterns of the SSEP captured with the ECoG grid. Approach. Intraoperatively, SSEPs were recorded from eight patients using ECoG grids placed over the sensorimotor cortex. Neurosurgeons blinded to the electrophysiology identified the sensory and motor gyri using neuronavigation based on sulcal anatomy. We quantified the most discriminatory time points in SSEPs temporal profile between the primary motor (M1) and somatosensory (S1) cortex using the Fisher discrimination criterion. We visualized the amplitude gradient of the SSEP over a 2D heat map to provide visual feedback for the delineation of the CS based on electrophysiology. Subsequently, we employed spectral clustering using the entire the SSEP waveform without selecting any time points and grouped ECoG channels in an unsupervised fashion. Main results. Consistently in all patients, two different time points provided almost equal discrimination between anterior and posterior channels, which vividly outlined the CS when we viewed the SSEP amplitude distribution as a spatial 2D heat map. The first discriminative time point was in proximity to the conventionally favored ∼20 ms peak (N20), and the second time point was slightly later than the markedly high ∼30 ms peak (P30). Still, the location of these time points varied noticeably across subjects. Unsupervised clustering approach separated the anterior and posterior channels with an accuracy of 96.3% based on the time derivative of the SSEP trace without the need for a subject-specific time point selection. In contrast, the raw trace resulted in an accuracy of 88.0%. Significance. We show that the unsupervised clustering of the SSEP trace assessed with subdural electrode grids can delineate the CS automatically with high precision, and the constructed heat maps can localize the motor cortex. We anticipate that the spatiotemporal patterns of SSEP fused with machine learning can serve as a useful tool to assist in surgical planning.

A translational study of somatosensory evoked potential time-frequency components in rats, goats, and humans.

Somatosensory evoked potentials (SEPs) have been widely used to assess neurological function in clinical practice. A good understanding of the association between SEP signals and neurological function is helpful for precise diagnosis of impairment location. Previous studies on SEPs have been reported in animal models. However, few studies have reported the relationships between SEP waveforms in animals and those in humans. In this study, we collected normal SEP waveforms and decomposed them into specific time-frequency components (TFCs). Our results showed three stable TFC distribution regions in intact goats and rats and in humans. After we induced spinal cord injury in the animal models, a greater number of small TFC distribution regions were observed in the injured goat and rat groups than in the normal group. Moreover, there were significant correlations (P < 0.05) and linear relationships between the main SEP TFCs of the human group and those of the goat and rat groups. A stable TFC distribution of SEP components was observed in the human, goat and rat groups, and the TFC distribution modes were similar between the three groups. Results in various animal models in this study could be translated to future clinical studies based on SEP TFC analysis. Human studies were approved by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (approval No. UM 05-312 T/975) on December 5, 2005. Rat experiments were approved by the Committee on the Use of Live Animals in Teaching and Research of Li Ka Shing Faculty of Medicine of the University of Hong Kong (approval No. CULART 2912-12) on January 28, 2013. Goat experiments were approved by the Animal Ethics Committee of Affiliated Hospital of Guangdong Medical University (approval No. GDY2002132) on March 5, 2018.

Intra-operative neurophysiological monitoring in patients with dystrophic neurofibromatosis type 1 scoliosis

Objective To analyse the intra-operative neurophysiological monitoring (IONM) data in patients with dystrophic neurofibromatosis type 1 (NF1) associated scoliosis, and to investigate the possible risk factors for failed IONM monitoring. Methods Patients undergoing posterior spinal fusion from September 2015 to December 2019 were retrospectively reviewed. The latency (P37, N50) and amplitude of somatosensory evoked potentials (SEP) in bilateral lower extremities, latency and amplitude of motor evoked potentials (MEP) in bilateral lower extremities and unilateral upper extremity were recorded. The neurological status, curve pattern, Cobb angle of main curve, vertebral rotatory subluxation and dystrophic features at pre-operation were assessed for each patient. The failed IONM monitoring was defined as no reliable SEP or MEP waveforms of all monitored muscles. Results A total of 92 patients (53 M, 39 F) with an average age of 14.1 ± 2.7 years were included. Failed IONM monitoring was identified in 17 patients with overall success rates being 87.0 and 94.6% for SEP and MEP. The average P37 latency, N50 latency, SEP amplitude and MEP latency showed no significant difference between concave and convex sides (p > 0.05 for all). The MEP amplitudes of lower extremities were lower on concave side than convex side (334.5 ± 291.9 µV VS 417.5 ± 380.5 µV, p = 0.030). Higher risk of failed IONM monitoring was found in patients with neurological deficit (p = 0.014) and more dystrophic features (p = 0.002) at pre-operation. Conclusions The overall success rates were 87.0% for SEP and 94.6% for MEP in patients with NF1-associated scoliosis. Neurological deficit and more dystrophic features at pre-operation indicated higher risk of failed IONM monitoring.

Altered somatosensory evoked potentials associated with improved reaction time in a simple sensorimotor response task following repetitive practice.

IntroductionRepetitive practice of sensorimotor tasks is widely used for neurorehabilitation; however, it is unknown how practice alters sensory processing (e.g., recognition, discrimination, and attentional allocation) and associated cognitive processing, such as decision‐making. The purpose of this study was to investigate whether long‐latency somatosensory evoked potentials (SEPs) reflecting sensory processing, attention, and decision‐making are altered by sensorimotor learning.MethodsFifteen participants performed a simple sensorimotor response task (thumb opposition in response to surface electrical stimulation), with experimental recording sessions before and after three days of practice. We then compared multiple SEP waveforms and reaction times (RTs) between pre‐ and postpractice trials.ResultsThe RT was reduced after practice of three days, and we found a significant positive correlation between ΔRT and ΔN140lat at F3, Cz, and C3′, ΔRT and ΔN250lat at F3, and there was a significant negative correlation between ΔRT and ΔP300amp at C3′.ConclusionThe present study suggests that motor learning improves somatosensory processing and attentional allocation via neuroplasticity and that these alterations are reflected by specific SEP changes.

Somatosensory Evoked Responses Elicited by Haptic Sensations in Midair

The design of human-machine interfaces (HMIs) by virtual haptics is an emerging field of research. So far, the perception of virtual haptic feedback, e.g., generated by focused ultrasound in midair has not been objectively evaluated. This paper demonstrates the feasibility of eliciting somatosensory evoked potentials (SEPs) with ultrasonic stimuli in midair for the first time. The palm was stimulated by short ultrasonic focal points generated by an ultrasound board. The results are compared with a no stimulation condition as well as with the results of a vibro tactile stimulation. The SEPs are analyzed with the wavelet phase synchronization stability (WPSS) and the M-consecutive averaged WPSS. The results indicate a clear SEP waveform elicited by ultrasound. It can be significantly differentiated from a no stimulation condition by the M-consecutive averaged WPSS. These results could enable the possibility of developing an objective evaluation method for virtual haptic feedback in HMIs.

F103. Interside latency differences in somatosensory evoked potentials of inguinal nerves

Damage to the inguinal nerves (INs) can occur with surgical treatment of hernias and after other abdominal surgeries. Somatosensory evoked potentials (SSEP) may be used to document neurophysiological injury of the INs. Given the overlap of the sensory territories of the INs and their anatomical variations, limits of the interside latency differences may be the most valuable parameter when interpreting asymmetric SSEP recordings of the INs. The aim of this study was to analyze the normal upper limits of interside latency differences of SSEP from the ilioinguinal nerve (IIN), the iliohypogastric nerve (IHN) and the genitofemoral nerve (GFN) to determine asymmetry in normal subjects. We performed a prospective study in 87 healthy subjects aged 17–75 years (mean age ± SD, 48.9 ± 15.1; 47 females and 40 males) with no neurological disorders or groin pain. Cortical SSEP waveforms derived from the Cz’ -FPz montage were obtained by electrical stimulation of the INs. The stimulating electrodes were placed (1) In the skin over the inguinal ligament for IIN-SSEP; (2) In the skin of the hypogastric region, 2.5 cm. above the subcutaneous inguinal ring for IHN-SSEP; and (3) In the skin over the medial upper leg for GFN-SSEP, respectively. We analyzed the latencies of P37 waves and the amplitude of P37 for IIN, IHN and GFN SEP bilaterally. The interside differences for these parameters were calculated and analyzed. We obtained reproductible evoked responses of the three INs in all subjects. We found an upper limit (95%) for the interside latency differences from SSEP of 2.0 ms for IIN, 1.9 ms for IHN and 2.1 ms for GFN. No effects of age, sex or height were noted in the determination of the upper limits. The ratio of the smaller amplitude to the bigger amplitude less than 50% was present in up to 35% of the INs SSEP recordings. Reproductible SSEPs of the INs can be obtained in healthy adults with little side-to-side difference. The presented reference values of interside differences of SSEP latencies enable a more thorough comparison with patient data in cases of suspected inguinal neuralgia.

The effects of subclinical neck pain on sensorimotor integration following a complex motor pursuit task.

Recurrent subclinical neck pain (SCNP) may be associated with neural plastic changes in sensory processing and sensorimotor integration (SMI); however, its impact on motor learning has not been investigated. The aim of this study was to investigate whether SCNP alters neural markers of SMI during a complex motor acquisition task as compared to a healthy control group. Peripheral N9, spinal N13, brainstem N18, and cortical N20, P25, N24 and N30 early somatosensory evoked potentials (SEPs) were recorded following median nerve stimulation for 24 participants (12 control and 12 SCNP) before and after a 10-min tracing motor task intervention. Retention was assessed 24-48h later. Significant amplitude differences were observed for both N18 and N24 SEP waveforms between groups, indicating there may be a difference in SMI due to altered afferent input as a result of SCNP. Accuracy increased significantly for both groups post-motor training; however, at retention only the control group showed an additional increase in accuracy. Both N18 and N24 SEP peaks are linked with cerebellar pathways, suggesting that SCNP impacts these connections. Significant correlations between these peaks and performance data were also seen. The differential changes in neurophysiological markers of SMI seen in SCNP suggest that SEPs have the potential to be used as an early screening tool for those at risk of having maladaptive neural plastic changes in response to motor training as a result of SCNP.

Automatic Parametrization of Somatosensory Evoked Potentials With Chirp Modeling.

In this paper, an approach using polynomial phase chirp signals to model somatosensory evoked potentials (SEPs) is proposed. SEP waveforms are assumed as impulses undergoing group velocity dispersion while propagating along a multipath neural connection. Mathematical analysis of pulse dispersion resulting in chirp signals is performed. An automatic parameterization of SEPs is proposed using chirp models. A Particle Swarm Optimization algorithm is used to optimize the model parameters. Features describing the latencies and amplitudes of SEPs are automatically derived. A rat model is then used to evaluate the automatic parameterization of SEPs in two experimental cases, i.e., anesthesia level and spinal cord injury (SCI). Experimental results show that chirp-based model parameters and the derived SEP features are significant in describing both anesthesia level and SCI changes. The proposed automatic optimization based approach for extracting chirp parameters offers potential for detailed SEP analysis in future studies. The method implementation in Matlab technical computing language is provided online.

MEP Latencies Predict the Neuromodulatory Effect of cTBS Delivered to the Ipsilateral and Contralateral Sensorimotor Cortex.

BackgroundRecently, it was shown that the highly variable after-effect of continuous theta-burst stimulation (cTBS) of the primary motor cortex (M1) can be predicted by the latency of motor-evoked potentials (MEPs) recorded before cTBS. This suggests that at least part of this inter-individual variability is driven by differences in the neuronal populations preferentially activated by transcranial magnetic stimulation (TMS).MethodsHere, we recorded MEPs, TMS-evoked brain potentials (TEPs) and somatosensory-evoked potentials (SEPs) to investigate the effects of cTBS delivered over the primary sensorimotor cortex on both the ipsilateral and contralateral M1, and the ipsilateral and contralateral primary somatosensory cortex (S1).ResultsWe confirm that the after-effects of cTBS can be predicted by the latency of MEPs recorded before cTBS. Over the hemisphere onto which cTBS was delivered, short-latency MEPs at baseline were associated with an increase of MEP magnitude (i.e. an excitatory effect of cTBS) whereas late-latency MEPs were associated with reduced MEPs (i.e. an inhibitory effect of cTBS). This relationship was reversed over the contralateral hemisphere, indicating opposite effects of cTBS on the responsiveness of the ipsilateral and contralateral M1. Baseline MEP latencies also predicted changes in the magnitude of the N100 wave of TEPs elicited by stimulation of the ipsilateral and contralateral hemisphere, indicating that this TEP component is specifically dependent on the state of M1. Finally, there was a reverse relationship between MEP latency and the effects of cTBS on the SEP waveforms (50–130 ms), indicating that after-effects of cTBS on S1 are opposite to those on M1.ConclusionTaken together, our results confirm that the variable after-effects of cTBS can be explained by differences in the neuronal populations activated by TMS. Furthermore, our results show that this variability also determines remote effects of cTBS in S1 and the contralateral hemisphere, compatible with inter-hemispheric and sensorimotor interactions.

Baseline and alert level of somatosensory evoked potential monitoring in scoliosis surgery

To explore the choice of timing for baseline and alert levels of somatosensory evoked potential (SEP) monitoring during scoliosis surgery. From March 2011 to December 2014, a total of 113 patients with kyphoscoliosis deformity were monitored intraoperatively by SEP. There were 52 males and 61 females with a mean age of (20 ± 15) years. All the patients were recorded preoperativeandintraoperative SEPs on double lower limbs. Latency and amplitude of SEPs were recorded after anesthesia and vertebral laminae exposure respectively and compared with each other. Intraoperative SEPs were compared to baseline as SEP after exposure and divided into 4 groups of A (<40%), B (40%-50%), C (50%-60%) and D (>60%) according to the reduced amplitude. Nerve functions were recorded during follow-ups. Significant statistical difference existed between SEPs post-anesthesia and SEPs after vertebral laminae exposure (P < 0.01). Compared with SEP post-anesthesia, the latency of SEP after exposure was prolonged with (3.28 ± 1.72) ms (left lower limb) and (3.30 ± 2.09) ms (right lower limb) and amplitude decreased with 0.17(0.39) µV (left lower limb) and 0.19(0.40) µV (right lower limb). There was a positive relationship of impaired nerve function between groups C and D (P < 0.05). Adopting SEP waveform after exposure as a baseline can improve the accuracy of SEP monitoring during scoliosis surgery. Intraoperative alarm with a reduced amplitude over 50% as the standard may be too sensitive. Alert with a reduced amplitude of over 60% reduces the false positive rate of alarm.

Exploring The Mechanisms Of Exercise-induced Hypoalgesia Using Somatosensory Evoked Potentials

The effects of acute exercise on reducing pain in healthy individuals are well documented, but the underlying mechanisms are unclear. PURPOSE: To explore the mechanisms of exercise-induced hypoalgesia (EIH) using neurophysiological techniques. METHODS: Somatosensory evoked potentials (SEPs) and pressure pain thresholds (PPTs) were assessed in 16 healthy volunteers before and after a 3 min sustained isometric contraction of the right elbow flexors at 40% maximal voluntary force. Procedures were repeated in the same session before and after an equivalent period of quiet rest in a counterbalanced design. Pressure pain thresholds were assessed using algometry over the biceps brachii and first dorsal interosseous muscles on the right side of the body. Somatosensory evoked potentials were recorded using electroencephalography (EEG) at four sites (Cz, Fz, Pz and C3; 10-20 International System) in response to non-painful and painful electrical stimulation of the digital nerve of the right index finger. The SEP waveforms were averaged from responses to ∼500 stimuli and the peak-to-peak amplitude of the N2P2 component of the potential was measured. Electrode impedance was recorded throughout the experiment. Effect sizes (unbiased Cohen’s d) and 95% confidence intervals were calculated to permit statistical comparisons between conditions. RESULTS: There was a large and moderate effect, respectively, of isometric exercise on increasing PPT at the bicep (0.84, 0.45 to 1.3) and first dorsal interosseous muscles (0.56, 0.28 to 0.9), indicative of EIH. There was no effect of exercise on SEP amplitude (-0.02, -0.23 to 0.19). This was despite clear modulation of SEP amplitude in response to different intensities of electrical stimulation and accompanying pain for each participant (-1.18, -1.89 to -0.58). CONCLUSIONS: N2P2 peak-to-peak amplitude did not change following exercise, although increased PPTs demonstrated clear EIH. The most parsimonious explanation is that electrically activating the axons of sensory neurons to evoke pain potentials in the EEG bypassed their receptors (nociceptors) and that these receptors are involved in EIH. Changes in the sensitivity of peripheral nociceptors might be the primary mechanism of EIH.

Neurophysiological Monitoring During Spinal Cord Stimulator Placement Surgery.

The objective of this retrospective study was to study the frequency of intraoperative neuromonitoring (IONM) alerts during the spinal cord stimulator (SCS) placement surgery, postoperative neurological complications and effectiveness of Somatosensory evoked potential (SSEP) and electromyography (EMG) methods to determine laterality of the SCS lead placement. Records of 111 consecutive SCS placement surgeries monitored by a commercial IONM company between August 1, 2013 and December 31, 2013 were reviewed. IONM alerts, surgical interventions, and patient outcomes were assessed. Significant decreases of lower extremity SSEPs following the placement of the SCS paddle electrodes into the epidural space were recorded in two (1.9%) patients prompting alerts to the surgeons and removal of the electrode. Somatosensory system dysfunction due to stimulated limb malpositioning was identified by continuous SSEP in four cases (3.8%). All waveform changes resolved and SSEP waveforms returned back to baselines in all six patients after adjustments were made. There was no evidence of sustained neurological injury in any patients in this study. The location of the stimulator was adjusted based on IONM feedback in 8/43 (18.6%) cases. IONM is an effective tool in detecting potential neurological event and facilitating lead placement and potentially avoiding revision surgery.

Intraoperative changes in transcranial motor evoked potentials and somatosensory evoked potentials predicting outcome in children with intramedullary spinal cord tumors

Intraoperative dorsal column mapping, transcranial motor evoked potentials (TcMEPs), and somatosensory evoked potentials (SSEPs) have been used in adults to assist with the resection of intramedullary spinal cord tumors (IMSCTs) and to predict postoperative motor deficits. The authors sought to determine whether changes in MEP and SSEP waveforms would similarly predict postoperative motor deficits in children. The authors reviewed charts and intraoperative records for children who had undergone resection for IMSCTs as well as dorsal column mapping and TcMEP and SSEP monitoring. Motor evoked potential data were supplemented with electromyography data obtained using a Kartush microstimulator (Medtronic Inc.). Motor strength was graded using the Medical Research Council (MRC) scale during the preoperative, immediate postoperative, and follow-up periods. Reductions in SSEPs were documented after mechanical traction, in response to maneuvers with the cavitational ultrasonic surgical aspirator (CUSA), or both. Data from 12 patients were analyzed. Three lesions were encountered in the cervical and 7 in the thoracic spinal cord. Two patients had lesions of the cervicomedullary junction and upper spinal cord. Intraoperative MEP changes were noted in half of the patients. In these cases, normal polyphasic signals converted to biphasic signals, and these changes correlated with a loss of 1-2 grades in motor strength. One patient lost MEP signals completely and recovered strength to MRC Grade 4/5. The 2 patients with high cervical lesions showed neither intraoperative MEP changes nor motor deficits postoperatively. Dorsal columns were mapped in 7 patients, and the midline was determined accurately in all 7. Somatosensory evoked potentials were decreased in 7 patients. Two patients each had 2 SSEP decreases in response to traction intraoperatively but had no new sensory findings postoperatively. Another 2 patients had 3 traction-related SSEP decreases intraoperatively, and both had new postoperative sensory deficits that resolved. One additional patient had a CUSA-related SSEP decrease intraoperatively, which resolved postoperatively, and the last patient had 3 traction-related sensory deficits and a CUSA-related sensory deficit postoperatively, none of which resolved. Intraoperative TcMEPs and SSEPs can predict the degree of postoperative motor deficit in pediatric patients undergoing IMSCT resection. This technique, combined with dorsal column mapping, is particularly useful in resecting lesions of the upper cervical cord, which are generally considered to be high risk in this population. Furthermore, the spinal cord appears to be less tolerant of repeated intraoperative SSEP decreases, with 3 successive insults most likely to yield postoperative sensory deficits. Changes in TcMEPs and SSEP waveforms can signal the need to guard against excessive manipulation thereby increasing the safety of tumor resection.

Outcomes of Combined Somatosensory Evoked Potential, Motor Evoked Potential, and Electroencephalography Monitoring during Carotid Endarterectomy

While much has been written about multiple methods of neuromonitoring during carotid endarterectomy (CEA), there has been relatively little discussion of the use of triple monitoring via somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in conjunction with electroencephalography (EEG). Our objective was to evaluate the rate of detection and prevention of neurologic events by multinerve SEP, MEP, and EEG in patients undergoing CEA while under general anesthesia. A prospective study of 181 consecutive patients undergoing CEA between June 2005 and September 2010 was reviewed. Intraoperative changes, including a 50% reduction in the amplitude of SEP waveforms, loss of MEP, and/or a 50% change in EEG frequency were noted as indications for shunting. This was correlated with the actual use of intraoperative shunting and postoperative neurologic sequelae at both 24 hours and 30 days. Median and tibial nerve SEPs and MEPs were also correlated. Eleven patients (6%) experienced intraoperative monitoring changes (SEP: 11/11; MEP: 6/11). Five of 11 patients with MEP/SEP changes underwent shunting, while the other 6 had normalization with the elevation of their blood pressure. Of the 11 patients that had neurophysiologic changes, 54% (6/11) were patients with symptomatic disease. No patients had significant EEG changes. The total shunt rate was 2.7% (5/181). No postoperative neurologic sequelae were noted. The ratio of shunting at 2.7% is equal to the lowest rates reported in the awake patient literature. Interestingly, the predicted synergy of multimodality monitoring cannot be directly attributed to an increased specificity resulting from the addition of SEP and MEP to EEG, because no patients had EEG changes. In addition, in today's cost-conscious world of health care, our results do not justify implementing this particular technique of neuromonitoring across the board-but it is apparent that the combination of these 3 modalities is both safe and effective with potential applications in symptomatic patients.

Comparison of somatosensory evoked potentials between adolescent idiopathic scoliosis and congenital scoliosis without neural axis abnormalities

Background contextAbnormal somatosensory evoked potentials (SEPs) have been documented in patients with adolescent idiopathic scoliosis (AIS) with different cure severity. However, few studies investigated whether abnormal SEPs were the cause or effect of idiopathic scoliosis. PurposeThe purpose of this study was to investigate the significance of abnormal SEPs in patients with AIS, and to explore its effect on the etiopathogenesis of AIS. Study design/SettingThis study evaluated SEPs in patients with AIS and congenital scoliosis (CS) with similar curve pattern and severity both in coronal and sagittal planes. Patient sampleFemale patients with AIS and CS in our spine surgery center from 2000 to 2009 were recruited for this study. Outcome measuresRate of abnormal SEPs. MethodsPosterior tibial nerve SEPs (PTN-SEPs) were performed on female patients with AIS and CS. The inclusion criteria were patients with AIS with a Lenke type 1 curve and patients with CS with right thoracic curve (apex between T5 and T12) and normal sagittal profile (kyphosis less than 50° measured from T2 to T12). All patients were evaluated with total spine magnetic resonance imaging, and those with neural axis abnormalities were excluded. The patients with neurological deficits on detailed physical examination were also excluded. Absence of SEPs waveforms or prolongation of peak latency or asymmetrical peak latency were defined as pathological change. The incidence of pathological SEPs and clinical characteristics were compared between patients with AIS and patients with CS. ResultsForty-six patients with AIS and 33 patients with CS were included in this study. There was no significant difference in coronal and sagittal Cobb angle between the two groups. The rate of abnormal SEPs was 32.6% (15/46) and 12.1% (4/33) in AIS and CS groups, respectively, and the difference was statistically significant (p<.05). ConclusionSomatosensory pathway dysfunction could be found in both AIS and CS without neural axis abnormalities, and the patients with AIS tended to have higher rates of somatosensory disorders than patients with CS with similar scoliosis curve, which indicates that both scoliosis curve and primary etiopathogenic factor contribute to the sensory deficit in patients with AIS.