Somatosensory Evoked Potentials Data Research Articles

Standardized Kalman filtering for dynamical source localization of concurrent subcortical and cortical brain activity

ObjectiveWe introduce standardized Kalman filtering (SKF) as a new spatiotemporal method for tracking brain activity. Via the Kalman filtering scheme, the computational workload is low, and by spatiotemporal standardization, we reduce the depth bias of non-standardized Kalman filtering (KF). MethodsWe describe the standardized KF methodology for spatiotemporal tracking from the Bayesian perspective. We construct a realistic simulation setup that resembles activity due to somatosensory evoked potential (SEP) to validate the proposed methodology before we run our tests using real SEP data. ResultsIn the experiments, SKF was compared with standardized low-resolution brain electromagnetic tomography (sLORETA) and the non-standardized KF. SKF localized the cortical and subcortical SEP originators appropriately and tracked P20/N20 originators for investigated signal-to-noise ratios (25, 15, and 5 dB). sLORETA distinguished those for 25 and 15 dB suppressing the subcortical originators. KF tracked only the evolution of cortical activity but mislocalized it. ConclusionsThe numerical results suggest that SKF inherits the estimation accuracy of sLORETA and traceability of KF while producing focal estimates for SEP originators. SignificanceSKF could help study time-evolving brain activities and localize landmarks with a deep contributor or when there is no prior knowledge of evolution.

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.

Cathodal Genesis of Ipsilateral Hand (Crossover) Motor Evoked Potentials: Evidence from a Patient with Previous Stroke

ABSTRACT A case is described where baseline transcranial electrical motor evoked potentials (TcMEP) and somatosensory evoked potentials (SSEP) results were unilaterally absent in a patient with previous hemispheric stroke undergoing a right-sided carotid endarterectomy. SSEP data confirmed right cortical pathology and excluded a technical rationale for absent motor evoked responses. Attempts at generating left-hand (contralateral) TcMEP from right cortical anodal stimulation failed despite high stimulus intensities. However, TcMEP responses from anodal stimulation of the right cortex were recorded from the right-hand (ipsilateral) which were attributed to “crossover.” Ipsilateral TcMEP onset latencies derived from the stimulus-response data supports the idea that crossover is a product of cathodal stimulation initially acting on pericortical motor pathways.

Anatomical and neurophysiological localization of the leg motor area at the medial central sulcus

ObjectiveThe exact location of the leg motor area is still in debate due to the lack of landmarks such as ‘precentral knob’ in the medial cortex. This study tried to identify the leg motor area based on intraoperative neurophysiological data and neuroimaging techniques. MethodsIntraoperative data of somatosensory evoked potential (SEP) elicited by tibial nerve stimulation and motor evoked potential (MEP) of the leg muscles induced by direct cortical stimulation were recorded using subdural electrodes placed in the medial cortex. We displayed the neurophysiological data on the individual MR images and the MNI52. ResultsDefinite N40-P40 phase reversal was observed with the shallow grooves in the medial cortex in 5 cases. Leg MEP was successfully obtained in all 12 cases preserving the leg motor function. Superimposed SEP and leg MEP data on the MNI152 indicated the leg motor area was predominantly located in the posterior two-thirds between the vertical lines passing through the anterior commissure and the posterior commissure (VCP). ConclusionsOur study revealed the location of the leg motor area and the presence of the ‘medial central sulcus’ in the medial cortex. SignificanceThe VCP can be useful landmark to identify the sensorimotor border in the medial cortex.

Feasibility of non-invasive recording of somatosensory evoked potential in pigs

BackgroundNon-invasive measurement of somatosensory-evoked potentials (SEP) in a large animal model is important to translational cognitive research. We sought to develop a methodology for neurophysiological recording via a transcranial electroencephalography (EEG) cap under an effective sedative regimen with dexmedetomidine, midazolam, and butorphanol that will produce sedation instead of anesthesia while not compromising data quality.ResultsPigs received intramuscular dexmedetomidine, midazolam, and butorphanol for SEP assessment with peroneal nerve stimulation. Semi-quantitative sedation assessment was performed after the animal was sufficiently sedated and 30 min later, during the transcranial SEP recording. SEP data were analyzed with commercial software. Binary qualitative analysis of the recording was categorized by an experienced neurophysiologist. All four animals had adequate surface SEP recordings. Animals received 43 [21–47] mcg/kg of dexmedetomidine, 0.3 [0.2–0.3] mg/kg of midazolam, and 0.3 [0.3–0.3] mg/kg of butorphanol IM. All treatments resulted in moderate to deep sedation (Baseline median sedation score 11.5 [11–12]; median score at 30 min: 11.5 [10.5–12]). Heart rate (median [range]) (55 [49–71] beats per minute), respiratory rate (24 [21–30] breaths per minute), and hemoglobin oxygen saturation (99 [98–100]%) and body temperature (37.7 [37.4–37.9] °C) remained within clinically acceptable ranges. There were no undesirable recovery incidents.ConclusionsIn this pilot study, we demonstrate the feasibility of SEP recording via a transcranial EEG cap under an effective sedative regimen in pigs. Our approach will expand the use of a large animal model in neurotranslational research.

Reconstructing subcortical and cortical somatosensory activity via the RAMUS inverse source analysis technique using median nerve SEP data

This study concerns reconstructing brain activity at various depths based on non-invasive EEG (electroencephalography) scalp measurements. We aimed at demonstrating the potential of the RAMUS (randomized multiresolution scanning) technique in localizing weakly distinguishable far-field sources in combination with coinciding cortical activity. As we have shown earlier theoretically and through simulations, RAMUS is a novel mathematical method that by employing the multigrid concept, allows marginalizing noise and depth bias effects and thus enables the recovery of both cortical and subcortical brain activity. To show this capability with experimental data, we examined the 14–30 ms post-stimulus somatosensory evoked potential (SEP) responses of human median nerve stimulation in three healthy adult subjects. We aim at reconstructing the different response components by evaluating a RAMUS-based estimate for the primary current density in the nervous tissue. We present source reconstructions obtained with RAMUS and compare them with the literature knowledge of the SEP components and the outcome of the unit-noise gain beamformer (UGNB) and standardized low-resolution brain electromagnetic tomography (sLORETA). We also analyzed the effect of the iterative alternating sequential technique, the optimization technique of RAMUS, compared to the classical minimum norm estimation (MNE) technique. Matching with our previous numerical studies, the current results suggest that RAMUS could have the potential to enhance the detection of simultaneous deep and cortical components and the distinction between the evoked sulcal and gyral activity.

Modulation of the Somatosensory Evoked Potential by Attention and Spinal Cord Stimulation.

Introduction: Spinal Cord Stimulation (SCS) is a last-resort treatment for patients with intractable chronic pain in whom pharmacological and other treatments have failed. Conventional tonic SCS is accompanied by tingling sensations. More recent stimulation protocols like burst SCS are not sensed by the patient while providing similar levels of pain relief. It has been previously reported that conventional tonic SCS can attenuate sensory-discriminative processing in several brain areas, but that burst SCS might have additional effects on the medial, motivational-affective pain system. In this explorative study we assessed the influence of attention on the somatosensory evoked brain responses under conventional tonic SCS as well as burst SCS regime.Methods: Twelve chronic pain patients with an implanted SCS device had 2-weeks evaluation periods with three different SCS settings (conventional tonic SCS, burst SCS, and sham SCS). At the end of each period, an electro-encephalography (EEG) measurement was done, at which patients received transcutaneous electrical pulses at the tibial nerve to induce somatosensory evoked potentials (SEP). SEP data was acquired while patients were attending the applied pulses and while they were mind wandering. The effects of attention as well as SCS regimes on the SEP were analyzed by comparing amplitudes of early and late latencies at the vertex as well as brain activity at full cortical maps.Results: Pain relief obtained by the various SCS settings varied largely among patients. Early SEP responses were not significantly affected by attention nor SCS settings (i.e., burst, tonic, and sham). However, late SEP responses (P300) were reduced with tonic and burst SCS: conventional tonic SCS reduced P300 brain activity in the unattended condition, while burst SCS reduced P300 brain activity in both attended and unattended conditions.Conclusion: Burst spinal cord stimulation for the treatment of chronic pain seems to reduce cortical attention that is or can be directed to somatosensory stimuli to a larger extent than conventional spinal cord stimulation treatment. This is a first step in understanding why in selected chronic pain patients burst SCS is more effective than tonic SCS and how neuroimaging could assist in personalizing SCS treatment.

Trading baseline with forelimbs somatosensory evoked potential for longitudinal analysis in thoracic transection spinal cord injury

Patients who suffered from spinal cord injury (SCI) that come to healthcare professionals for diagnosis and treatment do not have electrophysiology baseline of somatosensory evoked potential (SSEP). The SSEP has always been used in research for data comparison to detect onset and severity of the SCI as well as for assessing its progress, endogenous and therapeutic recovery. This unmet need has motivated us to develop a new tool to substitute the baseline data with forelimb SSEP data of the same day. In this study, we report the development and investigation of three distinctive thoracic transections (right T10 hemi-transection (Rxl), left T8 and right T10 double hemi-transection (Dxl) and T8 complete transection (Cxl)) spinal cord injuries in an adult rat model. We used our well-established monitoring methods to obtain SSEP baselines as well as post-injury signals from days 4, 7, 14 and 21. We observed that spectral coherences obtained from non-injured spinal cord pathways are always above 0.8. The spectral coherence is dimensionless measure with values between 0 and 1 and measures the correlation between two time signals in the frequency domain. Analysis of variance (ANOVA) results also showed that there is a significant difference between the spectral coherence componanet means before and after injury with reaching p = 0.05 for Rxl, p = 0.02 for DxI, and p = 0.00 for CxI. Our signal processing enables us to replicate comparable detection of the natural history of injuries longitudinally without the implication of baseline SSEP signals, highlighting the potential of this analysis method for clinical studies.

Neurophysiological Findings and Brain Injury Pattern in Patients on ECMO.

Introduction. Brain injury is a major determinant of outcomes in extracorporeal membrane oxygenation (ECMO). Neurologic prognostication in ECMO has not been established. Absent electroencephalogram (EEG) reactivity and absent N20 on somatosensory evoked potential (SSEP) are associated with poor outcome in other types of brain injuries, especially following cardiopulmonary arrest. It is currently known if the same criteria are applicable in patients on ECMO. Methods. Continuous EEG (cEEG) was performed for patients with a Glasgow Coma Scale (GCS) <8 and SSEP data were performed for patients with a motor GCS < 4 in a prospective observational cohort undergoing ECMO at a tertiary center. EEG variables including reactivity were collected. SSEPs were categorized into absence, delay, or presence of N20. Poor outcome was defined as cerebral performance category 3 to 5 at discharge. Results. We present 13 consecutive patients who underwent both cEEG and SSEP. The median time from cannulation to EEG and SSEP were 3 (interquartile range [IQR] = 1-6) and 5 (IQR = 2-7) days, respectively. All patients were in coma and 12 (92%) had poor outcomes. Ten (77%) underwent brain computed tomography, the findings of which explained coma in only 2. Patients (n = 12) with poor outcome had poor variability, absent reactivity, and lack of sleep features with diffusely slow theta-delta background on the EEG. Despite poor outcomes, all had relatively preserved or normal N20 responses. One patient with preserved reactivity and sleep features on the EEG and intact SSEP had a good outcome. Conclusions. Absent EEG reactivity with the preservation of SSEP N20 was associated with poor outcome in comatose ECMO patients. We advise caution in interpreting electrophysiological tests in prognosticating ECMO patients until the patterns and outcomes are better understood.

Giant somatosensory evoked potentials are uncommon in patients with post-anoxic coma and paroxysmal electroencephalographic activity

Objectives Post-anoxic encephalopathy (PAE) is a severe neurological condition associated with poor outcome. As part of a multi-modal evaluation, electrophysiological investigations such as electroencephalography (EEG) and somatosensory evoked potentials (SSEPs) have been shown to be reliable outcome predictors in the assessment of comatose survivors, particularly with PAE [3] . The aim of the study was firstly to evaluate the feasibility of performing SSEPs in post-anoxic comatose patients with paroxysmal activity on EEG and secondly to assess the relationship between EEG cortical hyperexcitability and giant cortical N20 SSEPs responses. Methods In this retrospective study between 2016 and 2018, patients with PAE, paroxysmal activity on EEG and available median nerve SSEPs data were included in the analysis. Paroxysmal activity was identified on the EEG performed in the last 48 h preceding SSEPs. We evaluated the N20 amplitude from baseline, and P14-N20 and N20-P24 peak to peak amplitudes. Giant SSEPs were defined as a N20 exceeding 2.7 μV or N20–N24 exceeding 5.5 μV [2] or a late giant component exceeding 5 μV [1] . Results Twenty-one patients were included; 14 men (67%) mean age 66 ± 18 years. A total of 62% of PAE cases were due to cardiac arrest. Nineteen patients died following withdrawal of life support, one died spontaneously and one patient survived. Three patterns of EEG paroxysmal activity were identified: continuous rhythmic activity (n = 3), periodic generalized discharges (GPDs) on a low frequencies background (n = 12) and GPDs on a flat background (burst-suppression) (n = 6). SSEPs were giant in 3 patients (14%), normal in 7 patients (34%), reduced in 3 patients (14%) and absent bilaterally in 8 (38%). Conclusions Our study shows that performing SSEPs is feasible in PAE patients with EEG paroxysmal activity. Giant SSEPs are uncommon in these patients. The EEG cortical hyperexcitability reflects different stages of brain injury, as it can be associated with preserved (even giant), or absent SSEPs.

Platform Session – Evoked potentials & NIOM: Somatosensory evoked potentials and central motor conduction times help predict outcomes from deep brain stimulation (DBS) in children with dystonia

DBS of the Globus pallidus internus has dramatic benefits in primary dystonia. Responsiveness of secondary dystonia is more modest and varies markedly between individuals. Predictive markers are lacking and the underlying pathophysiology of secondary dystonia is poorly understood. We report Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) in children with dystonia and test the hypothesis that these parameters relate to outcome from DBS. Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary DBS assessment (mean age 10 years; range 2.5–19). Transcranial Magnetic Stimulation was applied to motor cortex and Motor Evoked Potentials were recorded in the activated contralateral hand and foot muscles. CMCT to each limb was calculated using the F-wave method. Median nerve SEPs were recorded over ipsilateral Erb’s point, 7th and 2nd cervical vertebrae and contralateral centroparietal scalp. Posterior tibial nerve SEPs were recorded over ipsilateral popliteal fossa and midline centroparietal scalp. A mid-frontal reference was used. Electrical stimuli of 0.2millisecond duration were applied at 2.1 Hz, just above motor threshold. SEPs were classed as abnormal if delayed, absent or of abnormal waveform. Technically unsatisfactory recordings were excluded. Structural abnormalities were assessed with cranial MRI. Outcome from DBS at 1 year was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). Of the 146 children with satisfactory CMCT data, 28(19%) had an abnormal CMCT to at least one limb. Of the 100 children with satisfactory cortical SEP data, 47 had at least one abnormal cortical potential. Abnormal CMCTs and SEPs were both observed more frequently in secondary than primary/primary plus dystonia (CMCT: 22% vs. 9%, SEP: 53% vs. 24%). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney p = 0.002) and in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney p = 0.001). On sub-group analysis, these relationships were preserved regardless of aetiology (primary versus secondary) or cranial imaging (normal vs abnormal MRI). CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia. Abnormal CMCTs and SEPs relate to DBS outcome, therefore contributing to patient selection and counselling of families about potential benefit from neuromodulation.

The FieldTrip-SimBio pipeline for EEG forward solutions

BackgroundAccurately solving the electroencephalography (EEG) forward problem is crucial for precise EEG source analysis. Previous studies have shown that the use of multicompartment head models in combination with the finite element method (FEM) can yield high accuracies both numerically and with regard to the geometrical approximation of the human head. However, the workload for the generation of multicompartment head models has often been too high and the use of publicly available FEM implementations too complicated for a wider application of FEM in research studies. In this paper, we present a MATLAB-based pipeline that aims to resolve this lack of easy-to-use integrated software solutions. The presented pipeline allows for the easy application of five-compartment head models with the FEM within the FieldTrip toolbox for EEG source analysis.MethodsThe FEM from the SimBio toolbox, more specifically the St. Venant approach, was integrated into the FieldTrip toolbox. We give a short sketch of the implementation and its application, and we perform a source localization of somatosensory evoked potentials (SEPs) using this pipeline. We then evaluate the accuracy that can be achieved using the automatically generated five-compartment hexahedral head model [skin, skull, cerebrospinal fluid (CSF), gray matter, white matter] in comparison to a highly accurate tetrahedral head model that was generated on the basis of a semiautomatic segmentation with very careful and time-consuming manual corrections.ResultsThe source analysis of the SEP data correctly localizes the P20 component and achieves a high goodness of fit. The subsequent comparison to the highly detailed tetrahedral head model shows that the automatically generated five-compartment head model performs about as well as a highly detailed four-compartment head model (skin, skull, CSF, brain). This is a significant improvement in comparison to a three-compartment head model, which is frequently used in praxis, since the importance of modeling the CSF compartment has been shown in a variety of studies.ConclusionThe presented pipeline facilitates the use of five-compartment head models with the FEM for EEG source analysis. The accuracy with which the EEG forward problem can thereby be solved is increased compared to the commonly used three-compartment head models, and more reliable EEG source reconstruction results can be obtained.

O135 Sensory evoked potentials and central motor conduction times in children with dystonia help predict outcomes from Deep Brain Stimulation (DBS)

Objectives Deep Brain Stimulation (DBS) of the Globus Pallidus Internus produces dramatic benefits in primary dystonia. Improvements in patients with secondary dystonia are smaller and vary markedly between individuals. Predictive markers are lacking. This study tests the hypothesis that Somatosensory Evoked Potentials (SEPs) and Central Motor Conduction Times (CMCT) may predict outcome from DBS in childhood dystonia. Methods Data were obtained from 180 consecutive children with dystonia undergoing multidisciplinary assessment for DBS (mean age 10 years; range 2.5–19). CMCT to each limb was obtained using Transcranial Magnetic Stimulation and the F-wave method. Median and posterior tibial nerve SEPs were recorded over contralateral and midline centro-parietal scalp. Technically unsatisfactory data were excluded. Structural abnormalities were assessed with cranial MRI. Outcome from DBS at 1 year was assessed as percentage improvement in Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS-m). Results Satisfactory CMCT data were obtained from 146 children, of whom 28 (19%) had an abnormal CMCT to at least one limb. Satisfactory cortical SEP data were obtained from 100 children, of whom 47 had at least one abnormal cortical potential. Abnormal CMCTs and SEPs were both observed more frequently in secondary than primary/primary plus dystonia (CMCT abnormal in 22% secondary versus 9% primary patients; SEP abnormal in 53% secondary vs 24% primary patients). Of children proceeding to DBS, improvement in BFMDRS-m was greater in those with normal (n = 78) than abnormal CMCT (n = 11) (Mann Whitney test p = 0.002) and was also greater in those with normal (n = 35) versus abnormal SEPs (n = 16) (Mann Whitney test p = 0.001). On sub-group analysis, the relationships between CMCT/SEPs and BFMDRS-m scores were independent of aetiology (primary versus secondary) and MRI findings (normal versus abnormal). Discussion/Conclusion CMCTs and SEPs provide objective evidence of motor and sensory pathway dysfunction in children with dystonia and relate to DBS outcome. These markers may therefore contribute to patient selection and counselling of families about potential benefit from neuromodulation. Significance We identify neurophysiological markers that can guide the selection of patients for DBS.

Alarm Value of Somatosensory Evoked Potential in Idiopathic Scoliosis Surgery

Somatosensory evoked potential (SSEP) monitoring is performed to examine postoperative clinical findings when a monitoring event was noted intraoperatively and to ascertain the alarm threshold for intraoperative neural damage. The tibial SSEP of both lower limbs was recorded intraoperatively in patients with idiopathic scoliosis. Change of SSEP amplitude as opposed to the baseline was categorized into 4 levels: decrease <40%, decrease of 40%-50%, decrease of 50%-60%, and decrease >60%. Postoperative neurologic function of patients was examined and compared with SSEP data. The baseline amplitude before incision was significantly different from the amplitude after spine exposure. An amplitude reduction of >60% during scoliosis correction procedures was observed in 6 legs, and 4 of them had postoperative deterioration in motor status. As the measure of threshold for alarm, an amplitude reduction of >50% compared with baseline resulted in more false-positive outcomes compared with amplitude attenuation of >60%. Compared with the traditional SSEP baseline before skin incision, the baseline acquired after spine exposure results in more accurate monitoring. A >60% decrease in SSEP amplitude could be a more suitable alarm threshold.

The features of sensorimotor integration in patients with levodopa-induced dyskinesia in Parkinson’s disease

Introduction. Parkinson’s disease (PD) is characterized not only by motor but also by a number of nonmotor symptoms, such as sensory, vegetative, and psycho-emotional disorders. Objective. To study the states of the somatosensory system and the sensorimotor integration in patients with levodopa-induced dyskinesia (LID). Materials and methods. Fifty-two patients with LID associated with PD (Hoehn and Yahr stage III–IV) and 29 patients free of dyskinesia were examined. The somatosensory evoked potentials (SSEPs) and blink reflex (BR) were studied. Results. LID in PD were observed significantly more often among females than among males. No differences in disease duration and duration of levodopa administration were observed among patients free of dyskinesia and patients with LID. In the group of patients with LID, MRI examination showed increased brainstem reflex excitability. The acceleration of signal passing from the medulla oblongata to the cortex revealed according to the SSEP data in this group of patients is indicative of the increased reflex excitability at the spinal cord and brainstem, thalamic, and cortical levels. Significant differences in passage of sensory information were found between the two patient groups. Hence, in patients with LID, the latency N20 was 20 (19.6; 21.3) ms; P18, 16.0 (15.1; 16.6) ms; and N13, 13.7 (13.1; 14.8) and was reliably shorter than in the group of patients free of LID, where the latency N20 was 20.9 (20; 21.4) ms; Р18, 16.9 (16.2; 17.6); and N13, 14.2 (13.5; 15.2) ms. Conclusions. The revealed alterations in parameters of blink reflex and SSEPs are hypothetically genetically determined in patients with LID. Objectification of these disorders at the earliest stages of the disease can help in assessing their role as predictor factors for development of LID. Allowance for these factors will make it possible to choose an appropriate treatment strategy and reduce the risk of complications associated with drug therapy.

POSSIBILITIES FOR ANTIEPILEPTIC DRUGS USE IN THE TREATMENT OF TIC HYPERKINESIS AND TOURETTE SYNDROME IN CHILDREN

Objective: to evaluate the efficacy of topiramate at a dose of 1–2 mg/kg in 34 patients aged 7–17 with tic hyperkinesis and Tourette syndrome (TS). Materials and methods. We performed clinical evaluation of hyperkinesis severity along with the assessment of somatosensory evoked potentials (SSEP) and the analysis of surface electromyography (EMG) data prior to treatment initiation and after 6 weeks of therapy. SSEP investigation was carried out in accordance with a standard protocol. Interpeak latencies on the tracks Cp–Fpz (D, S), Cerv6–Fpz (D, S), Erb’i–Erb’c (D, S) were evaluated in order to determine the afferentation between relevant brain structures: N9–N13, N13–N20, N9–N20. N20–P23 potentials reflected primary activity of somatosensory cortex. The investigation of tic hyperkinesis was conducted using surface EMG of facial muscles (m. orbicularis oculi), the muscles of the shoulder girdle (m. supraspinatus), and the muscles of the upper extremities (m. flexor digitorum superficialis) according to the standard protocol. Interference curve was recorded at rest and after hyperkinesis stimulation with the use of provocative tests. High-amplitude (more than 500 mkV) oscillations were considered as burst activity. The severity of clinical manifestations was evaluated using the Yale Global Tic Severity Scale (1989) and the method of tics counting during 20 minutes (V.P. Zykov, 2009). The control group comprised 15 healthy children matched for sex and age. Results. The use of topiramate in patients with chronic motor/vocal tics and TS has significantly decreased the severity of hyperkinesis manifestations, evaluated both by the Yale Global Tic Severity Scale (p < 0,05) and by the method of tics counting during 20 minutes (p < 0,05). It also helped to decrease the prevalence of burst activity in EMG while registering hyperkinesis in different muscle groups. SSEP data showed the normalization of interpeak latency values and the decrease of N20–P23 potentials amplitude, which reflects the decline in the activity of brain somatosensory system, represented by thalamo-cortical structures. Conclusion. Surface EMG and SSEP methods can be used for evaluation of treatment efficacy in cases of tic hyperkinesis and TS.

Diagnostic utility of somatosensory evoked potentials in chronic polyradiculopathy without electrodiagnostic signs of peripheral demyelination.

Diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) remains uncertain when nerve conduction studies (NCS) fail to show demyelination. We conducted a retrospective study of patients who presented with clinical criteria of CIDP in whom electrodiagnostic (EDx) criteria of definite or probable CIDP were missing [axonal sensorimotor neuropathy (n = 23), normal EDx with pure sensory presentation (n = 3)]. All patients received immunomodulatory treatment. Twenty-six patients were evaluated with somatosensory evoked potentials (SSEPs), MRI of spinal roots, cerebrospinal fluid analysis, and/or nerve biopsy. Diagnosis of CIDP was considered to be confirmed in patients who responded to immunotherapy. Twenty-two of 26 patients (85%) had SSEPs reflecting abnormal proximal conduction in sensory fibers, including 14 who had only clinical and SSEP data in favor of CIDP. SSEPs were abnormal in 16 of 20 responders (80%) to immunotherapy. SSEP recording contributes to the diagnosis of CIDP when nerve conduction studies fail to detect peripheral demyelination.

Brainstem auditory and somatosensory evoked potentials: a methodological study to evaluate the reproducibility of two devices

We aimed to determine whether statistical significant differences exist between the sets of results obtained from two devices used in our department for measuring brainstem auditory evoked potentials (BAEPs) and somatosensory evoked potentials (SEPs). We obtained BAEP and median and posterior tibial nerve SEP values bilaterally in ten healthy subjects. The tests were performed on the same subject using two devices consecutively. The equipment consisted of a Nicolet Viking-IV (Nicolet, Madison, WI, USA) and a Viking Select (Viasys Healthcare, Madison, WI, USA), and the same recording electrodes and stimulator (auditory and electrical) were used without modifying any postural position of the subject. The stimuli and recording parameters were the same for both devices. We obtained 20 sets of data for each type of test. The Bland–Altman plots as well as the one-sample t-test or Wilcoxon signed rank test were used to compare data between the two groups of data sets. We found no significant differences between the sets of values obtained with the two devices. Our analysis indicates that the two devices are equal in recording all different variables of BAEP and SEP, which allows us to combine the BAEP and SEP data obtained from the two devices for follow-up studies involving quantitative statistical methods.This study received institutional approval (protocol number PRAG-154/2013).

109. Multicenter evaluation of somatosensory evoked potentials (SEPs) normative data in infancy

Somatosensory evoked potentials (SEPs) represent a useful electrophysiological diagnostic tool in neuropediatry; normative data covering the full range of age, from neonate to adolescent, are rarely attainable from a single Laboratory. Purpose of the study was to collect normative data from several Laboratories to compare the reliability among laboratories; verify weather pooling of data can satisfy statistical requirement as if the data were collected in a single laboratory. Upper limbs and lower limbs SEP of 172 subjects from four Centers (Milan, Padua, Florence, Rome) were analysed. Age ranged from neonate to adolescents. Neonates and infants had a high variability of cortical responses; central conduction time (CCT) of the upper limbs was shorter than CCT of lower limbs; intra-spinal CCT of lower limbs was shorter than the cervical to cortical CCT; cortical upper limbs SEP grow faster than the lower limbs. The variability of cortical SEP in neonates and infancy probably reflects a variability of awake-sleep state but also the types of sensory fibres stimulated and the central sensory pathways organisation might play e role. Multicenter collection of SEP data is very useful to compare normative data, improve interpretation and deeper our knowledge on maturation of sensory systems.

Particle Swarm Optimization Applied to EEG Source Localization of Somatosensory Evoked Potentials

One of the most important steps in presurgical diagnosis of medically intractable epilepsy is to find the precise location of the epileptogenic foci. Electroencephalography (EEG) is a noninvasive tool commonly used at epilepsy surgery centers for presurgical diagnosis. In this paper, a modified particle swarm optimization (MPSO) method is used to solve the EEG source localization problem. The method is applied to noninvasive EEG recording of somatosensory evoked potentials (SEPs) for a healthy subject. A 1 mm hexahedra finite element volume conductor model of the subject's head was generated using T1-weighted magnetic resonance imaging data. Special consideration was made to accurately model the skull and cerebrospinal fluid. An exhaustive search pattern and the MPSO method were then applied to the peak of the averaged SEP data and both identified the same region of the somatosensory cortex as the location of the SEP source. A clinical expert independently identified the expected source location, further corroborating the source analysis methods. The MPSO converged to the global minima with significantly lower computational complexity compared to the exhaustive search method that required almost 3700 times more evaluations.