Somatosensory Evoked Potentials Amplitude Research Articles

Somatosensory Evoked Potentials Help Prevent Positioning‐Related Brachial Plexus Injury during Skull Base Surgery

Evaluate the use of somatosensory evoked potentials (SSEP) monitoring to detect positioning-related brachial plexus injury during skull base surgery. Prospective cohort observational study. University Hospital. Patients undergoing skull base surgery had a focused neurologic exam of the brachial plexus performed before and after surgery. Under stable anesthesia, brachial plexus SSEP values were obtained before and after surgical positioning. Significant SSEP changes required a readjustment of arm or neck positions. SSEPs were assessed every 30 minutes. If changes were noted, position was readjusted and SSEPs were reassessed until surgical completion. Demographic data, neurologic exams, SSEP latency, and amplitude values were recorded. Persistent changes were correlated with postoperative neurologic findings. Sixty-five patients, 15 to 77 years old, were studied. Six patients (9.2%) developed SSEP amplitude changes after positioning (average amplitude decrease 72.8%). One patient had a significant latency increase. The sensitivity of SSEP for detection of injury was 57%, while specificity was 94.7%. The average body mass index (BMI) of patients with normal and abnormal SSEPs was 28.7 ± 5.6 versus 29.2 ± 8.0, respectively. Average BMI of patients with postoperative symptoms regardless of SSEP findings was 33.8 ± 4.3. Two patients who had persistent SSEP changes after positioning had BMIs of 40.1 and 31.2 kg/m(2), respectively. Improvement in neurologic findings occurred in all patients after surgery. This study demonstrates that upper extremity nerve stress can be detected in real time using SSEP and may be of value in protecting patients from nerve injury undergoing lateral skull base surgery.

Subclinical ischemia verified by somatosensory evoked potential amplitude reduction during carotid endarterectomy: negative effects on cognitive performance

Although the mechanisms underlying neurocognitive changes after carotid endarterectomy (CEA) are poorly understood, intraoperative ischemia and postoperative hemodynamic changes may play a role. Data from 81 patients who underwent unilateral CEA with routine shunt use for carotid artery stenosis were retrospectively evaluated. These patients underwent neuropsychological examinations (NPEs), including assessment by the Wechsler Adult Intelligence Scale-Third Edition and the Wechsler Memory Scale-Revised before and 6 months after CEA. results of NPEs were converted into z scores, from which pre- and postoperative cognitive composite scores (CSpre and CSpost) were obtained. The association between the change of CS between pre- and postoperative NPEs (that is, CSpost - CSpre [CSpost - pre]) and various variables was assessed. These latter variables included ischemic or hemodynamic parameters such as 1) intraoperative hypoperfusion detected by somatosensory evoked potential (SSEP) change-that is, an SSEP amplitude reduction more than 50% and longer than 5 minutes (SSEP< 50%, > 5 min); 2) new lesions on postoperative diffusion-weighted imaging studies; and 3) preexisting hemodynamic impairment. Paired t-tests of the NPE scores were performed to determine the net effect of these factors on neurocognitive function at 6 months. A significant CSpost - pre decrease was observed in patients with SSEP< 50%, > 5 min when compared with those without SSEP< 50%, > 5 min (-0.225 vs 0.018; p = 0.012). Multiple regression analysis demonstrated that SSEP< 50%, > 5 min independently and negatively correlated with CSpost - pre (p = 0.0020). In the group-rate analysis, postoperative NPE scores were significantly improved relative to preoperative scores. Hypoperfusion during cross-clamping, as verified by SSEP amplitude reduction, plays a significant role in the subtle decline in cognition following CEA. However, this detrimental effect was small, and various confounding factors were present. Based on these observations and the group-rate analysis, the authors conclude that successful unilateral CEA with routine shunt use does not adversely affect postoperative cognitive function.

Intraoperative Neurophysiological Monitoring in Spinal Root Surgical Interventions

Background and Objective: Surgical interventions around spinal roots may result in rootlets injury and neurological deficits. Multimodal introperative neurophysiological monitoring (MIOM) can allow for early detection and then reversal of nerve roots potential injuries. These utilities have been currently used to evaluate spinal sensorimotor pathways and nerve root function during posterior spinal approches for transpedicular screw fixations in a rotine base in our setting (Vali-e ASR Hospital, Arak, Iran) since 1998. Methods: In three consecutive patients (1 male, 16 years old. and 2 female, 17 and 16 years old) kyphoscoliosis corrections, patient’s history, preoperative physical examination and MIOM were performed using a multimodal 40-channel electrophysiologic monitoring system (Nicolet Endeavor, VIASYS Healthcare, 2005, USA). In all cases somatosensory evoked potentials (SSEPs) and F-wave responses corresponding tothe related myotome, were recorded 2 days prior surgery. The SSEPs, bilateral EMGs of paravertebrals and related muscle, stimulus-evoked evoked EMGs by mid-dural spinal stimulation, stimulus-evoked EMGs through root stimulation (pre/post foraminal) were performed when required during different stages of operation procedure. The compound muscle action potentials (CMAPs) were recorded using a pair of 1 Cm2 golden cup surface electrode. A paired-pulse stimulation consisting of two pulses with 2 ms interstimulus interval (ISI), 100-300 µs duration and 10-40 mA intensity was applied through a surgical probe pair electrode touched to the intact dura, over the midline of dorsal column, 2 segments above the involved root, to evoke constant reproducible EMGs in paravertebrals and/or approperiate myotomes of the segment in both lower limbs. Latency of CMAPs were measured for dorsal culumn, foramen entrance and root exit site stimulations. Following the measurements of the F-wave latencies, the central root conduction time and foramenal segments were calculated and used for further monitoring.The SSEPs of ascending valleis from medial tibial nerve stimulation were recorded at C7 spine and C3´ or C4´of the operation side. A unilateral, sustained loss of 50% of the SSEP amplitude and/or increase by 10% of latency from average values after anesthesia, and SSEP/CMAP waveform change to an asynchronous polyphasic wave, were considered to be pathologic. Drilling and screw positionings were evaluated intraoperatively with standard posteroanterior and lateral radiographs.Results: None of the 3 patients showed significant change in the SSEPsor post-operative radiculopathies distinct from their preoperative presentations. One hour after the start of surgery, when the spinal column was exposed to the operating theatre temperature, a minimal prolongation of latencies as well as amplitude reduction of SSEPs was observed. The SSEP waveforms were not affected subsequently. A reverse change appeared again after paravertebral muscles stitching at the final hour of surgery.In our cases, latencies of different root segments were kept intact during the operation and also during the transfer to the recovery room. Propofol or Propofol/Ketamine mixture plus narcotic is suitable to obtain stable reproducible SSEPs and EMGs. Atracurium or other nondepolarizing skeletal muscle relaxants should be avoided. Muscle relaxants application or mean arterial pressure (MAP) below 70 mmHg may cause bilateral reduction or loss of SSEPs and EMGs. There was no postoperative clinically detectable complication.Conclusions: Findings of our study demonstrated that MIOM should be used in all patients undergoing surgery around spinal roots. Monitoring can practically reduce possibilities of neurological deficit. Futhermore, it can be concluded that the use of SSEPs to evaluate the pedicle screw placement or similar interventions is not an appropriate tool itself, since, , it could be practically limited to sensory fibers of root. In these settings and similar procedures, if IOM is required, alternative multimodal methods with greater sensitivity and efficacy should be explored. To aquire MIOM modalities, close collaboration of an anesthesioloist is nessesary.

Tract-based spatial statistics of diffusion tensor imaging in hereditary spastic paraplegia with thin corpus callosum reveals widespread white matter changes

We aimed to investigate white matter diffusivity abnormalities in hereditary spastic paraplegia with thin corpus callosum (HSP-TCC) patients in relation with electrophysiological findings. Brain magnetic resonance imaging (MRI) and diffusion tensor imaging were performed on four HSP-TCC patients and 15 age-matched healthy subjects. Voxel-wise statistical analysis of fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity maps were carried out using tract-based spatial statistics, and significantly affected voxels were labeled using a human white matter atlas. Conventional nerve conduction studies, cortical and spinal-root motor evoked potentials, and somatosensory evoked potentials were examined in three patients. On MRI, all patients had a thin corpus callosum with mild T2 hyperintensity in the periventricular white matter. Compared to control subjects, we detected widespread significant decreases in fractional anisotropy, and increases in axial diffusivity, radial diffusivity, and mean diffusivity in structures including in the corpus callosum, motor, and non-motor white matter tracts in HSP-TCC patients. Several different regions showed significant reduction in axial diffusivity. Electrophysiological studies revealed prolonged central motor conduction times and reduced cortical motor evoked potentials and somatosensory evoked potentials amplitudes in all patients. One patient had low sural sensory nerve action potential suggestive of axonal neuropathy. Tract-based spatial statistics of diffusion tensor imaging revealed a more widespread involvement of white matter in HSP-TCC patients than has previously been detected by conventional MRI. This may explain the broad spectrum of electrophysiological and neurological abnormalities that complicate hereditary spastic paraplegia in these patients.

Theta burst repetitive transcranial magnetic stimulation attenuates somatosensory evoked potentials from the lower limb

BackgroundContinuous theta burst stimulation (cTBS) is a form of repetitive transcranial magnetic stimulation which has been shown to alter cortical excitability in the upper limb representation of primary somatosensory cortex (SI). However, it is unknown whether cTBS modulates cortical excitability within the lower limb representation in SI. The present study investigates the effects of cTBS over the SI lower limb representation on cortical somatosensory evoked potentials (SEPs) and Hoffmann reflex (H-reflex) following tibial nerve stimulation at the knee. SEPs and H-reflex were recorded before and in four time blocks up to 30 minutes following cTBS targeting the lower limb representation within SI.ResultsFollowing cTBS, the P1-N1 first cortical potential was significantly decreased at 12–16 minutes. CTBS also suppressed the P2-N2 second cortical potential for up to 30 minutes following stimulation. The H-reflex remained statistically unchanged following cTBS although there was a modest suppression observed.ConclusionWe conclude that cTBS decreases cortical excitability of the lower limb representation of SI as evidenced by suppressed SEP amplitude. The duration and magnitude of the cTBS after effects are similar to those observed in upper limb studies.

Human Embryonic Stem Cell-Derived Oligodendrocyte Progenitors Aid in Functional Recovery of Sensory Pathways following Contusive Spinal Cord Injury

BackgroundTransplantations of human stem cell derivatives have been widely investigated in rodent models for the potential restoration of function of neural pathways after spinal cord injury (SCI). Studies have already demonstrated cells survival following transplantation in SCI. We sought to evaluate survival and potential therapeutic effects of transplanted human embryonic stem (hES) cell-derived oligodendrocyte progenitor cells (OPCs) in a contusive injury in rats. Bioluminescence imaging was utilized to verify survivability of cells up to 4 weeks, and somatosensory evoked potential (SSEPs) were recorded at the cortex to monitor function of sensory pathways throughout the 6-week recovery period.Principal FindingshES cells were transduced with the firefly luciferase gene and differentiated into OPCs. OPCs were transplanted into the lesion epicenter of rat spinal cords 2 hours after inducing a moderate contusive SCI. The hES-treatment group showed improved SSEPs, including increased amplitude and decreased latencies, compared to the control group. The bioluminescence of transplanted OPCs decreased by 97% in the injured spinal cord compared to only 80% when injected into an uninjured spinal cord. Bioluminescence increased in both experimental groups such that by week 3, no statistical difference was detected, signifying that the cells survived and proliferated independent of injury. Post-mortem histology of the spinal cords showed integration of human cells expressing mature oligodendrocyte markers and myelin basic protein without the expression of markers for astrocytes (GFAP) or pluripotent cells (OCT4).ConclusionshES-derived OPCs transplanted 2 hours after contusive SCI survive and differentiate into OLs that produce MBP. Treated rats demonstrated functional improvements in SSEP amplitudes and latencies compared to controls as early as 1 week post-injury. Finally, the hostile injury microenvironment at 2 hours post-injury initially caused increased cell death but did not affect the long-term cell proliferation or survival, indicating that cells can be transplanted sooner than conventionally accepted.

Evaluation of pulsed electromagnetic field therapy in the management of patients with discogenic lumbar radiculopathy

This randomized clinical trial was designed to evaluate the effect of pulsed electromagnetic field therapy (PEMF) in the management of patients with discogenic lumbar radiculopathy. Forty patients suffering from lumbar radiculopathy due to lumbar disc prolapse were randomly assigned to one of two groups: a study group that included 20 patients who received PEMF therapy and a control group that included 20 patients who received placebo treatment. Both groups were evaluated at bases line and after 3 weeks by using a visual analogue scale (VAS) (0-10), somatosensory evoked potentials (SSEPs) for selected dermatomes and Modified Oswestry Low Back Pain Disability Questionnaire (OSW), and findings were compared before and after treatment. Significant differences were observed between both groups before and after application of PEMF therapy relative to VAS (P=0.024), total OSW (P<0.001), and other domains of OSW score (pain intensity [P=0.009], personal care [P=0.01], lifting [P<0.001], walking [P<0.001], sitting [P<0.001], standing [P<0.001], sleeping [P<0.001], social life [P<0.001] and employment [P=0.003]). Other significant differences were observed between both groups relative to SSEP latency and amplitude of the evaluated dermatomes on the right side (P=0.022 and P=0.001, respectively), and left side latency and amplitude (P=0.016 and P=0.002, respectively). PEMF therapy is an effective method for the conservative treatment of lumbar radiculopathy caused by lumbar disc prolapse. In addition to improvement of clinically observed radicular symptoms, PEMF also seems effective in reducing nerve root compression as evidenced by improvement of SSEP parameters after treatment.

An evaluation of in vivo voltage-sensitive dyes: pharmacological side effects and signal-to-noise ratios after effective removal of brain-pulsation artifacts

In the current study, we investigated pharmacological side effects and signal-to-noise ratios (SNRs) of two commonly used voltage-sensitive dyes (VSDs): the blue dye RH-1691 (1 mg/ml) and the red dye di-4-ANEPPS (0.1 mg/ml), applied in vivo to the rat barrel cortex. Blue dyes are often favored over red dyes in in vivo studies due to their apparent superior SNR, partly because their fluorescence spectrum is farther away from the hemoglobin absorption spectrum, making them less prone to heartbeat-associated brain-pulsation artifacts (BPA). We implemented a previously reported template-based BPA removal algorithm and evaluated its applicability to di-4-ANEPPS before comparing characteristics of the two dyes. Somatosensory-evoked potentials (SEPs) were also recorded. Whereas SEPs recorded before and after application of di-4-ANEPPS failed to exhibit demonstrable differences, RH-1691 caused a significant and prolonged increase in SEP amplitude for several hours. In contrast, neither dye influenced the spontaneous cortical activity as assessed by the spectral content of the EEG. Both dyes turned out to be strikingly similar with respect to changes in fractional fluorescence as a function of SEP response amplitude, as well as regarding shot noise characteristics after removal of the BPA. Thus there is strong evidence that the increased SNR for RH-1691 is a consequence of an artificially increased signal. When applying an appropriate BPA removal algorithm, di-4-ANEPPS has proven to be suitable for single-trial in vivo VSD imaging (VSDI) and produces no detectable neurophysiological changes in the system under investigation. Taken together, our data argue for a careful re-evaluation of pharmacological side effects of RH-1691 and support the applicability of di-4-ANEPPS for stable single-trial in vivo VSDI recordings.

Intraoperative Decrease in Amplitude of Somatosensory-Evoked Potentials of the Lower Extremities With Interbody Fusion Cage Placement During Lumbar Fusion Surgery

A retrospective analysis was performed. To characterize neurophysiological data of patients who had a decrease in amplitude of somatosensory-evoked potentials (SSEP) of the lower extremities secondary to interbody fusion cage placement during lumbar fusion surgery with no alert of the electromyography (EMG). The most consistently used and studied modalities of neurophysiological monitoring during spine surgery are SSEPs, motor-evoked potentials (MEPs), and EMG. In general, it is accepted that MEPs along with SSEPs are used to detect spinal cord injury and EMGs are used to detect nerve root injury. The medical records of a consecutive series of 115 patients who had undergone a transforaminal lumbar interbody fusion (TLIF) procedure in which SSEPs, MEPs, and EMGs were utilized for neurophysiological monitoring were retrospectively reviewed. One hundred fifteen cases of TLIF procedures were reviewed. The follow-up was 2 years after the last procedure. A total of 5 cases that demonstrated intraoperative SSEP changes were found. The age range for these cases was from 39 to 81 years (mean age, 61 yr). All 5 patients developed SSEP changes that were secondary to interbody fusion cage placement. All 5 cases demonstrated reversal of the SSEP changes to baseline after removal of the interbody cage. Three of these cases had no new postoperative neurological findings. However, given that these 3 cases of SSEP change were associated with a surgical event that improved secondary to an intervention (in this case removal of the interbody cage), those cases were classified as presumed positive. Two of the 5 cases were in fact associated with a new postoperative neurological deficit. To our knowledge this study demonstrates the first reported SSEP alerts that were associated with a posterior lumbar interbody cage placement without a corresponding EMG alert.

Intraoperative Decrease in Amplitude of Somatosensory-Evoked Potentials of the Lower Extremities with Interbody Fusion Cage Placement During Lumbar Fusion Surgery

STUDY DESIGN A retrospective analysis was performed. OBJECTIVE To characterize neurophysiological data of patients who had a decrease in amplitude of somatosensory-evoked potentials (SSEP) of the lower extremities secondary to interbody fusion cage placement during lumbar fusion surgery with no alert of the electromyography (EMG). SUMMARY OF BACKGROUND DATA The most consistently used and studied modalities of neurophysiological monitoring during spine surgery are SSEPs, motor-evoked potentials (MEPs), and EMG. In general, it is accepted that MEPs along with SSEPs are used to detect spinal cord injury and EMGs are used to detect nerve root injury. METHODS The medical records of a consecutive series of 115 patients who had undergone a transforaminal lumbar interbody fusion (TLIF) procedure in which SSEPs, MEPs, and EMGs were utilized for neurophysiological monitoring were retrospectively reviewed. RESULTS One hundred fifteen cases of TLIF procedures were reviewed. The follow-up was 2 years after the last procedure. A total of 5 cases that demonstrated intraoperative SSEP changes were found. The age range for these cases was from 39 to 81 years (mean age, 61 yr). All 5 patients developed SSEP changes that were secondary to interbody fusion cage placement. All 5 cases demonstrated reversal of the SSEP changes to baseline after removal of the interbody cage. Three of these cases had no new postoperative neurological findings. However, given that these 3 cases of SSEP change were associated with a surgical event that improved secondary to an intervention (in this case removal of the interbody cage), those cases were classified as presumed positive. Two of the 5 cases were in fact associated with a new postoperative neurological deficit. CONCLUSION To our knowledge this study demonstrates the first reported SSEP alerts that were associated with a posterior lumbar interbody cage placement without a corresponding EMG alert.

Impaired pain processing in Parkinson's disease and its relative association with the sense of smell

Background and purposeMany non-motor symptoms are associated with Parkinson's disease (PD). Of these, pain and olfactory disturbance tend to be common premotor symptoms. PD has been shown to exhibit abnormal central pain processing, although underlying mechanisms are not yet fully understood. In order to investigate this further, we assessed PD patients by specific Aδ stimulation with intra-epidermal needle electrode and determined olfactory function. MethodsForty-two patients (18 males and 24 females) with PD and 17 healthy control subjects (8 males and 9 females) were studied. A thin needle electrode was used to stimulate epidermal Aδ fibers, and somatosensory evoked potentials (SEPs) recorded at the vertex. Olfactory function was evaluated using the Odor Stick Identification Test for Japanese (OSIT-J) and its relationship with pain-related SEPs was investigated. ResultsThere were no significant differences in N1 latencies or P1 latencies although N1/P1 peak-to-peak amplitudes were significantly lower (p < 0.01) in PD patients than in control subjects. In PD patients, there were significant correlations between N1/P1 amplitudes and disease duration (r = −0.35, p < 0.05), Hoehn-Yahr stage (r = −0.38, p < 0.05) and UPDRS part III (r = −0.42, p < 0.01). Furthermore, the OSIT-J scores correlated with SEP amplitude (r = 0.41, p < 0.01). ConclusionPain processing in PD patients was impaired under specific nociceptive stimulation of Aδ fibers and significant correlation with smell dysfunction was detected. We suggest that this mechanism may involve the limbic system during PD pathology.

Electrophysiological effects of single point transcutaneous 650 and 808 nm laser irradiation of rat sciatic nerve: a study of relevance for low-level laser therapy and laser acupuncture.

The purpose of this study was to evaluate effects of transcutaneous 650 and 808 nm laser irradiation (LI) to a single point overlying rat sciatic nerve; a comparison to four point LI and relevance to the clinical application of low-level laser therapy (LLLT) and laser acupuncture (LA). Transcutaneous LI inhibits somatosensory and motor conduction when delivered to four points overlying sciatic nerve; however, effects of the same total energy delivered to a single point over the nerve, equating to laser acupuncture, are undefined. Transcutaneous 808 nm, 450 mW, (13.5 or 54 J) continuous wave (cw) mode or 650 nm, 35 mW, (1.1 or 4.4 J), cw LI or sham LI, was applied for 30 or 120 sec to a single point overlying the midpoint of rat sciatic nerve. Somatosensory evoked potentials (SSEPs) and compound muscle action potentials (CMAPs) were then recorded after 10 and 20 min, and after 24 and 48 h. 120 sec of 808 nm LI increased SSEP amplitudes only at 10 min, with no effect of 30 or 120 sec at other time points on SSEPs or on CMAPs. LI 650 nm for 30 or 120 sec did not alter SSEPs or CMAPs at any time point. Localized transcutaneous 808 LI to a single point overlying sciatic nerve increases SSEP amplitudes when compared with delivery of the same total energy to four points, which causes decreased SSEP amplitudes and conduction block. Therefore, the area and duration of delivery are important, independent variables with implications for clinical delivery of both LLLT and LA.

Application of multi-adaptive filter based on radial basis function neural network for real-time somatosensory evoked potential monitoring

Objective To design multi-adaptive filter based on radial basis function (MAF-RBF) for efficiently extracting somatosensory evoked potential (SEP) in real-time SEP monitoring.Methods With the optimization of important parameters that influence the performance of radial basis function neural network,the performance of extracting SEP was compared to that of a multi-adaptive filter (MAF),which developed from the combination of well-developed adaptive noise canceller and adaptive signal enhancer.Results In this simulation study,the outputs of MAF-RBF showed a similar waveform with SEP template signals,and a smoother waveform than the.output of MAF.Conclusion With appropriate parameter values,MAF-RBFNN is able to extract the latency and amplitude of SEP from the extremely noisy background rapidly and reliably without averaging. Key words: Somsatosensory evoked potential; Aadial basis function; Adaptive signal enhance; Adaptive noise canceller; Multi-adaptive filter,Least mean square error algorithm

Impact of Multimodal Intraoperative Monitoring During Surgery for Spine Deformity and Potential Risk Factors for Neurological Monitoring Changes

Retrospective review. To evaluate the efficacy of multimodal intraoperative neuromonitoring for predicting iatrogenic neurological injury during surgical correction of a spine deformity and evaluate the potential risk factors for neurological monitoring changes. Single modal intraoperative neuromonitoring is insufficient to predict neurological injury during surgical correction of spine deformity. Multimodal monitoring can provide more accuracy. Some risk factors were reported to be correlated with high rates of neurological deficits during scoliosis correction. But few studies have reported on the risk factors for neurological monitoring changes (NMCs). The records of 176 consecutive patients who underwent surgery for the treatment of spinal deformities were reviewed. The patients were monitored using transcranial electric motor-evoked potential (MEP) and/or somatosensory-evoked potential (SEP). Alterations with the MEP wave amplitude decreasing more than 75% and SEP amplitude decreasing more than 50%, as compared with the baseline, were diagnosed as positive changes. Risk factors related to NMCs were evaluated, in light of preoperative neurological deficits, comorbidity of spinal cord deformity, procedure of osteotomy, main curve Cobb angle, and a diagnosis of kyphosis. Combined MEP/SEP monitoring was successfully achieved in 175 of 176 cases. Eleven cases were presented with true NMCs according to MEPs. One patient had an irreversible neurological deficit and 4 patients had transient neurological deficits after waking up from the operation. SEP lagged MEP for an average of 15 minutes when both were presented with positive changes. The sensitivity and specificity of MEP were 91.7% and 98.8%, respectively. Solo SEP were 50% and 95.2%. Combined MEP and SEP were 92.9% and 99.4%. The procedure of osteotomy, curve Cobb angle more than 90 degrees, and preoperative kyphosis were correlated with a higher incidence of NMCs. Multimodal intraoperative monitoring provides higher sensitivity for monitoring during spine deformity surgery and can predict events of neurological injury. The detection of NMCs and adjustment of surgical strategy may prevent irreversible neurological deficits. The possible risk factors for NMCs during spine deformity surgery include an osteotomy procedure, kyphosis correction, and preoperative Cobb angle more than 90 degrees.

Modulation of somatosensory evoked potentials during force generation and relaxation

This study investigated the modulation of somatosensory evoked potentials (SEPs) during precisely controlled force generation and force relaxation in a visuomotor tracking task. Subjects were instructed to track a target line with a line that represented their own force generated by grip movement with the right hand as accurately as possible during concurrent electrical stimulation. The target force line moved up continuously from 0 to 20 % of maximal voluntary contraction (MVC) (the force generation phase: FG phase) and moved down from 20 to 0 % of MVC (the force relaxation phase: FR phase) in 7 s at a constant velocity. We separately obtained SEPs following electrical stimulation of the median nerve at the wrist in each phase. During the visuomotor tracking task, compared with the stationary condition, the N30 at Fz and P27 at C3' showed a significant reduction in amplitude in the FG and FR phases. In addition, the N30 and P27 were significantly smaller in amplitude in the FG than FR phase. Although the average amount of force exertion was the same in the FG and FR phases, the modulation of SEP amplitude was larger in the FG phase. These results indicated that sensorimotor integration in the somatosensory area was dependent on the context of movement exertion.

Chronic Cervical Spinal Cord Injury: DTI Correlates with Clinical and Electrophysiological Measures

Diffusion tensor imaging (DTI) is rarely applied in spinal cord injury (SCI). The aim of this study was to correlate diffusion properties after SCI with electrophysiological and neurological measures. Nineteen traumatic cervical SCI subjects and 28 age-matched healthy subjects participated in this study. DTI data of the spinal cord were acquired with a Philips Achieva 3 T MR scanner using an outer volume suppressed, reduced field of view (FOV) acquisition with oblique slice excitation and a single-shot EPI readout. Neurological and electrophysiological measures, American Spinal Injury Association (ASIA) impairment scale scores, and motor (MEP) and somatosensory evoked potentials (SSEP) were assessed in SCI subjects. Fractional anisotropy (FA) values were decreased in the SCI subjects compared to the healthy subjects. In upper cervical segments, the decrease in FA was significant for the evaluation of the entire cross-sectional area of the spinal cord, and for corticospinal and sensory tracts. A decreasing trend was also found at the thoracic level for the corticospinal tracts. The decrease of DTI values correlated with the clinical completeness of SCI, and with SSEP amplitudes. The reduced DTI values seen in the SCI subjects are likely due to demyelination and axonal degeneration of spinal tracts, which are related to clinical and electrophysiological measures. A reduction in DTI values in regions remote from the injury site suggests their involvement with wallerian axonal degeneration. DTI can be used for the quantitative evaluation of the extent of spinal cord damage, and eventually to monitor the effects of future regeneration-inducing treatments.

Potential long-term benefits of acute hypothermia after spinal cord injury

Neuroprotection by hypothermia has been an important research topic over last two decades. In animal models of spinal cord injury, the primary focus has been assessing the effects of hypothermia on behavioral and histologic outcomes. Although a few studies have investigated electrophysiological changes in descending motor pathways with motor-evoked potentials recorded during cooling, we report here hypothermia induced increased electrical conduction in the ascending spinal cord pathways with somatosensory-evoked potentials in injured rats. In our experiments, these effects lasted long after the acute hypothermia and were accompanied by potential long-term improvements in motor movement. Laboratory investigation. University medical school. Twenty-one female Lewis rats. Hypothermia. All animals underwent spinal cord contusion with the NYU-Impactor by a 12.5-mm weight drop at thoracic vertebra T8. A group (n = 10) was randomly assigned for a systemic 2-hr hypothermia episode (32 ± 0.5°C) initiated approximately 2.0 hrs postinjury. Eleven rats were controls with postinjury temperature maintained at 37 ± 0.5°C for 2 hrs. The two groups underwent preinjury, weekly postinjury (up to 4 wks) somatosensory-evoked potential recordings and standard motor behavioral tests (BBB). Three randomly selected rats from each group were euthanized for histologic analysis at postinjury day 3 and day 28. Compared with controls, the hypothermia group showed significantly higher postinjury somatosensory-evoked potential amplitudes with longer latencies. The BBB scores were also higher immediately after injury and 4 wks later in the hypothermia group. Importantly, specific changes in the Basso, Beattie, Bresnahan scores in the hypothermia group (not seen in controls) indicated regained functions critical for motor control. Histologic evaluations showed more tissue preservation in the hypothermia group. After spinal cord injury, early systemic hypothermia provided significant neuroprotection weeks after injury through improved sensory electrophysiological signals in rats. This was accompanied by higher motor behavioral scores and more spared tissue in acute and postacute periods after injury.

Effects of total intravenous anesthesia on evoked potentials during aneurysm clip placement surgery

To explore the influences of total intravenous anesthesia (TIVA) on the feasibility and success rate of monitoring the evoked potentials (EP) and examine the correlations between EP changes and clinical outcomes in intracranial aneurysm surgery. Thirty-one patients undergoing intracranial aneurysm surgery received TIVA. TIVA was maintained with a target controlled infusion (TCI) of propofol and a continuous infusion of remifentanyl. The bilateral SEP (somatosensory evoked potential) and MEP (motor evoked potentials) were monitored intra-operatively. And the changes of evoked potential and success rate were recorded. The preoperative and postoperative neurological outcomes and radiological manifestations were compared. Bilateral SEP was detected in all cases. And the control side MEP was unsuccessfully monitored. Three patients had postoperative neurological deficits. The amplitudes of MEP and SEP declined simultaneously and failed to revert back to the baseline levels in 1 case. There was postoperative hemiplegia. And computed tomography showed multiple sites of ischemic brain infarction. The administration of TIVA with propofol and remifentanyl enables successful SEP and MEP monitoring during intracranial aneurysm surgery. This protocol may detect early cerebral ischemia and reduce the incidence of ischemic stroke.

The relationship in gating effects between short-latency and long-latency somatosensory-evoked potentials

We investigated the relationship between short-latency and long-latency somatosensory-evoked potentials (SEPs) relating to voluntary movement. In general, the amplitudes of short-latency components in SEPs are attenuated during movement, whereas those of long-latency are enhanced, and this phenomenon is termed 'gating effects'. This study aimed to examine the relationship of changes in amplitude between short-latency and long-latency SEPs. SEPs were recorded from 11 participants at Fz, Cz, Pz, and C4' by stimulating the left median nerve. Two tasks were conducted; Control and Movement. In Control, the participant was asked to relax with no specific task. In Movement, the participant was encouraged to continue a rapid drumming motion of all fingers of the left hand at a self-paced rate. The amplitudes of short-latency SEPs, the P25 at C4' and N30 at Fz, were significantly smaller in the Movement than Control condition. By contrast, the amplitudes of long-latency SEPs, the N140 at Fz, Cz, and Pz were significantly larger in Movement than Control condition. Moreover, a significant positive correlation was observed in the rate of amplitude change between the frontal N30 and vertex N140, indicating that for the participants with a frontal N30 of smaller amplitude during Movement, the amplitude of the vertex N140 was smaller. We inferred that the neural activities in movement-related cortices affected the sources for the frontal N30 and vertex N140 in the same neuronal network simultaneously.

Human proprioceptive adaptations during states of height-induced fear and anxiety

Clinical and experimental research has demonstrated that the emotional experience of fear and anxiety impairs postural stability in humans. The current study investigated whether changes in fear and anxiety can also modulate spinal stretch reflexes and the gain of afferent inputs to the primary somatosensory cortex. To do so, two separate experiments were performed on two separate groups of participants while they stood under conditions of low and high postural threat. In experiment 1, the proprioceptive system was probed using phasic mechanical stimulation of the Achilles tendon while simultaneously recording the ensuing tendon reflexes in the soleus muscle and cortical-evoked potentials over the somatosensory cortex during low and high threat conditions. In experiment 2, phasic electrical stimulation of the tibial nerve was used to examine the effect of postural threat on somatosensory evoked potentials. Results from experiment 1 demonstrated that soleus tendon reflex excitability was facilitated during states of height-induced fear and anxiety while the magnitude of the tendon-tap-evoked cortical potential was not significantly different between threat conditions. Results from experiment 2 demonstrated that the amplitudes of somatosensory-evoked potentials were also unchanged between threat conditions. The results support the hypothesis that muscle spindle sensitivity in the triceps surae muscles may be facilitated when humans stand under conditions of elevated postural threat, although the presumed increase in spindle sensitivity does not result in higher afferent feedback gain at the level of the somatosensory cortex.