Motor Evoked Potentials Threshold Research Articles

Intraoperative DBS targeting of the globus pallidus internus by using motor evoked potentials

ObjectivesTarget localization for deep brain stimulation (DBS) is a crucial step that influences the clinical benefit of the DBS procedure together with the reduction of side effects. In this work, we address the feasibility of DBS target localization in the globus pallidus internus (GPi) aided by intraoperative motor evoked potentials (MEP) with emphasis on the reduction of capsular side effects. Material and methodsMicro-macroelectrode recordings were performed intraoperatively on 20 patients that underwent DBS treatment of the GPi (GPi-DBS). MEP were elicited intraoperatively by microelectrode stimulation during stereotactic DBS surgery. We studied the relationship between MEP thresholds and the internal capsule (IC) proximity. ResultsWe found a significant correlation between intraoperative MEP thresholds and IC proximity. ConclusionsWe provide further evidence of the role of MEPs for DBS target localization in the GPi, which extends and confirms the usefulness of MEPs as previously reported by DBS target localization studies dealing with the subthalamic and thalamic nuclei. Our approach is advantageous in that it provides criteria to determine the DBS target without the need to rely on a patient's response while avoiding capsular effects.

Cortical and spinal responses to short-term strength training and detraining in young and older adults in rectus femoris muscle

IntroductionStrength training mitigates the age-related decline in strength and muscle activation but limited evidence exists on specific motor pathway adaptations.MethodsEleven young (22–34 years) and ten older (66–80 years) adults underwent five testing sessions where lumbar-evoked potentials (LEPs) and motor-evoked potentials (MEPs) were measured during 20 and 60% of maximum voluntary contraction (MVC). Ten stimulations, randomly delivered, targeted 25% of maximum compound action potential for LEPs and 120, 140, and 160% of active motor threshold (aMT) for MEPs. The 7-week whole-body resistance training intervention included five exercises, e.g., knee extension (5 sets) and leg press (3 sets), performed twice weekly and was followed by 4 weeks of detraining.ResultsYoung had higher MVC (~ 63 N·m, p = 0.006), 1-RM (~ 50 kg, p = 0.002), and lower aMT (~ 9%, p = 0.030) than older adults at baseline. Young increased 1-RM (+ 18 kg, p < 0.001), skeletal muscle mass (SMM) (+ 0.9 kg, p = 0.009), and LEP amplitude (+ 0.174, p < 0.001) during 20% MVC. Older adults increased MVC (+ 13 N·m, p = 0.014), however, they experienced decreased LEP amplitude (− 0.241, p < 0.001) during 20% MVC and MEP amplitude reductions at 120% (− 0.157, p = 0.034), 140% (− 0.196, p = 0.026), and 160% (− 0.210, p = 0.006) aMT during 60% MVC trials. After detraining, young and older adults decreased 1-RM, while young adults decreased SMM.ConclusionHigher aMT and MEP amplitude in older adults were concomitant with lower baseline strength. Training increased strength in both groups, but divergent modifications in cortico-spinal activity occurred. Results suggest that the primary locus of adaptation occurs at the spinal level.

Mapping of Capsular Side Effects by using Intraoperative Motor-Evoked Potentials during Asleep Deep Brain Stimulation Surgery of the Subthalamic Nucleus for Parkinson’s Disease

Introduction: The aim of this study was to present a novel technique for subthalamic nucleus (STN) deep brain stimulation (DBS) implantation under general anesthesia by using intraoperative motor-evoked potentials (MEPs) through direct lead stimulation and determining their correlation to the thresholds of postoperative stimulation-induced side effects. Methods: This study included 22 consecutive patients with advanced Parkinson’s disease who underwent surgery in our institution between January 2021 and September 2023. All patients underwent bilateral implantation in the STN (44 leads) under general anesthesia without microelectrode recordings (MERs) by using MEPs with electrostimulation directly through the DBS lead. No cortical stimulation was performed during this process. Intraoperative fluoroscopic guidance and immediate postoperative computed tomography were used to verify the electrode’s position. The lowest MEP thresholds were recorded and were correlated to the postoperative stimulation-induced side-effect threshold. The predictive values of the MEPs were analyzed. Five DBS leads were repositioned intraoperatively due to the MEP results. Results: A moderately strong positive correlation was found between the MEP threshold and the capsular side-effect threshold (RS = 0.425, 95% CI, 0.17–0.67, p = 0.004). The highest sensitivity and specificity for predicting a side-effect threshold of 5 mA were found to be at 2.4 mA MEP threshold (sensitivity 97%, specificity 87.5%, positive predictive value 97%, and negative predictive value 87.5%). We also found high sensitivity and specificity (100%) at 1.15 mA MEP threshold and 3 mA side-effect threshold. Out of the total 44 leads, 5 (11.3%) leads were repositioned intraoperatively due to MEP thresholds lower than 1 mA (4 leads) or higher than 5 mA (1 lead). The mean accuracy on postoperative CT was 1.05 mm, and there were no postoperative side-effects under 2.8 mA. Conclusion: Intraoperative MEPs with electrostimulation directly through the contacts of the DBS lead correlate with the stimulation-induced capsular side effects. The lead reposition based on intraoperative MEP may enlarge the therapeutic window of DBS stimulation.

Corticospinal excitability after 5-day Dry Immersion in women.

In light of the development of manned astronautics and the increasing participation of women in space flights, the question of female body adaptation to microgravity conditions becomes relevant. Currently, one of the important directions in this issue is to study the effects of support withdrawal as a factor of weightlessness on the human sensorimotor system. Dry Immersion is one of the well-known ground-based models, which adequately reproduces the main physiological effects of space flight. The aim of this study was to evaluate the changes in motor evoked potentials of the lower leg gravity-dependent muscles in women after a 5-day Dry Immersion. We analyzed evoked responses to transcranial and trans-spinal magnetic stimulation. In this method, areas of interest (the motor cortex and lumbosacral thickening of the spinal cord) are stimulated with an electromagnetic stimulus. The experiment was conducted with the participation of 16 healthy female volunteers with a natural menstrual cycle. The thresholds, amplitudes, and latencies of motor potentials evoked by magnetic stimulation were assessed. We showed that 5-day exposure to support withdrawal leads to a decrease in motor-evoked potential thresholds and central motor conduction time, although changes in motor response amplitudes were ambiguous. The data obtained correspond to the results of previous research on Dry Immersion effects on the sensorimotor system in men.

An investigation of the control of quadriceps in people who are hypermobile; a case control design. Do the results impact our choice of exercise for people with symptomatic hypermobility?

BackgroundPeople with symptomatic hypermobility have altered proprioception however, the origin of this is unclear and needs further investigation to target rehabilitation appropriately. The objective of this investigation was to explore the corticospinal and reflex control of quadriceps and see if it differed between three groups of people: those who have symptomatic hypermobility, asymptomatic hypermobility and normal flexibility.MethodsUsing Transcranial Magnetic Stimulation (TMS) and electrical stimulation of peripheral nerves, motor evoked potentials (MEPs) and Hoffman (H) reflexes of quadriceps were evoked in the three groups of people. The threshold and latency of MEPs and the slope of the input–output curves and the amplitude of MEPs and H reflexes were compared across the groups.ResultsThe slope of the input–output curve created from MEPs as a result of TMS was steeper in people with symptomatic hypermobility when compared to asymptomatic and normally flexible people (p = 0.04). There were no other differences between the groups.ConclusionCorticospinal excitability and the excitability at the motoneurone pool are not likely candidates for the origin of proprioceptive loss in people with symptomatic hypermobility. This is discussed in the light of other work to suggest the receptor sitting in hypermobile connective tissue is a likely candidate. This suggests that treatment aimed at improving receptor responsiveness through increasing muscle tone, may be an effective rehabilitation strategy.

Motor Evoked Potentials Improve Targeting in Deep Brain Stimulation Surgery

ObjectivesOne of the main challenges posed by the surgical deep brain stimulation (DBS) procedure is the successful targeting of the structures of interest and avoidance of side effects, especially in asleep surgery. Here, intraoperative motor evoked potentials (MEPs) might serve as tool to identify the pyramidal tract. We hypothesized that intraoperative MEPs are useful to define the distance to the pyramidal tract and reduce the occurrence of postoperative capsular side effects. Materials and MethodsMotor potentials were evoked through both microelectrode and DBS-electrode stimulation during stereotactic DBS surgery on 25 subthalamic nuclei and 3 ventral intermediate thalamic nuclei. Internal capsule proximity was calculated for contacts on microelectrode trajectories, as well as for DBS-electrodes, and correlated with the corresponding MEP thresholds. Moreover, the predictivity of intraoperative MEP thresholds on the probability of postoperative capsular side effects was calculated. ResultsIntraoperative MEPs thresholds correlated significantly with internal capsule proximity, regardless of the stimulation source. Furthermore, MEPs thresholds were highly accurate to exclude the occurrence of postoperative capsular side effects. ConclusionsIntraoperative MEPs provide additional targeting guidance, especially in asleep DBS surgery, where clinical value of microelectrode recordings and test stimulation may be limited. As this technique can exclude future capsular side effects, it can directly be translated into clinical practice.

NAIAD-2020: Characteristics of Motor Evoked Potentials After 3-Day Exposure to Dry Immersion in Women.

As female astronauts participate in space flight more and more frequently, there is a demand for research on how the female body adapts to the microgravity environment. In particular, there is very little research on how the neuromuscular system reacts to gravitational unloading in women. We aimed to estimate changes in motor evoked potentials (MEPs) in the lower leg muscles in women after 3-day exposure to Dry Immersion (DI), which is one of the most widely used ground models of microgravity. Six healthy female volunteers (mean age 30.17 ± 5.5 years) with a natural menstrual cycle participated in this experiment. MEPs were recorded from the gastrocnemius and soleus muscles twice before DI, on the day of DI completion, and 3 days after DI, during the recovery period. To evoke motor responses, transcranial and trans-spinal magnetic stimulation was applied. We showed that changes in MEP characteristics after DI exposure were different depending on the stimulation site, but were similar for both muscles. For trans-spinal stimulation, MEP thresholds decreased compared to baseline values, and amplitudes, on the contrary, increased, resembling the phenomenon of hypogravitational hyperreflexia. This finding is in line with data observed in other experiments on both male and female participants. MEPs to transcranial stimulation had an opposing dynamic, which may have resulted from the small group size and large inter-subject variability, or from hormonal fluctuations during the menstrual cycle. Central motor conduction time remained unchanged, suggesting that pyramidal tract conductibility was not affected by DI exposure. More research is needed to explore the underlying mechanisms.

Establishing the Minimum Intensity of Transcranial Magnetic Stimulation Superconditioning Pulses to Effect Inhibition and Facilitation of Motor Evoked Potentials.

Previously, we showed that a three-pulse train of weak transcranial magnetic stimulation (TMS) pulses-a superconditioning (SC) train-when followed by a stronger TMS pulse could enhance the inhibition or facilitation of the resultant motor evoked potential (MEP) compared with that seen with traditional dual-pulse inputs. The purpose of the present study was to establish the relative minimum intensity of SC pulses needed to influence MEP output and whether this differed for upper- versus lower-limb muscles. We examined 33 older adult subjects, targeting abductor pollicis brevis and tibialis anterior muscles. Older subjects were included in the anticipation of using findings from this study to guide further studies in persons with amyotrophic lateral sclerosis. Three-pulse trains of SC inputs of different intensities were delivered either 1 millisecond before (for inhibition) or 10 millisecond before (for facilitation) a stronger TMS test pulse. Motor evoked potential magnitudes for SC +test sets were normalized to test input responses and were compared within and between subjects. For inhibition, the minimum intensity of SC pulses needed to influence the follow-on MEP was found to be 60% of the target muscle's resting three-pulse MEP threshold for most abductor pollicis brevis and tibialis anterior muscles (2-millisecond interpulse intervals). For facilitation, somewhat higher intensities (70%) were typically needed to cause facilitation. Both values of SC pulses for inhibition/facilitation are considerably lower than the intensity of the conditioning pulse-often reported as 80% of the single-pulse threshold-typically used in dual-pulse TMS paradigms. This approach may allow testing of upper motor neuron function using weaker stimulus pulse intensities than are typically employed, improving testing compliance in persons whose thresholds are elevated because of injury or disease.

Motor Evoked Potential Recordings During Segmented Deep Brain Stimulation-A Feasibility Study.

Segmented deep brain stimulation (DBS) leads, which are capable of steering current in the direction of any 1 of 3 segments, can result in a wider therapeutic window by directing current away from unintended structures, particularly, the corticospinal tract (CST). It is unclear whether the use of motor evoked potentials (MEPs) is feasible during DBS surgery via stimulation of individual contacts/segments in order to quantify CST activation thresholds and optimal contacts/segments intraoperatively. To assess the feasibility of using MEP to identify CST thresholds for ring and individual segments of the DBS lead under general anesthesia. MEP testing was performed during pulse generator implantation under general anesthesia on subjects who underwent DBS lead implantation into the subthalamic nucleus (STN). Stimulation of each ring and segmented contacts of the directional DBS lead was performed until CST threshold was reached. Stereotactic coordinates and thresholds for each contact/segment were recorded along with the initially activated muscle group. A total of 34 hemispheres were included for analysis. MEP thresholds were recorded from 268 total contacts/segments. For segmented contacts (2 and 3, respectively), the mean highest CST thresholds were 2.33 and 2.62 mA, while the mean lowest CST thresholds were 1.7 and 1.89 mA, suggesting differential thresholds in relation to CST. First dorsal interosseous and abductor pollicis brevis (34% each) were the most commonly activated muscle groups. MEP threshold recording from segmented DBS leads is feasible. MEP recordings can identify segments with highest CST thresholds and may identify segment orientation in relation to CST.

Direct cortical stimulation with cylindrical depth electrodes in the interhemispheric fissure for leg motor evoked potential monitoring

ObjectiveTo evaluate cylindrical depth electrodes in the interhemispheric fissure as an alternative to subdural strip electrodes for direct cortical stimulation (DCS) leg motor evoked potential (MEP) monitoring. MethodsA cylindrical depth electrode was positioned in the interhemispheric fissure of 37 patients who underwent supratentorial brain surgery. Leg sensory and motor cortices were localized by highest tibial nerve somatosensory evoked potential amplitude and lowest DCS leg MEP threshold; the lowest-threshold electrode was then used for DCS leg MEP monitoring. ResultsIntraoperative leg MEPs were obtained from all the patients in the series. The mean intensity applied for leg MEP monitoring with the cylindrical depth electrode was 15.2 ± 4.0 mA. No complications secondary to neurophysiological monitoring were detected. ConclusionsLower extremity MEPs were consistently recorded using a multi-contact cylindrical depth electrode in the interhemispheric fissure by DCS. SignificanceCylindrical depth electrodes may be a safe and effective alternative for DCS in the interhemispheric fissure, where subdural strips are difficult to place.

Transspinal stimulation decreases corticospinal excitability and alters the function of spinal locomotor networks.

Locomotion requires the continuous integration of descending motor commands and sensory inputs from the legs by spinal central pattern generator circuits. Modulation of spinal neural circuits by transspinal stimulation is well documented, but how transspinal stimulation affects corticospinal excitability during walking in humans remains elusive. We measured the motor evoked potentials (MEPs) at multiple phases of the step cycle conditioned with transspinal stimulation delivered at sub- and suprathreshold intensities of the spinally mediated transspinal evoked potential (TEP). Transspinal stimulation was delivered before or after transcranial magnetic stimulation during which summation between MEP and TEP responses in the surface EMG was absent or present. Relationships between MEP amplitude and background EMG activity, silent period duration, and phase-dependent EMG amplitude modulation during and after stimulation were also determined. Ankle flexor and extensor MEPs were depressed by suprathreshold transspinal stimulation when descending volleys were timed to interact with transspinal stimulation-induced motoneuron depolarization at the spinal cord. MEP depression coincided with decreased MEP gain, unaltered MEP threshold, and unaltered silent period duration. Locomotor EMG activity of bilateral knee and ankle muscles was significantly depressed during the step at which transspinal stimulation was delivered but fully recovered at the subsequent step. The results support a model in which MEP depression by transspinal stimulation occurs via subcortical or spinal mechanisms. Transspinal stimulation disrupts the locomotor output of flexor and extensor motoneurons initially, but the intact nervous system has the ability to rapidly overcome this pronounced locomotor adaptation. In conclusion, transspinal stimulation directly affects spinal locomotor centers in healthy humans.NEW & NOTEWORTHY Lumbar transspinal stimulation decreases ankle flexor and extensor motor evoked potentials (MEPs) during walking. The MEP depression coincides with decreased MEP gain, unaltered MEP threshold changes, and unaltered silent period duration. These findings indicate that MEP depression is subcortical or spinal in origin. Healthy subjects could rapidly overcome the pronounced depression of muscle activity during the step at which transspinal stimulation was delivered. Thus, transspinal stimulation directly affects the function of spinal locomotor networks in healthy humans.

P19-F Variability of Intraoperation monitoring parameters in patients with degenerative cervical myelopathy

Background motor cortex transcranial electric stimulation in Intraoperative monitoring (IOM) is used to assess the corticospinal functional state by measuring the fast axons conduction (registration of D-wave), motor evoked potentials (MEPs) threshold and amplitude. While D-wave is considered to be a stable parameter independent of anesthesia, the informativeness of MEPs amplitude is controversial due to its instability, especially when in cervical spine surgery. Material and methods 20 patients with cervical degenerative myelopathy underwent surgical decompression with anterior cervical discectomy. In Group 1 (10 patients) the TIVA anaestiological protocol was used and in Group 2 (10 patients) the Sevoflurane 0.6–0.8 MAC was added. In all patients before intubation MEPs threshold for m. abd. pollicis brevis, m.add. digiti minimi, m. tibialis anterior, m. add. hallucis were assessed in response to a train of 5 pulses with a duration of 0.5 ms and inter-pulse interval 2 ms. Results In the course of operation MEPs threshold increase and amplitude decrease were detected in all patients Group2. In 6 patients of Group 1 (4 – unilaterally, 2 – bilaterally) and 4 patients of Group 2 (2– unilaterally, 2 – bilaterally) during surgery MEPs responses were lost; though there were observed no signs of additional neurological deficit after surgery. Unilateral MEP changes in patients operated on cervical spine can be attributed to compression of the plexus related to the position and patient fixation; bilateral – because of traction manipulations and spinal cord ischemia. Conclusions for detection of intraoperational ischemia Multimodal IOM will be preferred.

Peculiarities of motor evoked potential in healthy children of different age

Aim of the work The implementation of the database for reference values of motor evoked potentials (MEP) in healthy children of different ages. Methods 95 healthy children were enrolled. Age ranged from 1 to 204 months. Three subgroups were established: children of 1-12 months (n=31, 18 males, 13 females), 12-144 months (n=27, 14 males, 13 females) and 144-204 (n=37, 20 males, 17 females) months. All children were healthy. Diagnostic transcranial magnetic stimulation (TMS) was performed in all patients. MEP shape, threshold, latency and amplitudes were recorded for hands (m. Abductor pollicis brevis) and legs (m. Abductor Hallucis). Central motor conduction time (CMCT) was calculated. Results. Along with age there was observed the elongation of MEP latency, gain in amplitudes and shape normalization. There were significant differences in the elongation of MEP latency between children aged of 1-12 months and children from two other subgroups (12-144 and 144-204 months). Conclusions. Our normative data can be usedfor comparative studies in the broad spectrum of pediatric disorders. Age restrictions have to be taken in a consideration when performing the TMS in pediatric population.

Contribution of corticospinal drive to ankle plantar flexor muscle activation during gait in adults with cerebral palsy.

Impaired plantar flexor muscle activation during push-off in late stance contributes importantly to reduced gait ability in adults with cerebral palsy (CP). Here we used low-intensity transcranial magnetic stimulation (TMS) to suppress soleus EMG activity during push-off as an estimate of corticospinal drive in CP adults and neurologically intact (NI) adults. Ten CP adults (age 34years, SD 14.6, GMFCS I-II) and ten NI adults (age 33years, SD 9.8) walked on a treadmill at their preferred walking speed. TMS of the leg motor cortex was elicited just prior to push-off during gait at intensities below threshold for motor-evoked potentials. Soleus EMG from steps with and without TMS were averaged and compared. Control experiments were performed while standing and in NI adults during gait at slow speed. TMS induced a suppression at a latency of about 40ms. This suppression was similar in the two populations when differences in control EMG and gait speed were taken into account (CP 18%, NI 16%). The threshold of the suppression was higher in CP adults. The findings suggest that corticospinal drive to ankle plantar flexors at push-off is comparable in CP and NI adults. The higher threshold of the suppression in CP adults may reflect downregulation of cortical inhibition to facilitate corticospinal drive. Interventions aiming to facilitate excitability in cortical networks may contribute to maintain or even improve efficient gait in CP adults.

Corticospinal excitability, assessed through stimulus response curves, is phase-, task-, and muscle-dependent during arm cycling

The purpose of the present study was to examine corticospinal excitability to the biceps and triceps brachii during arm cycling and an intensity-matched tonic contraction using stimulus response curves (SRCs) elicited via transcranial magnetic stimulation (TMS). Corticospinal excitability was assessed using TMS elicited motor-evoked potentials (MEPs) at eight different stimulation intensities (85–190% of MEP threshold). MEPs were recorded during arm cycling at two different positions, mid-elbow flexion (6 o’clock relative to a clock face) and mid-elbow extension (12 o’clock relative to a clock face), in addition to an intensity-matched (12 o’clock) tonic contraction. At the 12 o’clock position, the slope of the SRC was significantly lower during arm cycling than the tonic contraction for the biceps brachii (Cycling: 0.64 ± 0.47, Tonic: 1.02 ± 0.38, P < 0.05) but was not different for the triceps brachii (Cycling: 1.33 ± 0.49, Tonic: 1.48 ± 0.43, P = 0.42). Within arm cycling, the SRC slope was significantly greater at the 6 o’clock position than 12 o’clock position for the biceps brachii (6 o’clock: 1.37 ± 0.24, 12 o’clock: 0.64 ± 0.47, P < 0.05) but was not different for the triceps brachii (6 o’clock: 1.11 ± 0.28, 12 o’clock: 1.33 ± 0.49, P = 0.34). These findings demonstrate that corticospinal excitability to the biceps brachii is task-dependent during the extension phase of arm cycling. Neither position nor task influenced corticospinal excitability to the triceps brachii, providing further support that the motor control of locomotor outputs is muscle-specific.

Operant conditioning of the tibialis anterior motor evoked potential in people with and without chronic incomplete spinal cord injury.

The activity of corticospinal pathways is important in movement control, and its plasticity is essential for motor skill learning and re-learning after central nervous system (CNS) injuries. Therefore, enhancing the corticospinal function may improve motor function recovery after CNS injuries. Operant conditioning of stimulus-induced muscle responses (e.g., reflexes) is known to induce the targeted plasticity in a targeted pathway. Thus, an operant conditioning protocol to target the corticospinal pathways may be able to enhance the corticospinal function. To test this possibility, we investigated whether operant conditioning of the tibialis anterior (TA) motor evoked potential (MEP) to transcranial magnetic stimulation can enhance corticospinal excitability in people with and without chronic incomplete spinal cord injury (SCI). The protocol consisted of 6 baseline and 24 up-conditioning/control sessions over 10 wk. In all sessions, TA MEPs were elicited at 10% above active MEP threshold while the sitting participant provided a fixed preset level of TA background electromyographic activity. During baseline sessions, MEPs were simply measured. During conditioning trials of the conditioning sessions, the participant was encouraged to increase MEP and was given immediate feedback indicating whether MEP size was above a criterion. In 5/8 participants without SCI and 9/10 with SCI, over 24 up-conditioning sessions, MEP size increased significantly to ~150% of the baseline value, whereas the silent period (SP) duration decreased by ~20%. In a control group of participants without SCI, neither MEP nor SP changed. These results indicate that MEP up-conditioning can facilitate corticospinal excitation, which is essential for enhancing motor function recovery after SCI. NEW & NOTEWORTHY We investigated whether operant conditioning of the motor evoked potential (MEP) to transcranial magnetic stimulation can systematically increase corticospinal excitability for the ankle dorsiflexor tibialis anterior (TA) in people with and without chronic incomplete spinal cord injury. We found that up-conditioning can increase the TA MEP while reducing the accompanying silent period (SP) duration. These findings suggest that MEP up-conditioning produces the facilitation of corticospinal excitation as targeted, whereas it suppresses inhibitory mechanisms reflected in SP.

Effects of pulse width, waveform and current direction in the cortex: A combined cTMS-EEG study

Backgroundthe influence of pulse width, pulse waveform and current direction on transcranial magnetic stimulation (TMS) outcomes is of critical importance. However, their effects have only been investigated indirectly with motor-evoked potentials (MEP). By combining TMS and EEG it is possible to examine how these factors affect evoked activity from the cortex and compare that with the effects on MEP. Objectivewe used a new controllable TMS device (cTMS) to vary systematically pulse width, pulse waveform and current direction and explore their effects on global and local TMS-evoked EEG response. MethodsIn 19 healthy volunteers we measured (1) resting motor threshold (RMT) as an estimate of corticospinal excitability; (2) global mean field power (GMFP) as an estimate of global cortical excitability; and (3) local mean field power (LMFP) as an estimate of local cortical excitability. ResultsRMT was lower with monophasic posterior-to-anterior (PA) pulses that have a longer pulse width (p < 0.001). After adjusting for the individual motor threshold of each pulse type we found that (a) GMFP was higher with monophasic pulses (p < 0.001); (b) LMFP was higher with longer pulse width (p = 0.015); (c) early TEP polarity was modulated depending on the current direction (p = 0.01). ConclusionsDespite normalizing stimulus intensity to RMT, we found that local and global responses to TMS vary depending on pulse parameters. Since EEG responses can vary independently of the MEP, titrating parameters of TMS in relation to MEP threshold is not a useful way of ensuring that a constant set of neurons is activated within a cortical area.

P311 The effectiveness of the complex repetitive peripheral magnetic stimulation (rPMS) in treatment of lumbosacral radiculopathy

Objective In the modern society the low back pain (LBP) is the most common cause of temporary disability with estimated life time prevalence as high as 23–80% (Pedisic et al., 2013). LBP with radiculopathy is considered as the most unfavorable prognostic risk factor for the development of chronic pain syndrome and low quality of life (Konstantinou et al., 2013). The aim of this study is to evaluate the short-term efficacy of repetitive peripheral magnetic stimulation (rPMS) in the treatment of lumbosacral radiculopathy. Methods Patients with pain and sensory symptoms resulting from lumbosacral radiculopathy has been enrolled into the study. All patients received conventional drug therapy. A magnetic stimulator MagProO100 (Magventure, Denmark) with CC-coil Cool-125 was used. We assessed the individual motor evoked potential (MEP) thresholds before the rPMS. Treatment consisted of 10 or 15 sessions, each lasting 20 min, with frequency 1 Hz and intensity of stimulus above the MEP threshold. The duration of rPMS treatment depended on the severity of pain syndrome. Patients were evaluated before, immediately after finalizing the rPMS treatment and one month later. Results Fifteen patients (mean age 41.8 ± 14.5 years, 5 men, 10 women) has been included into the study. All participants reported the improvement in the functional status (confirmed by Oswestry questionnaire): 34.4 ± 11.3% before and 17.6 ± 8% at the end of the rPMS course (primary endpoint). The VAS pain level has been decreased by 50% in comparison to the baseline. Reduction of pain and disability remained unchanged for one month after completion of the combined treatment. Conclusion The preliminary results of our study demonstrate that the combination of traditional drug therapy and the rPMS can have positive short-term effects on functional status and pain in patients with lumbosacral radiculopathy. Further investigations are warranted for development of the individualized rPMS treatment algorithm.

A randomized crossover study of the effects of lidocaine on motor- and sensory-evoked potentials during spinal surgery

Background ContextLidocaine has emerged as a useful adjuvant anesthetic agent for cases requiring intraoperative monitoring of motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SSEPs). A previous retrospective study suggested that lidocaine could be used as a component of propofol-based intravenous anesthesia without adversely affecting MEP or SSEP monitoring, but did not address the effect of the addition of lidocaine on the MEP and SSEP signals of individual patients. PurposeThe purpose of this study was to examine the intrapatient effects of the addition of lidocaine to balanced anesthesia on MEPs and SSEPs during multilevel posterior spinal fusion. Study DesignThis is a prospective, two-treatment, two-period crossover randomized controlled trial with a blinded primary outcome assessment. Patient SampleForty patients undergoing multilevel posterior spinal fusion were studied. Outcome MeasuresThe primary outcome measures were MEP voltage thresholds and SSEP amplitudes. Secondary outcome measures included isoflurane concentrations and hemodynamic parameters. MethodsEach participant received two anesthetic treatments (propofol 50 mcg/kg/h and propofol 25 mcg/kg/h+lidocaine 1 mg/kg/h) along with isoflurane, ketamine, and diazepam. In this manner, each patient served as his or her own control. The order of administration of the two treatments was determined randomly. ResultsThere were no significant within-patient differences between MEP threshold voltages or SSEP amplitudes during the two anesthetic treatments. ConclusionsLidocaine may be used as a component of balanced anesthesia during multilevel spinal fusions without adversely affecting the monitoring of SSEPs or MEPs in individual patients.

EP 62. Motor evoked potentials mapping improves detection of capsular side effects during deep brain stimulation

Introduction One of the main reasons to perform deep brain stimulation (DBS) on awake patient is detection of activation of descending capsular motor pathways as they represent therapy-limiting side effect. Current technique of capsular activation detection is based on visual detection of muscular contraction during stimulation with standard “tonic” DBS stimulation parameters. Intraoperative mapping of subcortical motor evoked potentials (MEP) during DBS surgery, as already shown in the literature, is feasible and time-efficient, also in patients under general anesthesia. We investigate value of motor evoked potentials mapping in basal ganglia as alternative measurement of safe therapeutic window in stimulation parameters. Methods This study includes recording data of 7 Patients, undergoing awake DBS surgery in subthalamic nucleus or in thalamus and of 1 DBS patient under general anesthesia. Recording data of 16 trajectories and 32 stimulation sites was available. Anodal stimulation was applied in stereotactic target on the macroelectrode tip (microTargeting electrodes, FHC, USA) using train-of-five technique in 1 mA steps 0–5 mA. Recordings were obtained using skin surface electrodes on projection of m. mentalis, m. abductor pollicis brevis, m. flexor digitorum, m. tibialis anterior on contralateral to stimulation side. Visual detection of motor contraction under 130 Hz 60 μs stimulation in 1 mA steps (0–5 mA) was used as standard control parameter. Results MEP recordings were successful in all stimulation sites. MEP threshold current correlated with current values of 130 Hz stimulation, which caused visually detectable muscle contractions and with postoperative DBS side effect thresholds. Detection of muscle response activation was very sensitive and muscle-specific and remained stable under repeated stimulation. Patients described very little or no discomfort during MEP mapping, significantly lower comparing to classical 130 Hz stimulation on motor-threshold. MEP threshold detection was easily obtainable under propofol-remifentanyl general anesthesia and had same current values as “tonic” stimulation postoperatively. Conclusions MEP mapping in basal ganglia is safe and feasible alternative to standard motor side-effect detection, which can improve safety and comfort of DBS procedure. MEP motor threshold correlates well to capsular activation with standard DBS parameters and can be obtained under general anesthesia.