Comparison of primary motor cortex localization using functional magnetic resonance imaging and magnetoencephalography

The primary goal of the study was to compare estimates of motor cortex localization from functional magnetic resonance imaging (FMRI) and magnetoencephalography (MEG). Thirteen normal volunteers were studied using both methods. FMRI was performed on a clinical 1.5 T system using gradient-echo acquisitions and basic t-test processing. MEG primary motor field was characterized by a single dipole model. Comparisons between the location of the best-fitting MEG dipole and the FMRI activation results were made using both fixed regions-of-interest weighted averaging and clustering analysis to reduce the observed FMRI activations to a single representative location. Both FMRI and MEG identified expected anatomic regions of primary motor activity and there was overall agreement to within 10 mm between these two functional imaging modalities. Given the observed agreement between these two techniques, it does not appear that the proposed artifactual mechanisms of local bulk motions or large-vessel sensitivity will seriously preclude the clinical utility of FMRI for preoperative localization of sensorimotor cortex. © 1996 Wiley-Liss, Inc.     

脑磁图定位皮质运动区与术中皮质电刺激运动诱发电位的对照研究

目的评价脑磁图（MEG）术前定位初级运动皮质（M1）的准确性。方法选取顺序入院的中央区胶质瘤26例,术前均运用MEG定位皮质运动区,与MRI导航影像融合,在神经导航下定位MEG激活区。术中对MEG成功定位的病例行直接皮质电刺激（DCES）,比较两种技术的吻合度。结果因病人不能配合,MEG定位失败2例,余24例均定位成功,每例激活区1～5个。DCES成功监测24例,所有选择的DCES靶点共41个,阳性靶点24个,1个/例。以所有的41个靶点分析,MEG定位M1区与DCES定位的吻合率为58.5%;而以第1组病灶侧M1区和第2组病灶侧中央区的MEG激活区中27个靶点分析,两者吻合率为88.9%;仅以第1组M1区的MEG激活区中17个靶点分析,两者吻合率为100%。结论 MEG可以灵敏而可靠地定位M1区,可用于中央区胶质瘤病人术前手术规划。     

Abnormalities of somatosensory and motor evoked potentials in adrenomyeloneuropathy: Comparison with magnetic resonance imaging and clinical findings

We studied 6 patients with adrenomyeloneuropathy (AMN) showing mild signs of central nervous system involvement. All patients underwent brain and spinal magnetic resonance imaging (MRI) and somatosensory (SEP) and motor (MEP) evoked potential study. Whereas SEPs and MEPs were abnormal in all patients, only 1 patient showed brain MRI abnormalities; spinal MRI showed hypotrophy without focal abnormalities in 4 of 6 patients. Median nerve SEPs, which were recorded with noncephalic reference montage, revealed delayed or absent scalp P14 far-field potential in all patients and abnormal spinal N13 in 2. Moreover, tibial nerve SEPs revealed abnormalities of the subcortical P30 response in all 4 patients in whom scalp-to-ear recording was employed. These findings strongly suggest that in the early stages of disease neurological dysfunction is localized in the spinal cord, where it is difficult to assess using MRI. However, SEPs and MEPs, which show a typical pattern of abnormality in these patients, could be useful in disclosing signs of long tract involvement and in monitoring treatment. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1249–1257, 1997     

直接皮质刺激运动诱发电位在累及运动区胶质瘤切除术中运动通路保护研究

目的在累及运动区的胶质瘤切除术中．利用直接皮质刺激产生的运动诱发电位（MEP）去判断运动传导通路纤维的数量和功能，并分析其变化和术后病人四肢运动功能的关系。方法对42例累及运动区的胶质瘤病人．术中利用微弱电流直接刺激运动区皮质并记录产生的运动诱发电位，比较肿瘤切除前、中、后MEP的变化，分析肿瘤切除后MEP下降程度和术后3个月四肢运动功能的关系。结果切瘤后MEP较切瘤前波幅下降50％以上26例，其中出现严重运动功能障碍17例（65．4％）．轻度运动功能障碍9例（34．5％）；MEP下降50％以下16例，其中出现严重运动功能障碍2例（1.3％），轻度运动功能障碍10例（62．5％）．基本正常4例（25．0％）。两组严重运动功能障碍经Х^2检验，P〈0．05，差异有统计学意义。结论术中行直接皮质刺激运动诱发电位监测可直接反映运动传导纤维的数量和功能，预测术后肢体运动情况。MEP波幅下降50％可作为将发生严重运动功能障碍的临界警戒点．     

Comparison of Rossini–Rothwell and adaptive threshold‐hunting methods on the stability of TMS induced motor evoked potentials amplitudes

Several methods can be used to determine the resting motor threshold (RMT) and by that recording transcranial magnetic stimulation (TMS) induced motor evoked potentials (MEPs). However, no research has compared the test retest reliability of these methods. Thus, the aim of this study was to determine intra‐ and inter‐session reliability of Rossini–Rothwell (R–R) and parameter estimation by sequential testing (PEST) methods on TMS‐induced MEPs and comparison of these two methods on RMT. Twelve healthy individuals participated in this study three times (T1, T2 and T3) over two days. TMS was applied using both R–R and PEST to estimate RMT and average of 25 MEPs were acquired at each of the three time points. The intra‐class correlation coefficient indicated high intra‐session reliability in the MEP amplitudes for both methods (0.79 and 0.88, R–R and PEST respectively). The RMT and MEP amplitudes had higher inter‐session reliability in both methods (0.99 and 0.998, R–R and PEST respectively; 0.84 and 0.76, R–R and PEST respectively). There was no significant difference between methods for RMT at both T1 (maximum stimulator output of R–R vs. PEST, 33.7% ± 7.7% vs. 33.8% ± 7.6%, p = 0.75) and T3 (maximum stimulator output of R–R vs. PEST, 33.5% ± 7.3% vs. 33.7% ± 7.3%, p = 0.19). There was a significant positive correlation between the methods' estimates of RMT, with PEST requiring significantly fewer stimuli. This study shows that the R–R and PEST methods have high intra‐and inter‐session reliability and the same precision, with PEST having the advantage over R–R in speed of estimation of RMT.     

Megnetic motor evoked potentials (MEP) in diseases of the spinal cord

Transcranial magnetic stimulation (TMS) is a non-invasive diagnostic method particularly suited to investigation of the long motor tracts. The clinical value of this method in many cortical and subcortical diseases has been well established, but comparable studies for most spinal cord diseases have still to be made. Forty patients in whom spinal cord disease was established by clinical examination, cerebrospinal fluid examination, and magnetic resonance imaging (MRI) were studied by means of somatosensory evoked potentials (SEP, median and tibial nerve stimulation) and magnetic motor evoked potentials (MEP, first dorsal interosseus and tibialis anterior muscle recordings after transcranial and spinal stimulation). The underlying pathology was neoplastic (n= 16), inflammatory (n= 15) or ischemic (n = 9). Clinical signs and symptoms ranged from slight sensory disturbances to complete paraplegia and had developed within minutes (ischemia) or over many years (benign neoplastic disease). The overall frequency of pathological SEP was slightly higher than that of MEP (78% vs 68%) which was statistically not significant (p > 0.05). This was also true for the subgroups, except for pure motor disorders, which gave the same yield for both methods. Decreased amplitudes or absence of MEP were more frequent in neoplastic than in inflammatory lesions (75% vs 33%, p < 0.05). In the latter, however, MEP more often occurred with increased latencies (40% vs 31%, p > 0.05, n. s.). Pathological SEP were found in 75% of patients presenting with pure motor abnormalities, while pathological MEP were found in 30% of patients with pure sensory disturbances. We conclude, in common with the SEP, the MEP are helpful in the examination of spinal cord diseases, even in subclinical disturbances, although the SEP would seem to yield a larger percentage of pathological results.     

Etomidate dose-response on somatosensory and transcranial magnetic induced spinal motor evoked potentials in primates

Abstract

There is growing interest and need to monitor reliably both motor (MEP) and somatosensory (SEP) evoked potentials under anesthesia. On a pre-established primate model, the present study examined the effect of incremental etomidate (ET) dosages on spinal neural MEPs to transcranial magnetic stimulation (TMS) and posterior tibial rate (PTN) SEPs. Through a small thoracic Tl 1-T12 laminotomy, an insulated double bipolar electrode was inserted epidurally in seven cynomolgus monkeys. Spinal TMS-MEPs, PTN-SEPs, and frontal EEC were tested against graded increase of ET doses. Etomidate 0.5 mg kg-1 i.v. was initially given and followed by 30 min continuous infusion of 0.01 mg kg^1 min~1, 0.018, 0.032, 0.056, 0.1, and 0.18 mg kg'1 min"1 in that order. Measurable spinal MEPs and SEPs were recorded under deep ET anesthesia (total 12.38 mg kg-1 cumulative dose over 180 min). The EEC showed marked slow wave and graded burst suppression at cumulative dose of ^3.14 mg kg~'. The direct (D) and subsequent initial indirect (I) waves (Ij, l2,13) were reproducible at doses <0.18 mg kg~7 min~1 infusion. The latter l-waves (l4 and l5) showed graded loss at infusion dosage 0.056 mg kg'1 min~1. Etomidate remains an anesthetic of attractive features in neuroanesthesia. In the primate model, neural MEPs-SEPs were reproducible despite the exceedingly high dose of ET and markedly depressed EEC. Moreover, MEP-SEP can be monitored during ET burst-suppressive neuroprotective state. The study may set a model in humans for intra-operative multi-modality neurophysiologic recording under ET-based anesthesia. [Neurol Res 1999; 21: 714-7201     

Central fatigue as revealed by postexercise decrement of motor evoked potentials

We have previously shown that the amplitudes of motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) were transiently decreased after exercise, indicating fatigue of motor pathways in the central nervous system. The responsible mechanism is apparently decreased efficiency in the generation of the descending volleys in the motor cortex. We also noted a progressive decrement inamplitude from the first to the fourth MEP. To further clarify the mechanism of this phenomenon, 5 subjects were studied with TMS deliveredat the rates of 0.1, 0.15, 0.3, 1, 3, and 6 Hz. The effect was best demonstrated at 0.3 Hz, and occurred after both isometric and isotonic exercise. Three of the subjects also had 0.3-Hz percutaneous electrical stimulation of the brainstem, and a decrement in MEP amplitude did not occur. Further, the delivery of TMS during muscle contraction after muscle fatigue failed to produce a decrement. The results are similar to those found at the neuromuscular junction in myasthenia gravis and are consistent with a reduced safety factor of cortical synaptic transmission in central nervous system fatigue. © 1994 John Wiley & Sons, Inc.     

Superior colliculus lesions and flash evoked potentials from rat cortex

It is generally assumed that the primary response of the rat flash evoked potential (FEP) is activated by a retino-geniculate path, and that the secondary response reflects input to the cortex by way of the superior colliculus (SC) or other brainstem structures. In the present study, male Long-Evans rats were implanted with monopolar screw electrodes placed over the left visual cortex, and a pair of twisted monopolar depth electrodes, which were used to produce electrolytic lesions, were placed in each SC. One half of the animals did not receive the electrolytic treatment (controls). FEP waveforms were obtained from all animals prior to treatment, and 2 and 5 days after treatment. Histological analysis was performed to verify electrode placement and determine lesion size. Electrolytic lesions resulting in massive destruction of the SC produced no decrement in any portion of the rat FEP but did produce an increase in amplitude of the N2P3 component. The data show that the secondary response is not generated by SC in rats, but that SC may modulate amplitude of the response.     

Facilitation of motor evoked potentials: Timing of jendrassik maneuver effects

Remote voluntary contraction, such as the classical Jendrassik maneuver (JM), is a procedure routinely used to increase the amplitude of tendon reflexes in the lower limb. In 8 healthy subjects we studied the effects of JM on the motor evoked potentials (MEP) recorded from tibialis anterior muscle, produced by transcranial magnetic stimulation (stimulus output of 5–10% over motor threshold). In this study, JM consisted here of a bilateral violent handgrip, preceding magnetic stimulation from 100 to 50 ms (steps of 100 ms). Compared to the control test, latencies remained unchanged. MEP amplitudes were greatly enhanced with a JM test interval from 200 to 400 ms (170% of control amplitude at 300 ms). We also studied 6 patients with severe alterations of MEPs from tibialis anterior muscle. In each case, JM preceding magnetic stimulation (stimulus output 100%) from 300 ms induced reappearance of response or marked enhancement of amplitude, allowing calculation of central conduction time. Such a technique, which is easy to perform, may be useful in clinical practice to calculate central motor conduction time, where it would otherwise be difficult or impossible. © 1995 John Wiley & Sons, Inc.     

Magnetically evoked motor potentials in demyelinating and axonal polyneuropathy: a comparative study

We investigated the value of magnetically evoked motor potentials (MEPs) for the differentiation of demyelinating and axonal polyneuropathies. The study population comprised 107 patients, with polyneuropathy verified by electromyography (EMG) and nerve conduction study (NCS), who had also been examined by means of MEP. MEPs were evoked by magnetic stimulation of the cortex and the spinal roots and were recorded from three upper limb muscles and two lower limb muscles bilaterally. From the EMG/NCS results 53 patients were characterized as having primary demyelination (demyelinating patients) and 54 as having axonal involvement (axonal patients). Demyelinating patients were classified as acute (acute inflammatory demyelinating polyradiculoneuropathy: AIDP) or chronic (chronic inflammatory demyelinating polyradiculoneuropathy: CIDP) according to the duration of illness. A series of indices were calculated from MEP results. One demyelinating patient and two axonal patients had normal MEPs. The MEPs of the demyelinating patients showed significantly longer peripheral conduction times, larger interside differences and lower amplitudes than the axonal patients. The central conduction index and the amplitudes upon cortical stimulation were significantly higher in patients with CIDP than in those with AIDP. Peripheral conduction time prolonged by more than 85% in at least one of the 10 muscles studied or a peripheral conduction index of above 9.4 were pathognomonic for demyelination. By combining all criteria 75% of the patients could be categorized as CIDP vs. AIDP in accordance with the EMG/NCS diagnosis. Likewise, 83% were categorized correctly as demyelinating versus axonal according to the EMG/NCS data.     

Monitoring spinal cord motor and somatosensory evoked potentials in anesthetized primates

Abstract

Monitoring Motor Evoked Potential (MEP) to Transcranial Stimulation (TMS) monitoring (MEP) is a growing technique to assess motor function under anesthesia. The following primate study was conducted to analyze the non-myogenic spinal motor and sensory volleys and to examine their reproducibility under nitrous oxide-methohexidone anesthesia. The traveling periodic spinal descending MEP to TMS and ascending somatosensory (SEP) to posterior tibial nerve stimulation across the thoracic cord were recorded in 12 cynomolgus monkeys. Through a small Tn~Tu laminotomy, an insulated stainless steel electrode was inserted into the epidural thoracic space. The potentials were analyzed under 50 vol% NO in 02 with methohexital (0.1-0.2 mg kg~1 min~1). A well-defined periodic TMS-MEPs and PTN-SEPs were recorded with high reproducibility and consistency in repeated trials under N20-methohexital anesthesia. MEP tracing consisted of an initial peak (direct (D) wave), occurring at 2.43 (±0.28) msec followed by subsequent five positive (indirect (I) waves). Spinal SEPs-MEPs were clearly defined, morphologically stable, and consistent over time under N20-methohexitone anesthesia. The present primate study may set a model to monitor both modalities in anesthetized neurosurgical patients.[Neurol Res 1999; 21: 359-367]     

Visual evoked potentials in cerebral white matter hyperintensity on MRI

OBJECTIVES: To investigate the correlation of the cerebral white matter hyperintensities (WMH) on MRI, and latency and amplitude of visual evoked potentials (VEPs) in elderly subjects. PATIENTS AND METHODS: Pattern VEP (PVEP) and flash VEP (FVEP) were recorded in 25 patients with WMH consisting of 12 patients with frontal dominant WMH (FMH) and 13 patients with occipital dominant WMH (OMH) and 25 patients with basal ganglionic hyperintensities (BGH). RESULTS: In WMHs, there were significantly larger P100 and P2 amplitudes than in BGHs and controls. Regarding the distribution of WMH, OMH showed significantly larger P100 amplitudes than FMH. In OMH in males, there was significantly prolonged P100 latency compared with females, and in females, there were significantly larger P100 and P2 amplitudes compared with males. CONCLUSION: Appropriate clinical values in VEP should take into consideration WMH in addition to gender and age-related changes.     

帕金森病患者运动皮质兴奋性的经颅磁刺激研究

目的:本研究拟应用低频重复性经颅磁刺激(rTMS)分别刺激帕金森病(PD)患者M1手代表区(M1Hand)及运动前区(PMC),探讨不同干预手段对运动皮质兴奋性的影响,以及M1与PMC间的联系。方法:对18名确诊PD患者先后进行4种不同干预,即口服美多芭、低频rTMS刺激M1Hand(0.5Hz,100%静息阈值,共1600次脉冲)、低频rTMS刺激PMC(0.5Hz,100%静息阈值,共1600次脉冲)以及假刺激。于每次干预前后各进行临床评价并测定运动诱发电位(MEP)相关指标。结果:①口服美多芭后UPDRSⅢ(P=0.001)以及其中有关僵直(P=0.001)、运动迟缓(P<0.001)的评分均较服药前显著改善。三种不同磁刺激干预产生结果不同,M1Hand组UPDRSⅢ减低(P=0.015),僵直(P=0.010)、运动迟缓(P=0.004)亦有所改善;PMC组UPDRSⅢ较干预前减低(P=0.046),僵直评分亦减低,但无显著性意义(P=0.163);②口服美多芭1h后MEP120减低(P=0.002),CSP延长(P=0.006);M1Hand组MEP120无著变,而CSP延长(P=0.015);PMC组MEP120减低(P=0.004),而CSP无著变;假刺激组则均无显著性改变。结论:低频rTMS对不同脑区产生的效应不同:刺激M1可使CSP延长;而刺激PMC可使MEP波幅减低。     

磁刺激运动诱发电位及磁共振对脊髓炎定位诊断的对比分析

目的比较磁刺激运动诱发电位(MEP)和脊髓磁共振(MRI)检查对急性横贯性脊髓炎(ATM)和视神经脊髓炎(NMO)病人进行定位诊断的价值。方法对临床确诊为ATM 40例和25例NMO的住院患者的MEP和MRI检查结果进行分析,比较两种检查定位符合率。结果MRI显示ATM患者以胸脊髓损害为主,NMO组患者以颈胸段联合损害为主。MEP显示ATM组患者主要表现为上肢锥体束传导正常、下肢锥体束传导异常,而NMO组患者在表现为上下肢锥体束传导均异常。当病变位于颈髓时,ATM组患者定位符合率为92.8%,NMO组患者定位符合率为95.2%;当病变位于胸髓时,ATM符合率100%,NMO符合率80%。结论在ATM和NMO患者中,MEP提示的锥体束异常部位与MRI所证实的病变部位相吻合。     

Focal enhancement of motor cortex excitability during motor imagery: a transcranial magnetic stimulation study

OBJECTIVES: In order to learn more about the physiology of the motor cortex during motor imagery, we evaluated the changes in excitability of two different hand muscle representations in the primary motor cortex (M1) of both hemispheres during two imagery conditions. MATERIALS AND METHODS: We applied focal transcranial magnetic stimulation (TMS) over each M1, recording motor evoked potentials (MEPs) from the contralateral abductor pollicis brevis (APB) and first dorsal interosseus (FDI) muscles during rest, imagery of contralateral thumb abduction (C-APB), and imagery of ipsilateral thumb abduction (I-APB). We obtained measures of motor threshold (MT), MEP recruitment curve (MEP-rc) and F waves. RESULTS: Motor imagery compared with rest significantly decreased the MT and increased MEPs amplitude at stimulation intensities clearly above MT in condition C-APB, but not in condition I-APB. These effects were not significantly different between right and left hemisphere. MEPs simultaneously recorded from the FDI, which was not involved in the task, did not show facilitatory effects. There were no significant changes in F wave amplitude during motor imagery compared with rest. CONCLUSIONS: Imagery of unilateral simple movements is associated with increased excitability only of a highly specific representation in the contralateral M1 and does not differ between hemispheres.     

A study of clinical, MRI and multimodality evoked potentials in neurologic Wilson disease

The aims of this study were evaluate motor, somatosensory, visual and auditory brainstem evoked potential (MEP, SEP, VEP, ABER) changes in Wilson disease (WD) and correlate these with magnetic resonance imaging (MRI) and clinical findings.
Neurologic WD diagnosed on the basis of clinical, ceruloplasmin and Kayser–Fleischer ring were evaluated including pedigree charting, hepatic, renal, hematologic and osteoarticular manifestations. Blood counts, serum chemistry, MRI, MEP to tibialis anterior, tibial SEP, VEP and ABER were performed. Evoked potential (EP) changes were correlated with clinical and MRI findings.
Eighteen WD patients were recruited from 17 families whose mean age was 16 years. Movement disorders were present in 14, cognitive decline in 12 and pyramidal signs in 12 patients. MRI revealed involvement of basal ganglia in 80%, thalamus in 40%, brain stem in 46.7% and subcortical white matter in 53.3%. MEP was abnormal in 35.7%, SEP in 30.8%, VEP in 57% and ABER in 61.5% patients; the latter three EP changes were subclinical. Frequency and number of EP abnormalities were higher with increasing severity of illness.
SEP, VEP and ABER reveals subclinical abnormality and MEP helps in documenting both clinical and subclinical abnormalities. Number of EP abnormalities increases with increasing clinical severity of WD.     

Intrarectal ground electrode improves the reliability of motor evoked potentials recorded in the anal sphincter

Motor evoked potentials (MEPs) can be recorded in the external anal sphincter in response to magnetic stimulation of the cerebral cortex or sacral roots. However, the magnitude of the stimulus artifact may alter the reliability of anal MEP recording. An intrarectal ground electrode substantially reduces stimulus artifact and technical failure, improving MEP latency determination to sacral root stimulation in particular.     

磁刺激运动诱发电位对大脑半球切除术前运动功能的评估价值

目的探讨应用经颅磁刺激运动诱发电位（TMS—MEP）评估双侧肢体运动功能的半球支配情况。方法对10例顽固性癫痫、准备行改良大脑半球切除术的病人进行TMS—MEP检查。检查时蝶形线圈置于双侧大鱼际肌的皮质运动功能区，单侧刺激，同时记录双侧大鱼际肌的皮质TMS—MEP。将结果分为功能完全代偿、部分代偿和不能代偿。结果功能完全代偿2例，部分代偿6例．不能代偿2例。完全代偿的病人术后无运动功能损害加重．部分代偿的病人术后短期运动功能损害加重，3个月内运动功能恢复到术前水平。不能代偿的病人行改良大脑半球切除术。结论TMS—MEP能够客观评估顽固性癫痫病人双侧肢体运动功能的半球支配情况．是一种有效、可靠且无创的评估手段。