Frontal component of the somatosensory evoked potential

Electric stimulation of the median nerve at the wrist evokes a series of electric potentials that can be recorded from the scalp or directly from the cortex. These somatosensory evoked potentials (SEP) include a parietal negativity with a maximum 20 ms after the stimulus, which originates in the somatosensory cortex, probably area 3b (Allison et al. [1991a], Brain 114:2465–2503 and Desmedt et al. [1987], Electroenceph Clin Neurophysiol 68:1–19). Thirty milliseconds after the stimulus, a negative potential (N30) occurs at frontal recording sites. Recently it was observed that the amplitude of this potential is altered in patients with dystonia, Parkinson's disease, and Huntington's chorea. It has been argued that the N30 potential stems from cortical areas other than the somatosensory cortex, for example, the supplementary motor area. We used multichannel recordings to investigate the scalp distribution of the N20 and the N30 potentials in healthy subjects. We found that the N20 as well as the N30 potentials were accompanied by a corresponding positivity at frontal and parietal recording sites, respectively. The N20/P20 and the N30/P30 potential fields had a mirrorlike appearance, and both showed a polarity reversal near the central sulcus. This and the results of correlation analyses led us to the conclusion that the N30 generator is located near the central sulcus. © 1995 Wiley-Liss, Inc.     

Neurological associations of absent P60 component of the posterior tibial nerve somatosensory evoked potential

Abstract. The cortically generated P60 component of the posterior tibial nerve somatosensory evoked potential (PTSEP) is occasionally found to be absent in neurological patients,while the preceding P40 is preserved (Absent P60 pattern). A retrospective analysis of 24 such cases showed them to represent a different clinical population from that represented by 24 age- and sex-matched but otherwise unselected patients with entirely normal PTSEPs. The most frequent diagnoses of the patients with normal PTSEPs (conversion disorder and definite or suspected multiple sclerosis) were significantly less prevalent in the patients with the Absent P60 pattern, while miscellaneous other diseases affecting the peripheral and/or central sensory pathways were more frequent. In comparison with a second matched patient group with abnormal P40 in addition to P60, the patients with the Absent P60 pattern had a significantly lower incidence of large fibre sensory deficits (impaired vibration and/or joint-position sense). The incidence of small fibre deficits (impaired pain and/or temperature sensation) was similar in both groups with PTSEP changes. In conjunction with previously published findings in normal subjects, the data suggest that the P60 is a late response of the primary sensorimotor cortex due to activation of large diameter myelinated sensory fibres, but which is also tonically influenced by small fibre input. The Absent P60 pattern may be recognized as a distinct PTSEP abnormality, although its occurrence in some normal individuals should be noted.     

Recovery of sensation and somatosensory evoked potentials following toe-to-digit transplantation in man

Recovery of digital nerve function in 21 patients with toe-to-digit transplantation was evaluated by clinical sensory tests and somatosensory evoked potentials (SEPs) to median and digital nerve stimulation. The mean interval between injury and surgery was 7 months, and that between surgery and study was 31 months. The transplanted toes achieved a satisfactory but incomplete recovery in temperature (warm and cold), pinprick, touch, vibration, and two-point discrimination in that order. The overall sensory status of the transplanted toes appeared to be closer to normal toes than to normal fingers. In SEPs from the transplanted side, median N9, N13, and N20 components had normal latency but reduced amplitude, whereas digital N9 component was usually absent, but N13 and N20 components had prolonged latency and reduced amplitude. Transplantation performed within 1 month after injury prevented amplitude reduction in median SEPs and latency prolongation in digital SEPs. The SEP data suggest that timing of surgery was critical in preventing retrograde effect on the median nerve, and that recovery of digital nerve function was incomplete correlating with clinical sensory findings. © 1995 John Wiley & Sons, Inc.     

Short latency somatosensory evoked potential in children

The short latency somatosensory evoked potential was studied in 90 normal children of 1 month to 16 years old and 7 adults. Somatosensory stimuli were delivered through a disc electrode placed over the median nerve at the wrist joint. The uniform recording sites used were the central region of the scalp, and the seventh cervical spine or Erb's point. Reference electrodes were placed on the hand contralateral to the median nerve stimulated. Three positive peaks (P1, P2 and P3) and one negative peak (N1) were consistently recorded, a further positive peak (P4) after N1 was not always observed. The latency of each peak per 1 m body length decreased with age until 2 or 5 years of age. The latency of each peak after 2 years of age was positively correlated with the body length and arm length. The value of P1 peak latency per 1 m body length reaches adult values at an earlier rate than the value of P3 peak latency and P2-P3 latency per 1 m body length. This suggests that central lemmiscal pathways mature at a slower rate than peripheral nerve fibers. The wave form pattern of the short latency somatosensory evoked potential changed to the adult pattern at 10 years of age. The peak latency of P4 during deep sleep was slightly prolonged. In recording on infants during sleep, the EEG should be monitored to determine the stage of sleep.     

Short- and long-latency tibial somatosensory evoked potentials in cerebral lesions affecting rolandic leg areas

Summary Short- and long-latency tibial somatosensory evoked potentials (SEPs) were studied in nine patients with clinical presentation primarily involving one lower extremity. In group 1, with extensive infarcts in the territory of anterior cerebral artery, tibial cortical SEPs were uniformly absent. In group 2, with small infarcts involving Rolandic leg areas, tibial SEPs showed a decrease in overall response amplitude and attenuation of P40. In group 3, with discrete mass lesions compressing Rolandic leg areas, P40 was preserved but might be delayed. Late SEP components (N75, P100 and N135) tended to be preserved in the patients of group 2 and 3. The data suggest that Rolandic leg areas and the neighboring cortex are crucial for short- and long-latency tibial cortical SEPs and that small lesions affecting Rolandic leg areas tend to affect short-and mid-latency SEP components.     

Cortical evoked potential changes in a rat model of acute ischemic stroke Detection of somatosensory evoked potential and motor evoked potential

BACKGROUND:Studies have shown that latency changes of some elements in a somatosensory evoked potential (SEP) and motor evoked potential (MEP) can reflect electrical activity of cerebral cortical neurons and conduction of white matter nerve fibers. However, there is a paucity of information regarding the dynamic observation of SEP and MEP following cerebral ischemic injury. OBJECTIVE:To explore SEP and MEP changes following acute ischemic stroke, and investigate the role of evoked potentials in monitoring brain function in stroke. DESIGN, TIME AND SETTING:A randomized, controlled, animal experiment was performed at the Chongqing Key Laboratory of Neurology, Affiliated Hospital of Chongqing Medical University from September 2007 to August 2008.MATERIALS:Hydrogen blood flow detector was purchased from Soochow University Medical Instrument Co., China, and Power lab system was purchased from AD Instruments, Inc., USA. METHODS:A total of 36 healthy, adult, male, Sprague Dawley rats were randomly assigned to four groups (n = 9), including three ischemia groups (12, 24 and 72 hours of ischemia) and a sham-surgery group. The rat model of acute ischemic stroke was established by middle cerebral artery occlusion (MCAO) in the left hemisphere.MAIN OUTCOME MEASURES:SEP and MEP of the left limbs were detected, and cerebral blood flow was measured by the hydrogen cleaning method.RESULTS:The latency of positive wave 1 (P1), negative wave 1 (N1) and positive wave 2 (P2) waves in SEP, and latency of negative wave 1, 2 (N1, N2) waves in MEP were significantly prolonged with increasing ischemic duration following MCAO (P < 0.01), but cerebral blood flow was significantly decreased (P < 0.05, or P < 0.01).CONLUSION:Ischemic stroke prolongs the latency of SEP waves (P1, N1, P2) and MEP waves (N1, N2), and cerebral cortical evoked potential may correlate with cerebral blood flow changes. This indicates that SEP and MEP can be used to evaluate brain function following acute ischemic stroke.     

Electroencephalogram and somatosensory evoked potential changes after administration of six convulsant drugs

Electrophysiological effects of convulsant drugs in mammalian brain have been reported, but it has not been clear whether the changes described were indicative of general increases in neuronal excitability or whether they varied as a function of the different modes of convulsant action. Cats with chronically implanted electrodes were administered intraperitoneal injections of six convulsant drugs: allylglycine, bemegride, bicuculline, picrotoxin, pentylenetetrazol, and strychnine. The electroencephalogram (EEG) was monitored continuously and somatosensory evoked potentials were elicited during the period to seizure onset. Enhancement of the primary response of the evoked potentials recorded at the cortex paralleled the increases in EEG paroxysmal activity. Both EEG and evoked potential changes were regarded as indicating general preseizure excitability rather than varying with the presumed mechanisms of the individual drugs.     

体感诱发电位在复杂动脉瘤血管架桥及重建术中的应用

目的探讨体感诱发电位（SEP）在复杂动脉瘤血管架桥及重建手术中的应用。方法回顾分析2002～2008年24例复杂动脉瘤病人进行动脉瘤血管架桥及重建手术,术中分别采用动脉瘤切除远近端血管吻合,动脉瘤孤立加大隐静脉高流量搭桥或颞浅动脉低流量搭桥等方式处理动脉瘤,实时进行体感诱发电位监测：胫后神经刺激,记录双侧皮层的SEP。将P40波幅下降一半作为脑缺血的预警信号,潜伏期延长3ms作为参考。结果4例行动脉瘤切除远近端血管吻合,16例行大隐静脉高流量血管搭桥术,4例行颞浅动脉低流量血管搭桥。监测结果：Ⅰ型无变化16例;Ⅱ型加重但逐渐恢复：波幅下降一半,但稳定且略有回升4例;Ⅲ型加重无恢复：波幅下降一半,且继续下降,升高血压也无明显改善3例;Ⅳ型波形扁平且无恢复1例;Ⅴ型波形消失0例。结论在复杂动脉瘤手术中,术中体感诱发电位的监测可以提示血流阻断后脑供血情况及功能区脑灌注状态。对颅内动脉瘤手术的安全性提供了一定的保障,减少了手术风险,是一种简便、安全有效的监测技术。     

Recovery of somatosensory deficits in acute stroke

Objectives –  To study the recovery of somatosensory deficits after acute stroke.
Material and methods –  A detailed clinical examination of sensation, median nerve somatosensory evoked potentials (SEP), quantitative sensory tests (QST), and subjective evaluation were performed in five acute stroke patients at three control time points up to 12 months after the stroke.
Results –  The deficit recovered at least partially in all patients, mostly within 3 months after stroke. The improvement in warm and vibration detection thresholds occurred between 3 and 12 months. The SEP improved both by 3 and 12 months.
Conclusion –  The recovery of subjective sensory disturbance occurred in line with the improvement of the clinical sensory tests and QST. The most sensitive measure for somatosensory dysfunction at the early phase was graphesthesia. In our patients, initially normal SEP with a sensory deficit resulted in excellent clinical recovery, whereas initially absent SEP did not necessarily predict poor outcome.     

Effects of different sensory inputs on the median-derived somatosensory evoked potential

We studied the effect of a variety of "interfering" stimuli on the median-derived somatosensory evoked potentials recorded over Erb's point, cervical spine, and scalp. We found that the amplitude of N20 and P27 recorded over the scalp was attenuated by active movement, vibration, and tactile stimulation of the ipsilateral hand but not by passive movement. Cervical and peripheral responses were unaffected. The pathophysiologic basis and clinical significance of these findings are discussed.     

The blink reflex and somatosensory evoked potential in optic neuritis in South India

Optic Neuritis (ON) proceeds to multiple sclerosis (MS) in a considerable number of patients. The blink reflex (BR) and somatosensory evoked potential (SSEP) are useful non-invasive tests that can detect silent lesions in the central nervous system in patients with clinically suspect MS. In the present study, the BR and SSEP were done in 20 healthy controls and 20 patients with ON. Abnormalities of the SSEP were seen in 20%, and of the BR in 30% of the patients with ON. On combining the results of SSEP and BR studies, 45% of the ON patients were seen to have abnormalities. Over a short period of follow-up, 2 of the 20 ON patients developed clinical MS and both of them had had abnormalities of the BR. These findings suggest that ON proceeding to MS in India may be more common than suspected at present.     

Median nerve somatosensory evoked potentials in migraine

In visual evoked potential studies, habituation during stimulus repetition with the same stimulus at a constant intensity has been found to be abnormal in migraineurs between attacks. The purpose of this study was to investigate habituation of somatosensory evoked potentials (SEPs) and the effects of migraine on them. Eighty-five subjects were included in the study: 30 healthy volunteers (HVs) and 55 migraineurs [30 with migraine without aura (MO), 25 with migraine with aura (MA)]. During continuous stimulation at 3 Hz, four blocks of 100 responses were sequentially averaged of Erb's point (N9), cervical (N13), and cortical (N20) median nerve SEPs. Mean amplitude changes in the second, third and fourth blocks are expressed as percentages of the first block. There was habituation to N13 and N20 in the second, third and fourth blocks in HVs. In the migraine groups, there was no habituation; on the contrary, potentiation was found. This potentiation was statistically significant only in the second blocks for N13 (MO P=0.007, MA P=0.01 versus HVs). However, in both migraineur groups, the rate of N20 potentiations was statistically significant versus that in HVs for all blocks (all P < 0.05). It is concluded that whilst physiological habituation occurs in HVs for cervical and cortical SEPs, in migraine patients there is an interictal deficit of habituation of this sensory modality.     

The clinical significance of the P15 wave of the somatosensory evoked potential in tentorial herniation

Somatosensory evoked potentials (SEPs) to median nerve stimulation and auditory brainstem evoked potentials (BAEPs) were recorded in 16 comatose patients who had suffered transtentorial herniation (TH) due to intracranial haematoma, hydrocephalus or tumour. An attempt was made to correlate the changes in the N14-P15 component of the central conduction time (CCT) and the I-V interpeak latencies (IPLs) of the BAEP with the clinical severity of TH. The N14-P15 component was not affected in seven patients at the diencephalic or early third-nerve stage, and six of these seven showed normal I-V IPLs. All six patients at the late third-nervel midbrain stage or worse, however, showed abnormalities in the N14-P15 components. Interestingly, five patients showed dissociation of SEP and BAEP abnormalities suggesting a differential sensitivity of the medial and lateral lemnisci in the brainstem to ischaemia and/or compression. All five patients in whom the P15 potential was absent on either side had a poor outcome and there was a correlation between the electrical failure in the N14-P15 component and the degree of brainstem damage caused by TH as assessed clinically. Reversible loss of the P15 potential by brainstem retraction has been shown in intraoperative SEP monitoring during aneurysm surgery. Prolonged compression of the upper brainstem seems to cause irreversible loss of the P15 which should be regarded as being due to irrecoverable brainstem dysfunction.     

Ataxic hemiparesis syndrome: Sensory disturbances and somatosensory evoked potentials

26 patients with ataxic hemiparesis syndrome (AHS), due to acute ischemic cerebrovascular disease, have been submitted to clinical and electrophysiological evaluation, in order to assess the frequency of sensory disturbances in this condition. Sensory impairment were present in 78% and SEP abnormalities in 54% of the patients, while they were entirely absent in 23% of them. Lesions responsible for AHS, detected by CT scan, were mainly located in the thalamus, capsula interna, subcortical white matter, centro parietal cortex; sensory and SEP changes were more frequent in gross infarct involving the cortex and in smaller infarcts involving the thalamus, less frequent in the lacunar infarcts of the capsula interna and subcortical white matter, relatively rare in patients with CT scan without hypodense lesions. Although a statokinesthesic defect and/or major SEP abnormalities were often present (38% of patients), our findings do not support the view that they are involved in the pathogenesis of the ataxia, which may rather be attributed to a derangement of cerebro-cerebellar and cerebello-cerebral connections.

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Sommario 36 pazienti che presentavano una sindrome di Emiparesi Atassica (EA) sono stati studiati sotto il profilo clinico ed elettrofisiologico al fine di stabilire la frequenza dei disturbi sensitivi nel quadro in esame. Disturbi sensitivi e alterazione dei PES furono riscontrati rispettivamente nel 73% e nel 54% dei soggetti. Le lesioni responsabili della EA, documentate dalla TAC, risultavano localizzate nel talamo, nella capsula interna, nella sostanza bianca sottocorticale, nella corteccia centro-parietale. I disturbi sensitivi e le alterazioni dei PES erano più frequenti nei vasti infarti ad interessamento corticale e nei piccoli infarti talamici, meno frequenti negli infarti lacunari della capsula interna e della sostanza bianca, relativamente rari nei casi a TAC negativa per lesioni focali. Benché disturbi della sensibilità statochinestesica e/o alterazioni dei PES siano stati rilevati nel 38% dei soggetti studiati, gli AA. sono propensi a ritenere che la EA sia più provatamente ascrivibile ad interessamento delle connessioni cortico-cerebellari e cerebello-corticali.

     

脑干听觉诱发电位及体感诱发电位在重型颅脑损伤患者预后评估中的作用

目的 分析探讨脑干听觉诱发电位(BAEP)及体感诱发电位(SEP)与重型颅脑损伤病人预后的关系.方法 对33 例重型颅脑损伤患者早期行BAEP 及SEP 测定并进行动态监测,同时行头颅CT 检查并记录GCS 评分.结果 BAEP 及SEP 预测预后的敏感性、特异性、准确性均较高.BAEP、SEP 异常程度低,则预后较好;异常程度高,则预后不良.结论 BAEP、SEP 可以比较准确地评估重型颅脑损伤患者的预后.     

Effect of antiepileptic drugs on short-latency somatosensory evoked potentials

Short-latency somato sensory evoked potentials (SEPs) were recorded in 45 freshly diagnosed cases of epilepsy before starting treatment. Follow-up recordings were made 6 weeks and 3 months after diphenylhydantoin, carbamazipine and phenobarbitone monotherapy were started. Serum drug levels were monitored. Both amplitude and latency of the initial component (N20) remained unchanged and were identical to a group of 30 age- and sex-matched normal individuals in whom SEPs were recorded during the period of study.     

皮质体感诱发电位与肌电图监测在椎管内疾病手术中的应用

目的初步探讨神经电生理监测技术在椎管内疾病手术中的临床应用价值。方法回顾性分析30例椎管内疾病病人的临床资料。术前Frankel分级:C级4例,D级16例,E级10例。术中应用皮质体感诱发电位(CSEP)与肌电图(EMG)监测脊髓和神经根功能,分析手术过程并评价其效果。结果肿瘤全切10例,次全切13例,大部切除2例,部分切除2例;另有脊髓栓系综合征3例,术中完全松解黏连病变。术后10 d Frankel分级:改善6例,无变化22例,加重2例;术后1年Frankel分级:改善14例,无变化15例,加重1例。术前Frankel分级3组病人进行比较,术后10 d和1年的疗效差异均无统计学意义(均P>0.05)。结论在椎管内手术中联合应用CSEP与EMG监测可以更好地保护脊髓和神经根功能。     

Superior sensitivity of motor over somatosensory evoked potentials in the diagnosis of cervical spondylotic myelopathy

Myelopathy secondary to cervical spondylosis is often a difficult clinical diagnosis. Furthermore, with the introduction of magnetic resonance imaging (MRI) an increasing number of patients are identified with spondylotic cervical spinal cord compression. We analyzed the value of functional assessment of the spinal cord by motor and sensory evoked potentials (MEP and SEP) in the detection of myelopathy, with special emphasis on the correlation of clinical and electrophysiological findings. Fifty-one patients with at least some degree of spinal cord compression because of cervical spondylosis, as shown by MRI, were included in the study, grouped according to clinical symptoms. We found that patients who had no clinical symptoms whatsoever indicating myelopathy (they were referred to MRI examination mostly because of cervical radiculopathy), had in the large majority normal MEP and SEP findings. Patients with slight, unspecific and non-confirmative symptoms without pyramidal signs had mostly abnormal MEP but normal SEP findings. This points to the superior sensitivity of MEP over SEP in detecting myelopathy in its early stages. Patients with obvious clinical signs of myelopathy, including pyramidal signs had both abnormal MEP and SEP findings. Altogether these findings may help clinicians in interpreting MRI signs of cervical spinal cord compression.     

Evaluation of degree of nerve root injury by dermatomal somatosensory evoked potential following lumbar spinal stenosis

BACKGROUND:Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can display the site of lumbar spinal stenosis and predict nervous compression at the morphological level; however,pure morphological changes cannot reflect functional alterations in a compressed nerve root. Dermatomal somatosensory evoked potential (DSEP) provides a means to assess the functional state of a nerve root. OBJECTIVE: To evaluate the clinical significance of DSEP,assessing the degree of nerve root injury following lumbar s...     

Evaluation of degree of nerve root injury by dermatomal somatosensory evoked potential following lumbar spinal stenosis*☆

BACKGROUND： Computed Tomography （CT） and Magnetic Resonance Imaging （MRI） can display the site of lumbar spinal stenosis and predict nervous compression at the morphological level; however, pure morphological changes cannot reflect functional alterations in a compressed nerve root. Dermatomal somatosensory evoked potential （DSEP） provides a means to assess the functional state of a nerve root. OBJECTIVE： To evaluate the clinical significance of DSEP, assessing the degree of nerve root injury following lumbar spinal stenosis. DESIGN, TIME AND SETTING： A case-control study was performed in the Department of Orthopaedic Surgery, Hainan People＇s Hospital, China, between September 2004 and December 2007. PARTICIPANTS： Forty-seven patients diagnosed with lumbar spinal stenosis by CT or MRI were selected as the case group; fifty healthy subjects were collected as the control group. METHODS： A KEYPOINT myoelectric evoked potential apparatus （DANTEC Company, Denmark） was used to measure DSEP, and stimulative spots were determined in accordance with the skin key sensory spot standards established by The American Spinal Injury Association： L4 in the medial malleolus, L5 in the third metatarsophalangeal joint of the dorsum of foot and S1 in the lateral heel. The needle electrode used as the recording electrode was located at the Cz point of the cranium, and the reference electrode at the Fz point. MAIN OUTCOME MEASURES： Latency of the P40 peak of DSEP, P1-N1 amplitude, P40 waveform and differentiation and disappearance of various waves. RESULTS： The sensitivity and diagnostic concurrence with surgery of nerve root injury following lumbar spinal stenosis evaluated by DSEP was 95.7 %. P40 latencies at L4, L5 and S1 in the case group were significantly longer than in the control group （P 〈 0.05）, and the P1-N1 amplitude in the case group was significantly lower than the control group （P 〈 0.05-0.01）. Nerve root injury was categorized according to DSEP latency as follows： severe da