Neurophysiological evaluation of sensorimotor functions of the leg: comparison of evoked cortical potentials following electrical and mechanical stimulation,long-latency muscle responses,and transcranial magnetic stimulation

Summary Twenty-two patients with localized lesions of the central nervous system (unilateral cerebral ischaemia, cervical myelopathy, spinal tumour, familial spastic paraplegia) underwent neurophysiological evaluation of sensorimotor deficits of the leg. Functional methods using muscle stretch as stimulus, i.e. long-latency muscle responses and cortical potentials evoked by dorsiflection of the foot, were compared with transcranial magnetic stimulation and somatosensory evoked cortical potentials following electrical stimulation of the posterior tibial nerve. The functional neurophysiological methods yielded no diagnostic superiority with respect to the procedures using artificial (i.e. magnetic and electrical) stimulation. However, in most cases of missing compound motor action potentials following transcranial magnetic stimulation or missing electrically evoked cortical potentials, the long-latency muscle responses still allowed quantitative assessment of sensorimotor function.     

Differential influence of posture and intentional movement on human somatosensory evoked potentials evoked by different stimuli

Somatosensory evoked potentials (SEP) recorded from humans were elicited by a cutaneous shock to the index finger or with a ramp displacement of the finger that stretched the first dorsal interosseous muscle. A somatosensory stimulus was presented while a subject maintained a steady posture of the metacarpophalangeal joint or during a rapid voluntary abduction of the index finger. Both activities were performed against a constant opposing load of 0.15 Nm or without a load. SEPs were recorded over the postcentral arm area, together with the electromyogram of the first dorsal interosseous muscle. The major components of the SEPs were P56, N130, P174, N232 and P294. The amplitudes of all components were diminshed substantially during active movement. A constant load opposing postural fixation or active movement did not influence the SEP amplitude. The amplitude of the P56 component was differentially affected by the shock or ramp stimuli. The findings demonstrate that active movement gates sensory input, while sustained tonic muscular activity with an opposing constant load does not, and that different somesthetic inputs may be processed differently during movement.     

Bulbocavernosus reflex latencies and somatosensory evoked potentials after pudendal nerve stimulation in the diagnosis of impotence

Summary The bulbocavernosus reflex (BCR) was examined in 39 normal potent men and in 252 patients with impaired potency of varying aetiology. For BCR evaluation minimum, maximum and mean latencies, the temporal dispersion in ten successive responses, together with minimum and maximum side differences from simultaneous recordings of the left and right bulbocavernosus muscles were determined. Pathological findings were deteced in 125 patients. Somatosensory evoked potentials (SSEPs) recorded from the scalp after stimulation of the penile dorsal nerves and the terminal branches of the pudendal nerve were investigated in 30 controls and in 246 patients. An abnormal SSEP was found in 63 patients.     

Subcortical somatosensory evoked potentials after median nerve and posterior tibial nerve stimulation in high cervical cord compression of achondroplasia

Children with achondroplasia may have high cervical myelopathy from stenosis of the cranio-cervical junction resulting in neurological disability and an increased rate of sudden death. To detect myelopathy we recorded somatosensory evoked potentials after median nerve (MN) and posterior tibial nerve (PTN) stimulation in 77 patients with achondroplasia aged 0.3–17.8 years (mean 2.7 years). In addition to the conventional technique of recording the cortical components and the central conduction time (CCT) we employed non-cephalic and mastoid reference electrodes to record the subcortical waveforms N13b and P13 (MN-SEP) as well as P30 (PTN-SEP), respectively, which are generated near the cranio-cervical junction. The findings were related to the MRI results. Thirty-four patients had abnormal MRI findings including spinal cord compression (n = 28) and/or myelomalacia (n = 24) at or below the cranio-cervical junction. The sensitivity of the MN-SEPs was 0.74 including all abnormal upper cervical cord MRI findings (specificity 0.98), and the sensitivity was 0.79 (specificity 0.92) for cervical cord compression, respectively. The sensitivity of the PTN-SEPs was 0.52 (specificity 0.93) for all abnormal MRI findings and 0.59 (specificity 0.92) for cervical cord compression. The subcortical SEPs N13b and P13 as well as P30 were more sensitive than the conventional recordings. The MN-SEPs, notably the subcortical tracings, are useful for the detection of cervical myelopathy in children with achondroplasia. The PTN-SEPs are less sensitive. However, the tibial nerve SEPs might contribute additional information from the lumbar or thoracic spinal cord, which was, however, not tested in this study.     

EDSS correlated analysis of median nerve somatosensory evoked potentials in multiple sclerosis

Median nerve somatosensory evoked potentials (SEP) were recorded in 30 patients with multiple sclerosis. The examined patients had an expanded disability status scale (EDSS) between 0 and 6. The primary cortical potential N20, the subcortical potentials P14, N13b, N13a and the peripheral potential P9 were recorded simultaneously. In 5 patients normal SEP were observed (group 1) and in 6 patients there were consecutive disturbances of the somatosensory pathway (group 3). In 19 patients subcortical potentials were abnormal or absent while the following potentials were normal or identified which pattern corresponds to amplification within CNS structures (group 2). The EDSS of groups 1 and 2 were similar and lower than the EDSS of group 3, which indicates that amplification mechanisms could represent a positive prognostic factor in SEP diagnosis of multiple sclerosis. Received: 15 March 2000 / Accepted in revised form: 4 September 2000     

Changes of somatosensory evoked potential accompanying ischaemia and hypoxia in cats

Changes of evoked potential accompanying haemorrhagic hypotension and hypoxia were investigated on cats to evaluate the usefulness of SEP as a monitor in an intensive care unit (ICU), and the following results were obtained. (1) Positive-negative diphasic potential was elicited at posterior sigmoid gyrus (PSG) by contralateral superficial radial nerve stimulation.

This potential was recorded at the restricted area of the posterior border of PSG and regarded as primary somatosensory evoked potential. (2) In the initial stage of haemorrhagic hypotension, both positive and negative components of SEP occasionally increased in amplitude. In profound hypotension in which CBF fell to less than the critical level of 30 ml 100 g^–1 min^–1, the latency was retarded and the amplitude was decreased. At CBF less than 10 ml 100 g^–1 min^–1, SEP disappeared. Within the range of CBF between 10 and 30 ml 100 g^–1 min^–1, a close correlation was noted between CBF and SEP amplitude. Transient increase of SEP amplitude was also observed during hypoxia induced by inhalation of nitrogen gas. (3) In normal state SEP was decreased in amplitude by conditioning stimulation of the nucleus lateralis posterior (LP nucleus) of the thalamus. This might be explained by the fact that intracortical inhibitory interneurons were activated by stimulation of LP nucleus, After haemorrhagic hypotension and hypoxia, however, the inhibitory effect on SEP elicited by LP nucleus stimulation attenuated or disappeared. Because of the initial impairment of the inhibitory interneurons by ischaemia and hypoxia, the amplitude of SEP might increase transiently.

In conclusion, the authors thought that SEP might be less useful than EEC in ICU, because of its insensible change to hypoxia and ischaemia.     

Subcortical somatosensory evoked potentials after posterior tibial nerve stimulation in children

We report our normative data of somatosensory evoked potentials (SEP) after posterior tibial nerve (PTN) stimulation from a group of 89 children and 18 adults, 0.4-29.2 years of age. We recorded near-field potentials from the peripheral nerve, the cauda equina, the lumbar spinal cord and the somatosensory cortex. Far-field potentials were recorded from the scalp electrodes with a reference at the ipsilateral ear. N8 (peripheral nerve) and P40 (cortex) were present in all children but one. N20 (cauda equina) and N22 (lumbar spinal cord) were recorded in 94 and 106 subjects, respectively. P30 and N33 (both waveforms probably generated in the brainstem) were recorded in 103 and 101 subjects, respectively. Latencies increased with age, while central conduction times including the cortical component, decreased with age (up to about age 10 years). The amplitudes of all components were very variable in each age group. We report our normative data of the interpeak latencies N8-N22 (peripheral conduction time), N22-P30 (spinal conduction time), N22-P40 (central conduction time) and P30-P40 (intracranial conduction time). These interpeak latencies should be useful to assess particular parts of the pathway. The subcortical PTN-SEPs might be of particular interest in young or retarded children and during intraoperative monitoring, when the cortical peaks are influenced by sedation and sleep, or by anesthesia.     

听觉诱发电位及体感诱发电位在颅脑外伤致昏迷患者的应用

严重颅脑损伤昏迷患者脑功能的监测是判断预后和指导治疗的重要手段。听觉诱发电位(BAEP)及体感诱发电位(SSEP)因其方便、无创并能连续实时监测昏迷患者相关神经传导通路电生理的变化,间接反映脑干上行激活系统、大脑皮层结构与功能的完整性,越来越成为临床对严重颅脑损伤昏迷患者预测预后和指导治疗的重要手段。本文就近年来相关研究进行综述,旨在指导临床实践。     

N10 component in median nerve somatosensory evoked potentials (SEPs) is not an antidromic motor potential.

OBJECTIVE: To test the hypothesis that the N10 far-field potential in median nerve somatosensory evoked potentials is generated by the motor axons by examining patients with amyotrophic lateral sclerosis (ALS). METHODS: Subjects were 5 ALS patients showing pronounced or complete denervation of median-innervated small hand muscles. We evaluated N10 over scalp, and proximal plexus volleys (PPVs) at lateral or anterior cervical electrode. RESULTS: N10 and PPVs were definitely preserved for every ALS subject. N10 amplitudes of ALS subjects were even significantly larger than control subjects. In one ALS patient completely lacking motor axons, N10 was larger than the largest one among control subjects. CONCLUSIONS: Present results clearly indicate that N10 is not predominantly generated by motor axons but by the whole median nerve dominated by sensory axons. We propose a theory that N10 is a junctional potential generated by the entrance of the median nerve into bone at the intervertebral foramen, producing a positive pole at the non-cephalic reference electrode. Significantly larger N10 in ALS subjects may be due to the lack of cancellation by slower motor axons. SIGNIFICANCE: The hypothesis that N10 is generated by motor axons is refuted, and a new theory of its generation is presented.     

short-latency somatosensory evoked potentials to median nerve stimulation: components N 13-P 13, N 14-P 14, P 15, P 16 and P 18 with different recording methods

Summary Comparative recordings of short-latency somatosensory evoked potentials with midfrontal (Fz), ear and non-cephalic reference electrodes were obtained in 12 normal subjects to define the site of the generators of the different components and the spatial distribution and interference of the different components recorded at the neck and scalp. Such investigations provide the basis for identical investigations in patients with focal lesions of the central nervous system. The N 13 recorded from the neck (C 2-Fz) and the inconsistently recorded component N 14 were quite similar in latency to the far-field potentials P 13 and P 14 recorded at the scalp (C₃, C₄—ear or hand). The component P 15 was clearly visible only in scalp-Fz leads and occurred 0.2–0.9 ms (mean 0.5 ms) later than P 14 in ear or hand reference recordings. This is evidence against the identity of these two components proposed by others. In a larger group of 48 subjects, using an exclusive Fz-reference lead, normal values were established of the components P 15, P 16 and P 18, as well as their scalp distribution.

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Zusammenfassung An 48 Normalpersonen wurden die Normalwerte der spinalen und subkortikalen SEP-Komponenten (einschließlich P 16 und P 18) nach Medianus-Stimulation am Handgelenk ermittelt, wobei eine frontomediane Referenz (Fz) gewählt wurde. Bei einem Teil der Probanden (n=12) erfolgten zusätzliche Ableitungen der Reizantworten gegen eine Ohr- sowie eine extrakephale (Hand-) Referenz, um die Beziehungen der hierbei registrierbaren positiven Far-field-Potentiale zu den einzelnen Komponenten des Nacken-SEP zu klären. Die von der oberen Nackenpartie (C 2-Fz) abgeleiteten Komponenten N 13 und N 14 stimmten in ihrer Latenz mit den von der Kopfhaut abgeleiteten Komponenten P 13 und P 14 überein, wobei ein Teil der Probanden anstelle zweier deutlich unterscheidbarer P 13- und P 14-Komponenten lediglich eine positive Potentialschwankung aufwies. Die bei frontomedianer Referenz konstant sichtbare P 15-Komponente wies bei allen Untersuchten eine 0,2–0,9 ms längere Latenz auf als das mit extrakephaler Referenz registrierte Far-field-Potential P 14, was gegen die von anderer Seite vermutete Identität dieser beiden Komponenten spricht. Die klare gegenseitige Abgrenzung der frühen somatosensiblen Reizantworten nach Medianusstimulation bei Wahl unterschiedlicher Referenzorte ist Voraussetzung für eine verfeinerte Lokalisationsdiagnostik innerhalb des lemniskalen Systems der Somatosensorik.

     

The function of the lateral inhibitory mechanisms in the somatosensory cortex is normal in patients with chronic migraine

ObjectiveTo study lateral inhibition and habituation/sensitization in the somatosensory cortex of patients with chronic migraine (CM) and to identify correlations with clinical migraine features.MethodsSixteen patients with CM without medication overuse, and 17 healthy volunteers (HVs) received somatosensory evoked potentials (SSEPs) elicited by separate electrical stimulation of the right median (M) and ulnar (U) nerves at the wrist and by simultaneous nerve stimulation (MU). We measured the N20–P25 amplitudes and calculated the lateral inhibition (LI) percentage using the formula {100–[MU/(M + U) * 100]}. We also calculated sensitization (SSEP amplitude during block 1) and delayed habituation to M-nerve stimulation.ResultsThe percentage of LI did not differ between the groups (40.2% in HV, 47.4% in CM, p = 0.276) and was negatively correlated with the monthly headache-day number (r = −0.532, p = 0.034). Patients showed a generalized increase in SSEP amplitudes compared to HVs and habituated normally.ConclusionsWe showed a pattern of somatosensory response in CM similar to that observed during attacks of episodic migraine.SignificanceIn the transition process between episodic migraine and CM, LI attempts to physiologically counteract the mounting increase in attack frequency, but this is insufficient to allow patients to exit the chronic phase.     

Maturation of somatosensory cortical processing from birth to adulthood revealed by magnetoencephalography

ObjectiveTo evaluate the maturation of tactile processing by recording somatosensory evoked magnetic fields (SEFs) from healthy human subjects.MethodsSEFs to tactile stimulation of the left index finger were measured from the contralateral somatosensory cortex with magnetoencephalography (MEG) in five age groups: newborns, 6- and 12–18-month-olds, 1.6–6-year-olds, and adults. The waveforms of the measured signals and equivalent current dipoles (ECDs) were analyzed in awake and sleep states in order to separate the effects of age and vigilance state on SEFs.ResultsThere was an orderly, systematic change in the measured and ECD source waveforms of the initial cortical responses with age. The broad U-shaped response in newborns (M60) shifted to a W-shaped response with emergence of a notch by 6 months of age. The adult-type response with M30 and M50 components was present by 2 years. The ECDs of M60 and M30 were oriented anteriorly and that of M50 posteriorly. These maturational changes were independent of vigilance state.ConclusionsThe most significant maturation of short latency cortical responses to tactile stimulation takes place during the first 2 years of life.SignificanceThe maturational changes of somatosensory processing can noninvasively be evaluated with MEG already in infancy.     

Somatosensory evoked potentials to median nerve stimulation after partial section of the corpus callosum

Summary Cortical somatosensory evoked potentials (SEPs) to electrical stimulation of the median nerve were studied in four patients with intractable epilepsy who had undergone callosotomy and in a patient with infarction in the corpus callosum in order to determine whether the corpus callosum was involved in the generation of ipsilateral frontal components. Both pre- and postoperative SEPs were recorded in three of four epileptic patients. There were no significant differences in the latencies and amplitudes of the bilateral frontal components (P20, N26) between pre- and postoperative recordings. Furthermore, irrespective of the extent of the section or lesion in the corpus callosum, the nature of the impairment and the existence of the disconnection syndrome, the SEP findings showed no significant differences compared with those of normal subjects. It thus appears unlikely that the ipsilateral SEP responses are transmitted from the contralateral hemisphere through at least the anterior portion of the corpus callosum.     

Somatosensory cortex responses to median nerve stimulation: fMRI effects of current amplitude and selective attention.

OBJECTIVES: The aim of this study was to localize and to investigate response properties of the primary (SI) and the secondary (SII) somatosensory cortex upon median nerve electrical stimulation. METHODS: Functional magnetic resonance imaging (fMRI) was used to quantify brain activation under different paradigms using electrical median nerve stimulation in healthy right-handed volunteers. In total 11 subjects were studied using two different stimulus current values in the right hand: at motor threshold (I(max)) and at I(min) (1/2 I(max)). In 7 of these 11 subjects a parametric study was then conducted using 4 stimulus intensities (6/6, 5/6, 4/6 and 3/6 I(max)). Finally, in 10 subjects an attention paradigm in which they had to perform a counting task during stimulation with I(min) was done. RESULTS: SI activation increased with current amplitude. SI did not show significant activation during stimulation at I(min). SII activation did not depend on current amplitude. Also the posterior parietal cortex appeared to be activated at I(min). The I(min) response in SII significantly increased by selective attention compared to I(min) without attention. At I(max) significant SI activity was observed only in the contralateral hemisphere, the ipsilateral cerebellum, while other areas possibly showed bilateral activation. CONCLUSIONS: Distributed activation in the human somatosensory cortical system due to median nerve stimulation was observed using fMRI. SI, in contrast to SII, appears to be exclusively activated on the contralateral side of the stimulated hand at I(max), in agreement with the concept of SI's important role in processing of proprioceptive input. Only SII remains significantly activated in case of lower current values, which are likely to exclusively stimulate the sensible fibres mediating cutaneous receptor input. Selective attention only enhances SII activity, indicating a higher-order role for SII in the processing of somatosensory input.     

椎旁定位腰骶体感诱发电位对腰椎间盘突出症的诊断意义

目的探讨椎旁定位腰骶体感诱发电位（LSSEP）在腰椎间盘突出症中的变化及其诊断意义。方法对84例有L4、L5和S1神经根损害表现的腰椎间盘突出症的患者进行胫后神经体感诱发电位（SEP）、皮节体感诱发电位（DSEP）和椎旁定位LSSEP检查，测定其N40的潜伏期，并对多水平突出症患者的LSSEP与腰椎MRI比较。结果胫后神经SEP检测异常率为42．86％；L5、S1 DSEP检测的异常率为90．48％；椎旁定位LSSEP异常率为95．24％，比胫后神经SEP检测异常率明显增高（P〈0．005）。在L3。椎间盘突出中，以L4的LSSEP异常为主；在L4-5椎间盘突出中以L5的LSSEP为主。结论椎旁定位LSSEP检测可能是诊断腰椎间盘突出症快捷、可靠、敏感的检测方法，其结果与神经根受累水平相一致。     

Somatosensory evoked potentials following stimulation of the trigeminal nerve in man

Summary Somatosensory evoked potentials following trigeminal nerve stimulation can regularly be recorded from the contralateral scalp on C5/C6 (10–20 system), a region which overlies the primary face region of the somatosensory cortex. From the first three peaks analyzed (N 13, P 19 and N26), the first positive peak (P 19) is most prominent and reliable and therefore is recommended for the routine measurements of neurophysiological examination.

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Zusammenfassung Nach der Stimulation des N. trigeminus am Mund lassen sich regelmäßig sensible evozierte Potentiale über dem kontralateralen somatosensorischen Cortex ableiten. Innerhalb der ersten 50 msec nach Reizbeginn treten typischerweise zwei negative und zwei positive Potentialschwankungen mit sehr variabler Amplitude auf. Aufgrund der an 55 Normalpersonen ermittelten mittleren Latenzzeiten kann der erste negative Gipfel als N 13, der erste positive Gipfel als P 19 und der zweite negative Gipfel als N 26 definiert werden. N 13 und P 19 zeigen eine Altersabhängigkeit mit leichter Latenzzunahme in der höheren Altersgruppe. P 19 ist wegen seiner konstanten Ausprägung für die klinische Diagnostik besonders geeignet.

     

Determining the appropriate stimulus intensity for studying the dipole moment in somatosensory evoked fields: a preliminary study.

OBJECTIVE: To establish a simple method of determining the appropriate stimulus intensity for studying the dipole moment in somatosensory evoked fields. METHODS: In 17 patients (20 hemispheres), the authors studied the relationship between the dipole moment and stimulus intensity, which was quantified using the threshold of thenar muscle twitch (TMT). The dipole moment was measured at 1.0, 1.5 and 2.0 TMT. Two measurements were obtained at 1.5 TMT to determine the procedure's margin of error. RESULTS: There was no significant difference between the dipole moments measured at 1.5 and 2.0 TMT. CONCLUSIONS: Setting the stimulus intensity at 1.5 TMT or more ensures a consistent response.     

Modulation of visual evoked potentials by high-frequency repetitive transcranial magnetic stimulation in migraineurs

Objective

High-frequency repetitive transcranial magnetic stimulation (rTMS) modulates cortical excitability. We investigated its effect on visual evoked potentials (VEPs) in migraine.

Methods

Thirty-two headache-free controls (CO), 25 interictal (MINT) and 7 preictal migraineurs (MPRE) remained after exclusions. VEPs to 8′ and 65′ checks were averaged in six blocks of 100 single responses. VEPs were recorded before, directly after and 25 min after 10 Hz rTMS. The study was blinded for diagnosis during recording and for diagnosis and block number during analysis. First block amplitudes and habituation (linear amplitude change over blocks) were analysed with repeated measures ANOVA.

Results

With 65′ checks, N70-P100 habituation was reduced in MINT compared to CO after rTMS (p = 0.013). With 8′ checks, habituation was reduced in MPRE compared to MINT and CO after rTMS (p < 0.016). No effects of rTMS on first block amplitudes were found.

Conclusion

RTMS reduced habituation only in migraineurs, indicating increased responsivity to rTMS. The magnocellular visual subsystem may be affected interictally, while the parvocellular system may only be affected preictally.

Significance

Migraineurs may have increased responsiveness to rTMS because of a cortical dysfunction that changes before a migraine attack.     

急性脑梗死脑磁图体感诱发磁场发生源ECD强度研究

目的:研究急性脑梗死患者脑磁图(magnetoencephalography,MEG)体感诱发磁场发生源等价电流偶极子(equivalentcurrentdipole,ECD)强度变化特征。方法:对15例急性脑梗死患者于发病后3～4周进行体感诱发磁场(SEFS)检测;同时检测16例健康志愿者作为对照。电刺激部位为腕部正中神经处,电流脉冲宽度0.3ms,刺激间隔0.5s。SEFS波峰由ECD评估。结果:所有受检者SEFs的最基本波形为M20,急性脑梗死患者患侧ECD强度减小(P<0.01)。结论:MEG可灵敏地检测出急性脑梗死患者体感皮层中枢功能损伤。     

术中皮质体感诱发电位与电刺激术定位脑功能区

目的探讨脑功能区手术中利用脑皮质体感诱发电位(SEP)及直接皮质电刺激定位脑功能区的方法及意义。方法对10例脑功能区病变病人在唤醒麻醉下进行手术，利用皮质SEP及皮质直接电刺激定位感觉区、运动区及语占区，住保护脑功能区的前提下，手术切除病变。结果7例病人利用SEP及皮质电刺激确定出运动感觉区，其中4例利用SEP位相倒置确定出中央沟，3例病变位于左侧额颞叶的病人通过皮质直接电刺激确定出语言区?术后功能均较术前明显好转。结论术中SEP及直接皮质电刺激可准确、实时确定脑功能区，最大程度地保护功能，切除病变。