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Results for “Evoked Potentials, Motor”

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At least 19 recordsLinked to original sources

PubMed2004

Effects of anesthetic agents and physiologic changes on intraoperative motor evoked potentials.

Motor evoked potentials (MEPs) have shown promise as a valuable tool for monitoring intraoperative motor tract function and reducing postoperative plegia. MEP monitoring has been reported to contribute to deficit prevention during resection of tumors adjacent to motor structures in the cerebral cortex and spine, and in detecting spinal ischemia during thoracic aortic reconstruction. Many commonly used anesthetic agents have long been known to depress MEP responses and reduce MEP specificity for motor injury detection. Although new stimulation techniques have broadened the spectrum of anesthetics that can be used during MEP monitoring, certain agents continue to have dose-dependent effects on MEP reliability. Understanding the effects of anesthetic agents and physiologic alterations on MEPs is imperative to increasing the acceptance and application of this technique in the prevention of intraoperative motor tract injury. This review is intended as an overview of the effects of anesthetics and physiology on the reproducibility of intraoperative myogenic MEP responses, rather than an analysis of the sensitivity and specificity of this monitoring method in the prevention of motor injury.

Anesthetics↗

PubMed2001

Effect of conditioning transcranial stimulation on motor evoked potentials.

Motor evoked potentials (MEPs) were recorded from extensor carpi radialis muscle in response to paired transcranial magnetic stimuli (interstimulus intervals (ISI) of 3 and 13 ms) with a test stimulus intensity of 120%. The intensity of the subthreshold conditioning stimulus ranged from 55% to 85% of the motor threshold. The threshold of intracortical inhibition (ICI: ISI--3 ms) was significantly lower than the threshold of intracortical facilitation (ICF: ISI--13 ms). The values of test MEP area at 3 ms ISI showed U-shaped dependence on the conditioning intensity while the values of test MEP area at 13 ms ISI recorded over the ICF threshold were augmented with increasing conditioning intensities. The changes of MEP latencies were polyphasic and in one and the same direction for ISIs of 3 and 13 ms. The results are suggesting a simultaneous action of ICF and ICI mechanisms.

Adult↗

PubMed1989

Vestibulospinal evoked potential versus motor evoked potential monitoring in experimental spinal cord injuries of cats.

Changes in vestibulospinal evoked potentials (VsEP) and motor evoked potentials (MEP) were examined in 10 cats before and after two different weight-dropping spinal cord injuries. In six animals somatosensory evoked potentials (SEP) were also monitored. The recordings were done from epidural spinal cord electrodes. Before and after severe and light weight-dropping spinal cord injuries all 3 modalities were recorded at the same time intervals till the end of 4th hour postinjury. According to a scoring system, evoked potential changes below and above the level of injury were monitored, and compared with each other. This study showed that the different motor stimulation methods use different descending spinal tracts, and both can be useful as a monitoring tool. Both descending tracts carrying VsEP and MEP had similarly remarkable changes after severe spinal cord injury. These consisted of major deformation, development of an evoked injury potential and complete potential loss. During the 4 hour monitoring period, no case showed EP recovery in the severe injury group. Light spinal cord injury caused somewhat more deterioration in MEPs than VsEP. The higher numbers of severe potential alterations in the lightly injured animals suggest that MEP is a more sensitive method for spinal cord monitoring compared to VsEP and also to SEP. On the other hand, this sensitivity might be a disadvantage during intraoperative monitoring, if MEP alone were used.

Action Potentials↗

PubMed1991

Cerebellar evoked potentials and motor evoked potentials in the spinal cord of rats.

In rats, the cerebellar evoked potentials (CEPs) were monitored along the spinal cord following the electrical stimulation of cerebellar cortex. The CEPs monitored at thoracic and lumbar cord consisted of from 1 to 3 waves with conduction velocities of 16-20.28 m/sec. The amplitudes of these waves declined dramatically as the frequency of the stimulation increased above 50 Hz, indicating that the CEPs were either evoked or conducted polysynaptically. The pathway conducting CEPs were studied using acute spinal cord lesioning and intracord recording methods. The pathways conducting CEP and MEP were also compared in the same preparation in controlled spinal-cord-lesioned animals. The CEPs were mainly conducted along the ventral and lateral funiculi where the reticulospinal tracts and the vestibulospinal tracts are located. Simultaneous disappearance of both MEP and CEP after controlled spinal cord section seems to suggest the 2 different evoked potentials are conducted along the same pathways in the spinal cord of rats. Species difference in conduction pathways of MEP and CEP were compared and discussed.

Animals↗

PubMed2004

Influence of electrode impedance on threshold voltage for transcranial electrical stimulation in motor evoked potential monitoring.

Motor potentials evoked by transcranial electrical stimulation (TES) are used for monitoring the motor pathways, with emphasis on the spinal cord and brainstem. The stimulus voltage threshold is the voltage below which no motor response can be elicited. It has frequently been used as a monitoring parameter. However, its value can be limited, because it is affected by the impedance of the stimulus electrode. For example, the voltage threshold can change owing to formation of oedema of the scalp. The relationship between the TES voltage threshold and the electrode impedance of different electrode types was studied and discussed in the context of neuromonitoring: 323 impedance and voltage threshold pairs were studied, and TES was performed with disc cup EEG electrodes (six), corkscrew electrodes (type I: seven, type II: eight), multiple EEG needle electrodes (16) and a large needle electrode Cz' (anode) together with a ground strip over the forehead (cathode) (286). The study found the voltage threshold to be strongly dependent on electrode impedance when the impedance was higher than 460 omega (correlation: R2=0.87; p < 0.001). Below 460 omega, which included 91% of the category with the largest electrode surfaces, 25% of the multiple EEG electrodes and 75% of type II corkscrew electrodes, no significant correlation (R2=0.0064; p=0.15) was found. It was concluded that the correlation between the TES voltage threshold and electrode impedance can be markedly reduced by using TES electrodes with large contact surfaces, resulting in limit values for these parameters. This also may improve the reliability of TES motor evoked potential monitoring.

Electric Impedance↗

PubMed2006

[Motor evoked potentials].

Motor dysfunction following spinal surgery and thoracoabdominal aortic surgery remain as one of their devastating complications. Since the development of postoperative motor dysfunction can deteriorate quality of life of patients, the prevention of such complications is an important clinical challenge. Recently, advances in stimulation technique using multipulse made intraoperative monitoring of functional integrity of motor pathways possible by recording myogenic motor evoked potentials (MEPs). However, myogenic MEPs can be affected by most of anesthetic agents and muscle relaxants. Anesthesiologists are therefore required to properly understand MEPs and to manage anesthesia carefully. We summarize the methods for monitoring of myogenic MEPs and anesthetic techniques during intraoperative MEP monitoring.

Anesthesia↗

PubMed2006

Asymmetrical facilitation of motor-evoked potentials following motor practice.

Use-dependent facilitation of motor-evoked potentials evoked by transcranial magnetic stimulation with repetition of simple movements has been well established. Motor-evoked potentials were recorded from two intrinsic hand muscles before and after blocks of motor practice in which study participants made repeated ballistic pinch responses with either their left or their right hand. Despite similar increases in behavioral performance by each hand (measured by the peak acceleration of the force generated by the index finger), practice-related increases in the amplitude of the motor-evoked potentials were greater in the left than in the right motor cortex of right-handed participants. This finding supports the hypothesis that the dominant motor cortex has a greater ability to reorganize with experience than the non-dominant motor cortex.

Acceleration↗

PubMed1995

[Somesthetic evoked potentials and serial motor evoked potentials in the study of proximal peripheral nerve conduction. Apropos of 7 cases].

The study of proximal motor and sensory nerve conduction in the thoracic outlet syndrome is still difficult and laborious in 1994. However, these conductions can be measured at different levels by means of somaesthetic evoked potentials and motor evoked potentials, when one takes the time to perform them. The study in normal subjects demonstrates that the proximal sensory and motor conduction delays are approximately 3.2 ms and are therefore comparable to that of the median nerve at the wrist. The study of 7 cases related to various diseases shows that these techniques, performed after electromyogram of both upper limbs, an essential prerequisite to their interpretation, are able to clearly demonstrate abnormalities of proximal conduction in patients suffering from of a scalene syndrome, a cervical epiduritis, radiation plexopathy, hereditary sensible to pressure neuropathy, motor neuropathy with persistent multifocal conduction blocks, or, on the contrary, may confirm the normality of conduction, for example in anterior horn disease.

Adult↗

PubMed2001

Motor potentials evoked by transcranial magnetic stimulation during isometric and dynamic masseter muscle contraction in humans.

The facilitation of muscle motor potentials evoked by transcranial magnetic stimulation (TMS) has been demonstrated convincingly during both isometric and dynamic activity in the limbs but not in the jaw muscles. An experimental design involving TMS, surface electromyography and controlled muscle-activity was employed to investigate the motor response of the human masseter during voluntary isometric and dynamic voluntary conditions. During the isometric condition, an increase in muscle facilitation resulted in a progressive increase in motor-evoked potential (MEP) amplitude that was consistently greater on the side contralateral to that subjected to TMS (P < 0.05). No difference in MEP amplitude or laterality of response was revealed for the two dynamic conditions. The sample size may have been too small to reveal any differences. The modulation of MEPs during isometric activity was probably due to cortical and brainstem mechanisms. Putative variation in masseter MEPs during dynamic conditions cannot be discounted.

Adult↗

PubMed2003

Influence of propofol concentrations on multipulse transcranial motor evoked potentials.

BACKGROUND: Motor evoked potentials can be affected by propofol anaesthesia. We studied how increasing target concentrations of propofol altered transcranial motor evoked potentials (tcMEP) during scoliosis surgery. METHODS: Fifteen patients undergoing surgery for scoliosis were anaesthetized with remifentanil and propofol without nitrous oxide or neuromuscular blocking agents (BIS<60). tcMEP were elicited by transcranial electric multipulse stimulation of the motor cortex and recording of compound action potentials from the anterior tibialis muscle. tcMEP were obtained before surgery with propofol target values set from 4 to 8 mg litre(-1), and then during surgery. Arterial propofol concentrations were measured for each tcMEP recording. RESULTS: Before surgery, increasing propofol reduced tcMEP amplitude in a dose-dependent manner, with no effect on latency. During surgery, at equivalent propofol concentrations, tcMEP were not statistically different from those obtained before surgery. In all except one patient, tcMEP signals were present during the entire procedure. In this patient the loss of tcMEP was unfortunately related to an anterior spinal cord lesion, which was confirmed by a wake-up test. CONCLUSION: We found that, although propofol had a dose-dependent effect on tcMEP amplitude, anaesthesia could be maintained with remifentanil and propofol to allow recording and interpretation of tcMEP signals.

Adult↗

PubMed2003

Electrical stimulation of the human common peroneal nerve elicits lasting facilitation of cortical motor-evoked potentials.

Motor-evoked potentials (MEP) in the tibialis anterior (TA) muscle were shown to be facilitated by repetitive electrical stimulation of the common peroneal (CP) nerve at intensities above motor threshold. The TA electromyogram (EMG) and ankle flexion force were recorded in response to transcranial magnetic stimulation (TMS) of the leg area of the motor cortex to evaluate the excitability of cortico-spinal-muscular pathways. Repetitive stimulation of the CP nerve at 25 Hz for 30 min increased the MEP by 50.3 +/- 13.6% (mean +/- S.E.) at a TMS intensity that initially gave a half-maximum MEP (MEPh). In contrast the maximum MEP (MEPmax) did not change. Ankle flexion force (103 +/- 21.9%) and silent period duration (75.3 +/- 12.9%) also increased. These results suggest an increase in corticospinal excitability, rather than total connectivity due to repetitive CP stimulation. Facilitation was evident after as little as 10 min of stimulation and persisted without significant decrement for at least 30 min after stimulation. The long duration of silent period following CP stimulation (99.2 +/- 14.8 ms) suggests that this form of stimulation may have effects on the motor cortex. To exclude the possibility that MEPh facilitation was primarily due to sensory fibre activation, we performed several control experiments. Preferentially activating Ia muscle afferents by vibration in the absence of motor activity had no significant effect. Cutaneous afferent activation via stimulation of the superficial peroneal nerve increased the amplitude of responses at MEPmax rather than MEPh. Concurrent tendon vibration and superficial peroneal nerve stimulation failed to facilitate TA MEP responses. In summary, repetitive electrical stimulation of the CP nerve elicits lasting changes in corticospinal excitability, possibly as a result of co-activating motor and sensory fibres.

Adult↗

PubMed1996

Sensory component of cervically evoked motor potentials.

The purpose of this paper is to present the hypothesis that cervically elicited motor evoked potentials which have recently gained clinical acceptance for monitoring spinal cord motor function during spine surgery, may be due, in part or in whole, to neural signals travelling through sensory rather than motor tracts. If true, then the interpretation of cervically elicited motor evoked potentials may lead to false conclusions about the status of motor tracts and postoperative motor function.

Electroencephalography↗

PubMed1996

[Motor potentials evoked by magnetic stimulation--a tool for objective assessment of motor conduction along the spinal cord and its roots].

Magnetic stimulation of the motor cortex and nerve roots in conjunction with F-wave recording was used for assessment of central and peripheral motor conduction times in 98 patients suffering from myelopathy and cervical or lumbo-sacral radiculopathy. Significant prolongation of the central motor conduction times was found in the myelopathy group. The Motor Evoked Potential was of low amplitude and distorted shape. The amplitude of the F-wave was markedly increased. The main feature of the radiculopathy group was prolonged motor root conduction time as evident by delayed F-wave. Motor evoked potentials proved to be a reliable objective tool in the functional evaluation of conduction along the spinal cord and its roots.

Evoked Potentials, Motor↗

PubMed1995

Prognostic significance of electrophysiological investigations in stroke patients: somatosensory and motor evoked potentials and sympathetic skin response.

A prospective 3-month follow-up examination was carried out in 12 patients with supratentorial stroke. Motor evoked potentials (MEP), somatosensory evoked potentials (SEP) and sympathetic skin responses (SSR) were performed 1-7 days, 30 days and 3 months after stroke. The functional outcome measured by a daily activity index (Barthel index) was assessed 3 months after the stroke. There was a significant correlation between SEP and MEP results obtained for the first week and recovery of sensation and motility 3 months later. When initially normal, motor potentials evoked by transcranial magnetic stimulation had a significant predictive value for long-term functional outcome, whereas SEP and SSR did not. SSR present at the initial stage was correlated with the state of consciousness.

Adult↗

PubMed2001

Prognostic value of lower limb motor evoked potentials for motor impairment and disability after 8 weeks of stroke rehabilitation--a prospective investigation of 100 patients.

We investigated 100 patients with a one-sided, functionally relevant hemiparesis after stroke. Motor evoked potentials (MEPs) were obtained from the anterior tibial muscle four or more weeks after the insult as well as after an eight week period of inpatient rehabilitation. The MEP results were correlated with motor deficit, walking ability, and activities of daily living (ADLs). Patients with loss of MEP had lower scores on the Motricity Index (MI) both at the beginning and at the end of the rehabilitative treatment (p < 0.001) and also gained fewer points on the MI than patients with preserved MEP. This was the case even when analyzing the lower limb scores alone (p < 0.001 before treatment, p = 0.003 after eight week rehabilitation). When the MEP was preserved, patients were more likely to regain independence in walking (specificity 0.67, positive predictive value 0.96) and stair climbing (specificity 1.0, positive predictive value 1.0). Patients with preserved MEP also scored higher on global outcome scales such as Barthel Index (BI), Functional Independence Measure (FIM) and Glasgow Outcome Scale (GOS). However, these differences did not reach statistical significance (p > 0.05). According to our results, MEPs of the lower extremity are of predictive value for the rehabilitative treatment of patients in the postacute phase after stroke. This is especially true for the extent of the motor impairment and walking ability. The utilization of MEPs for prediction of future levels of disability and handicap is limited and only useful taking into consideration other clinical and diagnostic findings as well as the patients' cognitive, emotional and social state.

Adult↗

PubMed1996

[Alterations of various parameters of evoked motor potentials in amyotrophic lateral sclerosis].

To assess their interest, we studied different motor evoked potentials (MEP) parameters in 18 amyotrophic lateral sclerosis (ALS) patients and compared them to those obtained in 20 subjects unaffected by neurological diseases: cortical threshold (CT), latency and amplitude of primary responses (PR), central conduction time (CCT), silent period (SP) contralateral to the stimulated cortex and late muscular responses (LMR). In normal subjects MEP parameters were in agreement with those described in the literature, except for LMR. These were only recorded in upper limbs with latencies around 200 ms in 9 out of 20 subjects. In ALS patients, LMR were not modified as compared to normal subjects. Except for mean CCT, in upper and lower limbs, all parameters were altered. We conclude that all MEP parameters are useful in ALS and disclose the involvement of the entire pyramidal tract in this disease.

Amyotrophic Lateral Sclerosis↗

PubMed1991

Motor potentials evoked by magnetic stimulation of the motor cortex in normal subjects and patients with motor disorders.

Motor evoked potentials (MEPs) elicited by magnetic coil stimulation of motor cortex were studied at rest and during maximum voluntary muscle contraction in 20 normal subjects and 42 patients with motor disorders. MEP parameters employed in this study included: onset latency, amplitude, MEP/M wave amplitude ratio and background EMG/MEP area ratio. Maximum voluntary contraction increased the amplitude of MEPs compared to the size of M waves elicited by peripheral nerve stimulation. A reduced MEP/M wave amplitude ratio had a higher correlation with pyramidal tract involvement than did a prolonged MEP onset latency. Analysis of MEP parameters may help in the differential diagnosis of cerebral infarction, ALS and cervical spondylotic radiculomyelopathy. The inhibitory period which follows MEPs during voluntary contraction was observed in all subjects; the mean duration in normal subjects was 126.6 +/- 29.5 msec. The mean duration of the inhibitory period in patients with cerebral infarction, ALS and cervical spondylotic radiculomyelopathy was 73.9 +/- 41.7 msec, 79.5 +/- 54.5 msec and 85.1 +/- 36.5 msec, respectively. These values were significantly shorter than in normal subjects.

Adult↗

PubMed1997

Motor evoked potentials and disability in secondary progressive multiple sclerosis.

BACKGROUND: To investigate the mechanisms underlying disability in multiple sclerosis (MS), 40 patients with the relapsing-remitting form of the disease and 13 patients with secondary progressive MS underwent multimodal evoked potential (EP), motor evoked potential (MEP), and spinal motor conduction time evaluation. Clinical disability was evaluated by the expanded disability status scale (EDSS) and functional system scales. In secondary progressive MS patients, magnetic resonance imaging (MRI) was used to obtain a semiquantitATive estimate of the total lesion load of the brain. RESULTS: Spinal motor conduction time was significantly longer in secondary progressive MS patients than controls (p < 0.001) and relapsing-remitting MS patients (p < 0.05), but did not differ between relapsing-remitting patients and controls. Spinal motor conduction times also correlated directly with EDSS scores (p < 0.001) and pyramidal functional system scores (p < 0.001). Brain lesion load (4960.3 +/- 3719.0 mm2) and the total number of lesions (67.7 +/- 37.0) in secondary progressive MS did not correlate with disability scores. For the following EPs, the frequencies of abnormalities were significantly higher in secondary progressive MS patients than relapsing-remitting patients: visual evoked potentials (p < 0.05), somatosensory evoked potentials and upper limb motor evoked potentials (p < 0.01), and brainstem auditory evoked potentials, lower limb somatosensory evoked potentials and lower limb motor evoked potentials (p < 0.001). CONCLUSIONS: These findings suggest that disability in secondary progressive MS patients is mainly due to progressive involvement of corticospinal tract in the spinal cord.

Adult↗