Nerve SEPs Research Articles

Use of evoked potentials in preterm neonates.

This paper has reviewed the techniques used for recording evoked potentials in the premature infant and the early developmental changes. The maturational changes in the evoked potentials, including morphological changes, and the very rapid latency changes within the first months of life, provide an invaluable means for assessing and monitoring development within the central nervous system. The maturational changes are such that normative values are requisite, and the norms must take into account both the infant's gestational age at birth as well as the postnatal age. These norms can then be used to aid in the assessment of gestational age, and whether there has or has not been normal maturational development, either in utero or during the postnatal preterm period. Evoked potentials are of increasing value clinically in preterm neonates, primarily because of the difficulty in obtaining reliable neurological evaluation of these infants. Median nerve SEPs may provide reliable information in preterm infants at risk of PVL, and when recorded in the second week of life, predict cerebral palsy. PTN SEPs seem to be even more reliable indicators of outcome, but the difficulty in obtaining them in preterm infants needs to be taken into consideration. Further study is needed in some areas, such as in apnoeic preterm babies clearly to establish the role that evoked potentials (in this case BAEPs) may have in understanding both the aetiology and the clinical course of this dysfunction. In other conditions, such as delayed intrauterine growth, that may lead to neurological sequelae, evoked potentials can provide objective CNS assessment. Evoked potentials may also prove useful in the monitoring of treatment modalities for preterm infants. The evoked potentials are a valuable adjunct in the assessment of preterm neonates and, as their value is recognised, we expect their use to increase.

PS-6-9 The mechanism that mixed nerve SEP suppresses pure sensory nerve SEP

PS-6-9 The mechanism that mixed nerve SEP suppresses pure sensory nerve SEP

Recovery functions of early cortical median nerve SSEP components: normative data

The recovery functions of parietal P14-N20, N20-P27 and frontal P22-N30 amplitudes were assessed in 17 healthy controls aged 20–50 years by means of the paired stimulus technique. One unpaired and 4 paired stimuli with interstimulus intervals (ISIs) of 25, 50, 75 and 100 msec were cyclically presented in a single run. Responses to the unpaired stimulus were subtracted off-line from paired stimulus responses. The highest suppression was reached at shorter ISIs for components with shorter latencies. The mean suppression of P22-N30 was influenced by the subject's age, being greater in younger subjects. Normative data are reported.

PS-39-4 Relationship between clinical sensory deficit and posterior tibial nerve SEP in stroke patients

PS-39-4 Relationship between clinical sensory deficit and posterior tibial nerve SEP in stroke patients

WS-1-3 P15 in tibial nerve SEP as a simple example of the junctional potential

WS-1-3 P15 in tibial nerve SEP as a simple example of the junctional potential

Origin and distribution of P13 and P14 far-field potentials after median nerve stimulation. Scalp, nasopharyngeal and neck recording in healthy subjects and in patients with cervical and cervico-medullary lesions

We studied median nerve SEPs in 10 healthy subjects, by means of simultaneous recording over the scalp, around the neck and near the ventral surface of the medulla using a nasopharyngeal (NP) electrode. This recording technique enabled us to clearly differentiate P13 and P14 potentials. The former was always found in NP records, while the latter was more evident in scalp traces. The same technique was used to study 9 patients with various lesions of the cervical cord or cervico-medullary junction. Patients with high cervical lesions demonstrated abnormalities of both P13 and P14 potentials, while patients with lesions of the cervico-medullary junction demonstrated a clear dissociation between normal P13 in scalp and NP traces, and abnormal scalp P14. Patients with lower cervical lesions, selectively involving the central grey matter, showed normal P13 and P14 potentials, in spite of abnormal N13 cervical responses. Our findings strongly suggest that both scalp and NP P13 have the same generators in higher segments of the cervical cord, and that NP more than scalp records are effective in analyzing the P13 response. We suggest that the selective recording of the P13 potential could be useful in the assessment of focal lesions of the higher cervical cord or of the cervico-medullary junction.

PS-38-6 Which time-points are best suited as the standard points of latency measurement in median nerve SEP? A statistical analysis

PS-38-6 Which time-points are best suited as the standard points of latency measurement in median nerve SEP? A statistical analysis

The different characteristics of the tibial nerve and sural nerve SEP

The different characteristics of the tibial nerve and sural nerve SEP

Scal‐recorded p14 in median nerve SEPs is abolished by cuneate nucleus lesion

Scal‐recorded p14 in median nerve SEPs is abolished by cuneate nucleus lesion

Clinically silent dysfunction of dorsal columns and dorsal spinocerebellar tracts in hereditary spastic paraparesis

Hereditary spastic paraparesis (HSP) is a neurodegenerative disorder, of which progressive spastic paraparesis is the clinical hallmark. Given the neuropathological evidence of degeneration of pyramidal tracts, dorsal columns, and dorsal spinocerebellar tracts, it is surprising that sensory symptoms are so indistinct compared to motor symptoms. We investigated the involvement of peripheral conduction and spinal proprioceptive pathways by nerve conduction studies, somatosensory evoked potentials of the median and tibial nerves, and quantitative assessment of the vibration perception thresholds of the hands and feet respectively in 32 patients suffering from HSP and healthy control groups. We did not find peripheral conduction abnormalities in HSP patients. Log-transformed vibration perception thresholds of the feet were abnormal in 13 32 HSP patients and in 0 64 controls ( p < 0.00001), while tibial nerve somatosensory evoked potentials were abnormal in 20 32 patients and in 1 17 controls ( p = 0.00001). The values for the upper extremities were within normal limits for nearly all subjects. In the HSP group, the neurophysiological disturbances did not correlate significantly with duration or severity of the disease, when age was controlled for, except for median nerve SSEP latency, which was affected by severity ( p = 0.0072). We conclude that neurophysiological methods detected proprioceptive, subclinical abnormalities in several HSP patients, which may reflect degeneration of the dorsal columns, and/or dorsal spinocerebellar tracts. Since we found no correlation with several disease variables, the fact that not all HSP patients displayed these abnormalities may be caused by anatomical variations in proprioceptive pathways, rather than by phenotypical heterogeneity.

Preoperative localization of the central sulcus by dipole source analysis of early somatosensory evoked potentials and three-dimensional magnetic resonance imaging.

Surgery of lesions within or close to the central area of the brain always carries the risk of iatrogenic motor or sensory deficits. Functional localization by means of intraoperative direct stimulation of the motor area or by recording somatosensory evoked potentials (SSEP's) from the surface of the somatosensory cortex is believed to reduce the operative risk. The authors introduce the combination of dipole source analysis of scalp-recorded SSEP's with three-dimensional (3-D) magnetic resonance (MR) imaging as a tool for preoperative localization of the central sulcus. This provides information on both functional and structural localization for preoperative planning. Four repeated measurements of right and left median nerve SSEP's were obtained from 20 subjects. Dipole source analysis showed a retest reliability of the 3-D localization error of 2.9 +/- 2.0 mm. Compared to the MR evaluation, dipole source analysis was found to mark the central sulcus within 3 mm for 15 conditions (subjects x side of stimulation), while the 3-D MR measurement was accurate to within 6 mm for 10 conditions and 9 mm for 14 conditions. Dipole locations were confirmed in six patients who underwent surgery of the central region. With respect to this application, dipole source analysis combined with 3-D MR imaging appears to be a valuable tool for preoperative functional localization. The accuracy in localization will be further improved when realistic head models become available that can take into account individual head geometry. Further development of the proposed new method holds promise that evoked potentials and electroencephalography will gain greater use in presurgical functional localization.

Clinical application of paraspinal somatosensory evoked potentials (PS-SEPs) for the diagnosis of spinal cord lesion.

To evaluate the clinical utility of somatosensory evoked potentials elicited by stimulation of the paraspinal region (PS-SEPs), waveform characteristics and scalp topography were studied in 23 normal controls. PS-SEPs were recorded in 22 patients with spinal lesions, and the relation between the abnormal PS-SEPs and clinico-radiological findings was investigated. 1) The normal control study showed clear waveforms on the scalp elicited by stimulation of the paraspinal region from C7 to the L2 spinous process level, with both bilateral and unilateral stimulation. The latency of PS-SEPs was gradually decreased when stimulation was moved in the caudo-rostral direction. 2) The normal range of spinal conduction time and conduction velocity was wide. The conduction velocity resulting from stimulation of the lumbar region tended to be slower than that from stimulation of the thoracic region, perhaps due to the difference in the length of the peripheral cutaneous nerves. 3) There was no correlation between the height and the latency of PS-SEPs. 4) Amplitudes of PS-SEPs after unilateral stimulation of the C7 and Th5 spinous levels were larger on the scalp contralateral to the side of stimulation. These findings were similar to SEPs elicited by median nerve stimulation. There was no significant amplitude laterality of PS-SEPs when the Th10 and L2 spinous levels were stimulated. Posterior tibial nerve SEPs showed a larger amplitude at the scalp ipsilateral to the side of stimulation than at the contralateral side. All these findings suggest that the cortical generator sites of PS-SEPs elicited by C7 and Th5 stimulation are located near the hand area, and those from Th10 and L2 stimulation are between the hand and the foot area. 5) Unilateral stimulation disclosed a clear laterality of sensory disturbance that was obscure when only bilateral stimulation was employed. PS-SEPs showed a high degree of abnormality when the patient had deep sensory disturbance. Generally, abnormal PS-SEPs were found caudal to the clinical sensory level, and a few cases showed abnormal PS-SEPs rostral to the sensory level. The latter might indicate that PS-SEPs detected subclinical sensory disturbance. It was therefore concluded that PS-SEPs are a useful tool for the objective evaluation of sensory disturbance, especially in cases of thoracic lesion, because conventional SEP studies, utilizing non-cephalic references do not provide clear identification of abnormal sensory levels along the thoracic spinal cord.

P30 and N33 of posterior tibial nerve SSEPs are analogous to P14 and N18 of median nerve SSEPs

Generator sources of far-field P30 and N33 components produced bosterior tibial nerve stimulation were compared with those of the P14 and N18 components of median nerve stimulated somatosensory evoked potentials. Intracranial spatio-temporal distributions of P30 and N33 were similar to those of the P14 and N18 obtained by median nerve stimulation. In clinical cases, the changes in P30 and N33 were correlated with those in P14 and N18, indicative that P30 and N33 are derived from activities similar to those that produce P14 and N18.

Derivation of different P14 segments of median nerve SEP in coma and brain death: Experiences in 106 patients

Derivation of different P14 segments of median nerve SEP in coma and brain death: Experiences in 106 patients

Mechanically and electrically elicited median nerve SEPs in ischaemic stroke — 1 year follow-up study

We consider a class of nonlinear time series expressed as a local mixture of a finite number of linear autoregressions. The mixing weights are continuous functions of lagged observations while the densities of the innovation terms in each autoregression can be very general and are only assumed to possess finite moments of some order. We focus on the probabilistic properties of the model and provide mild sufficient conditions for geometric ergodicity and existence of moments.

Median nerve SEPs: Effects of ideation, sensory deprivation and different types of motor tasks on parietal and frontal components

Median nerve SEPs: Effects of ideation, sensory deprivation and different types of motor tasks on parietal and frontal components

Tibial nerve SEPs in the diagnosis of epiconus lesions

Tibial nerve SEPs in the diagnosis of epiconus lesions

Visual pattern comparison, working memory load, and event related potentials

This chapter reviews certain studies on somatosensory evoked field (SEF) dipolar source modeling to show how clinical and physiological SEP studies can benefit from this type of approach. Studies on dipolar source modeling of the early lower limb SEPs have offered a significant contribution in identifying the tibial nerve SEP generators. By using the brain electrical source analysis (BESA), two different dipoles contributing to the potential field in the N37–P40 latency range are shown. A tangential dipole oriented perpendicularly to the mesial hemispheric wall generated both the N37 potential and a subcomponent of the P40 potential located in the ipsilateral parietal region, whereas a radial dipole in the crown of the perirolandic cerebral cortex represented the source of the vertex subcomponent of the P40 SEP. In the presurgical assessment of patients with space occupying lesions around the sensorimotor cortex, the localization of the central fissure by brain magnetic resonance imaging (MRI) is made difficult by the displacement induced by the lesion. The chapter underlines the technical limitations that have to be considered in evaluating the results of dipolar analysis.

Der Kieferöffnungsreflex: Eine neue elektrophysiologische Methode zur objektiven Untersuchung trigeminaler Sensibilitätsstörungen - I. Methodik und Normwerte

Retrospective analysis of trigeminal nerve evoked potentials in 40 consecutive patients, most of them with traumatic nerve lesions, showed that in 12 cases no trigemial nerve SEP were obtainable, and 11 of the remaining 28 patients had normal trigeminal nerve SEP. Therefore the jaw-opening reflex was investigated as a potential tool for electrophysiologic analysis of facial sensory disturbances. The jaw-opening reflex was investigated in 60 healthy subjects (31 female, 29 male) aged 23-82 years. It was elicited by electrical 0.1 ms square wave pulses delivered to the lower and upper lips and to the infraorbital region on either side at a rate below 1 per 5 s. The EMG responses were recorded from the bilateral masseter and temporalis muscles at a moderate voluntary activation. Under these conditions, the jaw-opening reflex reveals itself as two inhibitory pauses of the ongoing EMG on both sides, the onset latency of the first EMG-suppression being 10-15 ms, and of the second 35-50 ms. Particular attention was paid to the stimulus strength at threshold (TR) to evoke the jaw-opening reflex. We found that the jaw-opening reflex was constantly evoked by weak stimuli applied to the 2nd and 3rd trigeminal branches. Bilateral reflex responses with unilateral stimulation were a regular finding. The reflex responses increase with increasing stimulus strength (Fig. 1). Moderate to forcible activation of the jaw closing muscles is a prerequisite for optimum recordings of the jaw-opening reflex (Fig. 2). TR may range between 8 and 26 mA, but in one individual is almost symmetric on both sides as well as between the trigeminal branches on one side (Tab. 1, Fig. 3), the mean differences are around 1 mA and 2 mA, respectively. TR somewhat increases with age, and ranges around the threefold of the strength liminal for detection of the stimulus (Fig. 4).

P15 in tibial nerve SEPs as an example of the junctional potential

Tibial nerve stimulation at the ankle elicited a stationary, dipolar potential P15/N15 over the buttock with a reference electrode at the contralateral greater trochanter (GTc). P15 was distributed in the rostral and contralateral region and N15 in the caudal and ipsilateral region. The derivation from the contralateral iliac crest to the ipsilateral greater trochanter (ICc-GTi) registered a large P (= P15−N15) potential which was well free from artifacts. The Cz′-contralateral knee lead, which had been employed in previous studies, registered a smaller P15 of poor quality. Sequential bipolar recording along the course of the sciatic nerve indicated that P15 was generated around the greater sciatic foramen. Comparison with a simulation study suggested that P15 is a junctional potential which is generated when the sciatic nerve enters the bone at the greater sciatic foramen. P15 is expected to be a useful tool to evaluate the proximal segment of the tibial nerve.