Short latency somatosensory evoked potentials following median nerve stimulation in children

We investigated short latency somatosensory evoked potentials (SSEP) to median nerve stimulation in normal children and children with neurological disorders. The waveform of SSEP in normal children was almost the same as that in adults. The peak latency and interpeak latency in normal children changed during their development. Moreover, after 3 years of age, each peak latency was positively correlated with the body length and arm length. Each peak latency per 1 m of body length decreased with age. We examined SSEP in children with various neurological disorders and found that SSEP was useful for evaluating sensory functions and somatosensory damages in children who were unable to cooperate in clinical examinations. Using SSEP, we could estimate the distal margin of the lesion in the somatosensory pathway, but it was difficult to determine the accurate range of the lesion.     

Short latency somatosensory evoked potentials from radial, median and ulnar nerve stimulation in man

Short latency somatosensory evoked potentials (SEPs) were elicited by stimulation at the wrist of median, radial, and ulnar nerves, singly or in combination, using normal subjects. Amplitude of P10 was strikingly lower with radial stimulation than with median stimulation, while ulnar-derived P10 was intermediate in amplitude. This difference probably reflects the antidromic firing of motor fibers contained in median nerves as compared with the superficial branch of radial nerve, which is entirely sensory. Beyond P10, there appear to be no significant differences between median, radial and ulnar-derived SEPs. With simultaneous stimulation of several nerves within one arm, larger potentials were sometimes achieved but with poorer definition of P12 and P14. The clinical utility of radial, ulnar, and median stimulation for localizing peripheral lesions derives from the distinct anatomical pathways of the stimulated fibers through the brachial plexus and from the separable motor and sensory components of P10. SEP is less invasive than EMG; this fact, plus its freedom from sampling error, make it potentially more suitable than conventional EMG for sequentially following a patient's clinical course.     

Early evoked potentials detected from the scalp of man following infraorbital nerve stimulation

Stimulation of the infraorbital nerve evoked a short latency scalp response characterized by a large amplitude triphasic potential (W1), followed by two smaller negative deflections (W2 and W3). All these waves were presynaptic in origin (as shown by double pulse stimulation), but appeared to be generated by separate dipoles. Short distance bipolar recording showed that W1 travelled from the zygoma to the mastoid. This wave was thought to be generated in a nearby neural structure, presumably the proximal part of the maxillary nerve, the gasserian ganglion and possibly even the trigeminal root. W2 and W3 components were probably generated by the trigeminal root fibres running through the brain-stem. Their origin from slowly conducting trigeminal fibres was ruled out by their absence in short distance bipolar records along the line from the zygomatic bone to the mastoid process, and by studies on their thresholds, which were shown to be identical to those of W1. Control experiments with concurrent facial muscle recording excluded any possible contamination of the scalp response to infraorbital nerve stimulation by electromyographic activity, and demonstrated gross muscular artefacts, picked up as far-field activity by scalp electrodes, following electrical stimulation of the upper lip.     

Short latency somatosensory evoked potentials following the peripheral nerve stimulation of lower extremities in children

We have evaluated the short latency somatosensory evoked potentials (SSEPs) following peroneal and posterior tibial nerve stimulation in 27 normal children and adults, and then applied SSEPs examination following peroneal nerve stimulation to 6 children with neurological deficits. Features of the evoked potentials following peroneal nerve stimulation in normal children were almost similar to those in adults, but we found several points characteristic in children; a higher incidence of evoked potentials and a clearer appearance of "standing potential" at the lower thoracic vertebral level than in adults. Spinal afferent conduction velocity reached at a maximum at 3-4 years of age. The SSEPs following peripheral nerve stimulation in lower extremities are useful in pediatric neurology to determine the level of the spinal lesion, to reveal the distribution and pathophysiology of the spinal dysfunction, and to analyze the process of the disease progression.     

Origins of short latency somatosensory evoked potentials to median nerve stimulation

Short latency SEPs recorded in hand-scalp, ear-scalp and upper neck-scalp leads with stimulation of the median nerve were examined in 27 normal subjects and in 11 selected patients with unilateral complete loss of position sense in order to provide information concerning the generator sources of these potentials. Evidences obtained from both normal subjects and patients suggest the following origins for these short latency SEPs. In hand reference recording, P1 may arise in the brachial plexus just beneath the clavicle, P2 in the cervical dorsal column, P3 mainly in the caudal brain stem, and P4 primarily in the brain stem lemniscal pathways and partly in the thalamus. The initial negative potential recorded in upper neck-scalp leads may originate largely in the cervical dorsal columns. The early positive potential recorded in ear-scalp leads may reflect activity mainly in the brain stem lemniscal pathways and partly in the thalamus. The initial negative component of the cortical SEPs (N1) may arise in the thalamus, and the subsequent positive component (P1) may reflect activity in the primary somatosensory cortex.     

The origin of the scalp recorded P14 following electrical stimulation of the median nerve: intraoperative observations

Direct and far-field recorded somatosensory evoked potentials (SEPs) obtained from 2 patients during neurosurgical procedures are presented. A previous report (M?ller et al. 1986) has suggested that the P14 component of the SEP following median nerve stimulation is generated at the cuneate nucleus. The present data suggest that the scalp recorded P14 component (scalp-noncephalic electrode derivation) is generated rostral to the junction of the cervical cord and the medulla.     

Short latency somatosensory evoked potentials to peroneal nerve stimulation: scalp topography and the effect of different frequency filters

Short latency SEPs to peroneal nerve stimulation were recorded from the scalp of 22 normal adults. The scalp topography and the effect of different frequency filters on these potentials were investigated. Using a wider bandpass (5-3000 Hz), this response usually consisted of 3 positive potentials (peak latencies 17, 22 and 27 msec) followed by a negative potential (peak latency 34 msec). Using a narrower bandpass (150-3000 Hz), these potentials were fractionated into subcomponents and up to 6 positive potentials were followed by an often bilobed negative potential occurring 4-10 msec earlier than the first negative potential recorded with the wider bandpass filters. The negative potential and the preceding major positive potentials were well defined and stable within and across normal subjects which suggests they will be useful in the clinical evaluation of patients with spinal cord pathology and in monitoring patients during surgery. Certain of these potentials recorded using the wider bandpass were often characterized by progressive differences in their peak latencies over the scalp. Evidence is provided which suggests that this occurred because subcomponents of these potentials, observed in recordings using the narrower bandpass had different scalp distributions. Evoked potentials were also recorded from surface electrodes placed over the spine of some of these subjects. These recordings when combined with the scalp recordings provided information concerning the conduction characteristics of SEPs from cauda equina to cerebral cortex.     

Scalp topography of the short latency somatosensory evoked potentials following posterior tibial nerve stimulation in man

The scalp topography of the short latency somatosensory evoked potentials (SEPs) to unilateral posterior tibial nerve stimulation at the ankle was studied by using a non-cephalic reference in 22 normal young adults. At least 3 components (P28, N31 and N32) were identified preceding the major positive peak (P36). The first 2 components had similar peak latency at all scalp electrodes, and were considered to be generated in deep structures. However, N32 was localized to the hemisphere contralateral to the side of stimulation. P36 was maximal at the midline foot sensory area, or at the contralateral parasagittal area, and its amplitude decreased more steeply anteriorly than posteriorly. The peak latency of P36 progressively increased from ipsilateral to the side of stimulation in the coronal plane. P36 occurred earlier in the somatosensory area, and increased in peak latency anteriorly. Generator source of scalp-recorded far-field potentials (P28 and N31) remains to be elucidated. N32 might reflect activities of the thalamo-cortical pathway or an initial cortical response. P36 appeared to be generated in the somatosensory foot area.     

Short latency visual evoked potentials in man

Contrary to auditory and somatosensory evoked potentials, surface recorded visual evoked potentials which arise in subcortical neural elements have rarely been described. Considerable disagreement exists between the reports in the literature on such visual potentials. In this study, flash stimuli were used to evoke the potentials which were recorded from the skin overlying the infra-orbital ridge, outer canthus, middle of the forehead, vertex, mastoid ipsilateral to the stimulated eye and inion, using a non-cephalic reference. The potentials were amplified in a band which was chosen to omit slow retinal and cortical potentials, and to enhance activity which might include compound neural activity. Potentials were recorded from 9 subjects (13 eyes), and for each one the effects of eye position and stimulus intensity were studied. The results indicate that the series of components recorded within the first 100 msec following photic stimulation were volume-conducted activity generated by a subset of the visual system which is activated by luminosity changes. The generators of the first 4 or 5 components seem to be situated within the retina, the subsequent components seem to be generated in the optic nerve or tracts, and the later components may be thalamo-cortical in origin. These potentials may complement pattern evoked potentials in a more accurate definition of sites of lesions along the visual pathway.     

Cortical and subcortical somatosensory evoked potentials to median nerve stimulation in man

In order to define the precise locations of precentral and postcentral gyri during neurosurgical operations, somatosensory evoked potentials to contralateral median nerve stimulation were recorded from the cerebral cortex in 19 cases with organic cerebral lesions which located near the central sulcus. In addition to that, distribution patterns of early components of SEPs were displayed by Nihonkoden Atac 450 in 3 cases who had bone defects after wide decompressive craniectomy but were without any sensory disturbances In 4 cases, in whom deep electrodes were inserted for the stereotaxic operations or other reasons, frontal subcortical SEPs were recorded in order to know the origins of frontal components of SEPs. From the parietal cortex, N19, P22 and P23 were observed. And from the frontal cortex, P20 and N25 were obtained. Their average peak latencies were as follows; (table; see text) Because all subjects had organic lesion in the brain, the peak latencies were a little bit longer, and their standard deviations were larger than those in normal cases. Usually, clear-cut phase reversal could be observed between N19 and P20 across the central sulcus. So, the precentral and postcentral gyri were easily identified during the operations. N19 and P23 appeared over the wide areas of the parietal cortex. Also, P20 and N25 were recorded almost whole areas of the frontal cortex. On the other hand, P22 appeared from relatively restricted part of the postcentral gyrus where sensory hand area might have been located. Depth recording from the frontal subcortical area revealed that P20 could be recorded from the bilateral frontal subcortical areas and there observed no phase reversal between the cortical and subcortical SEPs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Morphological characteristics of the scalp far-field potentials evoked by median nerve stimulation in infants and children.

We investigated the somatosensory evoked potentials (SEPs) produced by median nerve stimulation in normal infants, children and adults, focussing upon the wave forms of the scalp far-field potentials (FFPs). In adolescents and adults, 3 or 4 positive FFPs preceded the widespread N18 component on the scalp, corresponding to P9, P11, P13 and P14 (or P13-14). In infants and children, however, the scalp FFPs often included 5 positive waves, the initial three of which were characteristically sharp and brief. This distinctive wave form, with 5 positive FFPs, was correlated with an Erb's potential having a bipeaked negative phase. We studied the temporal relationship of the 5 positive FFPs to the Erb's potential and the cervical SEPs and concluded that the initial 3 brief positive waves were produced by overlapping of a bipeaked "P9" and bipeaked "P11." Both "P9" and "P11" are stationary waves that are thought to originate in the first-order afferents, so they probably reflect the bipeaked appearance of the compound nerve action potential.     

Postsynaptic potentials recorded from medullary neurones following stimulation of carotid sinus nerve

Projections of the carotid sinus nerve (CSN) onto medullary neurones were studied with intracellular recording. Three types of postsynaptic potentials (EPSP, EP-IPSP and IPSP) were recorded by stimulation of the ipsilateral CSN. Of the total of 121 neurones, positions of 54 were identified by intracellular dye. The other 67 were positioned by extrapolation. They were distributed over 5 medullary nuclei: (1) nucleus of the solitary tract (NTS); (2) paramedian reticular nucleus (NPR); (3) perihypoglossal nucleus (PXII); (4) lateral tegmental field (FTL); and (5) nucleus ambiguus. Since penetration of microelectrodes and injection of dye into the NTS neurones was difficult, neurones of the other 4 nuclei were examined. The IPSPs were dominant in small NPR neurones, while the EPSPs were dominant in large neurones of the other 3 nuclei. Both the NA and PXII neurones showed forms of a motor type neurone, while the FTL neurones showed various forms. The EPSPs with onset latency as short as 2-4 msec were frequently recorded in different nuclei. This strongly suggests that the CSN projects monosynaptically onto different nuclei in the medulla.     

Short-latency somatosensory evoked potentials following median nerve stimulation in Down's syndrome

Short-latency somatosensory evoked potentials (SEPs) following median nerve stimulation were recorded in 42 patients with Down's syndrome and in 42 age- and sex-matched normal subjects. There were no significant differences between the 2 groups in the absolute peak latencies of N9, N11 and N13 components. However, interpeak latencies, N9-N11, N11-N13 and N9-N13, were prolonged significantly in Down's syndrome. These findings suggest impaired impulse conduction in the proximal part of the brachial plexus, posterior roots and/or posterior column-medial lemniscal pathway. Interpeak latency N13-N20, representing conduction time from cervical cord to sensory cortex, was not significantly different between the 2 groups. Cortical potentials N20 and P25 in the parietal area and P20 and N25 in the frontal area were of significantly larger amplitude in Down's syndrome. P25 had double peaks in 16 of 42 normal subjects, but these were not apparent in any of the patients.     

Comparison in man of short latency averaged evoked potentials recorded in thalamic and scalp hand zones of representation

Recordings were performed in the thalamus of 13 patients suffering from either abnormal movements or intractable pain, with the aim of delimiting the region to be destroyed or stimulated in order to diminish the syndrome. In 11 of these patients averaged evoked potentials were recorded simultaneously from the scalp and specific thalamus (VP) hand area levels following median nerve stimulation. These recordings were done during the operation or afterwards when an electrode was left in place for a program of stimulation. The latencies of onsets and peaks on the scalp 'P15' were compared with those of the VP wave; a clear correspondence was found. Moreover, when increased stimulation was used, both waves began to develop in parallel. Thus in the contralateral 'P15' a component exists due to the field produced by the thalamic response. To explain the presence of an ipsilateral scalp 'P15' wave, we propose that a second wave having the same latency and a slightly shorter peak exists on the scalp due to a field produced by a brain-stem response. This double origin of 'P15' is also shown by the different changes which the ipsilateral and contralateral waves present during changes in alertness. The scalp 'N18-N20' is also composed of at least 2 components. The first peak appears on the scalp with a latency shorter than that of the negativity which develops in the thalamus. The N wave, moreover, increases in latency with rapid stimulus repetition. We propose with others that 'N18' is a cortical event reflecting the arrival of the thalamo-cortical volley. The second component, 'N20,' has a peak latency closely correlated to that of the thalamic negativity. This component was present alone in 'N' when rapid stimulation (greater than 4/sec) was used, which did not change the thalamic response. It must be a field produced by the thalamic negativity.     

Short latency somatosensory evoked potentials to peroneal nerve stimulation in normal Japanese children

Short latency somatosensory evoked potentials (SSEP) were elicited by stimulation of the peroneal nerve in 68 normal children of 39 weeks to 15 years old. In all subjects, three positive potentials (P1, P2 and P3) and one negative potential (N1) were consistently recorded. A further positive potential (P4) after N1 was not always observed. There was no change of wave form with development. P1, P2, P3 and N1 might be generated in subcortical structures; caudal cervical spine, brainstem, thalamus and thalamocortical pathway, respectively. The latency of each peak per one meter body length decreased with age until 5 or 6 years of age. Moreover, the latency between peaks per one meter body length also decreased with age until 5 to 6 years of age. These findings are consistent with the development of SSEP on median nerve stimulation and with the developmental phenomenon of spinal conduction velocity, and might be related to the increase in the diameter and the progressive myelination of nerve fibers.