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 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.     

Short latency somatosensory evoked potentials in infants

Short latency somatosensory evoked potentials (SEPs) to unilateral median nerve electrical stimulation were recorded from normal infants at birth and at 2, 4, 6, 8, 10 and 12 months of age. Three channels were recorded: Erb's point-Fz; C II (over 2nd cervical vertebra)-Fz; contralateral C' (2 cm posterior to C3 or C4)-Fz. Sweep time = 50 msec. At birth, the C II potential was seen in all infants; the Erb's point and C' potentials were seen in two-thirds. All older infants had well developed potentials at all sites. The mean latency of the Erb's point potential was stable over time. The latency of the C II potential decreased with maturation. At C', 4 components were seen, the latencies of which decreased with maturation: N1, P1, N2 and P2. The duration of N1 and P1 decreased with maturation. Standard deviations were relatively small for latencies and large for amplitudes. SEPs were adversely affected by using the 60 c/sec filter. Increasing the low frequency filter from 1 to 30 c/sec changed SEP, particularly in younger infants. Abnormal SEPs were seen in prematures surviving periventricular hemorrhage.     

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.     

Short latency somatosensory evoked potentials in Charcot-Marie-Tooth Disease

9 patients with Charcot-Marie-Tooth Disease (CMTD) of intermediate type (PMA type II, 10), all from the same family, presented with a significant increase of the interpeak N9-N13 latency. This increase is already present in the pre-symptomatic phase of the disease and there is no significant difference between the various patients of different ages and clinical severity, indicating that the lesions appears very early and tends to establish itself equally early. Similar behaviour is also seen in the distal conduction velocity along the sensitive fibres, while the more proximal areas seem to be relatively spared. The authors interpret these data as an expression of a distal central peripheral sensory neuropathy. In contrast, the lesion of the peripheral motor fibres, particularly in the legs, has a different and more severe pattern of evolution. Alterations in central conduction time (N13-N20) were not seen in any of the 9 patients studied.     

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.     

Short latency mechanically evoked somatosensory potentials in humans.

Somatosensory potentials evoked by mechanical stimulation were recorded by surface electrodes over (1) the digital nerves in the index finger, (2) the median nerve at the wrist, (3) the median nerve near the axilla, (4) the brachial plexus, (5) the cervical cord at CII, (6) the scalp overlying the somatosensory cortex. Nerve conduction velocities varied inversely with age and ranged from 43 to 68 m/sec. Mechanically evoked potentials recorded from the electrodes overlying the digital nerves were an artifact of the finger movement. All other electrode configurations recorded potentials comparable to those evoked by electrical stimulation of nerves. These mechanically evoked potentials could prove useful in the assessment of clinical disorders of somatosensory function from receptor to cortex in man.     

Short latency somatosensory evoked potentials in children with autism

SSEP were recorded in normal volunteer, autism, MBD and MR groups in order to find electrophysiological evidence of a brain lesion. Peak latencies per 1 m body length, P1/H, P2/H and P3/H in MR, and P3/H in autism, were greater than those in normal controls. The values of interpeak latencies per 1 m body length, P1-P3/H and P2-P3/H in autism and MR, were greater than those in normal controls. These in MBD were not different from in normal controls. The cause of the increase in P1/H in MR is unknown. The increases in P1-P3/H and P2-P3/H suggest that in autism and MR there is brainstem dysfunction. It is not clear whether there is a relationship among autism, MBD and MR.     

Short latency somatosensory evoked potentials in patients with syringomyelia

Short latency somatosensory evoked potentials (SSEPs) following median nerve and posterior tibial nerve stimulation were studied in six patients with syringomyelia. Three patients had Chiari malformations, two patients experienced fracture of the spine and one patient had a cauda equina ependymoma. SSEPs following median nerve stimulation were abnormal in all patients, of which five patients showed abnormal SSEPs only in the unilateral stimulation on the side of sensory deficits. SSEPs obtained from three out of eight upper extremities which showed no disturbance of deep sensation, were abnormal, so SSEPs were able to detect subclinical abnormality indicating dorsal column dysfunction. Abnormal patterns of SSEPs were classified in three types as follows; Type 1: disappearance of P13, N16 and N18 (3 cases), Type 2: the prolonged interpeak latency P11-P13 (2 cases), and Type 3: abnormal N16 and N18 with preserving P13 (1 case with Chiari malformation). P9 and P11 were present without prolonged latencies in all cases. SSEPs following posterior tibial nerve stimulation were abnormal in two of the three tested patients. Those two patients had disturbance of deep sensations in the lower extremities. All patients underwent surgical treatment, syringo-peritoneal shunt in four patients, foramen magnum decompression with syringo-subarachnoid shunt in one patient, and total removal of an ependymoma of the cauda equina with syringotomy in one patient. Postoperative neurological improvement were found in three patients, of which two cases also showed improvement in SSEPs. On the contrary SSEPs were unchanged in two patients with posttraumatic syringomyelia, whose postoperative neurological condition was also unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Short latency somatosensory evoked potentials in patients with neurological lesions

Short latency somatosensory potentials following median nerve stimulation were recorded in patients grouped according to anatomic location of neurological lesion. Patients with cerebral lesions causing severe sensory deficit lacked a major positive wave of cortical origin that in normal subjects peaked at a mean latency of 20.5 ms. Patients with severe cervical spinal cord disease lacked all of the normal somatosensory response except for the earliest component attributed to peripheral nerve activity. Patients with brain-stem lesions showed delayed latencies of later waves and prolonged interwave latencies. However, auditory evoked potentials measured in the group with brain-stem lesions were more helpful in localization. Analysis of short latency somatosensory potentials can discriminate between peripheral nerve, spinal cord, brain-stem, and cerebral lesions. Further experience and refinement of technique of measurement should increase the value of this procedure.     

Imaging of the guinea pig cochlea following round window gadolinium application

Precise, non-invasive determination of the aetiology and site of pathology of inner ear disorders is difficult. The aim of this study was to describe an alternative method for inner ear visualization, based on local application of the paramagnetic contrast agent gadolinium. Using a 4.7 T MRI scanner, high contrast images of all four cochlear turns were obtained 3.5 h after placing gadolinium on the round window membrane. Gadolinium cleared from the cochlea within 96 h. Auditory brainstem response measurements performed on a separate group of animals showed no significant threshold shifts after the application, indicating that gadolinium is non-toxic to the guinea pig cochlea.     

Changes in latency of evoked potentials after caudate nucleus stimulation

The activation of the head of the caudate nucleus in cats which have undergone transection of the spinal cord at C1 produces inhibition of evoked potentials in the motor area (pre-cruciate region) and also reduces the peak latency of the negative slow wave. The results of decreased latency are discussed with reference to variations in intensity of the stimulation activating the motor cortex. The role played by the caudate nucleus in the control of the motor system is emphasized.     

Short and middle latency vestibular evoked responses to acceleration in man.

We have succeeded in recording short and middle latency vestibular evoked responses in human subjects. The head was held rigidly in a special, patented head holder, constructed individually for each subject, which gripped the teeth of the upper jaw. The stimulus consisted of 2/sec steps of angular acceleration impulses produced by a special motor with intensities of about 10,000 degrees/sec 2 and with a rise time of 1-2 msec. The electrical activity was recorded as the potential difference between special forehead and mastoid electrodes having a large, secure contact area with the skin. The activity was digitally filtered and averaged in 2 separate channels by means of a Microshev 2000 evoked response system. The short latency responses, with peaks at about 3.5 msec (forehead positive), 6.0 msec (forehead negative) and 8.4 msec (forehead positive; bandpass: 200-2000 Hz; average of 1024 trials), had amplitudes of about 0.5 microV. The middle latency responses had peaks at about 8.8 msec (forehead positive), 18.8 msec (forehead negative) and 26.8 msec (forehead positive; 30-300 Hz; N = 128 trials), with larger amplitudes (about 15 microV). These responses were consistently recorded in the same subject at different times and were similar in different normal subjects. Strenuous control experiments were conducted in order to ensure that these responses are not artefacts due to the movement of conducting media (head, electrodes and leads) in the electromagnetic field of the motor and are elicited by activation of normal labyrinths.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peak latency differences in evoked potentials elicited by painful dental and cutaneous stimulation

Long-latency evoked potentials (EPs) (50-400 msec) have been obtained from humans during both noxious stimulation of tooth and cutaneous sites in studies of pain and analgesic states. This study investigated whether EPs elicited by tooth and lip stimulation differed in peak latency and whether EPs obtained during painful cutaneous stimulation showed increasing peak latency values with increased conduction distance. Twelve volunteers received painful electrical stimulation at four sites: tooth, lip, thumb, and toe in counterbalanced orders. Evoked potentials recorded at vertex were summation averaged over 128 trials. Multivariate stepwise discriminate analysis was used to determine whether any of the peak latencies of the event-related potentials differed across stimulation sites. No significant latency differences were observed across lip, thumb or toe at any of the major peaks. Since peaks of these EPs did not vary in latency with conduction distance, they appear to reflect processing at higher levels rather than sensory transmission. The negative 140 msec peak of the dental waveform occurred significantly later than the same peak at cutaneous sites.