Somatosensory evoked potentials to posterior tibial nerve stimulation in children

The somatosensory evoked potentials (SEPs) to stimulation of the tibial nerve were studied in 88 children ranging in age from 1 day to 16 years. SEPs were not evidenced in 10 out of 44 infants less than 1 year old. In others it was a major positive wave (P) with a variable topographic distribution on the midline. The onset and peak latencies of this P were highly variable in different subjects of the same age or body-size, and in the same subject with the active electrode placed in different locations. The lowest values for latency were in subjects about 3 years old. The ascending time of P was the only parameter strictly correlated with age. The results are compared with SEPs to upper limb stimulation, which are constant and more reliable. These results indicate: that the maturation of the peripheral somatosensory pathway proceeds at a faster rate than that of the central somatosensory pathway; that the maturation of the somatosensory pathway of the upper limb precedes that of the lower limb; and that the ascending time of P is a good index of thalamo-cortical maturation. The clinical utility of these SEPs in pediatrics is discussed.     

Stability of N20 onset or peak latency in median somatosensory evoked potentials

We analyzed onset and peak latencies of the N20 response of median nerve somatosensory evoked potentials (SEPs) in 21 healthy subjects by simultaneous recordings with noncephalic or ear reference from multiple scalp sites. The cortical onset was defined as the fork at which the contralateral parietal and frontal or ipsilateral parietal waves diverged. We found the N20 onset unchanged between noncephalic and ear reference recordings, or among the recordings around the contralateral centroparietal scalp. The N20 peak was prolonged when the recording position moved posteriorly. We suggest that N20 onset latency is more stable than N20 peak.     

Abnormalities in event-related potential and brainstem auditory evoked response in children with nocturnal enuresis

To evaluate central nervous system functioning involvement in nocturnal enuresis, P300 and N200 event-related brain potentials and brainstem auditory-evoked potentials (BAER) were assessed in a group of 35 enuretic boys aged 7-9 years. The measurements of enuretic group were compared to those of age and sex matched non-enuretics. P300 latency in the enuretic group was significantly longer than in non-enuretic group (420 ms at parietal scalp (Pz), 414 ms at central scalp (Cz) versus 386 ms at Pz, 376 ms at Cz; P < 0.01 and P < 0.01, respectively). Both enuretic and non-enuretic subjects were divided into three subgroups his age. There was no significant difference in terms of both P300 amplitude and N200 latency and N200 amplitude between non-enuretic age subgroups. But, P300 latency over central scalp in 8 years old non-enuretic subgroup was significantly longer than in 9 years old non-enuretic subgroup (P < 0.01). No significant difference was found in latency and amplitude of P300 and N200 latency between enuretic subgroups. However, N200 amplitude at Cz in 8 years old enuretic subgroup was significantly lower than both in 7 years old enuretic subgroup and in 9 years old enuretic subgroup (P < 0.01 and P < 0.01, respectively). There were significant topographical differences in latency and amplitude of P300 and in N200 latency in enuretic age subgroups, only. There was no significant difference in interpeak latencies I-III, I-V and III-V and wave latencies I, III and V of BAERs between enuretic group and non-enuretic subgroup. Longer interpeak and wave latencies of BAERs were found both in 8 years old enuretic subgroup and 8 years old non-enuretic subgroup. CONCLUSION: Longer P300 latency in primer enuretics compare to non-enuretics is an evidence of a maturational delay of central nervous system functioning.     

Maturation of near-field and far-field somatosensory evoked potentials after median nerve stimulation in children under 4 years of age.

OBJECTIVES: The maturation of subcortical SEPs in young children. METHODS: Median nerve SEPs were recorded during sleep in 42 subjects aged 0-48 months. Active electrodes were at the ipsilateral Erb's point, the lower and upper dorsal neck, and the frontal and contralateral centroparietal scalp; reference electrodes were at the contralateral Erb's point, the ipsilateral earlobe and the frontal scalp; bandpass was 10-3000 Hz. The peaks were labelled by their latencies in adults. RESULTS: The peak latencies of N9 (brachial plexus potential) decreased exponentially with age during the first year, but increased with height thereafter. The interpeak latencies (IPLs) N9-N11, which measure conduction between brachial plexus and dorsal column, decreased with age (linear regression). The IPLs N11-P13 and N11-N13b, which measure conduction between the dorsal column and approximately the cervico-medullary junction, did not change across this age range. The IPLs N13a-N20, N13b-N20 and P13-N20, which measure central conduction, showed negative exponential regressions with rapidly decreasing latencies during the first year of life and slowly decreasing latencies thereafter. CONCLUSIONS: Maturation of the peripheral segments of the somatosensory pathway progresses more rapidly than that of the central segments. The maturation of central conduction is not completed within the first 4 years of age. Our maturational data may serve as a reference source for subsequent developmental and clinical studies.     

Developmental change of short latency somatosensory evoked potential waves between P3 and N1 components in children

We attempted to isolate and identify the negative waves between the conventional P3 and N1 components of short latency somatosensory evoked potentials (S-SEPs) in children. Twenty normal children ranging in age from 3 months to 12 years, and 11 adolescents and adults were studied. The median nerve was stimulated and recordings from F (F3 or F4) and C' (1-2 cm posterior to C3 or C4) contralateral to the stimulation site were simultaneously obtained in order to identify each negative wave in the C' recording. The wave of C' coincident with that of F was regarded as the far-field potential, and the wave of C' that diverged from F as the near-field potential at the scalp. There were one negative wave (N1) in the far-field potential and 2 negative waves (N2 and N1(3)) in the near-field potential, after the P3 component. "N1(3)" was conventional N1 and "N2" was the negative wave just before N1(3). In infants and younger children, the interpeak latencies of P3-N1(3) and P3-N2 were markedly elongated in comparison with that in older children. These interpeak latencies may be useful as an index of cerebral maturation.     

SEPs to median nerve stimulation: normative data for paediatrics

Somatosensory evoked potentials (SEPs) provide neurologists with an assessment of the neuraxis from peripheral nerve to sensory cortex. Their value is particularly relevant in paediatric neurology as sensory clinical examination can be difficult in young infants and children. The clinical utility of SEPs, however, requires knowledge of the alterations in wave form which occur with growth and development. This study presents normative SEP data from 4 months-35 years. Different non-linear maturational months-35 years. Different non-linear maturational patterns were seen in spinal and central segments of the nervous system. The cervical components (N12, N13) changed little in latency until 2-3 years, the N20 decreased in latency until 2-3 years and P22 decreased in latency until 6-8 years, after which latencies increased until adulthood. The greatest latency changes occurred in N12 and N13, the least in N20. Wave form morphology and interpeak latencies also changed with age. Adult morphology was achieved early (from 1 year), but central conduction time (N13-N20) reached adult values only at 6-8 years. This study provides normative values of SEPs during maturation and a functional assessment of pathways known to myelinate and mature at varying rates.     

Extrauterine maturation of somatosensory pathways in preterm infants: A somatosensory evoked potential study

ObjectiveTo evaluate the reliability of somatosensory evoked potential (SEP) recordings in preterm infants to monitor the intra-uterine and extrauterine maturation of somatosensory pathways.MethodsWe performed SEPs in 35 neurologically normal preterm babies (range 23–35 weeks gestational age – GA). Twenty-four of all infants were evaluated after the first 2 weeks of life, at a minimum post-menstrual age (PMA) of 31 weeks, and 31 at term corrected age. In 15 infants we obtained longitudinal recordings at both epochs. Cross-sectional and longitudinal values of first cortical potential (N1) were analyzed in relation of PMA and matched with those measured in a group of 11 fullterm babies.ResultsReproducible cortical SEPs were found in 92% of preterm babies at first recording, and in all 31 neonates at follow-up. A significant inverse correlation between the latency values of N1 and PMA at the time of first recording was observed, showing that latencies of these components rapidly decrease with increasing PMA. Regression analysis showed no significant effect on N1 latency at term correct age in dependence of GA, suggesting that extrauterine life does not affect maturation of somatosensory pathways. Interestingly, the occurrence of idiopathic respiratory distress (RDS) during clinical course after birth correlated with a delayed N1 latency at term corrected age.ConclusionsExtrauterine life does not affect maturation of somatosensory pathways in preterms without neurological deficit. Finally, the mild negative influence of RDS on maturational changes was evident.SignificanceSEPs could be considered a useful tool for a non-invasive assessment of somatosensory pathways integrity in preterm infants.     

Median nerve somatosensory evoked potentials: studies on latency variability as a function of subject height, limb length and nerve conduction velocity.

Report on the results of regression analysis studies concerning median nerve somatosensory evoked potentials (SEPs) latencies, as dependent variables, and subject height, limb length and nerve conduction velocity (NCV), as independent variables. The tests were performed on 23 normal volunteers. Absolute SEP latencies could be predicted by a linear regression model when the independent variable was arm length; when it was subject height, however, both exponential and polynomial models proved better, the latter showing the best coefficients of determination, R 2. Multiple linear regression with two independent variables (arm length and NCV) was found to be better than simple linear regression for predicting P/N13 latency. The regression line for EP-P/N13 latency on height was found to be a polynomial curve; although the regression was found to be significant by the "F" test (alpha = 1%), the model had a low R 2 value (0.41). The same applies to the P/N13-N19 interpeak latency regression curve, but the regression was significant for alpha = 5% in that case. Although interwave latencies are the most useful parameters for clinical interpretation of median SEPs, absolute latencies may occasionally be important, and should be corrected for body size. In unusually tall subjects, it might be useful to double-check EP-P/N13 interwave latency prolongation by estimating the maximum expected P/N13 latency, using a model that takes into account both limb length and NCV.     

Developmental assessment of spinal cord and cortical evoked potentials after tibial nerve stimulation: effects of age and stature on normative data during childhood

Somesthetic information from lower extremities is processed by cerebral cortex after traversing the sensory pathways of peripheral nerve, spinal cord, brain-stem and thalamus. Clinical utility of somatosensory evoked potentials (SSEPs) during human development requires systematic analysis of normative data acquired during various stages of body growth and nervous system maturation. Accordingly, SSEPs after tibial nerve stimulation were studied in 32 normal awake children (1-8 years old) and compared with values obtained in young adults (18-40 years old). Potentials were recorded from the tibial nerve (N5), first lumbar spinous process (N14), seventh cervical spinous process (N20) and from the scalp, 2 cm behind the vertex (P28). In all children studied, the N5, N14 and N20 latencies were positively correlated with age and height yielding a predictive nomogram. An extremely variable electropositive cortical SSEP was recorded from Cz' which did not show a highly predictable linear relationship in association with a relatively poor correlation coefficient for height and age. It may be concluded that between 1 and 8 years of normal postnatal development, latencies reflecting peripheral nerve and lumbar spinal cord vary directly with height and age and can be represented by a simple cable model of a lengthening myelinated pathway. In contrast, the latency of the cortical SSEP reflects asynchronous maturation of elongating polysynaptic pathways and apparently requires a more complex model for prediction in order to enhance its clinical utility.     

Brain stem auditory, visual and somatosensory evoked potentials in leukodystrophies

Brain stem auditory (BAERs), visual (VEPs) and somatosensory evoked responses (SEPs) were recorded in 12 patients with Pelizaeus-Merzbacher leukodystrophy (PMD), three with adrenoleukodystrophy (ALD) and three with metachromatic leukodystrophy (MLD). All the 3 evoked responses were abnormal in all patients except normal VEPs and SEPs in a patient with early ALD. In most patients wave I with and without wave II were the only components of the BAERs that remained, subsequent components (waves III-VII) were absent. VEPs were severely altered; either no identifiable response to flash or pattern reversal stimuli could be recorded or the major components were significantly delayed in latency. Short latency SEPs following median nerve stimulation usually showed a normally recorded Erb's potential (N10), but an absence or marked attenuation of cervical (N14) and early scalp components (N19 and P22) or the occurrence of the scalp components with a significant delay. Multimodality evoked responses provide more information regarding the functional integrity of several afferent systems in patients with white matter disorders.     

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.     

Effects of aging on central conduction in somatosensory evoked potentials: evaluation of onset versus peak methods.

OBJECTIVES: To investigate effects of aging on peripheral and central somatosensory conduction, and evaluate onset-to-onset and peak-to-peak measurements of each component and central conduction time (CCT) in somatosensory evoked potentials (SEPs). METHODS: We recorded SEPs with non-cephalic reference from the Erb's point, the posterior (cv 6) and anterior neck, and scalp (Fz and P4) after left median nerve stimulation in 138 normal subjects aged between 20 and 78 years. We determined onset or peak latencies of the Erb's potential (N9), the spinal N13-P13 in cv 6-to-anterior neck montage and the N20-P20 in scalp leads. Onset CCT was defined as a transit time from N13-P13 onset to N20-P20 onset. In each subject, interpeak latencies of the 'N13' component in cv 6-to-Fz montage and the N20-P20 in P4-to-Fz montage were also defined as conventional peak CCT. RESULTS: Using multiregression analysis, we found that the onset or peak latencies of each SEP component were correlated with the subject's height and age. So were the onset CCTs: Onset CCT (in ms) = 2.549+2.041x(height in meters) + 0.005 x (age in years) (P<0.0001). The conventional peak CCTs as well as onset-to-peak durations of the N20-P20 were correlated with the subject's age but not height: Peak CCT(in ms) = 5.458+0.012x (age in years) (P<0.0005). CONCLUSION: Conductive function is affected by normal aging in the central as well as peripheral somatosensory pathways. The peak CCT is more affected by aging than the onset CCT. However, the onset-to-peak duration of the N20-P20 increased by 0.8 ms between the 4th and 7th decades, suggesting that the peak CCT increase in older people reflects the age-related changes in N20-P20 profile but not in the fastest central conduction. We therefore conclude that the onset CCT measurement is preferable to the peak CCT measurement when assessing the central somatosensory conduction.     

Intracranial recording of short latency somatosensory evoked potentials in man: identification of origin of each component

In normal subjects the short latency SEPs generally consisted of 3 positive waves (P9, P11, P14) and a succeeding negative wave (N20). To determine the origins of these waves we have made intracranial records from 17 patients, which suggest the following results. P9 originates in stimulated median nerve peripheral to the dorsal roots such as brachial plexus, P11 in the dorsal column of the cervical cord, P14 in the cuneate nucleus and medial lemniscal pathway, and N20 in the cerebral cortex. On the basis of intracranial and intraspinal records, the onset of P11 indicates the arrival of the afferent volley at the cord entry and the peak latency of P11 its arrival time at the C1-2 level dorsal column. The onset latency of P14 indicates the onset of postsynaptic events in cuneate nucleus neurons and the peak latency of P14 arrival at the midbrain. From the ventral surface of the brain-stem 3 positive waves (P'9, P'11, P'14) like the initial positive components of the scalp short latency SEPs (P9, P11, P14) were recorded. The amplitude of P'14 was large compared to that of P14. The peak latencies of P'14 recorded at the medulla and the pons were shorter than that of P14 by 0.7-0.8 msec and 0.2-0.5 msec, respectively. The peak latency of P'14 at the midbrain was almost the same as that of P14. By measuring the distance between the recording electrodes in the brain-stem and the peak latency difference of P'14, the fastest lemniscal conduction velocity was estimated as 56 m/sec.     

Distinct fronto-central N60 and supra-sylvian N70 middle-latency components of the median nerve SEPs as assessed by scalp topographic analysis, dipolar source modelling and depth recordings.

OBJECTIVES: To investigate the possible contribution of the second somatosensory (SII) area in the generation of the N60 somatosensory evoked potential (SEP).METHODS: In 7 epileptic patients and in 6 healthy subjects scalp SEPs were recorded by 19 electrodes placed according to the 10-20 system. All epileptic patients but one were also investigated using depth electrodes chronically implanted in the parieto-rolandic opercular cortex. Scalp SEPs underwent brain electrical source analysis.RESULTS: In both epileptic patients and healthy subjects, scalp recordings showed two middle-latency components clearly distinguishable on the basis of latency and scalp distribution: a fronto-central N60 potential contralateral to stimulation and a later bilateral temporal N70 response. SEP dipolar source modelling showed that a contralateral perisylvian dipole was activated in the scalp N70 latency range whereas separate perirolandic and frontal sources were activated at the scalp N60 latency. Depth electrodes recorded a biphasic N60/P90 response in the parieto-rolandic opercular regions contra- and ipsilateral to stimulation.CONCLUSIONS: Two different middle-latency SEP components N60 and N70 can be distinguished by topographic analysis and source modelling of scalp recordings, the sources of which are located in the fronto-central cortex contralateral to stimulation and in the supra-sylvian cortex on both sides, respectively. The source location of the scalp N70 in the SII area is strongly supported by its spatio-temporal similarities with SEPs directly recorded in the supra-sylvian opercular cortex.     

Non-invasive evaluation of input-output characteristics of sensorimotor cerebral areas in healthy humans

The topography of scalp SEPs to mixed and sensory median nerve (MN) and to musculocutaneous nerve stimulation was examined in 20 healthy subjects through multichannel (12-36) recording in a 50 msec post-stimulus epoch. MN-SEPs in both frontal leads were characterized by an N18, P20, N24, P28 complex showing maximal amplitude at contralateral parasagittal sites. This was sometimes partly obscured by a wide wave N30 having a fixed latency, but a steep amplitude gradient moving toward the scalp vertex. A P40 component followed, having longer peak latencies, moving the recording sites from contralateral medial parietal toward the vertex and frontal ipsilateral positions. MN-SEPs in contralateral parietal leads contained a widespread N20 with a maximum source posterior to the Cz-ear line. The following P25 enveloped two subcomponents - early and late P25 - having different distributions. The late P25 showed a maximum - coincident with that of wave N20 - which was localized more posteriorly than that of the early P25. An inconstant wave N33 with progressively longer peak latencies from sagittal toward lateral positions was then recorded. MN-SEPs in contralateral central positions showed a well-localized P22 wave in which both the parietal early P25 and the frontal P20 were vanishing. Common or separate generators for frontal, central and parietal SEPs were discriminated by evaluating the influence of stimulus rate and intensity, as well as of general anesthesia and transient CBF deficits, investigated in 7 patients undergoing carotid endarterectomy. Unifocal anodal threshold shocks were separately delivered to each of the scalp electrodes and motor action potentials were recorded from the target muscle in order to delineate the scalp representation of the motor strip for the upper limb and, consequently, to monitor, through SEP tracings, the short-latency sensory input to the motor cortex for hand and shoulder muscles. This was characterized by a boundary zone separating the parietal N20-early P25 complex, from the fronto-central N18-P22 one. This zone had an oblique direction strongly resembling that of the central sulcus.     

Scalp topography of somatosensory evoked potentials following electrical stimulation of femoral nerve

Up to 29 channels of somatosensory evoked potentials (SEPs) were recorded in 10 normal volunteers following unilateral femoral nerve (FN) and tibial nerve (TN) electrical stimulation. Typical short latency FN SEPs consisted of 6 components, P15, N19, P26, N34, P44 and N56. P15 and N19 were widely distributed on the scalp. The first localized scalp component, P26, was strictly postrolandic and distributed on the contralateral parietal scalp close to midline with a prerolandic phase reversal, N26. This scalp distribution is clearly different from the first localized potential of tibial nerve SEPs. N34 and P44 were maximal at the vertex with a distribution that spread to the ipsilateral central and parietal scalp. The amplitude of P26 increased and latency shortened with increasing stimulus intensity and both values plateaued after the stimulus intensity reached motor threshold. No correlation was found between the peak latency of P26 and body height.     

Age-related variations in evoked potentials to auditory stimuli in normal human subjects.

Auditory evoked potentials were recorded from 47 subjects ranging in age from 6 to 76 years in order to assess the effects of maturation and aging on the evoked (N1 and P2) and event-related (N2 and P3) components. Because of clear differences in the effects of age on the event-related components between children (less than 15 years of age) and adults the subjects were divided into two populations for analysis. For adults there was a systematic increase in the latency and decrease in amplitude of each component with age. Also the rate of the age-related increase in latency was proportional to the latency of the component. The scalp distributions of both the stimulus-evoked and event-related components were found to vary with age yielding a more nearly equipotential distribution for older subjects. For children the latencies of the event-related components decreased with age. The stimulus-evoked components had latencies which were not significantly different from those predicted from the adult data. In contrast to the adult data, age affected the scalp distributions of the stimulus-evoked components differently than the event-related components. These results suggest an aging process is relfected in the auditory evoked potential which is not the simple inverse of maturational processes.     

Short latency somatosensory evoked potential in children

The short latency somatosensory evoked potential was studied in 90 normal children of 1 month to 16 years old and 7 adults. Somatosensory stimuli were delivered through a disc electrode placed over the median nerve at the wrist joint. The uniform recording sites used were the central region of the scalp, and the seventh cervical spine or Erb's point. Reference electrodes were placed on the hand contralateral to the median nerve stimulated. Three positive peaks (P1, P2 and P3) and one negative peak (N1) were consistently recorded, a further positive peak (P4) after N1 was not always observed. The latency of each peak per 1 m body length decreased with age until 2 or 5 years of age. The latency of each peak after 2 years of age was positively correlated with the body length and arm length. The value of P1 peak latency per 1 m body length reaches adult values at an earlier rate than the value of P3 peak latency and P2-P3 latency per 1 m body length. This suggests that central lemmiscal pathways mature at a slower rate than peripheral nerve fibers. The wave form pattern of the short latency somatosensory evoked potential changed to the adult pattern at 10 years of age. The peak latency of P4 during deep sleep was slightly prolonged. In recording on infants during sleep, the EEG should be monitored to determine the stage of sleep.     

Scalp-recorded short and middle latency peroneal somatosensory evoked potentials in normals: comparison with peroneal and median nerve SEPs in patients with unilateral hemispheric lesions

Peroneal somatosensory evoked potentials (SEPs) were performed on 23 normal subjects and 9 selected patients with unilateral hemispheric lesions involving somatosensory pathways. Recording obtained from right and left peroneal nerve (PN) stimulations were compared in all subjects, using open and restricted frequency bandpass filters. Restricted filter (100-3000 Hz) and linked ear reference (A1-A2) enhanced the detection of short latency potentials (P1, P2, N1 with mean peak latency of 17.72, 21.07, 24.09) recorded from scalp electrodes over primary sensory cortex regions. Patients with lesions in the parietal cortex and adjacent subcortical areas demonstrated low amplitude and poorly formed short latency peroneal potentials, and absence of components beyond P3 peak with mean latency of 28.06 msec. In these patients, recordings to right and left median nerve (MN) stimulation showed absence or distorted components subsequent to N1 (N18) potential. These observations suggest that components subsequent to P3 potential in response to PN stimulation, and subsequent to N18 potential in response to MN stimulation, are generated in the parietal cortical regions.     

Middle-latency somatosensory evoked potentials following median and posterior tibial nerve stimulation in Down's syndrome.

Middle-latency somatosensory evoked potentials (SEPs) following median and posterior tibial nerve stimulation were studied in 40 patients with Down's syndrome and in age- and gender-matched healthy controls as well as in middle-aged and aged healthy subjects. In median nerve SEPs, latencies of the initial cortical potentials, N18 and P18, showed no significant difference, but the following potentials N22, P25, N32, P41 and P46 were relatively or significantly shorter in latency in Down's patients than in the controls. Amplitudes of all components in Down's patients were significantly larger than those of age- and gender-matched controls as well as of those of middle-aged healthy subjects, but there was only a small difference in their amplitudes from aged healthy subjects. Results of posterior tibial nerve SEPs were generally consistent with those of median nerve SEPs. Therefore, 'short latency with large amplitude' is the main characteristic of middle-latency SEPs in Down's syndrome, possibly related to accelerated physiological aging of the central nervous system.