Two distinct cervical N13 potentials are evoked by ulnar nerve stimulation

To investigate the dual nature of the posterior neck N13 potential, we attempted to establish the presence of a latency dissociation between caudal (cN13) and rostral (rN13) potentials on stimulating the ulnar nerve, in view of its lower radicular entry compared to the median nerve. SEPs were evaluated in 24 normal subjects after both median and ulnar nerve stimulation. cN13 was prominent in the lower cervical segments, and rN13 was localized mainly in the upper ones using anteroposterior and longitudinal bipolar montage, respectively. The N9-cN13 interpeak latency did not differ significantly from N9-rN13 when stimulating the median nerve. On the other hand, the N9-rN13 interpeak was significantly longer than the N9-cN13 interpeak when the ulnar nerve was stimulated. The rN13 presented the same latency as P13-P14 far-field potentials in 17 out of 24 ulnar nerves tested. Therefore, the ulnar nerve stimulation evokes two distinct posterior neck N13 potentials. It is widely accepted that the caudal N13 is a postsynaptic potential reflecting the activity of the dorsal horn interneurons in the lower cervical cord. We suggest that the rostral N13 is probably generated close to the cuneate nucleus, which partly contributes to the genesis of P13-P14 far-field potentials.     

Spinal and cortical potentials evoked by tibial nerve stimulation in humans: effects of sex, age and height.

Somatosensory evoked potentials by posterior tibial nerve stimulation at the ankle were performed in 74 healthy volunteers (36 females and 38 males) aged 14-76 years. Cortical potentials were obtained in all subjects and spinal potentials (N22) in 71 subjects. All parameters were related to subject's age, height and sex. Sex influenced only P40-N50 amplitude, which was greater in females. All latencies of spinal and cortical components increased in a similar manner with subject's height (about 0.16-0.18 ms per cm), whereas the N22-P40 interpeak latency was independent from height, but related to T12-Cz distance. Absolute latencies of the spinal and of most cortical components, but not interpeak latencies, increased with subject's age (about 0.06-0.09 ms per year). The parameters to compute normative data (according to univariate or bivariate regression models) are furnished. Limits of right-left differences are reported.     

SEPs in two patients with localized lesions of the postcentral gyrus

Scalp distributions of median nerve SEPs were studied in normal controls and 2 patients with localized lesions of the postcentral gyrus. In controls, parieto-occipital electrodes registered N20-P27 while frontal electrodes registered P20-N27. Other small components, parieto-occipital P22 and frontal N22, were recognized in about half of the control records. The wave forms at a frontal and a parieto-occipital electrode, both distant from the central region, formed exact mirror images of each other concerning N20-(P22)-P27 and P20-(N22)-N27. Electrodes near the central region contralateral to the stimulation registered cP22-cN30 (central P22 and central N30). When the postcentral gyrus was damaged, N20/P20-P27/N27 and cP22-cN30 were eliminated and the only remaining components were a frontal negative wave (frN) and a contralateral parieto-occipital positive wave (poP). Digital nerve stimulation also evoked poP and frN in both cases. In case 2, poP coincided with P22 of the non-affected side. The following generators were proposed; N20/P20-P27/N27: area 3b, cP22-cN30: areas 1 and 2, poP/early frN (= P22/N22): area 4 at the anterior wall of the central sulcus (due to direct thalamic inputs to motor cortex), late frN: uncertain (SMA?, SII?).     

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.     

The somatosensory central conduction time: physiological considerations and normative data

The somatosensory central conduction time (CCT) can be measured from the peak of N13 to the peak of N20 (peak CCT) or from the onset of N11 to the onset of N20 (onset CCT). The onset and peak CCT were measured concomitantly in 40 normal subjects and the mean peak CCT was significantly shorter than the mean onset CCT. Records with different reference electrodes (linked earlobes, F3, over the ipsilateral parietal scalp, non-cephalic reference in some subjects) showed no significant latency change of the N11 onset, the N20 onset, the peak and onset CCT in contrast with the significant latency changes of the N13 and N20 peak with different montages. The onset CCT was divided by the onset of the P14 far-field in 2 parameters, the N11-P14 interval predominantly concerned with spinal conduction and the P14-N20 interval which reflected only supraspinal conduction. The onset and peak CCT, the N11-P14 and P14-N20 intervals were not correlated with height or age. Three independent recording sessions over 1 year in 16 subjects showed that the parameters were reproducible. From the physiological point of view the onset and peak CCT are different parameters and the anatomical correlates of both parameters are discussed.     

The relationship between median nerve somatosensory evoked potential latencies and age and growth parameters in young children

Median nerve somatosensory evoked potentials (SEPs) were recorded in a group of 35 normal children aged 6–36 months and related to body length, body weight and head circumference. Recordings were made while the child was awake using the following derivations: ipsilateral clavicle - Fpz; seventh cervical vertebra (CV7) - Fpz; contralateral C′ - Fpz. the clavicular-Fpz response was bilobed in 77% of the recordings, the initial being designated CL1 and the following negativity, CL2. Early negativities, coincident in latency with CL1 and CL2, were often present inin CV7-Fpz recordings, however, a negativity longer in latency than CL2 was always present, was designated CVN, and preceded a prominent positivity. A scalp-recorded early negativity (N1) and a following positivity (P1) were well defined in all recordings.The latency of CL1, CL2 and CVN increased with an increase in age and stature. In contrast, significant negative correlations were found between the latency of N1, P1, age and statur. The CL1-CVN interpeak latency did not correlate significantly with age, while the central conduction time (CVN-N1) declined with an increase in age and stature. These findings confirmed the complexity of SEP absolute and interpeak latency changes with an increase in age and stature in young children.     

Auditory evoked potentials in Down's syndrome

Short-, middle- and long-latency auditory evoked potentials (SAEPs, MAEPs and LAEPs) were examined in 12 subjects with Down's syndrome and in 12 age-matched normal subjects. In comparison with the normal subjects, Down subjects showed shorter latencies for SAEP peaks II, III, IV and V (and correspondingly shorter interpeak intervals I–II and I–III) so long as stimulus intensity was at least 45 dB SL. The MAEP peak Na had a longer latency in Down subjects than in normal subjects, but not the Pa latency. In passive oddball experiments for LAEPs, the latencies of all components from N1 to P3 were progressively longer in Down subjects, and the N2-P3 amplitude increased slightly between the first and fourth blocks of stimuli (whereas in the normal subjects it decreased). These alterations in auditory evoked potentials, which may correlate with cerebral alterations in organization and responsiveness responsible for deficient information processing, may constitute an electrophysiological pattern that is characteristic of Down's syndrome.     

Clinical and neuroimaging correlates of abnormal short-latency Somatosensory Evoked Potentials in elderly vascular dementia patients: A psychophysiological exploratory study

BACKGROUND: Short Latency Somatosensory Evoked Potentials (SEPs) may serve to the testing of the somatosensory tract function, which is vulnerable and affected in vascular encephalopathy. The aim of the current study was to search for clinical and neuroimaging correlates of abnormal SEPs in vascular dementia (VD) patients. MATERIALS AND METHODS: The study included 14 VD patients, aged 72.93 PlusMinus; 4.73 years, and 10 controls aged 71.20 PlusMinus; 4.44 years. All subjects underwent a detailed clinical examination, blood and biochemical testing, brain MRI and were assessed with the MMSE. SEPs were recorded after stimulation from upper and lower limbs. The statistical Analysis included 1 and 2-way MANCOVAs and Factor analysis RESULTS: The N13 latency was significantly prolonged, the N19 amplitude was lower, the P27 amplitude was lower and the N11-P27 conduction time was prolonged in severely demented patients in comparison to controls. The N19 latency was prolonged in severely demented patients in comparison to both mildly demented and controls. The same was true for the N13-N19 conduction time, and for the P27 latency. Patients with subcortical lesions had all their latencies prolonged and lower P27 amplitude. DISCUSSION: The results of the current study suggest that there are significant differences between patients suffering from VD and healthy controls in SEPs, but these are detectable only when dementia is severe or there are lesions located in the subcortical regions. The results of the current study locate the abnormal SEPs in the white matter, and are in accord with the literature.     

γ-氨基丁酸、荷包牡丹碱和L-谷氨酸钠对猫和家兔同侧和对侧图形视觉诱发电位的影响

在猫和家兔大脑半球一侧视区17/18交界处施加γ—氨基丁酸(GABA)、荷包牡丹碱和L—谷氨酸钠,以及用氯化钾和冷冻阻遏的方法,记录对侧和同侧皮层相应处图形视觉诱发电位(PVEP)的变化。讨论了GABA、荷包牡丹碱和L—谷氨酸钠对猫和兔的对侧和同侧PVEP的影响。     

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 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 from 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.     

Absence of spinal N13-P13 and normal scalp far-field P14 in a patient with syringomyelia

Short latency somatosensory evoked potentials to median or ulnar nerve stimulation were recorded in a patient with syringomyelia. Scalp-recorded far-field P14 was clearly preserved, but spinal N13-P13 components disappeared. Our findings support the hypothesis that spinal N13-P13 is generated by structures intrinsic to the cervical cord, most likely in the ventral central gray matter.     

Pre-stimulus spectral EEG patterns and the visual evoked response

The relationship between the latencies and amplitudes of the N1 and P2 components of the visual evoked potential (VEP) and the psychophysiological state of the brain immediately preceding the time of the stimulus has been investigated in 7 male subjects. Power spectral measures in the delta, theta, alpha and beta bands of the 1 sec pre-stimulus EEG were used to assess the brain state, and low intensity flashes, delivered randomly between 2 and 6 whole seconds, were used as the stimuli. Trials were ranked separately according to the relative amounts of pre-stimulus power in each EEG band and were partitioned into groups by an equal pre-stimulus spectral power criterion. Averaged EPs were computed from these groups and multiple regression analysis was used to relate pre-stimulus spectral power values to EP features. Five of the 7 subjects displayed consistent increases in N1-P2 amplitude as a function of increasing pre-stimulus relative alpha power. The between-subjects effect of pre-stimulus EEG on N1 latency was small, but was moderate for P2 latency (both significant). Both N1 and P2 latency were found to decrease with increasing amounts of pre-stimulus relative delta and theta power.     

Age-related changes in event-related potentials in visual discrimination tasks

Visual event-related potentials and reaction times in physical and semantic discrimination tasks were studied in 29 normal subjects between the ages of 21 and 74 years. The NA, N2 and P3 components of the evoked potential, and simple and GO/NOGO reaction times were observed in both kinds of discrimination. Significant age-related slowing of the GO/NOGO reaction time was observed only in the semantic discrimination task. The N2 and P3 latencies elicited by both the physical and semantic stimuli were significantly and positively correlated with age, although there was no significant correlation between the NA latency and age. The interpeak latency between N2 and P3 showed no age-related changes. The decline of cognitive information processing with advancing age was evident from the classification of a perceived event as reflected by the N2 component.     

Auditory event-related potentials in well-characterized groups of children

Sixty-eight subjects ranging in age from 6 to 23 years were studied in an ‘auditory oddball’ event-related potential (ERP) paradigm. Our results replicate other studies, finding P3 as the most consistent component of ERPs since childhood, although great variability of this component was found in the 6-year-old group. Separate age/ERP component latency and amplitude linear regressions were computed for subjects 6–14 and 6–23 years old. Our data show in both groups a significant negative and positive correlation between age and P3 latency and N1-P2 amplitude respectively. The age/P3 latency slope for the subjects under 15 years old was −19.00 msec/year versus 8.15 msec/year for all subjects (6–23 years old). Our results indicate that P3 latency during childhood decreases with age, reaching an asymptote after or during the second decade of life. No curvilinear relationship between age and P3 latency was found over the child groups, although a significant curvilinear relationship was found over the entire age range.This study showed no significant gender differences in latency at any age group. However, in the adult group females showed significantly larger amplitudes than males.     

Somatosensory evoked potentials: Correlations with height

Somatosensory evoked potentials (SEPs) to median and posterior tibial nerve stimulation were studied in 160 subjects aged 20–90 years. Height was highly correlated with latencies of spinal and cortical SEPs (N13, N20, N22, and P40). Although tibial central conduction (N22-P40) was also highly correlated with height, median conduction (N13–N22) was not correlated with the latter.Multiple correlation and regression analysis showed that except for the median N13–N20 latency, height provided the best prediction of the remaining SEP latencies. Age alone was not correlated with SEP latencies, but its significance was observed when age and height were considered together as the predictors. Effects of age and height on SEP latencies were independent of gender.The present data indicate that except for the N13–N20 conduction, height is the most important parameter for SEP latencies and can be used for construction of normograms.     

Topography of middle-latency somatosensory evoked potentials following painful laser stimuli and non-painful electrical stimuli

The aim of this study was to compare cerebral evoked potentials following selective activation of Aβ and Aδ fibers. In 15 healthy subjects, Aβ fibers were activated by electrical stimulation of the left radial nerve at the wrist. Aδ fibers were activated by short painful radian heat pulses, applied to the dorsum of the left hand by a CO₂ laser. Evoked potentials were recorded with 15–27 scalp electrodes, evenly distributed over both hemispheres (bandpass 0.5–200 Hz). The laser-evoked potentials exhibited a component with a mean peak latency of 176 msec (N170). Its scalp topography showed a parieto-temporal maximum contralateral to the stimulus side. In contrast, the subsequent vertex negativity (N240), which appeared about 60 msec later, had a symmetrical scalp distribution. Electrically evoked potentials showed a component at 110 msec (N110), that had a topography similar to the laser-evoked N170. The topographies of the N170 and N110 suggest that they may both be generated in the secondary somatosensory cortex. There was no component in the electrically evoked potential that had a comparable interpeak latency to the following vertex potential: for N60 it was longer, for N110 it was shorter. On the other hand, in the laser-evoked potentials no component could be identified the topography of which corresponded to the primary cortical component N20 following electrical stimulation.     

两种经皮穴位电刺激方法对脑卒中患者体感诱发电位影响的比较

摘要目的：比较经皮穴位电刺激（TAES）患侧上肢及双上肢两种不同方法对脑卒中患者体感诱发电位（SEP）的影响。方法：24名脑卒中患者根据TAES治疗的部位分为2组,刺激患侧上肢组（12名）和同时刺激双上肢组（12名）。两组对象分别接受一次30min的TAES治疗,刺激参数为频率4Hz,脉宽250μs,强度为患者最大耐受量。分析5R．上肢SEPN9,N20的波幅和潜伏期,比较两组患侧上肢电刺激前后SEP值的变化。结果：两种方法都能使患侧上肢SEPN9和N20的波幅明显增高而潜伏期明显缩短。虽然治疗后两组间SEP各参数比较差异无显著性,但两组间各参数变化率的比较差异有显著性（P〈0．05）。结论：单上肢或双上肢TAES治疗能改善脑卒中患者偏瘫肢体的SEP值,但双上肢组对SEP值的改变更明显。     

Reliability and upper normal variability limits of pattern reversal visual evoked potential parameters.

Twenty healthy volunteers aged 21-48 years (10 males, 10 females) were submitted to pattern reversal visual evoked potentials with 15' and 30' checks. The recordings were repeated after 7 days to assess reliability and upper normal variability limits of the following parameters: latencies of N70, P100, N140 and peak-to peak amplitudes of N70-P100, P100-N140. Reliability was tested with intraclass correlation coefficient, which was excellent or good for all parameters. Test-retest variability limits were computed with = 0.01 for absolute latency differences and relative amplitude differences.     

Single-trial latency variability does not contribute to fast habituation of the long-latency averaged auditory evoked potential in the albino rat

Fas habituation (FH) is defined as a general reduction in long-latency, vertex-recorded, averaged auditory evoked potential (AEP) amplitude that occurs in response to the second of a pair of acoustic stimuli. Our laboratory has been studying FH in a variety of human populations with different paradigms and has interpreted it to be a measure of neural attentional mechanism(s) and/or resource allocation related to the processing of cognitive information. We have also reported an analogous phenomenon in the rat. In the present investigation, we examined the relationship between FH (viz., averaged AEP component amplitude decrement) and the single-trial latency variability of the AEP peaks comprising that component. Specifically, AEPs were obtained to 60 paired-tone stimuli from unanesthetized and restrained albino rats previously implanted with chronic skull electrodes. Using a template-matching algorithm similar to that used by Michalewski et al. (Electroenceph. clin. Neurophysiol., 1986, 65:59–71), the latency variability for each animal was computed for the N1 and P2 peaks of the single-trial AEPs that were used to compose the averaged wave form. Findings indicated that (a) there was no difference in single-trial latency variability for these peaks either within or across tones, and (b) there was no relationship between single-trial latency variability for either the N1 or the P2 peaks and the overall peak-to-peak amplitude (N1-P2) of the averaged wave form in response to the second tone. Thus, FH of the N1-P2 (i.e. Peak 2) amplitude in the rat is not due to an increase in latency variability across tones.