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.     

The effects of stimulus rates upon median,ulnar and radial nerve somatosensory evoked potentials

We examined the effect of stimulus rates on the somatosensory evoked potential (SEP) amplitude following stimulation of the median nerve (MN) and the ulnar nerve (UN) at the elbow or wrist, and the radial nerve (RN) at the wrist in 12 normal subjects. We measured the amplitude of frontal (P14-N18-P22-N30) and parietal peaks (P14-N20-P26-N34) at a stimulus rate of 1.1, 3.5 and 5.7 Hz. The amplitude attenuation was found at frontal P22 and N30 and to a lesser degree at parietal N20 and P26 peaks with an increasing stimulus rate from 1.1 to 5.7 Hz. The amplitude attenuation was greatest at the elbow when compared to the wrist stimulation for both MN and UN. The attenuation was least for wrist stimulation for the RN. The UN block by local anesthesia just distal to the stimulus electrode at the elbow abolished the amplitude attenuation caused by the fast stimulus rate. The observed amplitude attenuation with the faster stimulus rate is probably due, in part, to interference from the “secondary” afferent inputs. The secondary afferent inputs arise from peripheral receptor stimulation (muscle, joint and/or cutaneous) as a subsequent effect of efferent volleys initiated from the point of stimulation. The greater number of peripheral receptors being activated as more proximal sites of stimulation in a mixed nerve would result in greater attenuation of the SEP recorded from scalp electrodes. We postulate that the attenuation of frontal peaks by the fast stimulus rate is due to the frontal projection of interfering “secondary” afferent inputs.     

Effect of sleep stage on somatosensory evoked potentials by median nerve stimulation

The effects of sleep stage on early cortical somatosensory evoked potentials (SEPs) and short-latency components elicited by median nerve stimulation were studied in 12 normal volunteers. The latency of P13 in the awake stage was not significantly different from that in any sleep stage. The latencies of N16, N20 and P20 were significantly prolonged while the amplitude of N20 was decreased during the non-rapid eye movement (NREM) sleep stage. P22, P23 and N24 components showed double peaks (P23a, P23b, N24a, N24b) during the NREM sleep stage in 6 subjects, while N24 showed a single peak and only P22 and P23 showed double peaks in 5 other subjects. The latencies and morphologies of SEPs during rapid eye movement sleep stage were almost the same as those during the awake stage. These findings suggest that NREM sleep affects the latency, amplitude and morphology of N16 and early cortical components.     

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.     

Age-dependent changes of short-latency somatosensory evoked potentials in healthy adults

Age-dependent changes of short-latency somatosensory evoked potentials following median nerve stimulation in humans were investigated in two groups of healthy adults aged 20-30 and 50-60 years. Normative values for both age groups are given. Compared to the younger group, in the older one P27 latency and N20-P27 interpeak latency were about 2 ms longer, and P27-N35 and P27-P45 interpeak latencies were significantly decreased. These findings suggest that N20 and P27 are generated by different structures and that the subsequent components do not depend on P27.     

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.     

Rapid-Rate Paired Associative Stimulation over the Primary Somatosensory Cortex

Rapid-rate paired associative stimulation (rPAS) involves repeat pairing of peripheral nerve stimulation and Transcranial magnetic stimulation (TMS) pulses at a 5 Hz frequency. RPAS over primary motor cortex (M1) operates with spike-timing dependent plasticity such that increases in corticospinal excitability occur when the nerve and TMS pulse temporally coincide in cortex. The present study investigates the effects of rPAS over primary somatosensory cortex (SI) which has not been performed to date. In a series of experiments, rPAS was delivered over SI and M1 at varying timing intervals between the nerve and TMS pulse based on the latency of the N20 somatosensory evoked potential (SEP) component within each participant (intervals for SI-rPAS: N20, N20-2.5 ms, N20 + 2.5 ms, intervals for M1-rPAS: N20, N20+5 ms). Changes in SI physiology were measured via SEPs (N20, P25, N20-P25) and SEP paired-pulse inhibition, and changes in M1 physiology were measured with motor evoked potentials and short-latency afferent inhibition. Measures were obtained before rPAS and at 5, 25 and 45 minutes following stimulation. Results indicate that paired-pulse inhibition and short-latency afferent inhibition were reduced only when the SI-rPAS nerve-TMS timing interval was set to N20-2.5 ms. SI-rPAS over SI also led to remote effects on motor physiology over a wider range of nerve-TMS intervals (N20-2.5 ms – N20+2.5 ms) during which motor evoked potentials were increased. M1-rPAS increased motor evoked potentials and reduced short-latency afferent inhibition as previously reported. These data provide evidence that, similar to M1, rPAS over SI is spike-timing dependent and is capable of exerting changes in SI and M1 physiology.     

Detailed analysis of the latencies of median nerve somatosensory evoked potential components, 1: selection of the best standard parameters and the establishment of normal values

In order to objectively select the standard parameters best suited for the evaluation of somatosensory conduction in median nerve somatosensory evoked potentials (SEP), we performed a detailed statistical analysis of intersubject variability for the latencies of SEP components based on the recordings of 62 normal subjects. Multiple regression analyses for height, age, (age - 20)² and sex were performed for the latencies of 13 components and 78 intercomponent intervals, and the residual variance was used as an indicator of the stability of each parameter. As a result, N9 onset in EPi-NC lead, N11′ onset in C6S-Fz lead, P13/14 onset in scalp-NC leads, for which N13′ onset recorded in C6S-Fz lead may substitute, and N20 onset in CPc-Fz lead were the most stable time-points selected as standards. N11 onset in C6S-NC, which other authors have recommended as the standard point representing spinal entry, was not recorded consistently, and P11 onset in scalp-NC leads was also unstable. N20 and peak and N13′-N20 interval (equivalent to conventional central conduction time) were extremely unstable. We presented the nomograms to find normal limits of the standard parameters corresponding to the given values of the predictor variables (height, age or sex). As the standard recording montage in routine clinical examinations, we recommended a simple method using Fz reference, for example (1) EPi-Fz, (2) C6S-Fz, (3) CPc-Fz, because this montage is sufficient to measure the stable standard parameters.     

正常小儿胫神经诱发短潜伏时头皮体感区电位及脑瘫对该电位的影响

本研究观察了20例正常小儿和49例脑瘫小儿的下肢胫后神经刺激性短潜伏时头皮体感诱发电位(PTN-SSEP)。正常小儿在刺激后出现6个反应波(P18、N23、P31、N42、P54和N68),大脑左右两体感头皮的SSEP波形相似;时相基本相等,t检验表明两侧间无差异;电压除波P31外其余波也无显著差异。脑瘫小儿PTN-SSEP异常率达91.84％,有4种类型:正常型占8.16％、混合异常型57.14％、反应低下型6.12％及电压不对称型28.57％。经统计患儿左右头皮的SSEP、潜伏时和电压均有显著差异(P<0.05),其中P31和N42电压差值>50％。与正常小儿比较,患儿双侧反应降低,多数波潜伏时延长。患侧电压损失率>50％(P<0.001),波P18、N23和P31的潜伏时差异显著。结果提示.(1)正常小儿体感通路反应稳定,左右侧活动基本对称;(2)脑瘫小儿体感通路左右侧活动不对称,患侧传导机能下降,体感皮层反应减退。     

Changes in amplitude and temporal characteristics of evoked potentials in the sensomotor cortex after division of the spinocervical tracts in cats

Temporal and amplitude characteristics of evoked potentials of the sensomotor cortex in waking cats were studied during variation in the intensity of electrodermal stimulation. The results obtained in experiments on intact animals and on the same animals for several months after division of the spinocervical tracts at the cervical level were compared. After blocking of the inflow of afferent impulses along these tracts of the spinal cord, statistically significant changes in evoked potentials were observed, mainly in response to medium and strong stimulation. These changes were more clear in the motor and second somatosensory areas of the cortex. A decrease in sensitivity to pain also was found. During recovery of the motor functions, cutaneous sensation remained impaired and the amplitude characteristics of the evoked somatosensory activity were not restored. The results suggest that thinner fibers predominate among the primary afferent fibers of the spinocervical tract, and their projections are more widely represented in the second somatosensory and motor areas of the cortex.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 516–523, September–October, 1972.     

Glossopharyngeal evoked potentials in normal subjects following mechanical stimulation of the anterior faucial pillar

The anterior faucial pillar, which is innervated by the glossopharyngeal nerve, is thought to be important in eliciting the pharyngeal swallow in awake humans. Glossopharyngeal evoked potentials (GPEP), elicited by mechanically stimulating this structure, were recorded from 30 normal adults using standard averaging techniques and a recording montage of 16 scalp electrodes. Ten of the subjects experienced a desire to swallow in response to stimulation. Repeatable responses were recorded from all 30 subjects. The GPEPs recorded from the posterior scalp were W-shaped and consisted of P1, N1, P2, N2 and P3 peaks. Mean latencies of P1, N1 and P2 were 11, 16 and 22 msec, respectively, for both left and right pillar stimulation. In contrast, latencies of N2 and P3 varied significantly between left and right pillar stimulation. Mean latencies of N2 and P3 were 27 and 34 msec for left, and 29 and 35 msec for right pillar stimulation. Topographical maps acquired at peak latencies for P1, N1 and P2 revealed consistent asymmetrical voltage distributions between the two hemispheres; the largest responses were recorded from the hemisphere ipsilateral to the side of stimulation. The scalp topography of N2 and P3 varied between male and female subjects as well as between left and right pillar stimulation. These findings support the hypothesis that mechanical stimulation to the anterior faucial pillar alone can elicit repeatable responses from the central nervous system. The integration of this subcortical/cortical activity with that of the medullary swallowing center may play an important role in eliciting the pharyngeal swallow.     

Parameters of somatosensory evoked potentials in normal subjects in relation to age and height

Cortical SEPs by stimulation of median nerve at wrist (159 measurements; 144 subjects, 63 M - 81 F; mean age 39.7, range 11-70; mean height 162.5, range 134-190) and cortical SEPs by stimulation of posterior tibial nerve at ankle (100 measurements; 81 subjects, 37 M - 44 F; mean age 34.7, range 11-60; mean height 161.1, range 134-180 cm) have been performed. The latencies of N1 of median SEPs and of N1 and P1 of tibial SEPs significantly increase with the height of subjects. The statistical evaluation of latency values of each subject normalized at a height of 165 cm show a little increase of latency according to the age of the subjects; this increase is quite evident for the latency of P1 of tibial SEP.     

The development of the somatosensory evoked potential in the unanaesthetized fetal sheep

Somatosensory evoked potentials were recorded in utero from 13 chronically instrumented fetal lambs (97 to 148 days of gestation) following electrical stimulation of the upper lip or upper limb. Several clear and reproducible peaks were observed. Following upper lip stimulation, peaks were seen with mean peak latencies of 9, 13.2, 17.8, 21.3, 33.8 and 206 ms at a gestational age of 125 days. Similar peaks, but of slightly later mean latencies, were seen following limb stimulation. These peaks demonstrated significant gestational age related falls in peak latencies (P less than 0.05). Several of the mid to late latency peaks, notably those occurring at 21.3, 33.8 and 206 ms, demonstrated changes (P less than 0.05) in both latency (longer in low voltage) and amplitude (reduced in low voltage) dependent on electrocorticographic state. Rate of stimulus presentation also had a significant effect on both amplitude and latency of several peaks (P less than 0.05) with this effect lessening with advancing gestational age. Evoked potentials can thus be successfully obtained from chronically instrumented fetal lambs and provide a useful indice for studies of neural maturation.     

Functional deficits of central sensory and motor pathways in patients with cervical spinal stenosis: a study of SEPs and EMG responses to non-invasive brain stimulation

The central conduction time of the descending and ascending fibers of the spinal cord were examined in patients with radiologically defined cervical spinal stenosis (antero-posterior diameter of the spinal canal less than 13 mm). Nineteen patients were examined, only 4 of whom showed clinical signs of spastic weakness or ataxia. The electromyographic response after non-invasive stimulation of the leg area of the motor cortex was delayed in13 of the 15 clinically unaffected patients. The central latency (N21-P39) of the somatosensory evoked response after stimulation of the tibial nerve (tibialis SEP) was increased in 12 of the 15 individuals. The 4 patients with clinical signs showed abnormal latencies with both methods.The use of both techniques for the examination of the function of the spinal cord revealed increased latencies in the central motor and/or sensory pathways in all patients. The technique of non-invasive stimulation of the corticospinal system therefore provides an additional tool to detect and quantity subclinical and clinically apparent lesions in patients with defined cervical spinal stenosis.     

Determination of conduction times of the peripheral and central parts of the sensory pathway using evoked somatosensory potentials

Determination of conduction times of the peripheral and central parts of the sensory pathway using evoked somatosensory potentials. Acta physiol. pol., 1985, 36 (3): 216-223. Simultaneous recording of the somatosensory evoked potentials (SEP) from Erb's point, neck and scalp allows investigation of the peripheral and central conduction times. The early components of the SEP produced by stimulation of the median nerve at the wrist were recorded using standardized electrode locations in 15 normal subjects. The difference of the latencies between the first peak of the cortical response (N20) and the peak of the neck response (N14) reflects, probably, the conduction time between the dorsal column nuclei and the cortex. Its value was 6 +/- 0.7 msec. The conduction time difference (between peak Erb's point response (N9) and N14) was 5.5 +/- 0.5 msec and it reflected the peripheral conduction time. For diagnostic application the lower limit of the response amplitudes was determined also for every component.     

Serial recording of sensory,corticomotor, and brainstem-derived motor evoked potentials in the rat

A method is presented for serial recording of corticomotor evoked potentials (CMEPs), brainstem-derived motor evoked potentials (BMEPs), and somatosensory evoked potentials (SEPs) via permanently implanted cranial screws. One screw was positioned posterior to lambda (posterior screw), and two screws were positioned over the cortical hind limb areas (cortical screws). SEPs were elicited by stimulation of the hind paw and recorded from the contralateral cortex. BMEPs were stimulated via the posterior screw and recorded from both hind limbs, whereas CMEPs were elicited by repeated bipolar stimulation of the cortex and recorded from the contralateral hind limb. BMEPs and CMEPs differed in several points and can be considered as completely separate motor evoked potentials. While BMEPs consisted of a prominent negative peak with short latency (5–7.5 ms), CMEPs were represented by polyphasic signals with long latencies (17–22 ms). The cortical origin of the CMEPs was confirmed by transecting the corticospinal tracts, which abolished the CMEPs but spared the BMEPs. SEPs consisted of three consecutive peaks with mean latencies of the initial peak ranging between 15 and 17 ms. Dorsal column transection also abolished SEPs. In healthy rats, all three signals were recorded for six consecutive weeks. Signal parameters did not change significantly within this observation period. Rats tolerated the screws and the repeated measurements very well and no negative affect on animal behavior was noted. Thus, this method allows serial recording of SEPs, CMEPs, and BMEPs in chronic rat models.     

Serial recording of sensory, corticomotor, and brainstem-derived motor evoked potentials in the rat

A method is presented for serial recording of corticomotor evoked potentials (CMEPs), brainstem-derived motor evoked potentials (BMEPs), and somatosensory evoked potentials (SEPs) via permanently implanted cranial screws. One screw was positioned posterior to lambda (posterior screw), and two screws were positioned over the cortical hind limb areas (cortical screws). SEPs were elicited by stimulation of the hind paw and recorded from the contralateral cortex. BMEPs were stimulated via the posterior screw and recorded from both hind limbs, whereas CMEPs were elicited by repeated bipolar stimulation of the cortex and recorded from the contralateral hind limb. BMEPs and CMEPs differed in several points and can be considered as completely separate motor evoked potentials. While BMEPs consisted of a prominent negative peak with short latency (5-7.5 ms), CMEPs were represented by polyphasic signals with long latencies (17-22 ms). The cortical origin of the CMEPs was confirmed by transecting the corticospinal tracts, which abolished the CMEPs but spared the BMEPs. SEPs consisted of three consecutive peaks with mean latencies of the initial peak ranging between 15 and 17 ms. Dorsal column transection also abolished SEPs. In healthy rats, all three signals were recorded for six consecutive weeks. Signal parameters did not change significantly within this observation period. Rats tolerated the screws and the repeated measurements very well and no negative affect on animal behavior was noted. Thus, this method allows serial recording of SEPs, CMEPs, and BMEPs in chronic rat models.     

Topography of somatosensory evoked potentials to median nerve stimulation in patients with cerebral lesions

Scalp distributions and topographies of early cortical somatosensory evoked potentials (SEPs) to median nerve stimulation were studied in 22 patients with 5 different types of cerebral lesion due to cerebrovascular disease or tumor (thalamic, postcentral subcortical, precentral subcortical, diffuse subcortical and parieto-occipital lesions) in order to investigate the origins of frontal (P20, N24) and central-parietal SEPs (N20, P22, P23).In 2 patients with thalamic syndrome, N16 was delayed in latency and N20/P20 were not recorded. No early SEP except for N16 was recorded in 2 patients with pure hemisensory loss due to postcentral subcortical lesion. In all 11 patients with pure hemiparesis or hemiplegia due to precentral subcortical lesion N20/P20 and P22, P23/N24 components were of normal peak latencies. The amplitude of N24 was significantly decreased in all 3 patients with complete hemiplegia. These findings support the hypothesis that N20/P20 are generated as a horizontal dipole in the central sulcus (3b), whereas P23/N24 are a reflection of multiple generators in pre- and post-rolandic fissures. P22 was very localized in the central area contralateral to the stimulation.Topographical studies of early cortical SEPs are useful for detecting each component in abnormal SEPs     

Interaction of influences from the auditory and somatosensory afferent systems on neurons of the primary auditory cortex

In experiments on anesthetized cats, 80 neurons of the primary auditory cortex (A1) were studied. Within the examined neuronal population, 66 cells (or 82.5%) were monosensory units, i.e., they responded only to acoustic stimulations (sound clicks and tones); 8 (10.1%) neurons responded to acoustic stimulation and electrocutaneous stimulation (ECS); the rest of the units (7.4%) were either trisensory (responded also to visual stimulation) or responded only to non-acoustic stimulations. In the A1 area, neurons responding to ECS with rather short latencies (15.6–17.0 msec) were found. ECS usually suppressed the impulse neuronal responses evoked by sound clicks. It is concluded that somatosensory afferent signals cause predominantly an inhibitory effect on transmission of an acoustic afferent volley to the auditory cortex at a subcortical level; however, rare cases of excitatory convergence of acoustic and somatosensory inputs toA1 neurons were observed.     

Visual event-related potentials evoked by using a virtual reality display

This study aimed at investigating whether a virtual reality display (VRD) is an appropriate tool for evoking visual event-related potentials (VEPs). VEPs evoked by VRD stimuli were highly similar in form to VEPs evoked by using a computer monitor, both having two dominant peaks, labeled P100 and N200. Monitor and VRD N200 latencies and amplitudes were highly correlated. However, peak latencies were longer and the peaks were broader when stimuli were presented on the VRD. Besides, VRD P100 amplitude was smaller, and an N75 peak could be seen usually only on monitor VEPs.