Sex Differences in the Human Group Mean SEP*

Abstract: With 200 SEPs of normal human subjects, the sex differences in the waveform of the Group Mean SEP were established eliminating those attributable to the peripheral factors, the statures and the nutritional conditions represented by Rohrer's index. The differences in baseline amplitude of the Group Mean SEP between sexes, in the sections between 25–110 msec and behind 400 msec in latency, were verified removing those between the tallers and the shorters and those between with high and with low values of Rohrer's index, not attributable to these peripheral factors and might be the central origin. The differences in the Scaled Group Mean SEP were also verified similarly, being more a significant indication of the sex difference itself than those in the Group Mean SEP.     

Differences in Human Group Mean SEP Between Sexes: With Reference to Statures*

Abstract: With 200 SEPs of normal human subjects, the differences in the Group Mean SEP between sexes were denned, removing those attributable to the peripheral factor, the statures.
The differences in baseline amplitude in the sections roughly 1) between 29–110 msec, where there were the most remarkable differences in the waveform of the Group Mean SEP, between P₂ and N₆, with a high convex arch peaking at P₄ (80 msec) for females but not for males, 2) around 320 msec, and 3) behind 400 msec in latency, were verified, not attributable to the different statures, and might be the central origin.
With Scaled SEPs, which were converted from SEPs by the Amplitude Scaling, results similar to those with the unsealed SEPs were obtained.     

The Group Mean SEP of Normal Human Subjects

Abstract: The following conclusions were deduced from the SEPs of 100 normal human subjects, whose mean age was 21.80 ± 1.62. It was confirmed that the waveform of a Group Mean SEP and of a Group SD each converges to a waveform different from a flat horizontal line. The waveform of the Group Mean SEP consisted of 12 components, and was roughly tetraphasic within 500 msec in latency. Large discrepancies were found in the later components between the Group Mean SEP and the Group Schematic SEPs reported by others, although some coincidences were shown in the early components within 100 msec in latency.
The results derived from the Scaled SEPs, which were converted from the (unscaled) SEPs, indicated the possibility of a reduction of the data by the Amplitude Scaling.     

The Waveforms of the Group Mean SEP of Each Sex*

Abstract: With SEPs recorded from age-matched normal human subjects, 100 males and 100 females, 22.34 ± 1.69 years, it was confirmed that the Group Mean SEP of each sex each converges to a given waveform which significantly differed from each other. The waveform of the Group Mean SEP for females consisted of the 12 components, and was approximately tetraphasic within 500 msec in latency, while that for males consisted of the same components except for N₄ and P₄. There was a high convex arch with P₄ (82 msec) between P₂ and N₆ for females, but a low hollow slope without the peak for males. With Scaled SEPs, which were converted from SEPs by Amplitude Scaling, the results similar to those with SEPs were obtained.     

Central and peripheral conduction times in multiple sclerosis

Somatosensory evoked potentials (SEPs) were recorded simultaneously from the cervical spine and scalp in 25 normal subjects and 105 patients with established or suspected multiple sclerosis (MS) using median nerve stimulation. The normal latency of the main peak of the cervical SEP (N14) following median nerve stimulation at the wrist was 13.7 +/- 0.8 msec. The peak latency of the first cortical event of the scalp SEP (N20) was 19.1 +/- 0.9 msec. The difference in these latencies (N20 -- N14) reflects a conduction time between the dorsal column nuclei and cortex. It measured 5.45 +/- 0.7 msec. The conduction times between the wrist and Erb's point and Erb's point and N14 measured 8.6 +/- 0.7 msec and 5.1 +/- 0.6 msec respectively. There was a 68.6% overall incidence of abnormalities of N14, N20 or (N20 -- N14) in the patients. This incidence was over 80% in definite and early probable or latent MS, 68.2% in progressive spinal MS and 40.0% in suspects. SEPs were also simultaneously recorded from the lower thoracic spine (T12) and scalp in a different group of 25 normal subjects using tibial nerve stimulation. The latency of the thoracic SEP (N21) was 21.4 +/- 1.5 msec and that of the first cortical event of the scalp SEP (P40) was 38.6 +/- 2.2 msec. The difference in these latencies (P40 -- N21) which reflects conduction between T12 and the cortex measured 17.2 +/- 1.7 msec. Conduction between the ankle and popliteal fossa was 7.0 +/- 0.65 msec and between the popliteal fossa and N21, it was 14.5 +/- 1.1 msec. All of a small group of MS suspects showed abnormality of P40 or (P40 -- N21).     

Sex differences in the human group mean SEP

The following results were obtained with SEPs recorded from strictly age-matched normal human subjects, 100 males and 100 females, 22.29 +/- 1.90 years. (1) The sex factor on the wave form of SEP was confirmed highly significant by MANOVA. (2) It was confirmed that the group mean SEP of each sex each converges to a given wave form which significantly differed from each other. (3) The differences in the wave form of the group mean SEP between sexes were established. The group mean SEP for females consisted of the 12 components, N1, P1, N2, P2, N3, P3, N4, P4, N5, P5, N6 and P6, and was approximately tetraphasic within 500 msec in latency, while that for males consisted of the same components except for N4 and P4. The baseline amplitude of the wave form of the group mean SEP, smaller in males than in females, differed significantly between sexes, corresponding to the most remarkable difference in its wave form, in the descending slope from the highest positive peak P2 to the deep negative trough N6, where there was a high convex arch with P4 (80 msec) in females, a low hollow slope without the peak in males. The latencies of the components tended to be longer in males than in females. (4) With scaled SEPs, which were converted from SEPs by amplitude scaling, results were similar to those with SEPs, and the sex difference in the scaled group mean SEP was also verified to be significant. These results indicate the further possibility of data reduction by amplitude scaling.     

Latency and amplitude variability in serial median nerve SEP recordings.

OBJECTIVES: Intra-individual variability of SEP parameters was investigated by serial SEP recordings. METHODS: Median nerve SEP of 53 normal subjects (mean age 25.5+/-2.7 years) were evaluated. Recordings were repeated 1 week, 2 weeks, and 6 months after the initial recording. RESULTS: Mean values of latencies from right median nerve stimulation were slightly longer (+0.1 ms) as compared to the left. The intra-individual (within stimulation side) variance did not depend on the time interval between recordings. The total within-stimulation-side variance of latencies was 0.056 ms2 for N20 (C3/4' vs. Fz), 0.070 ms2 for N13 (C7 vs. Fz), 0.048 ms2 for N10 (Erb's point vs. Fz), 0.111 ms2 for P9 (C3/4' vs. contralateral forearm), and 0.148 ms2 for P14 (C3/4' vs. contralateral forearm), and was about 3 times smaller than between-side variability with regard to cortical or spinal potentials. Upper limits for latency differences and lower limits for amplitude ratios in repeated recordings, as well as upper and lower limits for between-side latency differences and amplitude ratios were calculated, using F distributions with worst-case assumptions for degrees of freedom and error probability P = 0.05. Upper limits of within-stimulation-side latency differences were 0.55 ms for N20, 0.62 ms for N13, 0.51 ms for N10, 0.78 ms for P9, and 0.90 ms for P14, and corresponding lower limits of amplitude ratios were 0.69, 0.62, 0.66, 0.45, and 0.50, respectively. CONCLUSIONS: Our results demonstrate a small systematic, and a larger random difference between right and left side stimulation, one arising from the peripheral, and the other one from the central pathway proximal to the source of N10.     

Latency differences of N20, P40/N60, P100/N140 SEP components after stimulation of proximal and distal sites of the median nerve.

The latencies of SEP N20, P40, N60, P100, and N140 components were measured after stimulation of two different sites, and the differences in relation to conduction velocity and their central functions are discussed. Subjects were 8 healthy right-handed males (age 22-31 years, height 164-184 cm). An electrical pulse of 200micro sec duration with an intensity of 2 times the motor threshold was delivered to the wrist and to the elbow alternately at a random rate of 0.1 to 0.3 Hz. Recording electrodes were Cz', C3', and C4' referenced to linked ears. Analysis time was 50 msec before and 450 msec after the stimulus. The band pass was 0.5 Hz to 2 kHz. Subjects were asked to mentally count the number of stimuli. The averaging was interrupted after every 16 to 24 stimuli and checked to determine whether the subject was attentive to the stimuli by verifying the number of stimuli counted. A total of 100 responses each from elbow and wrist stimuli were averaged. Differences in peak latency between elbow and wrist stimuli for N20, P40, N60, P100, and N140 were 3.7 +/- 0.7 msec, 5.0 +/- 1.8, 4.3 +/- 1.2, 8.1 +/- 6.3, and 7.4 +/- 2.6 msec, respectively. According to the latency differences, SEP components can be divided into 3 groups: the shortest difference for N20, medium difference for P40 and N60 and longest difference for P100 and N140. Similar latency differences and similar potential distribution for P40 and N60, and for P100 and N140, and their differences from N20 confirmed that each of N20, P40/N60, and P100/N140 has a different function centrally. In addition, central processing time was longer with the more distal site stimulation.     

Pattern electroretinography and visual evoked potentials in optic nerve diseases.

BACKGROUND: To evaluate transient pattern electroretinography (PERG) and pattern visual evoked potential (VEP) for the diagnosis, differential diagnosis and follow-up of optic nerve diseases. METHODS: Twenty-nine consecutive patients (14 female, 15 male) with the diagnosis of ischaemic optic neuropathy (n=14) and optic neuritis (n=15) were included in this study. Mean age of the patients with ischaemic optic neuropathy was 63.3+/-3.3 (60-78) years and the mean age of the patients with optic neuritis was 28.3+/-8.4 (19-43) years. In each patient ophthalmological examination and systemic evaluation were done and VEP and PERG were recorded. As a control group, VEP recordings of 35 healthy subjects were included. RESULTS: In the ischaemic optic neuropathy group (group 1), mean VEP amplitude (+/-SD) (1.96+/-0.95 microV) was found to be decreased significantly in the affected eyes in comparison to the control group and the unaffected eyes. The delay in latency (116.3+/-20.14 msec in the affected eyes compared with 101.31+/-6.19 msec in unaffected eyes) was statistically significant when compared with the healthy subjects. In the optic neuritis group (group 2), VEP amplitude was decreased (4.13+/-4.04 microV vs 6.97+/-3.35 microV and 6.97+/-4.43 microV) and latency was increased (122.59+/-20.09 msec vs 101.31+/-6.19 msec and 108.76+/-13.57 msec) in affected eyes significantly in comparison to the unaffected eyes and control group, respectively. Even though there were no significant differences for P50 latency and N95/P50 ratios between affected and unaffected eyes in both groups, N95 amplitude decreased significantly in the affected eyes of the ischaemic optic neuropathy patients and N95 latency was found to be decreased in optic neuritis patients. There was no correlation between VEP and PERG findings in both groups. CONCLUSION: VEP amplitude decreased significantly in ischaemic optic neuropathies while latency delay was more significant in patients with optic neuritis. PERG findings showed decreased N95 amplitude in ischemic optic neuropathy without associated latency changes.     

Sensory group Ia proximal conduction velocity

The fastest median and ulnar velocities derived by recording motor and mixed nerve action potentials, F waves, H-reflexes, and somatosensory evoked potentials (SEPs) were compared. H-reflex recording was facilitated by employing selective group Ia excitation during voluntary muscular contraction. Mixed nerve, SEP, and H velocities, considered to predominantly reflect group Ia conduction, measured 63.2 +/- 3.2 m/sec, 63.4 +/- 4.5 m/sec, and 67.2 +/- 4.3 m/sec, respectively, between the wrist and elbow. Conventional motor conduction velocity was significantly slower (58.3 +/- 5.1 msec), but F velocity, which although nonuniform is also a measure of motor conduction, was 68.4 m/sec. Mean F latency was considered more reliable and representative than minimum F latency. F and H velocities accelerated proximally by 4.5 m/sec. They complement each other when evaluating motor and sensory group Ia conduction. The H-reflex and SEP use identical stimulus characteristics and when simultaneously recorded allow direct comparison of the fastest conducting peripheral and central sensory pathways.     

Extended latency of the cortical component of the somatosensory-evoked potential accompanying moderate increases in cerebral blood flow during systemic hypoxia in cats

In 24 adult cats, the somatosensory-evoked potential (SEP) and cerebral blood flow (CBF) were measured under paralyzed, anesthetized conditions during exposure to two different ventilatory regimens. Group I cats (ventilated from 20 to 2% oxygen) responded with a significant increase in white matter blood flow from 25.0 +/- 7.8 to 43.8 +/- 10.5 ml/100 g/min recorded at 7% O2. Gray matter blood flows in these animals increased but not to significant levels above the control blood flow measured at 20%. No significant changes in blood flow were observed in group II animals ventilated over the range of 25-3% oxygen as gray matter rose slightly (but not significantly) with hypoxia and white matter flows remained at levels of 25-30 ml/100 g/min. The latency of the cortical component of the SEP was related to the degree of hypoxia. For both groups, significant extensions in the latency to the occurrence of the cortical component of the SEP (normalized to the % of control SEP) occurred in each case (P less than 0.05). An inverse, linear relationship existed between the latency to the appearance of cortical component (ms) and the percentage oxygen concentration of the ventilatory mixture. No significant changes in thalamocortical conduction times were found, which indicates that hypoxia may have generalized effects on the synaptic pathways supporting the conduction of the SEP. The variation in blood flow and the latency of the cortical component observed between groups I and II may reflect the oxygen concentration used at the beginning of the experiment (25 vs 20%) and the gradations between them vs 3 and 2%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Somatosensory evoked potentials in Huntington's disease

Scalp recorded somatosensory evoked potentials (SEPs) elicited by left and right median nerve stimulation were obtained in 21 patients with Huntington's disease (HD), 14 individuals at risk (AR) for HD, and 21 non-patient controls matched for age and sex. Although SEP abnormalities were not uniform in the HD group, no HD patient had SEPs that conformed fully to the normal configuration with respect to peak latencies, presence of all components and spatial distribution. The most common abnormality was non-specific in nature, consisting of amplitude reduction or virtual abscence of components after 100 msec. More specific deviations were noted in the early SEP events. In half of the HD patients, peak P30 seemed to occur at approximately 45 msec poststimulus; this peak could have been taken as the normal P45 had it not reversed in phase between the central and frontal leads. In these cases peak P45 prepared to be missing. Peak N20 latency values were longer in the HD group than in the non-patient controls, whereas the P15 latencies did not differ significantly. The conduction time between P15 and N20 was significantly longer in HD patients than the non-patient controls. SEPs of the majority of the ARs were similar to those of the non-patients controls in terms of overall configuration, although mean amplitudes were generally lower for ARs than non-patient controls and 4 ARs exhibited prolonged P15-N20 latency differences.     

Conduction time in central somatosensory pathways in man.

Simultaneous recording of the somatosensory evoked potential (SEP) from the neck and from the scalp allows investigation of conduction of somatosensory impulses within the central nervous system alone. The early components of the SEP produced by stimulation of the median nerve at the wrist were recorded from standardized electrode locations on the scalp and neck in 21 normal subjects. The peak latency of both the initial negative potential from the scalp, N20 (19.4 +/- 1.1 msec), and the major negative negative potential from the neck, N14 (13.8 +/- 0.9 MSEC), CORRElated positively with arm length and with height. The difference between the peak latencies of N20 and N14 (5.6 +/- 0.5 msec) was independent of both arm length and height. As the latency and distribution of N14 indicate that this potential probably arises from the dorsal column nuclei, the N20--N14 latency difference provides a measure of conduction time within central pathways which is independent of conduction time in the limbs and spinal cord. Recording of the SEP from the neck, simultaneously with that from the scalp, also facilitates clinical investigation of the somatosensory system.     

Spatial distribution of somatosensory responses evoked by tapping the tongue and finger in man

Early components of the somatosensory potential (SEP) evoked by tactile stimulation of the tongue were recorded from the scalp in 7 normal subjects and compared with those resulting from taps on the middle finger. (1) Unipolar but not bipolar recording of SEP to tapping the tongue failed to differentiate the early components from large EEG deflections of myogenic origin. No such contamination was seen in either unipolar or bipolar recording of SEP following taps on the finger. (2) The early components evoked by tapping the tongue consisted of 4 main deflections; the first negative wave (N1) peaking at about 13 msec after the stimulus was followed by the first positive (P1), second negative (N2) and second positive (P2) wave peaking at about 23, 32 and 44 msec, respectively. Each wave had a shorter latency by several msec than the corresponding wave elicited by taps on the finger. (3) To demonstrate the spatial distribution of a SEP wave over the scalp, a method of amplitude transformation of bipolar records was developed. Topography of the transformed amplitudes of P1 wave, thus obtained while tapping the tongue differed from that obtained while tapping the finger; the former indicated bilateral distribution of the P1 with the maximal amplitude at contralateral (T3 or T5) and ipsilateral (T4 or T6) temporal loci, whereas, in the latter, the distribution was most prominent over the contralateral posterior quadrant with the maximum at parietal locus (C3). P1 wave in SEP thus appeared to represent excitation of the primary cortical neurons responding to tactile stimulation of the different body areas.     

Projections of the septum to the lateral hypothalamus

Evoked potentials recorded in the lateral hypothalamus (LH) of the rat to stimulation of the septum were observed to have response components of 3–6, 10–14, and 18–23 msec. These components were elicited from different regions of the septum; the 3–6 and 10–14 msec components from dorsal and midline regions corresponding to the projection field of the precommissural fornix from the hippocampus and the 18–23 msec component from a ventrolateral region corresponding to projections of the stria terminalis. Stimulation of the hippocampus and stria terminalis evoked responses in the LH of similar configuration but with latencies longer than the 10–14 and 18–23 msec components, respectively. Lesions in the dorsal midline and ventrolateral septum attenuated these responses suggesting that the precommissural fornix and stria terminalis are the pathways mediating the septal evoked components. These data provide a neuroanatomical framework for the dual role of the septum on response patterns elicited from the hypothalamus.     

Recovery functions of common peroneal, posterior tibial and sural nerve somatosensory evoked potentials.

We studied recovery functions of the somatosensory evoked potentials (SEPs) of common peroneal (CPN), posterior tibial (PTN) and sural nerves (SN) using a paired conditioning-test paradigm. The interstimulus interval (ISI) of paired stimuli ranged from 2 to 400 msec. In all SEPs with ISIs of 12-20 msec, the amplitude recovery was close to or beyond 100% of the control response, though their latencies and wave forms were not the same as the control. Further increases of the ISI resulted in significant depression of SEP (late phase suppression), most markedly in CPN, and less prominently in SN-SEP. With a longer than 50 msec ISI there was progressive recovery of SEP, but full recovery differed depending on the nerve stimulated; 400 msec ISI was required for CPN-, 250 msec for PTN- and 100 msec for SN-SEP. The peroneal nerve block by local anesthetic injected just distal to the stimulus electrodes abolished the late phase SEP suppression observed before the nerve block. These findings suggest that the late phase SEP suppression is attributable to the "secondary" afferents as a result of activation of peripheral receptors (muscle, joint and/or cutaneous) by the efferent volley initiated from the stimulus point. The greater and longer duration of peripheral receptor activation in CPN than in PTN or SN stimulation could explain the more pronounced and the longer duration of late phase suppression in CPN-SEP.     

The Effects of Low Spinal Injury on the Latencies of Cortical Evoked Responses from Forelimb Stimulation

A previous report showed that following spinal cord transection well below the C₇ level in cats, later components of the cortical somatic evoked potential (SEP) (40 msec or longer) produced in response to median or radial nerve stimulation were abnormal (Katz et al., 1977). Evidence presented here shows that early components of the radial nerve SEP are also altered following spinal cord transection. Latencies of both early and late components were increased as higher functional transections ofthe spinal cord were made. This monotonic increase in latency of the primary components supports the hypothesis that the results may be due to increasing loss of excitatory input. Correlation of latency change with level of injury may serve as a useful diagnostic tool.     

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.     

The value of somatosensory-evoked potentials and bulbocavernosus reflex in patients with impotence

In 14 normal male adults and 97 male patients having impotence alone or together with systematic and/or neuro-psychiatric symptoms and signs, the somatosensory cerebral-evoked potentials were obtained by glans penis stimulation (penile SEP); by peroneal nerve stimulation (peroneal SEP) and by electrically-induced bulbocavernous (BC) reflex. In normal subjects, the configurations of both SEPs were basically similar, except that the onset of latency was 10-15 msec longer and the amplitude in the P1-N1 component was higher in penile SEP. BC-reflex latency was abnormally prolonged, especially in diabetic impotence and in patients with cauda/conus lesions, while the abnormalities on the penile and peroneal SEP were more frequent in patients with spinal cord injuries. MS and parkinsonism. In impotent patients with epilepsy, chronic prostatis and psychogenic problems, all the tests were generally normal.     

Effect of voluntary self-paced movements upon auditory and somatosensory evoked potentials in man.

The effect of voluntary self-paced movements upon auditory (AEPs) and somatosensory (SEPs) evoked potentials has been investigated according to the temporal relationship between movement and delivery of test stimuli. EPs were recorded in 7 subjects and averaged in 10 successive epochs extending from 880 msec before to 2500 msec after movement. AEPs were attenuated in all epochs. The decrease was greatest in the 220 msec epoch just following movement and involved components N85 and P170. SEPs were attenuated similarly to AEPs when movements were performed by the hand contralateral to somatosensory stimulation. Of the 5 SEP components, only P40 failed to reflect the attenuation, while P95 showed the greatest amplitude decrease. When stimulation was ipsilateral, SEP amplitude was attenuated only when close to the movement. N65 and P95 decreased while N130 increased. In all subjects the results were consistent for treatments of AEP and SEP (with contralateral movements), whereas large inter-individual differences were observed for the SEP with ipsilateral movements.