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.     

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.     

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.     

Brainstem auditory evoked potentials in the fetal sheep, in utero

We studied brainstem auditory evoked potentials (BAEPs) in 8 fetal sheep in utero, ranging in gestational age from 105 to 142 days gestation (normal term 147 days). We could not elicit BAEPs prior to 117 days of gestation. After this age rapid maturation was seen, with three discernible peaks observed prior to 120 days and five peaks after 120 days. A significant (P less than 0.05) gestational age related fall in peak latencies and interpeak latencies was observed. The rate of stimulus presentation that could be tolerated without significant changes in wavepeak latency or amplitude also increased with advancing gestational age. In older fetuses (greater than 125 days), where a differentiated electrocorticogram (ECOG) was observed, differences were seen in latency and amplitude of several of the BAEP wavepeaks dependent upon the state. In high voltage ECOG states the amplitudes of wave IV and V were significantly (P less than 0.05) greater than in the low voltage ECOG state and the latencies of wave I, II and V were significantly (P less than 0.05) longer in low as compared to high voltage ECOG state. The BAEP, being obtainable over very short periods of time, appears to provide a useful indice of neural maturation for the sheep fetus in utero.     

Short latency trigeminal evoked potentials: normative data and clinical correlations

A very short latency trigeminal evoked potential (STEP) to electrical stimulation of the upper lip has been recorded from over the scalp. This potential consists of 5 distinct peaks within the 12 msec range.Normative data were obtained from 25 healthy volunteers. The impact of the stimulus rate and intensity on the response was studied in each subject.These results were compared to those of 19 patients suffering from lesions involving the trigeminal system in its peripheral aspect or the brain-stem. The STEP was consistently abnormal whenever the involved side was stimulated. Changes in peak latencies and in interpeak latency differences (IPLD) correlated well with clinical and radiological findings and improved with the removal of the offending lesion. The STEP proved to be a reliable method for evaluating the trigeminal system in its peripheral and central pathways; it may thus serve as an additional parameter for studying brain-stem functions.     

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.     

Respiratory-related cortical potentials evoked by inspiratory occlusion in humans

It has long been recognized that humans can perceive respiratory loads. There have been several studies on the detection and psychophysical quantification of mechanical load perception. This investigation was designed to record cortical sensory neurogenic activity related to inspiratory mechanical loading in humans. Inspiration was periodically occluded in human subjects while the electroencephalographic (EEG) activity in the somatosensory region of the cerebral cortex was recorded. The onset of inspiratory mouth pressure (Pm) was used to initiate signal averaging of the EEG signals. Cortical evoked potentials elicited by inspiratory occlusions were observed when C3 and C alpha were referenced to CZ. This evoked potential was not observed with the control (unoccluded) breaths. There was considerable subject variability in the peak latencies that was related to the differences in the inspiratory drive, as measured by occlusion pressure (P0.1). The results of this study demonstrate that neurogenic activity can be recorded in the somatosensory region of the cortex that is related to inspiratory occlusions. The peak latencies are longer than analogous somatosensory evoked potentials elicited by stimulation of the hand and foot. It is hypothesized that a portion of this latency difference is related to the time required for the subject to generate sufficient inspiratory force to activate the afferents mediating the cortical response.     

Whole-head mapping of middle-latency auditory evoked magnetic fields

We recorded middle-latency auditory evoked magnetic fields from 9 healthy subjects with a 122-channel whole-head SQUID gradiometer. The stimuli were click triplets, 2.5 msec in total duration, delivered alternately to the two ears once every 333 msec. Contralateral clicks elicited P30m responses in 16 and P50m responses in 12 out of 18 hemispheres studied; ipsilateral clicks did so in 7 and 13 hemispheres, respectively. The field patterns were satisfactorily explained by current dipoles in 16 and 4 hemispheres for contra- and ipsilateral P30m, and in 4 and 10 hemispheres for contra- and ipsilateral P50m. The peak latencies of P30m and P50m were not affected by stimulation side. The results show that middle-latency auditory evoked responses receive a strong contribution from auditory cortical structures, and that differences of input latency to cortical auditory areas, evaluated from MLAEF latencies, do not explain the latency differences seen in late auditory evoked fields to contralateral vs. ipsilateral stimulation.     

Dynamics of acoustical evoked potentials on a background of habituation to verbal stimulus in persons with different individual anxiety levels

Changes in the amplitude and the latencies of peak P300 of acoustical evoked potential on a background of the verbal stimulus novelty loss were used for determination of the brain activity specifity in individuals with various anxiety levels. The increase of the peak P300 latency of acoustical evoked potential on a background of trace processes arising after habituation was determined. This parameter did not depend on an anxiety level. However, the latency change depended on the attentional level to a submitted signal. The peak P300 amplitude in the right temporal cortex field was connected with the anxiety level--there was a growth of amplitude on a habituation background with the low anxious subjects, and with the highly anxious people the changes of this parameter were not observed. The anxiety level has rendered influence to dehabituation reaction. Dehabituation is observed with the low-anxiety subjects.     

From Genus to Phylum: Large-Subunit and Internal Transcribed Spacer rRNA Operon Regions Show Similar Classification Accuracies Influenced by Database Composition

We compared the classification accuracy of two sections of the fungal internal transcribed spacer (ITS) region, individually and combined, and the 5′ section (about 600 bp) of the large-subunit rRNA (LSU), using a naive Bayesian classifier and BLASTN. A hand-curated ITS-LSU training set of 1,091 sequences and a larger training set of 8,967 ITS region sequences were used. Of the factors evaluated, database composition and quality had the largest effect on classification accuracy, followed by fragment size and use of a bootstrap cutoff to improve classification confidence. The naive Bayesian classifier and BLASTN gave similar results at higher taxonomic levels, but the classifier was faster and more accurate at the genus level when a bootstrap cutoff was used. All of the ITS and LSU sections performed well (>97.7% accuracy) at higher taxonomic ranks from kingdom to family, and differences between them were small at the genus level (within 0.66 to 1.23%). When full-length sequence sections were used, the LSU outperformed the ITS1 and ITS2 fragments at the genus level, but the ITS1 and ITS2 showed higher accuracy when smaller fragment sizes of the same length and a 50% bootstrap cutoff were used. In a comparison using the larger ITS training set, ITS1 and ITS2 had very similar accuracy classification for fragments between 100 and 200 bp. Collectively, the results show that any of the ITS or LSU sections we tested provided comparable classification accuracy to the genus level and underscore the need for larger and more diverse classification training sets.     

A prospective 1 year follow-up study with somatosensory potentials evoked by stimulation of the posterior tibial nerve in patients with supratentorial cerebral infarction

Somatosensory potentials evoked by stimulation of the posterior tibial nerve (tibial nerve SEPs) were studied in 40 patients with supratentorial non-haemorrhagic cerebral infarction and in 25 control subjects. SEPs were recorded twice in 39 patients and thrice in 35 patients. The first examination was carried out 4–19 days after the onset of the symptoms, the second examination 56–100 days after the stroke, and the third examination 348–393 days after the stroke. Increased side-to-side differences in the P57 and N75 peak latencies and absence of the P40 peak were the most frequent abnormal findings. The latency abnormalities were associated with involvement of the subcortical white matter of the rolandic region. The absence of the P40 peak was, in contrast, closely related to the extension of the infarcted area into the cortical gray matter of during the acute stage, 51% of patients had abnormal SEPs in the second examination and 43% of patients in the third examination. A nearly significant decrease was observed in the number of latency abnormalities, but the number of amplitude abnormalities, including absent responses, did not change during the 1 year follow-up period.     

Effects of localized pontine lesions on auditory brain-stem evoked potentials and binaural processing in humans

Objectives and mehtods: Four sets of measurements were obtained from 11 patients (44–80 years old) with small, localized pontine lesions due to vascular disease: (1) Monaural auditory brain-stem evoked potentials (ABEPs; peaks I to VI); (2) Binaural ABEPs processed for their binaural interaction components (BICs) in the latency range of peaks IV to VI; (3) magnetic resonance imaging (MRI) of the brain-stem; and (4) psychoacoustics of interaural time disparity measures of binaural localization. ABEPs and BICs were analyzed for peak latencies and interpeak latency differences. Three-channel Lissajous' trajectories (3-CLTs) were derived for ABEPs and BICs and the latencies and orientations of the equivalent dipoles of ABEP and BICs were inferred from them.Results: Intercomponent latency measures of monaurally evoked ABEPs were abnormal in only 3 of the 11 patients. Consistent correlations between sites of lesion and neurophysiological abnormality were obtained in 9 of the 11 patients using 3-CLT measures of BICs. Six of the 11 patients had absence of one or more BIC components. Seven of the 11 had BICs orientation abnormality and 3 had latency abnormalities. Trapezoid body (TB) lesions (6 patients) were associated with an absent (two patients with ventral-caudal lesions) or abnormal (one patient with ventral-rostral lesions) dipole orientation of the first component (at the time of ABEPs IV), and sparing of this component with midline ventral TB lesions (two patients). A deviant orientation of the second BICs component (at the time of ABEPs V) was observed with ventral TB lesions. Psychoacoustic lateralization in these patients was biased toward the center. Rostral lateral lemniscus (LL) lesions (3 patients) were associated with absent (one patient) or abnormal (two patients) orientation of the third BICs component (at the time of ABEPs VI); and a side-biased lateralization with behavioral testing.Conclusions: These results indicate that: (1) the BICs component occurring at the time of ABEPs peak IV is dependent on ventral-caudal TB integrity; (2) the ventral TB contributes to the BICs component at the time of ABEPs peak V; and (3) the rostral LL is a contributing generator of the BICs component occurring at the time of ABEP peak VI.     

Computer techniques for the processing of evoked potentials

A computer technique is described for the systematic characterization of brain evoked potentials. Preprocessing of the data by a causal digital filter is followed by a peak search and identification procedure. A latency histogram of the peaks found is constructed to determine the ranges or clusters of peaks within the single evoked potential. Peaks found within the clusters are then corrected to the mean latency of the cluster and a latency corrected average version of the evoked potential constructed.     

Automatic and effortful processes in auditory memory reflected by event-related potentials. Age-related findings

Mismatch negativity (MMN) and N2b were elicited during a selective dichotic-listening task in 16 young (Y), 16 middle-aged (M) and 19 elderly (E) subjects to evaluate automatic and effortful memory comparison of auditory stimuli. Sequences of standard (80%) and deviant (20%) tones were dichotically presented to subjects in two runs. In each run, subjects were instructed to give a button-press response to the deviant (target) tones in the ear designated as attended and to ignore the input to the other ear.Peak latencies, peak amplitudes and mean amplitudes were calculated for MMN and N2b components in each subject. MMN latency and amplitude were quite stable regardless of age, while N2b latency was significantly longer in M and E subjects than in Y subjects. These results are interpreted as reflecting that automatic processes of comparison in auditory memory of stimuli presented at short interstimulus intervals remain quite stable from 23 to 77 years of age; however, those requiring attentional effort decline with age.     

Auditory event-related potentials in waking infants and adults: a developmental perspective

Auditory event-related potentials (AERPs) were recorded in waking 1 month olds, 3 month olds, 6 month olds and adults in order to study the morphology and development of the wave form in the waking subject. Previous data were generally obtained in sleeping or drowsy infants.The findings indicated that there were 3 quantitative changes in the AERP over the first 6 months of life in waking infants: an increase in the latency of peaks, an increase in peak amplitude, and a decrease in intersubject variability. Adult peak latencies were generally shorter than those for 3 month olds and 6 month olds. Further, latencies ofearlier AERP peaks for 1 and 6 month olds, in the present study, were comparable to those reported in previous investigations with sleeping infants. However, latencies oflater AERP peaks differed from those of previous reports and were closer to those reported for waking adults.With respect to the amplitude, the 6 month olds, in general, had the highest amplitudes, the 1 month olds the lowest, and the 3 month olds and adults fell in between the two groups. Some differences were present between early and late components.The findings of this study are significant in that the AERPs were quantitatively different from those reported in earlier work with sleeping or drowsy infants. If cognitive and perceptual development is to be studied, it is necessary to obtain data on waking subjects. The data presented in this report are consistent with behavioral studies of biobehavioral shifts that are associated with changes in responsivity of the organism to stimuli during the first 6 months of life.     

The interaction between sex and click polarity in brain-stem auditory potentials evoked from control subjects of Oriental and Caucasian origin

Brain-stem auditory evoked potentials (BAEPs) were performed on 30 male and 30 female young normal Oriental subjects, using both condensation and rarefaction stimulation. The effects of sex and click polarity on the BAEP latencies and amplitudes were studied. Females had shorter absolute and interpeak latencies and higher absolute amplitudes than the males. These sex-related BAEP differences were independent of the click polarity. Rarefaction clicks produced shorter wave I latency and longer I–III interpeak latency, but the differences were significant in the female only. The polarity-related BAEP amplitude differences were essentially independent of the sex. BAEPs performed on 60 sex- and age-matched young Caucasian subjects produced similar results. The importance of establishing control BAEP values according to the sex and click polarity is emphasised.     

Effects of timing of inspiratory occlusion on cerebral evoked potentials in humans

Previous studies from these laboratories have shown that airway occlusion applied from the onset of inspiration or during midinspiration is associated with cerebral evoked potentials in human subjects. The hypothesis tested in the present study was that the more abrupt decrease in mouth pressure produced by midinspiratory occlusion will be associated with evoked potentials that have shorter peak latencies and greater peak amplitudes than those produced by occlusions from the onset of inspiration. The second objective of the present study was to determine whether there is bilateral projection of inputs from the respiratory system to the somatosensory cortex. Random presentation of 64 midinspiratory occlusions and 64 occlusions from the onset of inspiration was performed in eight subjects. The inspirations preceding the occlusions served as control. Evoked potentials were recorded from the scalp with electrode pairs Cz-C3 and Cz-C4. Reaction time to each type of occlusion was measured from the burst in electromyogram activity produced by contraction of the muscles encircling the eye. Each type of inspiratory occlusion was associated with evoked potentials that could be recorded bilaterally. The peak amplitudes of the evoked potentials recorded over the right cerebral hemisphere were significantly greater than those recorded from the left side. The peak amplitude was greater and the peak latency shorter for the evoked potentials produced by the midinspiratory occlusions. The results are consistent with the hypothesis that afferents mediating these potentials are stimulated by added loads to breathing and project bilaterally to the somatosensory cortex in humans.     

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.     

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.