Short latency vestibular evoked potentials (VsEPs) to linear acceleration impulses in rats

In this study, short latency (t<12.7 ms) vestibular evoked potentials (VsEPs) in response to linear acceleration impulses were recorded in 37 rats. A new technique (based on a solenoid) was used for generating linear force impulses that were delivered to the animal's head. The impulse had a maximal peak acceleration of 12 g. During the impulse, the displacement was 50 μm (at 4 g) and the rise time was 1.0 ms. A stimulation rate of 2/s was usually used. The VsEPs (averaged responses to 128 stimulations, digital filter: 300–1500 Hz) were recorded with electrodes on pinna and vertex, and were composed of 4–6 clear waves with mean amplitudes (for a 4 g stimulus) of 1–5 μV. The VsEPs were resistant to white noise masking, and were significantly suppressed (P<0.05) following bilateral application of a saturated KCl solution to the inner ear, showing that contributions of the auditory and somatosensory systems are negligible. The latency of the response decreased as a power law function of stimulus magnitude, and the amplitude of the first wave increased as a sigmoid function of stimulus magnitude. VsEP responses were still present at the lowest intensities attainable (0.06–0.4 g) and reached saturation at 9 g. The amplitude of the later components was reduced when stimulus rate was elevated to 20/s. These results suggest that VsEPs in response to linear accelerations are similar in their nature to VsEPs in response to angular acceleration impulses that were previously recorded. These VsEPs to linear accelerations are most likely initiated in the otolith organs.     

Analysis of the middle latency evoked potentials to angular acceleration impulses in man

The middle latency vestibular evoked potential (ML-VsEP) recorded with scalp electrodes in man in response to impulses of angular acceleration is dominated by a forehead positive peak at about 15 ms and a negative peak at about 20 ms; the peak amplitude of this component is about 30 μV. This is followed by slower, smaller amplitude activity. The latency of this initial peak is similar to the latency of the vestibulo-ocular reflex (VOR) in monkeys. The present study was undertaken to elucidate the possible relation between the ML-VsEPs and VOR. This included recordings from forehead-mastoid electrodes (sites used to record VsEP) and other scalp electrodes and the recording of potentials due to eye movement: the electro-oculogram. Direct recording of eye movements was also conducted using an infra-red reflection device in those experiments in which the head was not moved. The recordings were conducted in man during vestibular stimulation eliciting VsEPs, during voluntary eye movements and during caloric and optokinetic stimulation. These experiments indicated that the 15–20 ms component of the ML-VsEP was not due to movements of the eye (corneoretinal dipole). The large amplitude 15–20 ms component of the ML-VsEP was similar in general magnitude, waveform, polarity, duration and rise time to the highly synchronous pre-saccadic spike (neural and/or myogenic) which precedes nystagnys and voluntary saccades. It therefore probably represents vestibular-initiated electrical activity in motor units of the extra-ocular muscles which then produce anti-compensatory saccades.     

Short latency vestibular evoked potentials in the Japanese quail (Coturnix coturnix japonica)

Short-latency vestibular-evoked potentials to pulsed linear acceleration were characterized in the quail. Responses occurred within 8 ms following the onset of stimuli and were composed of a series of positive and negative peaks. The latencies and amplitudes of the first four peaks were quantitatively characterized. Mean latencies at 1.0 g ms⁻¹ ranged from 1265 ± 208 μs (P1, N = 18) to 4802 ± 441 μs (N4, N = 13). Amplitudes ranged from 3.72 ± 1.51 μV (P1/N1, N = 18) to 1.49 ± 0.77 μV (P3/N3, N = 16). Latency-intensity (LI) slopes ranged from −38.7 ± 7.3 μs dB⁻¹ (P1, N = 18) to −71.6 ± 21.9 μs dB⁻¹ (N3, N = 15) and amplitude-intensity (AI) slopes ranged from 0.20 ± 0.08 μV dB⁻¹ (P1/N1, N = 18) to 0.07 ± 0.04 μV dB⁻¹ (P3/N3, N = 11). The mean response threshold across all animals was −21.83 ± 3.34 dB re: 1.0 g ms⁻¹ (N = 18). Responses remained after cochlear extirpation showing that they could not depend critically on cochlear activity. Responses were eliminated by destruction of the vestibular end organs, thus showing that responses depended critically and specifically on the vestibular system. The results demonstrate that the responses are vestibular and the findings provide a scientific basis for using vestibular responses to evaluate vestibular function through ontogeny and senescence in the quail. Accepted: 18 January 1997     

Age-related changes in human middle latency auditory evoked potentials

We recorded middle latency auditory evoked potentials (MAEPs) in young (20–40 years) and elderly (60–80 years) subjects with normal hearing. The Pa component was prolonged in latency and markedly enhanced in amplitude in the elderly subjects. No changes were found in Na, or in the binaural interaction of the MAEP. Differences in Pa amplitude and latency were not due exclusively to changes in auditory thresholds, since they were not duplicated by changes in stimulus intensity, and persisted when MAEPs from selected young and old subjects were compared at similar SPL levels. The enhancement of Pa amplitude appears to reflect age-related central modifications in auditory processing.     

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.     

Inconsistency of auditory middle latency and steady-state responses in infants

Auditory middle latency and steady-state responses (MLR/SSRs) were recorded in normal infants (aged 3 weeks to 28 months) and adults. SSR amplitudes were maximum using stimulus presentation rates near 40 Hz in adults. By contrast, the infant data showed no consistent amplitude maximum across the rates tested (9–59 Hz). With the exception of the brain-stem response wave V to MLR Na deflection, MLR components in infant's responses to 10.85 Hz clicks did not show any consistent pattern. To investigate the hypothesis that the 40 Hz SSR is derived from overlapping of the 10 Hz MLR components, 43.4 Hz SSRs were synthesized from the responses recorded at 10.85 Hz and compared with those recorded at 43.4 Hz. The predictive accuracy of the synthesized 43.4 Hz SSRs was significantly better in adults than in infants. The results of these studies indicate the presence of large age-related differences in the auditory MLR and SSR, and in the relationship between the two responses.     

The contribution of the lateral semicircular canal to the short latency vestibular evoked potentials in cat

Short latency vestibular evoked potentials (VsEPs) to angular acceleration impulses (maximal intensity 20,000°/sec², rise time 1.5–3 msec) were recorded by skin electrodes in cats before and after various surgical procedures. Under general anesthesia, the animals underwent unilateral labyrinthectomy and the VsEPs in response to stimulation of the remaining inner ear in the plane of the lateral semicircular canal (SCC) with the head flexed 20°–25° were recorded as a baseline. The lateral SCC was then selectively obliterated near its ampulla. This induced major changes in the VsEPs recorded in response to stimulation of the remaining inner ear in this plane: the first 2 VsEP waves were absent, and only longer latency, smaller amplitude waves were present in response to both clockwise and counterclockwise stimulation. On the other hand, obliteration of the anterior and posterior SCCs and, in addition, destruction of both maculae were without major effects on the first 2 VsEP waves in response to excitatory stimulation. The results confirm that when the head is flexed 20°–25° and stimulated with angular acceleration impulses in the horizontal plane, the major site of initiation of the VsEPs in cats and probably in man is the crista ampullaris of the lateral SCC.     

Short latency somatosensory evoked potentials recorded around the human upper brain-stem

We analyzed the intracranial spatiotermporal distributions of the N18 component of short median nerve somatosensosry evoked potentials (SSEPs) in 3 patients with epilepsy. In these patients, depth electrodes were implanted bilaterally into the frontal and temporal lobes, with targets including the amygdala and hippocampus; the latter two targets are close to the upper pons and midbrain.In this study N18 was divided into the initial negative peak (N18a) and the following prolonged negativity (N18b). Mapping around the upper pons and midbrain showed that: (1) the amplitude of the first negativity, which coincided with scalp N18a, was larger contralateral to the side of stimulation, but showed no polarity change around the upper brain-stem; and (2) the second negativity, which was similar to scalp N18b, did show an amplitude difference or a polarity change. This wave appeared to reflect a positive-negative dipole directed in a dorso-ventral as well as dorso-lateral direction from the midbrain, where positivity arises from the dorsum of the midbrain, contralateral to the side of the stimulation.Recordings from depth electrode derivations oriented in a caudo-rostral direction suggest that N18a and N18b may in part reflect neural activity originating from the upper pons to midbrain region which projects to the rostral subcortical white matter of the frontal lobe as stationary peaks.     

大鼠脑干听觉诱发电位和中潜伏期反应的生后发育

目的：探讨大鼠脑干听觉诱发电位（BAEP）和听觉中潜伏期反应(MLR)生后发育模式的异同。方法：在同一批新生SD纯种大鼠连续10周同时观察BAEP和MLR生后发育的变化。结果：BAEP和MLR分别在生后14d和17d出现;BAEP各波峰潜伏期（PL）随鼠龄增长而递减,生后3－4周是PL缩短的主要时期,I波PL在生后29d达成年值,其余各波PL在生后70d全部达成年值;首次出现的MLR,其Po和Na两波PL已达成年值,而Pa、Nb和Pb和PL也随鼠龄增长而缩短,但生后20－23d很快就达成年值;BAEP的Ⅰ、Ⅲ、Ⅳ波和MLR的Nb、Pb波波幅在生后3－4周期间迅速递增,且峰值明显大于成年值,然后逐渐回降。结论：大鼠MLR和BAEP生后发育的模式基本相同,但MLR各波PL较早达成年值。     

Effect of repetition rate on middle latency auditory evoked potentials in humans

Middle Latency Auditory Evoked Potentials (MLAEPs) were recorded from 15 healthy subjects in order to evaluate the influence of different repetition rates on the latency and the amplitude of their main components Na, Pa and Nb. MLAEPs were obtained from Cz-ipsilateral ear lobe by averaging responses to 2000 monaural clicks delivered to both ears, at 65 dB SL of intensity, for each of 3 different repetition rates (1.1, 4.1, 8.1 Hz). Time base was 100 ms, analogical band-pass filter 5-1000 Hz (off-line digital bandpass: 20-100 Hz). The statistical analysis (repeated measures analysis of variance), demonstrated that, the latency and the amplitude of the Nb component were slightly influenced by repetition rate while Pa and Na were not. Moreover Nb showed the greatest interindividual variability (as already pointed out by other authors too); thus, we suggest that a stimulus rate of 8.1 Hz and the analysis of Na and Pa component only, can be regarded as the best assessment for MLAEPs evaluation when they are used for clinical purposes.     

Effect of stimulus mode on middle latency auditory evoked potentials in humans

Middle Latency Auditory Evoked Potentials (MLAEPs) were recorded in 35 healthy subjects; all underwent monaural stimulation and 18 of them additionally underwent binaural stimulation. The aim of the study was to determine the effect of stimulus mode on MLAEP Na, Pa and Nb components and to assess normative data for clinical purposes. MLAEPs were respectively obtained from Cz-ipsilateral ear lobe (monaural mode) and from Cz-A1 and Cz-A2 (binaural mode) by twice averaging 1000 responses to 65 dBHL alternating clicks delivered at a repetition rate of 8.1 Hz. Time base was 100 msec; analogical band-pass filter setting was 5-1000 Hz (off-line digital badpass: 20-100 Hz). The statistical analyses (paired t-test, repeated measures analysis of variance) were not able to demonstrate any differences that derived from differing sides of stimulation (monaural mode) or from differing recording derivations (binaural mode); on the contrary, we demonstrated a slight increase in waveform amplitudes when the binaural mode was employed. In particular, we observed an increase in Na-Pa peak-to-peak amplitude, whereas Pa-Nb amplitude was unmodified. This finding is explicable in terms of a binaural interaction effect. Finally, we propose some guidelines for the correct performance and evaluation of MLAEPs in clinical practice.     

体温过高对大鼠脑干听觉诱发电位和中潜伏期反应的影响

目的 :探讨体温过高对大鼠脑干听觉诱发电位 (BAEP)和听觉中潜伏期反应 (MLR )的影响。方法 :诱发电位仪颅表记录大鼠BAEP和MLR ;体表物理升温法逐步升高麻醉大鼠体温 ,传感探头式数字体温计监测大鼠直肠体温 ;主要观察BAEP和MLR的波峰潜伏期 (PL)、波峰间潜伏期 (IPL)和波幅随体温升高而发生的变化及它们消失的临界体温。结果 :BAEP各波PL及Ⅰ Ⅱ、Ⅰ Ⅲ、Ⅰ ⅣIPL随体温升高 ( 3 7～ 41.5℃ )而逐步缩短 ,但当体温升高至 42℃和超过 42℃时各波PL及Ⅰ Ⅱ、Ⅰ ⅣIPL不再继续缩短 ,并略有反向延长 ;MLR各波PL和P1 P3、P2 P3IPL也随体温升高 ( 3 7～ 43℃ )而缩短。随体温升高 ,BAEP和MLR波幅的主要表现为降低 ,特别是在体温升高至42℃以后。BAEP和MLR在体温 ( 4 3 .1± 0 .5)℃时出现不可逆性消失 ,且两者同步消失。结论 :体温过高对大鼠BAEP和MLR有相似的显著影响 ,体温过高至一临界值时会造成BAEP和MLR的不可逆性损害。     

Cross-correlation and latency compensation analysis of click-evoked and frequency-following brain-stem responses in man

Cross-correlation (CC) and latency compensation (LC) analyses were applied to the human click-evoked brain-stem auditory evoked response (BAER) and the brain-stem frequency-following response (FFR). FFRs were elicited by pure tone stimuli (230 Hz and 460 Hz) or by complex tones derived from the sum of 3rd (920 Hz), 4th (1150 Hz), and 5th (1380 Hz) harmonics of the missing 230 Hz fundamental. The lower and upper harmonics always began in sine phase, while the middle harmonic varied in starting phase, resulting in harmonically complex stimuli with differing amplitude and phase patterns.Cross-correlations were computed between individual trials and a wave form t emplate (smoothed wave V for BAER, pure tone stimulus sinusoids for FFR). Trials were included in the analysis only if values of r² exceeded 0.5 (negative values of r were thus included, which controlled for the chance occurrence of positive correlations). Although brain-stem recordings are noisy, requiring as many as 1000 stimuli/average, correlation analysis consistently identified more positive than negative trials (approximately 2:1 ratio). Trials were also deleted if the lag associated with the selected r² was at the maximum shift position (‘extreme lag’).Averaging trials that satisfied the correlation and lag criteria led to sizeable enhancement of BAER (mean = 114%) and FFR (mean = 68% for 230 Hz stimulus) amplitudes. LC analysis resulted in additional, albeit smaller, increases in amplitude (approximately 10%). FFRs to harmonically complex stimuli were characterized by a clear periodicity at the missing fundamental frequency (230 Hz). However, amplitudes varied according to the modulation depth of the stimulus and, in certain cases, actually exceeded that of the FFR response to a 230 Hz pure tone.The results demonstrate the effectiveness of cross-correlation and, to a lesser degree, latency compensation analysis, applied to two classes of brain-stem potentials. It is anticipated that such techniques will prove useful in the study of auditory signal processing at the level of the brain-stem.     

Long latency transient evoked potentials to rapid random stimulation: responses to single and multiple concurrent stimuli

In EP testing, regular (periodic) stimulation at increasing rates produces progressive fusion of responses into steady-state wave forms. When stimuli are presented randomly in time this fusion does not occur. Medium and long latency transient EPs can be recorded to stimulation at interstimulus intervals which are much shorter than the EP wave form latencies. Individual transient EPs can be obtained to multiple independent stimuli presented concurrently when the stimuli are presented randomly to one another. The ability to obtain responses to rapid stimulation and to multiple independent stimuli provides opportunities for increased efficiency and complexity of testing, particularly involving long latency responses.     

Brain-stem,middle latency and late cortical evoked potentials in children with speech and language disorders

The topography of the brain-stem (ABR), middle latency (MLR) and cortical (ACR) evoked responses was investigated in chilfren with nornal speech and language development and those with either a language or motor speech disorder. The aim was to determine whether it is possible to discriminate between the groups of children in terms of the evoked potential characteristics.There were significant inter-group differences, particularly relating to the amplitude of the different responses. The ABR in both the language and motor speech groups exhibited smaller amplitudes for waves I, III and V than the control group, with no change in latency. Two explanations were suggested; firstly abnormal functioning of the peripheral hearing mechanism even though the hearing thresholds were normal which could be a secondary effect due to deprivation normal speech recording effects due to differences in the electrical conductivity of tissue and the distance separating the generator site and recording electrodes. The MLR in the motor speech group was significantly larger at the mastoid and temporal electrode sites than either the control or language groups. This was considered to be an enhanced myogenic response like the other exaggerated brain-stem reflexes seen in congenital suprabulbar paresis. Significantly larger amplitudes of the ACR were also recorded from the motor speech group at the Cz electrode site. This was thought to be due to underactivity of some normal cortical inhibitory system and not a direct result of increased MLR amplitude.The ACR in the language disordered children exhibited an abnormal left temporal hemispheric dominance and a more inverted or ‘dissimilar’ wave from at the T3 electrode site on the correlation analysis. These findings suggest impaired functioning of the left temporal cortex in our children who have failed to develop language normally. We feel that this has more significance for the language abnormality than the low amplitude ABRs which were observed in both the language and motor speech disordered children.     

A longitudinal study of short latency somatosensory evoked responses in healthy newborns and infants

Maturational changes in short latency somatosensory evoked responses (SERs) were studied in 18 healthy full-term newborns in the first week of life and consequently repeated at 2–3 and 6–7 months of age. Both median nerves were electrically stimulated individually and evoked responses were recorded at 3 levels: Erb's point (EP), second cervical vertebra (CII), and contralateral parietal scalp (C′c). In the neonatal period, results of 32 stimulated nerves were obtained in all cases at the EP and CII levels. At the parietal level, potentials were present in 85% of cases, absent in 9% and questionable in 6%. Parietal potentials were occasionally noted on one side only. Repeat examinations at 2–3 and 6–7 months of age demonstrated significant maturational changes in the SERs. These changes were most prominent in the neonatal period and 2 months of age. They included decreased interpeak latencies, increased amplitude and markedly diminished dispersion of parietal potentials. Minimal changes in wave form configuration and latency were noted at the EP and CII level. These findings most likely reflect myelination and increased synaptic efficiency predominantly in the central sensory pathway. The purpose of this investigation was to delineate a reliable technique for SERs in newborbs and infants that could be applied both to research and clinical settings. Normative data were established in newborns and infants as this will help us in accurately differentiating a nomal from an abnormal group of neonates and infants.     

Eye movements and brainstem neuronal responses evoked by cerebellar and vestibular stimulation in chicks

Summary The vestibulo-ocular reflex undergoes adaptive changes that require inputs from the cerebellar flocculus onto brainstem vestibular neurons. As a step toward developing an in vitro preparation in chicks for studying the synaptic basis of those changes, we have elucidated the organization of the pathways through which the flocculus influences vestibulo-ocular movements. Electrical stimulation of the vestibular ampulla evoked brief, contralaterally directed movements in both eyes. Although single current pulses to the flocculus elicited no response, conjunctive stimulation of the flocculus and the vestibular apparatus significantly reduced the vestibularly-evoked movement. Trains of current pulses applied to the flocculus and ampulla evoked eye movements directed toward and away from the side of stimulation, respectively. Recordings from the brainstem revealed neurons that were activated by ipsilateral vestibular stimulation and inhibited by ipsilateral floccular stimulation. Our sample included neurons in the lateral vestibular nucleus, the ventrolateral portion of the medial vestibular nucleus, and the superior vestibular nucleus. Similarities between these findings and those of similar studies in mammals indicate that the chick will provide a good model system for cellular studies of adaptive changes in the vestibulo-ocular reflex.Abbreviations FTN flocculus target neuron - VOR vestibuloocular reflex     

Short latency somatosensory evoked potentials following mechanical taps to the face. Scalp recordings with a non-cephalic reference

Trigeminal somatosensory evoked potentials were recorded over the scalp using non-cephalic reference sites following mechanical taps to the face. A negative wave form, Nf17, was recorded bilaterally with its highest amplitude over the frontal scalp contralateral to the side of stimulation. A localized negative form, Np25, was recorded over the centro-parietal scalp contralateral to the side of stimulation. Np25 had an onset latency of 16.46 msec. The location and restricted spatial distribution of Np25 suggest that it represents the initial activation of the face area of the primary sensory cortex. The widespread bilateral nature of Nf17 and its latency of onset preceding that of Np25 suggest that Nf17 may be a ‘far-field’ potential reflecting activity in subcortical sensory pathways subserving the face.     

Comparison in man of short latency averaged evoked potentials recorded in thalamic and scalp hand zones of representation

Recordings were performed in the thalamus of 13 patients suffering from either abnormal movements or intractable pain, with the aim of delimiting the region to be destroyed or stimulated in order to diminish the syndrome. In 11 of these patients averaged evoked potentials were recorded simultaneously from the scalp and specific thalamus (VP) hand area levels following median nerve stimulation. These recordings were done during the operation or afterwards when an electrode was left in place for a program of stimulation.The latencies of onsets and peaks on the scalp ‘P15’ were compared with those of the VP wave; a clear correspondence was found. Moreover, when increased stimulation was used, both waves began to develop in parallel. Thus in the contralateral ‘P15’ a component exists due to the field produced by the thalamic response. To explain the presence of an ipsilateral scalp ‘P15’ wave, we propose that a second wave having the same latency and a slightly shorter peak exists on the scalp due to a field produced by a brain-stem response. This double origin of ‘P15’ is also shown by the different changes which the ipsilateral and contralateral waves present during changes in alertness.The scalp ‘N18–N20’ is also composed of at least 2 components. The first peak appears on the scalp with a latency shorter than that of the negativity which develops in the thalamus. The N wave, moreover, increases in latency with rapid stimulus repetition. We propose with others that ‘N18’ is a cortical event reflecting the arrival of the thalamo-cortical volley. The second component, ‘N20,’ has a peak latency closely correlated to that of the thalamic negativity. This component was present alone in ‘N’ when rapid stimulation (> 4/sec) was used, which did not change the thalamic response. It must be a field produced by the thalamic negativity.