Modulation by head and trunk positions of the vestibulo-spinal reflexes evoked by galvanic stimulation of the labyrinth. Observations by labyrinthine evoked EMG

Modulation by head and trunk positions of the vestibulo-spinal reflexes was studied in the soleus muscle activities induced by galvanic stimulation of the labyrinth. The stimulation was applied using a bipolar-biaural method with the cathode on the right ear and the anode on the left ear. The intensity was 1 mA and duration 3 s. 1) When the labyrinth was stimulated with the head facing forward, soleus muscle activities increased on the right side and decreased on the left, with a latency of about 100 ms. In spite of the same stimulation, activities of the soleus muscle on both sides decreased with the head rotated to the right and increased with the head rotated to the left. 2) The responses in upper-body rotation were the same as in the case of head rotation. 3) In trunk rotation, some cases showed the same responses as with the trunk facing forward in rotation to the right and left, while others showed changes in muscular activities with the head rotation caused by rotating the trunk. 4) Changes in labyrinthine evoked EMG by head and trunk positions were considered to be due to interaction of vestibular and proprioceptive inputs on the interneurons of the spinal cord.     

年龄因素对直流电刺激诱发的前庭诱发肌源性电位的影响

目的 评估年龄因素对直流电刺激(GVS)诱发的颈肌前庭诱发肌源性电位(cVEMP)和眼肌前庭诱发肌源性电位(oVEMP)的影响。 方法 选择健康志愿者61名(122耳)作为研究对象,22~81岁,平均(45.0±13.8)岁。按年龄分为20~40岁组(26例,52耳)、41~60岁组(24例,48耳)以及>60岁组(11例,22耳),分别记录GVS-cVEMP和GVS-oVEMP。计算GVS-c/oVEMP在不同年龄段的引出率、阈值、潜伏期、振幅、振幅不对称比(interaural amplitude asymmetryratio,IAR),采用SPSS18.0软件进行统计学分析。 结果 GVS-cVEMP在20~40岁、41~60岁、>60岁年龄段的引出率分别为96.15%、89.58%和95.45%,组间比较差异无统计学意义(P>0.05)。GVS-oVEMP在20~40岁、41~60岁、>60岁年龄段的引出率分别为98.07%、91.67%和72.13%,随着年龄增长逐渐降低(P<0.05)。从参数分析来看,cVEMP的引出率、阈值、p1潜伏期、n1潜伏期、振幅和振幅不对称比在不同年龄组间差异无统计学意义(P>0.05);随着年龄增大,oVEMP的引出率下降、阈值增高、振幅减小(P<0.05),其他参数年龄组间差异无统计学意义(P>0.05)。 结论 随着年龄的增长,周围前庭系统的功能降低,有可能会对直流电刺激诱发的VEMP产生影响。     

Effects of galvanic stimulation of the mastoid process on the gastric motility induced by caloric stimulation.

The effects of galvanic stimulation to the mastoid portion on the vestibuloautonomic symptoms induced by caloric stimulation, such as nausea, vomiting, and vertigo, were evaluated in this study. Gastric motility was measured by electrogastrography (EGG) in 20 healthy volunteers (11 male and nine female) aged 20-30 (average: 25.4) years. Electrical stimulation of the mastoid process with 1.0-3.0 mA, 1.0 ms, 100 Hz was applied using a bipolar-biaural method during caloric stimulation of the external auditory canal. The dominant frequency and power of EGG were determined using running spectral frequency analysis and the time-course of EGG was evaluated in a pseudo three dimensional graphic. Frequency of EGG was classified into normogastria with 3 cpm, bradygastria with lower than 3 cpm, and tachygastria with higher than 3 cpm. At quiescent period, normogastria was 78.7 +/- 3.7%, bradygastria 5.0 +/- 1.1%, and tachygastria 16.4 +/- 3.7%. Caloric stimulation with warm water in the unilateral ear and cold water in the contralateral ear elicited vestibuloautonomic symptoms, with accompanied decreases in normogastria (57.7 +/-4.6%, P < 0.01) and increases in tachygastria (34.8 +/- 4.8%, P < 0.01). Cathodal stimulation to the mastoid process ipsilateral to cold water irrigation during caloric stimulation restored normal pattern of gastric motility: normogastria in 77.1 + 5.3% and tachygastria in 19.3 +/- 4.7%, and relieved vestibuloautonomic symptoms. Cathodal stimulation to the inhibited vestibular system ameliorates the vestibular symptoms induced by caloric stimulation.     

Measurement of auditory brainstem responses evoked by electrical stimulation with a cochlear implant

Auditory brainstem responses evoked by electrical stimulation with a Nucleus/Cochlear implant can be measured if care is taken to prevent stimulus artefacts. A simple procedure is described which relies upon a passive LCR filter to prevent the radiofrequency carrier from entering the input of the recording amplifier. The filter simply prevents saturation of the amplifier by the carrier.     

Patient and normal three-dimensional eye-movement responses to maintained (DC) surface galvanic vestibular stimulation.

HYPOTHESIS: That disease or dysfunction of vestibular end organs in human patients will reduce or eliminate the contribution of the affected end organs to the total eye-movement response to DC surface galvanic vestibular stimulation (GVS). BACKGROUND: It was assumed that DC GVS (at current of 5 mA) stimulates all vestibular end organs, an assumption that is strongly supported by physiological evidence, including the activation of primary vestibular afferent neurons by galvanic stimulation. Previous studies also have described the oculomotor responses to vestibular activation. Stimulation of individual semicircular canals results in eye movements parallel to the plane of the stimulated canal, and stimulation of the utricular macula produces changes in ocular torsional position. It was also assumed that the total three-dimensional eye-movement response to GVS is the sum of the contributions of the oculomotor drive of all the vestibular end organs. If a particular vestibular end organ were to be diseased or dysfunctional, it was reasoned that its contribution to the GVS-induced oculomotor response would be reduced or absent and that patients thus affected would have a systematic difference in their GVS-induced oculomotor response compared with the response of normal healthy individuals. METHODS: Three-dimensional video eye-movement recording was carried out in complete darkness on normal healthy subjects and patients with various types of vestibular dysfunction, as diagnosed by independent vestibular clinical tests. The eye-movement response to long-duration bilateral and unilateral surface GVS was measured. RESULTS: The pattern of horizontal, vertical, and torsional eye velocity and eye position during GVS of patients independently diagnosed with bilateral vestibular dysfunction, unilateral vestibular dysfunction, CHARGE syndrome (semicircular canal hypoplasia), semicircular canal occlusion, or inferior vestibular neuritis differed systematically from the responses of normal healthy subjects in ways that corresponded to the expectations from the conceptual approach of the study. CONCLUSION: The study reports the first data on the differences between the normal response to GVS and those of patients with a number of clinical vestibular conditions including unilateral vestibular loss, canal block, and vestibular neuritis. The GVS-induced eye-movement patterns of patients with vestibular dysfunction are consistent with the reduction or absence of oculomotor contribution from the end organs implicated in their particular disease condition.     

Evaluation of patients for cochlear implant by promontory stimulation. Psychophysical responses and electrically evoked brainstem potentials

The protocol for assessing patients for cochlear implantation at University College Hospital and the Royal National Institute for the Deaf, London, includes a session of electrophysiological tests and electrical stimulation of the cochlea. Electrocochleography is performed with the object of excluding non-organic hearing loss and of clarifying the site of deafness. Using the same transtympanic needle, AC and DC electrical stimulation is performed to establish whether patients perceive a sensation of sound, dynamic range and ability to detect frequency shifts. Tinnitus suppression was produced by AC and DC stimulation. It is likely that AC suppression of tinnitus occurs by a masking effect. Electrically evoked auditory brainstem potentials were recorded in one patient.     

Effect of stimulation parameters on electrically evoked auditory brainstem responses

It is evident that the conventional technique for cochlear implant adjustment is not suitable for children in their first years of life. In order to find a solution to this problem, the possibility of electrically evoked auditory brainstem response (EABR) recording was investigated. EABRs were recorded in 9 patients with the Nucleus multichannel cochlear implant. The main problems that have to be solved during EABR recording in cochlear implantees are: i) EABR distortion due to the stimulus artefact: and ii) difference in the stimulus presentation rate during EABR registration (low pulse rate) and conventional psychophysical threshold estimation (high pulse rate) in cochlear implant patients. The influence of stimulus artefact on the recording results was minimized by setting the implant to the widest amplifier frequency band and by zeroing the initial segment containing the stimulus artefact with subsequent zero-phase digital filtering. The dependence of the EABR amplitude and latency on the stimulus intensity, width, electrode location and interstimulus interval was investigated. It was concluded that despite the difference revealed between absolute values of EABR thresholds and psychophysical threshold levels, it is possible to calculate implant adjustment parameters based on the EABR data with the proper correction applied.     

Effect of head position on vestibular evoked myogenic potentials with toneburst stimuli

Conclusion. The present study demonstrated the robustness of VEMP testing with toneburst stimuli, since it is hardly affected by head position, i.e. base or tonic excitation levels of the saccule and inferior vestibular nerve. However, the small but highly significant difference found in latency should not be neglected: the gravitational axis in the upright position may have some special effect on tonic excitation of the saccule. Objectives. To evaluate the effect of head positions on vestibular evoked myogenic potentials (VEMPs) with toneburst stimuli. Materials and methods. VEMPs were recorded with short tonebursts of 500 Hz in 14 normal subjects in 5 head positions (upright, nose up, ear up, nose down, and ear down). The three parameters analyzed were: 1) latency of p13, 2) latency of n23, and 3) corrected amplitude of p13-n23 (CA p13-n23). Results. One-way repeated measures ANOVA showed significant effects on both p13 (p=0.0245) and n23 (p<0.0001) latencies, but not on CA p13-n23. Bonferroni's post hoc test demonstrated that there were significant differences in n23 latency between the upright position and all other head positions leaning on the bed.     

Effect of head position on vestibular evoked myogenic potentials with toneburst stimuli

CONCLUSION: The present study demonstrated the robustness of VEMP testing with toneburst stimuli, since it is hardly affected by head position, i.e. base or tonic excitation levels of the saccule and inferior vestibular nerve. However, the small but highly significant difference found in latency should not be neglected: the gravitational axis in the upright position may have some special effect on tonic excitation of the saccule. OBJECTIVES: To evaluate the effect of head positions on vestibular evoked myogenic potentials (VEMPs) with toneburst stimuli. MATERIALS AND METHODS: VEMPs were recorded with short tonebursts of 500 Hz in 14 normal subjects in 5 head positions (upright, nose up, ear up, nose down, and ear down). The three parameters analyzed were: 1) latency of p13, 2) latency of n23, and 3) corrected amplitude of p13-n23 (CA p13-n23). RESULTS: One-way repeated measures ANOVA showed significant effects on both p13 (p=0.0245) and n23 (p<0.0001) latencies, but not on CA p13-n23. Bonferroni's post hoc test demonstrated that there were significant differences in n23 latency between the upright position and all other head positions leaning on the bed.     

Some experimental observations of responses evoked from the cochlea during two-tone stimulation

When the gerbil cochlea is stimulated with two closely spaced tones, a broad frequency spread of distortion is generated which can be detected in both the meatal sound field and in the round window cochlear microphonic (CM) response. When the frequency ratio f2/f1 is 1.025 or less and f2 = 6 kHz, there is evidence that more than one group of distortion components combines to give the pattern seen in the two cochlear responses. One group is apparently limited to frequencies below 4.5 kHz. This group may be an expression at close stimulus frequency ratios of the 'pulse' described for more widely spaced, lower frequency stimulus conditions, but shown here to be low-pass filtered. Acoustic and CM components within this group show comparable behaviour. A second distortion group consists of a symmetrical distribution of components above and below the stimuli, with no evidence of low-pass filtering. Acoustic and CM manifestations of this symmetrical grouping show little comparable behaviour. It is suggested that interaction could occur between these two groups of distortion to cause some of the complex behaviour reported for 2f1-f2.     

Comparing auditory steady-state responses amplitude evoked by simultaneous air- and bone-conducted stimulation in newborns

Objective: The aim of this study was to evaluate the potential interactions of the simultaneous presentation of air- and bone-conducted stimuli on auditory steady-state responses (ASSR) amplitude in newborns. Design: Bone- and air-conducted stimuli were sinusoidal carrier tones of 500 and 2000?Hz respectively modulated in amplitude (95% depth). Air- and bone- conducted stimuli were either simultaneously recorded in the same ear using insert earphones and bone vibrator respectively, or recorded individually (single stimulation). Study sample: Sixty-nine well babies (135 ears) with ages ranging from 1 to 16 days (mean of 9.2?±?7.9 days) were tested in this study. Results: No significant changes in ASSR amplitude by air-conducted stimuli were observed when evoked by simultaneous or single stimulation. The same trend prevailed for ASSR amplitudes evoked by bone-conducted stimuli. Conclusions: The results of this study suggest that the simultaneous stimulation of air-and bone-conducted stimuli does not alter ASSR amplitude values in well babies. Therefore, the results support the use of this technique as a potential hearing screening tool to discriminate between conductive and sensorineural hearing loss.     

Influence of head position on the vestibulo-ocular reflex during rotational testing

The influence of two static head positions on the horizontal nystagmus induced by sinusoidal rotational stimulation in a group of 24 healthy subjects was investigated. The rotation test was performed with the subject's head in the primary position (upright) and with the head 30 degree pitched down. Computerized electronystagmography was used to measure the maximum slow component velocity of the horizontal nystagmus and to calculate gain, phase and asymmetry. The vestibulo-ocular reflex (VOR) gain obtained during rotation with the head in the primary position was significantly higher than with the head bent 30 degree forward. No other significant differences were found.     

Thermal stimulation of the vestibular labyrinth during orbital flight

Summary During the European Spacelab mission (SL1) in 1983, caloric testing was performed for the first time in long-term weightlessness. After 2 days into orbital flight an unequivocal caloric nystagmus was observed in both subjects tested which corresponded in both quality and intensity with that measured in one-g conditions on Earth. The subsequent D1 mission enabled the experiment to be repeated on further subjects and with improved measurement procedures. As with the SL1 findings, the observed caloric nystagmus response proved to be equivalent to that measured during baseline testing on Earth. Renewed consideration of peripheral and central mechanisms, which might be involved in the elicitation of the caloric response — both in one-g and zero-g environments — has led to the reopening of a number of associated issues. One important observation which has been addressed by various research groups concerns the influence of the labyrinth's orientation to the gravity vector on the caloric response. The present authors have examined a group of healthy subjects in various body positions in the sagittal plane. The interindividual variability in the response behavior was found to be high; indeed single cases were observed in which the nystagmus response did not invert from the supine to the prone positions. These findings are discussed together with earlier reports in the literature.Part of the Round Table Conference presented at the Collegium ORLAS, Munich, Federal Republic of Germany, 7–10 September 1986     

Thermal stimulation of the vestibular labyrinth during orbital flight

During the European Spacelab mission (SL1) in 1983, caloric testing was performed for the first time in long-term weightlessness. After 2 days into orbital flight an unequivocal caloric nystagmus was observed in both subjects tested which corresponded in both quality and intensity with that measured in one-g conditions on Earth. The subsequent D1 mission enabled the experiment to be repeated on further subjects and with improved measurement procedures. As with the SL1 findings, the observed caloric nystagmus response proved to be equivalent to that measured during baseline testing on Earth. Renewed consideration of peripheral and central mechanisms, which might be involved in the elicitation of the caloric response--both in one-g and zero-g environments--has led to the reopening of a number of associated issues. One important observation which has been addressed by various research groups concerns the influence of the labyrinth's orientation to the gravity vector on the caloric response. The present authors have examined a group of healthy subjects in various body positions in the sagittal plane. The interindividual variability in the response behavior was found to be high; indeed single cases were observed in which the nystagmus response did not invert from the supine to the prone positions. These findings are discussed together with earlier reports in the literature.     

Auditory brainstem responses evoked by direct mechanical stimulation of the ossicular chain. Objective preoperative testing of candidates for implantable hearing aids

BACKGROUND AND OBJECTIVE: The function of several implantable hearing systems is based on the vibratory excitation of the ossicular chain. For preoperative testing, malleus vibration audiometry has been described [7]. In special cases, it could be desirable to perform objective testing before implantation. We therefore studied the auditory brainstem responses (ABR) evoked by vibratory stimulation of the ear drum. METHOD: The ABR evoked by vibratory and acoustical click stimulation were recorded in 20 subjects with normal hearing at four different stimulus intensities. For the vibratory stimulation (v-ABR), the transducer rod was brought into mechanical contact with the eardrum under microscopic control. This setup was further used for the determination of the individual subjective threshold. The v-ABR were compared to conventional ABR recordings. RESULTS: In all subjects, the v-ABR could clearly be identified. At high stimulus levels, the complete wave pattern was observed in 15 of 20 cases. There is no essential difference between v-ABR and conventional ABR with respect to the incidence and parameters of the potentials. At high stimulus levels, a pronounced stimulus artefact impedes the identification of wave I in some cases. Moreover, the quality of v-ABR is limited by the uncomfortable situation and incomplete relaxation of the subject. CONCLUSIONS: The measurement of vibratory evoked ABR is practicable without hazards for the patient and it yields reliable results. The hearing threshold for click stimuli can be determined from the incidence and amplitude of the responses. The loudness associated with the click stimuli can be estimated from the response latency. Therefore, the investigation of v-ABR not only gives evidence of the individual suitability for implantable hearing aids but its outcome may also be useful as an orientation for the postoperative fitting.     

Phase-locking of auditory-nerve discharges to sinusoidal electric stimulation of the cochlea.

The activity of auditory-nerve fibers was recorded in anesthetized cats in response to sinusoidal electric stimuli applied through a bipolar electrode pair inserted about 5 mm into the cochlea through the round window. The synchronization index was calculated from period histograms for frequencies ranging from 0.2 to over 10 kHz. The stimulus artifact was largely eliminated through the use of differential micropipettes and an adaptive digital filter. Measured synchronization indices were many times larger than the indices that could be attributed to the residual stimulus artifact. Synchronization indices at each stimulus frequency varied considerably from fiber to fiber, even in the same animal. The dependence of synchrony on stimulus frequency was also variable, decreasing monotonically in some fibers and nonmonotonically in others. The average electric synchronization index for all fibers did not fall as steeply with frequency as does the average synchrony for acoustic stimuli. The finding of significant phase locking to electric stimuli well above 1 kHz suggests that the poor frequency discrimination of cochlear-implant recipients for single-channel stimulation above this frequency may be due to the inability of the central processor to make effective use of the available phase-locking information for monaural stimulation.