Galvanic-Induced Postural Movements As a Test of Vestibular Function in Humans

Galvanic stimulation produces postural sway and eye movements in humans. Since galvanic currents are thought to exert their effect at the trigger zone of the vestibular nerve, an intact vestibular nerve should be necessary to produce a response. We have used galvanic stimulation in humans to test the hypothesis that intact vestibular nerve fibers are required to obtain a postural sway response. Experimental subjects included normal subjects, patients who had undergone resection of an acoustic neuroma, and patients who had undergone vestibular neurectomy and surgical labyrinthectomy. Our results support the hypothesis that an intact vestibular nerve is necessary to produce a response. Moreover, two patients with recurrent vertigo following vestibular neurectomy and labyrinthectomy, who had absent ice-water caloric test responses in the operated ears, were found to have a positive galvanic response. This result suggested that their recurrent vertigo was based on intact residual vestibular nerve fibers. Although previous research has not yielded a routine clinical use for galvanic stimulation, our results suggest that galvanic stimulation of the vestibular system can provide unique and valuable diagnostic information.     

Significance of pressor input from the human feet in lateral postural control. The effect of hypothermia on galvanically induced body-sway

The significance to human postural control of pressor information from the feet was investigated during vestibular disturbance in seven normal subjects who were exposed to bipolar biaural galvanic stimulation of the vestibular nerves before and after their feet were anaesthetized with hypothermia. The increase in body sway in the lateral plane induced by the galvanic stimulus was enhanced when the feet were anaesthetized, and adaptation of postural control to the galvanic stimulus was delayed. It is concluded that pressor information from the feet contributes significantly to postural control in humans and is important in compensating for vestibular disturbance.     

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.     

Habituation to galvanic vestibular stimulation

OBJECTIVE: To examine the response decline that occurs upon repetitive galvanic vestibular stimulation (GVS) and hampers long-term clinical evaluations. MATERIAL AND METHODS: This was a prospective experimental study conducted in a tertiary referral centre. In a previous study we developed a standardized procedure for reproducible quantification of galvanic-induced body sway (GBS). The most reproducible responses were found using a continuous 1-cosinusoidal stimulus (0.5 Hz; 2 mA) preceded by a pre-habituating stimulus. This binaural prestimulation reduced the short-term (<5 min) response decline to a non-significant level. The response decline without prestimulation was interpreted as habituation to the galvanic stimulation. In the present study we evaluated possible long-term habituation to GVS, which may hamper longitudinal clinical evaluations. Possible long-term habituation using the short-term habituating prestimulus concept was studied by quantifying GBS in 40 subjects at 5 consecutive time points. Subjects were subdivided into four equal groups who were tested with four different time intervals between the five measurements, ranging from 1 day to 2 weeks. RESULTS: The absolute test results did not vary with the time interval (p=0.217; repeated measurement test). Irrespective of the time interval between the tests, habituation occurred after the first stimulation and remained stable at all consecutive measurements. GVS habituation did not depend on either the degree of daily life activity (moderate practice of sport) or on gender. CONCLUSION: The current protocol, using a prehabituating binaural stimulus, showed that reproducible assessment of the GVS over a time course of days to weeks was possible starting from the second test.     

Postural adaptation in elderly patients with instability and risk of falling after balance training using a virtual-reality system

Our aim in this study was to assess postural control adaptation quantitatively in unsteady elderly patients at risk of falls in open spaces and given balance training with a virtual-reality system reproducing environmental stimulation. Using a balance rehabilitation unit based on a virtual-reality system that changes sensory information (visual, vestibular, and somatosensory), we treated 26 elderly, unsteady patients who were prone to falling (age range, 73-82 years) and who were enrolled in a customized vestibular rehabilitation program. We assessed postural responses by posturography before and after 6 weeks in the vestibular rehabilitation program under two conditions: (1) standing, eyes open, static visual field, and (2) standing, eyes open, dynamic visual field through virtual-reality goggles, generating horizontal optokinetic stimulation (70 degrees per second angular velocity). We recorded postural responses with a platform measuring the confidential ellipse of the center-of-pressure distribution area and sway velocity with a scalogram analyzing postural behavior by wavelets. After 6 weeks of treatment, postural response confidential ellipse and sway velocity values were lower, evincing decreased amplitudes and sway frequency contents in the scalogram by wavelet under both stimulation paradigm conditions. These findings suggest postural adaptation under the two perceptual conditions when patients had static and dynamic visual fields. The possibility of treating elderly fallers with balance disorders using a virtual-reality environmental stimulation reproduction system is discussed.     

Balance sensory organization in children with profound hearing loss and cochlear implants

OBJECTIVES: (1) To determine the feasibility of the use of a modified postural control test under altered sensory conditions in children over 8 years of age, and (2) to assess how deaf children use sensory information for postural control when they have normal or abnormal vestibular responses, and if hearing input from a unilateral cochlear implant, changes their postural behavior. PATIENTS: We selected 36 children, 8 to 11 years of age, with congenital or early-acquired profound sensorineural hearing loss, 13 of them with unilateral cochlear implantation and 22 normal-hearing children. METHODS: The Postural Control (PC) test consists of a force platform with 2 stimulation paradigm conditions: (1) standing on the platform with opened eyes; (2) standing on foam placed on the force platform with closed eyes. Implanted children were tested with the implant turn on and turn off in this condition, in order to evaluate eventual change in the postural control parameters when they have hearing habilitation. The body center of pressure distribution area (COP) and the body sway velocity (SV) were the parameter to evaluate the postural control. RESULTS: Deaf children were classified into two groups according with the vestibular responses: group A (n=28) Children with normal vestibular rotary responses; group B (n=8) children with hypoactive responses. Children in group A had diagnoses of syndromic and non-syndromic hereditary deafness, and children in group B had inner ear malformations, post-meningitis deafness, and one child had non-syndromic hereditary deafness with hypoactive vestibular response. In condition 1, when vestibular, somatosensory and visual information were enabled, the COP and SV values did not show any statistically significant differences between groups A, B and control. In condition 2, when visual information was removed and the somatosensory input strongly modified by standing on the foam, group B showed significant higher COP and SV values than groups A and control (p<0.05). In addition, the scalograms by wavelets of children in group B had higher amplitudes increasing the sway frequencies contents up to 3 Hz, not allowing them to maintain the up right stance in similar stimulation than in condition. Implanted children of the group A and B with the implant turn on, in the condition 2, did not show any significant difference in the SV, comparing when they had the implanted turn off. Group A p=0.395 and group B p=0.465 (Wilcoxon ranked test). CONCLUSION: These findings allow us to confirm that this postural test can be performed in children over 8 years old. Also our results suggest that deaf children with associated hypoactive vestibular responses included in our study, despite the etiology of the deafness, primarily use visual and somatosensory information to maintain their postural control. Hearing habilitation with a unilateral cochlear implant has no effect on the observed sensory organization strategy.     

Direction of galvanically-induced vestibulo-postural responses during active and passive neck torsion

The direction of a postural response induced by galvanic vestibular stimulation depends on the head and trunk position. The relative importance of afferent information (proprioception) and efferent motor command/corollary discharge is unknown. We studied the direction of body sway evoked by galvanic vestibular stimulation in 9 healthy subjects during active and passive head positioning at 0 degrees frontal position, 35 degrees to the left, and 75 degrees to the right, using a custom-built collar. At 0 degrees and 75 degrees there were no significant differences in sway direction between active and passive head positioning. The galvanic stimulation invoked sway toward the anode, mainly in the inter-aural direction. The sway direction differed significantly between active and passive positioning at 35 degrees to the side (p < 0.05). When the head was actively kept in this position, the body sway was mainly in an inter-aural direction. The sway shifted to a naso-occipital direction when the head was passively positioned at 35 degrees. Our results indicate that the afferent proprioceptive information has the largest influence on the direction of the galvanically-induced postural response, although some dependence on efferent motor commands and non-linear cervical proprioception cannot be ruled out entirely.     

Adaptive mechanisms of VOR compensation after unilateral peripheral vestibular lesions in humans.

To further elucidate possible central plastic adaptive processes during the recovery from a unilateral peripheral vestibular lesion, we investigated vestibular functions in humans over a period of 2 months after an acute unilateral labyrinthine lesion. A unilateral peripheral vestibular lesion creates both a tonic imbalance that causes spontaneous nystagmus and a decrease and directional asymmetry of dynamic vestibular responses. We establish that the tonic imbalance expressed by the spontaneous nystagmus rapidly decreased (similar to other species), whether the lesion remained complete or not. This rebalancing, in the case of complete lesions, is at least partly due to restoration of central vestibular tone on the lesioned side. This restoration of tone also explains, in the case of a complete lesion, the recovery of dynamic vestibular responses for high-velocity inhibitory stimulation of the remaining labyrinth. A clear recovery of the dynamic response for excitatory stimulation of the remaining labyrinth cannot be proven, as has been shown in monkeys during the first 4 days after a unilateral vestibular lesion. This is probably due to the fact that in our patients the first recording could not be performed before day 3 after the onset of symptoms. Therefore, any fast dynamic recovery may have been missed.     

Recovery of postural control after an acute unilateral vestibular lesion in humans.

Postural control during stance was investigated using the EQUITEST system in 10 patients during recovery after an acute unilateral vestibular lesion and was compared to the time course of recovery of the static and dynamic vestibulo-ocular imbalance. During the acute phase the patients showed a characteristic pattern with normal upright stance as long as at least one accurate sensory input (visual or somatosensory) was provided and severe postural disturbances when they had to rely primarily on vestibular afferences. Both static vestibulo-ocular and vestibulo-spinal balance recovered very fast, showing basically normal results on postural testing within about 2 weeks after the lesion. Thereafter, no pathological pattern was detectable during postural testing even in patients with persistent complete unilateral vestibular lesions. Reflexive postural responses to unexpected rapid displacements of the support surface seemed not to be influenced by vestibular imbalance even in the acute phase of the lesion.     

Direction of Galvanically-induced Vestibulo-postural Responses during Active and Passive Neck Torsion

The direction of a postural response induced by galvanic vestibular stimulation depends on the head and trunk position. The relative importance of afferent information (proprioception) and efferent motor command/corollary discharge is unknown. We studied the direction of body sway evoked by galvanic vestibular stimulation in 9 healthy subjects during active and passive head positioning at 0° frontal position, 35° to the left, and 75° to the right, using a custom-built collar. At 0° and 75° there were no significant differences in sway direction between active and passive head positioning. The galvanic stimulation invoked sway toward the anode, mainly in the inter-aural direction. The sway direction differed significantly between active and passive positioning at 35° to the side (p&lt;0.05). When the head was actively kept in this position, the body sway was mainly in an inter-aural direction. The sway shifted to a naso-occipital direction when the head was passively positioned at 35°. Our results indicate that the afferent proprioceptive information has the largest influence on the direction of the galvanically-induced postural response, although some dependence on efferent motor commands and non-linear cervical proprioception cannot be ruled out entirely.     

Adaptation of Vestibular Tone Studied with Electrical Stimulation of Semicircular Canal Afferents

Damage to one vestibular labyrinth or nerve causes a central tone imbalance, reflected by prominent spontaneous nystagmus. Central adaptive mechanisms eliminate the nystagmus over several days, and the mechanisms underlying this process have received extensive study. The characteristics of vestibular compensation when the tone imbalance is presented gradually or repeatedly have never been studied. We used high-frequency electrical stimulation of semicircular canal afferents to generate a vestibular tone imbalance and recorded the nystagmus produced when the stimulation was started abruptly or gradually and when it was repeatedly cycled on and off. In the acute-onset protocol, brisk nystagmus occurred when stimulation started, gradually resolved within 1 day, and reversed direction when the stimulation was stopped after 1 week. Repeated stimulation cycles resulted in progressively smaller nystagmus responses. In the slow-onset protocol, minimal nystagmus occurred while the stimulation ramped-up to its maximum rate over 12 h, but a reversal still occurred when the stimulation was stopped after 1 week, and repeated stimulation cycles did not affect this pattern. The absence of nystagmus during the 12 h ramp of stimulation demonstrates that central vestibular tone can rebalance relatively quickly, and the reduction in the stimulation-off nystagmus with repeated cycles of the acute-onset but not the slow-onset stimulation suggests that dual-state adaptation may have occurred with the former paradigm but not the latter.     

Changes in postural control parameters after vestibular rehabilitation in patients with central vestibular disorders

OBJECTIVE: The aim of this study was to determine postural responses before and after a vestibular rehabilitation program (VRP) in 14 patients with central vestibular disorders (CVD). MATERIAL AND METHODS: The confidence ellipse (CE) of the center of pressure distribution area and the sway velocity (SV) were the parameters used for the quantitative assessment of postural control (PC). These two parameters were analyzed before and after a VRP for two visual conditions. Behavioral postural responses were studied by means of the time-frequency scalogram using wavelets and the sway frequency content was measured in arbitrary units of energy density. RESULTS: Ten patients showed a significant decrease in the CE and SV after the rehabilitative treatment, thus improving their PC. Seven of these patients were assessed again after a period of 12 +/- 5 months, during which they had not received any physical training. All of them showed increases in the CE and SV, indicating an impairment of PC. CONCLUSIONS: Many CVD patients damage the neural mechanisms involved in retaining the plastic changes in the PC parameters after rehabilitative treatment. Continuation of training may be necessary in order to maintain the improvement in PC obtained with a VRP.     

Vestibular system in infants after systemic aminoglycoside therapy

OBJECTIVES: The ototoxic action of systemic therapy with aminoglycoside antibiotics leading to the loss of inner ear hair cells is well recognized. The mitochondria-mediated pathway of apoptosis may play a role in inducing the apoptosis of vestibular hair cells due to aminoglycoside toxicity. Aminoglycosides are, nevertheless, routinely used for treatment of vital infections in neonatologic departments. Although there is a strong supposition that aminoglycosides can influence the vestibular function in infants, the routine examination of the infants' inner ear does not include vestibular tests. The purpose of the present study was to evaluate vestibular function in a group of infants prior to and after administration of systemic aminoglycosides, using caloric tests and vestibular-evoked myogenic potentials (VEMPs). METHODS: VEMPs and auditory brainstem responses were recorded and caloric stimulation was performed in 68 infants aged 2.5-3.5 months: 40 healthy controls and 28 infants after therapy with amikacin, 15mg/(kgday) in three doses. The therapy duration varied from 10 to 14 days. In 18 infants antibiotic therapy was administered for a respiratory infection, and in 10 for sepsis. Infants with other risk factors of inner ear damage and treated with more than one ototoxic drug were excluded from the study. The tests were performed on the day of admission to hospital and repeated on the day of discharge. RESULTS: The results of all tests were normal on admission. On the day of discharge, no reaction to caloric stimulation was elicited in six patients and no VEMPs were recorded in four subjects. Hearing thresholds were normal in all the individuals during both examinations. CONCLUSIONS: The vestibular organ in infants after systemic therapy with amikacin may be damaged more frequently than the cochlear organ. The horizontal canal is more vulnerable to aminoglycosides, as compared to the saccule. The vestibular organ should be routinely examined in infants after systemic treatment with aminoglycosides.     

Direct evidence of nitric oxide production in guinea pig vestibular sensory cells

Production of nitric oxide (NO) in the vestibular organ of the guinea pig was investigated using the new fluorescence indicator, DAF-2DA, for direct detection of NO. The utricular maculae and isolated vestibular sensory cells were examined to locate NO production sites. The fluorescence intensity of the sensory cells was augmented by stimulation with L-arginine, and significantly increased after inoculation with LPS. This is the first direct evidence of NO production in the vestibular end organs. NO may play an important role for the vestibular physiology and also be involved in disease of the inner ear.     

Direct Evidence of Nitric Oxide Production in Guinea Pig Vestibular Sensory Cells

Production of nitric oxide (NO) in the vestibular organ of the guinea pig was investigated using the new fluorescence indicator, DAF-2DA, for direct detection of NO. The utricular maculae and isolated vestibular sensory cells were examined to locate NO production sites. The fluorescence intensity of the sensory cells was augmented by stimulation with L-arginine, and significantly increased after inoculation with LPS. This is the first direct evidence of NO production in the vestibular end organs. NO may play an important role for the vestibular physiology and also be involved in disease of the inner ear.     

Effects of hypothermic anesthesia of the feet on vibration-induced body sway and adaptation

The aim of this study was to investigate the significance of information from the plantar cutaneous mechanoreceptors in postural control and whether postural control could compensate for reduced cutaneous information by adaptation. Sixteen healthy subjects were tested with eyes open or eyes closed with hypothermic and normal feet temperature during posturography where body sway was induced by vibratory proprioceptive stimulation towards both calf muscles. The hypothermic anesthesia was obtained by cooling the subject's feet in ice water for 20 minutes. Body movements were evaluated by analyzing the anteroposterior and lateral torques induced towards the supporting surface by a force platform during the posturography tests. The reduction of cutaneous sensor information from the mechanoreceptors of the feet significantly increased the vibration-induced torque variance mainly in the anteroposterior direction. However, the effects of disturbed mechanoreceptors information was rapidly compensated for through postural adaptation and torque variance was in level with that without anesthesia within 50 to 100 seconds of stimulation, both when standing with eyes open and eyes closed. Our findings suggest that somatosensory input from mechanoreceptors in the foot soles contribute significantly in maintaining postural control, but the sensory loss could be compensated for.     

The effects of stochastic monopolar galvanic vestibular stimulation on human postural sway

Galvanic vestibular stimulation (GVS) is a technique in which small currents are delivered transcutaneously to the afferent nerve endings of the vestibular system through electrodes placed over the mastoid bones. The applied current alters the firing rates of the peripheral vestibular afferents, causing a shift in a standing subject's vestibular perception and a corresponding postural sway. Previously, we showed that in subjects who are facing forward, stochastic bipolar binaural GVS leads to coherent stochastic mediolateral postural sway. The goal of this pilot study was to extend that work and to test the hypothesis that in subjects who are facing forward, stochastic monopolar binaural GVS leads to coherent stochastic anteroposterior postural sway. Stochastic monopolar binaural GVS was applied to ten healthy young subjects. Twenty-four trials, each containing a different galvanic input stimulus from among eight different frequency ranges, were conducted on each subject. Postural sway was evaluated through analysis of the center-of-pressure (COP) displacements under each subject's feet. Spectral analysis was performed on the galvanic stimuli and the COP displacement time series to calculate the coherence spectra. Significant coherence was found between the galvanic input signal and the anteroposterior COP displacement in some of the trials (i.e., at least one) in nine of the ten subjects. In general, the coherence values were highest for the mid-range frequencies that were tested, and lowest for the low- and high-range frequencies. However, the coherence values we obtained were lower than those we previously reported for stochastic bipolar binaural GVS and mediolateral sway. These differences may be due to fundamental characteristics of the vestibular system such as lower sensitivity to symmetric changes in afferent firing dynamics, and/or differences between the biomechanics of anteroposterior and mediolateral sway.     

庆大霉素对豚鼠前庭功能影响的动态研究

为研究庆大霉素破坏前庭感觉上皮所致的生理功能障碍，观察庆大霉素对前庭功能影响的动态变化过程，应用正弦摆动试验和旋转试验进行动态观察。分别对白色和杂色豚鼠按每日125mg／kg体重皮下注射硫酸庆大霉素连续12天。结果示：用药7天豚鼠的前庭功能无明显改变，用药后10天出现明显的前庭功能受损，停药后5天受损程度最明显，停药14天前庭功能稍有恢复，但仍明显低下，直到停药后3个月，未见前庭功能明显改善；且杂色豚鼠前庭功能损害程度较白色豚鼠为轻。此研究为氨基式类抗生索性内耳损伤的防护和治疗提供了实验依据。     

An Animal Model of Sudden Onset Sensorineural Hearing Loss with Vestibular Function Disturbances Induced By Mitochondrial Toxin

Objective To establish an animal model of sudden onset sensorineural hearing loss (SSNHL) to study its mechanisms. Materials and methods The inner ear was exposed to 3-nitropropionic acid at 0.5 mol/L (3-NP (H)) and 0.3 mol/L (3-NP (L)) through the round window membrane for 30 minutes in 50 male guinea pigs. Thresholds of auditory brainstem responses(ABR) were established before the treatment and retested at 4 hours, 1 day, 3 days and 6 days following 3-NP exposure. Control animals were treated with phosphate buffered saline (PBS) and their ABRs were retested at 4 hours and 1 day after the treatment. Animals were monitored for nystagmus and postural signs of vestibular dysfunction, using a digital video camera, following the treatment procedure. Specimens were taken at 12 hours, 1 day, 3 days and 7 days following 3-NP(H) exposure and embedded in JB4 for light microscopy observation. Results ABRs were lost in all animals tested at 4 hours following 3-NP (H) exposure. The rate of complete ABR loss decreased as post-treatment test time increased. ABRs were lost in 80% (4/5) of the animals at 1 day after exposure to 3-NP (L). Spontaneous horizontal nystagmus with a fast phase away from the treated ear developed in all 3-NP (H)-treated animals and in 20 % ( 1/5) of the animals exposed to 3-NP (L), except for the one treated bilaterally. Various degree of postural disturbances consistent with unilateral vestibular dysfunction, such as spontaneous barrel rolling towards the exposure side while walking, were seen in all animals exposed to 3-NP(H) and 40% (2/5) of animals exposed to 3-NP(L), except for the one animal treated bilaterally, which showed no signs of imbalance. Both nystagmus and postural disturbances resolved in 2 days following 3-NP exposure. Histological study showed temporary edema tin the organ or Corti, Claudius cells and the inner sulcus cells 3 days after 3-NP (H) treatment. Enlargement of intercellular space in the spiral prominence was first noticed at 12 hours post-3-NP (H) exposure, progressed at day 3 and recovered at day 7. Vacuoles in the cellular plasm and nucleus was seen as early as at 12 hours post-3-NP exposure in the spiral ganglion cells, and signs of degeneration were visible at day 7. Conclusion Inner ear exposure to 3-NP through the round window membrane appears to reproduce clinic manifestations and may serve as a legitimate animal model of SSNHL     

Effect of retroauricular galvanic stimulation on the central vestibular system--immunohistochemical evaluation of GABA

The changes of the neurotransmitter (GABA) distribution in the brain stem of the rats by retroauricular galvanic stimulation were investigated using immunohistochemical method. Twenty-one rats were divided into two groups: the control group which received no galvanic stimulation, and the galvanically stimulated group which received anodal galvanic stimulation (unipolar monoauricular, 5 mA in intensity, 500 msec of duration, 1 Hz in frequency) for 30 minutes. The specimens obtained as usual strict procedure for histological investigation were stained immunohistochemically using antisera against GABA. The results were as follows: 1. In the control group, GABA-like immunoreactivity was observed in all four main vestibular nuclei. In the superior, medial, and descending vestibular nuclei GABA-like immunoreactivity was found in the small cells and the terminals. Giant cells in the lateral vestibular nucleus were surrounded by GABA immunoreactive terminals. 2. In the galvanically stimulated group GABA-like immunoreactivity showed recognizable laterality in the lateral vestibular nucleus where GABA-like immunoreactivity surrounding giant cells showed more intensive on the side ipsilateral to the stimulation compared with the opposite side. On the other hand GABA-like immunoreactivity showed no laterality in the superior, medial, and descending vestibular nuclei. 3. It can be concluded that the retroauricular galvanic stimulation cause some changes in the inhibitory activity of the lateral vestibulo-spinal tract and of the spinal motor neuron.