Stimulation Of Labyrinth Research Articles

P 53. Galvanic labyrinth polarization for holistic musculoskeletal therapy

Introduction. Acute and chronic pain syndromes of the spine are caused by multiple factors. Often pain syndromes are induced by imbalanced posture due to defective position in facette joints of the spine and by pathological stress of the autochthone and spinal muscles and tendons. From this a vicious circle follows. Due to high permanent pressure on one side and high permanent pull on the other, pain induced by inflammation and finally structural lesions of the bone develop. In this study the application of galvanic labyrinth polarization (Swing Symphonie) is used to interrupt the mentioned circuit of imbalance and pain. Material and Methods. Tests were performed on 14 subjects. All subjects were free of any cardiovascular, CNS, cochlear or vestibular disorder. Further, the integrity of the peripheral vestibular system was examined by head impulse testing (Halmagyi & Curthoys, 1988; Halmagyi et al., 1990) and additional one-sided galvanic labyrinth stimulation in combination with oculography, both of which confirmed the healthy vestibular status of the volunteers. In two pilot series Swing Symphonie was employed. In series 1 (n=10) the effect to stress relaxation and autonomic function were examined. Before and after stimulation a questionnaire had to be filled. Also, skin resistance, heart rate and respiratory frequency were measured. In series 2 (n=5x3) the effect to pain reduction was examined. Five subjects were investigated three times. Two subjects suffered from headache, three from spinal pain induced by degenerative disease. For series 2 the common diagnostic tests and scans were performed beforehand. No necessary therapy was missed. Swing Symphonie to the inner ear does not influence the labyrinth or cochlea as such, but rather the activity of the neurons in the vestibular nerve at the postsynaptic membrane (Goldberg et al., 1982, 1984; Smith &Goldberg, 1986; Schlosser, 1999). Sinusoidal stimulation was employed throughout the study. Electrodes were attached to the right and left mastoids and two additional electrodes were attached interscapular just medial to the superior angulus of the scapula A 2.0-Hz sinusoidal waveform was used to drive the current output of a custom-manufactured stimulator (Neurotronix, Berlin, Germany). In all cases, pendular perception was accompanied by ocular response (videooculography), demonstrating adequate vestibular stimulation. Results . In series 1, subjects reported to feel relaxed (8/10), comfortable (9/10) and calmed (6/10) after Swing Symphonie. Heart rate (9/10) and Skin resistance (8/10) decreased significantly. In series 2 after Swing Symphonie subjects reported a distinct reduction of pain symptoms (15/15). Discussion. In this pilot study Swing Symphonie induces relaxation and relieves pain syndromes. A pain inhibiting mechanism on the level of the posterior insula has to be discussed.

Alternobaric vertigo – An uncommon medical hazard

Alternobaric vertigo (AV) is a type of barotrauma of the middle ear which occurs if the asymmetric middle ear pressure in both sides. If pressure differential exceeds a threshold, asymmetric stimulation of the labyrinth will occur, leading to vertigo, called as AV. The classical presentations is transient vertigo which appear sudden onset during the time of diving or flying, typically when ascends or when a Valsalva manoeuvre is performed. Other symptoms associated with AV are nausea, vomiting, disorientation and generalised malaise. If the descent or ascent is reversed immediately, vertigo suddenly disappears or may cause sudden spatial disorientation which may lead to catastrophic outcome. AV is often overlooked but this mishap should not be ignored as it may lead to fatal accident. The patient should be properly counselled for aetiology and nature of AV and its potential risks including aspiration and death. This review article focuses on the prevalence, etiopathology, clinical presentations and current management of the AV amongst underwater divers and aviators. This article will surely increase awareness amongst the clinicians and people those are practicing underwater diving or in aviation and help them to resolve this problem to a great extent.

Features of the diagnosis of meniere's disease on the example of a clinical case

Introduction. Meniere’s disease is accompanied by a non-infectious pathology of the inner ear, during which can lead to systemic labyrinth dizziness, nausea, vomiting, hearing loss and tinnitus in one ear. It is a rare disease, affecting up to 200 cases per 100,000 people. Aim. The purpose of this article was to analyze the clinical case of a patient with Meniere's disease. Materials and methods. Patient S., was admitted to the Department of Vascular Pathology of the Brain and Rehabilitation of the State Institution «Institute of Neurology, Psychiatry and Narcology of the NAMS of Ukraine» with complaints of regular attacks of systemic vertigo with a frequency of up to 7 times a week lasting 1–4 hours, sometimes accompanied by vomiting, constant noise and whistling in the left ear. He considers himself ill since 05.11.19, when during training in the gym there was the first case of dizziness and vomiting, which lasted 3 hours. In August 2019, the attacks continued, became more frequent and prolonged, passed on their own, sometimes in a specific position of the head - the head tilted forward with the neck stretched out. Neurological examination revealed that the palpebral fissures and pupils were equal. Eye movements are full, painless. Convergence insufficiency was examined. Corneal reactions are reduced. Horizontal positioning nystagmus was examined. There are no pathological signs, no sensory disturbances. The patient performed coordination tests with uncertainty. The patient showed unsteadiness during Romberg's test. The patient felt pain during the palpation of paravertebral points. The patient experienced exaggerated changes in mood. Results. 1. Brain MRI results showed a thinning and a decrease in the MR signal on T2 from the cochlea of the inner ear to the left. CT scanning of the mastoid processes revealed an increased density of bone structures of the labyrinth nucleus on the left. 2. During the otoneurological examination, the asymmetry of vestibular responses along the labyrinth, slight stimulation of the left labyrinth were established. The patient was diagnosed with peripheral cochleovestibular syndrome on the left, Meniere's syndrome. Conclusions. This clinical case illustrates the importance of collecting a detailed medical history and examination of a patient with complaints of dizziness, hearing loss, tinnitus, and repeated vomiting. To establish a diagnosis and develop a treatment plan for a patient, the coordinated work of a multidisciplinary group is required, which should consist of a neurologist, audiologist, and otolaryngologist.

Single neuron activity and c-Fos expression in the rat striatum following electrical stimulation of the peripheral vestibular system.

Connections between the vestibular system and the basal ganglia have been postulated since the early 20th century. However, the results of electrophysiological studies investigating neuronal responses to electrical stimulation of the vestibular system have been inconsistent. The aim of this study was to investigate the effects of electrical stimulation of the vestibular labyrinth on single neuron activity and c‐Fos expression in the rat striatum. We used electrical stimulation of the vestibular labyrinth (various intensities delivered to the round window) to examine the electrophysiological response of striatal neurons and c‐Fos expression. From 507 single neurons recorded (n = 20 rats), no vestibular‐responsive neuron was found at 1× and 2× the nystagmus threshold; however, 6 neurons were found at 3× the threshold. These neurons were found bilaterally, with a response latency of ~50 msec from the end of the stimulus. For the c‐Fos study, the number of neurons expressing c‐Fos was quantified using stereological methods. Stimulation at 2× the threshold for nystagmus (n = 5 rats) resulted in a significant decrease in the number of neurons expressing c‐Fos in the bilateral striatum compared to both the sham control group (n = 5) and the lower stimulus intensity group (n = 5) (P ≤ 0.0001 for both). The results of this study demonstrate that: (1) some single striatal neurons respond to electrical vestibular stimulation, however, these responses are circumscribed and infrequent; (2) electrical stimulation of the vestibular labyrinth results in a decrease in the number of striatal neurons expressing c‐Fos, in a current‐dependent manner.

Effects of electrical stimulation of the rat vestibular labyrinth on c-Fos expression in the hippocampus

Several studies have demonstrated that electrical activation of the peripheral vestibular system can evoke field potential, multi-unit neuronal activity and acetylcholine release in the hippocampus (HPC). However, no study to date has employed the immediate early gene protein, c-Fos, to investigate the distribution of activation of cells in the HPC following electrical stimulation of the vestibular system. We found that vestibular stimulation increased the number of animals expressing c-Fos in the dorsal HPC compared to sham control rats (P ≤ 0.02), but not in the ventral HPC. c-Fos was also expressed in an increased number of animals in the dorsal dentate gyrus (DG) compared to sham control rats (P ≤ 0.0001), and to a lesser extent in the ventral DG (P ≤ 0.006). The results of this study show that activation of the vestibular system results in a differential increase in the expression of c-Fos across different regions of the HPC.

Evaluation of vestibulo-ocular reflex in patients with damage to the central nervous system (GCS score 5–3)

PurposeThe aim of our study was to evaluate the vestibulo-ocular reflex (VOR) in patients with severe damage to the central nervous system (CNS) in the diagnosis of brain death and survival prognosis. Material and methodsThe study was conducted in 20 patients with extensive primary central nervous system damage against spontaneous intracranial haemorrhage or craniocerebral trauma and secondary central nervous system damage as a result of cardiac arrest with Glasgow Coma Scale (GCS) score from 3 to 5 treated in the Intensive Care Unit, University Hospital in Bialystok. For labyrinth stimulation we used water at 30°C, recording the reactions with ENG appliance. Records were analyzed in Nathanson–Bergman four-level scale. The first assessment was performed on the second day after the trauma and subsequently the assessments were repeated at 2-day intervals. ResultsOf the 20 patients studied, the reflex was recorded in nine, which accounted for 45%. In the remaining 11 (55%) patients the reflex was not reported in any test and all of them died. Among patients with recorded VOR, five died and four survived. ConclusionsThe results of our study show the usefulness of performing the vestibulo-ocular test in patients with severe brain injury to predict their survival.

Body Balance Rehabilitation in Older Persons with Peripheral Chronic Vestibular Disease

Objectives: Evaluate the efficacy of a balance rehabilitation program in older persons with chronic vestibular disease. Methods: Prospective clinical trial conducted from September 2011 to December 2012. Setting: University center for balance disorders. Eligible patients (over 60 years old) with chronic vestibular disease underwent 12 to 16 sessions of individual body balance rehabilitation program (BRP). Each session lasted 60 minutes, twice per week, and was associated with diet orientation and daily exercises for labyrinth stimulation. Before and after therapy, the following data were collected: patient complaints, the Functional Gait Assessment, the Brazilian OARS Multidimensional Functional Assessment Questionnaire, the Dizziness Handicap Inventory (DHI) and static posturography parameters (limit of stability and balance functional reserve in ten visual, vestibular, and somatosensory conflicts). Results: Of 20 patients, 90.9% were female, with mean age of 71.70 years old. After BRP, there was reduction of most of symptoms (dizziness, imbalance and nausea), improvement in functional capacity ( P < 0.05), gait stability ( P = 0.003) and reduction in DHI scores ( P = 0.001). The limit of stability measure increased ( P = 0.001) and also the body balance functional reserve, mainly in conditions 2, 3 and 4 ( P = 0.001) and 5 ( P = 0.020). Conclusions: A body balance rehabilitation program was effective in reduction of symptoms, fall risk, and dizziness impact on quality of life in elderly patients with vestibular disorders, improving functional capacity, gait stability, and increasing the limit of stability and the balance functional reserve.

P6 Acupressure Effectiveness on Acute Vertiginous Patients: A Double Blind Randomized Study

The purpose of this study was to evaluate the effectiveness of P6 acupressure on vertigo and neurovegetative symptoms, its possible interference with vestibular-ocular reflex (VOR), and its clinical usefulness during acute vertigo. Two hundred and four patients, either affected by acute vertigo (n=124) or undergoing labyrinth stimulation (n=80), were randomly divided in two homogeneous groups: an experimental group A and a placebo group B. Each patient rated severity of vertigo and neurovegetative symptoms on a visuo-analogue scale ranging from 0 to 10, before and after bilateral placement of a P6 device. The latter was placed on the P6 acupressure point (appropriate placement) in Group A patients or on the dorsal part of the carpus (inappropriate placement) in the Group B patients. Furthermore, qualitative and quantitative nystagmus parameters were collected via recorded video-oculoscopy and electronystagmography. Eighty-five percent of Group A patients reported improvement of symptoms, which was significant for neurovegetative symptoms, but not for vertigo. In contrast, only 11% of the Group B patients reported improvement. VOR analysis did not show any significant variation of qualitative and quantitative nystagmus variables. This study demonstrated that the P6 device is effective in improving neurovegetative symptoms in patients affected by spontaneous and provoked vertigo, without any interference with VOR. Given the low cost and lack of side-effects of the P6 device, its routine application is suggested for acute vertigo and during labyrinth stimulation.

Focused ultrasound as a tool to input sensory information to humans (Review)

This review is devoted to the analysis of studies and implementations related to the use of focused ultrasound for functional effects on neuroreceptor structures. Special attention was paid to the stimulation of neuroreceptor structures in order to input sensory information to humans. This branch of medical and physiological acoustics appeared in Russia in the early 1970s and was being efficiently developed up to the late 1980s. Then, due to lack of financial support, only individual researchers remained at this field and, as a result, we have no full- fledged theoretical research and practical implementations in this area yet. Many promising possibilities of using functional effects of focused ultrasound in medicine and physiology have remained unimplemented for a long time. However, new interesting ideas and approaches have appeared in recent years. Very recently, very questionable projects have been reported related to the use of ultrasound for targeted functional effects on the human brain performed in some laboratories. In this review, the stages of the development of scientific research devoted to the functional effects of focused ultrasound are described. By activating the neuroreceptor structures of the skin by means pulses of focused ultrasound, one can cause all the sensations perceived by human beings through the skin in everyday life, such as tactile sensations, thermal (heat and cold), tickling, itching, and various types of pain. Stimulation of the ear labyrinth of humans with normal hearing using amplitude-modulated ultrasound causes auditory sensations corresponding to an audio modulating signal (pure tones, music, speech, etc.). Activation of neuroreceptor structures by means of focused ultrasound is used for the diagnosis of various neurological and skin diseases, as well as hearing disorders. It has been shown that the activation is related to the mechanical action of ultrasound, for example, by the radiation force, as well as to the direct action of ultrasonic vibrations on nerve fibers. The action of the radiation force is promising for the realization of the possibility of blind and even deaf-and-blind people to perceive text information on a display using tactile sensations caused by ultrasound. Very different methods of using ultrasound for local stimulation of neuroreceptor structures are discussed in this review. Among them are practical methods that have been already tested in a clinic, as well as pretending to be sensational methods that are hardly feasible in the foreseeable future.

P.2.d.026 Chronic administration of quetiapine increases norepinephrine and serotonin neurotransmission in the rat brain

Experiments performed in precollicular decerebrate cats have shown that dorsal pontine structures, including the LC and the related dorsal pRF, play an important role not only in the control of posture but also in the gain regulation of the VS reflexes. The LC neurons, which are not only noradrenergic but also NE-sensitive due to the existence of self-inhibitory synapses acting on a2-adrenoceptors, send inhibitory afferents to the dorsal pRF; on the other hand, these pontine reticular neurons, which are presumably cholinergic as well as cholinoceptive due to the existence of self-excitatory synapses, project excitatory afferents to the medullary inhibitory RS system. The increased discharge of these pontine reticular neurons and the related inhibitory RS neurons following local injection of cholinergic agonists into the dorsal pRF decreased the postural tonus in the ipsilateral limbs but greatly enhanced the amplitude of the EMG modulation and thus the response gain of ipsilateral limb extensors to labyrinth stimulation. This finding did not depend on the decreased postural activity, since it was still observed when the EMG activity was reflexly maintained by an increased static stretch of the muscle. Similar results were also obtained when the discharge of the pontine reticular neurons and the related inhibitory RS neurons was raised after local injection of an a2-adrenergic agonist into the LC, leading to functional inactivation of the noradrenergic LC neurons. On the other hand, an increased postural activity in the ipsilateral limbs as well as a reduced gain of the corresponding VS reflexes were obtained when the discharge of the pontine reticular neurons and the related inhibitory RS neurons was reduced, as shown after local injection of cholinergic agonists into the LC leading to activation of the noradrenergic neurons. There was also evidence that cholinergic excitatory afferents to the LC originated from the ipsilateral dorsal pRF. The effects described above were dose-dependent as well as site-specific, as shown by histological controls. In conclusion, the pontine structures described above operate as a variable-gain regulator acting at the motoneuronal level during the VS reflexes. Since the same structures are also responsible for the spontaneous fluctuations in posture related to the sleep waking cycle, they may well intervene as a control system in order to adapt to the animal state the response gain of limb extensors following labyrinth stimulation.

Origin of isolated vertigo in rotational vertebral artery syndrome

Rotational vertebral artery syndrome (RVAS) is characterized by recurrent attacks of paroxysmal vertigo, nystagmus, and ataxia induced by head rotation. Although recent report has described the RVAS as an important but unrecognized cause of isolated vascular vertigo, the locus of injury site responsible for isolated vertigo in RVAS is still unclear. We report here two patients with RVAS who had a stereotypic clinical presentation characterized by recurrent attacks of isolated vertigo induced by head rotation. The pattern of nystagmus observed in our patients with RVAS can be best explained by the stimulation of the vestibular labyrinth bilaterally or unilaterally. In RVAS, the isolated vertigo may occur due to transient ischemia of the superior vestibular labyrinth. RAVS should be considered in the differential diagnosis of positional vertigo, especially when vertigo is developed while sitting or standing position.

Vestibular evoked myogenic potential in vestibular neuritis

This study wants to show the diagnostic value of vestibular evoked myogenic potential (VEMP) in the diagnosis of vestibular neuritis (VN), independently of the caloric test results. Twenty patients were enrolled with acute vertigo caused by VN. VEMP was tested with the binaural simultaneous stimulation method. Surface electromyographic activity was recorded in the supine patients from symmetrical sites over the upper half of each sternocleidomastoid muscle, with a reference electrode on the lateral end of the upper sternum. During the acute attack, 8 days, 1 month and 3 months after the beginning of the acute attack, all the patients underwent the following examinations: Dix-Hallpike manoeuvre, Pagnini-McClure manoeuvre, head shaking test, pure-tone audiometry, tympanometry, caloric labyrinth stimulation according to the Fitzgerald-Hallpike method and VEMP. At the last visit, the 11 patients diagnosed with superior branch vestibular neuritis did not show any improvement at the caloric labyrinth stimulation and presented VEMP on both sides with normal amplitude and latency; in the 9 cases diagnosed with inferior branch vestibular neuritis, there was an improvement of the VEMP reflex and normal caloric test. Our experience highlights that VEMP recording is applicable for patients with VN as a screening test.

The conjugacy of the vestibulo-ocular reflex evoked by single labyrinth stimulation in awake monkeys

It is well known that the vestibulo-ocular reflex (VOR) is conjugate when measured in the dark with minimal vergence. But the neural basis of the VOR conjugacy remains to be identified. In the present study, we measured the VOR conjugacy during single labyrinth stimulation to examine whether the VOR conjugacy depends on reciprocal stimulation of the two labyrinths. There are conflicting views on this issue. First, since the vestibular signals carried by the ascending tract of Deiters' are distributed exclusively to the motoneurons of the ipsilateral eye, the neural innervations after single labyrinth stimulation are not symmetrical for the two eyes. Thus, single labyrinth stimulation may generate disjunctive VOR responses. Second, the only published study on this issue was an electrooculography (EOG) study that reported disjunctive VOR responses during unilateral caloric irrigation (Wolfe in Ann Otol 88:79-85, 1979). Third, the VOR during unilateral caloric stimulation performed in clinical vestibular tests is routinely perceived to be conjugate. To resolve these conflicting views, the present study examined the VOR conjugacy during single labyrinth stimulation by recording binocular eye position signals in awake monkeys with a search coil technique. In contradiction to the previous EOG study and the prediction based on the asymmetry of the unilateral brainstem VOR circuits, we found that the VOR during unilateral caloric irrigation was conjugate over a wide range of conditions. We conclude that the net neural innervations received by the two eyes are symmetrical after single labyrinth stimulation, despite the apparent asymmetry in the unilateral VOR pathways. A novel role for the ascending tract of Deiters' in the VOR conjugacy is proposed.

Tuning of human vestibulospinal reflexes by leg rotation

Changing the foot position modifies the mechanical action exerted by the ankle extensor and flexor muscles over the body. We verified, in two groups of healthy subjects standing with the heels touching or apart, whether a 90° external rotation of the right leg and foot also changes the pattern of vestibulospinal reflexes elicited by electrical stimulation of the labyrinth. With the head oriented forward, leg rotation did not modify the labyrinthine-driven displacements of the center of pressure (CoP). When the head was rotated in the horizontal plane, either to the right or to the left, the CoP displacement increased along the y axis in all subjects. Changes in the x component in most instances appropriate to preserve unmodified the direction of body sway elicited by the stimulus were observed. Right leg rotation increased the basal EMG activity of ankle extensors and flexors on the left side, while the right side activity was unaffected. The EMG responses to labyrinthine stimulation were modified only on the left side, in a way appropriate to correct the effects of the altered torque pattern exerted on the body by right leg muscles. It appears, therefore, that somatosensory signals related to leg rotation and/or copy of the corresponding voluntary motor commands modify the pattern of vestibulospinal reflexes and maintain the postural response appropriate to counteract a body sway in the direction inferred by labyrinthine signals.

Prediction of outcome in severe traumatic brain injury: Vestibulo-ocular monitoring as a novel tool

Dear Sir, Outcome prediction is a major part of the present-day management protocol for severe traumatic brain injury (sTBI). The introduction of vestibulo-ocular monitoring (VOM) using galvanic labyrinth polarization (GaLa) by Schlosser and his colleagues represents a novel method of assessing brainstem function and predicting outcome in sTBI. VOM is likely to replace oculo-cephalic and caloric tests in assessing brainstem function in the near future and may play an important role in the diagnosis of brain death. Prediction of outcome in sTBI is an integral part of the present-day management of TBI. It allows proper stratification of patients and allocation of scarce resources in the overall planning of care. As discussed by Schlosser and his colleagues,[1] the use of prediction tools such as the post-resuscitation Glasgow Coma Score(GCS), electroencephalogram (EEG), electrical potentials (EPs), cranial computed tomography (CT) findings, cerebral metabolism measured by, for example, microdialysis and infrared spectroscopy, among others, is usually attended by several limitations. The authors’ introduction of VOM using GaLa represents a novel method of assessing brainstem function and predicting outcome in sTBI. In their paper, the authors introduced VOM as a means of testing brainstem function. This is intended to complement the findings of brainstem imaging and thus should improve the prognostication of the long-term outcome in sTBI. They performed VOM through video-oculographic (VOG) recording of eye movements during GaLa stimulation of both labyrinths. The eye movement response is elicited via the vestibulo-ocular reflex arc (VOR), i.e. via the afferents from the peripheral neurons to the vestibular nuclei and, subsequently, to the oculomotor neurons. They performed the test in comatose sTBI patients within 3 days of injury while on intensive care unit (ICU) admission and recorded the oculomotor response (OMR) to stimulation of the labyrinths. In their study of 26 patients, GaLa induced OMR in 15 (57.7%) but not in 11 (42.3%) patients. All the patients in the latter group had an unfavorable Glasgow outcome score (GOS) of 1–2, with death in 10 (90.9%) of them within 15 days of trauma despite operative interventions in six of them. VOM is likely to replace oculo-cephalic and caloric tests in assessing brainstem function in the near future and may play an important role in the diagnosis of brain death. Its depression by muscle relaxants is a considerable limitation of its usefulness as it may preclude its application in many sTBI patients who are often given such agents to allow for adequate ventilation and optimization of metabolism in the early phase of ICU admission. Thus, it may be worthwhile to perform VOM later than the first 3 days after TBI used by the authors to increase its global usage. This will no doubt require an evaluation of its correlation with the eventual outcome when performed during this period. The authors’ stratification of patients into favorable outcome (GOS > 2) and unfavorable outcome (GOS < 3) is at variance with the established convention, in which the five outcome categories are collapsed into a dichotomous distinction between, on one hand “poor” or “unfavorable” outcome (dead, vegetative state or severe disability) and, on the other, an “independent” or “favorable” outcome (moderate disability or good recovery).[2] Proper stratification would have given a P-value of 0.004 and not the <0.001 stated by the authors. This, however, does not appear to undermine the predictive value of OMR between the two groups.

Transcranial Doppler ultrasound during galvanic labyrinth polarization depicts central vestibular processing, demonstrating bilateral vestibular projection

The combination of galvanic labyrinth polarization and transcranial Doppler ultrasound was employed to depict the neurovascular coupling in the cerebral vestibular areas. For galvanic stimulation, surface electrodes were attached to the right and left mastoid and two further electrodes were fixed near to each shoulder blade. Thus, each pair of electrodes (mastoid to shoulder) facilitated unilateral stimulation of the ipsilateral vestibular labyrinth. Blood flow in the middle cerebral artery and the internal carotid artery in both hemispheres was measured by means of Doppler ultrasound. The transcranial Doppler ultrasound system was head-fixed and allowed continuous monitoring of the blood flow throughout the trials. Using a series of different stimulation modes (bilateral, unilateral left, unilateral right and sham), the changes in mean blood flow velocity were evaluated by comparing baseline blood flow under resting conditions to blood flow during stimulation. A total of 18 trials were performed with each of seven volunteer subjects. Galvanic labyrinth polarization elicited a clear sensation of pendular body movement in all subjects. Significant blood flow increase (P < 0.05) in both hemispheres was observed during bilateral stimulation. Of more interest is that unilateral stimulation also elicited a significant increase in flow in both the ipsilateral and the contralateral hemispheres, demonstrating the existence of bilateral projections from each vestibular labyrinth. The combination of galvanic labyrinth polarization with transcranial Doppler ultrasound blood flow measurement provides a novel approach to the functional assessment of the vestibular system (deep cerebral structures and cortical areas). This novel technique provides a useful tool for clinical examinations.

Morphology of the mammalian vestibulo‐ocular reflex: The spatial arrangement of the human fetal semicircular canals and extraocular muscles

The vestibulo-ocular reflex is the system of compensatory ocular movements in response to stimulation of the kinetic labyrinth seen in all vertebrates. It allows maintenance of a stable gaze even when the head is moving. Perhaps the simplest influence on the VOR is the spatial orientation of the planes of the semicircular canals relative to the extraocular muscles. It is hypothesized that the extraocular muscles are in parallel alignment with their corresponding semicircular canals in order to reduce the amount of neural processing needed and hence keep reflex times to a minimum. However, despite its obvious importance, little is known of this spatial arrangement. Moreover, nothing is known about any ontogenetic changes in the relative orientations of the extraocular muscles and semicircular canals. The morphologies of fetal and adult specimens of Homo sapiens were examined using magnetic resonance (MR) images. Three-dimensional co-ordinate data were taken from the images and used to calculate vector equations of the extraocular muscles and planes of best fit for the semicircular canals. The relative orientations of the muscles and canals were then calculated from the vectors and planes. It was shown that there are significant correlations between both the anterior and lateral semicircular canals and their corresponding extraocular muscles during ontogeny. In the case of the lateral canal with the medial rectus, the lateral canal with the lateral rectus, and the anterior canal with the inferior oblique, the trend is towards, though never reaching, alignment, whereas the anterior canal and the superior rectus muscle move out of alignment as age increases. Furthermore, it was noted that none of the six muscle-canal pairs is in perfect alignment, either during ontogeny or in adulthood. It was also shown that the three semicircular canals are not precisely orthogonal, but that the anterior and posterior canals form an angle of about 85 degrees , while the anterior and lateral canals diverge by approximately 100 degrees . Overall, it was shown that there is significant reorientation of the extraocular muscles and semicircular canals during ontogeny, but that, in most cases, there is little realignment beyond the fetal period.

Electronystagmography finding in children with peripheral and central vestibular disorders

Dizziness and imbalance are uncommon in children, but often alarming for their families: a detailed interview and otoneurological examination are important for reaching a specific diagnosis and treatment. Children with vestibular disorders are thought to be difficult to examine: vestibular tests (caloric test, roto-acceleratory test, electronystagmography, opto-kinetic nystagmus, cranio-corpography and posturography) are used less frequently for children than in adult patients. The aim of the study was to determine whether the results of electronystagmography testing improve an emergency physician's diagnosis of dizziness in children. Patients were selected on the basis of the following inclusion criteria: aged between 2 and 12 years and affected with vertiginous symptoms. All patients underwent the following instrumental examinations: blood tests, audiological screening, electronystagmography of spontaneous nystagmus or provoked by vestibular and optical stimulation and electroencephalogram. The results underlines an high incidence of central vertigo (83%): 52% of the children presented a prevailing unidirectional nystagmus at labyrinth stimulation and 48% of the children an asymmetry in the response of nystagmus at optical kinetic stimulation with quality alteration of shocks. Electronystagmography can register and evaluate the qualitative and quantitative characteristics of the nystagmic response and allow to distinguish between central or peripheric vertigo: different degrees and various combinations of the abnormal responses shown in optokinetic central test were the most characteristic of electronystagmography in patients with vestibular central vertigo.

Electrical stimulation of labyrinths and vestibular reactions

Stimulation of the labyrinth in rabbits and guinea pigs with ascending (cathode) or descending direct current (anode) induced deviation and nystagmus of the eyes, head turn and tilt, and other reactions. Anodization of both labyrinths was followed by the disappearance of reflexes, suppression of vestibular reactions to adequate stimulation, and loss of swimming ability. The state of animals returned to normal after breaking the electric circuit.

Commissural Inputs to Secondary Vestibular Neurons in Alert Cats After Canal Plugs

Gaze is stabilized during head movements primarily by the vestibuloocular reflex (VOR). After a unilateral canal plug, the VOR's response is reduced. Recovery of the VOR may be brought about by changes in the efficacy of brain stem synapses or by other mechanisms. We measured the responses of horizontal secondary vestibular neurons (HSNs) to stimulation of the contralateral labyrinth. HSN responses in normal alert cats were compared with those in cats that had recovered from unilateral horizontal semicircular canal (HSCC) plugs. After recovery, excitatory commissural inputs to HSNs on the plugged side elicited significantly smaller responses than in normal cats with no change in mean discharge rates. However, mean discharge rates tended to be higher after recovery for cells receiving inhibitory commissural inputs. The change in resting rate invalidates any direct comparison of inhibitory inputs. These results are interpreted in terms of possible mechanisms for recovery from unilateral vestibular loss by the VOR neural network. We conclude that after unilateral HSCC plugs, changes in brain stem excitatory synapses and/or excitability of secondary vestibular neurons may participate in the restoration of normal vestibular reflexes.