A re-investigation of the role of utricular asymmetries in Space Motion Sickness

During the first days of spaceflight, about 50-70% of the astronauts experience symptoms of Space Motion Sickness (SMS). It has been proposed that an asymmetry between the left and right otolith organs contributes to an astronaut's individual susceptibility. A recently developed test to measure unilateral utricular function enabled us to re-investigate this so-called otolith asymmetry hypothesis, while using the paradigm of sustained centrifugation as a ground based model for SMS. This latter paradigm has been shown to elicit symptoms similar to those of SMS and is referred to as Sickness Induced by Centrifugation (SIC). In 15 healthy subjects unilateral utricular function was assessed by recording ocular counter rolling during a unilateral centrifugation paradigm. In addition, saccular function was assessed by recording Vestibular Evoked Myogenic Potentials (VEMPs), and horizontal semicircular canal function was assessed using bithermal caloric stimulation. SIC-susceptible subjects showed a marginally higher degree of utricular asymmetry, utricular sensitivity and semicircular canal sensitivity (p < 0.1) than the non-susceptible group. Interestingly, a logistic regression model using both utricular and semicircular canal parameters led to a correct classification of 91% of the subjects. As such, these results suggest that otolith asymmetry is at most one factor - and not present in all susceptible subjects - in defining susceptibility to SMS and SIC. Both the utricular and the canal system might be involved as well.     

Laser destruction of labyrinthine receptors as a treatment for benign paroxysmal postural vertigo and otolith symptoms

Outcomes of surgical laser treatment are presented for 15 patients with resistant to conservative therapy benign paroxysmal postural vertigo (BPPV) and otolith-related disorders. Nine patients with Meniere's disease with BPPV (n=3) and otoliths (in all the patients) were exposed to laser impulses on the bony wall of the horizontal semicircular canal. The impulse was directed in the lumen of the canal in 6 patients with BPPV and otolith symptoms. In Meniere's patients vertigo stopped, hearing was at the preoperative level. Neither threy had BPPV nor otolith problems. The same results were obtained in 6 patients with the other diseases. Vestibular excitability of all surgically treated patients decreased to the fifth degree.     

Vestibulo-ocular responses during static head roll and three-dimensional head impulses after vestibular neuritis

This study aimed to investigate whether unilateral vestibular neuritis (VN) causes the same deficits of ocular counter-roll during static head roll (OCR(S)) and dynamic vestibulo-ocular reflex gains during head impulses (VOR(HI)) as unilateral vestibular deafferentation (VD). Ten patients with acute and 14 patients with chronic vestibular paralysis after VN were examined. The testing battery included fundus photography of both eyes with the head upright (binocular cyclorotation) and dual search coil recordings in a three-field magnetic frame. With one dual search coil on the right eye and the other on the forehead, the following stimuli were given: i) Halmagyi-Curthoys head impulses about the vertical, horizontal and torsional axes. ii) Static roll positions of the head up to 20 degrees right- and left-ear-down by movement of the neck. The comparison group consisted of 19 healthy subjects. Compared with the VD-patients, as reported in the literature, acute VN-patients showed the same pattern of OCR(S) gain reduction and binocular cyclorotation (CRb). The main feature that distinguished chronic VN-patients from chronic VD-patients was the normalization of the torsional VOR(HI) gain to the affected side, whereas the VOR(HI) gains in the horizontal and vertical directions did not show recovery (as in the patients with chronic VD). Chronic VN-patients differed from acute VN-patients by: i) symmetrical OCR(S) gains, ii) a less pronounced CRb toward the affected side, and iii) a normal torsional VOR(HI) gain toward the affected side. Since the ipsilesional torsional VOR(HI) gain did not recover in VD-patients, the normalization of this gain in our VN-patients can only be explained by a (partial) recovery of otolith function on the side of the lesion after the neuritis.     

Adverse effect of the Epley maneuver: Anterior canal crisis

ObjectiveIn the Epley maneuver performed on patients with posterior semicircular canal-benign paroxysmal positional vertigo-canalolithiasis (P-BPPV-Can), an intense downbeat nystagmus and retropulsion rarely appear as soon as they reach the last upright sitting position. It is considered an anterior canal crisis that appears when the otoliths move to the ampullofugal direction in the anterior semicircular canal by changing head and body positions from the healthy-ear-down 135° head position (the third head position) to the upright sitting position (the fourth head position). This study aimed to determine the prevention of this anterior canal crisis.MethodsThe anterior canal crisis frequency was compared among the 178 cases that underwent general Epley maneuver (uncorrected Epley maneuver) and the 228 cases that underwent Epley maneuver (corrected Epley maneuver) by preventing head rotation beyond 135° to the healthy ear and the top of the head going down at the third head position.ResultsIn 6% of patients with P-BPPV-Can who underwent the Epley maneuver, a transient mixed downbeat and torsional nystagmus to the affected ear and retropulsion were observed at the fourth head position (anterior canal crisis). The corrected Epley maneuver significantly reduced the incidence of unpredictable anterior canal crisis (p = 0.017). Additionally, there was no difference in the effect of the Epley maneuver the next day regardless of the anterior canal crisis appearance.ConclusionAnterior canal crisis is an adverse effect of the Epley maneuver, and its prevention is important for safety. Avoiding head rotation beyond 135° to the healthy ear and/or the top of the head going down at the healthy-ear-down 135° head position is expected to reduce anterior canal crisis.     

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.     

Caloric nystagmus in three dimensions under otolithic control in rhesus monkeys. A preliminary report

The caloric nystagmus of rhesus monkeys in the 'optimum' supine or prone position was recorded three-dimensionally using magnetic search coils. The horizontal component of the nystagmus was in the direction expected from the convection flow theory of Bárány. The torsional component changed its direction according to the side of caloric stimulation independent of head position with regard to gravity, i.e., counterclockwise nystagmus by right ear stimulation and clockwise nystagmus by left ear stimulation both in the supine or in the prone positions. The direction of the vertical component depended upon the head position and not upon the side of stimulation, i.e., up-beating nystagmus in the supine position and down-beating nystagmus in the prone position. The durations and the contours of slow phase velocity of the horizontal, vertical and torsional components were different from each other. The origins of the first phase of caloric nystagmus in three dimensions may be explained by activation of all the three semicircular canals. As for the second phase of caloric nystagmus in the supine or in the prone position, the torsional component was comparatively strong and lasted the longest among the three components. The second phase of caloric nystagmus was markedly modified by head position with regard to gravity. These findings suggest that it is the otolithic organs that determine the moving plane of second phase caloric nystagmus.     

Three-dimensional analysis of caloric nystagmus in the rhesus monkey.

The aim of this study was to investigate whether caloric nystagmus contains response components that can be attributed to a stimulation of the vertical semicircular canals. Three dimensional eye movement recordings with a dual search coil technique revealed important horizontal, vertical and torsional nystagmus components following irrigation of the external ear canal with cold water in various head positions relative to gravity. Horizontal nystagmus components, i.e. lateral semicircular canal vectors, followed a cosine function of both the pitch and yaw angle of the head relative to gravity, confirming a mainly thermovective mechanism for stimulation of the horizontal canals. Vertical and torsional nystagmus components behaved differently following left and right ear irrigations. Right-left symmetrical vectors emerged only when the vertical and torsional components were transposed into vectors of single semicircular canal directions. The intensity of these vertical semicircular canal vectors as a function of the position of the corresponding canal relative to gravity, however, excludes important thermovective mechanisms acting at the vertical canals. It remains an open question whether these vertical canal vectors represent a non-thermovective caloric stimulation of vertical canal afferents.     

General remarks on the role of the vestibular system in weightlessness

Different methods are described to experimentally achieve weightlessness. Since the function of the otolith system depends on the presence of contact forces opposing gravity, it is disabled in weightlessness and may send misleading positional information to the brain. Without the contributions of the otolith system it is difficult in space to distinguish self-motion from object motion. Furthermore, the disintegration of information from the neck position receptors from those of the otolith system can lead to additional illusory positional sensations. Since the function of the semicircular canal system in previous space flights was found to be essentially undisturbed, the vestibular experiments in the Spacelab-D1 missions concentrated more on the otolith system. The function of other orientational cues from the visual system, the semicircular canal system and proprioception can be studied in isolation from the otolith system in space. In the Spacelab-D1 mission, the space vestibular sled was used as a device for studying linear acceleration. The vestibular helmet "permitted" video and EOG recordings of all eye movements and provided caloric and optokinetic stimulation. Various factors contributing to static and dynamic forms of space sickness are identified.     

Three-component analysis of caloric nystagmus in humans.

Three-component analysis of caloric nystagmus, focusing on the horizontal, vertical, and torsional, using a computerized eye movement analysis system, was carried out in 10 normal human subjects. The caloric response was induced by cold stimulation to the right ear of the subjects in the supine and prone positions. In the supine position, the three components of nystagmus were toward the left (10 subjects), upward (eight subjects) or downward (two subjects), and clockwise (10 subjects). In the prone position, on the other hand, the three components were directed toward the right (10 subjects), downward (five subjects), upward (three subjects), and counterclockwise (10 subjects); there was no vertical direction in two subjects. These findings indicate that caloric stimulation activates the three semicircular canals simultaneously. Also the changes in the nystagmus direction in the supine and prone positions could be explained, at least partially, by the nonconvective component of caloric stimulation.     

Persistent direction-changing geotropic positional nystagmus

The aims of the study were to clarify whether persistent direction-changing geotropic positional nystagmus contains vertical and torsional components, and to quantify the asymmetry. We analyzed nystagmus in four positions (healthy-ear-down, affected-ear-down, supine, nose-down) using three-dimensional video-oculography. Subjects were 18 patients with persistent direction-changing geotropic positional nystagmus, 16 females and 2 males, with a mean age of 55 years. Nystagmus was recorded using an infrared camera and the findings were converted to digital data. Using ImageJ, we performed three-dimensional video-oculography and measured maximum slow-phase velocity (MSV) of three components. Positional nystagmus was not purely horizontal. Eight (44%) patients revealed a vertical component (upward) and 15 (83%) patients had a torsional component in the healthy-ear-down position. Seven (39%) patients revealed a vertical component (downward) and 10 (56%) patients showed a torsional component in the nose-down position. The mean value of MSV of the horizontal component in the supine position was 9.3°/s and that in the nose-down position was 15.7°/s. The latter was significantly greater than the former (p < 0.05). Eye movements in the supine position and the nose-down position were not mirror images. These results suggest that vertical and torsional components occur from the horizontal semicircular canal, and that horizontal canal ocular reflex is influenced by input from the otolithic organs.     

The effect of gravity on the stability of human eye orientation

Objective: The stabilization of both the horizontal (H) and vertical (V) eye movements during voluntary fixation is believed to depend upon the visual feedback system in the upright position. However, ocular stability in the tilted position has been less well investigated. Therefore, in the present study, we examined the gaze stability of healthy human subjects in the three dimensions in the tilted position using a video image analysis system (VIAS). Methods: In 10 healthy human subjects, the eye movements were recorded after fixating the eye on a target in an upright position and also in the tilted position. The standard deviations of the eye movements in the three dimensions were calculated to evaluate the stability of the movements. Results: In the tilted position, there were no significant changes in the horizontal and vertical eye movements as compared those in the upright position. However, the standard deviation of the torsional (T) segment was significantly larger in the tilted position, compared to that in the upright position. Conclusion: From these results, we speculate that, a combination of otolith and somatosensory inputs play a major role in maintaining the stability of eye movements.     

Vestibulo-ocular reflex in eccentric rotation in squirrel monkeys.

In addition to angular acceleration, eccentric rotation (ECR) imparts linear acceleration to the head positioned eccentric to the axis of rotation. Using ECR in squirrel monkeys, the effects of otolith organ stimulation by linear acceleration on vestibulo-ocular reflex (VOR) gain were investigated. With the animal's head facing away from the rotation axis, ECR significantly enhanced VOR gain over that seen in centric rotation (CR) at 1.0 Hz, but not at 0.5 Hz. However, no enhancement of VOR gain at 1.0 Hz was observed in eccentriclateral rotation when the animal faced tangentially. After bilateral ablation of the otolith organs (sacculectomy and utricular neurectomy), the ECR did not increase VOR gain, even at 1.0 Hz. In animals in which the lateral and posterior semicircular canals were plugged bilaterally, horizontal sinusoidal eye movements were induced by ECR at 1.0 Hz; no clear compensatory eye movement occurred during CR at 1.0 Hz. These findings demonstrate that during ECR, tangential acceleration along the interaural axis stimulates the utricular maculae, inducing horizontal eye movements in addition to those induced by the semicircular canal, thus resulting in an enhancement of VOR gain. Our results also suggest synergistic interactions of the otolith organs and semicircular canals. We conclude that ECR is a useful clinical test of the function of the otolith organs.     

Three dimensional analysis of caloric nystagmus using computerized image recognition]

Three-component analysis of caloric nystagmus, focusing on horizontal, vertical, and torsional directions, using a newly developed computerized eye movement analysis system was carried out in ten normal human subjects. The caloric response was induced by cold stimulation to the right ear while the subjects were in supine and prone positions. The directions of the three components of nystagmus, were left in ten subjects (10), upward (8) or downward (2), and clockwise (10) in the supine position. In the prone position, on the other hand, the three components were directed toward the right (10), downward (5), upward (3), and counterclockwise (10) or were not present (2). These findings indicate that caloric stimulation activates the three semicircular canals simultaneously. In addition the changes in the direction of nystagmus in the supine and prone positions could not be explained in detail by the convection theory of caloric response alone.     

Positional and positioning down-beating nystagmus without central nervous system findings

We report the clinical features of 4 cases with positional or positioning down-beating nystagmus in a head-hanging or supine position without any obvious central nervous system disorder. The 4 cases had some findings in common. There were no abnormal findings on neurological tests or brain MRI. They did not have gaze nystagmus. Their nystagmus was observed only in a supine or head-hanging position and it was never observed upon returning to a sitting position and never reversed. The nystagmus had no or little torsional component, had latency and tended to decrease with time. The positional DBN (p-DBN) is known to be indicative of a central nervous system disorder. Recently there were some reports that canalithiasis of the anterior semicircular canal (ASC) causes p-DBN and that patients who have p-DBN without obvious CNS dysfunction are dealt with anterior semicircular canal (ASC) benign paroxysmal positional vertigo (BPPV). There are some doubts as to the validity of making a diagnosis of ASC-BPPV in a case of p-DBN without CNS findings. It is hard to determine the cause of p-DBN in these cases.     

An unusual complication of cochlear implant: benign paroxysmal positional vertigo

Three days after the initial fitting of the cochlear device a 40-year-old woman complained of severe rotational vertigo following head movements associated with neurovegetative symptoms. Otoneurological evaluation revealed a horizontal paroxysmal positional nystagmus beating towards the lowermost ear, induced by rolling the patient's head from supine both to the right or to the left lateral position suggesting the diagnosis of benign paroxysmal positional vertigo of the left horizontal semicircular canal. The nystagmus characteristics were the same whether the cochlear device was switched on or off. The hypothesis of an otolith dislodging due to the electrical stimulation during the initial fitting is discussed.     

Plasticity of the human otolith-ocular reflex.

The eye movement response to earth vertical axis rotation in the dark, a semicircular canal stimulus, can be altered by prior exposure to combined visual-vestibular stimuli. Such plasticity of the vestibulo-ocular reflex has not been described for earth horizontal axis rotation, a dynamic otolith stimulus. Twenty normal human subjects underwent one of two types of adaptation paradigms designed either to attenuate or enhance the gain of the semicircular canal-ocular reflex prior to undergoing otolith-ocular reflex testing with horizontal axis rotation. The adaptation paradigm paired a 0.2 Hz sinusoidal rotation about a vertical axis with a 0.2 Hz optokinetic stripe pattern that was deliberately mismatched in peak velocity. Pre- and post-adaptation horizontal axis rotations were at 60 degrees/s in the dark and produced a modulation in the slow component velocity of nystagmus having a frequency of 0.17 Hz due to putative stimulation of the otolith organs. Results showed that the magnitude of this modulation component response was altered in a manner similar to the alteration in semicircular canal-ocular responses. These results suggest that physiologic alteration of the vestibulo-ocular reflex using deliberately mismatched visual and semicircular canal stimuli induces changes in both canal-ocular and otolith-ocular responses. We postulate, therefore, that central nervous system pathways responsible for controlling the gains of canal-ocular and otolith-ocular reflexes are shared.     

视频头脉冲试验在眩晕疾病诊断中的应用研究

目的 探讨视频头脉冲试验(vHIT)评估周围性眩晕患者前庭眼反射(VOR)的临床价值.方法 选取2019年4月-2020年10月收治的52例良性阵发性位置性眩晕(BPPV)患者和57例前庭性神经炎(VN)患者为研究对象,并选取同期30名健康者作为对照.采用vHIT定量测定一对水平半规管平面、两对垂直半规管平面的VOR增...     

General remarks on the role of the vestibular system in weightlessness

Summary Different methods are described to experimentally achieve weightlessness. Since the function of the otolith system depends on the presence of contact forces opposing gravity, it is disabled in weightlessness and may send misleading positional information to the brain. Without the contributions of the otolith system it is difficult in space to distinguish self-motion from object motion. Furthermore, the disintegration of information from the neck position receptors from those of the otolith system can lead to additional illusory positional sensations. Since the function of the semicircular canal system in previous space flights was found to be essentialy undisturbed, the vestibular experiments in the Spacelab-D1 missions concentrated more on the otolith system. The function of other orientational cues from the visual system, the semicircular canal system and proprioception can be studied in isolation from the otolith system in space. In the Spacelab-D1 mission, the space vestibular sled was used as a device for studying linear acceleration. The vestibular helmet permitted video and EOG recordings of all eye movements and provided caloric and optokinetic stimulation. Various factors contributing to static and dynamic forms of space sickness are identified.Part of the Round Table Conference presented at the Collegium ORLAS, Munich, Federal Republic of Germany, 7–10 September 1986     

Semicircular Canal-Otolith Organ Interaction During Off-Vertical Axis Rotation in Humans

The aim of this study was to examine the interaction of signals from the semicircular canals and the otolith organs during off-vertical axis rotation (OVAR). We recorded horizontal eye position using electro-oculography in 22 young normal human subjects and stimulated the vestibulo-ocular reflex with both constant velocity trapezoids and sinusoidal yaw rotations, using both earth-vertical axis rotation (EVAR) and OVAR. We found that per-rotatory long vestibulo-ocular reflex (VOR) time constants during velocity trapezoids were shorter for OVAR than for EVAR, suggesting a reduction in the efficacy of the velocity storage system during OVAR. However, when we tested with very-low-frequency sinusoids (0.01 Hz and below), the phase lead of the VOR re head velocity was smaller during OVAR than EVAR, suggesting a longer time constant and enhanced efficacy of velocity storage during OVAR. These rotational responses can be explained by two competing influences of signals from the otolith organs, one that diminishes the effectiveness of velocity storage and another that contributes to an estimate of head velocity.     

The influence of caloric stimulation on the otolith organs in the cat

Summary The influence of caloric stimulation on the otolith organs was investigated in cats by recording the firing rate of the single vestibular nerve fiber originating from each otolith organ. Sixty-six percent of the vestibular nerve fibers originating from the otolith organs responded to the caloric stimulation. The caloric nystagmus occurred not only by the activities of the semicircular canal system but also by those of the otolith system. Offprint requests to: J. Tsuji