Visual suppression of vestibular nystagmus in rhesus monkeys

Eye Movement Research in the Twenty-First Century-a Window to the Brain, Mind, and More

The study of eye movements not only addresses debilitating neuro-ophthalmological problems but has become an essential tool of basic neuroscience research. Eye movements are a classic way to evaluate brain function-traditionally in disorders affecting the brainstem and cerebellum. Abnormalities of eye movements have localizing value and help narrow the differential diagnosis of complex neurological problems. More recently, using sophisticated behavioral paradigms, measurement of eye movements has also been applied to disorders of the thalamus, basal ganglia, and cerebral cortex. Moreover, in contemporary neuroscience, eye movements play a key role in understanding cognition, behavior, and disorders of the mind. Examples include applications to higher-level decision-making processes as in neuroeconomics and psychiatric and cognitive disorders such as schizophrenia and autism. Eye movements have become valued as objective biomarkers to monitor the natural progression of disease and the effects of therapies. As specific genetic defects are identified for many neurological disorders, ocular motor function often becomes the cornerstone of phenotypic classification and differential diagnosis. Here, we introduce other important applications of eye movement research, including understanding movement disorders affecting the head and limbs. We also emphasize the need to develop standardized test batteries for eye movements of all types including the vestibulo-ocular responses. The evaluation and treatment of patients with cerebellar ataxia are particularly amenable to such an approach.

A review on screening tests for vestibular disorders

Although many studies have reported on tests of the vestibular system a valid and reliable, evidence-based screening battery for easy clinical use remains elusive. Many screening tests attempt to assess the vestibulo-ocular reflex. Therefore, head shaking, the Dix-Hallpike maneuver, the supine roll test, and head impulse tests are discussed. Other tests address the spatial orientation functions of the vestibular system, such as the Bucket Test and the Fukuda Stepping test. Still, other tests are based on the known correlates with balance skills, both static and dynamic, such as tandem walking and the modern variation of the Romberg test, the modified Clinical Test of Sensory Interaction and Balance. This review provides a critical overview of the literature on some of these tests and their value for clinical use and in epidemiological studies.

Vestibular Function Impairment in Alzheimer's Disease

BACKGROUND

Falls and fractures due to impaired balance in patients with Alzheimer's disease (AD) have an adverse effect on the clinical course of the disease.

OBJECTIVE

To evaluate balance impairment in AD from the viewpoint of vestibular functional impairment.

METHODS

The subjects were 12 patients with AD, 12 dementia-free elderly adults, and 12 younger adults. Vestibular function was assessed using a stepping test, caloric nystagmus, and a visual suppression (VS) test.

RESULTS

The stepping test was abnormal in 9 of the 12 patients in the AD group. An abnormal stepping test was not associated with self-reported dizziness or tendency to fall. Significant VS abnormalities were present in the AD group. The suppression rate of VS was lower in AD patients with either a tendency to fall or constructional apraxia than in AD patients without either. The velocity of the rapid phase of caloric nystagmus before the VS test was similar in the AD group and the elderly control group. Significant abnormalities of both caloric nystagmus and VS were not present in either the elderly or the younger control groups.

CONCLUSION

AD could involve impairments in the vestibular control of balance. The VS test is useful for assessing the tendency to fall in AD. Impairment of VS in AD might arise from cerebral vestibular cortex impairment rather than comorbid peripheral vestibular disorders.

Clinical roles of fixation suppression failure in dizzy patients in the ENT clinic

Abstract Conclusion: Any test for visual fixation suppression by itself is insufficient for screening central pathology and should be interpreted in conjunction with other neurotologic findings.

OBJECTIVES

We evaluated the correlation of visual fixation suppression (VFS) under three different test conditions (spontaneous nystagmus, caloric stimulation, and slow harmonic acceleration, SHA), as well as the diagnostic accuracy of each test for predicting central pathology, in dizzy patients.

METHODS

We retrospectively reviewed cases in a tertiary referral center; 504 consecutive dizzy patients who visited the ENT clinic were enrolled. The fixation index (FI, slow component velocity during fixation/slow component velocity before fixation × 100%) for the caloric test and spontaneous nystagmus was calculated and failure was indicated when the FI was greater than 60%. VFS during the SHA test at a frequency of 0.04 Hz was also performed and gain more than 0.2 was considered as failure of VFS.

RESULTS

The incidence of VFS failure was 5.4% in the caloric test, 3.4% in spontaneous nystagmus, and 2.3% in the SHA test, respectively. Significant correlation was found only between the caloric test and the SHA test (r = 0.341, p < 0.001). The sensitivity of VFS in different tests did not exceed 35%. The specificity of VFS was highest (96.4%) in the 0.04 Hz SHA test, and exceeded 80% in the other tests.

Cupulolithiasis of the horizontal semicircular canal

To clarify whether positional nystagmus of horizontal cupulolithiasis 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 3-dimensional video-oculography. Subjects were 20 patients with direction-changing apogeotropic positional nystagmus, 11 females and 9 males, with a mean age of 58.1 years. Nystagmus was recorded using an infrared camera and the findings were converted to digital data. Using ImageJ, we performed 3-dimensional video-oculography and measured maximum slow-phase velocity (MSV) of three components. Positional nystagmus was not purely horizontal. Eleven (55%) patients revealed a vertical component, and 14 (70%) patients had a torsional component in the healthy-ear-down position. The mean value of MSV of the horizontal component in the healthy-ear-down position was 18°/s and that in the affected-ear-down position was 7.8°/s. For the horizontal component, MSV in the healthy-ear-down position was significantly greater than that in the affected-ear-down position (p < 0.01). These results suggest that vertical and torsional components occur from the horizontal semicircular canal, and the response to ampullopetal bending is more than two times as strong as that to ampullofugal bending.

A head-tilt caloric test for evaluating the vertical semicircular canal function

CONCLUSIONS

The caloric test with head-tilt can be used as a tool for assessing vertical canal function as an office procedure.

OBJECTIVE

Evaluation of vertical canal function.

PATIENTS AND METHODS

We provoked caloric response by cold water in the vertiginous patients in supine position. During the culmination of the response we rotated the head 45 degrees from the sagittal plane to place the posterior canal to earth-vertical. Thereafter we rotated the head 45 degrees to the opposite direction to place the anterior canal to earth-vertical. The eye movements were recorded by two-dimensional electronystagmography. The data collected from the examination of 100 ears with normal caloric response in horizontal component were analyzed.

RESULTS

The down-beating vertical component intensified when the posterior canal was placed to earth-vertical. The up-beating vertical component intensified when the anterior canal was placed to earth-vertical. These findings suggested that the vertical canals were functioning.

Clinical significance of vertical component of caloric response including its second phase in vertiginous patients

CONCLUSIONS

Up-beating vertical component recorded in the caloric first phase was attributed mainly to the inhibitory endolymph flow in the anterior canal. Down-beating vertical component recorded in the caloric second phase provoked by a positional change could be explained by a reversed endolymph flow in vertical canal(s).

OBJECTIVE

To investigate the origin of a vertical component in caloric response.

MATERIALS AND METHODS

We analyzed electronystagmography (ENG) of caloric responses, which had measurable horizontal component in the caloric first phase in both ears in 200 ears of 100 vertiginous patients. A caloric first phase was provoked by cold water in the supine position with the lateral semicircular canal earth-vertical. A caloric second phase was provoked by re-orienting the lateral canal from the earth-vertical to earth-horizontal after the cessation of the first phase (provoked second phase). The nystagmus of the whole procedure was recorded by two-dimensional ENG.

RESULTS

We recorded the vertical component in 103/200 ears in the caloric first phase, which was directed mostly upward (92/103 ears). We also recorded the vertical component in 91/200 ears in the provoked second phase, which was directed almost exclusively downward (90/91 ears).

Spatial orientation of caloric nystagmus in semicircular canal-plugged monkeys

We studied caloric nystagmus before and after plugging all six semicircular canals to determine whether velocity storage contributed to the spatial orientation of caloric nystagmus. Monkeys were stimulated unilaterally with cold ( approximately 20 degrees C) water while upright, supine, prone, right-side down, and left-side down. The decline in the slow phase velocity vector was determined over the last 37% of the nystagmus, at a time when the response was largely due to activation of velocity storage. Before plugging, yaw components varied with the convective flow of endolymph in the lateral canals in all head orientations. Plugging blocked endolymph flow, eliminating convection currents. Despite this, caloric nystagmus was readily elicited, but the horizontal component was always toward the stimulated (ipsilateral) side, regardless of head position relative to gravity. When upright, the slow phase velocity vector was close to the yaw and spatial vertical axes. Roll components became stronger in supine and prone positions, and vertical components were enhanced in side down positions. In each case, this brought the velocity vectors toward alignment with the spatial vertical. Consistent with principles governing the orientation of velocity storage, when the yaw component of the velocity vector was positive, the cross-coupled pitch or roll components brought the vector upward in space. Conversely, when yaw eye velocity vector was downward in the head coordinate frame, i.e., negative, pitch and roll were downward in space. The data could not be modeled simply by a reduction in activity in the ipsilateral vestibular nerve, which would direct the velocity vector along the roll direction. Since there is no cross coupling from roll to yaw, velocity storage alone could not rotate the vector to fit the data. We postulated, therefore, that cooling had caused contraction of the endolymph in the plugged canals. This contraction would deflect the cupula toward the plug, simulating ampullofugal flow of endolymph. Inhibition and excitation induced by such cupula deflection fit the data well in the upright position but not in lateral or prone/supine conditions. Data fits in these positions required the addition of a spatially orientated, velocity storage component. We conclude, therefore, that three factors produce cold caloric nystagmus after canal plugging: inhibition of activity in ampullary nerves, contraction of endolymph in the stimulated canals, and orientation of eye velocity to gravity through velocity storage. Although the response to convection currents dominates the normal response to caloric stimulation, velocity storage probably also contributes to the orientation of eye velocity.

Quantitative changes in mRNA expression of glutamate receptors in the rat peripheral and central vestibular systems following hypergravity

In order to investigate the mechanisms responsible for adaptation to altered gravity, we assessed the changes in mRNA expression of glutamate receptors in vestibular ganglion cells, medial vestibular nucleus, spinal vestibular nucleus/lateral vestibular nucleus, cerebellar flocculus, and uvula/nodulus from rats exposed to hypergravity for 2 h to 1 week using real-time quantitative RT-PCR methods. The mRNA expression of GluR2 and NR1 receptors in the uvula/nodulus and NR1 receptors in the medial vestibular nucleus increased in animals exposed to 2 h of hypergravity, and it decreased gradually to the control level. The mRNA expression of GluR2 receptors in vestibular ganglion cells decreased in animals exposed to 1 week of hypergravity. Neither the metabotropic glutamate receptor 1 nor delta2 glutamate receptor in flocculus and uvula/nodulus was affected by a hypergravity load for 2 h to 1 week. It is suggested that the animals adapted to the hypergravity by enhancing the cerebellar inhibition of the vestibular nucleus neurons through activation of the NR1 and GluR2 receptors on the Purkinje cells in uvula/nodulus especially at the early phase following hypergravity. In the later phase following hypergravity, the animals adapted to the hypergravity by reducing the neurotransmission between the vestibular hair cells and the primary vestibular neurons via down-regulation of the postsynaptic GluR2 receptors in the vestibular periphery.

Spatial orientation of caloric nystagmus

The spatial orientation of the slow-phase eye velocity of caloric nystagmus was investigated in cynomolgus monkeys after all six semicircular canals had been plugged. Normal animals generate responses that have dominant convective components produced by movement of the endolymph in the lateral canal toward or away from gravity. As a result, the direction of horizontal slow-phase velocity induced by cold-water irrigation changes direction with changes in head position with regard to gravity. Plugging produced a dense overgrowth of bone that blocked the flow of endolymph, but the end organs were intact. Robust caloric nystagmus was elicited after recovery, but the horizontal (yaw) component was now always toward the stimulated (ipsilateral) side, regardless of head position re gravity. The induced caloric nystagmus had strong spatial orientation properties after canal plugging. With animals upright, the three-dimensional velocity vector of the caloric nystagmus was close to the yaw axis with small vertical and roll components. Roll components became stronger in supine and prone positions and vertical components were enhanced in the right- and left-side down positions. In each instance, the addition of the roll and vertical components moved the velocity vector of the nystagmus closer to the spatial vertical. Modeling supported the postulate that the caloric nystagmus after canal plugging is influenced by three factors: (1) a reduction in neural activity in the ampullary nerves on the stimulated side due to cooling of the nerves; (2) contraction of the endolymph in the closed space between the cupula and the plug due to cooling, which resulted in deflection of the cupula and hair cells toward the plug (ampullofugal deflection); and (3) alignment of eye velocity to gravity due to the orientation properties of velocity storage. Although convection is the most prominent factor in producing caloric responses in the normal state, our results suggest that alteration of nerve activity due to thermal effects, endolymph contraction or expansion, and velocity storage are also likely to contribute to the total response.

Electronystagmographic findings in patients with cerebral degenerative disease

Cerebral degenerative diseases produce a variety of abnormal neuro-otological findings on electronystamography (ENG). To assess their diagnostic value and determine which manifestations are helpful in making a diagnosis, ENG findings from 72 cases of confirmed cerebral degenerative disease were analyzed. We observed a high incidence of saccadic pursuit and upward ocular dysmetria, which is likely to be useful in diagnosing cerebral degenerative disease. In contrast, moderate incidences of horizontal ocular dysmetria, gaze-evoked and rebound nystagmus, vertical positioning nystagmus and impaired visual suppression appeared to reflect the degree of dysfunction, while optokinetic nystagmus appeared to reflect both the presence of disease and its severity. Cases of spinocerebellar ataxia 6 and spinocerebellar ataxia 3 tended to produce horizontal and vertical gaze-evoked nystagmus, whereas progressive supranuclear palsy produced a higher incidence of upward gaze-evoked nystagmus, and positioning nystagmus at the sagittal plane appeared frequently in cases of non-hereditary spinocerebellar degeneration.

Control and modulation of canal driven vestibulo-ocular reflex

It has been well known that the canal driven vestibulo-ocular reflex (VOR) is controlled and modulated through the central nervous system by external sensory information (e.g. visual, otolithic and somatosensory inputs) and by mental conditions. Because the origin of retinal image motion exists both in the subjects (eye, head and body motions) and in the external world (object motion), the head motion should be canceled and/or the object should be followed by smooth eye movements. Human has developed a lot of central nervous mechanisms for smooth eye movements (e.g. VOR, optokinetic reflex and smooth pursuit eye movements). These mechanisms are thought to work for the purpose of better seeing. Distinct mechanism will work in appropriate self motion and/or object motion. As the results, whole mechanisms are controlled in a purpose-directed manner. This can be achieved by a self-organizing holistic system. Holistic system is very useful for understanding human oculomotor behavior.

Slow eye movements

Monkeys and humans are able to perform different types of slow eye movements. The analysis of the eye movement parameters, as well as the investigation of the neuronal activity underlying the execution of slow eye movements, offer an excellent opportunity to study higher brain functions such as motion processing, sensorimotor integration, and predictive mechanisms as well as neuronal plasticity and motor learning. As an example, since there exists a tight connection between the execution of slow eye movements and the processing of any kind of motion, these eye movements can be used as a biological, behavioural probe for the neuronal processing of motion. Global visual motion elicits optokinetic nystagmus, acting as a visual gaze stabilization system. The underlying neuronal substrate consists mainly of the cortico-pretecto-olivo-cerebellar pathway. Additionally, another gaze stabilization system depends on the vestibular input known as the vestibulo-ocular reflex. The interactions between the visual and vestibular stabilization system are essential to fulfil the plasticity of the vestibulo-ocular reflex representing a simple form of learning. Local visual motion is a necessary prerequisite for the execution of smooth pursuit eye movements which depend on the cortico-pontino-cerebellar pathway. In the wake of saccades, short-latency eye movements can be elicited by brief movements of the visual scene. Finally, eye movements directed to objects in different planes of depth consist of slow movements also. Although there is some overlap in the neuronal substrates underlying these different types of slow eye movements, there are brain areas whose activity can be associated exclusively with the execution of a special type of slow eye movement.

Projections of the lateral terminal accessory optic nucleus of the common marmoset (Callithrix jacchus)

The connections of the lateral terminal nucleus (LTN) of the accessory optic system (AOS) of the marmoset monkey were studied with anterograde 3H-amino acid light autoradiography and horseradish peroxidase retrograde labeling techniques. Results show a first and largest LTN projection to the pretectal and AOS nuclei including the ipsilateral nucleus of the optic tract, dorsal terminal nucleus, and interstitial nucleus of the superior fasciculus (posterior fibers); smaller contralateral projections are to the olivary pretectal nucleus, dorsal terminal nucleus, and LTN. A second, major bundle produces moderate-to-heavy labeling in all ipsilateral, accessory oculomotor nuclei (nucleus of posterior commissure, interstitial nucleus of Cajal, nucleus of Darkschewitsch) and nucleus of Bechterew; some of the fibers are distributed above the caudal oculomotor complex within the supraoculomotor periaqueductal gray. A third projection is ipsilateral to the pontine and mesencephalic reticular formations, nucleus reticularis tegmenti pontis and basilar pontine complex (dorsolateral nucleus only), dorsal parts of the medial terminal accessory optic nucleus, ventral tegmental area of Tsai, and rostral interstitial nucleus of the medial longitudinal fasciculus. Lastly, there are two long descending bundles: (1) one travels within the medial longitudinal fasciculus to terminate in the dorsal cap (ipsilateral >> contralateral) and medial accessory olive (ipsilateral only) of the inferior olivary complex. (2) The second soon splits, sending axons within the ipsilateral and contralateral brachium conjunctivum and is distributed to the superior and medial vestibular nuclei. The present findings are in general agreement with the documented connections of LTN with brainstem oculomotor centers in other species. In addition, there are unique connections in marmoset monkey that may have developed to serve the more complex oculomotor behavior of nonhuman primates.

Use of the visual suppression test using post-rotatory nystagmus to determine skill in ballet dancers

Twelve ballet dancers with various levels of dancing experience and skill were examined with the visual suppression test using post-rotatory nystagmus (PRVST) and caloric stimulation (CVST). The PRVST results showed a suppression rate that was higher than in untrained subjects. The CVST results showed a suppression rate similar to that in untrained subjects. A correlation between the PRVST and CVST suppression rates and the length of dancing experience showed that the suppression rate increased as the level of experience and skill rose. These results indicate that the PRVST and CVST can aid in the clinical and quantitative assessment of the function of the central nervous system in visual-vestibular interactions in ballet dancers. Additionally, testing may have determined function of vestibulo-cerebellar pathways through habituation of visual-vestibular interactions. Findings indicate that it may be possible to use suppression rates of PRVST and CVST to determine the approximate level of a dancer's experience and skill.

[Automatic analysis by computer of the visual suppression test of pendular rotatory vestibular nystagmus]

This study presents an automatic computerized analysis of the visual suppression test of vestibular nystagmus. Visual suppression is measured during rotatory nystagmus examination. The amplitude variations and the frequency of the nystagmus are computed in the dark and in the light. This allows the computer to furnish with the help of an algorithm the percentage of nystagmus suppressed by ocular fixation. The results of the computerized analysis are compared to a qualitative evaluation. A percentage of 70% and more indicates a normal suppression reflex and corresponds qualitatively to a total or subtotal visual suppression. A percentage smaller than 70% indicates a pathological reflex corresponding qualitatively to a partial, weak or absent visual suppression. The study is based on 149 examinations realised in 12 healthy subjects and 137 patients. The patients are classified into 4 groups: a) 59 patients with peripheral vestibular lesions (Ménière's diseases 21, vestibular neuronitis 15, cupulolithiasis 16, ototoxicity 7), b) 67 patients with central lesions of the cerebellum and the brainstem (multiple sclerosis 23, infratentorial tumors 14, vascular brainstem lesions 14, degenerative diseases of the central nervous system 16), c) 6 patients with supratentorial central lesions (hemispheric vascular lesions 4, supratentorial tumors 2), d) 5 patients with congenital nystagmus. All healthy subjects and all patients with peripheral vestibular lesions have a total or subtotal visual suppression corresponding to computed rates greater than 70% (mean: 86.7% and 83.1%). In cerebellar and brainstem lesions about half the patients (56.8%) present a partial, weak or absent visual suppression corresponding to computed rates inferior to 70% (mean: 52.7%). In supratentorial disorders the visual suppression is total or subtotal with computed rates superior to 70% (mean: 79.2%). By patients with congenital nystagmus the visual suppression is uniformly pathological with computed rates inferior to 70% (mean: 19.2%). The results of the visual suppression test are concordant with those of smooth pursuit in 92.6% of cases and with those of optokinetic nystagmus in 89.3% of cases. This study confirms that the visual suppression test is a useful examination to detect disorders of the cerebellum and brainstem.

A visual suppression test using post-rotatory nystagmus

The visual suppression test is one method for examining the function of visual fixation and visual influence on vestibular nystagmus. In this study the visual suppression test using post-rotatory nystagmus was investigated in 65 normal subjects and 142 clinical cases with cerebellar lesions. In 65 normal subjects the mean +/- standard deviation of visual suppression of the slow phase velocity on post-rotatory nystagmus was 69 +/- 11%. As to the stimulation for visual suppression test, the post-rotatory method using rotatory stimulation is milder than caloric stimulation. This method is far simpler to analyze than the visual suppression test using pendular rotatory nystagmus and other vestibulo-ocular reflex tests. In the 142 patients with cerebellar lesions, reduced or abolished visual suppression on post-rotatory nystagmus was seen in 89 patients with radiologically confirmed disturbances in the vestibulo-cerebellum. And this method could identify the lesion side in the cerebellum. These results showed a correlation between the visual suppression test using post-rotatory nystagmus and one using caloric nystagmus in 65 normal subjects and 142 clinical cases with cerebellar lesions.

Visual suppression test using post-rotatory nystagmus. Clinical course in patients with motion sickness

With the results of VS test (%) we were able to classify patients into three groups as follows: Group I, hyper range of visual suppression, VS (%) = 100-90; Group II, normal range of VS (%) = 89-45; Group III, reduced or abolished range of VS (%) = less than 44. The results with VS test using post-rotatory nystagmus (PRN) were in Group I 58 cases, in Group II 28 cases and in Group III 1 case, and using caloric nystagmus (CN) the results in Group I were 39 cases, Group II 29 cases, and Group III 1 case. With the correlation of VS test between PRN and CN we were able to classify patients into four types as follows: Type I, hyper range of VS in both PRN and CN; Type II, hyper range of VS in PRN; however, normal range of VS in CN; Type III, normal range of VS in both PRN and CN; Type IV reduced or abolished range of VS in both PRN and CN. It was very interesting in the clinical course of motion sickness that patients under 11 years of age (18 cases) of Type I (31 cases) showed marked improvement to Type III (11 cases) at the time of disappearance of symptoms; however, patients over 12 years of age (13 cases) of Type I remained stationary Type I (9 cases) at the time of disappearance of symptoms.

The effects of gravitoinertial force level and head movements on post-rotational nystagmus and illusory after-rotation

The effect of Coriolis, cross-coupled stimulation on the vestibuloocular reflex and the elicitation of motion sickness depends on background gravitoinertial force level (DiZio et al. 1986, 1987; Graybiel et al. 1977; Lackner and Graybiel 1984, 1986). We have explored whether this response dependency is related to the unusual patterns of sensorimotor activity present during exposure to non-terrestrial gravitoinertial force levels, to alterations in the encoding of head movements in different gravitoinertial force environments, or to some combination thereof. Blindfolded subjects were exposed to sudden stops after constant velocity, vertical z-axis rotation, sometimes with and sometimes without post-rotational head movements, in the 0 G, 1 G, and 1.8 G force phases of parabolic flight. After sudden stops without head movements, the time constant of decay of post-rotational nystagmus was significantly lower in 0 G than in 1 G and lower to a smaller extent in 1.8 G. Post-rotational head movements decreased the decay time constants in 1 G and in 1.8 G, but not in free fall. The same pattern emerged for the duration of illusory after-rotation. Systematic changes were not found in the peak slow phase velocity of nystagmus. These results suggest that tonic levels of otolithic and somatosensory activity in combination with canalicular, cervical, and motor activity regulate the velocity storage mechanism of the horizontal vestibuloocular reflex (Cohen et al. 1977; Raphan et al. 1979) and sensations of after-rotation. These same factors are likely to be important etiological elements in space motion sickness.

Effects of flunarizine on induced nystagmus and cochlear blood flow

The effects of flunarizine on induced nystagmus and cochlear blood flow were compared with those of cinnarizine and diphenidol. Flunarizine significantly inhibited caloric (cool water)-induced nystagmus frequency and duration of nystagmus in rabbits at 5 mg/kg i.v., whereas cinnarizine and diphenidol only slightly decreased the frequency of nystagmus at 5 mg/kg, i.v. As for optokinetic stimuli-induced nystagmus in rabbits, flunarizine significantly decreased the amplitude of nystagmus at 2.5 mg/kg i.v., and cinnarizine and diphenidol inhibited nystagmus at 5 mg/kg, i.v. Flunarizine had no effect on nystagmus induced by electrical stimulation of the lateral geniculate body in rabbits at doses up to 5 mg/kg, i.v. Flunarizine increased the cochlear blood flow in anesthetized guinea pigs dose-dependently (0.312-1.25 mg/kg i.v.) On the other hand, cinnarizine (0.625-2.5 mg/kg i.v.) and diphenidol (0.625-2.5 mg/kg i.v.) increased cochlear blood flow, but the duration of action of both cinnarizine and diphenidol was shorter than that of flunarizine at the same dose. As stated above, flunarizine inhibited nystagmus experimentally induced by caloric or optokinetic stimuli. Increased cochlear blood flow suggested that the enhancement of vestibular blood flow might play an important role in the treatment of vestibular dysfunctions with this drug.

Responses of Purkinje cells and mossy fibres in the flocculus of the monkey during sinusoidal movements of a visual pattern

1. Discharges of Purkinje cells (P cells) and mossy fibres were recorded from the cerebellar flocculus of monkeys trained to fixate a stationary visual target. The units were tested with a sinusoidally moving random dot pattern (background) which was projected on an entire screen or on part of it. The receptive field organization of the units was tested by changing the area of stimulus presentation on the screen and by changing the direction of visual fixation. 2. When stimulated with sinusoidal movements of the background in the horizontal plane, ninety-two of 684 Purkinje cells (13.5%) responded to the retinal-slip velocity. Seventy-eight of the ninety-two visually responsive Purkinje cells (84.8%) also showed cyclic modulations in activity during horizontal smooth-pursuit eye movements (these were so-called horizontal gaze-velocity Purkinje cells). 3. In response to the sinusoidal retinal-slip velocity, the visual Purkinje cells showed six types of discharge patterns. Type 1 Purkinje cells (28/92 or 30.4%) were directionally selective: they showed a peak activity during background movement in one direction and a trough in the other. Both peaks and troughs were related to stimulus velocities. Their receptive fields were relatively large (greater than 45 deg) and included the fovea. 4. Type 2 (8/92 or 8.7%) and type 3 (5/92 or 5.4%) Purkinje cells showed sinusoidal responses similar to those of type 1 Purkinje cells, but the visual inputs were primarily excitatory in type 2 Purkinje cells and inhibitory in type 3 Purkinje cells. Only the peaks in type 2 and troughs in type 3 were related to stimulus velocities. 5. Type 4 (4/92 or 4.3%) and type 5 (11/92 or 12.0%) Purkinje cells showed responses to stimulus movements in both directions (bidirectional). When the moving background was projected with 10 deg of fixation, type 4 Purkinje cells were excited bidirectionally in relation to retinal-slip velocities. When the periphery of either hemiretina was stimulated, type 5 Purkinje cells were inhibited and the trough activity was stimulus-velocity dependent. Receptive fields were found in the ipsilateral hemiretinae in seven type 5 Purkinje cells and in the contralateral hemiretinae in the remaining four type 5 Purkinje cells. 6. Type 6 (36/92 or 39.1% Purkinje cells received an excitatory input from the central retina and an inhibitory input from the periphery. The peripheral receptive fields were either in the ipsilateral (69.4%) or contralateral (30.6%) hemiretinae of both eyes.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of the cerebellum in the visual guidance of movement

Mathematicians, control engineers and information technologists are beginning to take a greater interest in neuroscience. They are perhaps starting to realize that they may be able to learn a few tricks from nature with which to improve their machines. At the same time there is a good chance that neuroscientists will benefit from their input of fresh ideas and techniques with which to attack the problems of understanding neural processing. One area of the brain which seems particularly promising in these respects is the cerebellum.

Discharges of Purkinje cells in monkey's flocculus during smooth-pursuit eye movements and visual stimulus movements

Modulations in discharges of Purkinje cells (P cells) associated with movements of visual patterns were studied in the flocculus of monkeys trained to execute smooth-pursuit eye movements and to suppress optokinetic nystagmus. One class of P cells responded to the movements of visual stimulus regardless of whether the eyes remained stationary (produced retinal-slip velocity) or moved with the stimulus produced eye velocity). These P cells processed high-order information concerning the absolute velocity of stimulus movements and thereby the eye velocity had already been incorporated in the visual responses (visuomotor P cells). The other class of P cells responded to visual inputs resulting from the retinal slip (visual P cells). The majority of visual P cells (82%) also modulated their activities during smooth pursuit. When sinusoidal trackings were executed against a stationary visual background, various types of interactions occurred in the P-cell responses between the converging visual and oculomotor inputs. The type of interaction was related to the preferred direction for the P cell during eye movements and the side of the peripheral receptive field.

The influence of physostigmine on visual-vestibular interaction in hereditary ataxias

Visual suppression of caloric nystagmus was studied in five patients with hereditary ataxia before and after administration of physostigmine. All patients had an initial abnormal ocular fixation index that improved after physostigmine was given. The data indicate that there is a partly reversible disturbance of visual-vestibular interaction in patients with hereditary ataxia, caused by an impairment of a central cholinergic mechanism.

Aqueductal stenosis--results of vestibular function tests

A case of aqueductal stenosis is reported. The patient was a 14-year-old Japanese girl who was suffering from bilateral tinnitus and unsteadiness of gait. A series of neuro-otological tests revealed prolonged acoustically evoked brain stem response (ABR) latency, disturbed standing reflex, inhibited optokinetic nystagmus (OKN) and ataxic eye tracking test (ETT). Marked distension of the lateral and third ventricles was noticed on CT examination of the brain. A positive contrast ventriculogram using iotalamic acid showed occlusion of the cerebral (Sylvian) aqueduct. All of these results are suggestive of benign, non-neoplastic aqueductal stenosis with associated hydrocephalus. The patient underwent ventriculo-peritoneal shunt and, following the surgery, the results of neuro-otological, including radiological, re-examination indicated a remarkable recovery.

Pretectal and brain stem projections of the medial terminal nucleus of the accessory optic system of the rabbit and rat as studied by anterograde and retrograde neuronal tracing methods

The projections of the medial terminal nucleus (MTN) of the accessory optic system have been studied in the rabbit and rat following injection of 3H-leucine or 3H-leucine/3H-proline into the MTN and the charting of the course and terminal distribution of the MTN efferents. The projections of the MTN, as demonstrated autoradiographically, have been confirmed in retrograde transport studies in which horseradish peroxidase (HRP) has been injected into nuclei shown in the autoradiographic series to contain fields of terminal axons. The following projections of the MTN have been identified in the rabbit and rat. The largest projection is to the ipsilateral nucleus of the optic tract and dorsal terminal nucleus (DTN) of the accessory optic system. Labeled axons course through the midbrain reticular formation and the superior fasiculus, posterior fibers of the accessory optic system, to reach the nucleus of the optic tract and the DTN in both rabbit and rat. Axons also run forward to traverse the lateral thalamus and to distribute to rostral portions of the nucleus of the optic tract in rat only. A second, large projection is to the contralateral dorsolateral portion of the nucleus parabrachialis pigmentosus of the ventral tegmental area together with an adjacent segment of the midbrain reticular formation. The patchy terminal field observed has been named the visual tegmental relay zone (VTRZ). This fiber projection courses within the posterior commissure and along its path to the VTRZ, provides terminals to the interstitial nucleus of Cajal and the nucleus of Darkschewitsch, both bilaterally. A third, large MTN projection distributes ipsilaterally to the deep mesencephalic nucleus, pars medialis, and the oral pontine reticular formation. Further, this projection also supplies input to the medial nucleus of the periaqueductal gray matter, bilaterally in the rabbit and rat, and in the rabbit also to the ipsilateral superior and lateral vestibular nuclei. A fourth projection crosses the midline and courses caudally to reach, contralaterally, the dorsolateral division of the basilar pontine complex and the above nuclei of the vestibular complex. A fifth projection of the MTN utilizes the medial longitudinal fasciiculus to reach the rostral medulla, in which its axons distribute ispilaterally to the dorsal cap, its ventrolateral outgrowth, and the beta nucleus of the inferior olivary complex. There is also a contralateral contingent of this projection that leaves the medial longitudinal fasciculus to innervate a small rostral segment of the contralateral dorsal cap.(ABSTRACT TRUNCATED AT 400 WORDS)

Visual suppression test and ocular dysmetria: some electronystagmographic findings relevant to the assessment of size of cerebellopontine angle tumors

Patients with cerebellopontine angle tumors underwent vestibular examination, testing of voluntary fast and slow conjugate eye movements and of visual-vestibular interaction (visual suppression test--VST) by electronystagmography (ENG). Both spontaneous and evoked nystagmus (Ny) and dysmetric alterations of the voluntary conjugate eye movements are relevant to cerebellopontine pathology. This study shows that ENG may reveal damage to the vestibular brain-stem and archicerebellar structures, the ENG signs of which very often precede the clinical signs of compression. In cranial nerve VIII neuromas vestibular and oculomotor instrumental investigations yield valuable clues for early diagnosis of tumor transition from the otological to the neurosurgical stage.

Vestibulo-ocular reflex, optokinetic response and their interactions in the cerebellectomized cat

The effects of total ablation of the cerebellum on eye movements were studied in alert adult cats. The normal cat could easily hold a steady eye position after a saccadic movement in the dark. The cerebellectomized animal could not: after a saccade the eye position shifted towards a more central position. Vision reduced this 'post-saccadic drift'. The sinusoidal vestibulo-ocular reflex (v.o.r.) was strongly affected by total cerebellectomy. In darkness the v.o.r. gain remained stable at high frequencies (0.5 and 1 Hz) but decreased markedly at lower frequencies to as low as 0.18 at 0.05 Hz. A phase advance (up to 65 degrees at 0.05 Hz) paralleled this gain depression. Velocity characteristics of optokinetic nystagmus (o.k.n.) and optokinetic after-nystagmus (o.k.a.n.) induced by constant-velocity full-field rotation of 60 deg/s amplitude and 60 s duration were studied. The features of o.k.n. (initial velocity, maximal velocity and time constant) were only mildly affected by cerebellectomy. On cessation of visual stimulation when the animal was plunged into darkness, the velocity of the eyes decreased progressively (o.k.a.n.). The time constant of o.k.a.n. was 12.5 s in the normal cat and 4.2 s in the cerebellectomized cat. Furthermore cerebellectomy abolished the secondary o.k.a.n. Optokinetic response was also tested by a set of sinusoidal (0.05-1 Hz; 3-20 degrees) full-field stimuli. The o.k.n. was not abolished but dramatically decreased, especially at higher frequencies. No response could be detected above 0.15 Hz. Visual suppression of inappropriate vestibulo-ocular reflex was still possible but was mildly impaired after cerebellectomy. Visual suppression could only be detected with stimuli below 0.25 Hz. Visual suppression of caloric nystagmus was studied in the normal cat. A clear dependence of the effectiveness of visual suppression on the velocity of the nystagmus was demonstrated. In the cerebellectomized cat, the visual suppression of caloric nystagmus was lost when tested on nystagmus velocities above 20 deg/s but remained when tested on nystagmus velocities below 20 deg/s. The relationship between cerebellectomy and the loss of visual suppression of caloric nystagmus was found to be at least partially indirect: cerebellectomy increased the velocity of caloric nystagmus, and visual suppression was usually less effective at higher velocities.

Vertical optokinetic nystagmus and vestibular nystagmus in the monkey: up-down asymmetry and effects of gravity

Vertical optokinetic nystagmus (OKN) i.e., OKN in the sagittal plane, was asymmetrical in the monkey when it was induced with animals lying on their sides in a 90 degrees roll position. In typical monkeys the slow phase velocity of downward OKN (slow phases up) increased proportionally with stimulus velocity at close to unity gain to about 60 degrees/s and saturated at about 100 degrees/s. Upward OKN (slow phases down) increased with close to unity gain only to about 40 degrees/s and saturated at about 60 degrees/s. The slow phase velocity of upward OKN was usually irregular and its frequency was lower than that of downward or horizontal OKN. Upward and downward optokinetic after-nystagmus (OKAN) were also asymmetrical. Upward OKAN was weak or absent and when present it usually saturated at 10 degrees/s. Downward OKAN was stronger, increasing with a gain of about 0.7 with regard to stimulus velocity to a saturation velocity of about 50-60 degrees/s. This was usually about 10-30 degrees/s less than the saturation velocity of horizontal OKAN. The weak or absent upward OKAN indicates that stored activity related to slow phase eye velocity contributes little to the production of upward OKN. In agreement with this, there was little or no slow rise in slow phase velocity to a steady state level during upward OKN. Instead eye velocity rose to its peak velocity at the onset of stimulation. The lack of stored velocity information is probably largely responsible for the differences in regularity, gain and frequency between upward and downward OKN. Vertical vestibular nystagmus was induced by rotating monkeys in darkness with steps of velocity about a vertical axis, while they were lying on their sides in a 90 degree roll position. The velocities of the initial upward and downward slow phases were approximately equal. Gains of the vertical VOR ranged from about 0.5 to 0.98 for stimuli up to 150 degrees/s. Despite equivalent initial gains for upward and downward nystagmus, the vertical VOR was asymmetrical in that downward nystagmus had a higher frequency and generally lasted longer than upward nystagmus. Time constants of downward nystagmus (slow phases up) were about 15 s on average and were similar to those of horizontal nystagmus. Mean time constants of upward nystagmus (slow phases down) were about 8 s. This is only slightly longer than the average time constant of afferent activity in the semicircular canal nerves induced by steps of velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of units in the rat cerebellar flocculus during optokinetic and vestibular stimulation

The simple (SS) and complex spike (CS) responses of Purkinje (P-cells) and non-Purkinje (non P-cells) in the cerebellar flocculus were studied in alert pigmented rats (DA-HAN) during binocular and monocular optokinetic stimulation (OKS), vestibular stimulation and a combination of the two. Of a total of 98 P-cells whose SS discharges were activated by rotary stimulation of the horizontal canal in the dark (type I and type II P-cells), the vast majority (72%) responded to constant velocity binocular OKS that was produced by means of a horizontal shadow projector system. The remaining P-cells responded only to vestibular stimulation (19%), to OKS or to the presumed fast components of optokinetic and vestibular nystagmus (9%). The optokinetic responses of P-cells were generally bidirectional but asymmetrical, i.e., the increases in rate in one direction were larger in magnitude than decreases on opposite OKS and were synergistic with the semicircular canal input. During constant velocity OKS, the discharge of a few P-cells rose approximately exponentially, outlasted the stimulus by as much as 10-13.5s and, thus, resembled OKS responses of vestibular nucleus neurons. However, the majority exhibited a phasic-tonic response governed by a short "time constant" of from 0.5-3s. The velocity tuning curves of vestibular/OKS responding P-cells showed peak sensitivities with retinal slip velocities of 1.5-2 degrees/s. This is higher than the ca. 1 degree/s determined for other relay nuclei of the horizontal optokinetic pathway. The responses of non P-cells suggest that they originate from mossy fiber projections from vestibular, visual (optokinetic) and saccadic eye movement-related areas of the brainstem. Most of the units carried a combined vestibular and optokinetic signal. The majority showed a bidirection-selective response to OKS, and a small percentage showed unidirectional responses only. Monocular testing of P-cells revealed that most received a bidirection-selective, but asymmetrical, OKS input. Slightly more than half of these had a strongest OKS drive from the contralateral eye; the remaining units were driven most strongly by the ipsilateral eye. Unidirection-selective P-cells, driven by OKS to the ipsi- or contralateral eye, were uncommon; yet this class is common among other portions of the horizontal optokinetic system (e.g., vestibular nuclei, praepositus hypoglossi nucleus, nucleus reticularis tegmenti pontis).(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics of nystagmus produced by reversible lesions of the medial cerebellar nuclei in the alert monkey

Synaptic activity of the medial cerebellar nuclei was reversibly blocked in 6 Cebus monkeys by cooling through a sheath implanted alongside the fastigial nucleus. Such lesions produced in the dark a strong nystagmus (slow phase velocity 100-200 deg/sec). The slow phase of nystagmus was predominantly in the horizontal plane and was towards the side of the lesion (ipsilateral drift). The maximum velocity of drift was independent of eye position and was directly related to the degree of cooling. Vision abolished the nystagmus. If lights were turned on during nystagmus the drift velocity rapidly decreased to zero with an instantaneous and an exponential component. It is suggested that these results emphasize the importance of the medial cerebellum, possibly by way of the fastigial nucleus, in balancing the output of the paired vestibular nuclei.

Visual suppression of caloric nystagmus and optokinetic responses in cats

Previously it was reported that loss of visual suppression (VS) was accompanied by disturbance of optokinetic nystagmus (OKN) in monkeys with lesions at the flocculus. In the present experiment with cats, OKN was investigated after inflicting lesions on either superior colliculus (SC) or inferior olive (IO), both of which are considered to be the main prefloccular relay nuclei to mediate visual signals to the flocculus. VS of caloric nystagmus was recognized in all the IO-lesioned cats and OKN remained normal except in one cat. After the left SC lesions, loss of VS was evidently revealed and optokinetic stimuli produced directional preponderance to the left with diminished responses to the right in 7 of 9 cats. The present findings suggest that the SC may be an important relay nucleus to the flocculus in conveying visual signals responsible for VOR gain.

Projections of the nucleus of the basal optic root in the pigeon: an autoradiographic and horseradish peroxidase study

The efferent projections of the nBOR complex, have been studied with both anterograde autoradiographic and retrograde horseradish peroxidase (HRP) techniques. The nBOR complex includes three distinct subdivisions: the nucleus of the basal optic root (nBOR), the nBOR pars dorsalis (nBORd) and the nBOR pars lateralis (nBOR1). Unilateral injections of 3H-leucine or 3H-proline/3H-leucine mixtures into the nBOR complex have demonstrated prominent bilateral projections upon (1) the vestibulocerebellum, (2) the inferior olivary complex, (3) the oculomotor nuclear complex, (4) the nucleus interstitialis, contralateral projections upon (5) the contralateral nBOR complex and ipsilateral projections upon (6) a pretectal nucleus, the nucleus lentiformis mesencephali, pars magnocellularis. Unilateral injections of HRP confined to folia IXc,d and paraflocculus of the cerebellum, the contralateral nBOR complex or the nucleus lentiformis mesencephali resulted in retrograde labeling of predominantly medium and large size cells within the entire nBOR complex. Unilateral injections of HRP within the inferior olive resulted in retrograde labeling of small, spindle-shaped cells within nBOR and nBORd. Unilateral injections of the oculomotor complex which included the trochlear nucleus resulted in retrograde labeling of small cells within the ipsilateral nBORd and predominantly medium and large cells in the contralateral nBOR. The displaced ganglion cells of the retina give rise to a prominent and distinct projection upon the nBOR complex (Karten et al., '77). The nBOR complex in turn projects upon the oculomotor nuclear complex, the nucleus interstitialis and the vestibulocerebellum, regions which have been implicated in oculomotor function. These findings strongly suggest that the displaced ganglion cells and the accessory optic system have a major influence upon oculomotor reflexes including eye and head movements.

Interaction between the horizontal vestibulo-ocular reflex and optokinetic response in rabbits

Dynamic characteristics of the horizontal vestibulo-ocular reflex (HVOR), the optokinetic response (OKR), and their interactions were investigated in alert albino rabbits. For stimulation of the horizontal semicircular canals, the whole rabbit was rotated sinusoidally on a motor-driven turntable at peak-to-peak amplitudes of 5 degrees to 30 degrees over a frequency range of 1/30 to 1/2 Hz. Optokinetic stimulation was provided by a narrow vertical slit light source presented in front of the eye to be tested. The evoked horizontal eye movements were observed and measured by means of a closed circuit television system adapted to provide an analog signal proportional to the eye movement. The net HVOR was obtained by rotation of the turntable in darkness and the net OKR by rotation of the light source. Combining rotation of the turntable with a stationary light source immediately increased the gain and reduced the phase shift of the HVOR. The light source moving in phase with the turntable, but at twice the angular amplitude, reduced the gain and advanced the phase of the HVOR. Eye movement curves of the HVOR modified by a fixed or moving slit light could be reconstructed approximately by a linear combination of the net HVOR and OKR.

Inhibition of labyrinthine nystagmus by visual fixation: effects of ablation of visual cortex and superior colliculi

A study was conducted to destroy two specific areas of the cat's visual system in order to determine if these lesions would affect the visual inhibition of calorically-induced vestibular nystagmus. The occipital visual cortex was removed in eight cats and the superior colliculi were removed bilaterally in nine cats. Postoperative vestibular testing revealed no significant change in the electronystagmography tracings and response to visual fixation. These findings suggest that, in cats, the visual inhibition of labyrinthine nystagmus is not dependent upon the integrity of the visual cortex or superior colliculi. The hypothesis is brought forward that the visual inhibition of the vestibular nystagmus is merely a reflex of the brain stem to light stimulus, mediated via the cerebellum.

Visual suppression of caloric nystagmus in cats

A newly devised animal box with which caloric tests can be easily performed in the awake cat is presented. This device is also useful for position and optokinetic tests. Visual suppression of caloric nystagmus was investigated in such vertebrates as monkeys, cats and rabbits. There was a definite species difference in the rate of visual suppression of caloric nystagmus. It may be that the difference among species is due to a difference in fixation function among animal species.

Alcohol and the oculomotor system

The influence of alcohol on the oculomotor system was observed by means of the caloric eye tracking pattern (CETP) test, the visual suppression test on caloric nystagmus, and the positional nystagmus, eye tracking and gaze nystagmus tests. In Group A (nine cases whose CETP before the intake of alcohol was normal), the influence of alcohol consumption appeared regularly and consistently in the following order: abnormality of CEPT greater than or equal to positional alcohol nystagmus greater than or equal to abnormality of the eye tracking pattern greater than or equal to alcohol gaze nystagmus. On the contrary, in Group B (eight cases whose CETP before the consumption of alcohol was already abnormal), with one exception, the regularity noted in Group A was not observed. This phenomenon may be attributable to the presence of latent disorders of the oculomotor system. In both groups, the duration of the caloric nystagmus itself was slightly shortened and its amplitude somewhat suppressed after the consumption of alcohol. The results were confirmed by experiments in which the subjects kept their eyes open in darkness. On the other hand, when the eyes were kept open in light surroundings, the duration and amplitude of the caloric nystagmus were exaggerated in appearance because the mechanism of visual suppression was disturbed by alcohol.

Visual suppression test

The visual suppression test is one of the visual fixation tests. It is performed by recording caloric nystagmus by ENG, and the maximum slow phase velocity of caloric nystagmus in darkness is compared with the slow phase velocity in light with eyes open. Visual suppression of slow phase velocity of caloric nystagmus is 54 +/- 12% in 52 normal adults ageing from 21 to 40. Visual suppression in normal subjects is not influenced by water temperature used for the caloric test and not changed by background illumination in light. Visual suppression is stronger when the target is closer to the eyes of the subjects. The following abnormalities have been diagnosed by this test: flocculus and nodulus lesions on the side of the lesion; inferior olive lesions; parietal lobe lesions; compensation after unilateral sudden loss of inner ear function.

Visual suppression of caloric nystagmus in normal individuals

The effects of opening of the eyes and of ocular fixation upon caloric nystagmus were investigated during the period of maximum intensity of caloric nystagmus in a series of 32 normal individuals. The percentage reduction in slow-phase velocity induced depended upon the test conditions, but, on the other hand, did not depend upon the temperature of the water applied as caloric stimulus. This latter fact favors the theory of visual suppression of the caloric test. Another striking finding was that a clear correlation definitely existed between the percentage reduction of suppression in slow-phase velocity and that in the multiplication product of amplitude by nystagmus frequency (P.A.F.) during the period of eye opening and ocular fixation. The percentage of suppression in slow-phase velocity is interchangeable with that in P.A.F., which broadens the practical scope of the routine test.

Visual suppression test

Visual suppression of caloric nystagmus was studied in normal adults and in 98 clinical cases in order to justify the application of the procedure as a clinical test. The maximum slow phase velocity during ten seconds in darkness and the slow phase velocity during ten seconds in light were taken from the recordings and measured. The mean values of these slow phase velocities were calculated and the mean slow phase velocity in darkness was assigned a value of 100%. The value which the slow phase velocity in light subtracts from the slow phase velocity in darkness, represents the visual suppression. It was determined that visual suppression of the slow phase velocity of caloric nystagmus was 48 +/- 10% in 22 normal adults. This was caused by the visual fixation mechanisms. Cases in which lesions were diagnosed in the cerebellum, such as spinocerebellar degeneration and cerebelitis, showed reduced or abolished visual suppression. The lesion side can be determined by this test. Compensation following unilateral sudden loss of inner ear function can be measured by the visual suppression test.