Caloric Nystagmus Research Articles

Impact of Alcohol on Vestibular Function in Relation to the Legal Limit of 0.25 mg/l Breath Alcohol Concentration

The aim of this study was to investigate the effect of alcohol on sacculocollic and vestibulo-ocular reflex systems, when the breath alcohol concentration (BrAC) is close to the legal limit of 0.25 mg/l. Twenty healthy male volunteers underwent vestibular evoked myogenic potential and caloric coupled with visual suppression tests. These tests were conducted prior to imbibing alcohol at a dosage of 0.5 g/kg to achieve a peak BrAC of around 0.25 mg/l. Once the peak BrAC was reached, these tests were performed again. Predosing and postdosing analytical results were compared, as were those with BrAC levels ≧ 0.25 mg/l and <0.25 mg/l. After ingesting alcohol, 36 ears (90%) showed vestibular evoked myogenic potential responses, with a significantly increased latency of peak p13. The mean slow-phase velocity of caloric nystagmus in 40 ears after dosing was significantly reduced, and that with BrAC ≧0.25 mg/l was significantly less than that with BrAC <0.25 mg/l. Likewise, the visual suppression index decreased considerably after alcohol ingestion. In conclusion, from the perspective of vestibular function, the 0.25-mg/l BrAC limit gains clinical significance, because the vestibulo-ocular reflex performance deteriorates further, when the BrAC exceeds 0.25 mg/l. However, impaired performance of sacculocollic reflex and vestibulocerebellar interaction has occurred, when the BrAC was <0.25 mg/l, suggesting that a lower legal threshold is appropriate.

Effects of caloric vestibular stimulation on serotoninergic system in the media vestibular nuclei of guinea pigs

Anatomic and electrophysiological studies have revealed that the neurons located in the media vestibular nuclei (MVN) receive most of the sensory vestibular input coming from the ipsilateral labyrinth and the responses of MVN neurons to caloric stimulation directly reflect changes in primary vestibular afferent activity. The aim of this study was to clarify the intrinsic characteristics of serotonin (5-hydroxytryptamine, 5-HT) release in the MVN during the period of vertigo induced by caloric stimulation. We used an in vivo microdialysis technique to examine the effects of caloric stimulation on the serotoninergic system in MVN. Twenty four guinea pigs were randomly divided into the groups of irrigation of the ear canal with hot water (n = 6), ice water (n = 6) and 37 degrees C water (n = 4), and the groups of irrigation of the auricle with hot water (n = 4) and ice water (n = 4), according to different caloric vestibular stimulation. We examined the animal's caloric nystagmus with a two-channel electronystagmographic recorder (ENG), and meanwhile examine serotonin (5-hydroxytryptamine, 5-HT) level in the MVN with microdialysis technique after caloric stimulation. In the caloric test the hot water (44 degrees C) irrigation of the right external auditory canal induced horizontal nystagmus towards the right side lasting about 60 seconds and the ice water irrigation of the right external auditory canal induced it towards the left side lasting for about 90 seconds. No nystagmus was induced by 37 degrees C water irrigation of the external ear canal. Therefore, it was used as a negative control stimulation to the middle ear. The MVN 5-HT levels significantly increased in the first 5-minute collecting interval and increased to 254% and 189% of the control group in the second collecting interval in response to caloric vestibular stimulation with ice water and hot water respectively. The serotonin release was not distinctly changed by the irrigation of the auricle with ice water or hot water. Neither somato-sensory stimulation of the middle ear nor nonspecific cold or hot stress affects the serotonin release. The rise of 5-HT in MVN may be involved in the mechanism of vertigo induced by caloric stimulation.

Aspekty otoneurologiczne wczesnych postaci stwardnienia rozsianego (SM)

Sclerosis multiplex (SM) is characterized by multifocality of neurological changes and polyphasic course. The disease is caused by indefinite factors in the circumstances of genetically determined immune disorders. The aim of study. An attempt was made to identify otoneurological symptoms accompanying the early stage of sclerosis multiplex (SM). Material and research methods. 103 patients (diagnosed with uncharacteristic otoneurological symptoms, in further clinical observation defined as SM prodromes) were retrospectively examined. The following factors were taken into consideration: character and intensity of dizziness, results of static and dynamic tests, electronystagmography (ENG), caloric test, eye tracking and optokinetic nystagmus. Conclusion. Disorders of: vestibulospinal reflexes, eye tracking, optokinesis, time and regularity of caloric nystagmus occur in the very early stages of SM.

Eye movement disorders in myotonic dystrophy type 1

Conclusions. No definite sign was found of central oculomotor system disorders being independent of saccadic slowing because (1) diminished maximum slow phase velocity of the optokinetic nystagmus (OKNspv) was closely related to saccadic slowing (p<0.01, r=0.59), (2) maximum frequency of optokinetic nystagmus (OKNfq) was normal, (3) visual suppression (VS) change was mild, and (4) the diminished maximum slow phase velocity of the caloric nystagmus (CNspv) seen in some patients is explained by both peripheral and central vestibular involvement. These findings support the extraocular muscle hypothesis. Objective. To assess whether eye movement disorders seen in patients with myotonic dystrophy type 1 (DM1) are caused by central oculomotor system involvement or extraocular muscle damage. Patients and methods. Oculomotor functions and their correlation with (CTG)n length were studied in 29 DM1 patients and 12 age-matched controls. Results. Values for saccadic velocity (p<0.005), maximum OKNspv (p<0.005), and maximum CNspv (p<0.01) in the patient group were markedly lower than in the control group. VS of caloric nystagmus in the patient group was slightly lower than that in the controls. No significant difference was found between the two groups in the maximum OKNfq. Patients with greater (CTG)n lengths had lower saccadic velocities (p<0.01, r=0.71).

Triple Semicircular Canal Occlusion in Guinea Pigs with Endolymphatic Hydrops

Triple semicircular canal occlusion will eliminate rotatory stimulation to the vestibular peripheral system (as it blocks endolymphatic fluid movement) and therefore release rotatory vertigo attack. This surgery is safe in ears with endolymphatic hydrops. Semicircular canal occlusion has been used as an alternative treatment of intractable benign paroxysmal positional vertigo with varied success. Triple semicircular canal occlusion in animal models blocks the responses of the semicircular canals to rotation and spares cochleae and the otolithic apparatus. This result suggests that triple semicircular canal occlusion is a prospective method in vertigo management for patients with Ménière's disease. However, the effectiveness and safety of triple semicircular canal occlusion has not been fully evaluated in ears with endolymphatic hydrops. Endolymphatic hydrops was established in 20 guinea pigs by endolymphatic sac obliteration. Triple semicircular canal occlusion was performed in 12 of them 120 days after endolymphatic hydrops surgery, whereas 8 others were killed for morphologic observation to confirm endolymphatic hydrops. Auditory and vestibular functions were monitored from the time before endolymphatic hydrops until 1 month after triple semicircular canal occlusion. Endolymphatic hydrops and canal occlusion were confirmed by morphologic observation. Successful establishment of endolymphatic hydrops was indicated by mild elevation of the auditory brainstem response threshold and tentative asymmetry in nystagmus. Endolymphatic hydrops was confirmed by cochlear morphology in all eight animals that were killed 120 days after endolymphatic hydrops surgery. After triple semicircular canal occlusion, all 12 animals showed spontaneous nystagmus with a slow component toward the side that had been operated on, head tilt, rotated walking, and tentative asymmetry in rotatory nystagmus. The static symptoms disappeared within 1 month after triple semicircular canal occlusion. Caloric nystagmus was only slightly reduced after endolymphatic hydrops as compared with the contralateral ears but could not be elicited at all after triple semicircular canal occlusion. No significant elevation in auditory brainstem response threshold was found after triple semicircular canal occlusion. The canal occlusion and endolymphatic hydrops were confirmed in all surgical ears. Triple semicircular canal occlusion is effective for eliminating the response of semicircular canals to rotation and caloric stimulation and is safe in ears with endolymphatic hydrops. Also, the static compensation to the disequilibrium is quick and complete. These results suggest that triple semicircular canal occlusion should be an option for controlling rotatory vertigo in Ménière's disease.

音像定位能力に対する前庭刺激の影響

Using dichotic sound, the effect of vestibular stimulation on the orientation of sound lateralization was investigated in 13 subjects. The interaural time difference (ITD) discrimination test was performed in a dark room while caloric nystagmus was induced by iced water irrigated into the external auditory canal. The amplitudes for the ITD discrimination tests after caloric stimulation (experimental group) were significantly greater than those before caloric stimulation (control group). During caloric stimulation, all subjects reported that their perceptual body axes shifted toward the slow phase side of nystagmus, and the median line of amplitude for the ITD discrimination test shifted to the slow phase side of the nystagmus. In contrast, when subjects were gazing a visual target fixed straight ahead of subjects, there was no significant difference in the amplitudes or the median line shift of amplitude was observed between the control and experimental groups. The current study suggests that sound lateralization sensitivity during ITD discrimination may be altered by vestibular stimulation.

Valores poblacionales de referencia para videooculografía en el test de agitación cefálica y la prueba calórica bitérmica

ObjectiveTo obtain reference values for the vestibulo-ocular reflex response to the head-shaking nystagmus and the bithermal caloric test in the spanish population Patients and methods: DesingA descriptive study. Set up: General hospital Set upGeneral hospital IndividualsOne hundred and seven healthy sex and age stratified voluntiers were included. The final sample included 97 individuals over 18 years of age InterventionSpontaneous nystagmus (SN), head-shaking nystagmus (HSN) and caloric induced nystagmus were explored. The eyes movement was recorded by a video-oculographic system. The SN or HSN was considered significant when at least 6 consecutive beats with a slow phase velocity of 2º/sec were detected. The caloric test was performed with water flow at 250mL/20 s at 30ºC and 44ºC with an interval of 10 minutes between irrigations. The percentage of canal paresis (CP) and directional preponderance (DP) was calculated using maximum slow phase velocity and the Jongkees index formula Main outcome measurementsPresence of SN, horizontal and vertical SHN, percentage of CP and DP ResultsSN was found in 10,3% individuals (6 women and 4 men). Horizontal HSN was also observed in 9 women and 10 men (19,5%), and vertical HSN in 8 women and 10 men (18,6%). The mean and 95 percentil for CP were 13,10 and 28,60 in women and 11,02 and 27,30 in men. For DP, the mean and 95 percentil were 11,76 and 35,80 in women and 11,58 and 28,65 in men. The 5 percentils for slow phase velocity of nystagmus after each irrigation were 6,30; 5,14; 5,96; 4,02 º/s (left ear 44º, right ear 44º, left ear 30º, right ear 30º, respectively) in the group of women; and 5,82; 6,99; 5,67; 4,55 º/s in men (with the same irrigation sequence) ConclusionResults presented should be considered as a population-based norms and may be useful as references for water bithermal test for VOG studies. The SN or HSN could be observed in subjects without vestibular pathology

前庭神経炎症例における健側耳の温度眼振反応の検討

We studied caloric responses of the unaffected side of patients with vestibular neuritis (VN). Six patients with VN, who underwent sequential caloric tests, were enrolled in this study. In all 6 subjects, the maximum slow phase eye velocity of caloric nystagmus on the unaffected side to ice water was smaller at the earlier stage after the vertigo attack (within one month after the attack) than that at the later stage. This phenomenon might be associated with the suppression of contralateral vestibular nuclei, which would be a part of vestibular compensation. We should take into consideration that caloric responses on the unaffected side could be altered according to the stage of the disease.

Aseptic Meningoencephalitis Presenting with Bilateral Vestibular Ataxia: a Case Report

Bilateral vestibular dysfunction is a rare condition, of which peripheral disorders are most common, whereas central disorders are extremely rare. A 35-year-old woman developed fever, headache, dizziness, convulsion, and disturbance of consciousness at the same time. MRI findings were normal. Based on the neurological findings and laboratory abnormalities, she was diagnosed as having aseptic meningoencephalitis. Steroid pulse therapy successfully ameliorated her encephalitis sign. However, isolated bilateral vestibular ataxia and dizziness, together with severe decrease of Caloric nystagmus, became apparent and lasted for the following 3 months, without cerebellar/brainstem involvement.

Thalamic infarctions cause side-specific suppression of vestibular cortex activations

H2O15-PET was performed during caloric vestibular stimulation of the right and left external ears in eight right-handed patients with acute unilateral infarctions or haemorrhages of the posterolateral thalamus (four right, four left). The posterolateral thalamus is the relay station for ipsi- and contralateral ascending vestibular input to the multiple multisensory vestibular cortex areas. The aim of this study was to evaluate the differential effects of unilateral vestibular thalamic lesions on thalamo-cortical projections, right hemispheric dominance and reciprocal inhibitory visual-vestibular interaction, as well as perceptual and ocular motor consequences during caloric irrigation. The major findings of the group analyses of the patients with right-sided and those with left-sided lesions were as follows: (i) activation of the multisensory vestibular temporo-parietal cortex was significantly reduced in the hemisphere ipsilateral to the thalamic lesion when the ipsilesional or contralesional ear was stimulated; (ii) activation of multisensory vestibular cortex areas of the hemisphere contralateral to the irrigated ipsilesional ear was also diminished; and (iii) the right hemispheric dominance in right-handers described above was preserved in those with right and left thalamic lesions. Simultaneous deactivations were often restricted to only one hemisphere--the one contralateral to the stimulation and contralateral to the vestibular cortex areas activated. There was, however, one area in the inferior insula which was also activated by either right or left ear stimulation in the hemisphere ipsilateral to the lesion. This supports the assumption that there is a bilateral direct ascending vestibular projection from the vestibular nuclei to the inferior part of the insula, which bypasses the posterolateral thalamus and is stronger in the right hemisphere. The cortical asymmetry of the pattern of activation during horizontal semicircular canal stimulation by calorics was not associated with a significant direction-specific asymmetry of caloric nystagmus or perceived body motion. Thus, the data demonstrate the functional importance of the posterolateral thalamus as a unique relay station for vestibular input to the cortex, of the dominance of the right hemisphere in right-handedness, and of ipsilateral ascending pathways. Furthermore, the normal interaction between the two sensory systems--the vestibular and the visual--appears to be impaired.

Three-dimensional analysis of eye movements using four times high-speed video camera

In order to record and analyze the rapid eye movement non-invasively in human subjects, a four times high-speed video camera (4TC) with a new computer software was developed and utilized. Nine healthy volunteers and four patients with vestibular dysfunction participated in this study. Caloric stimulation was applied to the healthy subjects and the eye movements were recorded using a standard camera (SC) and a 4TC. In four patients, the positional and/or positioning nystagmus was recorded using SC and 4TC. Analysis of the eye speed of the quick phase of nystagmus was performed manually from the print out of the chart. The quick phase of the caloric nystagmus was adequately analyzed from the data using 4TC. However, using SC the sampling rate was not sufficiently enough for this purpose, as prospected. The adaptability of the 4TC in clinical examination is exactly similar to that of SC, because of the size and weight of the camera. Although the time taken to analyze eye movements using 4TC is about four times longer than that using SC, this system is quite useful and adequate for analyzing the quick eye movements in vestibular nystagmus, in an out-patient clinic set up.

ＨＣ‐ＢＰＰＶ（外側半規管型良性発作性頭位めまい症）の患側と半規管機能について

We report horizontal canal BPPV (HC-BPPV) targeting its pathophysiology, the affected side, and the function of the horizontal semicircular canal, together with a review of the literature. Subjects were 13 patients with HC-BPPV visiting our vertigo outpatient clinic at Nara medical university hospital and a related hospital in the 2.5 years from January 2000 to June 2002. Subjects were classified into 7 with canalolithiasis and 6 patients of cupulolithiasis after a neurotological examination. CP was positive in 54% of all patients, 71% of those with canalolithiasis, and 33% of those with cupulolithiasis. To determine the affected side in HC-BPPV, we used the affected side by using the law of Ewald in canalolithaisis patients and the detection of a neutral diminishing nystagmus in cupulolithiasis patients. CP positive in caloric testing indicated insignificant dysfunction of the horizontal semicircular canal in canalolithiasis patients compared to that in cupulolithasis patients. The mechanism behind caloric nystagmus was thought to be a convection of endolymphatic fluid interrupted consequently by an otolith in the semicircular canal in canalolithiasis patients. In contrast, CP was positive in cupulolithiasis patients regarded as having no convection of endolymphatic fluid. The mechanism causing a difference in caloric test results between canalolithiasis and cupulolithiasis patients thus requires a larger patient population and further examination to be conclusive.

Cognitive functioning in Lyme borrellosis

Lyme borreliosis is a tick-borne disease, transmitted by Ixodes ticks, most frequently diagnosed in the USA and in many European countries. Its etiologic agent is a spirochete Borrelia burgdorferi sensu lato. One of the forms of Lyme borreliosis is neuroborreliosis. This disease attacking the central and peripheral nervous systems causes many diagnostic and therapeutic difficulties. It is the most prevalent form of B. burgdorferi infection in Europe, less frequently observed in the United States. Neurological disorders accompanying B. burgdorferi infections are caused by direct influence of the Borrelia and their products on nervous cells.Lesions of the central and peripheral nervous systems associated with neuroborreliosis that may affect the function of the vestibular organ have incited the authors to carry out research assessing the function of the labyrinth in a group of infected patients and to compare the results with a control group of healthy subjects.The research covered 32 patients with the infection, aged 21–64 (x = 42,3 years) including 13 (40%) women and 19 (60%) men hospitalized due to Lyme borreliosis.The following factors were taken into consideration: character and intensity of dizziness, results of static and dynamic tests, electronystagmography (ENG), caloric test, hearing test.In 56% of subjects with neuroborreliosis, vertigo and balance disorders were observed (in over 25% regular, and in 22% – very intense). Spontaneous nystagmus was found in 16% of subjects, directional in 25%. The caloric tests showed, statistically more frequent than in the control group, disorders in the regularity of nystagmus, directional preponderance and canal paresis.Disorders of: vestibulospinal reflexes, time and regularity of caloric nystagmus occur in the neuroborreliosis.

Subclassification of vestibular disorders by means of statistical analysis in caloric labyrinth testing

ObjectiveIn the past, various attempts were made to perform a quantitative analysis of nystagmographic findings but their diagnostic value was limited. Therefore, the authors present a multivariate analysis of nystagmus findings with the aim of increasing the precision of diagnostic differentiation in cases of vestibular dysfunction.Material and MethodsA group of 387 patients and 40 healthy volunteers were examined over a 14-month period using electronystagmography after stimulation by bithermal, bilateral irrigation of the labyrinth. Amplitude, slow-phase velocity, frequency and directional preponderance were evaluated.ResultsNo defined normal values for caloric nystagmus parameters could be obtained. However, by using the Mann–Whitney U-test and logistic regression analysis a differentiation between pathological and healthy findings as well as between central and peripheral vestibular disorders and even between distinct vestibular disease entities is possible. Using these methods, the nystagmus amplitude was found to be the strongest discriminating parameter. Therefore, sole assessment of nystagmographic findings by selective calculation of the nystagmus slow-phase velocity falls short of the potential offered by electronystagmographic registration.ConclusionFor daily clinical routine, counting nystagmus beats leads to the same diagnostic precision as the analysis of slow-phase velocities. In contrast, multivariate analysis of several nystagmus parameters can distinguish between distinct diseases with fairly high precision. This stepwise analysis of nystagmographic data could create the basis for an expert-system tool in the near future.

Inner Ear Changes With Intracochlear Gentamicin Administration in Guinea Pigs

Transtympanic administration of gentamicin is reported to be a useful treatment for vertigo in such conditions as Meniere's disease, and determining appropriate clinical dosage of gentamicin is difficult. The authors examined the relation between gentamicin dosages and inner ear function in guinea pigs. This study is a basic science project designed to examine cochlear and vestibular function in animal models. Various concentrations of gentamicin solution were infused into the right inner ear of guinea pigs by osmotic pumps. Caloric nystagmus as a marker of vestibular function and the change in auditory brainstem response (ABR) threshold as a marker of cochlear function were observed. After 14 days of treatment, high gentamicin concentrations of 40 mg/mL caused canal paralysis and a rapid shift in ABR threshold. Animals exposed to low gentamicin concentrations of 4 mg/mL showed no obvious change in either vestibular or cochlear function. Animals exposed to moderate gentamicin concentrations of 12 mg/mL showed a moderate shift in ABR threshold and caloric malfunction. Histopathological examination revealed that after 14 days of treatment with 40 mg/mL gentamicin, severe cytoplasmic damage occurred in both vestibular and cochlear end organs. In animals treated with 12 mg/mL gentamicin, hair cells remained in the cochlear third turn and ampulla of the lateral semicircular canal. The authors established an animal model that showed the moderate damage of inner ear with moderate-dose gentamicin. The study results indicated that the appropriate administration of gentamicin could establish a stable effect on the inner ear. It may be important to select the protocol that delivers a stable dosage of gentamicin to treat patients with Meniere's disease safely and effectively.

Dominance for vestibular cortical function in the non-dominant hemisphere.

The aim of this (15)O-labelled H(2)O bolus positron emission tomography (PET) study was to analyse the hemispheric dominance of the vestibular cortical system. Therefore, the differential effects of caloric vestibular stimulation (right or left ear irrigation with warm water at 44 degrees C) on cortical and subcortical activation were studied in 12 right-handed and 12 left-handed healthy volunteers. Caloric irrigation induces a direction-specific sensation of rotation and nystagmus. Significant regional cerebral blood flow increases were found in a network within both hemispheres, including the superior frontal gyrus/sulcus, the precentral gyrus and the inferior parietal lobule with the supramarginal gyrus. These areas correspond best to the cortical ocular motor centres, namely the prefrontal cortex, the frontal eye field and the parietal eye field, known to be involved in the processing of caloric nystagmus. Furthermore, distinct temporo-parietal activations could be separated in the posterior part of the insula with the adjacent superior temporal gyrus, the inferior parietal lobule and precuneus. These areas fit best to the human homologues of multisensory vestibular cortex areas identified in the monkey and correspond to the parieto-insular vestibular cortex (PIVC), the visual temporal sylvian area (VTS) and areas 7 and 6. Further cortical activations were seen in the anterior insula, the inferior frontal gyrus and anterior cingulum. The subcortical activation pattern in the putamen, thalamus and midbrain is consistent with the organization of efferent ocular motor pathways. Cortical and subcortical activation of the described areas was bilateral during monaural stimulation, but predominant in the hemisphere ipsilateral to the stimulated ear and exhibited a significant right hemispheric dominance for vestibular and ocular motor structures in right-handed volunteers. Similarly, a significant left hemispheric dominance was found in the 12 left-handed volunteers. Thus, this PET study showed for the first time that cortical and subcortical activation by vestibular caloric stimulation depends (i) on the handedness of the subjects and (ii) on the side of the stimulated ear. Maximum activation was therefore found when the non-dominant hemisphere was ipsilateral to the stimulated ear, i.e. in the right hemisphere of right-handed subjects during caloric irrigation of the right ear and in the left hemisphere of left-handed subjects during caloric irrigation of the left ear. The localization of handedness and vestibular dominance in opposite hemispheres might conceivably indicate that the vestibular system and its hemispheric dominance, which matures earlier during ontogenesis, determine right- or left-handedness.

Nystagmus-sensation Dissociation in Spinocerebellar Degeneration

Objective—To study nystagmus-sensation dissociation (NSD), i.e. caloric nystagmus without the sensation of vertigo, in patients with spinocerebellar degeneration (SCD).Material and Methods—The neuro-otological and neuro-radiological records of 179 patients clinically diagnosed as having SCD (91 males, 88 females; age range 20–89 years) and 48 patients diagnosed as having peripheral vestibular disorders (15 males, 33 females; age range 21–80 years) were reviewed. Subjects underwent caloric tests using cold water (20°C) in a totally dark room. Immediately after each test session, subjects were asked if they had experienced spinning or moving sensations during the test. Maximum slow phase eye velocities (SPEVs) were measured using electronystagmography.Results—Among patients with peripheral vestibular disorders, all patients with SPEVs >15°/s experienced spinning or moving sensations during testing. Among the 179 patients with SCD, 21 (39 sides) showed maximum SPEVs >15°/s without spinning or moving sensations. In particular, 8 patients (10 sides) had maximum SPEVs >25°/s without spinning or moving sensations. Common lesions in the cerebral cortex could not be detected using either MRI or single-photon emission CT.Conclusion—Patients with SCD may also have NSD, which may be attributable to subcortical lesions in the ascending pathways to the vestibular cortex.

Convection, buoyancy or endolymph expansion: what is the actual mechanism responsible for the caloric response of semicircular canals?

The mechanisms underlying caloric nystagmus are still matter of debate. The original theory proposed by Barany and more recently by Pau and Limberg suggested that convective endolymphatic currents were involved. In contrast Gentine et al. suggested that the main mechanism responsible for caloric nystagmus is buoyancy due to calorization of the endolymph, without the need of continuous convective currents. Finally, other authors (Scherer and Clarke, Arai et al.) proposed that thermal expansion or contraction of the endolymph were involved. In the present study experimental conditions have been considered able to discriminate between these different models. The experiments, were carried out on isolated labyrinth preparations of the frog. Only the predictions of the model based on buoyancy were fully consistent with the experimental results whereas those provided by the other models were not.

Cortical correlates of vestibulo-ocular reflex modulation: a PET study.

To elucidate cortical correlates of vestibulo-ocular reflex (VOR) modulation, we observed cortical activation during fixation suppression and habituation of caloric vestibular nystagmus in 12 normal subjects, using PET. Significant positive correlation between regional cerebral blood flow (rCBF) and slow phase eye velocity of caloric nystagmus was observed in the middle and posterior insula, inferior parietal lobule, temporal pole, right fusiform gyrus, lingual gyrus, and cerebellar vermis and hemisphere. The rCBF increase in the insular region and the inferior parietal lobule was lateralized depending on the direction of the nystagmus. Caloric nystagmus was suppressed as a result of visual fixation, during which time the area around the right frontal eye field, temporal pole, inferior temporal gyrus, a broad area in the visual cortex, including fusiform and lingual gyrus, cerebellar uvula/nodulus and flocculus, exhibited positive correlation with fixation suppression of caloric nystagmus, while vestibular cortices exhibited negative correlation. The caloric nystagmus habituated with repetition of stimulation. With habituation, we observed activation in the right anterior cingulate gyrus, left superior parietal lobule and right cuneus, and deactivation in the anterior insula, cingulate gyrus, inferior parietal lobule and occipito-temporal visual cortex. The region that showed significant co-activation with fixation suppression and habituation of caloric nystagmus was the right cuneus, and significant co-deactivation was observed in the anterior insula, cingulate gyrus, inferior parietal lobule and middle temporal visual cortex. The present results support previous observations that the parieto-insular cortex and inferior parietal lobule are involved in processing of vestibular information, and, in addition, suggest that activation may depend on the direction of nystagmus. Deactivation of vestibular cortices during visual fixation supports the concept of inhibitory visual-vestibular interaction in the cortex. Significant activation of the cingulate, superior parietal and visual cortices, and cerebellar vermis accompanying reduction of caloric response with repeated stimuli suggests possible involvement of these regions in vestibular habituation. Common activation of the cuneus in visual cortex and deactivation of vestibular and visuo-spatial association cortices by both visual suppression and habituation of VOR suggests that these two mechanisms are not completely independent but may share some cortical and subcortical regions.

Wallenberg's syndrome: neurotological classification

Objectives: Visually induced eye movements were investigated in 26 patients with Wallenberg's syndrome. Methods: Slow-phase optokinetic nystagmus (OKN) velocities, pursuit gains, and percentage fixation suppression (%FS) of caloric nystagmus were recorded by DC electrooculography (EOG), and stored directly onto FM magnetic tape. Results: OKN velocities, pursuit gains, and %FS decreased toward the lesion side (group A), whereas OKN velocities and pursuit gains decreased toward the side contralateral to the lesion side. %FS decreased toward the lesion side (group B). MR images in group A showed that lesions were only in and near to the vestibular nuclei, and images in group B showed that lesions extended to the cerebellum. Conclusion: Visually guided eye movements allow classification of Wallenberg's syndrome into two types, one with brainstem lesions and one with both brainstem and cerebellar lesions. This demonstrates that assessing eye movements is helpful in supplementing MRI data.