Nystagmus Slow Phase Velocity Research Articles

From nystagmus to the air and water caloric tests

The caloric test is an important tool for the assessment of labyrinthine function.Objective: To compare the nystagmus response in the caloric tests with air at 50°C and 24°C and with water at 44°C and 30°C. Study Design: Randomized crossover clinical trial.Materials and Methods: 40 healthy individuals were submitted to a neurotological evaluation, including caloric tests with air at 50°C and 24°C and water at 44°C and 30°C.Results: Comparing the air and water caloric tests, there were no significant differences among the post-caloric nystagmus slow-phase velocity in relation to the stimulation order, between ears and between the values of unilateral weakness and directional preponderance. The slow-phase velocity values were higher with water (p = 0.008, p < 0.001), and cold stimulation produced stronger responses (p < 0.001).Conclusion: Comparing 50°C and 24°C air caloric test and 44°C and 30°C water caloric test, we observed similar slow-phase velocity values for both ears, higher responses in the cold temperature and in the test with water, and similar results of unilateral weakness or directional preponderance for post-caloric nystagmus in both tests.

The video head impulse test during post-rotatory nystagmus: physiology and clinical implications

The aim of this study was to test the effects of a sustained nystagmus on the head impulse response of the vestibulo-ocular reflex (VOR) in healthy subjects. VOR gain (slow-phase eye velocity/head velocity) was measured using video head impulse test goggles. Acting as a surrogate for a spontaneous nystagmus (SN), a post-rotatory nystagmus (PRN) was elicited after a sustained, constant-velocity rotation, and then head impulses were applied. 'Raw' VOR gain, uncorrected for PRN, in healthy subjects in response to head impulses with peak velocities in the range of 150°/s-250°/s was significantly increased (as reflected in an increase in the slope of the gain versus head velocity relationship) after inducing PRN with slow phases of nystagmus of high intensity (>30°/s) in the same but not in the opposite direction as the slow-phase response induced by the head impulses. The values of VOR gain themselves, however, remained in the normal range with slow-phase velocities of PRN < 30°/s. Finally, quick phases of PRN were suppressed during the first 20-160 ms of a head impulse; the time frame of suppression depended on the direction of PRN but not on the duration of the head impulse. Our results in normal subjects suggest that VOR gains measured using head impulses may have to be corrected for any superimposed SN when the slow-phase velocity of nystagmus is relatively high and the peak velocity of the head movements is relatively low. The suppression of quick phases during head impulses may help to improve steady fixation during rapid head movements.

Vestibular findings in chronic pain

Background: Earlier evidence show that the insular cortex might play an important role in the building of the abstract idea of our body state suggesting that insular dysfunctions would lead to abnormal corporal perception in chronic pain. Neuroanatomical and functional studies show that the insular cortex modulate vestibular activity in the brain stem, however the vestibular activity has been poor studied in chronic pain. Objective: The aim of this research is to study the vestibular activity in chronic pain. Patients and method: 10 chronic pain patients, and 10 healthy subjects, were tested in aTonnies, Erben KG model rotary chair. The nystagmus was recorded by electronystagmography. For the appreciation of the symmetry between right or left vestibular activity we measured the nystagmus's slow phase velocity (SPV) induced by right and leftward rotation of the chair correspondingly. Results: The chronic pain subjects group showed an asymmetric vestibular pattern of activity, significantly different (p < 0.05) to the healthy group who presented symmetric vestibular activity. Conclusions: We found that the vestibular patterns of response to rotary testing in chronic pain were different than healthy ones. The physio-pathological significance of this finding should be the subject of further research. *I have obtained patient and/or Institutional Review Board (IRB) approval, as necessary.

Development and Understanding of Caloric Responses; An Overview of the First Hundred Years

In 1906 Robert Barany published his original research on the caloric test and his convection theory to explain the direction of nystagmus. Subsequent publications by others suggested different explanations, including the effect of temperature on the vestibular nerves, pressure changes in the ampulla related to temperature expansion, but also the possibility of otolith modulation of the response. Technical developments have allowed quantitative measurement of the caloric response using electronystagmography; caloric assessment consists of measuring the slow phase velocity of nystagmus and uses the Jongkees-Phillipszoon equation (difference over sum) to detect pathology. The caloric test has become an entrenched assessment in the evaluation of patients with vestibular complaints. Barany’s convection theory was accepted as the explanation for the fact that with the lateral semicircular canal at right angles to horizontal (30 degrees head up) the response to caloric irrigation was greater with the patient supine (face up) than prone (face down). The convection theory was questioned when caloric responses in the appropriate direction were documented during space flight. It seems that there are many factors affecting the underlying convection caloric response that has been advanced for the last century.

The Effects of Betahistine and Dimenhydrinate on Caloric Test Parameters; Slow-Phase Velocity of Nystagmus

OBJECTIVE: The aim of this study is to determine the effects of betahistine and dimenhydrinate on the slow phase velocity. MATERIALS and METHODS: Forty patients with complaints of vertigo and dizziness volunteered to be included in the study. All patients who were included the study were treated at the other medical centers. The patients were divided into two Groups. Patients in the first Group were given betahistine 24 mg three times per day. During this treatment, caloric testing was performed, and the dose was increased to 48 mg three times a day due to ongoing complaints. The test was then repeated four weeks after using this higher dosage. Patients in the second Group had caloric testing while using and four weeks after stopping dimenhydrinate. RESULTS: The study Group was comprised of 40 patients; 20 patients (13 female, 7 male, 18-68 years, median age 46) in the betahistine Group and 20 patients (14 female, 6 male, 24-74 years, median age 44.5) in the dimenhydrinate Group. The average slow phase maximum velocity in the first Group of patients was 18 -/+ 8.2 and 21.1 -/+ 10.8 deg/s at 24 mg betahistine three times a day and 48 mg three times a day, respectively. In the second Group of patients, the average slow phase velocity was 13.4 -/+ 5.1 and 18.2 -/+ 7.5 deg/s during and after stopping the treatment of dimenhydrinate, respectively. The caloric test-induced slow-phase velocity was decreased with dimenhydrinate and increased with the higher dosage of betahistine. CONCLUSION: To our knowledge, this is the first study to demonstrate that betahistine increases caloric-induced slow-phase velocity in humans. Dimenhydrinate and betahistine should not be used together because of their opposite effects on the vestibular system. Dimenhydrinate can be used to treat acute episodes of vertigo, whereas betahistine should not be used during the episode but may be used in the period between the attacks to stimulate the vestibular system.

Causes and characteristics of horizontal positional nystagmus

Direction changing horizontal positional nystagmus can be observed in a variety of central and peripheral vestibular disorders. We tested sixty subjects with horizontal positional nystagmus and vertigo on the Epley Omniax(®) rotator. Monocular video recordings were performed with the right or left ear down, in the supine and prone positions. Nystagmus slow-phase velocity (SPV) was plotted as a function of time. Thirty-one subjects diagnosed with horizontal canalolithiasis had paroxysmal horizontal geotropic nystagmus with the affected ear down (onset 0.8 ± 1 s, range 0-4.9 s, duration 11.7-47.9 s, peak SPV 79 ± 67°/s). The SPV peaked at 5-20 s and declined to 0 by 60 s; at 40 s from onset, the average SPV was 1.8 % of the peak. Nine subjects diagnosed with cupulolithiasis had persistent apogeotropic horizontal nystagmus (onset 0.7 ± 1.4 s, range 0-4.3 s). Peak SPV was 54.2 ± 31.8°/s and 26.6 ± 12.2°/s with unaffected and affected ears down, respectively. At 40 s, the average SPV had decayed to only 81 % (unaffected ear down) and 65 % (affected ear down) of the peak. Twenty subjects were diagnosed with disorders other than benign positional vertigo (BPV) [vestibular migraine (VM), Ménière's Disease, vestibular schwannoma, unilateral or bilateral peripheral vestibular loss]. Subjects with VM (n = 13) had persistent geotropic or apogeotropic horizontal nystagmus. On average, at 40 s from nystagmus onset, the SPV was 61 % of the peak. Two patients with Ménière's Disease had persistent apogeotropic horizontal nystagmus; the peak SPV at 40 s ranged between 28.6 and 49.5 % of the peak. Symptomatic horizontal positional nystagmus can be observed in canalolithiasis, cupulolithiasis and diverse central and peripheral vestibulopathies; its temporal and intensity profile could be helpful in the separation of these entities.

The Significance of 180-Degree Head Rotation in Supine Roll Test for Horizontal Canal Benign Paroxysmal Positional Vertigo

The relatively low success rate of the treatment maneuver for horizontal semicircular canal (HSC) benign paroxysmal positional vertigo (BPPV) may be caused by the difficulty determining the affected side. We developed a 180-degree supine roll test (SRT) by modifying the 90-degree SRT to increase diagnostic accuracy and evaluated its significance. A prospective study. Tertiary referral center. A total of 122 patients with HSC-BPPV performed both the 90- and 180-degree SRTs. The affected side was determined by the 90- and 180-degree SRTs. The bow and lean (BL) test was also performed in cases with ambiguous or opposite results on both SRTs. A comparison of the difference in slow phase velocity (SPV) of nystagmus among the 90- and 180-degree SRTs and BL test. The maximum SPV of nystagmus during the 180-degree SRT was significantly greater than that during the 90-degree SRT. The SPV difference was less in the 180-degree SRT than that in the 90-degree SRT. Although the 180-degree SRT showed fewer meaningful results (n = 65) than the 90-degree SRT (n = 71), the affected side was determined by the 180-degree SRT in 15 cases with ambiguous results on the 90-degree SRT. Among 10 cases showing opposite results, 7 were identified by the BL test. Five (71.4%) of 7 cases had consistent affected sides with the 180-degree SRT. The 180-degree SRT can be an additional method when it is difficult to determine the affected side from the 90-degree SRT.

4-Aminopyridine suppresses positional nystagmus caused by cerebellar vermis lesion

Dear Sirs, A 45-year old woman presented to our outpatient clinic with recurrent attacks of vertigo that were induced by changing of body position and lasted up to 1 min. MRI revealed a cystic lesion in the right cerebellar vermis, which was removed and identified as a hemangioblastoma. After resection of the tumor, positional symptoms did not change. Postoperative MRI showed a lesion in the right posterior vermis (lobules V/VI, Fig. 1a left). Backward head movements or supine body position induced a transient downbeat nystagmus (DBN) lasting 10–20 s, associated with vertigo (see video in supplement). Forward head and body movements did not elicit any symptoms or nystagmus. Eye movement recordings with the scleral search coil showed maximal nystagmus slow phase velocity of 28 /s; with a latency of up to 3 s after the head movement and a mean duration of 13 s. Otherwise the neuro-ophthalmological examination was normal, except for macro-square wave jerks. After treatment with 4-aminopyridine (4-AP) 5 mg t.i.d., symptoms disappeared within 3 days. Eye movement recordings during this treatment showed a complete cessation of the DBN during positional maneuvers (Fig. 1b). When 4-AP treatment was stopped, DBN reappeared on positioning provocation 2 days later. To elucidate the pathomechanism of positional DBN in our case and the mode of its suppression through 4-AP, a [F]-fluorodeoxyglucose-(FDG)-PET protocol was performed before and during 4-AP treatment and compared to a FDG-PET reference template of 15 healthy controls (HC): FDG was injected intravenously while the patient was provoking the symptoms by back-and-forth head movements, i.e., backward head extension versus straight ahead position, performed alternately in 30 s intervals over 10 min. First, the FDG-PET of the patient before 4-AP treatment was compared with the HC template in order to depict areas of altered regional cerebral glucose metabolism (rCGM) that may correspond to the positional DBN. HC showed a relatively increased rCGM in the right posterior vermis (as expected, because of the lesional defect), but also in the nodulus and (para-)flocculus bilaterally (Fig. 1a, middle). When the FDG-PET of the patient during 4-AP treatment was compared to the HC template, the relative difference in rCGM of the nodulus and (para-)flocculus decreased, which indicates 4-APinduced activation of the respective areas in the patient (Fig. 1a right). O. Kremmyda and A. Zwergal contributed equally to this work.

Suppression of spontaneous nystagmus during different visual fixation conditions

Analysis of spontaneous nystagmus is important in the evaluation of dizzy patients. The aim was to measure how different visual conditions affect the properties of nystagmus using three-dimensional video-oculography (VOG). We compared prevalence, frequency and slow phase velocity (SPV) of the spontaneous nystagmus with gaze fixation allowed, with Frenzel's glasses, and in total darkness. Twenty-five patients (35 measurements) with the peripheral vestibular pathologies were included. The prevalence of nystagmus with the gaze fixation was 40%, and it increased significantly to 66% with Frenzel's glasses and regular room lights on (p < 0.01). The prevalence increased significantly to 83% when the regular room lights were switched off (p = 0.014), and further to 100% in total darkness (p = 0.025). The mean SPV of nystagmus with visual fixation allowed was 1.0°/s. It increased to 2.4°/s with Frenzel's glasses and room lights on, and additionally to 3.1°/s, when the regular room lights were switched off. The mean SPV in total darkness was 6.9°/s. The difference was highly significant between all test conditions (p < 0.01). The frequency of nystagmus was 0.7 beats/s with gaze fixation, 0.8 beats/s in both the test conditions with Frenzel's glasses on, and 1.2 beats/s in total darkness. The frequency in total darkness was significantly higher (p < 0.05) than with Frenzel's glasses, and more so than with visual fixation (p = 0.003). The VOG in total darkness is superior in detecting nystagmus, since Frenzel's glasses allow visual suppression to happen, and this effect is reinforced with gaze fixation allowed. Strict control of visual surroundings is essential in interpreting peripheral nystagmus.

Relationship of slow-phase velocity to visual acuity in infantile nystagmus associated with albinism

To investigate the relationship between slow-phase velocity of nystagmus and visual acuity in children with albinism. Twelve children with infantile nystagmus associated with albinism had eye movements recorded by binocular video-oculography (10 patients) or by scleral search coil (2 patients). In children younger than 3 years of age visual acuities was assessed by means of Teller acuity cards and corrected for age. Histograms of horizontal eye velocities were fit by a gamma distribution in all patients (r2>0.85). The velocity at the peak of the gamma distribution was compared with the limiting velocity predicted by the dynamic visual acuity (DVA) model. All histograms of slow-phase eye velocity were skewed toward lower velocities, with the peak distribution ranging from 5 to 20 degrees/second. The velocity at the peak of the gamma distribution for each subject was uniformly equal to or below the limiting velocity predicted by the DVA model. The average of the gamma distribution across all subjects corresponded to an upper limit to eye velocity of 17 degrees/second. At this velocity the DVA model predicted visual acuity of 20/50, which is lower than the average visual acuity reported in albinism. The distributions of eye velocity were lower than the limiting eye velocity predicted on the basis of DVA almost 50% of the time. Visual acuity in albinism is limited by macular hypoplasia rather than by slow-phase eye velocity of nystagmus.

Effects of neck muscle vibration on subjective visual vertical: comparative analysis with effects on nystagmus

In patients with unilateral vestibular dysfunction, vibratory stimulation to the neck muscles not only induces shift of the subjective visual vertical (SVV), but also enhances the generation of nystagmus. In the present study, the effects of neck vibration on the SVV were compared with those on nystagmus in patients with unilateral vestibular schwannoma (14 patients; 6 males and 8 females, mean age 54.2 years). The results indicated that the presence of nystagmus and magnitude of the SVV were generally correlated, neck vibration significantly increased the abnormal shift of the SVV and the presence of nystagmus, and the effects of vibration to the ipsilateral dorsal neck were significantly larger than those to the contralateral dorsal neck on the SVV, whereas no significant difference was observed in slow phase velocity of nystagmus. The present study suggests that both SVV and nystagmus induced by vibration have many similar clinical features and may be important in assessing the unilateral vestibular dysfunction.

The ice-water caloric test

Conclusions: Three possible results are commonly seen after ice-water caloric irrigation and to correctly interpret them the function of the corresponding vestibular receptor and of normal endolymphatic flow must be taken into account. Bedside vestibular examination helps to interpret discrepant findings. Objective: To review the findings obtained with the ice-water caloric test in patients with dizziness and to compare the results with those of the bedside test. Patients and methods: The study was undertaken in a university hospital, tertiary medical center. The indications to perform the ice-water caloric test were: 1) unilateral canal weakness >90%; 2) a maximum slow phase velocity of nystagmus after hot (44°C) and cold (30°C) caloric stimulation in either ear of <9° s–1; or 3) in both ears <15° s–1. After irrigating the ear with ice water, nystagmus was recorded in the face-up and face-down positions. The result of the test was classified as a response (nystagmus beats away from the irrigated ear in the supine position and changes when in prone), a gravity-independent response (nystagmus does not change in direction in the prone position) or no response. The spontaneous and post head-shaking nystagmus, as well as the results of the head-impulse test, were also analyzed. When indicated, a rotatory chair test was performed. Results: In the 71 patients that displayed unilateral hypofunction, the ice-water test produced a normal response in 24, a gravity-independent response in 31, and no response in 14. In two of these patients a vertical gravity-independent nystagmus response was observed. Bilateral hypofunction was found in 12 patients and the results in the head-impulse test were in agreement with the results in the ice-water test.

Alexander's Law and the Oculomotor Neural Integrator: Three-Dimensional Eye Velocity in Patients With an Acute Vestibular Asymmetry

According to Alexander's law (AL), the slow phase velocity of nystagmus of vestibular origin is dependent on horizontal position, with lower velocity when gaze is directed in the slow compared with the fast phase direction. Adaptive changes in the velocity-to-position neural integrator are thought to cause AL. Although these changes have been described for the horizontal neural integrator, nystagmus often includes vertical and torsional components, but the adaptive abilities of the vertical and torsional integrators have not been investigated. We measured 11 patients with a peripheral vestibular asymmetry and used second-order equations to describe how velocity varied with position. Horizontal velocity changed with horizontal position in accordance with AL and the second-order term for horizontal position was also significant. Whereas velocity decreased in the slow phase direction, it was relatively unchanged >10 degrees into the fast phase direction. Vertical velocity was also highest in the vertical fast phase direction and the second-order term for vertical position was also significant, in that vertical velocity increased in the vertical fast phase direction, but was unchanging in the slow phase direction. Torsional velocity varied linearly with horizontal, but not vertical, position. These results show that the horizontal and vertical oculomotor neural integrators react to altered vestibular input by maintaining different integrating time constants depending on gaze direction.

Alexander’s Law in Patients with Acute Vestibular Tone Asymmetry—Evidence for Multiple Horizontal Neural Integrators

Alexander's law (AL) states that the slow-phase velocity of spontaneous nystagmus of peripheral vestibular origin is dependent on horizontal gaze position, with greater velocity when gaze is directed in the fast-phase direction. AL is thought to be a compensatory reaction resulting from adaptive changes in the horizontal ocular motor neural integrator. Until now, only horizontal eye movements have been investigated with respect to AL. Because spontaneous nystagmus usually includes vertical and torsional components, we asked whether horizontal gaze changes would have an effect on the 3D drift of spontaneous nystagmus and, thus, on the vertical/torsional neural integrator. We hypothesized that AL reduces all nystagmus components proportionally. Moreover, we questioned the classical theory of a single bilaterally organized horizontal integrator and searched for nonlinearities of AL implying a network of multiple integrators. Using dual scleral search coils, we measured AL in 17 patients with spontaneous nystagmus. Patients followed a pulsed laser dot at eye level jumping in 5 degrees steps along the horizontal meridian between 25 degrees right and left in otherwise complete darkness. AL was observed in 15 of 17 patients. Whereas individual patients typically showed a change of 3D-drift direction at different horizontal eye positions, the average change in direction was not different from zero. The strength of AL (= rate of change of total velocity with gaze position) correlated with nystagmus slow-phase velocity (Spearman's rho = 0.5; p < 0.05) and, on average, did not change the 3D nystagmus drift direction. In general, eye velocity did not vary linearly with eye position. Rather, there was a stronger dependence of velocity on horizontal position when subjects looked in the slow-phase direction compared to the fast-phase direction. We conclude that the theory of a simple leak of a single horizontal neural integrator is not sufficient to explain all aspects of AL.

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

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.

Cerebellar ataxia with bilateral vestibulopathy: description of a syndrome and its characteristic clinical sign.

We report four patients with the syndrome of cerebellar ataxia with bilateral vestibulopathy (CABV) and, using search coil oculography, we validate its characteristic clinical sign, namely impairment of the visually enhanced vestibulo-ocular reflex (VVOR) or doll's head reflex. In our four patients, CABV began in the sixth decade of life; they are still ambulant and self-caring 8-20 years after onset. The cause of CABV in our four patients is unknown. None has a family history of cerebellar or vestibular disease; spinocerebellar ataxia (SCA) 1, 2, 3, 6, 7 and Friedreich's ataxia were excluded by genetic testing. Three of the four have a sensory peripheral neuropathy but none has extrapyramidal or significant autonomic problems, and none has gluten sensitivity. We measured eye rotations in response to head-on-trunk head rotations and in response to head-and-trunk (en bloc) rotations. Horizontal smooth pursuit (SP), vestibulo-ocular reflex (VOR) and VVOR gains were measured in response to head rotations at 0.1, 0.3, 0.6 and 1.0 Hz. The optokinetic reflex (OKR) was tested by measuring optokinetic nystagmus slow phase velocity during constant 50 degrees /s rotation of the subject in light. The results showed that CABV patients had impairment of all three compensatory eye movement reflexes, the VOR, the OKR and SP. During VVOR testing, as the frequency of head rotation increased from 0.1 to 1.0 Hz, eye velocity failed to match head velocity, gaze velocity increased, and gaze position errors developed, which were corrected with bursts of saccades, the basis of the clinical sign of an impaired VVOR.

Ｃｏｌｄ ａｉｒ ｃａｌｏｒｉｃ ｔｅｓｔにおける眼振最大緩徐相速度と刺激温度の関係

We investigated the distribution of the maximum slow phase velocity of nystagmus (max.spv) induced by cold air caloric stimuli of both 5°C and 10°C at an insufflation flow rate of 5l/min for 60sec. Test subjects who had no spontaneous nystagmus with eyes open in darkness and showed max.spv of caloric nystagmus above 20°/sec (stimulation temperature 5°C) or above 10°/sec (stimulation temperature 10°C) were selected, and classified into three groups: the younger (21-39 years), middle aged (40-64 years) and older groups (above 65 years).In stimulation at 5°C, the distribution histogram of the value of max.spv in all 355 subjects was skewed and differed from the Gaussian distribution. Each max.spv value was much more concentrated above the mean value than at the level below it. Both the younger and middle aged groups showed similar distribution histograms, but the older group showed a flat histogram with no peaks.In stimulation at 10°C the distribution histogram of the value of the max.spv in all 403 subjects was not skewed as in Gaussian distribution, and the peak value of max.spv was close to the mean value covering a wide range. The younger and middle aged groups showed the same values in all subjects, but the older group showed a distribution histogram with a peak of max.spv below the mean value.The stimulation at 5°C in the cold air caloric test seems to approach maximum stimulation, judging from its distribution histogram. When we obtain normal range results in the cold air caloric test, we have to remain aware of the stimulation temperature and subjects'ages.

Evidence for interacting cortical control of vestibular function and spatial representation in man

The objective of this research was to determine the possible relation between deficits in spatial representation capability and vestibular function following cortical lesions. We thus investigated vestibulo-ocular behaviour in a group of 14 patients with unilateral cortical damage involving the occipito-temporo-parietal junction. Patients were divided in three sub-groups: (1) Group R+: five patients with right sided cortical lesions associated with a left hemi-neglect, (2) Group R−: four patients with right sided cortical lesions with no hemi-neglect and (3) Group L: five patients with left-sided cortical lesions. The patient groups were compared to a group of eight healthy age-matched subjects. The vestibulo-ocular reflex (VOR) was tested in complete darkness by rotating the subject around the vertical axis by sinusoidal rotation at different frequencies, and by steps of acceleration or deceleration. The nystagmus slow phase velocity was measured and plotted as a function of the head velocity and the VOR parameters including gain, bias, time constant and phase were calculated. The cortical lesions induced a significant VOR asymmetry in terms of: a directional preponderance of the VOR gain to the contralesion side, only during sinusoidal rotation, and, in contrast, a VOR bias and a directional preponderance of the VOR time constant and of the nystagmus frequency to the side of the cortical lesion. These latter VOR deficits were the most significant in the R+ group, i.e. in right cortical lesions with hemi-neglect syndrome. These results demonstrate in man, the existence of a cortical influence on vestibular function related to the mechanisms of spatial representation.

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