Search Coil Method Research Articles

Primate eye tracking with carbon-nanotube-paper-composite based capacitive sensors and machine learning algorithms

BackgroundAccurate real-time eye tracking is crucial in oculomotor system research. While the scleral search coil system is the gold standard, its implantation procedure and bulkiness pose challenges. Camera-based systems are affected by ambient lighting and require high computational and electric power. New MethodThis study presents a novel eye tracker using proximity capacitive sensors made of carbon-nanotube-paper-composite (CPC). These sensors detect femtofarad-level capacitance changes caused by primate corneal movement during horizontal and vertical eye rotations. Data processing and machine learning algorithms are evaluated to enhance the accuracy of gaze angle prediction. ResultsThe system performance is benchmarked against the scleral coil during smooth pursuits, saccades tracking, and fixations. The eye tracker demonstrates up to 0.97 correlation with the coil in eye tracking and is capable of estimating gaze angle with a median absolute error as low as 0.30°. ComparisonThe capacitive eye tracker demonstrates good consistency and accuracy in comparison to the gold-standard scleral search coil method. ConclusionsThis lightweight, non-invasive capacitive eye tracker offers potential as an alternative to traditional coil and camera-based systems in oculomotor research and vision science.

Stability of the aVOR to Repeat Head Impulse Testing.

The angular vestibulo-ocular reflex (aVOR) is known to be influenced by factors such as arousal and cognition during traditional vestibular function testing. However, the inherent variability of the aVOR to head impulse testing has not been explicitly examined. The purpose of this study was to determine the variability of the aVOR to active and passive head impulses using the gold standard scleral search coil method to record head and eye rotation. Descriptive. Tertiary referral center. Twenty six healthy control subjects agreed to active and passive horizontal head impulse testing on at least two separate sessions from two unique institutions. An additional 27 individuals with cochlear implantation (CI) underwent passive horizontal and vertical semicircular canal plane head impulse testing. Test sessions were separated from 3 to 210 days in the normal subjects and from 49 to 537 days in the subjects with CI. Reliability of the angular VOR gain (eye velocity/head velocity) over time. In the healthy control subjects, there was no difference in aVOR gain between right and left ears, between session one and session two, or between active (self-generated, 0.99 ± 0.08) or passive (imposed, 1.0 ± 0.08) head impulses. In the patients, we also found the aVOR gain very stable over time. However, the aVOR gains of the patients were different across the semicircular canal planes tested (p < 0.001) with the four vertical semicircular canals having lower aVOR gains than the two horizontal canals. Our data suggest the aVOR gain is quite stable when tested across unique days in healthy controls and patients with auditory-only inner ear pathology.

Finite size effect on Sm3+ doped Mn0.5Zn0.5SmxFe2−xO4 (0≤x≤0.5) ferrite nanoparticles

Samarium doped Mn–Zn ferrite nanoparticles of composition Mn0.5Zn0.5SmxFe2−xO4 (0≤x≤0.5) have been synthesized by a chemical co-precipitation method for developing low Curie temperature stable ferrofluid. These samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Electron Paramagnetic Resonance (EPR) spectroscopy and search coil method analytical techniques for their structural, morphological and magnetic properties. X-ray diffraction patterns confirmed the formation of crystalline single spinel phase of as grown nanoparticles. Lattice parameter and lattice strain increases with the increase in Sm3+ content. SEM images revealed the presence of ultrafine particles and their agglomerated structures in higher Sm3+ ions concentration analogues. The stoichiometry of the final product agreed well with the initial substitution composition as evidenced by EDS data. Electron paramagnetic resonance (EPR) spectra proved the ferromagnetic nature of nanoparticles. The magnetic measurements by search coil method showed superparamagnetism for x=0, 0.1 the samples with saturation magnetization of 23.95emu/g for Mn0.5Zn0.5Fe2O4 sample which increases with rise in Sm3+ ions content. The results are explained and correlated with the structural, morphological and magnetic properties for developing stable kerosene based ferrofluid by using these nanoparticles.

Effect of Gd3+ ion distribution on structural and magnetic properties in nano-sized Mn–Zn ferrite particles

Nanoparticles of Gd3+ ions doped Mn0.5Zn0.5GdxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4) mixed ferrite were prepared using chemical co-precipitation method. The X-ray diffraction measurements confirmed the formation of a cubic spinel structure. The structural parameters like crystallite size, lattice parameter and strain induced have been calculated. The lattice parameter increases with the increase in Gd3+ ion concentration and shows non linear behaviour. HRTEM investigation confirms the nano size formation of the Gd doped Mn–Zn ferrite nanoparticles. EPR was used to evaluate resonance peak intensity, Lande’s splitting factor (g value), peak to peak line width (ΔHp–p), spin concentration (Ns) and relaxation time (τs). Line width, line intensity, relaxation time and spin concentration increase with Gd3+ ions doping (for x=0.1 to x=0.3) and then decrease for x=0.4, whereas the g value shows the reverse trend for the same composition. IR spectra shows two strong absorption bands at 570cm−1 and 416cm−1 of tetrahedral and octahedral bond stretching respectively in all the samples. IR spectrum also shows that Gd3+ occupies the octahedral B-sites. Magnetic parameters such as saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) were measured by search coil method. The value of saturation magnetization increases from 29.94emu/gm for x=0.1 to 46.01emu/gm for x=0.4.

Evaluation of Quantitative Head Impulse Testing Using Search Coils Versus Video-oculography in Older Individuals

To evaluate the validity of 2D video-oculography (VOG) compared with scleral search coils for horizontal AVOR gain estimation in older individuals. Cross-sectional validation study. Tertiary care academic medical center. Six individuals age 70 and older. Simultaneous eye movement recording with scleral search coil (over right eye) and EyeSeeCam VOG camera (over left eye) during horizontal head impulses. Best estimate search coil and VOG horizontal AVOR gain, presence of compensatory saccades using both eye movement recording techniques. We observed a significant correlation between search coil and VOG best estimate horizontal AVOR gain (r = 0.86, p = 0.0002). We evaluated individual head impulses and found that the shapes of the head movement and eye movement traces from the coil and VOG systems were similar. Specific features of eye movements seen in older individuals, including overt and covert corrective saccades and anticompensatory eye movements, were captured by both the search coil and VOG systems. These data suggest that VOG is a reasonable proxy for search coil eye movement recording in older subjects to estimate VOR gain and the approximate timing of corrective eye movements. VOG offers advantages over the conventional search coil method; it is portable and easy to use, allowing for quantitative VOR estimation in diverse settings such as a routine office-based practice, at the bedside, and potentially in larger scale population analyses.

Binocular Eye Movement Control and Motion Perception: What Is Being Tracked?

We investigated under what conditions humans can make independent slow phase eye movements. The ability to make independent movements of the two eyes generally is attributed to few specialized lateral eyed animal species, for example chameleons. In our study, we showed that humans also can move the eyes in different directions. To maintain binocular retinal correspondence independent slow phase movements of each eye are produced. We used the scleral search coil method to measure binocular eye movements in response to dichoptically viewed visual stimuli oscillating in orthogonal direction. Correlated stimuli led to orthogonal slow eye movements, while the binocularly perceived motion was the vector sum of the motion presented to each eye. The importance of binocular fusion on independency of the movements of the two eyes was investigated with anti-correlated stimuli. The perceived global motion pattern of anti-correlated dichoptic stimuli was perceived as an oblique oscillatory motion, as well as resulted in a conjugate oblique motion of the eyes. We propose that the ability to make independent slow phase eye movements in humans is used to maintain binocular retinal correspondence. Eye-of-origin and binocular information are used during the processing of binocular visual information, and it is decided at an early stage whether binocular or monocular motion information and independent slow phase eye movements of each eye are produced during binocular tracking.

Video Head Impulse Test Diagnoses Vestibulotoxicity

ObjectiveVideo oculography is a simple, accurate alternative to the scleral search coil method measuring individual semicircular canal function in Head Impulse Testing (HIT). Here we compare the video HIT with the caloric test for the diagnosis of unilateral or bilateral vestibulotoxicity due to systemic gentamicin therapy.MethodUsing the video HIT (ICS Impulse – GN Otometrics, Taastrup, Denmark) we studied 23/126 patients with gentamicin vestibulotoxicity; 5 unilateral, 18 bilateral. All 126 had caloric testing (30°C, 44°C); 82 also had 0°C testing. The video HIT took about 15 minutes and gave immediate results.ResultsAll 126 patients had severe unilateral or bilateral impairment of lateral semicircular canal function on caloric testing. Slow phase velocity was under 5°/s for each 30 or 44°C irrigation and under 7°/s for each 0°C irrigation. The video HIT correctly detected this loss in all 23 patients tested. During the video HIT the gain of the vestibulo‐ocular reflex from each lateral semicircular canal varied from 0.3 to 0.9 (N &gt; 0.95). While a gain of 0.9 is near normal, the data in each patient showed covert or overt catch‐up saccades, confirming the vestibulo‐ocular reflex deficit.ConclusionThe video HIT is a simple, accurate way of immediately diagnosing unilateral or bilateral gentamicin vestibulotoxicity avoiding the need for caloric testing. It might be applicable for monitoring of patients receiving potentially vestibulotoxic drugs and might in time replace the caloric test for the diagnosis of peripheral vestibulopathies.

Invariance of vestibulo-ocular reflex gain to head impulses in pitch at different initial eye-in-orbit elevations: Implications for Alexander's law

Conclusions: These findings are in line with previous data on the horizontal vestibulo-ocular reflex (VOR) from this laboratory and suggest that eye position signals do not modulate natural vestibular responses. Hence, the Alexander's law (AL) phenomenon cannot be interpreted simply as a consequence of vestibular or oculomotor nuclei activity modulation with desired gaze. Background: AL states that the intensity of the spontaneous nystagmus of a patient with a unilateral vestibular lesion grows with increasing gaze in the direction of the fast phase. Some of the mechanisms proposed to account for the gaze effects assume a direct modification of the normal VOR by eye position signals. We tested the validity of these assumptions and investigated the effects of gaze direction on the normal vertical human VOR in the behaviorally relevant high frequency range. Methods: Head and eye movements were recorded with the search coil method during passive head impulses in pitch, while subjects were asked to hold gaze at various elevation angles in 8° steps within ± 16° from the straight ahead reference position. Results: Upward and downward head rotations produced VOR gains of similar magnitude. Furthermore, the gain remained unaffected by eye-in-orbit position for both upward and downward head impulses.

Search Coil법의 EMTP 분석을 통한 HVDC 케이블 상세 고장지점 판정 정확도 개선

In a previous paper, the EMTP modeling technique using search coil test is established through various transient analysis including system grounding condition and grounding resistance for HVDC submarine cables. It was also proved by comparison with real test results. Based on this EMTP modeling technique, in this paper, it will be applied for modeling of real HVDC submarine system(Jeju~Haenam). This paper variously analyses the effects of fault resistance including the resistance between core and sheath, the resistance between sheath and amore and the resistance between amore and sea water through EMTP modeling of search coil method. The results can contribute to the accuracy of detailed fault point prediction of search coil test for HVDC submarine cables.

Alexander's law during high-acceleration head rotations in humans

Alexander's law states that the amplitude of the spontaneous nystagmus grows with increasing gaze in the direction of the fast phase. Using the search-coil method we employed head impulses at various eye-in-orbit azimuth angles to test (i) whether the normal vestibulo-ocular reflex (VOR) in the behaviorally relevant high-frequency range has intrinsic properties that could account for Alexander's law and (ii) whether such properties can also be shown in patients with unilateral vestibulopathy. We showed that the gain of the VOR remained unaffected by eye-in-orbit position in contols and in patients, both on ipsilesional and contralesional stimuli. These findings suggest that eye-in-orbit position does not directly modulate the activity in VOR pathways, neither during unbalanced but reciprocal (in controls), nor during unbalanced and nonreciprocal natural vestibular stimulation (in patients).

Applying double-magnetic induction to measure head-unrestrained gaze shifts: calibration and validation in monkey

The double magnetic induction (DMI) method has successfully been used to record head-unrestrained gaze shifts in human subjects (Bremen etal., J Neurosci Methods 160:75-84, 2007a, J Neurophysiol, 98:3759-3769, 2007b). This method employs a small golden ring placed on the eye that, when positioned within oscillating magnetic fields, induces orientation-dependent voltages in a pickup coil in front of the eye. Here we develop and test a streamlined calibration routine for use with experimental animals, in particular, with monkeys. The calibration routine requires the animal solely to accurately follow visual targets presented at random locations in the visual field. Animals can readily learn this task. In addition, we use the fact that the pickup coil can be fixed rigidly and reproducibly on implants on the animal's skull. Therefore, accumulation of calibration data leads to increasing accuracy. As a first step, we simulated gaze shifts and the resulting DMI signals. Our simulations showed that the complex DMI signals can be effectively calibrated with the use of random target sequences, which elicit substantial decoupling of eye- and head orientations in a natural way. Subsequently, we tested our paradigm on three macaque monkeys. Our results show that the data for a successful calibration can be collected in a single recording session, in which the monkey makes about 1,500-2,000 goal-directed saccades. We obtained a resolution of 30 arc minutes (measurement range [-60,+60]°). This resolution compares to the fixation resolution of the monkey's oculomotor system, and to the standard scleral search-coil method.

Lesions of the Cerebellar Nodulus and Uvula Impair Downward Pursuit

We studied sinusoidal (SIN) and step-ramp (SR) pursuit in two rhesus monkeys, before and after surgical lesions of the cerebellar nodulus and uvula (Nod/Uv). Eye movements were recorded using the magnetic field scleral search coil method. Pursuit targets were generated by an LCD projector and back-projected onto a tangent screen in an otherwise dark room. After the Nod/Uv lesions, both monkeys showed a reduced eye velocity during downward pursuit (SIN: 42% decrease in M1, 91% decrease in M2; SR: 37% decrease in M1, 85% decrease in M2). For SR, the decrease was seen only for the closed-loop response; initial eye acceleration did not change (P>0.05). Upward pursuit gains increased for SIN (M1: 9%, M2: 11%); they decreased for SR (M1: 27%, M2: 18%), but to a lesser degree than for downward pursuit. Horizontal pursuit was little changed in M1 but was reduced in one direction in M2, the animal with the larger lesion. The deficit in downward tracking was limited to foveal pursuit; ocular following of random-dot stimuli was retained, even when the target subtended only several degrees. Our findings support a critical role for the Nod/Uv in vertical pursuit, particularly for sustained downward pursuit. Finally, in both monkeys, the lesion increased spontaneous upward ocular drift in the dark (mean prelesion, 1.43 degrees/s; postlesion, 5.92 degrees/s), suggesting a role for the Nod/Uv in holding the eyes still and in the genesis of downbeat nystagmus.

Cortical evoked responses to magnetic stimulation of macaque's abdominal wall in sleep-wake cycle.

EEG and eye movements (magnetic search coil method) were recorded in sleep and wakefulness in a monkey (Macaca fascicularis) while the animal was sitting in a primate chair. Single pulse magnetic stimulation was applied to the monkey's abdominal wall using a circular coil and a Magstim 200 stimulator. Magnetic stimuli did not wake the sleeping animal, and being applied during slow wave sleep evoked clear responses in EEG with a latency of 80-100 ms. These responses disappeared during wakefulness and rapid eye movement sleep. Control experiments confirmed that these responses were not caused by the acoustic clicks produced by the magnetic coil. Results of this study further confirm that during sleep, signals from visceral organs reach the cortical areas which in wakefulness process exteroceptive sensory information. This observation indicates that magnetic stimulation may be a useful tool for researching neural connectivity reorganization within the sleep-wake cycle.

Ocular Motor Disorders in Mitochondrial Encephalopathy With Lactic Acid and Stroke-Like Episodes With the 3271 (T-C) Point Mutation in Mitochondrial DNA

Ocular motor function can provide insights into areas of dysfunction within the nervous system. There are no published eye movement recordings in patients with mitochondrial encephalopathy with lactic acid and stroke-like episodes (MELAS). Our purpose in this study was to analyze the ocular motor features of a family with MELAS with a (T-C) mutation at nucleotide position 3271 in the mitochondrial tRNA-Leu gene. The search coil method was used to record visually-guided saccades, antisaccades, and triangular pursuit tasks in the horizontal and vertical planes in three patients in a Japanese family with MELAS. The patients showed saccadic dysmetria and prolonged saccadic reaction times, deficits in the ability to suppress reflex eye movements, and increased reaction time during antisaccades, downbeat nystagmus, square wave jerks, and impairment in pursuit. On the basis of eye movement recordings, patients with MELAS have frontal cortex as well as cerebellar dysfunction.

Saccade initiation in ocular motor apraxia

Sirs: Ocular motor apraxia (OMA) is characterized by the loss of voluntary saccade control but the simultaneous preservation of saccades of the optokinetic and the vestibulo-ocular reflex (VOR) [1, 4, 6]. While the suitability of the term is still being debated [6, 10], it is not yet clear which of the conceivable compensation strategies adult patients with OMA use to elicit saccades. Saccades can be initiated in three possible ways: by using the vestibulo-ocular reflex (VOR) [2], signals of voluntary head commands [11], or blinks [2]. We tested for the first time the competing hypotheses in two adult patients with OMA to elucidate the mechanism that helps to restore the saccadic behaviour. The first patient, a 32-year-old woman without a relevant medical history, complained of slowly progressive blurred vision over recent years. She could only produce small vertical but not horizontal saccades on command or to predictive and unpredictive visual targets without concomitant head movements. However, she was able to make small horizontal and vertical saccades in the head-free condition, i. e., during small horizontal head movements or while reading. The vestibular-ocular reflex and optokinetic nystagmus were normal. Neurological examination was otherwise unremarkable, and cranial MRI was normal. The second patient, a 60-yearold man, had had difficulty in reading for several years. A neurological examination revealed that he could hardly make any saccades on command or to predictive and unpredictive targets in the vertical direction without making concomitant head movements. However, saccades could be elicited by optokinetic and vestibular stimuli. In addition, the patient had a right hemiparesis. MRI showed a large left-sided frontoparietal cortical infarction and additional subcortical ischemic lesions on the right side. Eye, head, and lid movements were recorded with the scleral search-coil method, calibrated, and analysed as reported elsewhere [8, 9]. Statistical tests were performed using Student’s t-test and ANOVA with p-values of less than 0.05 for statistical significance. The subject’s head was measured with (head-fixed condition) and without a fixed head support (head-free condition) [8, 9]. Visually guided horizontal and vertical saccades (5 to 20 deg amplitudes) were examined in both conditions. Four healthy aged-matched subjects out of a group of 21 (aged 46 ± 13 years) were used as controls for the head-fixed condition. For the comparison of the two recording conditions (head-fixed vs. head-free) the patients’ latencies were individually compared with two aged-matched control subjects. In the head-fixed condition patient #1 made virtually no visually guided saccades in the horizontal direction (Fig. 1A); patient #2 made virtually none in the vertical direction. Saccades were delayed and hypometric compared with those of the healthy control subjects (Table 1). In the age-matched control subjects there was no difference in the latencies between the head-free (224 + 42 ms) and the head-fixed condition (217 + 38 ms) measured in the same experimental session. In the head-free condition horizontal and vertical visually guided saccades were elicited in both patients (Table 1; Fig. 1B). However, head movements were much more prominent in the patients than in controls (Fig. 1B and E, thin black LETTER TO THE EDITORS

Eye–hand coordination in essential tremor

Patients with essential tremor (ET) or with cerebellar lesions have in common oculomotor abnormalities, with the exception of saccadic eye movements, which do not seem to be involved in ET. Since grasping is prolonged in ET and might be related to saccadic dysmetria, we tested whether simultaneous hand pointing could unmask it. Twelve ET patients and 14 controls performed saccades with and without simultaneous pointing movements to the same targets, and with and without a gap between the disappearance of the fixation point and the appearance of the target. Eye movements were recorded with the magnetic search-coil method, hand movements with an ultrasound-emitting probe. ET patients did not have saccadic dysmetria, and contrary to normal subjects their saccadic latency did not decrease during combined eye-hand movements compared with saccades performed in isolation. Hand movements had a longer duration in ET patients, with decreased peak acceleration, an increased latency of the peak velocity, and peak deceleration. In conclusion, this first study on eye-hand coordination in ET revealed abnormal kinematic changes in the early phase of pointing movements. These changes might be related to cerebellar disease but they are independent of the intention tremor component and saccade performance.

Intra-Individual Variability of Saccadic Velocity Measured with the Infrared Reflection and Magnetic Scleral Search Coil Methods

Background. The infrared (IR) and the magnetic scleral search coil (MSC) systems for eye tracking were studied with regard to the intra-individual variability in saccadic eye movement recordings. Method. Three healthy subjects performed similar saccadic eye movement tasks at five different occasions with both the IR (Orbit XY-1000) and the MSC (Skalar Medical) techniques. The maximum velocity (VMAX) and slope constant (C) of the main sequence plots were analyzed with regard to the coefficient of variation (CV) and the intraclass correlation coefficient (Ricc). In addition, the possible reasons for variability in the IR recordings, especially different causes for noise, were analyzed and discussed. Results. The main sequence data showed intra-individual variation with both recording systems, but the coefficient of variation was higher for VMAX with the IR compared to the MSC method. Ricc analysis showed that 36% of the variance of VMAX and 49% of the variance of C resulted from intra-individual variability in recordings of the IR system. The corresponding results for the MSC recordings regarding VMAX and C were 48% and 88%. Conclusions. Saccadic eye movement recordings yielded a larger intra-individual variability with the IR system than with the MSC system. The effect that the MSC annulus may have on the ocular motor command signal and the possible low pass filter caused by the coil slipping on the surface of the eye may partly explain the relatively lower velocity in the MSC recordings. Also, noise in the IR recordings induces peaks of eye velocity, which can be reduced considerably by filtering. However, the variability in the recordings, which was larger in the IR than in the MSC recordings, did not seem to be decreased by filtering. The basic level of noise in the recordings was not clearly associated with the amount of reduction of VMAX when the IR recordings were filtered. We suggest that artefacts of the saccadic signal, which can be related to changes in the reflecting surface of the eyes and eyelids, are important factors for explaining the variability and high-velocity peaks in the IR recordings. Lighting conditions was confirmed as a cause for noise, but temperature and air humidity changes in the goggles were not suspected to influence data in the normal experimental setting. Although noise, shortcomings of the recording technique and procedure may offer explanations for the intra-individual variability, the calibration procedure and changes in attention and fatigue of the subject should also be considered.

A comparison between the magnetic scleral search coil and infrared reflection methods for saccadic eye movement analysis

A non-invasive eye tracking system, based on pulsed infrared light (IR), was compared with the magnetic scleral search coil method (MSC) for saccadic eye movement recordings. Ten normal subjects performed horizontal and vertical saccades recorded with both methods. Eight recordings were complete and analysed for maximum peak velocity (V(MAX)) and constant (C) of the main sequence curve. The IR recordings showed significantly higher peak velocity values than the MSC system and generally more inter-individual variability. No significant difference regarding peak velocity was detected between abducting and adducting saccades or between upward and downward saccades with either of the systems. Horizontal saccades had higher peak velocities with both techniques. Comparison of the main sequence plots of the IR and MSC eye tracking techniques reveals that the IR system yields higher values of maximum peak velocity and the constant, the differences being similar for eye movements in different directions. There are various possible explanations for the lower maximum velocity of the MSC recordings, e.g. slipping of the coil annulus on the surface of the eye and a change of the oculomotor command signal induced by wearing the coil. Also, artefacts associated with the IR recording system may cause over-estimations of the saccadic velocity and, furthermore, contribute to the higher variability of the IR recordings.

Selective Impairment of Downward Gaze Holding Observed in One-and-a-Half Syndrome

A 43-year-old man with pontine cavernous hemangioma in the left dorsal pons showed left facial nerve palsy and right hemiparesis and paretic pontine exotropia of the right eye. His conjugate horizontal eye movements were restricted except for abduction of the right eye. His convergence, however, was preserved. His eye movements were investigated using DC-EOG and magnetic search coil methods. Abduction of the right eye was hypermetric and followed by dissociated nystagmus, indicating left internuclear ophthalmoplegia. Downward visually guided saccades were hypermetric and followed by exponential drifts with an average time constant of 0.9 s. Leaky integration was not observed after upward saccades. Upward smooth pursuit was well preserved, while downward smooth pursuit was impaired. Impairment of neural integration for downward eye movements may accompany one-and-a-half syndrome. We speculate that downward and upward velocity-to-position integration signals may flow separately in the medial longitudinal fasciculus and its vicinity.

Vertical vestibular responses to head impulses are symmetric in downbeat nystagmus.

Downbeat nystagmus (DBN), a frequent ocular motor sign often caused by cerebellar lesions, is a fixational nystagmus with fast phases directed downward. Its precise etiology is not known. One hypothesis is that it is caused by a central imbalance of pathways of the vertical vestibulo-ocular reflex (VOR). Such an imbalance would cause not only ocular drift but also deficient and asymmetric vertical VOR responses. To test this hypothesis, the authors analyzed the functionally relevant VOR responses to head impulses in the roll, pitch, and yaw planes. Head and eye movements were measured with the search-coil method in 10 patients with DBN and 10 age-matched control subjects. Analysis revealed no gain difference in patients with DBN compared with control subjects. Specifically, upward and downward VOR responses in patients with DBN in the pitch plane were symmetric. These findings do not support the hypothesis of a vertical VOR imbalance and put into question the view that DBN is a central vestibular syndrome in the sense of vestibular dysfunction. Although DBN possibly involves vestibulocerebellar pathways, in the patients that we studied, DBN did not affect the immediate VOR responses in the high-frequency range that corresponds to natural head movements.