Translational Vestibulo-ocular Reflex Research Articles

Otolith Function in Young Skilled Football Players

Background and Aim: Regular physical activities, including sports, are associated with improved balance function. The objectives of our study were to conduct cervical Vestibular Evoked Myogenic Potentials (cVEMPs) and ocular VEMPs (oVEMPs) in young adult football players and to compare the test results with those who are not involved in regular physical activities as the control group. Methods: We recruited 11 young football players (9 right-leg and two left-leg dominant) who have been playing football regularly since childhood and have participated in inter-school or college/university-level football tournaments. The age-matched control group consisted of 11 healthy participants not involved in any physical activities regularly or as a hobby. Participants in both groups underwent cVEMP and oVEMP tests in both ears. Results: The peak-to-peak amplitude of both cVEMP and oVEMP were higher in football players than in the control group. The amplitude for left ear stimulation was higher than the right ear for both cVEMP and oVEMP in football players and it reached statistical significance for oVEMP in left ear stimulation (p<0.05). The n10 latency of oVEMP in both right and left ear stimulations and the p13 latency of cVEMP in left ear stimulation was significantly shorter in football players compared to the control group (p<0.05). Conclusion: Regular football players have stronger vestibule-collic and translational Vestibulo-Ocular Reflexes (t-VOR). The reflex strength, measured as the higher peak-to-peak amplitude of VEMPs, might also be influenced by factors like leg/eye dominance.Keywords: Vestibular function; football; adults; vestibular evoked myogenic potentials; balance function

Somatosensory Influence on Platform-Induced Translational Vestibulo-Ocular Reflex in Vertical Direction in Humans.

The vestibulo-ocular reflex (VOR) consists of two components, the rotational VOR (rVOR) elicited by semicircular canal signals and the translational VOR (tVOR) elicited by otolith signals. Given the relevant role of the vertical tVOR in human walking, this study aimed at measuring the time delay of eye movements in relation to whole-body vertical translations in natural standing position. Twenty (13 females and 7 males) healthy, young subjects (mean 25 years) stood upright on a motor-driven platform and were exposed to sinusoidal movements while fixating a LED, positioned at a distance of 50 cm in front of the eyes. The platform motion induced a vertical translation of 2.6 cm that provoked counteracting eye movements similar to self-paced walking. The time differences between platform and eye movements indicated that the subject's timing of the extraocular motor reaction depended on stimulus frequency and number of repetitions. At low stimulus frequencies (<0.8 Hz) and small numbers of repetitions (<3), eye movements were phase advanced or in synchrony with platform movements. At higher stimulus frequencies or continuous stimulation, eye movements were phase lagged by ~40 ms. Interestingly, the timing of eye movements depended on the initial platform inclination. Starting with both feet in dorsiflexion, eye movements preceded platform movements by 137 ms, whereas starting with both feet in plantar flexion eye movement precession was only 19 ms. This suggests a remarkable influence of foot proprioceptive signals on the timing of eye movements, indicating that the dynamics of the vertical tVOR is controlled by somatosensory signals.

Horizontal Vestibulo-Ocular Reflex Gain Measures During Convergence Using a Monocular Video Technique.

Vestibulo-ocular reflex (VOR) response measures during convergence, which are clinically important to measure peripheral vestibular organ function during rotational and translational rapid head movements, can be implemented using existing clinically available monocular video-oculography (VOG) systems. We have developed and validated a monocular VOG technique that allows for accurate measurement of the convergence angle immediately before a rapid translational or rotational head movement. We recorded binocular eye movements while subjects performed active or passive horizontal head impulses while viewing near and far targets. We calculated the convergence angles and VOR gains using monocular and binocular methods and compared them with a geometric model. The monocular VOG technique resulted in convergence angle and VOR gain (eye velocity/head velocity) calculations that differed by ∼10% compared with values calculated using the binocular data. The monocular VOG technique can be clinically implemented using any unmodified, commercially available, monocular VOG system, provided its camera can be positioned to track either eye. Many vestibular clinics already have access to such systems. This method makes possible reliable measurement of the near-viewing horizontal angular VOR during the head impulse test, the translational VOR during the head heave test in patients, and the clinical measurement of convergence insufficiency.

The influence of target distance on perceptual self-motion thresholds and the vestibulo-ocular reflex during interaural translation.

An elegant and influential mathematical model of eye movements is the geometric compensation required for visual fixation location in the translational vestibulo-ocular reflex (VOR). Compensatory eye velocity scales with the inverse of fixation distance during head translation because larger angular eye movements are required to minimize retinal slip during head translation when targets are closer. This model has been extensively verified in experiments. Since the VOR and vestibular perception have shared anatomic pathways, we asked whether the same scaling may affect motion perception. Since perception does not require the linear-to-angular transformation required for the translational VOR, we hypothesized that perception would not scale with target distance. Subjects were tested with a motion direction-recognition threshold task in which they reported their perception of small translations of their body. Thresholds were measured in three conditions: (1) with a near target (0.20m) that extinguished just before each motion; (2) with a far target (0.47m); 3) with no target. The subject was always in darkness during motion. Thresholds were 0.59, 0.61 and 0.61cm/s, respectively. Translational VOR sensitivity (eye angular velocity divided by head translation velocity) was also measured and modulated with target distance. The scaling ratio of responses for the near vs. far target was 0.97 for perceptual thresholds, which was significantly different from the compensatory ratio (2.35; P<0.001) and the translational VOR scaling ratio (1.59; P=0.007) but not from no compensation (1.00; P=0.93). Thus, we conclude that despite shared anatomy for the VOR and perception, the brain processes signals according to the geometric functional constraints of each task.

Vertical head translation impairs dynamic visual acuity during near viewing.

Dynamic visual acuity is an important clinical tool for assessment of the rotational vestibulo-ocular reflex (rVOR). It is based on the fact that the normal rVOR stabilizes vision and maintains visual acuity during head rotation. The translational VOR (tVOR) generates eye movements during linear head motion. Studies in humans have shown that gaze stabilization during translation is incomplete and that there is a strong effect of the visual environment: eye velocity is much greater in the light than in the dark. In this study, we measured visual acuity during vertical translation in 11 subjects and asked whether a more complex visual background would enhance the response and improve acuity. During 2 Hz whole-body translation, tumbling-E optotypes (0.0-0.9 logMAR in steps of 0.1 logMAR, six trials of each size randomly ordered) were flashed on a screen that was 30 cm in front of the subject's eyes. The subject reported the optotype's orientation with a joystick. Based on a threshold of 75% trials correctly identified, the group dynamic acuity was 0.72 logMAR, compared to a static acuity of 0.0 logMAR. When the background was enhanced with a stationary dot pattern, dynamic acuity improved to 0.42 logMAR. Our findings show that vertical head translation degrades vision more than head rotation. This may limit the use of dynamic acuity as a clinical measure of otolith function.

Effects of high intensity noise on the vestibular system in rats

Some individuals with noise-induced hearing loss (NIHL) also report balance problems. These accompanying vestibular complaints are not well understood. The present study used a rat model to examine the effects of noise exposure on the vestibular system. Rats were exposed to continuous broadband white noise (0–24 kHz) at an intensity of 116 dB sound pressure level (SPL) via insert ear phones in one ear for three hours under isoflurane anesthesia. Seven days after the exposure, a significant increase in ABR threshold (43.3 ± 1.9 dB) was observed in the noise-exposed ears, indicating hearing loss. Effects of noise exposure on vestibular function were assessed by three approaches. First, fluorescein-conjugated phalloidin staining was used to assess vestibular stereocilia following noise exposure. This analysis revealed substantial sensory stereocilia bundle loss in the saccular and utricular maculae as well as in the anterior and horizontal semicircular canal cristae, but not in the posterior semicircular canal cristae. Second, single unit recording of vestibular afferent activity was performed under pentobarbital anesthesia. A total of 548 afferents were recorded from 10 noise-treated rats and 12 control rats. Noise exposure produced a moderate reduction in baseline firing rates of regular otolith afferents and anterior semicircular canal afferents. Also a moderate change was noted in the gain and phase of the horizontal and anterior semicircular canal afferent's response to sinusoidal head rotation (1 and 2 Hz, 45°/s peak velocity). Third, noise exposure did not result in significant changes in gain or phase of the horizontal rotational and translational vestibulo-ocular reflex (VOR). These results suggest that noise exposure not only causes hearing loss, but also causes substantial damage in the peripheral vestibular system in the absence of immediate clinically measurable vestibular signs. These peripheral deficits, however, may lead to vestibular disorders over time.

Amplitude and frequency prediction in the translational vestibulo-ocular reflex.

The goal of this study was to assess the effect of amplitude and frequency predictability on the performance of the translational vestibulo-ocular reflex (tVOR). Eye movements were recorded in 5 subjects during continuous vertical translation that consisted of a series of segments with: 1) 3 amplitudes at constant frequency (2 Hz) or 2) 3 different frequencies (1.6, 2, 2.5 Hz). Stimulus changes were presented in a pseudo-random order. We found that there was little change in the tVOR immediately after an unexpected stimulus change, as if eye velocity were being driven more by an expectation based on previous steady-state motion than by current head translation. For amplitude transitions, only about 30% of the eventual response change was seen in the first half cycle. Similarly, a sudden change in translation frequency did not appear in eye velocity for 70 ms, compared to a 8 ms lag during similar yaw rotation. Finally, after a sudden large decrease in frequency, the eyes continued to track at the original higher frequency, resulting initially in an anti-compensatory tVOR acceleration. Our results elucidate further the complexity of the tVOR and show that motion prediction based on prior experience plays an important role in its response.

Scaling of compensatory eye movements during translations: Virtual versus real depth

Vestibulo-ocular reflexes are the fastest compensatory reflex systems. One of these is the translational vestibulo-ocular reflex (TVOR) which stabilizes the gaze at a given fixation point during whole body translations. For a proper response of the TVOR the eyes have to counter rotate in the head with a velocity that is inversely scaled to viewing distance of the target. It is generally assumed that scaling of the TVOR is automatically coupled to vergence angle at the brainstem level. However, different lines of evidence also argue that in humans scaling of the TVOR also depends on a mechanism that pre-sets gain on a priori knowledge of target distance.To discriminate between these two possibilities we used a real target paradigm with vergence angle coupled to distance and a virtual target paradigm with vergence angle dissociated from target distance. We compared TVOR responses in six subjects who underwent lateral sinusoidal whole-body translations at 1 and 2Hz. Real targets varied between distance of 50 and 22.4cm in front of the subjects, whereas the virtual targets consisting of a green and red light emitting diode (LED) were physically located at 50cm from the subject. Red and green LED’s were dichoptically viewed. By shifting the red LED relative to the green LED we created a range of virtual viewing distances where vergence angle changed but the ideal kinematic eye velocity was always the same. Eye velocity data recorded with virtual targets were compared to eye velocity data recorded with real targets. We also used flashing targets (flash frequency 1Hz, duration 5ms). During the real, continuous visible targets condition scaling of compensatory eye velocity with vergence angle was nearly perfect. During viewing of virtual targets, and with flashed targets compensatory eye velocity only weakly correlated to vergence angle, indicating that vergence angle is only partially coupled to compensatory eye velocity during translation. Our data suggest that in humans vergence angle as a measure of target distance estimation has only limited use for automatic TVOR scaling.

Single motor unit activity in human extraocular muscles during the vestibulo‐ocular reflex

Motor unit activity in human eye muscles during the vestibulo-ocular reflex (VOR) is not well understood, since the associated head and eye movements normally preclude single unit recordings. Therefore we recorded single motor unit activity following bursts of skull vibration and sound, two vestibular otolith stimuli that elicit only small head and eye movements. Inferior oblique (IO) and inferior rectus (IR) muscle activity was measured in healthy humans with concentric needle electrodes. Vibration elicited highly synchronous, short-latency bursts of motor unit activity in the IO (latency: 10.5 ms) and IR (14.5 ms) muscles. The activation patterns of the two muscles were similar, but reciprocal, with delayed activation of the IR muscle. Sound produced short-latency excitation of the IO muscle (13.3 ms) in the eye contralateral to the stimulus. Simultaneous needle and surface recordings identified the IO as the muscle of origin of the vestibular evoked myogenic potential (oVEMP) thus validating the physiological basis of this recently developed clinical test of otolith function. Single extraocular motor unit recordings provide a window into neural activity in humans that can normally only be examined using animal models and help identify the pathways of the translational VOR from otoliths to individual eye muscles.

Does orbital proprioception contribute to gaze stability during translation?

Translational motion induces retinal image slip which varies with object distance. The brain must know binocular eye position in real time in order to scale eye movements so as to minimize retinal slip. Two potential sources of eye position information are orbital proprioception and an internal representation of eye position derived from central ocular motor signals. To examine the role of orbital proprioceptive information, the position of the left eye was perturbed by microstimulation of the left abducens nerve during translational motion to the right or left along the interaural axis in two rhesus macaques. Microstimulation rotated the eye laterally, activating eye muscle proprioceptors, while keeping central motor commands undisturbed. We found that microstimulation-induced eye position changes did not affect the translational VOR in the abductive (lateral rectus) direction, but it did influence the responses in the adductive (medial rectus) direction. Our findings demonstrate that proprioceptive inputs appear to be involved in the TVOR responses at least during ipsilateral head movements and proprioceptive influences on the TVOR may involve vergence-related signals to the oculomotor nucleus. However, internal representation of eye position, derived from central ocular motor signals, likely plays the dominant role in providing eye position information for scaling eye movements during translational motion, particularly in the abducent direction.

Visual and vestibular determinants of the translational vestibulo‐ocular reflex

Prior studies indicate that the human translational vestibulo-ocular reflex (tVOR) generates eye rotations approximately half the magnitude required to keep the line of sight pointed at a stationary object--a compensation ratio (CR) of ∼0.5. We asked whether changes of visual or vestibular stimuli could increase the CR of tVOR. First, subjects viewed their environment through an optical device that required eye movements to increase by ∼50% to maintain fixation of a stationary visual target. During vertical translation, eye movements did increase, but tVOR CR remained at ∼0.5. Second, subjects viewed through LCD goggles providing 4 Hz strobe vision that minimized retinal image motion; this reduced tVOR CR. Finally, subjects were rotated in roll while they translated vertically; no increase in tVOR occurred. Taken with prior studies, we conclude that tVOR is optimally set to generate eye rotations that are about 50% of those required to stabilize the line of sight.

The human translational vestibulo‐ocular reflex in response to complex motion

We studied the translational vestibulo-ocular reflex (tVOR) in four healthy human subjects during complex, unpredictable sum-of-sines head motion (combination of 0.73, 1.33, 1.93, and 2.93 Hz), while subjects viewed a target 15 cm away. Ideal eye velocity was calculated from recorded head motion; actual eye velocity was measured with scleral coils. The gain and phase for each frequency component was determined by least-squares optimization. Gain averaged approximately 40% and did not change with frequency; phase lag increased with frequency to a maximum of 66°. Fitting actual to ideal eye velocity predicted a tVOR latency of 48 m/s for vertical and 38 m/s for horizontal translation. These findings provide further evidence that the normal tVOR is considerably undercompensatory, even at low frequencies if the stimulus is not predictable. The similarity of this behavior to that of pursuit suggests that these two eye movements may share some aspects of neural processing.

Ocular torsion and vertical misalignment

This article considers vertical misalignment and torsion of the eyes that arise from disorders of vestibulo-ocular reflex (VOR) pathways. Infarction of the nodulus is one of the causes of skew deviation, a vertical strabismus accompanied by torsion of the eyes and tilt of the subjective visual vertical. Vertical components of childhood strabismus may arise from dysgenesis of vestibular projections in the brainstem. If vertical misalignment decreases greatly in the supine position compared to the erect poison one may conclude that skew deviation rather than a fourth nerve palsy is responsible for the strabismus. Impairment of the horizontal translational VOR in patients with skew has provided further evidence that imbalance in the otolith-ocular pathway, caused by disruption of projections from the utricle to motor neurons, is the mechanism of skew deviation. Bedside examination showing a normal horizontal head impulse test, direction-changing nystagmus in eccentric gaze, or skew deviation is sensitive and specific for stroke. Skew deviation can identify stroke when an abnormal head impulse test falsely suggests a peripheral vestiblular lesion. Reduction in gain and failure of adaptation to vision of the torsional angular VOR in head positions away from the erect signify fundamental differences in the central organization of convergence of semicircular canal and otolith signals, when compared to the horizontal and vertical angular VORs. The effects of head position and of lesions of the nodulus are assuming increasing importance in analysis and differential diagnosis of vertical misalignment and torsion of the eyes.

The Cerebellar Nodulus/Uvula Integrates Otolith Signals for the Translational Vestibulo-Ocular Reflex

BackgroundThe otolith-driven translational vestibulo-ocular reflex (tVOR) generates compensatory eye movements to linear head accelerations. Studies in humans indicate that the cerebellum plays a critical role in the neural control of the tVOR, but little is known about mechanisms of this control or the functions of specific cerebellar structures. Here, we chose to investigate the contribution of the nodulus and uvula, which have been shown by prior studies to be involved in the processing of otolith signals in other contexts.Methodology/Principal FindingsWe recorded eye movements in two rhesus monkeys during steps of linear motion along the interaural axis before and after surgical lesions of the cerebellar uvula and nodulus. The lesions strikingly reduced eye velocity during constant-velocity motion but had only a small effect on the response to initial head acceleration. We fit eye velocity to a linear combination of head acceleration and velocity and to a dynamic mathematical model of the tVOR that incorporated a specific integrator of head acceleration. Based on parameter optimization, the lesion decreased the gain of the pathway containing this new integrator by 62%. The component of eye velocity that depended directly on head acceleration changed little (gain decrease of 13%). In a final set of simulations, we compared our data to the predictions of previous models of the tVOR, none of which could account for our experimental findings.Conclusions/ SignificanceOur results provide new and important information regarding the neural control of the tVOR. Specifically, they point to a key role for the cerebellar nodulus and uvula in the mathematical integration of afferent linear head acceleration signals. This function is likely to be critical not only for the tVOR but also for the otolith-mediated reflexes that control posture and balance.

The linear vestibulo-ocular reflex, locomotion and falls in neurological disorders

During locomotion, head perturbations, consisting of rotations and translations (linear movements), occur with predominant frequencies of 0.5-5.0 Hz. The vestibular reflexes act at short latency to safeguard clear vision and stable posture during locomotion. Much is known about the angular vestibulo-ocular reflex (aVOR) in response to head rotations, which depend on the semicircular canals of the vestibular labyrinth. However, the means to test reliably the linear or translational vestibulo-ocular reflex (tVOR), which depends on the otolithic organs, has only become available more recently. We used a moving platform to translate normal human subjects vertically at frequencies similar to those occurring during locomotion, under ambient illumination. Our findings suggested that, whereas aVOR is concerned with stabilizing images of visual targets on the retina to optimize visual acuity, tVOR seems best suited to minimize retinal image motion between objects lying in different depth planes, in order to optimize motion parallax information. We then asked whether the tVOR functioned abnormally in patients with two neurological disorders that often cause falls: progressive supranuclear palsy (PSP) and cerebellar ataxia. We found that patients with PSP cannot adjust tVOR responses appropriately during viewing of near objects, nor converge their eyes. Vestibular-evoked myogenic potentials (VEMPs), an otolith-spinal reflex, are also impaired in PSP patients. Patients with cerebellar ataxia also lack the ability to adjust tVOR for near viewing, even though they may be able to converge. Taken together, our studies suggest that abnormal otolithic vestibular reflexes contribute to postural instability in PSP and cerebellar ataxia, and deserve further investigation.

並進前庭動眼反射を実現した両眼視軸制御システムの構築

This paper proposes a robotic eye movement control system based on neural pathways of human binocular motor system. The ability so called “Translational Vestibulo-Ocular Reflex (TVOR)” in physiology area of eye movements is developed to compensate the motion bular caused by the translation head movement. Since TVOR depends on both the movements of the head and the position of the related target with the head, it cannot be realized as a single eye system. According from the physiology and anatomy studies, its target position information is from the angles of both eyes in ocular motor system of human. In this paper, the Smooth Pursuit eye movement, Rotational Vestibulo-Ocular Reflex (RVOR), and TVOR are successfully combined in one binocular motion control model. This model has been approved through the experiment by using a mobile robot with binocular active cameras, accelerometer, and gyroscope. Its result shows that the cameras can keep tracking on a moving target smoothly while the robot is violently moving. This ability cannot be realized by only using visual feedback control method.

Otolith inputs to pursuit neurons in the frontal eye fields of alert monkeys

The smooth-pursuit system must interact with the vestibular system to maintain the accuracy of eye movements in space during head movement. Maintenance of a target image on the foveae is required not only during head rotation which activates primarily semi-circular canals but also during head translation which activates otolith organs. The caudal part of the frontal eye fields (FEF) contains pursuit neurons. The majority of them receive vestibular inputs induced by whole body rotation. However, it has not been tested whether FEF pursuit neurons receive otolith inputs. In the present study, we first classified FEF pursuit neurons as belonging to one of three groups (vergence + fronto-parallel pursuit, vergence only, fronto-parallel pursuit only) based on their responses during fronto-parallel pursuit and mid-sagittal vergence-pursuit. We, then, tested discharge modulation of these neurons during fore/aft and/or right/left translation by passively moving the whole body sinusoidally at 0.33 Hz (+/-10 cm, peak velocity 19 cm/s; 0.04g). The majority of FEF pursuit neurons in all three groups were activated by fore/aft and right/left translation without a target in complete darkness. There was no correlation between the magnitude of discharge modulation and translational vestibulo-ocular reflex (VOR). Preferred directions of translational responses were distributed nearly evenly in front of the monkeys. Discharge modulation was also observed when a target moved together with whole body, requiring the monkeys to cancel the translational VOR. These results indicate that the discharge modulation of FEF pursuit neurons during whole body translation reflected otolith inputs.

Effects of active and passive viewpoint jitter on vection in depth

Recent studies have shown that the vection in depth experienced by stationary observers viewing constant velocity radial flow can be enhanced by adding simulated viewpoint jitter/oscillation. This study examined the effect of manipulating visual–vestibular conflict on the perceived strength and speed of vection in depth. Four conditions were examined: (i) radial flow without viewpoint jitter viewed by stationary observers (consistent visual–vestibular inputs); (ii) radial flow with viewpoint jitter synchronized to lateral head oscillation (consistent inputs); (iii) radial flow with viewpoint jitter viewed by stationary observers (inconsistent inputs); (iv) radial flow without viewpoint jitter viewed during head oscillation (inconsistent inputs). We found that the strength and perceived speed of vection in depth was always greater when simulated viewpoint jitter was introduced. No further vection enhancement was found when this jitter was generated by active head oscillation—even though passive jitter conditions should have generated significant sensory conflicts, whereas active jitter conditions would not. Active head oscillation without display jitter also had little effect, producing similar vection strength/speed ratings to stationary observation of non-jittering optic flow. Horizontal eye tracking suggested that retinal stimulation was similar between comparable active and passive viewing conditions. This stabilization of the retinal image across active and passive conditions appeared to be due to cooperative engagement of the translational vestibuloocular reflex and the visually driven ocular following response. Rather than providing evidence for synergistic integration of self-motion perception, these findings obtained with low-frequency sensory stimuli suggest that self-motion perception is dominated by visual processing centres.

Ocular vestibular evoked myogenic potentials (OVEMPs) produced by impulsive transmastoid accelerations

Objective Recent work has demonstrated the existence of ocular vestibular evoked myogenic potentials (OVEMPs), which likely reflect projections underlying the translational vestibular ocular reflex (TVOR). We examined extraocular muscle activity associated with impulsive acceleration of the head in the transmastoid plane. Methods Accelerometry was measured in 4 subjects in response to acceleration impulses produced by a gamma function delivered with a Minishaker (4810, Bruel & Kjaer). This stimulus produced peak head accelerations of 0.13–0.14 g occurring at between 3.1 and 4.0 ms at the mastoids for both right and left head movement. OVEMPs were recorded in 10 normal subjects with 5 directions of gaze, using electrode pairs placed lateral to, above and below the eyes. Results OVEMPs occurred at short latency, with initial peaks between 10.3 ms (p10) and 15.3 ms (n15). For a given recording site and gaze direction, the responses were determined solely by the direction of imposed acceleration. Conclusions We propose that, given the transtemporal nature of the stimuli, utricular afferents are likely to be powerfully activated. The OVEMPs evoked may be generated by the lateral recti and oblique muscles. Significance Sudden lateral accelerations of the head evoke the translational VOR and ocular counter rolling reflex and the pattern of muscle activations indicated by the OVEMPs appear to be a manifestation of these reflexes.

Why do patients with PSP fall?

Patients with progressive supranuclear palsy (PSP) fall frequently, beginning early in the course of their disease. Abnormal vestibulospinal reflexes are suspected, but the angular vestibulo-ocular reflex, which is mediated by the labyrinthine semicircular canals, survives late into the course of the disease. To test the hypothesis that otolithic-mediated reflexes are abnormal in PSP. We tested otolith-ocular reflexes (the translational vestibulo-ocular reflex [tVOR]) during combined rotation-translation in nine patients with PSP and nine age-matched control subjects; subjects viewed far and near targets. We also tested click-induced otolith-spinal reflexes (vestibular-evoked myogenic potentials [VEMPs]) in 10 patients with PSP and 30 age-matched controls. All patients with PSP had small tVOR responses during near viewing that were, on average, only 12% of those of control subjects (p = 0.001). Patients with PSP also showed a reduction of the amplitude of VEMPs compared to control subjects (median [range]: 54.3 [16.8 to 214] vs 149 [11.6 to 466], p = 0.001). Taken together, these results indicate that abnormal otolith-mediated reflexes may be at least partly responsible for frequent falls in progressive supranuclear palsy, and deserve further study.