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We investigated the translational vestibulo-ocular reflex (tVOR) in response toabrupt high-acceleration stimuli in normal humans. Using the search coil techniquewe recorded eye responses to head translation in six normal subjects while theyviewed an LED at 15 cm or 30 cm distance. Head position was monitored with a six-degrees-of-freedom miniBIRD device, and a linear accelerometer detected the onsetof head motion. Subjects looked at the LED in dim illumination while abrupt interau-ral head translations (2–3 cm amplitude, 0.4–1.4 g max acceleration) were deliveredmanually using a “head sled’”device

Purpose: We wanted to determine the mechanisms of motor vertical fusion in patients with superior oblique paresis and to correlate these mechanisms with surgical outcomes. Methods: Ten patients with superior oblique paresis underwent 3-axis, bilateral, scleral search coil eye movement recordings. Eye movements associated with fusion were analyzed. Results: Six patients had decompensated congenital superior oblique paresis and 4 had acquired superior oblique paresis. All patients with acquired superior oblique paresis relied predominantly on the vertical rectus muscles for motor fusion. Patients with congenital superior oblique paresis were less uniform in their mechanisms for motor fusion: 2 patients used predominantly the oblique muscles, 2 patients used predominantly the vertical recti, and 2 patients used predominantly the superior oblique in the hyperdeviated eye and the superior rectus in the hypodeviated eye. The last 2 patients developed the largest changes in torsional eye alignment relative to changes in vertical eye alignment and were the only patients to develop symptomatic surgical overcorrections. Conclusion: There are 3 different mechanisms for vertical fusion in individuals with superior oblique paresis, with the predominant mechanism being the vertical recti. A subset of patients with superior oblique paresis uses predominantly the superior oblique muscle in the hyperdeviated paretic eye and the superior rectus muscle in the fellow eye for fusion. This results in intorsion of both eyes, causing a large change in torsional alignment. The consequent cyclodisparity, in addition to the existing vertical deviation, may make fusion difficult. The differing patterns of vertical fusional vergence may have implications for surgical treatment. (J AAPOS 2002;6:145-53)

Opsoclonus-myoclonus syndrome (OMS) is a rare neurological disorder that is usually seen in conjunction with tumors (most commonly breast, lung and gynecological), infections or toxic-metabolic processes. In addition to opsoclonus and/or myoclonus, the clinical features of OMS may include ataxia and encephalopathy.1, 2 We describe a patient who presented with OMS and a strikingly exaggerated startle response, prompting an evaluation for an underlying malignancy which led to diagnosis of a small-cell lung carcinoma. A 64-year-old woman presented with a three month history of dizziness and unsteadiness. Her symptoms began suddenly with an attack of dizziness and unsteadiness that lasted only a few seconds. The dizziness was described as a light-headed feeling without vertigo. Over the next few weeks, she had similar episodes, lasting longer and occurring more frequently and eventually her symptoms became constant. Then, two weeks prior to her presentation, she developed “jumping” vision. The patient also had lost approximately 15 pounds over the past few months. She had a remote history of tobacco use. Before our evaluation she had a normal brain MRI. On examination, the patient had bursts of back-to-back, multi-directional saccades, with variable amplitude (i.e., opsoclonus), that were exacerbated during pursuit. The saccadic oscillations were also visible under closed eyelids.(video 1) She had occasional spontaneous myoclonic jerks of her head, and a strikingly exaggerated startle response to sound and light, that could be elicited even with expected stimuli.(video 2) Eye movements were otherwise remarkably intact A subtle intention and postural tremor of her hands was present, as well as a slight dysmetria on finger-to-nose and heel-to-shin testing, more on the left side. Her gait was wide-based and mildly unsteady and she could not walk in tandem unassisted. The remainder of her examination was normal. Routine blood studies showed no abnormalities. Cerebrospinal fluid analysis was normal. Viral PCRs including West Nile Virus were negative. An EEG was within normal limits and when she was startled there was no EEG correlate to her myoclonic jerk apart from muscle artifact. A comprehensive serum paraneoplastic antibody panel (including, among others, anti-Ri, amphiphysin, Yo, CV2 and Hu) was negative. A CT of the chest-abdomen-pelvis, mammograms, transvaginal ultrasound and FDG-PET/CT were performed and a 4.2cm lung mass was found in the left lower lobe with involvement of one lymph node. Lung biopsy showed this to be a small-cell lung carcinoma. PET also revealed physiologically increased uptake in the cerebrum and in the cerebellar hemispheres, though more so in the latter. Treatment for the malignancy was initiated with combination chemotherapy and radiation therapy. Over the course of several months her tumor shrunk, her ocular oscillations markedly improved and her startle myoclonus disappeared. Paraneoplastic neurological syndromes are considered to arise from an autoimmune response directed against neuronal antigens ectopically expressed by tumor cells.3 Specific auto-antibodies have been associated with OMS, especially anti-Ri and anti-amphiphysin, but most patients with OMS are seronegative for all known anti-neuronal antibodies, suggesting that cell-mediated immunity plays an important role.2-4 Alternatively, there may be associated novel autoantibodies that are yet to be identified. Localization of the lesion in OMS remains controversial with evidence supporting two predominant theories. One hypothesis states that cerebellar dysfunction leads to disinhibition of the fastigial nucleus by the Purkinje cells, resulting in OMS.4 In our case, this hypothesis correlates well with the relative hypermetabolism of the cerebellar cortex revealed on PET and the beneficial action of clonazepam, but does not provide a plausible explanation of the augmented startle response. Another view is that the culprit is the caudal pontine reticular formation and represents either dysfunction of pause neurons that inhibit the burst neurons that drive saccades, or primary hyperexcitability of the burst neurons themselves.5, 6 The exaggerated startle response of our patient is consonant with the second hypothesis, since the nucleus reticularis pontis caudalis plays an important role in the startle reflex, and therefore hyperexcitability of neurons here would account for her response.6 Finally, a caveat. An exaggerated startle response must be distinguished from reflex reticular myoclonus, a response that also originates in the caudal brainstem7. Unfortunately, we could not perform tests to make this distinction at at ime when our patient was symptomatic.

The three pairs of semicircular canals within the labyrinth are not perfectly aligned with the pulling directions of the six extraocular muscles. Therefore, for a given head movement, the vestibulo-ocular reflex (VOR) depends upon central neural mechanisms that couple the canals to the muscles with the appropriate functional gains in order to generate a response that rotates the eye the correct amount and around the correct axis. A consequence of these neural connections is a cross-axis adaptive capability, which can be stimulated experimentally when head rotation is around one axis and visual motion about another. From this visual-vestibular conflict the brain infers that the slow-phase eye movement is rotating around the wrong axis. We explored the capability of human cross-axis adaptation, using a short-term training paradigm, to determine if torsional eye movements could be elicited by yaw (horizontal) head rotation (where torsion is normally inappropriate). We applied yaw sinusoidal head rotation (+/-10 degrees, 0.33 Hz) and measured eye movement responses in the dark, and before and after adaptation. The adaptation paradigm lasted 45-60 min, and consisted of the identical head motion, coupled with a moving visual scene that required one of several types of eye movements: (1) torsion alone (-Roll); (2) horizontal/torsional, head right/CW torsion (Yaw-Roll); (3) horizontal/torsional, head right/CCW torsion (Yaw+Roll); (4) horizontal, vertical, torsional combined (Yaw+Pitch-Roll); and (5) horizontal and vertical together (Yaw+Pitch). The largest and most significant changes in torsional amplitude occurred in the Yaw-Roll and Yaw+Roll conditions. We conclude that short-term, cross-axis adaptation of torsion is possible but constrained by the complexity of the adaptation task: smaller torsional components are produced if more than one cross-coupling component is required. In contrast, vertical cross-axis components can be easily trained to occur with yaw head movements.

The function of extraocular muscle proprioception in the control of eye movements remains uncertain. In this study, we examined the effect of bilateral proprioceptive deafferentation of the extraocular muscles on eye movements in two rhesus monkeys. Before and after deafferentation, we analyzed baseline ocular alignment, saccades, pursuit, and vestibular eye movements. We also examined visually mediated adaptation of ocular alignment, saccades, and pursuit. Deafferentation of the eye muscles did not affect baseline ocular motor control, either acutely or over a 5-week period of study. Furthermore, visually mediated adaptation of the eye movement subtypes was also unaffected by deafferentation. These results suggest that ocular proprioception in primates is not used in the immediate, on-line control of eye movements and does not interact with visual cues in the adaptive modification of ocular motor function. We conclude that the efferent command (efference copy) provides sufficient information about eye kinematics to the brain for accurate eye movement control in normal monkeys, and that this information is modified by visual feedback independently of proprioception. We hypothesize that proprioception may be used to calibrate the efference copy during development and in response to perturbations by signaling potential mismatches between eye movement information derived from the efferent command and the actual motion of the eye transduced by the proprioceptive organs.

Neurologists are frequently called upon to evaluate patients with vertigo and dizziness and, in some cases, to make sense of abnormal vestibular tests. Consequently, it is useful to have some familiarity with the methods used to test vestibular function. The vestibulo-ocular reflex (VOR) is a reflex that acts at short latency to generate eye movements that compensate for head rotations in order to preserve clear vision during locomotion. The VOR is the most accessible gauge of vestibular function. Evaluating the VOR requires application of a vestibular stimulus and measurement of the resulting eye movements. This report reviews the advantages and limitations of the methods of stimulating the vestibular system: caloric irrigation, rotational chair testing, and auto-rotational testing. Vestibular testing in children is given additional consideration because of the paucity of recent reviews on the topic. This report will not address eye movement recording techniques, the neurophysiology of the VOR, which is reviewed elsewhere,1,2⇓ or interpretation of nystagmus. This evidence-based assessment was developed from a review of published articles obtained through the MEDLINE database of the National Library of Medicine. Relevant publications were rated by the strength of evidence according to a scheme approved by the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology (see Appendix 2). ### Bedside vestibular assessment. Not every dizzy patient needs quantitative vestibular testing. Clinical examination can provide some qualitative information about vestibular function ( table 1). Patients with dizziness should be examined for nystagmus in the supine and lateral head positions as well as following the Dix–Hallpike maneuver. Spontaneous and gaze-evoked nystagmus may help localize the lesion in a patient with a suspected vestibular disorder.2,3⇓ Peripheral vestibular nystagmus is often suppressed by visual fixation, but may be seen during funduscopic examination in the dark. Frenzel goggles have 10+ diopter lenses that prevent fixation, …

Rapid eye movements include saccades and quick phases of nystagmus and may have components around all three axes of ocular rotation: horizontal, vertical, and torsional. In this study, we recorded horizontal, vertical, and torsional eye movements in normal subjects with their heads upright and stationary. We asked how the eyes are brought back to Listing's plane after they are displaced from it. We found that torsional offsets, induced with a rotating optokinetic disk oriented perpendicular to the subject's straight ahead, were corrected during both horizontal and vertical voluntary saccades. Thus three-dimensional errors are synchronously reduced during saccades. The speed of the torsional correction was much faster than could be accounted for by passive mechanical forces. During vertical saccades, the peak torsional velocity decreased and the time of peak torsional velocity was delayed, as the amplitude of vertical saccades increased. In contrast, there was no consistent reduction of torsional velocity or change in time of peak torsional velocity with an increase in the amplitude of horizontal saccades. These findings suggest that 1) the correction of stimulus-induced torsion is neurally commanded and 2) there is cross-coupling between the torsional and vertical but not between the torsional and horizontal saccade generating systems. This latter dichotomy may reflect the fact that vertical and torsional rapid eye movements are generated by common premotor circuits located in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). When horizontal or vertical saccade duration was relatively short, the torsional offset was not completely corrected during the primary saccade, indicating that although the saccade itself is three-dimensional, saccade duration is determined by the error in the horizontal or the vertical, but not by the error in the torsional component.

A careful neuro-otologic examination is important in the diagnosis of vestibular disorders. This article reviews the bedside examination, beginning with the underlying physiologic principles. Techniques for testing static and dynamic vestibulo-ocular and vestibulospinal function are summarized. Finally, the use of specific provocative maneuvers is described.

One of the signs of the cerebellar ocular motor syndrome is the inability to maintain horizontal and vertical fixation. Typically, in the presence of cerebellar atrophy, the eyes show horizontal gaze-evoked and vertical downbeat nystagmus. We investigated whether or not the cerebellar ocular motor syndrome also includes a torsional drift and, specifically, if it is independent from the drift in the horizontal-vertical plane. The existence of such a torsional drift would suggest that the cerebellum is critically involved in maintaining the eyes in Listing's plane. Eighteen patients with cerebellar atrophy (diagnosis confirmed by magnetic resonance imaging) were tested and compared with a group of normal subjects. Three-dimensional eye movements (horizontal, vertical, and torsional) during attempted fixations of targets at different horizontal and vertical eccentricities were recorded by dual search coils in a three-field magnetic frame. The overall ocular drift was composed of an upward drift that increased during lateral gaze, a horizontal centripetal drift that appeared during lateral gaze, and a torsional drift that depended on horizontal eye position. The vertical drift consisted of two subcomponents: a vertical gaze-evoked drift and a constant vertical velocity bias. The increase of upward drift velocity with eccentric horizontal gaze was caused by an increase of the vertical velocity bias; this component did not comply with Listing's law. The horizontal-eye-position–dependent torsional drift was intorsional in abduction and extorsional in adduction, which led to an additional violation of Listing's law. The existence of torsional drift that is eye-position–dependent suggests that the cerebellum is critically involved in the implementation of Listing's law, perhaps by mapping a tonic torsional signal that depends on the direction of the line of sight. The magnitude of this signal might reflect the difference in torsional eye position between the torsional resting position determined by the mechanics of the eye plant and the torsional position required by Listing's law.

Hyperventilation can affect nystagmus in patients with vestibular disorders. However, the effects on nystagmus in patients with cerebellar disease have not been systematically studied. Using the magnetic field search coil technique, we studied the effects of hyperventilation on nystagmus in a series of cerebellar patients. In four of eight patients, hyperventilation produced an increase in the slow-phase velocity of downbeat nystagmus. We speculate that this effect may be mediated through metabolic effects on cerebellar calcium channels.

Drift of the eyes after saccades produces motion of images on the retina (retinal slip) that degrades visual acuity. In this study, we examined the contributions of proprioceptive and retinal afference to the suppression of postsaccadic drift induced by a unilateral ocular muscle paresis. Eye movements were recorded in three rhesus monkeys with a unilateral weakness of one vertical extraocular muscle before and after proprioceptive deafferentation of the paretic eye. Postsaccadic drift was examined in four visual states: monocular viewing with the normal eye (4-wk period); binocular viewing (2-wk period); binocular viewing with a disparity-reducing prism (2-wk period); and monocular viewing with the paretic eye (2-wk period). The muscle paresis produced vertical postsaccadic drift in the paretic eye, and this drift was suppressed in the binocular viewing condition even when the animals could not fuse. When the animals viewed binocularly with a disparity-reducing prism, the drift in the paretic eye was suppressed in two monkeys (with superior oblique pareses) but generally was enhanced in one animal (with a tenotomy of the inferior rectus). When drift movements were enhanced, they reduced the retinal disparity that was present at the end of the saccade. In the paretic-eye–viewing condition, postsaccadic drift was suppressed in the paretic eye and was induced in the normal eye. After deafferentation in the normal-eye–viewing state, there was a change in the vertical postsaccadic drift of the paretic eye. This change in drift was idiosyncratic and variably affected the amplitude and velocity of the postsaccadic drift movements of the paretic eye. Deafferentation of the paretic eye did not affect the postsaccadic drift of the normal eye nor did it impair visually mediated adaptation of postsaccadic drift. The results demonstrate several new findings concerning the roles of visual and proprioceptive afference in the control of postsaccadic drift: disconjugate adaptation of postsaccadic drift does not require binocular fusion; slow, postsaccadic drift movements that reduce retinal disparity but concurrently increase retinal slip can be induced in the binocular viewing state; postsaccadic drift is modified by proprioception from the extraocular muscles, but these modifications do not serve to minimize retinal slip or to correct errors in saccade amplitude; and visually mediated adaptation of postsaccadic drift does not require proprioceptive afference from the paretic eye.

Directional abnormalities of vestibular and optokinetic responses in patients with cerebellar degeneration are reported. Three-axis magnetic search-coil recordings of the eye and head were performed in eight cerebellar patients. Among these patients, examples of directional cross-coupling were found during (1) high-frequency, high-acceleration head thrusts; (2) constant-velocity chair rotations with the head fixed; (3) constant-velocity optokinetic stimulation; and (4) following repetitive head shaking. Cross-coupling during horizontal head thrusts consisted of an inappropriate upward eye-velocity component. In some patients, sustained constant-velocity yaw-axis chair rotations produced a mixed horizontal-torsional nystagmus and/or an increase in the baseline vertical slow-phase velocity. Following horizontal head shaking, some patients showed an increase in the slow-phase velocity of their downbeat nystagmus. These various forms of cross-coupling did not necessarily occur to the same degree in a given patient; this suggests that different mechanisms may be responsible. It is suggested that cross-coupling during head thrusts may reflect a loss of calibration of brainstem connections involved in the direct vestibular pathways, perhaps due to dysfunction of the flocculus. Cross-coupling during constant-velocity rotations and following head shaking may result from a misorientation of the angular eye-velocity vector in the velocity-storage system. Finally, responses to horizontal optokinetic stimulation included an inappropriate torsional component in some patients. This suggests that the underlying organization of horizontal optokinetic tracking is in labyrinthine coordinates. The findings are also consistent with prior animal-lesion studies that have shown a role for the vestibulocerebellum in the control of the direction of the VOR.

A number of mechanisms and strategies are used to help an individual compensate for loss of labyrinthine function. One important example is the ability to produce a preplanned motor response that anticipates the motion of the head and so compensates for it. Closely tied to this phenomenon is the gating, in or out, of a learned response on the basis of the context in which it must occur. This issue is particularly relevant to designing programs of physical therapy that optimize performance for natural behavior. Here we discuss a model of short-term vestibulo-ocular adaptation—adjustment of vestibulo-ocular phase (timing)—and how it can be used to study context-dependent vestibulo-ocular learning. We will show how vestibulo-ocular phase can be adjusted by selectively altering the common velocity-to-position ocular motor neural integrator for one type of eye movement (vestibular) and not for another (saccades), or for one type of head movement (sinusoidal) and not for another (step). These results are another example of the remarkable flexibility of the vestibulo-ocular adaptive mechanism and further show that the fundamental process of integration for eye movements can be modified according to the pattern of afferent information. (Otolaryngol Head Neck Surg 1998;119:60-4.)

Purpose: To describe the clinical features of a large pedigree with autosomal dominant congenital nystagmus linked to chromosome 6p12. Methods: In a prospective evaluation of 54 living family members in a single pedigree, 21 persons were affected with autosomal dominant congenital nystagmus, and clinical examinations were performed on 14. Selected persons underwent further studies, including electroretinography, scanning laser ophthalmoscopy, nerve fiber layer studies, visual evoked potential studies, and eye movement recordings. Results: Among seven affected persons whose parents were able to report whether the nystagmus was present congenitally, onset at birth was noted in two persons and between 3 and 6 months in five persons. Best-corrected binocular Snellen visual acuity ranged from 20/30 to 20/100, with a mode of 20/50. Strabismus was present in 14 examined patients (36%). Eye movement recordings, performed on five persons, included asymmetric pendular (three), asymmetric pendular combined with dual waveform jerk (one), and unidirectional jerk nystagmus (one). Conclusions: Autosomal dominant congenital nystagmus represents a disorder with variable expressivity. While onset is typically during infancy, it can be noted at birth. Intrafamilial variation in visual acuity, ocular alignment, and nystagmus waveform suggests a role for modifying influences on expression of disease.

Ataxia-telangiectasia is known for cerebellar degeneration, but clinical descriptions of abnormal tone, posture, and movements suggest involvement of the network between cerebellum and basal ganglia. We quantitatively assessed the nature of upper-limb movement disorders in ataxia-telangiectasia. We used a three-axis accelerometer to assess the natural history and severity of abnormal upper-limb movements in 80 ataxia-telangiectasia and 19 healthy subjects. Recordings were made during goal-directed movements of upper limb (kinetic task), while arms were outstretched (postural task), and at rest. Almost all ataxia-telangiectasia subjects (79/80) had abnormal involuntary movements, such as rhythmic oscillations (tremor), slow drifts (dystonia or athetosis), and isolated rapid movements (dystonic jerks or myoclonus). All patients with involuntary movements had both kinetic and postural tremor, while 48 (61%) also had resting tremor. The tremor was present in transient episodes lasting several seconds during two-minute recording sessions of all three conditions. Percent time during which episodic tremor was present was greater for postural and kinetic tasks compared to rest. Resting tremor had higher frequency but smaller amplitude than postural and kinetic tremor. Rapid non-rhythmic movements were minimal during rest, but were triggered during sustained arm postures and goal directed arm movements suggesting they are best considered a form of dystonic jerks or action myoclonus. Advancing age did not correlate with the severity of involuntary limb movements. Abnormal upper-limb movements in ataxia-telangiectasia feature classic cerebellar impairment, but also suggest involvement of the network between the cerebellum and basal ganglia.

In its original formulation, Listing's law referred only to eye positions during steady fixation. In recent years, however, several studies have suggested that Listing's law can be extended to the movements of the eyes, including during saccades and smooth pursuit. A major problem in deciding whether or not Listing's law is obeyed during eye movements is the influence of any spontaneous fluctuations in torsional eye position. To try to settle this question, the three-dimensional position of the eyes (around the three axes: horizontal, vertical, and torsional) was recorded with dual search coils in five normal subjects during fixations, 20 degrees saccades, blinks, and 20 degrees pursuit movements with a 20 degrees/s stimulus velocity. Eye movements across a wide range of horizontal positions were measured at different elevations of gaze during 11 min. Variability (as reflected in the standard deviation of torsional eye position) was used as a measure of the validity of Listing's law. After linear detrending single trials, each lasting 21.5 s, to remove the effects of drift over minutes, the reduction in the standard deviation of torsional position in tertiary eye positions was 54% assuming a planar and 58% assuming a second-order curved Listing's surface. We attributed this long-term fluctuation of the torsional signal to slippage of the coil on the eye. The remaining variability was mainly due to short-term fluctuation of eye torsion over seconds. The impact of hysteresis, associated with consecutive centrifugal-centripetal horizontal movements, on the variability of torsional eye position appeared negligible. Peak increases in the standard deviation from the fixation baseline after fitting individual Listing's planes for each trial were 348% during blinks, 141% during saccades, and 72% during pursuit movements (median value of five subjects). In conclusion, Listing's law during blinks, saccades, and pursuit is less valid than during fixations, which raises doubts about the existence of an internal "Listing's law operator" for eye movements. Possibly, central eye velocity commands do not comply with Listing's law.

We have examined to what extent the vertical semicircular canals contribute to the nonlinearity of the horizontal VOR imposed by the driving of primary vestibular afferents into inhibitory cutoff at high velocities of head rotation (Ewald's second law). The gain (eye velocity/head velocity) of the horizontal component of the VOR with the head pitched down 30 degrees and pitched up 30 degrees was examined during constant-velocity rotations in normal subjects and patients following unilateral vestibular nerve section. In normal subjects, VOR gain decreases as chair velocity increases from 60-300 degrees/s when the head is pitched up, but VOR gain remains constant when the head is pitched down. This finding implies that the mechanism by which the gain of the horizontal VOR gain remains constant at all velocities of rotation depends upon the pattern of labyrinthine stimulation. Following unilateral nerve section, we found that the directional preponderance (DP) in horizontal VOR depends upon whether the head is pitched up 30 (mean asymmetry = 5%) or pitched down 30 degrees (mean asymmetry = 20%). This is what is expected based on the degree to which the lateral and vertical semicircular canals sense horizontal head acceleration with the head in different degrees of pitch. Hence, following unilateral vestibular lesions, the DP of horizontal VOR gain is most easily elicited at high velocities of head rotation and with the head pitched down 30 degrees. Evidence for DP at the bedside using the "head-shaking nystagmus" technique may be optimally elicited with the head pitched down 30 degrees.

We investigated the effects of short-term vestibulo-ocular reflex (VOR) adaptation on the gain and phase of the VOR, and on eccentric gaze-holding in darkness, in five normal human subjects. For 1 h, subjects sat in a chair that rotated sinusoidally at 0.2 Hz while surrounded by a visual stimulus (optokinetic drum). The drum was rotated relative to the chair, to require a VOR with either a phase lead or lag of 45 deg (with respect to a compensatory phase of zero) with no change in gain, or a gain of 1.7 or 0.5 with no change in phase. Immediately before and after each training session, VOR gain and phase were measured in the dark with 0.2 Hz sinusoidal rotation. Gaze-holding was evaluated following 20 deg eccentric saccades in darkness. Adaptation paradigms that called only for a phase lead produced an adapted VOR with 33% of the required amount of phase change, a 20% decrease in VOR gain, and an increased centripetal drift after eccentric saccades made in darkness. Adaptation paradigms that called for a phase lag produced an adapted VOR with 29% of the required amount of phase change, no significant change in VOR gain, and a centrifugal drift after eccentric saccades. Adaptation paradigms requiring a gain of 1.7 produced a 15% increase in VOR gain with small increases in phase and in centripetal drift. Adaptation paradigms requiring a gain of 0.5 produced a 31% decrease in VOR gain with a 6 deg phase lag and a centrifugal drift. The changes in drift and phase were well correlated across all adaptation paradigms; the changes in phase and gain were not. We attribute the effects on phase and gaze-holding to changes in the time constant of the velocity-to-position ocular motor neural integrator. Phase leads and the corresponding centripetal drift are due to a leaky integrator, and phase lags and the corresponding centrifugal drift are due to an unstable integrator. These results imply that in the short-term adaptation paradigm used here, the control of drift and VOR phase are tightly coupled through the neural integrator, whereas VOR gain is controlled by another mechanism.

Previous reports have indicated that optokinetic afternystagmus (OKAN) becomes asymmetric after the occurrence of unilateral peripheral vestibular lesions, and suggested that OKAN may be used for localizing the side of the lesion. These studies did not take into account spontaneous nystagmus. We compared OKAN in 12 subjects with unilateral vestibular loss after resection of acoustic neuroma to OKAN in 30 normal subjects. After offsetting the data for spontaneous nystagmus, we calculated the initial amplitude, the time constant, and the slow-phase cumulative eye position (SCEP) parameters of OKAN. The directional asymmetry of parameters to rightward and leftward stimulation were also calculated. The mean SCEP, initial amplitude, and time constant parameters were reduced significantly in the patients, and each also showed a directional asymmetry, such that they were greater for stimulation toward the side of the lesion. The directional preponderance of the SCEP parameter had the highest sensitivity for the side of the lesion, being abnormally elevated in 58.3% of patients with unilateral loss. We conclude that OKAN might be useful in combination with other subtests of abattery, but that by itself OKAN is only moderately sensitive to unilateral peripheral vestibular loss.

International audience; We have investigated the contribution of ocular muscle proprioception (OMP) to the long-term maintenance of ocular alignment in normal human beings. Using a scleral suction lens, one eye was rotated laterally 30 deg away from the position of the other eye. This procedure selectively affects OMP without altering the efferent copy of the ocular motor command. The passively displaced eye was covered while the unimpeded eye fixed upon a stationary target. The suction lens was removed after 6 or 10 min and the measures of alignment begun immediately. Three tests were used to determine the effects of the deviation on ocular alignment: the Lancaster red-green test; saccadic eye movement responses to stepping targets; and hand pointing to monocularly presented targets. AU three tests indicated a change of ocular alignment of about 2-4 deg, lasting 5-10 min: sustained temporal deviation resulted in exophoria (relative divergence of the visual axis), and sustained nasal deviation induced esophoria (relative convergence). Binocular viewing rapidly abolished the effect. The hand pointing test showed a large shift in the perceived position of a target during monocular viewing with either eye and its amplitude was correlated with the change of ocular alignment. These results indicate that a sustained passive rotation of one eye can lead to a persistent change in ocular alignment even after the eye is released, without any disparity cues. We further suggest that central mechanisms, based upon ocular motor afferents, rather than passive orbital mechanical factors, are the main cause of this phenomenon.

We studied the influence of static head position relative to the rotation axis on the three-dimensional (3-D) vestibuloocular reflex (VOR). By means of a 3-D rotating chair and a 3-D magnetic search-coil system, eye movements were recorded in 6 normal human subjects during sinusoidal rotation about an earth-vertical axis (yaw) with the head positioned at different pitch angles and about an earth-horizontal axis (pitch) with the head positioned at different yaw angles. We confirmed that torsional VOR gain is about 2/3 of horizontal and vertical VOR gain leading to non-collinear axes of eye and head rotation whenever torsional head movement components were present with eye movement axes tilting away from the torsional direction. Despite this non-collinearity of stimulus and eye movement rotation axes there was close to perfect adjustment of the different VOR components depending on the angle between gaze direction and stimulation axis, indicating a vectorial summation of gains obtained for rotations in the major body axes (roll, pitch and yaw). The horizontal and vertical eye movement components followed a cosine function of the angle between the plane of rotation and gaze direction. The torsional component followed a sine function.

We investigated the effect of short-term vestibulo-ocular reflex (VOR) adaptation in normal human subjects on the dynamic properties of the velocity-to-position ocular motor integrator that holds positions of gaze. Subjects sat in a sinusoidally rotating chair surrounded by an optokinetic nystagmus drum. The movement of the visual surround (drum) was manipulated relative to the chair to produce an increase (x 1.7 viewing), decrease (x 0.5, x 0 viewing), or reversal (x (-2.5) viewing) of VOR gain. Before and after 1 h of training, VOR gain and gaze-holding after eccentric saccades in darkness were measured. Depending on the training paradigm, eccentric saccades could be followed by centrifugal drift (after x 0.5 viewing), implying an unstable integrator, or by centripetal drift [after x 1.7 or x (-2.5) viewing], implying a leaky integrator. The changes in the neural integrator appear to be context specific, so that when the VOR was tested in non-training head orientations, both the adaptive change in VOR gain and the changes in the neural integrator were much smaller. The changes in VOR gain were on the order of 10% and the induced drift velocities were several degrees per second at 20 deg eccentric positions in the orbit. We propose that (1) the changes in the dynamic properties of the neural integrator reflect an attempt to modify the phase (timing) relationships of the VOR and (2) the relative directions of retinal slip and eye velocity during head rotation determine whether the integrator becomes unstable (and introduces more phase lag) or leaky (and introduces less phase lag).

Palatal tremor (brief, rhythmic involuntary movements of the soft palate) apparently comprises two different nosological entities: essential palatal tremor (EPT) and symptomatic palatal tremor (SPT). The site of the abnormality in EPT is unknown, whereas SPT is believed to arise from a lesion of the brainstem or cerebellum (within the Guillain-Mollaret triangle). The clinical and physiological properties of these conditions were studied in four patients with EPT and six patients with SPT. Patients with EPT had normal cerebellar function, but those with SPT had clinical signs of cerebellar dysfunction. The palatal movements were consistent with activation of the tensor veli palatini muscle in EPT and of the levator veli palatini muscle in SPT. During sleep, EPT stopped, whereas SPT continued with only slight variations in the tremor rate. The cycle of palatal tremor could not be reset by stimulation of trigeminal afferents in either EPT or SPT patients, and Valsalva's manoeuvre did not consistently affect the rhythm of the tremor in either group. The palatal tremor cycle exerted remote effects on the tonic electromyographic activity of the upper and lower extremities only in patients with SPT. These effects were present only on the side of the cerebellar signs (opposite the side with the enlarged inferior olive) in patients with a unilateral syndrome. Essential palatal tremor patients had only polysynaptic brainstem reflex abnormalities, whereas SPT patients had abnormalities of monosynaptic, oligosynaptic and polysynaptic brainstem reflexes. Magnetic resonance imaging showed no evidence of structural abnormalities in EPT patients, but SPT patients had a hyperdense signal of the ventral upper medulla (the region of the inferior olive) on T2-weighted images. These observations support the hypothesis that EPT and SPT are two different diseases. In SPT, cerebellar dysfunction ipsilateral to the palatal tremor may be due, in part, to abnormal function of the contralateral hypertrophic inferior olive. The proposed basis of SPT is a disturbance of electrotonic coupling between the cells of the inferior olive induced by a lesion of the dentato-olivary pathway. Similar mechanisms could be responsible for postural tremors in general. The pathophysiological basis of EPT remains unknown.

We examined spatial localization, using open-loop pointing to visual targets, in a patient with a congenital trigeminal-oculomotor synkinesis. This patient demonstrated abnormal co-activation of the left medial rectus muscle when the left lateral pterygoid contracted. Because one eye could be deviated in the absence of a normal oculomotor innervational command, the efference copy (derived from monitoring of central oculomotor commands) could be dissociated from the proprioceptive afferent signal (determined by the mechanical state of the extraocular muscles). Under conditions of monocular viewing with the normal right eye, when the covered left eye was adducted by the aberrant trigeminal innervation, the patient pointed to the left of the actual position of the target. This finding indicates that proprioceptive afference from the adducted, covered left eye was used in the process of spatial localization. While synkinetic adduction produced a shift in pointing in the opposite direction of rotation of the non-viewing eye, previous studies using passive deviation of the non-viewing eye in normal subjects reported a shift in pointing in the same direction as eye rotation (Gauthier et al., 1990; Bridgeman and Stark, 1991). We propose that this discrepancy is due to the different effects of passive eye rotation and active muscle contraction on the tendon organs of the extraocular muscles. On this basis, we hypothesize that the tendon organs, rather than the muscle spindles, are primarily responsible for the transduction of proprioceptive information about eye position in the orbit.

• Objective. —To determine whether asymptomatic individuals at very high genetic risk for Huntington's disease (HD) have demonstrable cognitive or oculomotor abnormalities. Design. —A case-control study was employed. Presence of the chromosome-4 DNA marker linked to the HD phenotype was the criterion for HD risk. Setting. —The Baltimore Huntington's Disease Project Presymptomatic Testing Program at The Johns Hopkins University School of Medicine, Baltimore, Md. Participants. —Seventy-six asymptomatic adults at risk for HD, voluntarily enrolled for genetic testing, and determined by clinical examination to be free of major psychiatric disorder or evidence of HD. Twenty were determined to be at 95% risk for HD; 56 were at 15% risk. Measures. —The Hopkins Verbal Learning Test was used to assess verbal learning and memory. Oculomotor functioning was assessed using Novel-Stimulus, Mirror-Stimulus, and Predictive-Saccade paradigms. Outcome measures included number of correctly recalled words, recognition accuracy, and response bias, as well as saccade latency and number of errors on the Mirror-Stimulus Test. Results. —With one exception, all participants performed within the normal range on the Hopkins Verbal Learning Test. In a blind follow-up examination of the individual who performed aberrantly on the Hopkins Verbal Learning Test, she exhibited neurologic and psychiatric changes sufficient for a clinical diagnosis of HD. There were no group differences on the tests of oculomotor functioning. Conclusions. —Young, asymptomatic adults at very high genetic risk for HD are unimpaired in tests of verbal learning and memory and oculomotor functioning.

We investigated the influence of static head orientation and position, relative to the axis of body rotation, upon vestibular adaptation. With the head centered, displaced anterior to the axis of body rotation, or tilted 40∘ to 45∘ in roll or pitch, the gain of the vestibulo-ocular reflex (VOR) was trained (to go either up or down) for one hour using artificial manipulation of the visual surround to produce a visual-vestibular mismatch. Before and after each training session, the VOR was measured in darkness with the head in the training as well as in several non-training positions. We found that transfer of VOR adaptation to non-training positions was almost complete when comparing head eccentric versus head-centered rotations. For tilts, however, transfer of VOR learning was far less complete suggesting that static otolith signals provide a strong contextual cue that gates the expression of an adaptive VOR response. Finally, following training to increase than VOR, gain was greater for centripetally than centrifugally directed slow phases. Centripetally directed postsaccadic drift also developed. These fundings imply that the gain increase paradigm also leads to abnormal function of the velocity-to-position neural integrator, which holds eccentric positions of gaze.

1. We recorded eye movements in four normal human subjects during refixations between targets calling for various combinations of saccades and vergence. We confirmed and extended prior observations of 1) transient changes in horizontal ocular alignment during both pure horizontal saccades (relative divergence followed by relative convergence) and pure vertical saccades (usually divergence for upward and convergence for downward saccades); 2) occasional, high-frequency (20-25 Hz), conjugate oscillations along the axis orthogonal to the main saccade; and 3) the speeding up of horizontal vergence by both horizontal and vertical saccades. 2. To interpret these findings, we developed a hypothesis for the generation of vergence to step changes in target depth, both with and without associated saccades. The essential features of this hypothesis are 1) the transient changes in horizontal ocular alignment during pure horizontal saccades reflect asymmetries in the mechanical properties of the lateral and medial rectus muscles causing adduction to lag abduction; 2) pure vergence movements in response to step changes in target depth are generated by a neural network that uses a desired change in vergence position as its input command and instantaneous vergence motor error (the difference between the desired change and the actual change in vergence) to drive vergence premoter neurons; and 3) the facilitation of horizontal vergence by saccades arises from nonlinear interactions in central premotor circuits. 3. The hypothetical network for generating pure vergence to step changes in target depth is analogous in structure to the local feedback model for the generation of saccades and has the same conceptual appeal. With the assumption of a single nonlinearity describing the relationship between a vergence motor error signal and the output of the neurons that generate promoter vergence velocity commands, this model generates pure vergence movements with peak velocity-amplitude relationships and trajectories that closely match those of experimental data. 4. Several types of models are proposed for the central, nonlinear interaction that occurs when saccades and vergence are combined. Common to all models is the idea that omnidirectional pause neurons (OPN), which are thought to gate activity for saccade burst neurons, also gate activity for saccade-related vergence. In one model we hypothesize the existence of a separate class of saccade-related vergence burst neurons, which generate premotor horizontal vergence commands but only during saccades. In a second model we hypothesize separate right eye and left eye saccadic burst neurons that receive not only conjugate, but also equal but oppositely directed vergence error signals.(ABSTRACT TRUNCATED AT 400 WORDS)

We studied postural control, using quantitative moving-platform posturography, in 20 patients with Huntington's Disease (HD) and in 20 age-matched controls. HD patients showed considerably more anterior-posterior sway than normals, even when a correction for chorea was attempted. This increase in sway was especially true when, by eliminating visual and by attenuating proprioceptive cues, patients were forced to rely primarily on vestibular cues for balance. HD patients also showed increased latencies (30-50 ms) but normal amplitude, in response to translational perturbations of the platform. HD patients showed increased amplitude of responses to rotational perturbations of the platform but a normal decrease in response on successive trials. Thus, patients with HD show a consistent pattern of abnormality on posturography suggesting a role for the basal ganglia in a number of aspects of postural control.

To determine whether the use of 4 bedside tests (head-impulse, head-heave, head-shake, and vibration tests) can be as effective as the caloric test, a widely accepted standard, in the diagnosis and prediction of the time to recovery from vestibular neuritis.Inception cohort (1-year follow-up), criterion standard study.Primary referral center.All patients had acute vertigo, and those having a diagnosis of vestibular neuritis were eligible for inclusion in the study. Sixty-eight patients (43 men and 25 women; mean age, 54.9 years) met this criterion, and 53 of them (77.9%) completed the study.Spontaneous head-shaking and vibration-induced nystagmus elicited with a battery-powered device were tested wearing Frenzel goggles. The head-impulse and head-heave tests were performed manually. Caloric irrigation was administered with hot, cold, and ice water.At baseline, more than half of the patients exhibited positive signs with all 4 tests and all had caloric paralysis or paresis. Signs with the head-impulse and head-heave tests correlated highly (odds ratio, 24.9; P.001), as did those with the head-shake and vibration tests (odds ratio, 22.8; P.001). Patients with a positive sign with the head-impulse or vibration test were 70% less likely to recover than were those with a negative sign. Head-impulse (hazard ratio, 0.08; P = .002) and head-shake (hazard ratio, 0.23; P = .01) test results were associated with the outcome of the caloric test.Careful bedside examination of patients with vestibular neuritis has both diagnostic value in the short term and prognostic value in the long term.

In four normal human subjects we measured eye movements during full-field optokinetic stimulation (10–220 deg/s) and determined the relationship among retinal-slip velocity (drum velocity minus slow-phase eye velocity), the slow-phase velocity of optokinetic nystagmus (OKN) and the initial value of the slow-phase velocity of optokinetic afternystagmus (OKAN) measured in darkness. OKN and OKAN were maximum (63–84 and 11–19 deg/s, respectively) when retinal slip ranged from 30–100 deg/s. For higher values of retinal slip, OKN and OKAN fell (in 3 subjects) or reached a plateau (in the fourth). The amplitude of OKAN in human beings was much less than that reported in monkeys. The shape, however, of the curve relating retinal slip to the amplitude of OKAN was similar to that of monkeys. Furthermore, in both cases the curve resembles that obtained by plotting the results of experimental recordings of neural discharge in the nucleus of the optic tract as a function of retinal slip. These results imply that the processing of visual information for generation of OKAN is similar in monkeys and human beings but that the gain of the system is much less in human beings. We also found that fixation of a small target during optokinetic stimulation nearly completely prevented the development of OKAN while fixation of a small target for short periods after optokinetic stimulation did not alter the pattern of decay of OKAN. Thus, fixation may actively prevent the coupling of visual information into the velocity-storage mechanism.

PURPOSE. To investigate immediate and long-term changes in static ocular alignment with acute acquired superior oblique palsy (SOP) in monkeys. METHODS. The trochlear nerve was severed intracranially in two rhesus monkeys. After the surgery, the paretic eye was patched for 6 to 9 days, and then binocular viewing was allowed. Three-axis eye movements (horizontal, vertical, and torsional) were measured with binocular, dual search coils. Eye movements were recorded over a 20° horizontal and vertical range of fixations before the lesion and then, beginning the first day after surgery. Changes in alignment with 30° head tilt were also studied. RESULTS. The main findings were (1) misalignment (10 –12° vertical in adduction, down; 10 –12° torsional in abduction, down); (2) changes in vertical deviation (VD) with head tilt ( 2– 6° with left versus right 30° tilt); and (3) changes in comitance and VD over time. During the early postlesion period, before binocular viewing was allowed, VD decreased and comitance improved. Once binocular viewing was allowed, VD increased and comitance worsened. CONCLUSIONS. Rhesus monkeys with induced SOP show a characteristic pattern of misalignment that helps define the ocular motor signature of acute denervation of the superior oblique muscle. The animals also showed striking changes over time in the amount and comitance of the vertical misalignment that depended on whether viewing was monocular or binocular, suggesting a role for proprioception in adaptation to misalignment with habitual monocular viewing. (Invest Ophthalmol Vis Sci. 2007;48:2602–2611) DOI:10.1167/iovs.06-1316

Saccades are rapid eye movements that redirect the fovea from one object to another. A great deal has been learned about the anatomy and physiology of saccades, making them an ideal system for studying the neural control of movement. Basic research on normal eye movements has greatly increased our understanding of saccadic performance, anatomy and physiology, and led to a large number of control system models. These models simulate normal saccades well, but are challenged by clinical disorders because they often do not incorporate the specific anatomical and physiological substrates needed to model clinically important abnormalities. Historically, studies of saccadic abnormalities in patients have played a critical role in understanding the neural control of saccades because they provide information that complements basic research and thus restricts hypotheses to those that are biologically plausible. This review presents four examples of clinical disorders (slow saccades, interrupted saccades, high-frequency saccadic oscillations and macrosaccadic oscillations) that have provided insights into the neurobiology of saccades, have driven the development of new models, and have suggested an explanation or treatment for these disorders. We raise general questions for both scientists and clinicians that will assist in their efforts to understand the neural control of movement, improve diagnostic criteria and develop new treatments.

Multiple sclerosis (MS) is the most common disabling neurological disease in young people. Most CNS lesions involve neuroanatomically non-eloquent zones that often do not result in symptomatic complaints. By contrast, tissue-injury mechanisms involving inflammatory demyelination can involve more eloquent sites, such as the optic nerve and brainstem, which can correspondingly produce the development of well recognised syndromes such as optic neuritis and internuclear ophthalmoplegia, respectively. In this review we discuss the broad landscape of abnormalities that affect the afferent visual system and the ocular motor apparatus, and emphasise relevant features, the recognition and treatment of which are of importance to general neurological practice. The commonness of visual sensory and eye movement abnormalities in MS highlights the importance of understanding the principles addressed in this review.

For the neurologist, examination of eye movements at the bedside is a traditional mainstay of anatomic localization and often provides diagnostic certainty in complicated clinical problems. For the basic neuroscientist, recording and analysis of eye movements, both in behaving monkeys and in normal humans, have become powerful tools to understand normal ocular motor control and to probe higher-level cerebral mechanisms that underlie attention, memory, and decision making. The antisaccade task is an example of such a useful eye movement paradigm.1–3⇓⇓ In this task, the subject has to cancel willfully a “reflexive” saccade to a suddenly appearing visual stimulus (i.e., …

Background: Prevailing hypotheses suggest that attention deficit hyperactivity disorder (ADHD) is secondary to dysfunction of motor intentional systems mediated by prefrontal circuitry. Oculomotor paradigms provide a mechanism for examining and localizing dysfunction at the interface between movement and cognition.Objective: Three different saccade tasks (reflexive or prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and the execution of eye movements, including motor response preparation, response inhibition, and working memory.Methods: The study included 19 children with ADHD, divided into two groups: a group of 8 children on methylphenidate at the time of testing and a group of 11 children not taking any psychoactive medication. Results from the two groups were compared with those from 25 age- and gender-matched normal control children.Results: Both groups of children with ADHD made significantly more directional errors than did controls on the antisaccade task and significantly more anticipatory errors than did controls on the memory-guided saccade task, findings that are consistent with deficits in response inhibition. There were no significant differences in prosaccade latency, although unmedicated children with ADHD showed significantly greater variability in latency on the prosaccade task than did controls. On the memory-guided saccade task there were no significant differences in saccade accuracy; however, unmedicated children with ADHD showed longer saccade latency than did either controls or medicated children with ADHD.Conclusions: Oculomotor findings suggest that deficits in prefrontal functions, in particular response inhibition, contribute to behavioral abnormalities observed in ADHD. Findings also suggest that the administration of methylphenidate is associated with improvements in the consistency of motor response. Although there were no observed improvements in response inhibition with methylphenidate, conclusions await a design in which subjects complete testing both on and off medication.

Springer, 1999. £140.00, $249.00, DM 398 (xvii+503 pages)ISBN 3540199349Thomas Brandt has completely updated and rewritten his personal and unique approach to the clinical problem of vertigo, which was originally published in 1991. The revision is spectacular. I confess, I am addicted to Brandt’s approach and will be largely effusive in my praise of this book. It will have strong appeal to those physicians who must diagnose and treat such patients, and to scientists who are investigating how humans maintain their sense of equilibrium and spatial orientation. But what makes this book different from what is extant? Brandt eschews the traditional approach to the vestibular system: first the strict anatomy and physiology, and then the clinical implications. Instead he dives directly into the specific clinical problems and then provides the necessary correlations, that is, the relevant physiology and anatomy. And there is usually an appropriate scheme that allows one to put the clinical problem into a pathophysiological framework. Even in the introductory chapters, one is never far away from the clinical problems. This approach will be especially welcomed by the ‘dizzy doctors’ who have long struggled with these difficult clinical problems.Brandt’s compass is much more than the traditional focus on vertigo and nystagmus; he also emphasizes posture, gait, and, in particular, perception and misperception. This broad clinical approach is timely as neuroscience expands its idea of the vestibular system to include the more-inclusive concept of spatial orientation. Scientists now investigate how the neural networks in the cerebral hemispheres combine information from our labyrinths with that provided by our other senses and that derived from our internal expectations. PET and fMRI are allowing us to explore how this is all accomplished in normal humans and soon, in patients.A few features of the book should be particularly mentioned. The illustrations, especially the MRI scans, are outstanding. The text, which is concise, is richly supplemented with useful tables and diagrams. Each chapter has a relatively detailed introductory page that directs the reader’s attention. The book is well referenced with a good mixture of the classical and the latest citations. Perhaps one could quibble with the glossary with which Brandt begins the book. Does a ‘rotational vertebral artery occlusion’ imply that the artery is rotating? Why put ‘falls in the elderly’, ‘senile gait’ and ‘volvular epilepsy’ in a glossary in which terms such as ‘yaw, pitch and roll’ are much more appropriately defined? I also advise anyone who purchases this book to make sure that it is tightly and cleanly bound. The copy sent to me showed signs of crumbling. I hope this only reflected fortuitous damage in mailing.In some of the chapters, Brandt takes on problems that many clinicians prefer to avoid. The psychogenic aspects of dizziness and vertigo; psychogenic gait disorders; the controversies around perilymphatic fistulae and microvascular compression syndromes; migraine and vertigo; and autoimmune inner ear disease are all rationally discussed, and usually reflect the insightful investigations of Brandt and his colleagues. The entire section (about 100 pages) on nonvestibular vertigo is particularly helpful. Visual vertigo, motion sickness, cervical vertigo and the psychiatric syndromes are all given adequate treatment. One must acknowledge that this book is permeated with Brandt’s own opinions (though he certainly does not neglect to mention others), but when looked at critically, the majority of these ‘opinions’ have become the facts that we all use in our practices and in our teaching.Brandt’s approach is well illustrated from a conversation I had with him recently. His elderly Golden Retriever developed an acute unilateral vestibular syndrome and Brandt noticed that the dog had different strategies for maintaining balance when walking slowly and when running quickly. Immediately, a novel hypothesis emerged and Brandt ran back to the laboratory, retrieved the video camera and planned appropriate experiments with (human) patients. I am sure the results of this investigation will be in the next edition of his book. This anecdote reflects the philosophy underlying Brandt’s book: it combines science and clinical practice so that we not only bring science to the bedside but also let our patients teach us how the brain works.

Article abstract—Objective: To analyze the nystagmus evoked by hyperventilation in patients with unilateral vestibular schwannoma and to use this information to predict the effects of hyperventilation on individual ampullary nerves. Methods: Three-dimensional scleral search coil eye movement recording techniques were used to record the magnitude and time course of eye movements in six patients with unilateral vestibular schwannoma and hyperventilation-induced nystagmus. The presenting complaints in five of these patients were vertigo or dysequilibrium. Results: The eye movement response to hyperventilation was a “recovery” nystagmus with slow-phase components corresponding to excitation of the affected vestibular nerve. Projection of the eye velocity vector into the plane of the semicircular canals revealed that fibers arising from the ampulla of the horizontal canal were most affected by hyperventilation with lesser activation of fibers to the superior canal and smaller, more variable responses from posterior canal fibers. Conclusions: The three-dimensional characteristics of the nystagmus evoked by hyperventilation in patients with vestibular schwannoma provide insight into the vestibular end organs affected by the tumor and the mechanism responsible for the nystagmus. This finding indicates that hyperventilation resulted in a transient increase in activity from these partially demyelinated axons. Key words: Acoustic neuroma—Recovery nystagmus—Three-dimensional eye movements—Hyperventilation—Vestibular schwannoma. NEUROLOGY 1999;53:2158‐2167

Objectives: To present symptoms, patterns of nystagmus, and computed tomographic scan identification of patients with sound- and/or pressure-induced vertigo due to dehiscence of bone overlying the superior semicircular canal. To describe anatomical findings and outcome in 2 patients undergoing plugging of the superior semicircular canal for treatment of these symptoms. Design and Setting: Prospective study of a case series in a tertiary care referral center. Patients and Results: Eight patients with vertigo, oscillopsia, and/or disequilibrium related to sound, changes in middle ear pressure, and/or changes in intracranial pressure were identified in a 2-year period. Seven of these patients also had vertical-torsional eye movements induced by these sound and/or pressure stimuli. The direction of the evoked eye movements could be explained by excitation or inhibition of the superior semicircular canal in the affected ear. Computed tomographic scans of the temporal bones identified dehiscence of bone overlying the affected superior semicircular canal in each case. Disabling disequilibrium in 2 patients prompted plugging of the dehiscent superior canal through a middle cranial fossa approach. Symptoms were improved in each case. One patient developed recurrent symptoms requiring an additional plugging procedure and developed sensorineural hearing loss several days after this second procedure. Conclusions: We have identified patients with a syndrome of vestibular symptoms induced by sound in an ear or by changes in middle ear or intracranial pressure. These patients can also experience chronic disequilibrium. Eye movements in the plane parallel to that of the superior semicircular canal were evoked by stimuli that have the potential to cause ampullofugal or ampullopetal deflection of this canal’s cupula in the presence of a dehiscence of bone overlying the canal. The existence of such deshiscences was confirmed with computed tomographic scans of the temporal bones. Surgical plugging of the affected canal may be beneficial in patients with disabling symptoms.