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Vestibular velocity storage enhances the efficacy of the angular vestibulo-ocular reflex (VOR) during relatively low-frequency head rotations. This function is modulated by GABA-mediated inhibitory cerebellar projections. Velocity storage also exists in perceptual pathway and has similar functional principles as VOR. However, it is not known whether the neural substrate for perception and VOR overlap. We propose two possibilities. First, there is the same velocity storage for both VOR and perception; second, there are nonoverlapping neural networks: one might be involved in perception and the other for the VOR. We investigated these possibilities by measuring VOR and perceptual responses in healthy human subjects during whole-body, constant-velocity rotation steps about all three dimensions (yaw, pitch, and roll) before and after 10 mg of 4-aminopyridine (4-AP). 4-AP, a selective blocker of inward rectifier potassium conductance, can lead to increased synchronization and precision of Purkinje neuron discharge and possibly enhance the GABAergic action. Hence 4-AP could reduce the decay time constant of the perceived angular velocity and VOR. We found that 4-AP reduced the decay time constant, but the amount of reduction in the two processes, perception and VOR, was not the same, suggesting the possibility of nonoverlapping or partially overlapping neural substrates for VOR and perception. We also noted that, unlike the VOR, the perceived angular velocity gradually built up and plateau prior to decay. Hence, the perception pathway may have additional mechanism that changes the dynamics of perceived angular velocity beyond the velocity storage. 4-AP had no effects on the duration of build-up of perceived angular velocity, suggesting that the higher order processing of perception, beyond the velocity storage, might not occur under the influence of mechanism that could be influenced by 4-AP.

Here we investigated how well internal estimates of direction of gravity are preserved over time and if the subjective visual vertical (SVV) and horizontal (SVH) can be used inter-changeably. Fourteen human subjects repetitively aligned a luminous line to SVV, SVH or subjective visual oblique (± 45Âř) over 5 min in otherwise complete darkness and also in dim light. Both accuracy (i.e., the degree of veracity as reflected by the median adjustment error) and precision (i.e., the degree of reproducability as reflected by the trial-to-trial variability) of adjustments along the principle axes were significantly higher than along the oblique axes. Orthogonality was only preserved in a minority of subjects. Adjustments were significantly different between SVV vs. SVH (7/14 subjects) and between ±45Âř vs. −45Âř (12/14) in darkness and in 6/14 and 14/14 subjects, respectively, in dim light. In darkness, significant drifts over 5min were observed in a majority of trials (33/56). Both accuracy and precision were higher if more time was taken to make the adjustment. These results introduce important caveats when interpreting studies related to graviception. The test re-test reliability of SVV and SVH can be influenced by drift of the internal estimate of gravity. Based on spectral density analysis we found a noise pattern consistent with 1/ f & b e t a ; noise, indicating that at least part of the trial-to-trial dynamics observed in our experiments is due to the dependence of the serial adjustments over time. Furthermore, using results from the SVV and SVH inter-changeably may be misleading as many subjects do not show orthogonality. The poor fidelity of perceived ± 45Âř indicates that the brain has limited ability to estimate oblique angles.

Rotations of the head evoke compensatory reflexive eye rotations in the orbit to stabilize images onto the fovea. In normal humans, the angular vestibulo-ocular reflex (aVOR) gain (eye/head velocity) changes depending on the head rotation plane. For pitch and yaw head rotations, the gain is near unity, but during roll head rotations, the aVOR gain is ∼ 0.7. The purpose of this study was to determine whether this physiological discrepancy affects dynamic visual acuity (DVA)--a functional measure of the aVOR that requires subjects to identify letters of varying acuities during head rotation. We used the scleral search coil technique to measure eye and head velocity during passive DVA testing in yaw, roll, and pitch head impulses in healthy controls and patients with unilateral vestibular hypofunction (UVH). For control subjects, the mean aVOR gain during roll impulses was significantly lower than the mean aVOR gain during yaw and pitch impulses; however, there was no difference in DVA between yaw, roll, or pitch. For subjects with UVH, only aVOR gain during head rotations toward the affected side (yaw) were asymmetric (ipsilesional, 0.32 ± 0.17, vs. contralesional, 0.95 ± 0.05), with no asymmetry during roll or pitch. Similarly, there was a large asymmetry for DVA only during yaw head rotations, with no asymmetry in roll or pitch. Interestingly, DVA during roll toward the affected ear was better than DVA during yaw toward the affected ear--even though the ipsilesional roll aVOR gain was 60 % lower. During roll, the axis of eye rotation remains nearly perpendicular to the fovea, resulting in minimal displacement between the fovea and fixation target image projected onto the back of the eye. For subjects with UVH, the DVA score during passive horizontal impulses is a better indicator of poor gaze stability than during passive roll or pitch.

Here we review the state of the art using saccadic eye movements as windows to the function of the normal brain and of the abnormal brain plagued by disease or trauma. By combining sophisticated behavioral paradigms with rigorous mathematical analysis and the latest imaging techniques one can use saccades as biomarkers of the highest level decision making to the lowest level basic machinery that generates premotor saccade commands. As technology advances saccades will become even more useful as immediate monitors of the state of the brain in disease and trauma and as a way to evaluate therapies.

Summary Vertigo in and around magnetic resonance imaging (MRI) machines has been noted for years [1, 2]. Several mechanisms have been suggested to explain these sensations [3, 4], yet without direct, objective measures, the cause is unknown. We found that all of our healthy human subjects developed a robust nystagmus while simply lying in the static magnetic field of an MRI machine. Patients lacking labyrinthine function did not. We use the pattern of eye movements as a measure of vestibular stimulation to show that the stimulation is static (continuous, proportional to static magnetic field strength, requiring neither head movement nor dynamic change in magnetic field strength) and directional (sensitive to magnetic field polarity and head orientation). Our calculations and geometric model suggest that magnetic vestibular stimulation (MVS) derives from a Lorentz force resulting from interaction between the magnetic field and naturally occurring ionic currents in the labyrinthine endolymph fluid. This force pushes on the semicircular canal cupula, leading to nystagmus. We emphasize that the unique, dual role of endolymph in the delivery of both ionic current and fluid pressure, coupled with the cupula's function as a pressure sensor, makes magnetic-field-induced nystagmus and vertigo possible. Such effects could confound functional MRI studies of brain behavior, including resting-state brain activity.

Conductance-based models of reciprocally inhibiting burst neurons suggest that intrinsic membrane properties and postinhibitory rebound (PIR) determine the amplitude and frequency of saccadic oscillations. Reduction of the lowthreshold calcium currents (IT) in the model decreased the amplitude but increased the frequency of the simulated oscillations. Combined reduction of hyperpolarization-activated cation current (Ih )a ndIT in the model abolished the simulated oscillations. We measured the effects of a selective blocker of IT (ethosuximide) in healthy subjects on the amplitude and frequency of saccadic oscillations evoked by eye closure and of a nonselective blocker of Ih andIT (propronolol)inapatientwithmicrosaccadicoscillationandlimbtremorsyndrome(mSOLT).Ethosuximide significantly reduced the amplitude but increased the frequency of the saccadic oscillations during eye closure in healthy subjects. Propranolol abolished saccadic oscillations in the mSOLT patient. These results support the hypothetical role of postinhibitory rebound, Ih ,a ndIT, in generation of saccadic oscillations and determining their kinematic properties.

Measurement of eye movements often helps to diagnose ocular motor disorders in the clinic, and is also used as a research tool in ocular motor, vision and vestibular research. Eye movements, however, are usually recorded without simultaneous video recordings, making offline interpretation difficult. We developed a tool that converts the measured eye movement data into a three-dimensional (3D) movie of eye movements. Having useful functions such as slow-play, pause and exaggeration of the movements, this new software provides a research and teaching tool to aid interpretation of the recorded eye movements.

In this study, we used manual delineation of high-resolution magnetic resonance imaging (MRI) to determine the spatial and temporal characteristics of the cerebellar atrophy in spinocerebellar ataxia type 2 (SCA2). Ten subjects with SCA2 were compared to ten controls. The volume of the pons, the total cerebellum, and the individual cerebellar lobules were calculated via manual delineation of structural MRI. SCA2 showed substantial global atrophy of the cerebellum. Furthermore, the degeneration was lobule specific, selectively affecting the anterior lobe, VI, Crus I, Crus II, VIII, uvula, corpus medullare, and pons, while sparing VIIB, tonsil/paraflocculus, flocculus, declive, tuber/folium, pyramis, and nodulus. The temporal characteristics differed in each cerebellar subregion: (1) duration of disease: Crus I, VIIB, VIII, uvula, corpus medullare, pons, and the total cerebellar volume correlated with the duration of disease; (2) age: VI, Crus II, and flocculus correlated with age in control subjects; and (3) clinical scores: VI, Crus I, VIIB, VIII, corpus medullare, pons, and the total cerebellar volume correlated with clinical scores in SCA2. No correlations were found with the age of onset. Our extrapolated volumes at the onset of symptoms suggest that neurodegeneration may be present even during the presymptomatic stages of disease. The spatial and temporal characteristics of the cerebellar degeneration in SCA2 are region specific. Furthermore, our findings suggest the presence of presymptomatic atrophy and a possible developmental component to the mechanisms of pathogenesis underlying SCA2. Our findings further suggest that volumetric analysis may aid in the development of a non-invasive, quantitative biomarker.

When humans are accelerated along the body vertical, the right and left eyes show oppositely directed torsional modulation (cyclovergence). The origin of this paradoxical response is unknown. We studied cyclovergence during linear sinusoidal vertical motion in healthy humans. A small head-fixed visual target minimized horizontal and vertical motion of the eyes and therefore isolated the torsional component. For stimuli between 1 and 2 Hz (near the natural range of head motion), the phase of cyclovergence with respect to inertial acceleration was 8.7 ± 2.4° (mean ± 95% CI) and the sensitivity (in degrees per second per g) showed a small but statistically significant increase with frequency. These characteristics contrast with those of cycloversion (conjugate torsion) during horizontal (interaural) inertial stimuli at similar frequencies. From these and previous results, we propose that cyclovergence during vertical translation has two sources, one, like cycloversion, from the low-frequency component of linear acceleration, and another, which we term dynamic cyclovergence, with high-pass characteristics. Furthermore, we suggest that this cyclovergence response in humans is a vestige of the response of lateral-eyed animals to vertical linear acceleration of the head.

When environmental or sensory conditions change suddenly, the brain must be capable of learning different behavioral modes to produce accurate movements under multiple circumstances. A form of this dual-state adaptation known as “context-specific adaptation” has been widely investigated using the saccade gain adaptation paradigm in humans. In this study, we asked whether or not context-specific adaptation of saccade gain exists in monkeys and if so to explore its properties. Here, vertical eye position was used as a context cue for adaptation of horizontal saccade gain. We asked for a gain-increase in one context and gain-decrease in another context, and then determined if a change in the context would invoke switching between the adapted states. After training, our monkeys developed context-specific adaptation: in most cases gain-decrease adaptation could be induced, but there was little or no gain-increase adaptation. This context-specific adaptation developed gradually and switching of gains was evident on the first saccades with each change in context. Along with these results, the retention of an adaptation aftereffect overnight indicates that contextual-specific adaptation in monkeys is not a strategy, but involves a true adaptive process of reorganization in the brain. We suggest that context-specific adaptation in monkeys could be an important tool to provide insights into the mechanisms of saccade adaptation that occurs during the more natural circumstances of daily life.

Background/aims Visually guided saccades and gaze-fixation ability were recorded in patients with early Parkinson9s disease (PD). Methods Magnetic search coil system was used to measure horizontal and vertical eye positions. Results ‘Staircase’ visually guided saccades (multiple hypometric saccades separated by an intersaccadic interval) and ‘staircase’ square-wave jerks (SWJ) were present in all patients. The SWJ amplitude (total amplitude of the series of hypometric saccades comprising the SWJ) was abnormally large (mean 2°). SWJ frequency was also abnormally high (50–70 intrusions/min). Conclusion Loss of dopaminergic neurons in the substantia nigra pars compacta leading to phasic excitation of the substantia nigra pars reticulata and, in turn, phasic inhibition of the superior colliculus (SC), may account for ‘staircase’ visually guided saccades in these patients. This mechanism, however, does not explain abnormally large SWJ, which in the traditional view results from decreased inhibition upon SC. The abnormally large SWJ could be due to a compensatory increase in frontal eye field activity secondary to the increased inhibition upon the SC. Abnormally large and frequent SWJ are often used clinically to distinguish multi-system atrophy from idiopathic PD. Our study, however, suggests that idiopathic PD cannot be excluded if the patient has large-amplitude SWJ.

The inferior olivary nuclei clearly play a role in creating oculopalatal tremor, but the exact mechanism is unknown. Oculopalatal tremor develops some time after a lesion in the brain that interrupts inhibition of the inferior olive by the deep cerebellar nuclei. Over time the inferior olive gradually becomes hypertrophic and its neurons enlarge developing abnormal soma-somatic gap junctions. However, results from several experimental studies have confounded the issue because they seem inconsistent with a role for the inferior olive in oculopalatal tremor, or because they ascribe the tremor to other brain areas. Here we look at 3D binocular eye movements in 15 oculopalatal tremor patients and compare their behaviour to the output of our recent mathematical model of oculopalatal tremor. This model has two mechanisms that interact to create oculopalatal tremor: an oscillator in the inferior olive and a modulator in the cerebellum. Here we show that this dual mechanism model can reproduce the basic features of oculopalatal tremor and plausibly refute the confounding experimental results. Oscillations in all patients and simulations were aperiodic, with a complicated frequency spectrum showing dominant components from 1 to 3 Hz. The model's synchronized inferior olive output was too small to induce noticeable ocular oscillations, requiring amplification by the cerebellar cortex. Simulations show that reducing the influence of the cerebellar cortex on the oculomotor pathway reduces the amplitude of ocular tremor, makes it more periodic and pulse-like, but leaves its frequency unchanged. Reducing the coupling among cells in the inferior olive decreases the oscillation's amplitude until they stop (at approximately 20% of full coupling strength), but does not change their frequency. The dual-mechanism model accounts for many of the properties of oculopalatal tremor. Simulations suggest that drug therapies designed to reduce electrotonic coupling within the inferior olive or reduce the disinhibition of the cerebellar cortex on the deep cerebellar nuclei could treat oculopalatal tremor. We conclude that oculopalatal tremor oscillations originate in the hypertrophic inferior olive and are amplified by learning in the cerebellum.

The cerebellar peduncles are excellent candidates for composite indicators of regional degeneration in posterior fossa structures, as the peduncles show histopathological changes in degenerative ataxia. We postulate that magnetic resonance imaging will reveal evidence of disease specific peduncle degeneration through macro-structural (cross-sectional area) and microstructural (fractional anisotropy, mean diffusivity) measures. This study presents a “proof of principle” using orthogonal diffusion tensor imaging cross-sections of the cerebellar peduncles to distinguish categories of cerebellar disease.

To examine patterns of executive and oculomotor control in a group of both boys and girls with attention-deficit/hyperactivity disorder (ADHD).Cross-sectional study of 120 children aged 8 to 12 years, including 60 with ADHD (24 girls) and 60 typically developing controls (29 girls). Oculomotor paradigms included visually guided saccades (VGS), antisaccades, memory-guided saccades, and a go/no-go test, with variables of interest emphasizing response preparation, response inhibition, and working memory.As a group, children with ADHD demonstrated significant deficits in oculomotor response preparation (VGS latency and variability) and response inhibition but not working memory. Girls, but not boys with ADHD, had significantly longer VGS latencies, even after controlling for differences in ADHD symptom severity. The ADHD subtypes did not differ on response preparation or inhibition measures; however, children with the Inattentive subtype were less accurate on the working memory task than those with the Combined subtype.Sex differences in children with ADHD extend beyond symptom presentation to the development of oculomotor control. Saccade latency may represent a specific deficit among girls with ADHD.

In two monkeys, we recorded spontaneous eye movements before and after ablation of the cerebellar nodulus and uvula (Nod/Uv). In both monkeys, there was an increase in upward ocular drift (downbeat nystagmus [DBN]) in darkness (M1: 1.5 degrees/s pre, 3.4 degrees/s post; M2: 1.3 degrees/s pre, 7.0 degrees/s post), but not in light. There was little effect of orbital position on drift velocity. These findings suggest that the Nod/Uv may play a role in the bias component of DBN.

We studied the neural correlates of rapid eye movement during sleep (REM) by timing REMs from video recording and using rapid event-related functional MRI. Consistent with the hypothesis that REMs share the brain systems and mechanisms with waking eye movements and are visually-targeted saccades, we found REM-locked activation in the primary visual cortex, thalamic reticular nucleus (TRN), 'visual claustrum', retrosplenial cortex (RSC, only on the right hemisphere), fusiform gyrus, anterior cingulate cortex, and the oculomotor circuit that controls awake saccadic eye movements (and subserves awake visuospatial attention). Unexpectedly, robust activation also occurred in non-visual sensory cortices, motor cortex, language areas, and the ascending reticular activating system, including basal forebrain, the major source of cholinergic input to the entire cortex. REM-associated activation of these areas, especially non-visual primary sensory cortices, TRN and claustrum, parallels findings from waking studies on the interactions between multiple sensory data, and their 'binding' into a unified percept, suggesting that these mechanisms are also shared in waking and dreaming and that the sharing goes beyond the expected visual scanning mechanisms. Surprisingly, REMs were associated with a decrease in signal in specific periventricular subregions, matching the distribution of the serotonergic supraependymal plexus. REMs might serve as a useful task-free probe into major brain systems for functional brain imaging.

Background and aim: Ataxia–telangiectasia (A-T) is an autosomal recessive disorder characterised by progressive neurological deficits, including prominent ocular motor dysfunction. Unstable fixation often leads to difficulty reading and blurred vision. Here we characterise the disturbance of visual fixation in A-T. Methods: Eye movements were recorded from 13 A-T patients (with dual search coils in five patients and video oculography in seven) during attempted fixation. Results: Two abnormalities—nystagmus and saccadic intrusions—were common. Horizontal, vertical and torsional nystagmus was present in straight ahead (spontaneous nystagmus) and eccentric gaze (gaze evoked nystagmus). In eight patients the horizontal nystagmus changed directions—periodic alternating nystagmus (PAN). Two types of saccadic intrusions were seen—micro-saccadic oscillations (SO) and square wave saccadic intrusions (SWSI). SO were small amplitude (0.1–0.9°) and high frequency (14–33 Hz) back to back horizontal saccades. SWSI ranged between 1° and 18° (median 3°) with an intersaccadic interval ranging between 50 and 800 ms (median 300 ms). The potential impact of abnormal gaze stabilisation on vision was quantified. Discussion: Degeneration of cerebellar Purkinje neurons disinhibit the caudal fastigial oculomotor region (FOR) and vestibular nuclei (VN). Disinhibition of VN can cause nystagmus, including PAN, while disinhibition of FOR can affect saccade generating mechanisms, leading to SWSI and SO.

Background: Most patients with acute vestibular syndrome have vestibular neuritis or labyrinthitis. Some harbour strokes that can only be differentiated on the basis of subtle eye movement findings, including nystagmus. Peripheral nystagmus should be enhanced by removal of visual fixation. Current bedside methods for removing fixation require expensive equipment or technical skill not routinely available. We sought to test a new method for blocking fixation. Methods: Proof-of-concept study for a new bedside oculomotor diagnostic test using an established physiological measurement of eye movements (electro-oculography (EOG)) as the reference standard. We sampled unselected patients undergoing caloric testing (surrogate model for neuritis) in an academic vestibular clinic. During the brief (30–60 s) decay phase of caloric-induced peripheral vestibular nystagmus, we shone a penlight in the left eye while intermittently occluding the right. We assessed nystagmus intensity (slow-phase velocity) clinically in all subjects and quantified change in two exemplar cases. Results: Caloric responses frequently decayed before the test was complete, and artefacts rendered many EOGs uninterpretable during the short decay period. A clinically evident increase in nystagmus was seen 18 times in 10 patients and corroborated by EOG in 15. In quantified cases, slow-phase velocity increased as expected (mean change +42%) with fixation blocked. Conclusion: The penlight-cover test could offer a low-cost, simple means of disrupting visual fixation in clinical settings where differentiating peripheral from central vestibular disorders is crucial, such as the emergency department. Prospective studies are needed to determine the test’s utility for excluding dangerous central causes among patients with suspected peripheral lesions.

In a typical short-term saccadic adaptation protocol, the target moves intrasaccadically either toward (gain-down) or away (gain-up) from initial fixation, causing the saccade to complete with an endpoint error. A central question is how the motor system adapts in response to this error: are the motor commands changed to bring the eyes to a different goal, akin to a remapping of the target, or is adaptation focused on the processes that monitor the ongoing motor commands and correct them midflight, akin to changes that act via internal feedback? Here, we found that, in the gain-down paradigm, the brain learned to produce a smaller amplitude saccade by altering the trajectory of the saccade. The adapted saccades had reduced peak velocities, reduced accelerations, shallower decelerations, and increased durations compared with a control saccade of equal amplitude. These changes were consistent with a change in an internal feedback that acted as a forward model. However, in the gain-up paradigm, the brain learned to produce a larger amplitude saccade with trajectories that were identical with those of control saccades of equal amplitude. Therefore, whereas the gain-down paradigm appeared to induce adaptation via an internal feedback that controlled saccades midflight, the gain-up paradigm induced adaptation primarily via target remapping. Our simulations explained that, for each condition, the specific adaptation produced a saccade that brought the eyes to the target with the smallest motor costs.

Saccadic oscillations threaten clear vision by causing image motion on the retina. They are either purely horizontal (ocular flutter) or multidimensional (opsoclonus). We propose that ion channel dysfunction in the burst cell membrane is the underlying abnormality. We have tested this hypothesis by simulating a neuromimetic computational model of the burst neurons. This biologically realistic model mimics the physiologic properties and anatomic connections in the brainstem saccade generator. A rebound firing after sustained inhibition, called post-inhibitory rebound (PIR), and reciprocal inhibition between premotor saccadic burst neurons are the key features of this conceptual scheme. PIR and reciprocal inhibition make the circuits that generate the saccadic burst inherently unstable and can lead to oscillations unless stabilized by external inhibition. Our simulations suggest that alterations in membrane properties that lead to an increase in PIR, a reduction in external glycinergic inhibition, or both can cause saccadic oscillations.

To assess how frequently cardiovascular dizziness is vertigo. Recent studies suggest providers do not consider cardiovascular causes when a patient reports true vertigo (spinning/motion) as opposed to presyncope (impending faint). It is known that cardiovascular disease causes dizziness, but unknown how often such dizziness is vertiginous, as opposed to presyncopal.Systematic review of observational studies was made: Search--electronic (MEDLINE, EMBASE) and manual (references of eligible articles) search for English-language studies (1972-2007).Inclusions Studies ofor=5 patients with confirmed cardiovascular causes for dizziness and reporting a proportion with vertigo were included. Two independent reviewers selected studies for inclusion, with differences adjudicated by a third. Study characteristics and dizziness-type proportions were abstracted. Studies were rated on methodology and quality of dizziness definitions. Differences were resolved by consensus.We identified 1,506 citations, examined 125 full manuscripts, and included 5 studies. Principal reasons for exclusion were: abstracts--lack of original data, no cardiovascular diagnosis, or confounding exposure/disease (74%); manuscripts--failure to distinguish vertigo from other dizziness types (78%). In the three studies not using vertigo as an entry criterion (representing 1,659 patients with myocardial infarction, orthostatic hypotension, or syncope), vertigo was present in 63% (95% CI 57-69%) of cardiovascular patients with dizziness and the only dizziness type in 37% (95% CI 31-43%). Limitations include modest study quality and non-uniform definitions for vertigo.Published data suggest that dizziness from primary cardiovascular disease may often be vertigo. Future research should assess prospectively whether dizziness type is a meaningful predictor for or against a cardiovascular diagnosis.

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

The cerebellum is a key structure within a widely distributed neural network that controls movements including those of the eyes. Both the immediate, on-line control of movement and more long-term adaptive functions are within the purview of the cerebellum. Ocular motor abnormalities are prominent in patients with cerebellar disorders and aid clinical anatomical localization. Assigning specific functions to structures within the cerebellum, however, is more problematic. For example, each of the ocular motor subsystems – saccades, pursuit, vestibular, and vergence – has multiple representations in different parts of the cerebellum, and a functional distinction is not always possible. Furthermore, the cerebellum is so richly interconnected with other parts of the brain that understanding its function depends on considering the entire motor control circuit within which it resides. There are three major structural units in the cerebellum associated with control of eye movements: (1) the flocculus and paraflocculus (tonsil), (2) nodulus and uvula, and (3) the dorsal vermis (lobules VI–VII) and underlying fastigial nuclei. Here we review the main ocular motor deficits associated with cerebellar lesions and infer function accordingly.

The differential diagnosis of patients with vestibular symptoms usually begins with the question: is the lesion central or is it peripheral? The answer commonly emerges from a careful examination of eye movements, especially when the lesion is located in otherwise clinically silent areas of the brain such as the vestibular portions of the cerebellum (flocculus, paraflocculus which is called the tonsils in humans, nodulus, and uvula) and the vestibular nuclei as well as immediately adjacent areas (the perihypoglossal nuclei and the paramedian nuclei and tracts). The neural circuitry that controls vestibular eye movements is intertwined with a larger network within the brainstem and cerebellum that also controls other types of conjugate eye movements. These include saccades and pursuit as well as the mechanisms that enable steady fixation, both straight ahead and in eccentric gaze positions. Navigating through this complex network requires a thorough knowledge about all classes of eye movements to help localize lesions causing a vestibular disorder. Here we review the different classes of eye movements and how to examine them, and then describe common ocular motor findings associated with central vestibular lesions from both a topographic and functional perspective.

OBJECTIVE To quantify precision in patient reports of different attributes of dizziness. PATIENTS AND METHODS In a cross-sectional study, we interviewed consecutive adult patients with dizziness at 2 urban academic emergency departments (EDs) from July 2, 2005, to August 26, 2005. We excluded patients who were too sick for an interview or who posed a risk to the interviewer. We included those who were "dizzy, light-headed, or off-balance" for 7 days or less or previously "bothered" by the same conditions. We assessed descriptions of dizziness quality elicited by 4 questions in different formats (open-ended, multiresponse, single-choice, and directed). Clarity was assessed qualitatively (vague, circular) and quantitatively (overlap of types of dizziness). Consistency was measured by frequency of mismatched responses across question formats. Reliability was determined by test-retest. RESULTS Of 1342 patients screened, 872 (65%) were dizzy, light-headed, or off-balance in the past 7 days (n=677) or previously bothered by dizziness (n=195). Among these 872 patients with dizziness, 44% considered dizziness "the main reason" or "part of the reason" for the ED visit. Open-ended descriptions were frequently vague or circular. A total of 62% selected more than 1 dizziness type on the multiresponse question. On the same question, 54% did not pick 1 or more types endorsed previously in open description. Of 218 patients not identifying vertigo, spinning, or motion on the first 3 questions, 70% confirmed "spinning or motion" on directed questioning. Asked to choose the single best descriptor, 52% picked a different response on retest approximately 6 minutes later. By comparison, reports of dizziness duration and triggers were clear, consistent, and reliable. CONCLUSION Descriptions of the quality of dizziness are unclear, inconsistent, and unreliable, casting doubt on the validity of the traditional approach to the patient with dizziness. Alternative approaches, emphasizing timing and triggers over type, should be investigated.

Tremor disorders pose fundamental questions about disease mechanisms, and challenges to successful neurotherapeutics: What causes motor circuits to oscillate in disorders in which the central nervous system otherwise seems normal? How does inheritance 'determine' the clinical phenotype in familial tremor disorders? Here, we address these questions. Analogies between the neural circuits controlling rapid eye movements (saccades) and those controlling limb movements allow us to translate the interpretations from the saccadic systems to the limb movement system. Moreover, the relatively well understood neurophysiology of the ocular motor system offers a unique opportunity to test specific hypotheses about normal and abnormal motor control of both eye and limb movements. We describe a new familial disorder--'micro-saccadic oscillations and limb tremor (microSOLT)'--in a mother and daughter who had tiny saccadic oscillations of the eyes and tremor of the hands. This unique oscillatory movement disorder resembles other common tremor disorders (such as essential tremor) that occur in patients who have an otherwise normally functioning central nervous system. We hypothesize that microSOLT is caused by an inherited abnormality that results in abnormal membrane properties causing reduced external inhibition in the premotor neurons that generate the high-frequency discharge (burst) for saccades and for ballistic limb movements. To test this hypothesis, we recorded hand tremor and eye movements in two patients with microSOLT and particularly during natural circumstances when inhibition of the premotor saccadic burst neurons is removed (e.g. eye closure). We then simulated a conductance-based model for the premotor commands which included excitatory and reciprocally inhibitory burst neurons. The structure of this physiologically realistic model was based upon known cell types and anatomical connections in the brainstem (for saccades) and the thalamus (for limb movements). The physiological phenomenon of post-inhibitory rebound in premotor burst neurons makes the circuit inherently unstable and prone to oscillate unless prevented by external inhibition. Indeed, with simulated reduction of external inhibition (in this case glycinergic), saccadic oscillations and limb tremor were reproduced. Our results suggest that a single-inherited deficit can alter membrane properties, which impairs inhibition in an inherently unstable neural circuit causing the eye and limb oscillations in microSOLT. This concept has broad implications for understanding the mechanism and designing rationale pharmacotherapy for abnormal oscillations and may be applicable to other common disorders in which there are no structural abnormalities in the brain such as essential tremor.

The purpose was to assess intra- and post-saccadic torsion in superior oblique palsy (SOP) patients and the effect of surgery on torsion.Eleven patients with a presumed congenital SOP and five with acquired SOP performed 10 degrees vertical saccades over a range of +/-20 degrees. Eye movements were recorded with dual search coils. Dynamic torsion was calculated by subtracting the expected change in torsion during the saccade (based upon static torsion before and after the saccade) from the maximum intrasaccadic torsion. Eight healthy subjects were controls. We also examined the effects of surgery on dynamic torsion and the orientation of Listing's plane in patients with congenital SOP who were operated on either by weakening of the inferior oblique muscle on the affected eye (n=5), by recession of the inferior rectus muscle on the normal eye (n=4) or by both procedures (n=2). Postoperative recordings were obtained at least 1 month after surgery.Patients with congenital and acquired SOP showed an increased dynamic extorsion, primarily during downward saccades. Following a recession of the inferior oblique muscle in congenital SOP patients, half showed significant decreases in extorsion (up to 1.0 degrees) during downward saccades by the affected eye. Following surgery all showed a temporal rotation of Listing's plane (up to 15 degrees for primary position).Patients with a SOP show a characteristic pattern of dynamic torsion during vertical saccades differing from normals. Recession of the inferior oblique muscle leads to rotation of Listing's plane in all congenital SOP patients and causes large changes in dynamic torsion in a subgroup of them, perhaps reflecting the heterogeneity of congenital SOP.

We studied the effect of cerebellar lesions on the 3-D control of the rotational vestibuloocular reflex (RVOR) to abrupt yaw-axis head rotation. Using search coils, three-dimensional (3-D) eye movements were recorded from nine patients with cerebellar disease and seven normal subjects during brief chair rotations (200°/s2 to 40°/s) and manual head impulses. We determined the amount of eye-position dependent torsion during yaw-axis rotation by calculating the torsional-horizontal eye-velocity axis for each of three vertical eye positions (0°, ±15°) and performing a linear regression to determine the relationship of the 3-D velocity axis to vertical eye position. The slope of this regression is the tilt angle slope. Overall, cerebellar patients showed a clear increase in the tilt angle slope for both chair rotations and head impulses. For chair rotations, the effect was not seen at the onset of head rotation when both patients and normal subjects had nearly head-fixed responses (no eye-position-dependent torsion). Over time, however, both groups showed an increasing tilt-angle slope but to a much greater degree in cerebellar patients. Two important conclusions emerge from these findings: the axis of eye rotation at the onset of head rotation is set to a value close to head-fixed (i.e., optimal for gaze stabilization during head rotation), independent of the cerebellum and once the head rotation is in progress, the cerebellum plays a crucial role in keeping the axis of eye rotation about halfway between head-fixed and that required for Listing's Law to be obeyed.

Fragile X and Turner syndromes are two X-chromosome-related disorders associated with executive function and visual spatial deficits. In the present study, we used ocular motor paradigms to examine evidence that disruption to different neurological pathways underlies these deficits. We tested 17 females with fragile X, 19 females with Turner syndrome, and 40 females with neither disorder who comprised the comparison group. Group differences emerged for both the fragile X and Turner syndrome groups, each relative to the comparison group: Females with fragile X had deficits in generating memory-guided saccades, predictive saccades, and saccades made in the overlap condition of a gap/overlap task. Females with Turner syndrome showed deficits in generating memory-guided saccades, but not during either the predictive saccade or gap/overlap task. Females with Turner syndrome, but not females with fragile X, showed deficits in visually guided saccades and anti-saccades. These findings indicate that different brain regions are affected in the two disorders, and suggest that different pathways lead to the similar cognitive phenotypes described for fragile X and Turner syndromes.

We studied the dependence of ocular torsion on eye position during horizontal optokinetic nystagmus (OKN) elicited by random-dot translational motion (tOKN) and prolonged rotation in the light (rOKN). For slow and quick phases, we fit the eye-velocity axis to vertical eye position to determine the tilt angle slope (TAS). The TAS for tOKN was 0.48 for both slow and quick phases, close to what is found during translational motion of the head. The TAS for rOKN was less for both slow (0.11) and quick phases (0.26), close to what is found during rotational motion of the head. Our findings are consistent with the notion that translational and rotational optic flow are processed differently by the brain and that they produce different 3-D eye movement commands that are comparable to the different commands generated in response to vestibular signals when the head is actually translating or rotating.

Brief smooth eye-velocity responses to target position steps have been reported during smooth pursuit. We investigated position-error responses in eight healthy human subjects, comparing the effects of a step–ramp change in target position when imposed on steady-state smooth pursuit, vestibuloocular reflex (VOR) slow phases, or fixation. During steady-state pursuit or VOR, the target performed a step–ramp movement in the same or in the opposite direction relative to ongoing eye movements. When the step was directed backward relative to steady-state smooth pursuit, eye velocity transiently decreased (1.3 ± 0.4°/s; average peak change in amplitude ± SD), beginning about 100 ms after the step. The amplitude of position-error responses varied inversely with the step size. In contrast, there was little or no response in trials with forward steps during steady-state smooth pursuit, when step–ramps were imposed on VOR or when smooth pursuit began from fixation. We hypothesize that during ongoing smooth tracking when a sudden shift in target position is detected the pursuit system compares the direction of ongoing eye velocity with the relative positional error on the retina. In the case of different relative directions between ongoing tracking and a new target eccentricity, a position-error response toward the new target is initiated. Such a mechanism might help the smooth pursuit system to respond better to changes in target direction. These experimental findings were simulated by a mathematical model of smooth pursuit by implementing direction-dependent behavior with a position-error gating mechanism.

Torsional eye movements are rotations of the eye around the line of sight. Measuring torsion is essential to understanding how the brain controls eye position and how it creates a veridical perception of object orientation in three dimensions. Torsion is also important for diagnosis of many vestibular, neurological, and ophthalmological disorders. Currently, there are multiple devices and methods that produce reliable measurements of horizontal and vertical eye movements. Measuring torsion, however, noninvasively and reliably has been a longstanding challenge, with previous methods lacking real-time capabilities or suffering from intrusive artifacts. We propose a novel method for measuring eye movements in three dimensions using modern computer vision software (OpenCV) and concepts of iris recognition. To measure torsion, we use template matching of the entire iris and automatically account for occlusion of the iris and pupil by the eyelids. The current setup operates binocularly at 100 Hz with noise

The signals for adduction during conjugate horizontal eye movements are carried through the medial longitudinal fasciculus (MLF). Lesions in this pathway cause internuclear ophthalmoplegia (INO), characterized by impaired ipsilesional adduction, often with nystagmus of the contralateral abducting eye. Usually with INO straight-ahead fixation appears steady. Here we demonstrate quantitative recordings and videos of 2 unusual patterns of saccadic intrusions in a patient with bilateral INO and discuss a plausible mechanism.

OBJECTIVE: To test the effects of a sustained nystagmus on the head impulse response of the vestibulo-ocular reflex (VOR) in healthy subjects. METHODS: VOR gain (slow-phase eye velocity/head velocity) was measured using video-head impulse test (vHIT) goggles. Acting as a surrogate for a spontaneous nystagmus (SN) a post-rotatory nystagmus (PRN) was elicited after a sustained, constant-velocity rotation and then head impulses were applied. RESULTS: ‘Raw’ VOR gain, uncorrected for PRN, in healthy subjects in response to head impulses with peak velocities in the range of 150- 250 deg/s was significantly increased (as reflected in an increase of the slope of the gain versus head velocity relationship) after inducing PRN with slow phases of nystagmus of high intensity (>30deg/s) in the same but not in the opposite direction as the slow-phase response induced by the head impulses. The values of VOR gain themselves, however, remained in the normal range with slow-phase velocities of PRN

This chapter reviews the stimuli for vergence, the properties of fusional and accommodative vergence, as well as vergence made in combination with saccades or vestibular eye movements, or blinks. Different properties of horizontal, vertical, and torsional vergence are discussed. Current models are presented to account for interactions between vergence and saccades. The neural substrate for vergence movements is reviewed from ocular motoneurons to the midbrain supraoculomotor area, to visual cortical areas such as MST and frontal eye field, including pontine nuclei, cerebellar vermis, and fastigial nucleus. Adaptive properties of vergence are reviewed, especially phoria adaptation, discussing the role of the cerebellum. The bedside and laboratory evaluation of vergence is summarized and the pathophysiology of disorders of vergence discussed, including developmental disorders associated with childhood strabismus and acquired disorders such as convergence spasm, convergence insufficiency, vergence forms of nystagmus such as convergence-retraction nystagmus, and effects of focal pontine lesions.

This chapter reviews contributions of orbital tissues and extraocular muscles (EOM) to the control of eye movements. The anatomy of the orbit, fascia, fibromuscular pulleys, and EOM are described and related to the kinematics of 3-D eye rotations. Current concepts of the embryology of the EOM and their unique and diverse characteristics are described, suggesting why they are more vulnerable to certain neuromuscular disorders and less susceptible to others, compared with skeletal muscles. Electrophysiological properties of different EOM fiber types (and their motor neuron innervation) are contrasted, describing new models that attempt to account for nonlinear mechanical properties of the orbit. The substrate and roles of extraocular proprioception in the control of eye movements are summarized and related to clinical disorders affecting EOM. The anatomy of the cranial nerves supplying the EOM is summarized, diagrammed and highlighted to aid diagnosis of common palsies of the oculomotor, trochlear, and abducens nerves.

This chapter reviews the neural network that temporally integrates premotor, velocity-coded signals to achieve tonic contraction of the extraocular muscles to hold the eyes at an eccentric position in the orbits. The mechanical properties of the eye and its supporting tissues are quantified and related to the pulse-slide-step neural command for a saccadic change in eye position. The anatomical substrate and neuropharmacology of the neural integrator is reviewed, including nucleus prepositus hypoglossi, interstitial nucleus of Cajal and cerebellum. Mathematical and animal models for the neural integrator are discussed, addressing points about how a leaky or unstable integrator may arise. Clinical and laboratory evaluation of gaze holding is summarized. Effects of experimentally inactivating the neural integrator are compared with clinical disorders affecting gaze holding, including a discussion of the pathogenesis of gaze-evoked nystagmus and Alexander’s law. Compensatory mechanisms for a leaky neural integrator are discussed, including centripetal, rebound, and gaze-evoked nystagmus.

This new edition comprises a modern synthesis of the anatomical, physiological, and pharmacological substrate for eye movements, including current views on the reflexive and voluntary control of gaze. This synthesis is based on electrophysiological and inactivation studies in macaque, and behavioural studies in humans that incorporate functional imaging and transcranial magnetic stimulation (TMS) in normals, and clinicopathological studies in patients with neurological, visual, or vestibular disorders. Sophisticated experimental paradigms have been applied to both species to explore aspects of cognition, memory, volition, and reward. This large body of research has demonstrated the power of eye movements as experimental tools. The second part of this online resource applies this synthesis to the clinical and laboratory evaluation of patients with abnormal eye movements due to a broad range of disorders - from muscular dystrophy, and genetic disorders, to dementia, including visual and vestibular conditions.

This chapter reviews properties and neural substrate of vestibular and optokinetic eye movements. Geometric aspects of head rotations and translations (linear movements) are related to properties of rotational and translational vestibulo-ocular reflexes. The motion sensors of the vestibular labyrinth -the semicircular canals and otolith organs - are described. The contributions that direct and indirect central pathways make to the direction and temporal properties of vestibulo-ocular responses are summarized. Optokinetic-vestibular interactions during sustained rotations are discussed. Properties of vestibular and optokinetic responses -gain, phase, and time constant - are explained as well as how they are influenced by factors including target location, mental set, and changing visual demands (vestibular adaptation and the cerebellum). The multiple cerebral areas that contribute to vestibular sensation are reviewed. Clinical and laboratory evaluation of vestibulo-ocular function is summarized including rotational and caloric testing, and vestibular-evoked myogenic potentials (VEMPs). The pathogenesis of common vestibular and optokinetic disorders is reviewed.

This chapter reviews the behavioral properties of rapid eye movements, ranging from quick phases of nystagmus to cognitively controlled saccades, and their neural substrate. Properties of various types of saccades are described, including express saccades, memory-guided saccades, antisaccades, and saccades during visual search and reading. Current concepts of regions important for the generation of saccades are reviewed, integrating results of functional imaging and electrophysiology, including brainstem burst neurons and omnipause neurons, the superior colliculus, frontal eye field, supplementary eye field, dorsolateral prefrontal cortex, cingulate cortex, posterior parietal cortex, parietal eye field, thalamus, pulvinar, caudate, substantia nigra pars reticulata, subthalamic nucleus, cerebellar dorsal vermis, and fastigial nucleus. Saccade adaptation to novel visual demands is discussed, and the interaction between saccades and eyelid movements (blinks). Mathematical models of saccades are discussed. Clinical and laboratory evaluation of saccades and the pathophysiology of saccadic disorders, from slow saccades to opsoclonus, are reviewed.

This chapter summarizes the properties and neural substrate of smooth eye tracking movements, including visual fixation, smooth pursuit, the ocular following response (OFR), and optokinetic nystagmus (OKN). Fixational eye movements, including microsaccades and drifts, and the role of the OFR in stabilizing gaze are discussed. The properties of pursuit, OFR, and OKN are summarized, including anticipation, prediction, and target selection. The ability of pursuit adaptation to respond to new visual demands is reviewed. Pertinent cortical areas (MT+) and their projections to brainstem and cerebellum are discussed, as well as the accessory optic pathway, and nucleus of the optic tract. Current models for smooth pursuit that incorporate efference copy (corollary discharge), prediction, and Bayesian operators are summarized. Clinical and laboratory evaluation of fixation and visual tracking are reviewed, and the pathogenesis of disorders of these movements discussed, including latent nystagmus accompanying failure to develop binocular vision and infantile nystagmus syndrome.

This chapter draws on a range of studies of macaque and humans to forge an anatomical scheme for the control of gaze. At each stage, this scheme is used to predict effects of focal lesions on the control of gaze, with video examples. Contributions include the abducens nucleus, medial longitudinal fasciculus (MLF), and paramedian pontine reticular formation (PPRF) to horizontal gaze; the rostral interstitial nucleus of the medial longitudinal fasciculus (RIMLF), interstitial nucleus of Cajal, and posterior commissure to vertical gaze; cerebellar flocculus, paraflocculus, dorsal vermis, fastigial nucleus, and inferior olive to adaptive optimization of gaze. Cortical control of gaze by structures including primary visual cortex (V1), middle temporal visual area (MT, V5), medial superior temporal visual area (MST), posterior parietal cortex, frontal eye fields, supplementary eye fields, dorsolateral prefrontal cortex, cingulate cortex, descending pathways, thalamus, pulvinar, caudate, substantia nigra pars reticulata, subthalamic nucleus, and superior colliculus are each discussed.

This chapter reviews the approach to the patient with nystagmus or saccadic intrusions and their clinical features (with illustrative video cases), etiology, pathophysiology, and management. Nystagmus caused by peripheral vestibular disorders; downbeat, upbeat, and torsional nystagmus; periodic alternating nystagmus, seesaw and hemi-seesaw nystagmus; gaze-evoked nystagmus; Bruns nystagmus; centripetal and rebound nystagmus; nystagmus occurring in association with disease of the visual system; acquired pendular nystagmus with multiple sclerosis; oculopalatal tremor; convergence-retraction nystagmus; infantile nystagmus syndrome; fusional maldevelopment nystagmus syndrome and latent nystagmus; spasmus nutans syndrome; and lid nystagmus are discussed. Saccadic intrusions and oscillations and the clinical features, etiology, pathophysiology, and management of square-wave jerks, macrosaccadic oscillations, saccadic pulses, ocular flutter, opsoclonus, and voluntary saccadic oscillations are summarized. Treatments for nystagmus and saccadic intrusions are summarized, including pharmacological treatments, optical treatments, procedures to weaken the extraocular muscles (e.g., Kestenbaum-Anderson procedure), and measures such as biofeedback and vibration.

This chapter reviews the physiologic basis for diplopia, including Sherington’s law of reciprocal innervation and Hering’s law of motor correspondence. Clinical testing is reviewed, including cover tests, red glass, Maddox rod, the Bielschowsky head-tilt test, and abnormal head postures. Clinical features (with illustrative video cases), etiology, and management of abducens nerve palsy, trochlear nerve palsy, oculomotor nerve palsy, and combined neuropathies are discussed, as well as Miller Fisher syndrome, amyotrophic lateral sclerosis, neuromyotonia, Brown’s syndrome and superior oblique myokymia. Disorders of the neuromuscular junction are examined, including systemic botulism, Lambert-Eaton myasthenic syndrome, and myasthenia gravis. Disorders affecting the extraocular muscles are reviewed, including chronic progressive external ophthalmoplegia, Duchenne dystrophy, myotonic dystrophy, oculopharyngeal dystrophy, congenital myopathies, Kearns-Sayre syndrome and mitochondrial myopathies. The chapter also discusses thyroid eye disease, acquired restrictive ophthalmopathies, and congenital cranial dysinnervation disorders (CCDD), Duane syndrome, horizontal gaze palsy with scloliosis, and congenital fibrosis of the extraocular muscles.

This chapter reviews clinical features of eye movement disorders associated with vestibular disorders. The clinical history and examination are reviewed, pointing our key symptoms and signs (with illustrative video cases), for example, in distinguishing vertigo due to stroke from peripheral vestibular disease. Acute vertigo is discussed, including forms due to infections, trauma, and toxins as well as Tullio phenomenon, fistula, canal dehiscence. Recurrent vertigo is reviewed, including Ménière’s syndrome, otosclerosis, inflammatory disorders, migraine, vascular disorders, and epilepsy. The mechanism of hyperventilation-induced vertigo and nystagmus is discussed. Posturally induced vertigo is reviewed, detailing features and treatment of benign paroxysmal positional vertigo (BPPV), and central causes of positional vertigo. The symptom of oscillopsia is reviewed, whether due to an abnormal vestibulo-ocular reflex or paresis of extraocular muscles, or due to nystagmus and other abnormal eye movements. Finally, the topological diagnosis and pathogenesis of skew deviation and the ocular tilt reaction are discussed.

This chapter reviews clinical features (with illustrative video cases) and pathophysiology of medullary lesions, including Wallenberg’s syndrome and oculopalatal tremor. Manifestations and pathophysiology of three cerebellar syndromes are described (flocculus and paraflocculus, nodulus and ventral uvula, dorsal vermis and fastigial nucleus), applying these principles to interpret the effects of developmental disorders (e.g., Chiari malformation), hereditary ataxia, paraneoplastic cerebellar degeneration, cerebellar stroke, and cerebellar tumors. Characteristics of pontine lesions are discussed, including lesions of the abducens nucleus, paramedian pontine reticular formation (PPRF), internuclear ophthalmoplegia (INO), one-and-a-half syndrome, slow horizontal saccades, and saccadic oscillations. The effects of midbrain lesions are summarized, including lesions affecting the rostral interstitial nucleus of the medial longitudinal fasciculus (RIMLF), interstitial nucleus of Cajal, posterior commissure, and more diffuse processes causing slow vertical saccades or vertical gaze palsy (dorsal midbrain syndrome), including Whipple’s disease. Effects of lesions affecting the superior colliculus, thalamus, and pulvinar are also discussed.

This chapter reviews the visual requirements, properties, and neural substrate of eye movements and the advantages they offer to clinicians and scientists. Eye movements are easily observed, measured, and classified by the way they serve vision. The relationship between eye rotations and extraocular motoneuron discharge is approximately linear, making it possible to study how networks of neurons temporally integrate raw sensory signals. Gaze-holding vestibular eye movements act at short latency to guarantee clear vision during natural head movements. Gaze-shifting saccades, pursuit, and vergence movements are concerned with pointing each eye’s line of sight (fovea) at features of interest in the environment. By combining ingenious experimental design with functional imaging and electrophysiology, it has become possible to understand much about the neural substrate underlying each class of eye movements. Consequently, eye movements have become powerful tools to study cognition and memory, adaptation and motor learning, as well as aiding topological diagnosis.

This chapter reviews the relationship between ocular motor and cephalomotor systems, summarizing mechanical properties of head and neck tissues, head stability, and the roles of the cervico-ocular reflex (COR), vestibulo-collic reflex (VCR), and cervico-collic reflex. Visual consequences of head translation, and motion parallax, are discussed. Behavioral properties of eye-head saccades and smooth eye-head tracking are summarized along with their interactions with the vestibulo-ocular reflex (VOR). The neural substrate for rapid and smooth eye-head movements is discussed including the nucleus reticularis gigantocellularis, superior colliculus, cerebellar vermis and fastigial nucleus. Mathematical models for eye-head behavior are presented. Clinical and laboratory evaluation of eye-head movements are outlined, with geometric corrections required during measurement of eye and head movements. Discussion of the pathophysiology of abnormal eye-head movements includes vestibular hypofunction, progressive supranuclear palsy, spasmodic torticollis (cervical dystonia), spasmus nutans, epilepsy, ocular motor apraxia, and abnormal smooth eye-head tracking in parkinsonian syndromes and cerebellar disorders.

This chapter reviews (with illustrative videos) disorders of gaze in diseases involving the basal ganglia, including Parkinson’s disease, progressive supranuclear palsy (PSP), hyperkinetic movement syndromes such as oculogyric crisis, and Huntington’s disease. Ocular motor syndromes caused by lesions in the cerebral hemispheres are discussed, including gaze deviations. Distinctive features of ocular motor apraxia, both acquired and congenital, are highlighted. Eye movements during epilepsy, and abnormal eye movements in patients with dementia, including Alzheimer’s disease, frontotemporal dementia, and amyotrophic lateral sclerosis are reviewed. Eye movement disorders in psychiatric illnesses, including schizophrenia, bipolar affective disorder, and autism are summarized. Eye movements in stupor and coma are discussed. The range of ocular motor disturbances in multiple sclerosis (MS) is reviewed as well as the ocular motor manifestations of metabolic and deficiency disorders, including Niemann-Pick disease, Tay-Sachs disease, Gaucher’s disease, and Wernicke’s encephalopathy. Disorders of eye movements induced by drugs or toxins are tabulated.