Vertical Pursuit Research Articles

A Small Dorsal Pontine Infarction Presenting with Total Gaze Palsy Including Vertical Saccades and Pursuit

A small localized infarction in the dorsal pontine area can cause various eye-movement disturbances, such as abducens palsy, horizontal conjugate gaze palsy, internuclear ophthalmoplegia, and one-and-a-half syndrome. However, complete loss of vertical saccades and pursuit with horizontal gaze palsy has not been reported previously in a patient with a small pontine lesion. We report a 67-year-old man with a small dorsal caudal pontine infarct who exhibited total horizontal gaze palsy as well as loss of vertical saccades and pursuit.

Niemann-Pick disease Type C - Sea-blue histiocytosis: Phenotypic and imaging observations and mini review

We present a report on an 18-year-old boy with Niemann-Pick disease Type C (NP-C) who presented with progressive decline in scholastic performance since 9 years of age. At 12 years, he developed abnormal behavior and after 2 years had insidious onset, progressive gait ataxia and dysarthria followed by dystonia of the right upper extremity, excessive drooling, dysphagia and nasal regurgitation. He had coarse facies, depressed nasal bridge, high arched palate, crowded teeth, splenomegaly and peculiar facial grin. In addition, impaired vertical saccadic and pursuit eye movements, brisk muscle stretch reflexes and limb and gait ataxia were observed. He had a low IQ of 47 on Binet-Kamat test. The ultrasound examination of the abdomen confirmed the presence of moderate splenomegaly. Magnetic resonance imaging brain showed symmetrical leucoencephalopathy and mild cerebellar atrophy. Bone marrow aspiration showed numerous foamy macrophages and sea-blue histiocytes suggesting the diagnosis of NP-C.

A 62‐year‐old man with a family history of dementia, showing dementia and parkinsonism, presented with personality change and behavioral abnormality

The patient was a 62-year-old man. His mother, maternal uncle and grandfather had suffered from dementia. At the age of 57, the patient developed hypobulia, apathy and mental irritability, and showed disinhibited and stereotypical behaviors. At the age of 58, he showed personality change, poor understanding, restless and aimless walking, perseveration and echolalia as well as memory disturbance and disorientation. There was amnestic aphasia but no apraxia or agnosia. A CT scan and MRI disclosed localized symmetrical atrophy of the frontal and temporal lobes. Thereafter, he became mutistic and developed bradykinesia, rigidity of the extremities and impairment of vertical ocular pursuit movement. Sucking and grasp reflexes were positive with forced crying. He also revealed increased deep tendon reflexes in the extremities and bilateral Babinski signs. At the age of 59, he showed an oral tendency and could no longer walk. At the age of 60, he became bedridden, and tube feeding was started because of pseudobulbar palsy. At the terminal stage, he had repeated episodes of bronchopneumonia and died with akinetic mutism after a disease duration of about 5 years.

Smooth pursuit eye movements in children

Smooth pursuit eye movements consists of slow eye movements that approximate the velocity of the eyes to that of a small moving target, so that target image is kept at or near the fovea. Little information on smooth pursuit is available in children. We used an infrared eye tracker to record smooth pursuit in 38 typically developing children, aged 8-19 years. Participants followed a visual target moving sinusoidally at +/-10 degrees amplitude, horizontally and vertically at 0.25 or 0.5 Hz. The mean horizontal smooth pursuit gains, the ratio of eye to target velocities, were 0.84 at 0.25 Hz and 0.73 at 0.5 Hz. Mean vertical smooth pursuit gains were 0.68 at 0.25 Hz and 0.45 at 0.5 Hz. Smooth pursuit gains were significantly lower for vertical in comparison to horizontal tracking, and for 0.5 Hz in comparison to 0.25 Hz tracking (P<0.0001). Smooth pursuit gains increased with age (P<0.01, Pearson's correlation tests), with horizontal gains attaining reported adult values by mid adolescence. Vertical gains had large variability among participants. The median phase, the time interval between eye and target velocities, varied between 39 and 86 ms. Phase was not influenced by age. We conclude that smooth pursuit gains are lower in children than gains reported in adults. Vertical pursuit gain is significantly lower than horizontal pursuit gain. Gains improve with age and approach adult values in mid adolescence. Children have larger phases than reported adults values indicating that prediction in the smooth pursuit system is less mature in children.

Further evidence for selective difficulty of upward eye pursuit in juvenile monkeys: effects of optokinetic stimulation, static roll tilt, and active head movements

The smooth-pursuit system moves the eyes in space accurately to track slowly moving objects of interest despite visual inputs from the moving background and/or vestibular inputs during head movements. Recently, our laboratory has shown that young primates exhibit asymmetric eye movements during vertical pursuit across a textured background; upward eye velocity gain is reduced. To further understand the nature of this asymmetry, we performed three series of experiments in young monkeys. In Experiment 1, we examined whether this asymmetry was due to an un-compensated downward optokinetic reflex induced by the textured background as it moves across the retina in the opposite direction of the pursuit eye movements. For this, we examined the monkeys' ability to fixate a stationary spot in space during movement of the textured background and compared it with vertical pursuit across the stationary textured background. We also examined gains of optokinetic eye movements induced by downward motion of the textured background during upward pursuit. In both task conditions, gains of downward eye velocity induced by the textured background were too small to explain reduced upward eye velocity gains. In Experiment 2, we examined whether the frame of reference for low-velocity, upward pursuit was orbital or earth vertical. To test this, we first applied static tilt in the roll plane until the animals were nearly positioned on their side in order to dissociate vertical or horizontal eye movements in the orbit from those in space. Deficits were observed for upward pursuit in the orbit but not in space. In Experiment 3, we tested whether asymmetry was observed during head-free pursuit that requires coordination between eye and head movements. Asymmetry in vertical eye velocity gains was still observed during head-free pursuit although it was not observed in vertical head velocity. These results, taken together, suggest that the asymmetric eye movements during vertical pursuit are specific for upward, primarily eye pursuit in the orbit.

Eye Movements in Chorea-Acanthocytosis

To describe the eye movement abnormalities in patients with chorea-acanthocytosis (ChAc), a form of neuroacanthocytosis. This autosomal recessive, neurodegenerative disorder with aberrant erythrocyte morphology (acanthocytosis) is caused by mutations in the VPS13A gene. In contrast to Huntington's disease (for which ChAc has occasionally been mistaken), ocular involvement in ChAc has not been systematically studied. Three patients aged 26, 30, and 44 years with ChAc and six normal volunteers aged 31 to 48 years were included. Patients had dystonia, chorea, parkinsonism, dysarthria, dysphagia, seizures, cognitive abnormalities, and acanthocytosis. All had heterozygous VPS13A mutations and degeneration of the basal ganglia on magnetic resonance imaging (MRI) typical of ChAc. Patients had an extensive clinical and laboratory work-up. Neuro-ophthalmic examinations and eye movement recordings made with the magnetic search coil technique assessed patients' fixation characteristics, horizontal and vertical saccades, pursuit, and antisaccades. These were compared to the data of control subjects. Patients exhibited more than 30 square-wave jerks (small saccadic intrusions) per minute, versus 0 to 8 in the control subjects, as well as fractionated (multistep) and hypometric horizontal and vertical saccades. Decreased saccadic peak-velocity and reduced saccadic range were more pronounced for vertical saccades. Pursuit testing performed in two patients showed low gain. Results of antisaccade testing done in one patient were abnormal. The findings suggest brain stem involvement as an additional site of neurodegeneration outside the basal ganglia in ChAc. Patients with this progressive, intractable disease have pronounced ocular motor abnormalities. Eye movement recordings could assist in diagnosing ChAc, monitoring its progression and possible treatment evaluation.

Gravity modulates Listing's plane orientation during both pursuit and saccades.

Previous studies have shown that the spatial organization of all eye orientations during visually guided saccadic eye movements (Listing's plane) varies systematically as a function of static and dynamic head orientation in space. Here we tested if a similar organization also applies to the spatial orientation of eye positions during smooth pursuit eye movements. Specifically, we characterized the three-dimensional distribution of eye positions during horizontal and vertical pursuit (0.1 Hz, +/-15 degrees and 0.5 Hz, +/-8 degrees) at different eccentricities and elevations while rhesus monkeys were sitting upright or being statically tilted in different roll and pitch positions. We found that the spatial organization of eye positions during smooth pursuit depends on static orientation in space, similarly as during visually guided saccades and fixations. In support of recent modeling studies, these results are consistent with a role of gravity on defining the parameters of Listing's law.

Premotor Neurons Encode Torsional Eye Velocity during Smooth-Pursuit Eye Movements

Responses to horizontal and vertical ocular pursuit and head and body rotation in multiple planes were recorded in eye movement-sensitive neurons in the rostral vestibular nuclei (VN) of two rhesus monkeys. When tested during pursuit through primary eye position, the majority of the cells preferred either horizontal or vertical target motion. During pursuit of targets that moved horizontally at different vertical eccentricities or vertically at different horizontal eccentricities, eye angular velocity has been shown to include a torsional component the amplitude of which is proportional to half the gaze angle ("half-angle rule" of Listing's law). Approximately half of the neurons, the majority of which were characterized as "vertical" during pursuit through primary position, exhibited significant changes in their response gain and/or phase as a function of gaze eccentricity during pursuit, as if they were also sensitive to torsional eye velocity. Multiple linear regression analysis revealed a significant contribution of torsional eye movement sensitivity to the responsiveness of the cells. These findings suggest that many VN neurons encode three-dimensional angular velocity, rather than the two-dimensional derivative of eye position, during smooth-pursuit eye movements. Although no clear clustering of pursuit preferred-direction vectors along the semicircular canal axes was observed, the sensitivity of VN neurons to torsional eye movements might reflect a preservation of similar premotor coding of visual and vestibular-driven slow eye movements for both lateral-eyed and foveate species.

Smooth-pursuit eye-movement-related neuronal activity in macaque nucleus reticularis tegmenti pontis.

Neuronal responses that were observed during smooth-pursuit eye movements were recorded from cells in rostral portions of the nucleus reticularis tegmenti pontis (rNRTP). The responses were categorized as smooth-pursuit eye velocity (78%) or eye acceleration (22%). A separate population of rNRTP cells encoded static eye position. The sensitivity to pursuit eye velocity averaged 0.81 spikes/s per degrees /s, whereas the average sensitivity to pursuit eye acceleration was 0.20 spikes/s per degrees /s(2). Of the eye-velocity cells with horizontal preferences for pursuit responses, 56% were optimally responsive to contraversive smooth-pursuit eye movements and 44% preferred ipsiversive pursuit. For cells with vertical pursuit preferences, 61% preferred upward pursuit and 39% preferred downward pursuit. The direction selectivity was broad with 50% of the maximal response amplitude observed for directions of smooth pursuit up to +/-85 degrees away from the optimal direction. The activities of some rNRTP cells were linearly related to eye position with an average sensitivity of 2.1 spikes/s per deg. In some cells, the magnitude of the response during smooth-pursuit eye movements was affected by the position of the eyes even though these cells did not encode eye position. On average, pursuit centered to one side of screen center elicited a response that was 73% of the response amplitude obtained with tracking centered at screen center. For pursuit centered on the opposite side, the average response was 127% of the response obtained at screen center. The results provide a neuronal rationale for the slow, pursuit-like eye movements evoked with rNRTP microstimulation and for the deficits in smooth-pursuit eye movements observed with ibotenic acid injection into rNRTP. More globally, the results support the notion of a frontal and supplementary eye field-rNRTP-cerebellum pathway involved with controlling smooth-pursuit eye movements.

Effects of intravenous opioids on eye movements in humans: possible mechanisms

Oculomotor symptoms such as downbeat nystagmus can be due to side effects of drugs. We investigated the clinical effects as well as the eye movement symptoms after intravenous administration of opiates (pethidine and fentanyl). Eye movements were recorded with the magnetic search coil technique. All four normal subjects showed a transient disturbance of eye fixation with downbeat nystagmus, a range of saccadic intrusions and oscillations, including square wave jerks and saccadic pulses, lasting from 10 to 15 minutes. The gain of sinusoidal VOR and smooth pursuit was moderately decreased; in particular the vertical pursuit showed an upward velocity offset. On the basis of the clinical findings and of recent diprenorphine PET findings in humans, which detected opiod binding sites in the cerebellum and the known inhibitory action of opiates, we hypothesized that a cerebellar dysfunction occurs after opiate administration which could possibly be mediated by inhibition of the parallel fiber activation of the Purkinje cells. Furthermore, opiate binding sites in the vestibular nuclei could be responsible for the vertical vestibular tonus imbalance involved in the pathophysiolgy of downbeat nystagmus.

The cerebellar contribution to eye movements based upon lesions: binocular three-axis control and the translational vestibulo-ocular reflex.

The study of human cerebellar patients and monkeys with experimental cerebellar lesions has taught us much about the role of the cerebellum in normal ocular motor control. Here we emphasize recent findings that point to a role for the cerebellum in (1) the control of the three-dimensional axis about which the eye rotates in response to visual and vestibular stimuli, and (2) the generation of the translational VOR. Findings in cerebellar patients include abnormalities of eye torsion during attempted fixation that suggest a cerebellar role in the control of torsion so that Listing's law is obeyed. Abnormal torsion during vertical pursuit suggests that central processing of information for smooth pursuit may be based upon a phylogenetically old, semicircular canal coordinate scheme. Inappropriate and disconjugate vertical and torsional eye movements ("cross-coupling") occur during brief, high-acceleration rotations of the head. This suggests a role for the cerebellum in the binocular control of the rotation axis of the VOR. Finally, abnormalities of the modulation of the translational VOR with near viewing in cerebellar patients, but with sparing of the very initial 25-30 msec of response, suggests an important role for the cerebellum in the translational VOR.

Adaptive Eye Movements Induced by Cross-axis PursuitVestibular Interactions in Trained Monkeys

We showed previously that smooth pursuit training combined with whole-body rotation in the orthogonal plane induces adaptive cross-axis vestibulo-ocular reflex (VOR). To gain an insight into the possible pathways and the nature of error signals for cross-axis VOR adaptation, we examined further properties of adaptive responses. In the first series, we trained monkeys for vertical pursuit during sinusoidal yaw rotation at 0.5 Hz ( - 10°) by presenting a target spot either in phase with, or with phase shifts (lead or lag) of 90° to, the chair for 1 h. After training, sinusoidal or trapezoidal yaw rotation was tested in complete darkness without a target. Different training conditions resulted in different amounts of phase shift in cross-axis VOR. Trapezoidal yaw rotation (peak acceleration , 780°/s 2 ) revealed further differences in the direction, latency and time course of the adaptive responses depending on the conditions of the pursuit task. At least two (fast and slow) components with different latencies were induced in the cross-axis VOR by trapezoidal rotation after in-phase and phase-shift training. Adaptive responses were accurately simulated by the weighted sum of these two components. In the second series, we examined the effects of sequentially flashed (10 w s) targets in the horizontal plane during pitch rotation. The monkeys learned to track such targets by smooth pursuit, and cross-axis VOR was also induced after such apparent motion stimuli without retinal slip of the target image. These results indicate the importance of eye velocity for cross-axis VOR and suggest that this adaptation occurs most probably in the smooth pursuit pathways.

Functions of the nucleus of the optic tract (NOT). II. Control of ocular pursuit.

Ocular pursuit in monkeys, elicited by sinusoidal and triangular (constant velocity) stimuli, was studied before and after lesions of the nucleus of the optic tract (NOT). Before NOT lesions, pursuit gains (eye velocity/target velocity) were close to unity for sinusoidal and constant-velocity stimuli at frequencies up to 1 Hz. In this range, retinal slip was less than 2 degrees. Electrode tracks made to identify the location of NOT caused deficits in ipsilateral pursuit, which later recovered. Small electrolytic lesions of NOT reduced ipsilateral pursuit gains to below 0.5 in all tested conditions. Pursuit was better, however, when the eyes moved from the contralateral side toward the center (centripetal pursuit) than from the center ipsilaterally (centrifugal pursuit), although the eyes remained in close proximity to the target with saccadic tracking. Effects of lesions on ipsilateral pursuit were not permanent, and pursuit gains had generally recovered to 60-80% of baseline after about 2 weeks. One animal had bilateral NOT lesions and lost pursuit for 4 days. Thereafter, it had a centrifugal pursuit deficit that lasted for more than 2 months. Vertical pursuit and visually guided saccades were not affected by the bilateral NOT lesions in this animal. We also compared effects of these and similar NOT lesions on optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN). Correlation of functional deficits with NOT lesions from this and previous studies showed that rostral lesions of NOT in and around the pretectal olivary nucleus, which interrupted cortical input through the brachium of the superior colliculus (BSC), affected both smooth pursuit and OKN. In two animals in which it was tested, NOT lesions that caused a deficit in pursuit also decreased the rapid and slow components of OKN slow-phase velocity and affected OKAN. It was previously shown that slightly more caudal NOT lesions were more effective in altering gain adaptation of the angular vestibulo-ocular reflex (aVOR). The present findings suggest that cortical pathways through rostral NOT play an important role in maintenance of ipsilateral ocular pursuit. Since lesions that affected ocular pursuit had similar effects on ipsilateral OKN, processing for these two functions is probably closely linked in NOT, as it is elsewhere.

An optical device for patients with downgaze problems shown in a patient suffering from Steele-Richardson-Olszewski syndrome

Progressive supranuclear palsy (PSP) or Steele-Richardson-Olszewski syndrome is a degenerative disorder which includes vertical gaze paralysis, nuchal dystonia, parkinsonism, and dementia. Consequently, since patients suffering from this disorder tend to fall, sedentary occupations and interests predominate. Because of the relatively early appearing gaze palsy, patients are unable to read or to eat on their own. Personal dependence increases and the quality of life decreases. In this report, a patient suffering from PSP in an initial stage with an impairment of vertical ocular pursuit movements and consequent difficulties in reading and eating is described. With the help of a new device, where refraction and movable prism glasses in front of the eyes are integrated, the patient could be rehabilitated. Patients suffering from vertical ophthalmoplegia of other causes can also take advantage of this new optical device.

Episodic vertigo related to migraine (90 cases): vestibular migraine?

A retrospective study was conducted on 90 patients with episodic vertigo that could be related to migraine as the most probable pathomechanism. Since the majority of the patients did not fulfill the criteria of the International Headache Society (IHS) for basilar migraine, the diagnosis was substantiated by disease course, medical efficacy in treating (ergotamines) and preventing (metoprolol, flunarizine) attacks, ocular motor abnormalities in the symptom-free interval, and careful exclusion of the most relevant differential diagnoses, such as transient ischemic attacks, Menière's disease, and vestibular paroxysmia. The following clinical features were elaborated. The initial manifestation could occur at any time throughout life, with a peak in the fourth decade in men and a "plateau" between the third and fifth decades in women. The duration of rotational (78%) and/or to-and-fro vertigo (38%) could last from a few seconds to several hours or, less frequently, even days; duration of a few minutes or of several hours was most frequent. Monosymptomatic audiovestibular attacks (78%) occurred as vertigo associated with auditory symptoms in only 16%. Vertigo was not associated with headache in 32% of the patients. In the symptom-free interval 66% of the patients showed mild central ocular motor signs such as vertical (48%) and/or horizontal (22%) saccadic pursuit, gaze-evoked nystagmus (27%), moderate positional nystagmus (11%), and spontaneous nystagmus (11%). Combinations with other forms of migraine were found in 52%. Thus, migraine is a relevant differential diagnosis for episodic vertigo. According to the criteria of the IHS, only 7.8% of these patients would be diagnosed as having basilar migraine. However, to ensure that at least those presenting with monosymptomatic episodic vertigo (78% in our study) receive effective treatment, we propose the use of the more appropriate term "vestibular migraine."

Vertical Purkinje cells of the monkey floccular lobe: simple-spike activity during pursuit and passive whole body rotation.

To understand how the simian floccular lobe is involved in vertical smooth pursuit eye movements and the vertical vestibuloocular reflex (VOR), we examined simple-spike activity of 70 Purkinje (P) cells during pursuit eye movements and passive whole body rotation. Fifty-eight cells responded during vertical and 12 during horizontal pursuit. We classified P cells as vertical gaze velocity (VG) if their modulation occurred for movements of both the eye (during vertical pursuit) and head (during pitch VOR suppression) with the modulation during one less than twice that of the other and was less during the target-fixed-in-space condition (pitch VOR X1) than during pitch VOR suppression. VG P cells constituted only a minority of vertical P cells (19%). Other vertical P cells that responded during pitch VOR suppression were classified as vertical eye and head velocity (V/) P cells (48%), regardless of the synergy of their response direction during smooth pursuit and VOR suppression. Vertical P cells that did not respond during pitch VOR suppression but did respond during rotation in vertical planes other than pitch were classified as off-pitch V/ P cells (33%). The mean eye-velocity and eye-position sensitivities of the three types of vertical P cells were similar. One-third (2/7 VG, 2/11 V/, 6/13 off-pitch V/), in addition, showed eye position sensitivity during saccade-free fixations. Maximal vestibular activation directions (MADs) were examined during VOR suppression by applying vertical whole body rotation with the monkeys oriented in different vertical planes. The MADs for VG P cells and V/ P cells with eye and vestibular sensitivity in the same direction were distributed near the pitch plane, suggesting convergence of bilateral anterior canal inputs. In contrast, MADs of off-pitch V/ P cells and V/ P cells with oppositely directed eye and vestibular sensitivity were shifted toward the roll plane, suggesting convergence of anterior and posterior canal inputs of the same side. Unlike horizontal G P cells, the modulation of many VG and V/ P cells when the target was fixed in space (pitch VOR X1) was not well predicted by the linear addition of their modulations during vertical pursuit and pitch VOR suppression. These results indicate that the populations of vertical and horizontal eye-movement P cells in the floccular lobe have markedly different discharge properties and therefore may be involved in different kinds of processing of vestibular-oculomotor interactions.

Evidence for independent feedback control of horizontal and vertical saccades from Niemann-Pick type C disease

We measured the eye movements of three sisters with Niemann-Pick type C disease who had a selective defect of vertical saccades, which were slow and hypometric. Horizontal saccades, and horizontal and vertical pursuit and vestibular eye movements were similar to control subjects. The initial movement of oblique saccades was mainly horizontal and most of the vertical component occurred after the horizontal component ended; this resulted in strongly curved trajectories. After completion of the horizontal component of an oblique saccade, the eyes oscillated horizontally at 10-20 Hz until the vertical component ended. These findings are best explained by models that incorporate separate feedback loops for horizontal and vertical burst neurons, and in which the disease selectively affects vertical burst neurons.

Vertical oculomotor disorders in progressive supranuclear palsy and spino-cerebellar degeneration

We performed neuro-otological investigation of vertical oculomotor disorders in 35 patients with degenerative disease [progressive supranuclear palsy (PSP) and spino-cerebellar degeneration], and obtained the following results: 1) In the patients with PSP, in addition to vertical oculogyric disorder both saccade and pursuit eye movements were disturbed, and the disturbance of saccade movement was greater. Even the patients without an oculogyric disorder were all found to have decreased saccade velocity, suggesting that this disorder may occur earliest in PSP. 2) In olivo-ponto-cerebellar atrophy (OPCA), saccade movement was less disturbed than that in PSP. In contrast, pursuit movement was disturbed more frequently. 3) In late cortical cerebellar atrophy (LCCA), vertical ocular movement was hardly disturbed compared with OPCA. 4) Concerning dentate nuclear degeneration, we cannot reach a conclusion because of the few cases studied, but a variety of oculomotor disorders were seen; both saccade and pursuit movements were disturbed, but saccade movement was less disturbed than in PSP. 5) In visual suppression tests, enhancement in the light area was frequently seen in the patients with PSP and OPCA, but none with LCCA showed such change. In addition, enhancement of the light area under visual suppression was significantly correlated with vertical oculomotor disorder.

Comparison of horizontal, vertical and diagonal smooth pursuit eye movements in normal human subjects.

We compared horizontal and vertical smooth pursuit eye movements in five healthy human subjects. When maintenance of pursuit was tested using predictable waveforms (sinusoidal or triangular target motion), the gain of horizontal pursuit was greater, in all subjects, than that of vertical pursuit; this was also the case for the horizontal and vertical components of diagonal and circular tracking. When initiation of pursuit was tested, four subjects tended to show larger eye accelerations for vertical as opposed to horizontal pursuit; this trend became a consistent finding during diagonal tracking. These findings support the view that different mechanisms govern the onset of smooth pursuit, and its subsequent maintenance when the target moves in a predictable waveform. Since the properties of these two aspects of pursuit differ for horizontal and vertical movements, our findings also point to separate control of horizontal and vertical pursuit.

Torsional Nystagmus During Vertical Pursuit

We examined three patients with cavernous angioma within the middle cerebellar peduncle. Each patient had an unusual ocular motor finding: the appearance of a strong torsional nystagmus during vertical pursuit. The uncalled-for torsion changed direction when vertical pursuit changed direction. In one patient, we recorded eye movements with the magnetic field technique using a combined direction and torsion eye coil. The slow-phase velocity of the inappropriate torsional nystagmus was linearly related to the slow-phase velocity of vertical smooth pursuit, and changed direction when vertical pursuit changed direction. This torsional nystagmus also appeared during fixation suppression of the vertical vestibulo-ocular reflex (VOR), but was minimal during vertical head rotation when fixing a stationary target in the light. We suggest that inappropriately directed eye movements during pursuit might be another ocular motor sign of cerebellar dysfunction. Furthermore, we speculate that the signals used for vertical smooth pursuit are, at some stage, encoded in a semicircular canal VOR coordinate framework. To illustrate, for the vertical semicircular canals, vertical and torsional motion are combined on the same cells, with the anterior semicircular canals mediating upward movements and the posterior semicircular canals mediating downward movements. For the right labyrinth, however, both vertical semicircular canals produce clockwise slow phases (ipsilateral eye intorts, contralateral eye extorts). The opposite is true for the vertical semicircular canals in the left labyrinth; counterclockwise slow phases are produced. Hence, to generate a pure vertical VOR, the anterior or posterior semicircular canals on both sides of the head must be excited so that opposite-directed torsional components cancel. Thus, if pursuit were organized in a way similar to the VOR, pure vertical pursuit would require that oppositely-directed torsional components cancel in normals. If this did not happen, a residual torsional nystagmus could appear during attempted vertical pursuit.