Horizontal Optokinetic Nystagmus Research Articles

Difference between horizontal and vertical optokinetic nystagmus in cats at upright position.

The slow-phase velocity (SPV) of optokinetic nystagmus (OKN) and optokinetic after nystagmus (OKAN) in response to a velocity step of surround rotation in the horizontal direction is composed of the rapid and slow components in the cat: a rapid rise, a slow rise to a steady state, a rapid fall, and a slow decline to 0 deg/s. The rapid and slow components are attributed to the direct pathway and velocity storage neuronal mechanisms, respectively. The difference between horizontal and vertical OKN has been reported in the monkey at the upright position, but the slow and rapid components have not been distinguished. The present study compared horizontal OKN-OKAN with vertical OKN-OKAN in the cat at the upright position, distinguishing the rapid and slow components. Constant velocity rotation of a random dot pattern at a velocity of 5 to 160 deg/s was used for optokinetic stimulation. First, the amplitude of the rapid rise was relatively small in all SPV directions and all stimulus velocities investigated, with a slight upward-SPV preference to the downward-SPV (maximum 6.4, 6.0, and 3.4 deg/s in horizontal, upward, and downward SPV directions, respectively). Second, the steady state velocity was large during horizontal OKN (maximum 69.0 deg/s), small during upward-SPV OKN (12.9 deg/s), and missing (SPV is negligibly small and irregular) during downward-SPV OKN, indicating a large directional difference of OKN. Third, the acceleration of the slow rise decreased with the stimulus velocity at higher stimulus velocities >20 deg/s during both horizontal and upward-SPV OKN, suggesting strong nonlinearity in the velocity charge system. Fourth, the decay time course of the OKAN was described by the time constant of the exponential function, and the time constant was longer during horizontal (mean, 8.3 s at a stimulus velocity of 20 deg/s) than during upward-SPV (5.4 s) OKAN, suggesting that the velocity discharge system is relatively linear compared with the velocity charge system. It is concluded that horizontal OKN-OKAN is much larger than vertical OKN-OKAN in the cat at the upright position, and this directional difference is caused mainly by the directional difference in the velocity storage mechanism, but not in the direct pathway mechanism.

ABNORMAL VERTICAL OPTOKINETIC NYSTAGMUS IN INFANTS AND CHILDREN

AIMS—To determine if testing vertical optokinetic nystagmus (VOKN) has a role in the clinical assessment of infants and children. METHODS—A large field projection system was developed with which optokinetic nystagmus (OKN) could be stimulated in any direction. Gross abnormalities in the response were detected simply by observation. RESULTS—VOKN was tested in 144 children using this OKN projection system. 26 of these children had abnormal VOKN; 13 had a vertical saccade initiation failure ocular motor apraxia (in either direction, up/down, or in both) and 13 had absent VOKN (in either direction, up/down, or in both). Nine of the children with an up and/or down vertical saccade initiation failure (VSIF) had a neurometabolic disease (two had Niemann-Pick disease type C, five had Gaucher disease type III, one had Gaucher disease type II, and one had Gaucher disease type I). Five children with a VSIF had an abnormality identified by a magnetic resonance imaging (MRI) scan of the brain. In two of these children there was a focal lesion of the rostral midbrain. In 11 of the children with absent up and/or down VOKN an MRI scan revealed an abnormality. This involved the brainstem and/or the cerebellum in 10. Absent up and/or down VOKN was found in association with Joubert syndrome, Leigh disease, and cerebral palsy. CONCLUSION—VOKN testing has a useful role in detecting neurological abnormalities in infants and children. Detection of abnormal VOKN should indicate further investigations for a neurometabolic disease or an abnormality involving the cortex, brainstem, and/or cerebellum. Abnormal VOKN but normal horizontal OKN is highly suggestive of a rostral midbrain lesion.

Retinal ganglion cells projecting to the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system in macaque monkeys.

Using classical neuroanatomical retrograde tracing methods we investigated the retinal ganglion cells projecting to the nucleus of the optic tract and dorsal terminal nucleus of the accessory optic system (NOT-DTN) in macaque monkeys. Our main aim was to quantify the strength of the projection from the ipsilateral retina to the NOT-DTN. We therefore examined the number, distribution, and soma size of retinal ganglion cells involved in this projection. Electrophysiologically controlled small injections into the NOT-DTN revealed a clearly bilateral retinal projection originating mainly from the central retina but also involving peripheral retinal regions. Labelled cells were found nasally in the contralateral retina and temporally in the ipsilateral retina with some overlap in the fovea. The projection from the ipsilateral retina was 36-43% of that from the contralateral retina. On average, only 1-6% of the local population of ganglion cells projected to the NOT-DTN. Small soma size and large dendritic fields imply that in monkey rarely encountered, 'specialized' ganglion cells provide the direct retinal input to the accessory optic system (AOS). These results are discussed with respect to the symmetry of monocular horizontal optokinetic nystagmus (OKN) in primates.

Changes in horizontal oculomotor behaviour coincide with a shift in visual motion perception.

During full-field rotation of the visual field, subjects commonly experience an initial perception of object-motion which 'switches' to a perception of self-motion. We studied the characteristics of the horizontal optokinetic nystagmus responses evoked by a moving visual stimulus in these two perceptual states over a range of stimulus velocities. During self-motion perception mean eye position was found to shift more in the direction of the newly appearing stimulus elements with a slight reduction in slow phase gain in comparison to the nystagmus evoked during object-motion perception. The results may reflect a modified strategy of spatial attention with increased emphasis on anticipatory eye movements during visually induced self-motion perception.

Abnormal vertical optokinetic nystagmus in infants and children

AIMSTo determine if testing vertical optokinetic nystagmus (VOKN) has a role in the clinical assessment of infants and children.METHODSA large field projection system was developed with which optokinetic nystagmus (OKN)...

Optokinetic eye movements elicited by an apparently moving visual pattern in guinea pigs

Based on known anatomical and physiological properties, guinea pigs could be expected to show a lack of cortical impact on the basic properties of optokinetic nystagmus (OKN) such as eye movements elicited by a rotating striped drum. The present study aimed to clarify the question of whether the guinea pig's brainstem-mediated circuit is capable of generating horizontal OKN with the animal binocularly viewing a stationary stroboscopically illuminated striped pattern (apparent-motion OKN). A striped drum with a pattern periodicity of 2.37 degrees was rotated around the animal. The OKN buildup under real stimulation conditions was found to be largely devoid of a rapid initial rise in slow-phase eye velocity (direct OKN component). Only in a few recordings was a slight initially faster acceleration seen eliciting slow-phase eye velocities of 2 degrees/s at the most. The lack of a rapid initial rise proves that the optokinetic reflex loop does not possess a functionally significant cortically mediated component. To achieve apparent-motion OKN, initially in each recording real-motion OKN was elicited by the constantly illuminated rotating pattern. Then, 60 or 90 s later the drum was stopped and the illumination switched over from constant to flashing light. Following Grüsser and Behrens (1979), we calculated an apparent stimulus velocity (= flash frequency x 2.37 degrees) and an apparent OKN gain. We found that all animals continued in nystagmus under the flashing light condition. The slow-phase eye velocity was the same as under real pattern motion, with gain values of between 0.36 and 0.7. In two animals we produced an apparent gain close to unity by suddenly doubling the flash interval, i.e., halving the apparent drum velocity. This gain, however, did not remain at a high level: The slow-phase eye velocity decreased until the previous lower gain was reached again. The data indicate that cortical mechanisms are not necessary to produce nystagmus under apparent-motion stimulation and neither phi nor sigma phenomena of motion perception satisfactorily explain the apparent-motion OKN in the guinea pig. Our data provide evidence that the brainstem-located velocity storage mechanism plays a decisive role in keeping the eye in motion under apparent-motion stimulation.

Vertical or asymmetric nystagmus need not imply neurological disease

AIMTo indicate that congenital idiopathic nystagmus (CIN) and sensory defect nystagmus (SDN) can be vertical or asymmetric in some children.METHODSOf 276 children presenting with nystagmus for electrophysiological testing, 14 were...

Disjunctive Optokinetic Nystagmus in a Naturally Esotropic Macaque Monkey: Interaction between Nasotemporal Asymmetries of Versional Eye Movement and Convergence

Objective: To assess the interaction between versional and vergence eye movements in normal and strabismic monkeys. Methods: Horizontal optokinetic nystagmus (OKN) and vergence were measured using the magnetic scleral search coil technique in a normal adult monkey and a strabismic monkey who had naturally occurring early-onset esotropia. Mean eye velocity and vergence angles were calculated during the slow phases of OKN. Results: The strabismic monkey had a nasotemporal asymmetry of OKN favoring nasally directed motion in each eye. During monocular optokinetic stimulation, mean eye velocities were substantially greater for the adducting as compared to the abducting eye. The velocity of the abducting eye was between 55 and 80% of the velocity of the adducting eye (p < 0.01). As a consequence of the disjunctive movements, the eyes converged an average of 4 ± 2.8° during OKN. Saccadic analysis documented normal lateral rectus function in each eye. Neither an OKN asymmetry nor disjunctive OKN was observed in the normal monkey. Conclusion: Disjunctive OKN in the esotropic monkey suggests that the cerebral maldevelopment responsible for nasally biased OKN also contributes to nasal biases in vergence pathways.

サルにおける両側視索核間の投射遮断による視運動性眼振に及ぼす影響について

It has been shown that the nucleus of the optic tract (NOT) is an important visuomotor relay between the retina and preoculomotor structures, and is responsible for mediating horizontal optokinetic nystagmus (OKN) in monkeys, cats, rabbits, and rats. The details between the NOT and the vestibular nucleus in the brain stem concerning the morphology of fibers-of-passage and axon terminals have been disclosed in cats and monkeys. One is that they project to the contralateral NOT via the posterior commissure. In order to evaluate the role of the commissural fibers between the NOTs, the posterior commissure was cut in the present experient. Three fuscata monkeys (M17, M19, M22) were used. A magnetic search coil was sutured to the right eye to record eye position. Several bolts were embedded and secured with dental acrylic cement to fasten the animal's head during experiments. The animal was mounted on a turn table covered by an OKN screen, onto which OKN stripes were projected from above. The animals viewed the OKN stripes under three conditions: right eye viewing, left eye viewing, and bilateral eye viewing. OKN was recorded in response to counter clockwise (CCW) and clockwise (CW) stimulation at stimulus velocities of 30°/s, 60°/s, and 90°/s. After the control experiment was completed, the posterior commissure was transected by an operator knife. After follow-up studies were completed, an anterograde tracer was injected in the left NOT to ascertain the complete block between NOTs. Rapid rise (RR) and steady state (SS) of slow-phase OKN velocity and time-constants (TC) of optokinetic afternystagmus (OKAN) were measured. In three aniamis, OKN gains elicited with monocular viewing were approximately equal to the those of binocularly-evoked OKN before and after surgery. In the three monkeys, the commissurectomy decreased RR and SS to both sides during the three weeks immediately after surgery. In M22, TC showed the tendency to decrease by only 30°/s and 60°/s after surgery. There were no significant differences in TCs of other experiments.In conclusion, gain reduction in RR and SS can be explained by decrease of inhibiting the resting rate in NOT, which is conducted via commissural fibers. This was caused by interruption due to a middle-line lesions. Furthermore, interrupting the commissural fibers has nothing to do with the velocity storage mechanism.

Monocular horizontal OKN in observers with early- and late-onset strabismus

Several reports on monocular optokinetic nystagmus (OKN) in observers with strabismus have found that asymmetry of OKN tends to occur in both eyes of observers with an early onset of strabismus but only in the deviating eye of those with a later onset of strabismus. Our objective was to quantify and compare the magnitude of the OKN asymmetry in each eye as a function of observer’s age at onset of strabismus. We studied monocular OKN in ten observers with early-onset (up to 24 months of age), seven observers with late-onset (after 24 months of age) unilateral strabismus, and 12 normally sighted control observers. In the deviating eye, observers with early-onset strabismus showed large OKN asymmetries in favour of nasalward motion while observers with late-onset strabismus showed smaller OKN asymmetries in that eye. The majority of early- and late-onset observers showed near normal OKN in the non-deviating eye although the early-onset observers showed bilateral asymmetries more often. These findings may be due to both age at onset of strabismus and chronological age and are discussed in terms of the issue of plasticity or recovery of function.

Development of the optokinetic system in macaque monkeys

Optokinetic nystagmus in response to horizontal movement of a whole field random dot pattern was measured in infant macaque monkeys from the first week to about 5 months after birth using electrooculography. During monocular and binocular viewing conditions stimulus velocities were varied between 10 and 120 °/s. Monocular stimulation in the temporonasal direction yielded slow phase gain of the optokinetic system which was relatively constant for a given stimulus velocity over the whole period of observation. Gain during nasotemporal stimulation was also clearly present but significantly lower at early stages and increased during further development. This asymmetry of monocular horizontal optokinetic nystagmus (OKN) clearly depended on the stimulus velocity. At lower stimulus velocities (10–20 °/s) OKN was largely symmetrical at 2–5 weeks of age. At higher stimulus velocities (40 °/s) symmetry was reached at about 12 weeks of age or even much later (80–120 °/s).

The effect of d-amphetamine on optokinetic nystagmus in the guinea pig

The effect of d-amphetamine oral administration in doses of 1-2.5 mg/kg on horizontal optokinetic nystagmus (OKN) and after nystagmus (OKAN) was investigated in the guinea pig. Eye movements were recorded by means of the electromagnetic search-coil technique. After amphetamine administration the range of stimulus velocities effective for eliciting OKN was 10-20 deg/s higher than before treatment. The mean values and the fluctuations of the eye velocity during slow nystagmus phases before and after treatment did not differ. Administration of amphetamine led to 2-8 s increase in OKAN duration. The OKAN prolongation did not depend on stimulation velocity. The dependency of OKAN duration on stimulation velocity was well approximated by a linear regression. The slope of the regression line was 0.160 +/- 0.022 before and 0.177 +/- 0.028 after treatment. Similarity in the coefficients indicates that amphetamine did not alter the relationship between the velocity of optokinetic stimulus and the duration of after nystagmus. Constant prolongation of OKAN over the whole range of stimulation velocities could reflect a constant shift in activity of neurons representing the velocity storage. The effects observed on OKN gain curves and the increase in OKAN duration did not display a clear dependency on the dosages of d-amphetamine used in the experiments. We assume that the effects of treatment reflected a general increase in attentiveness and motility of animals resulting from the arousal action of amphetamine.

Effect of body positions in human optokinetic nystagmus and optokinetic after nystagmus

We determined whether whole body tilt would shift the axis of optokinetic nystagmus (OKN) and optokinetic-after nystagmus (OKAN) induced by full-field rotation at 35 degrees/sec. Fifteen normal people were positioned upright or tilted 30 degrees, 60 degrees or 90 degrees to both sides. Stripes of 5 degrees were projected on a 10-foot dome around the subject's yaw axis. Each trial lasted 45 sec. The lights were then extinguished, and the subject remained in darkness for 30 sec, while after nystagmus (OKAN) was recorded. Horizontal and vertical eye movements were recorded by video-oculography at 60 Hz. Eye position and velocity data were stored on optic disk cartridge by use of the data acquisition system. A. OKAN: For the subject in the upright position, the OKN velocity vector was aligned with both gravity and the subject's yaw axis with two minor exceptions. When the subject was tilted, a vertical OKN component (VOKN) appeared in a majority of subjects. For all 15 subjects, the mean angle of the OKN velocity vector regravity (Vectorg) was 22.6 +/- 7.2 degrees at 30 degrees tilted position. The Vectorg were 48.5 +/- 10.3 degrees at 60 degrees tilted position, and 76.4 +/- 12.6 degrees at 90 degrees tilted position. This represented shifts of the OKN velocity vector from the body axis of 7.4 degrees, 11.5 degrees and 13.6 degrees, respectively. The horizontal OKN (HOKN) gain remained unchanged in different positions. B. OKAN: The duration of HOKAN and initial slow phase velocity (SPV) of HOKAN decreased as the body position increased from upright to 30 degrees, 60 degrees and 90 degrees tilted position, respectively. The incidence and initial SPV of VOKAN and Re-Body did not change as the body position increased from upright to 30 degrees, 60 degrees and 90 degrees tilted position, respectively. Thus, VOKN was observed during HOKN as subjects were tilted and tended to vector to gravity, but VOKAN was not always observed during horizontal OKAN when subjects were tilted.

Effect of infantile strabismus on visuomotor development in the squirrel monkey (Saimiri sciureus): Optokinetic nystagmus, motion VEP and spatial sweep VEP

PURPOSE. To determine whether squirrel monkeys made artificially strabismic in infancy had ocular fixation abnormalities, directional asymmetries of horizontal optokinetic nystagmus (OKN) and asymmetries of motion visually evoked potentials (MVEPs) similar to those of humans with infantile strabismus. METHODS. Esotropia was produced in a newborn squirrel monkey by surgical tenotomy of both lateral rectus muscles. The alignment and eye rotations of the monkey were examined longitudinally and VEP testing was performed at the age of one year. Visual acuity was measured using spatial frequency sweep VEPs (SSVEP) in response to grating stimulation. OKN was tested under conditions of monocular viewing using full-visual-field, vertically oriented, moving stripes. MVEPs in response to horizontal motion were recorded with the animal sedated to reduce the possibility of eye movement artifact. RESULTS. The artificially strabismic squirrel monkey displayed a constant, comitant esotropic strabismus accompanied by latent nystagmus. Monocular SSVEP acuity was subnormal in one eye, consistent with mild monocular strabismic amblyopia. The monkey demonstrated asymmetric OKN favoring nasally-directed stimulus motion when viewing with either eye. Monocular MVEPs were also characterized by a horizontal asymmetry with a directional bias inverted 180 degrees between the right and the left eyes. The eye movements and MVEP asymmetries were similar to those observed in strabismic macaque monkeys and humans with early-onset strabismus. Neither the OKN asymmetry nor the MVEP asymmetry was evident in a normal squirrel or normal macaque monkey. CONCLUSION. The artificially strabismic squirrel monkey is an appropriate eye movement and VEP model for the study of neural mechanisms in human infantile strabismus.

Effects of Static Orientation upon Human Optokinetic Afternystagmus

?Normal? human subjects were placed in a series of 5 static orientations with respect to gravity and were asked to view an optokinetic display moving at a constant angular velocity. The axis of rotation coincided with the subject's rostro-caudal axis and produced horizontal optokinetic nystagmus and afternystagmus. Wall (1) previously reported that these optokinetic afternystagmus responses were not well characterized by parametric fits to slow component velocity. The response for nose-up, however, was larger than for nose-down. This suggested that the horizontal eye movements measured during optokinetic stimulation might include an induced linear VOR component as presented in the body of this paper. To investigate this hypothesis, another analysis of these data has been made using cumulative slow component eye position. Some subjects' responses had reversals in afternystagmus direction. These reversals were ?filled in? by a zero slow component velocity. This method of analysis gives a much more consistent result across subjects and shows that, on average, responses from the nose-down horizontal (prone) orientation are greatly reduced (p<0.05) compared to other horizontal and vertical orientations. Average responses are compared to responses predicted by a model previously used to predict successfully the responses to post-rotatory nystagmus after earth horizontal axis rotation. Ten of 11 subjects had larger responses in their supine than their prone orientation. Application of horizontal axis optokinetic afternystagmus for clinical otolith function testing, and implications for altered gravity experiments are discussed.

Objective assessment of minimum visual acuity by suppression of optokinetic nystagmus

To develop and to validate an objective method which allows an estimation of the visual acuity (VA) of adults. A horizontal optokinetic nystagmus (OKN) was elicited by a vertical rectangular grating presented on a PC-screen and was recorded by an infrared reflection method. Superimposition of three stationary black detection stimuli was used to suppress the OKN. The size of these stimuli was increased every two seconds, in ten steps. Suppression of the OKN was taken as an indication that the stimuli were detected. The relation between the smallest effective stimulus and logVA was evaluated in 65 healthy volunteers (130 eyes) with artificially reduced VA and 425 cooperative patients (842 eyes) whose VA was reduced due to different etiologies. The tolerance intervals of logVA related to the discrete detection stimuli were calculated. The method allows an estimation of the least expectable VA in steps of 0.8, 0.32, 0.25, 0.12, 0.1, 0.06, 0.03 und 0.025 due to the smallest value of three trials. The least VA of strabismic amblyopic eyes can only be estimated in steps of 0.16, 0.06, and 0.02. A VA > 0.02 can be proven with high reliability. The method allows a clinically useful, objective estimation of the least VA without observer bias in non-amblyopic eyes.

Optokinetic reflex in squirrel monkeys after long-term monocular deprivation.

Horizontal optokinetic nystagmus (OKN) as well as neuronal response properties in the nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system (NOT-DTN) were investigated in three monocularly deprived squirrel monkeys. In two monkeys occlusion of one eye was performed at birth (early) and in the third after 7 weeks (late). In adulthood, in early deprived monkeys monocular horizontal OKN tested through the non-deprived eye was symmetrical and in no way different from normal, i.e. stimulation in the temporonasal and nasotemporal direction elicited equal and robust responses. OKN through the early occluded eye, however, was grossly abnormal with low gain and great variability in the consistency of nasotemporal and temporonasal slow phase eye movements. When in the late deprived monkey the non-deprived eye was occluded a strong spontaneous nystagmus developed despite the deprived eye viewing a stationary pattern. The slow phases were directed from nasal to temporal for the deprived eye. When tested through the non-deprived eye all neuronal responses of the NOT-DTN were normal. The deprived eye's influence on NOT-DTN neurons was extremely weak. No neuron with a moderate or even dominant input from the deprived eye was found after early deprivation. In the late deprived case the deficit was not as severe but still the non-deprived eye was clearly dominating the responses in all neurons tested. Velocity tuning of neurons tested through the non-deprived eye was normal and qualitatively corresponded well to slow phase eye velocity in response to equivalent retinal slip during OKN. Through the early deprived eye, however, velocity tuning was extremely poor. It was somewhat better through the late deprived eye. We suggest that the dramatic deterioration in the optokinetic reflex found after long-term monocular deprivation for the amblyopic eye is probably caused by the almost complete loss of retinal and cortical input driven by that eye to the NOT-DTN. These results are discussed in relation to our previous results in cats and reports in the literature for humans with occlusion amblyopia.

Visually induced adaptation in three-dimensional organization of primate vestibuloocular reflex.

The adaptive plasticity of the spatial organization of the vestibuloocular reflex (VOR) has been investigated in intact and canal-plugged primates using 2-h exposure to conflicting visual (optokinetic, OKN) and vestibular rotational stimuli about mutually orthogonal axes (generating torsional VOR + vertical OKN, torsional VOR + horizontal OKN, vertical VOR + horizontal OKN, and horizontal VOR + vertical OKN). Adaptation protocols with 0.5-Hz (+/-18 degrees ) head movements about either an earth-vertical or an earth-horizontal axis induced orthogonal response components as high as 40-70% of those required for ideal adaptation. Orthogonal response gains were highest at the adapting frequency with phase leads present at lower and phase lags present at higher frequencies. Furthermore, the time course of adaptation, as well as orthogonal response dynamics were similar and relatively independent of the particular visual/vestibular stimulus combination. Low-frequency (0. 05 Hz, vestibular stimulus: +/-60 degrees ; optokinetic stimulus: +/-180 degrees ) adaptation protocols with head movements about an earth-vertical axis induced smaller orthogonal response components that did not exceed 20-40% of the head velocity stimulus (i.e., approximately 10% of that required for ideal adaptation). At the same frequency, adaptation with head movements about an earth-horizontal axis generated large orthogonal responses that reached values as high as 100-120% of head velocity after 2 h of adaptation (i.e., approximately 40% of ideal adaptation gains). The particular spatial and temporal response characteristics after low-frequency, earth-horizontal axis adaptation in both intact and canal-plugged animals strongly suggests that the orienting (and perhaps translational) but not inertial (velocity storage) components of the primate otolith-ocular system exhibit spatial adaptability. Due to the particular nested arrangement of the visual and vestibular stimuli, the optic flow pattern exhibited a significant component about the third spatial axis (i.e., orthogonal to the axes of rotation of the head and visual surround) at twice the oscillation frequency. Accordingly, the adapted VOR was characterized consistently by a third response component (orthogonal to both the axes of head and optokinetic drum rotation) at twice the oscillation frequency after earth-horizontal but not after earth-vertical axis 0.05-Hz adaptation. This suggests that the otolith-ocular (but not the semicircular canal-ocular) system can adaptively change its spatial organization at frequencies different from those of the head movement.

Optokinetic nystagmus under prolonged alteration in the direction of gravity

Optokinetic Nystagmus (OKN) exhibit different responses depending on the direction of gravity, with respect to head and body. In 13 normal healthy volunteers (10 experimental subjects and 3 controls), we studied the OKN evoked by horizontal and vertical stimuli, in upright, side-lateral, and repeated upright positions during a long time course of six test stages. Stage 1 was an upright sitting position. Stage 2 was a 90-degree recumbent lateral position immediately after Stage 1. Stage 3 was the same position as in Stage 2, but 2h later. Stage 4 was the same position, another 2h later (total of 4h). Stage 5 was a return to the upright position (the same as Stage 1) immediately after Stage 4. Stage 6 was a return to the same upright position, 2h after Stage 5. The results showed continuous modifications of OKN. A lateral tilt produced different effects on the horizontal and vertical optokinetic oculomotor systems. The gain in horizontal OKN (HOKN) decreased during Stages 2-4 with time, and returned to normal in Stages 5 and 6. As for vertical OKN (VOKN), the gain of upward (the direction by slow phase) OKN increased during Stages 2-4, and returned to normal in Stages 5 and 6. But the gain of downward OKN did not show any clear modulation. We showed that the change in gravity direction has a clear effect on OKN, and that it takes some time to reach the maximal and desirable level of modification. The difference in time-dependent modifications between HOKN and VOKN should be due to the difference in OKN-producing mechanisms and velocity storage systems.

Study of optokinetic nystagmus and spino-motor functions with cyclo-rotatory optokinetic stimulus

It has been shown that the neural channels from the otolith organs and the vertical semicircular canals connect to the cyclo-rotatory oculomotor system. However, only a few studies have been conducted to examine the relationship between the cyclo-rotatory optokinetic (COK) and the vestibular inputs. Accordingly, we have analyzed the cyclo-rotatory oculomotor output evoked by a COK stimulus, in 30 subjects; 21 normal adults, 4 elderly persons, and 5 persons with unilateral vestibular dysfunction. In addition, the spinal motor output was simultaneously recorded and comparatively analyzed. The increase in COK nystagmus (COKN) was less than that in horizontal and vertical OKN. There was a significant decline in the maximum slow phase eye velocity in the elderly subjects as well as in the subjects with unilateral vestibular dysfunction, compared to that in the normal adult subjects. Regarding the spinal motor output, in the subjects with unilateral vestibular dysfunction, a pronouned increase in the sway distance from the center of gravity was found with COK stimulus forward the lesioned side. However, with the COK stimulus, there was no significant correlation between the output functions of the cyclorotatory oculomotor system and those of the spinal motor system.