Horizontal Optokinetic Nystagmus Research Articles

ラット視索核のGABA作動性ニューロン

A specific neuronal group in the nucleus of the optic tract (NOT) is considered to play an important role in the development horizontal optokinetic nystagmus (OKN). We obtained morphological evidence on such data. In the present study, γ-Aminobutylic acid (GABA) positive cells and terminals were detected in the NOT in the rat. However, GABA positive cells in the NOT receiving projections directly from the retinal ganglion cells could not be identified. Also, the GABA reaction was not positive for the neurons in the NOT projecting to the Inferior olivary nucleus (JO). In the NOT, although GABA positive cells exists, they seem to act indirectly as intrinsic interneurons, when processing or transmitting the Information from the retina, and to the IO.

Visual response properties and afferents of nucleus of the optic tract in the ferret

Basic properties of responses to visual stimulation with large moving random dot patterns were studied in ferret nucleus of the optic tract. Retinal input to NOT was assessed by orthodromic electrical stimulation of the optic chiasm and optic nerves. Presence of an input from visual cortex was tested by orthodromic electrical stimulation of ipsilateral area 17. All 51 NOT neurons studied displayed a non-habituating, clearly direction-specific response: discharge rate strongly increased with the stimulus pattern moving horizontally in ipsiversive direction (motion directed towards the recorded hemisphere) and decreased with contraversive stimulus motion. Most latencies to visual stimulation ranged from 80 to 100 ms. Velocity tuning was studied using stimulus velocities between 4 deg/s and 100 deg/s. Discharge rates were most effectively modulated at a stimulus velocity of 20 deg/s. A large portion of the cells studied (91%) could be binocularly activated, although for almost all neurons the contralateral eye was dominant. Through stimulation of the optic chiasm 46 out of 51 NOT neurons could be electrically activated with a latency of 5.42 +/- 0.66 ms (mean +/- SD). For 15 fibers stimulated from both optic chiasm and contralateral optic nerve, conduction velocities between 2.5 and 8.9 m/s, with a mean of 5.1 m/s, were obtained. A major direct input from the ipsilateral retina was not found. Furthermore, 65% of all neurons could be activated through electrical stimulation of visual cortex with a mean latency of 3.7 +/- 1.5 ms, indicating a strong cortical projection to ferret NOT. The functional relevance of response properties of ferret NOT neurons for horizontal optokinetic nystagmus is discussed. Parameters that could be related to formation of a cortico-pretectal projection in mammals are considered.

Galvanically Induced Asymmetric Optokinetic After-nystagmus

The effect of an asymmetric vestibular input on the symmetry of horizontal optokinetic after-nystagmus (OKAN) was studied in twenty healthy subjects. Optokinetic nystagmus (OKN) was elicited by a whole-field optokinetic drug, rotating at 90 degrees/s, and eye-movements were recorded by a DC electro-oculographic technique (EOG). The ratio of OKAN following right and left-beating OKN respectively was computed. An asymmetric vestibular input was generated by a continuous bi-polar, bi-aural galvanic stimulus (1 mA) to the vestibular nerves during the optokinetic stimulation and the recording of the OKAN. During galvanic stimulation the relation between left and right-beating OKAN was asymmetric, compared with the OKAN found after optokinetic stimulation only. The galvanic stimulus caused a preponderance for OKAN with the fast phase beating toward the cathode. Thus, the small vestibular asymmetry induced by the galvanic stimulus, which was not strong enough to produce nystagmus by itself, caused an asymmetric OKAN. These findings suggest that examination of OKAN may be of value to detect small vestibular asymmetries in peripheral vestibular disorders in man.

OKN asymmetries and binocular function in amblyopia.

Asymmetrical optokinetic nystagmus (OKN) means that OKN has a lower gain (slow-phase eye velocity/stimulus velocity) for monocular temporalward than nasalward visual field motion. OKN tends to be asymmetric in amblyopia, leading to suggestions of a link between OKN asymmetry and binocularity in the literature. The present study measured OKN in 13 amblyopes and five normal subjects. In an attempt to identify those binocular cells used in the OKN response, the degree of OKN asymmetry was compared with binocularity assessed by two different techniques: (1) stereopsis and (2) interocular transfer of threshold elevation (IOT). Horizontal monocular OKN was recorded for three different stimulus velocities in each subject. All the amblyopes were found to be stereoblind, although three amblyopes showed OKN asymmetries close to those found for the normal group. More association was seen between interocular transfer of the threshold elevation and OKN asymmetry; not all amblyopes demonstrated reduced IOT, but those amblyopes with no IOT all had OKN asymmetries more than 125% of the mean of the normal group. However, no association was seen between the amount of OKN asymmetry and the degree of IOT. The results are discussed in terms of the role of different groups of binocular neurones for OKN and the effect of the sensitive periods of development on these binocular neurones.

Involvement of ON and OFF retinal channels in the eye and head horizontal optokinetic nystagmus of the frog

The specific role of ON and OFF retinal information channels in the generation of the horizontal optokinetic nystagmus (OKN) of the frog was studied. Coil recordings of monocular eye and head OKN were obtained before and after intravitreal injection of two drugs that block either ON or OFF channels. The intravitreal injection of 2-amino-4-phosphonobutyrate (APB), a glutamate analog that selectively blocks the ON retinal channel, strongly reduced or even cancelled the monocular OKN of the head and of the eye. The intravitreal injection of another glutamate analog, the cis-2,3-piperidine dicarboxylic acid (PDA) that especially blocks the OFF retinal channel, did not affect the gain velocity of the slow phase of both the horizontal monocular head and eye OKN, for low stimulus velocities. Our results suggest that the retinal ON information channel, but not the OFF channel, is involved in the generation of the slow phase of the OKN of the frog, at least at low drum velocities.

Cortical areas involved in horizontal OKN in cats: metabolic activity

Cerebral cortex improves optokinetic responses to high target velocities, but the specific cortical areas involved are unknown. Using the 14C-deoxyglucose technique, we compared local rates of cerebral glucose utilization in cats viewing a moving optokinetic nystagmus (OKN) drum (experimental group) with those in cats viewing a stationary OKN drum (control group). In the experimental group, glucose utilization was increased in areas 17 and 18 and in 4 areas in suprasylvian cortex (21a, 21b, PMLS, and VLS). There were no changes in glucose utilization in areas 7, 19, 20a, 20b, ALLS, AMLS, DLS, PLLS, the posterior suprasylvian area, and the splenial visual area. The increases in glucose utilization in areas 17 and 18 were most significant in the granular layers (inner III and IV). In areas 21a, 21b, PMLS, and VLS, the increases in glucose utilization extended from layers II through V. There was also a regional distribution of the increase in glucose utilization within each of these areas in the experimental animals. The increase in glucose utilization did not include the rostral portion of PMLS or the borders between areas PMLS and 21a, and VLS and 21b. In addition, there was a smaller increase in glucose utilization at the borders between areas 17 and 18 than in other portions of these 2 areas. The results indicate that areas 17, 18, 21a, 21b, PMLS, and VLS may be involved in the cortical modulation of horizontal OKN. The laminar distribution of label within the cortical areas corresponds with the distribution of projections from the dorsal lateral geniculate nucleus to areas 17 and 18, and from areas 17 and 18 to PMLS. The regional distribution of the metabolic activity within areas 17, 18, and PMLS coincides with that portion of cortex expected to be excited by either the spatial frequency of the stimulus or the retinalslip velocity (drum velocity minus slow phase eye velocity) occurring during the eye movements.

Chapter 16 Open-loop and closed-loop optokinetic nystagmus in Squirrel monkeys (Saimiri sciureus) and in man

Horizontal optokinetic nystagmus (OKN) was measured in 3 normal Squirrel monkeys by means of the electromagnetic search coil technique. Binocular and monocular stimulation of each eye to the left and right by moving vertical stripe patterns of 2.37 or 15 degree period were applied at angular velocities of 0.5 to 400 deg/s. After measurement of horizontal OKN under normal conditions, open-loop OKN gain was determined by monocular stimulation of an eyeball immobilized by means of retrobulbar injections of 11 units botulinum toxin (BoTx type A) and compared with the pre-injection data or with monocular stimulation of the other eye, which remained mobile. In normal Squirrel monkeys gain of optokinetic nystagmus reached values between 0.8 and 0.97 at angular velocities below 1.5 deg/s. Gain under these conditions was related to stimulus angular velocities Vs, i.e. Ge = Ve/Vs. A slightly higher gain was found for binocular than for monocular stimulation. No significant differences were found in OKN when monocular stimulation in the naso-temporal and in the temporo-nasal direction was applied. The upper cut-off angular velocity (-3 dB-point) reached values of 180-230 deg/s, significantly above those observed in man under similar stimulus conditions. Monocular optokinetic stimulation of an immobilized eye led to vigorous optokinetic nystagmus and OKAN of the other eye, whereby maximum gain (Gi = Ve/Vr) was found to be between 20 and 30 at lower retinal stimulus velocities (2-5 deg/s). Gain was related to retinal stimulus velocity Vr. Increase in Vr above 10 deg/s led to a decrease in gain with a slope of about 20 dB per decade. Measurement of gain of closed-loop OKN related to retinal stimulus velocity Vr (which was determined by the difference between Vs and Ve) led to a similar dependence of OKN as in closed-loop stimulus conditions. Differences in sensitivity between the temporal and the nasal visual hemifield stimulation evoking horizontal open-loop OKN are described. Directional selectivity appeared in these experiments. Open-loop OKN data from a human subject are reported. With highly attentive horizontal optokinetic gaze nystagmus, Ve depended on the duration of the pursuit phases of OKN. Ve accelerated with the duration of the individual slow phase of OKN and was reset by each backward saccade (of the covered mobile eye). OKN gain was considerably smaller when the subject intentionally pursued as many stripes as possible of the 1.15 degree period stripe pattern (gain related to Vr about 1.5-3).(ABSTRACT TRUNCATED AT 400 WORDS)

顔面痙攣症例に於ける聴覚,平衡系の機能異常の検討

Twenty four patients with hemifacial spasm underwent thorough examinations consisting of 1). taking subjective symptons (tinnitus and/or dizziness),2). the otoneurological examinations (auditory and equilibrium examinations) and 3). checking the serum lipids. X-rays (air CT and/or VAG) were taken in some cases. Abnormal findings were obtained in 6 patients in the auditory and in 17 patients in equilibrium examinations. Moreover, abnormal findings suggesting brain-stem disorders (elongation of I-V latency in bilateral sides, indefinite V peak in the healthy side, abnormal findings in the oculomotor system (saccadic or ataxic pursuit patterns, diminution or inversion in the horizontal OKN) were obtained in 11 patients. In 3 of them, the enlarged vertebral or basilar arteries were found by X-ray examination. In 3 of them, serum lipids (cholesterol or trigyceride) were high. One of them is medicated for hypertension. Therefore, we conclude that the abnormal otoneurological findings suggesting brain-stem disorders came from [1] brain-stem compression by enlarged vertebral or basilar arteries or [2] arteriosclerosis or hypertensive angiopathy in the brainstem.

Neurophysiological investigation of the pretectal nucleus lentiformis mesencephali in Rana pipiens.

Previous studies have demonstrated that the large-celled, optic pretectal nucleus lentiformis mesencephali (nLM) is essential for horizontal optokinetic nystagmus, yet little is known about its neurophysiology. In the present study, single-unit analysis of nLM utilized a large-field, patterned stimulus presented for 8 directions and 3 velocities of movement. All units localized in nLM were spontaneously active, motion sensitive, with response profiles that ranged from strongly directional and narrowly tuned to asymmetric and broadly tuned. Only about one-third of the units could be classified as directional, and no response bias for horizontal or temporal-to-nasal motion was observed. The majority of directional units showed greatest responsiveness at the lowest stimulus velocity, while the reverse occurred for many broadly tuned units. These low-velocity, highly directional units may be comparable to the 'retinal slip' neurons recently described in the large-celled pretectal nucleus of mammals. Directional information in the nLM of Rana pipiens thus appears to be represented in the activity of a large population of motion-sensitive units which includes both narrowly and broadly tuned individual response profiles. These results are consistent with the population-coding hypothesis recently advanced to account for directional coding in other sensorimotor systems, including primate motor cortex and superior colliculus.

Distribution of retinal ganglion cells projecting into the nucleus of the optic tract in the rat

Recent neurophysiological studies have disclosed that the nucleus of the optic tract (NOT) in the pretectum is the first relay station responsible for horizontal optokinetic nystagmus (OKN) both in non-foveate and foveate animals. However, what parts of the retina and what kinds of retinal ganglion cells project their fibers into the NOT have been controversial. In the present study, horseradish peroxidase conjugated with wheatgerm agglutinin (WGA-HRP) was injected into the NOT of rats. The retina and injection sites were processed for the histochemical demonstration of WGA-HRP in order to investigate the distribution of the retinal ganglion cells projecting into the NOT. The present study indicated that visual signals responsible for OKN are mainly conducted from the contralateral retinal ganglion cells, and only from the ventral area of the ipsilateral retina. The retinal ganglion cells projecting into the NOT ipsilateral to the injection site were larger than those on the contralateral side. Large retinal ganglion cells existed on the peripheral areas including ipsilateral ventral area. The density of the ventral ganglion cells of the retina contralateral to the injection site was lower than that in other areas of retina, and the density of the ventral ganglion cells ipsilateral to the injection site tented to be greater than that on the contralateral side. Since the ventral area of retina corresponded to the upper visual field in front of the nose, it may receive visual signal of OKN and fire OKN. In conclusion, visual signals responsible for OKN are conducted through the retinal ganglion cells mainly contralaterally, and only from the ventral area of the retina ipsilateral to the injection site.

Organizational Principles of Velocity Storage in Three Dimensions

1. Optokinetic nystagmus was elicited in alert monkeys by movement of the visual surround in their horizontal or yaw plane, and optokinetic after-nystagmus was recorded in darkness. The animals were upright or were statically tilted at various angles from the upright. While upright, the OKAN was horizontal, and there were no vertical or roll components. When animals were tilted to either side or forward or back, vertical or roll components appeared both in the primary and secondary OKAN. Such components were also observed during nystagmus and after-nystagmus induced by electrical stimulation of the nucleus of the optic tract. The characteristics of the cross-coupled components indicated that they were mediated through the velocity storage mechanism in the vestibulo-ocular reflex. 2. A principle was inferred that explained the appearance of cross-coupled vertical or roll components in the primary and secondary OKAN: With the animal in a tilted position, a vector of eye velocity during OKN along the body-vertical axis was converted during primary OKAN toward a spatial-vertical axis with the same sense by a right hand rule. Thus, slow phase velocity along a vector toward the top of the animal's head during horizontal OKN rotated so that it tended to be directed spatially upward during primary OKAN. The reverse was true for OKN with a velocity vector directed toward the animal's feet. It rotated during primary OKAN so that it tended to be aligned with the direction of gravity. The vector of velocity during secondary OKAN was opposite to the direction of the vector during primary OKAN and was approximately aligned with spatial vertical. 3. OKN and OKAN were elicited about the animal's pitch and roll axes while they were upright and statically tilted at various angles away from the spatial vertical. There was a graded increase in the strength of vertical and roll OKN and OKAN and in the falling time constant of OKAN as the animals were tilted so that the axis of pitch or roll eye movements was moved toward alignment with the spatial vertical. Thus, velocity storage during pure vertical and roll nystagmus was similar to that during yaw OKN and OKAN in tilted positions: it was maximal along the pitch and roll axes when these axes were aligned with gravity. 4. The data indicate that the gravitational field is of fundamental importance in imposing a spatial reference onto the velocity storage integrator.(ABSTRACT TRUNCATED AT 400 WORDS)

Analysis of vertebrate eye movements following intravitreal drug injections. I. Blockade of retinal ON-cells by 2-amino-4-phosphonobutyrate eliminates optokinetic nystagmus.

1. Horizontal optokinetic nystagmus (OKN) was examined in alert rabbits and cats following intravitreal injection of 2-amino-4-phosphonobutyrate (APB), an agent which selectively blocks the light-responsiveness of retinal ON-cells while having little effect on OFF-cells. The retinal actions of APB were assessed independently by electroretinography. 2. In five rabbits, doses of APB sufficient to eliminate the b-wave of the electroretinogram reduced drastically the ability of the injected eye to drive OKN at all stimulus speeds tested (1-96 degrees/s). Impairment of OKN was apparent within minutes of the injection, remained maximal for several hours, and recovered completely in 1-7 days. OKN in response to stimulation of the uninjected eye alone remained qualitatively and quantitatively normal. 3. Following administration of APB, OKN in response to binocular stimulation displayed a directional asymmetry. Stimuli moving in the preferred (temporal-to-nasal) direction for the uninjected eye became more effective than stimuli moving in the opposite direction, indicating that the injected eye could no longer contribute to binocular OKN. 4. When rabbits viewed stationary stimuli through the APB-treated eye alone, episodes of slow (less than 1 degrees/s) ocular drift were observed, similar to the positional instability seen when rabbits are placed in darkness or when the retinal image is stablized artifically (12). 5. APB had little effect on OKN in normal cats. In two cats that had previously received large lesions of the visual cortex, however, APB eliminated the ability of the injected eye to drive monocular OKN. The extent of the impairment was similar to that seen in rabbits. Because the cortex is thought to contribute more to OKN in cats than in rabbits, this result suggests that the optokinetic pathways disrupted by APB project subcortically. 6. This study demonstrates that the integrity of retinal ON-cells is required to sustain normal OKN. The results are consistent with additional anatomic and physiological evidence suggesting that a particular subclass of retinal ganglion cells, the ON-direction-selective cells, may provide a crucial source of visual input to central optokinetic pathways.

Horizontal optokinetic ocular nystagmus in wildtype (B6CBA+/+) and weaver mutant mice.

Horizontal optokinetic nystagmus (OKN) evoked by a random dot pattern moving at a constant speed around the animal was investigated in wildtype mice and "Weaver" mutants (cerebellar impairment) by means of chronically implanted EOG-electrodes. The shape of OKN in the homozygotic Weaver mouse was clearly different from that in normal mice. The OKN in the mutant showed inconstant velocity during the slow phase. Nystagmus frequency of the mutant was significantly below that of normal controls for velocities of 1.4 to 25 degrees.s-1. In one group of normals the mean slow-phase gain was relatively constant for stimulus angular velocities between 1.4 and 15 degrees.s-1 and declined thereafter. In a second group the mean slow-phase gain decreased gradually between stimulus angular velocities from 1.4 to 15 degrees.s-1 and thereafter with a steeper slope. In mutants gain decreases with increasing stimulus velocity over the entire range tested (1.4 to 42 degrees.s-1). Normals and mutants with one eye occluded exhibited strong OKN when the pattern was moved in a temporonasal direction; little response was obtained by stimuli moving in a naso-temporal direction.

Directional asymmetries of human optokinetic nystagmus.

Optokinetic nystagmus in the four principal directions was investigated on the occurrence of directional asymmetries in 7 normal human subjects. Instructions were aimed at obtaining a 'stare' type of OKN. The movement of both eyes was recorded simultaneously with a scleral sensor-coil method. Subjects viewed a full-field random dot pattern rotating at velocities of 9 to 57 deg/s binocularly, as well as monocularly with either eye. Gain was always less than 0.85 and decreased when the pattern velocity increased. Horizontal and vertical nystagmus differed in a number of respects. (1) We found no evidence for an overall asymmetry for rightward or leftward motion. However, human OKN showed a clear preference for upward stimulus motion. Mean gain was ca. 0.15 larger for upward than for downward motion. (2) The decrease of the gain of OKN as a function of increasing stimulus velocity was steeper for vertical than for the horizontal direction. (3) The eyes moved nearly perfectly yoked for vertical pattern movement, irrespective of the viewing conditions. In contrast, during horizontal OKN the gain of the eye tracking in the nasal direction was higher (by about 4%) than the gain of the other eye moving simultaneously in the temporal direction. This difference persisted irrespective of the viewing conditions and appears to be motor, not sensory in origin. In addition, for any direction of the pattern motion a statistically significant increase of the gain occurred when the pattern motion was seen binocularly instead of monocularly with either eye.

Stabilizing gaze reflexes in the pigeon (Columba livia). I. Horizontal and vertical optokinetic eye (OKN) and head (OCR) reflexes.

A quantitative study of horizontal and vertical optokinetic nystagmus (OKN) and optocollic reflex (OCR) has been performed in the pigeon using the search-coil technique. The reflexes were analysed in response to either velocity steps or sinusoidal stimulation. Results show that: 1. In response to a velocity step stimulation, the slow phase velocity of both OKN and OCR increases gradually to reach a steady state level. When the stimulation stops in the dark, After Responses (OKAN-I, OKAR-I) occur. Time constants of the OKN charge (or OCR charge) and of the After Responses are lower for vertical than for horizontal responses. 2. In the free-head condition, both the head and the eye display a synchronized nystagmus which add their effects. However, the head reflex (OCR) accounts for about 80-90% of the entire linear gaze response (head + eye), except for the vertical steady state responses which are wholly accomplished by the head (OCR). 3. Both closed-loop and open-loop gains of steady state responses are higher for horizontal than for vertical reflexes. Vertical OCR, horizontal OKN and vertical OKN show properties of binocular integration, the response gain being higher for binocular than for monocular stimulations. By contrast, the horizontal OCR shows little binocular integration but displays a higher response gain for monocular stimulation, compared to horizontal OKN. 4. The horizontal OKN elicited by both monocular and binocular stimulation is asymmetrical, the gain being higher when the eye is driven by a temporo-nasal stimulation. In contrast, both vertical OKN and vertical OCR are practically symmetrical. 5. While both the gain of horizontal OKN and its linear range (up to 20 degrees/s) are improved when the head is free (gaze gain close to 1 up to 40 degrees/s), the vertical OKN and the vertical OCR have similar gain profiles and similar domains of linearity (up to 10 degrees/s). 6. In response to increasing the frequency of a sinusoidal stimulation at constant peak velocity, all the reflexes display a drop in gain and a strong increase of phase lag. The phase increase is greater for horizontal than for vertical reflexes. On the other hand, both gain and phase are higher for OCR than for OKN, both in the horizontal plane as well as in the vertical plane. 7. For sinusoidal stimulations, when the peak velocity (PV) is increased at a constant frequency (0.03 Hz), nonlinearities appear (drop in gain, phase increase) both for OKN and OCR.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical considerations concerning horizontal optokinetic nystagmus.

During recent decades a vast amount of literature concerning horizontal optokinetic nystagmus has emerged, regarding which--and especially as regards our own work--this report is intended to consider the clinical value of optokinetic nystagmus.

Neuro-otological study of the craniovertebral junction anomalies

Five patients with craniovertebral junction anomalies were examined neuro-otologically.Three patients had Chiari I malformation and cervicobasilar bone anomalies. Magnetic resonance imaging (MRI) showed cervicomedullary kinking, in addition to peg-like tonsils below the level of the foramen magnum (Group A). Two patients had Chiari I malformation without any cervicobasilar bone anomalies (Group B). We noted the differences in neuro-otological findings between the two groups and the changes after operation.1. Differences in neuro-otological findings(1) Group A patients had downbeat nystagmus in the dark with the eyes open on forward and lateral gaze. Horizontal OKN abnormalities were as follows : at a stripe speed of 0-50°/s, pursuit of stripe movement showed stair-like swaying. When the stripe speed was increased further, pursuit of stripe movement became virtually impossible, and the number of nystagmus beats decreased markedly.(2) Group B patients had no nystagmus in the dark with the eyes open. Horizontal OKN abnormalities showed saccadic pursuit during stripe movement, and a decrease in the number of nystagmus beats at a high stripe speed (more than 100-110°/s).2. Changes in neuro-otological findings(1) In group A, surgery improved the areas of sway in stabilometry tests, the frequency of nystagmus and the visual suppression rate of the slow phase velocity of caloric nystagmus. Horizontal OKN abnormalities were unchanged.(2) In group B, surgery improved the areas of sway, visual suppression rate and horizontal OKN. These results provide evidence that Chiari I malformations should be divided into those with and those without cervicomedullary kinking.

GAD immunoreactivity in pretectal and accessory optic nuclei of the frog mesencephalon.

By an immunocytochemical technique using anti-GAD antibodies, we found a high density of GAD-immunoreactive puncta in the 5 pretectal nuclei and in the nucleus of the basal optic root. These results back up the suggestion that GABAergic modulation of the output of the visual pretectal relay nuclei might underlie the directional asymmetry of the horizontal optokinetic nystagmus and the directional selectivity of pretectal neurons.

Chapter 11: The role of the primate lateral terminal nucleus in visuomotor behavior

This chapter discusses the role of the primate lateral terminal nucleus in visuomotor behavior. The neural pathways subserving the optokinetic reflex and its interaction with the vestibulo-ocular reflex (VOR) are not fully understood, but they are thought to involve the accessory optic system (AOS). In the cat and rabbit, the AOS consists of three terminal nuclei (lateral, medial and dorsal; LTN, MTN, DTN) distributed along the mesencephalic brainstem and the nucleus of the optic tract (NOT) located in the pretectum. Although the anatomical organization of the monkey AOS has received some attention, relatively little is known about the signals it carries. Recently, it is shown that single NOT units encode the direction of visual movement and that electrical stimulation of the primate NOT elicits a horizontal optokinetic nystagmus (OKN) with most of the classic features present in visually induced OKN. In addition to responding to full-field visual motion, many of the LTN units discharged to movement of a small spot. This ability to respond to small visual stimuli has also been reported in the primate NOT.

Human optokinetic nystagmus in response to moving binocularly disparate stimuli

Physiological and behavioral evidence shows that the directionally preponderant subcortical control of optokinetic nystagmus (OKN) in lower mammals is supplemented in higher mammals by bidirectional cortical control. It is hypothesized that this cortical control allows higher mammals to cope with the parallactic movement of the scene produced by linear motion of the body. In particular, it is hypothesized that a coupling between OKN and stereopsis allows higher mammals to stabilize the images of objects within the plane of fixation while ignoring motion signals from objects at other distances. According to this hypothesis the gain of the slow phase of OKN should be highest for binocularly fused moving stimuli and attenuated for binocularly disparate displays. The results of Experiment 1 confirmed this prediction although the effects of accommodation were not ruled out completely. In Experiment 2 a display moving in one direction was presented across the central retina at the same time as one moving in the opposite direction was presented in the upper and lower periphery. It was found that subjects do not show OKN in the direction of the peripheral display unless it is binocularly fused and the central display is disparate. In Experiment 3 a stationary display of dots was superimposed on a moving display. It was found that OKN is not inhibited by the stationary display when it has a horizontal disparity and the moving display is fused. Experiment 4 found that horizontal OKN is disrupted by the sudden introduction of a vertical disparity in the stimulus. Since accommodative state was kept constant in the last three experiments, the data show that binocular disparities can help a person to stabilize selectively the image of one moving display while ignoring conflicting motion signals from another display.