Optokinetic response and visual suppression of the vestibulo-ocular reflex in the open loop condition in the cat

Changes in the dynamics of the vertical vestibulo-ocular reflex due to linear acceleration in the frontal plane of the cat

The vertical and horizontal components of the vestibulo-ocular reflex (VOR) were recorded in alert, restrained cats who were placed on their sides and subjected to whole-body rotations in the horizontal plane. The head was either on the axis or 45 cm eccentric from the axis rotation. During off-axis rotation there was a change in the linear force acting on the otolith organs due to the presence of a centripetal acceleration along the animal's vertical axis. Otolith forces (defined to be opposite to the centripetal acceleration) directed ventrally with respect to the animal (negative) decreased both the amplitude and time constant of the first-order approximation to the slow phase eye velocity of the vertical vestibulo-ocular reflex (VVOR). Otolith forces directed dorsally (positive) increased the amplitude and time constant. The effects were greater for the up VOR. The asymmetry in the VVOR time constant also depended on the otolith forces, being less in the presence of negative otolith forces that caused the resultant otolith force to move ventrally, towards the direction along which gravity normally acts when the animal is in the upright position. The effects of otolith forces on the up VVOR were independent of whether the animals were tested in the dark or in the light with a stationary visual surround (i.e., during visual suppression). In contrast, the changes in the time constant of the down VVOR were smaller during visual suppression. Simulations of the eye velocity storage mechanism suggest that the gain of the feedback in the storage integrator was modified by the angle between the resultant otolith force and an animal-fixed reference. This could be the animal's vertical, i.e., the direction along which gravity normally acts. For larger angles the feedback was less and the amplitude and time constant of the VVOR increased. The transformation of the otolith input was the same for both the up and down VOR, even though the final effect on the eye velocity was asymmetric (larger for up VOR) due to a separate, asymmetric gain element in the velocity storage feedback pathway.

A fuzzy set theoretical approach to automatic analysis of nystagmic eye movements

A new method for computer analysis of nystagmic eye movements in vestibulo-ocular (VOR) and optokinetic (OKN) reflexes is developed. A fuzzy set theoretical approach is used to construct the slow cumulative eye position (SCEP) curve by eliminating fast components (saccades) from eye movement signal. These procedures are able to perform automatically some pattern recognition tasks traditionally used--in classical interactive programs--when human operators distinguish between fast- and slow-phases of eye movements. The structure of the algorithm is as follows. 1) A fuzzy clustering of slow- and fast-phases is made. An iterative method is used to refine the membership function of slow-phases, step by step, until a sufficiently discriminating membership function is obtained. 2) Saccades are detected and removed from the eye position signal. 3) SCEP is then built by interpolating between slow phases. 4) A weighted least-squares curve fitting is made. Weighting coefficients are obtained from the last membership function resulting from iterations in step 1). This curve fitting is referenced to the SCEP and the parameters of VOR and OKN are calculated using this last curve. This approach permits an analysis of nystagmic eye movements with high reliability even when the data are of modest quality. The definitive innovative feature of the program is that it allows entirely automatic analysis without participation of a human operator. The main algorithm being independent of the shape of stimulus, the program can be generalized to fit any type of simulation.

Latent defect in monocular optokinetic nystagmus after neonatal removal of the lateral suprasylvian area in the cat

Three kittens underwent unilateral removal of the lateral suprasylvian area of cortex at the age of 1 month. After normal rearing for two years, their monocular optokinetic nystagmus was studied. During the experiment one eye was 'seeing' the optokinetic stimulus, but the other eye was 'covered'; by implanting scleral coils on both eyes, we measured movements not only in the 'seeing' eye, but also in the 'covered' eye. The stimulus was moved at a velocity between 1 and 40 degrees/s. Additionally, movements of the both eyes were simultaneously recorded in a normal cat. The previous results on movements of both eyes in normal cats which had been derived from the recordings by one coil (Vision Res., 26: 1311-1314, 1986) were confirmed by this experiment and were compared with the results of the lesioned cats. The gains (slow phase velocity/stimulus velocity) of the 'seeing' eye were not significantly different from the normal values. However, the gains of the 'covered' eye were significantly higher than the normal values when the stimulus was presented in the temporonasal direction, at the velocities between 1 and 40 degrees/s to the eye ipsilateral to the lesion and at the velocity of 40 degrees/s to the eye contralateral to the lesion; in the other conditions of stimulation the gains were not significantly different from the normal values.

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)

Disabling of the oculomotor neural integrator by kainic acid injections in the prepositus-vestibular complex of the cat

1. This study was intended to test the candidature of the prepositus-vestibular nuclear complex for being the location of the oculomotor neural integrator (Robinson's integrator). 2. Microinjections of kainic acid (2 micrograms dissolved in 1 microliter) were made in awake cats. Injection sites were located either in the prepositus hypoglossi nucleus (p.h.), the medial vestibular nucleus (m.v.n.), the medial longitudinal fasciculus (m.l.f.) or in the magnocellular tegmental field of the reticular formation. 3. Theory predicts that a complete disabling of the neural integrator will cause (a) an exponential post-saccadic drift whose time constant will be 0.16 s in the dark (b) a phase lead of +93 deg as the vestibulo-ocular reflex is tested at 0.10 Hz in the dark and (c) a nearly complete abolition of the optokinetic nystagmus (o.k.n.). 4. About 1 h after a unilateral kainic acid injection in the p.h., we observed (a) a large bilateral post-saccadic drift (time constant sometimes as low as 0.2 s) (b) a large phase lead at 0.10 Hz (range: from +69 to +98 deg) (c) an abolition of the o.k.n. control injection of phosphate buffer in the p.h. did not produce any deficit. 5. A unilateral kainic acid injection in the m.v.n. induced a nystagmus followed by signs of bilateral failure of the neural integrator similar to those observed after kainic acid injection in the p.h. 6. Injection near the mid-line, between the two p.h. nuclei, induced a defect of the neural integrator less than that observed after kainic acid injection in either the p.h. or the m.v.n. Injection of kainic acid in the magnocellular tegmental field of the reticular formation did not produce any sign of failure of the neural integrator. No post-saccadic drift was observed. 7. We have concluded that (a) the p.h. nucleus is involved in the integration processing, and that (b) the m.v.n. is involved either in the integration processing or in the relaying of the output of the neural integrator to the oculomotoneurones.

Proprioceptive knowledge of eye position

The peripheral and central apparatus for extraretinal (non-visual) sensing of eye position by proprioception (inflow) is documented. The functional significance of this inflowing signal is shown by its role in (1) providing oculomotor stability in fixation and conjugacy, (2) specification of visual direction, (3) development of some visual functions, and (4) depth and vergence responses. Inflow is seen as a slowly-operating calibrator of eye position, with outflow signals read out from the underlying inflow signal. Good "preparations" for studying inflow include humans having their extraocular muscles surgically manipulated in some way for treatment, or those with some deficit in the afferent pathways. A complete understanding of the oculomotor system, in normal and pathological conditions, demands the inclusion of inflow.