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At least 19 recordsLinked to original sources
PubMed1979

Response of the vestibulo-ocular reflex to differing programs of acceleration.

The vestibulo-ocular reflex of normal monkeys was tested by a modified Bárány spinning test (B-test) and by sinosoidal rotation. The two tests gave concordant estimates of the time constant and corner frequency. Deviation from concordance was caused largely by modification of the reflex during the testing procedures. As a means of estimating both time constant and corner frequency in the vestibulo-ocular reflex, the B-test is to be preferred to sinusoidal rotation because although both tests provide similar information, the B-test is the more rapidly performed and analyzed and the B-test modifies the reflex less.

Acceleration↗
PubMed1979

Modifications of vestibulo-ocular reflex induced by diazepam: experiments in the macaque.

The vestibulo-ocular reflex in the macaque was tested before and after intravenous administration of diazepam. The drug effect was marked by decrease in gain and increase in time constant of nystagmus in response to a modified Bárány test and by reduction in directional asymmetry of nystagmus. Because the time course of reduction in gain differed from the time course of increase in time constant, diazepam probably has more than one site of action. These results emphasize the complexity of neural processing in the vestibulo-ocular reflex arc.

Animals↗
PubMed1979

Modification of the macaque's vestibulo-ocular reflex after ablation of the cerebellar vermis.

In macaque, the vestibulo-ocular reflex (VOR) as evaluated by the time constant of nystagmus in a modified Bárány spinning test, shows a regular pattern of change with time after ablation of the vermis cerebelli. One day ablation the time constant is in the low normal range; it then increases, and after one week assumes values in the high normal range. While the time constant is high, the VOR is resistant to modification by repeated testing, but may be modified by unidirectional optokinetic nystagmus and by experience with reversing spectacles. These results suggest that the vermis of the cerebellum plays no crucial role in modifications of the VOR by visual inputs, but is involved when the VOR is modified by repeated vestibular experience.

Animals↗
PubMed1976

Clinically relevant physiology of the vestibulo-ocular reflex.

This review attempts to explain those aspects of the physiology of the vestibulo-ocular reflex (VOR) which could be of future clinical value. The literature cited has been selected for its didactic worth to readers with limited time, preferring concise reviews to detailed reports wherever possible. Physiological data provide the background for the following possible improvements in clinical diagnosis: 1) In gaze analysis, coordination of the VOR with other motor patterns can be analyzed. 2) Precision of vestibular tests can be improved by selecting stimuli within the range of natural movements.3) Resolution of the caloric test can be imporved when the change of temperature at the semicircular canal mimics endolymph pressure changes during natural movements. 4) A direct test of the three neuron VOR pathways is possible, but not practicable. 5) Integration of the input signal (transformation from head acceleration to eye position information) can be directly tested. 6) Plasticity (the adaptation to visual requirements) of the VOR can be examined. 7) It is possible to quantify vestibular damage and detect the side of lesion in one test analyzing gain and binocular symmetry of the vertical VOR.

Cerebellum↗
PubMed1977

Specific patterns of neuronal connexions involved in the control of the rabbit's vestibulo-ocular reflexes by the cerebellar flocculus.

1. In anaesthetized albino rabbits, the occurrence of Purkinje cell inhibition on canal-ocular reflexes was surveyed with a reflex testing method. 2. Test reflexes were elicited by electrical stimulation of the semicircular canals. The results were appaised by recording potentials and tension from extraocular muscles. Twelve reflexes were defined in terms of the receptor canal and the effector muscle. 3. Conditioning electrical stimuli were applied to the flocculus, the inferior olive, and optic pathways at the retinae, optic chiasm, pretectal area and upper medulla. 4. The conditioning stimulation at the ipsilateral flocculus induced depression in six of the twelve canal-ocular reflexes; four of the six arose from the anterior canal and the remaining two from the horizontal canal. 5. The effect of stimulation of the contralateral inferior olive was similar to that of the ipsilateral flocculus, though less clear in two of the four reflexes from the anterior canal because of a contaminating effect. 6. The two reflexes from the horizontal canal were depressed by stimulation of the ipsilateral optic pathway which reached the ipsilateral flocculus via the contralateral pretectal area and inferior olive. 7. The four reflexes from the anterior canal were affected by stimulation of optic pathways in a different manner from each other. One was depressed from the contralateral retina via the ipsilateral pretectal area, while another was depressed from the ipsilateral retina via the contralateral pretectal area, though only occasionally. The third reflex was depressed from the ipsilateral pretectal area but not from the retina. The fourth was affected from neither the retina nor the pretectal area. 8. On the basis of latency measurements, it was concluded that the depression of canal-ocular reflexes was due to inhibition of relay neurones of the testing reflexes by flocculus Purkinje cells which were activated either directly, or indirectly through olivocerebellar climbing fibre afferents. 9. The above conclusion was supported by the observation that the depression induced by stimulation of the inferior olive and optic pathways was abolished by acute destruction of the ipsilateral flocculus. 10. The possible functional significance of the specific patterns of connexions from flocculus Purkinje cells to canal-ocular reflex pathways is discussed, and specialization among flocculus Purkinje cells in relationship with vestibulo-ocular reflexes is postulated.

Action Potentials↗
PubMed1977

Plasticity in the adult vestibulo-ocular reflex arc.

Human subjects with maintained reversal of their horizontal field of vision exhibit very substantial adaptive changes in their 'horizontal' vestibulo-ocular reflex (v.o.r.). Short durations (8 min) of vision reversal during natural head movement led to 20% v.o.r. attenuation while long periods (4 weeks) eventually led to approximate reversal of the reflex. The reversed condition is approached by a complex, but highly systematic, series of changes in gain and phase of the reflex response relative to normal. Recovery after return to normal vision exhibits a similar duration, but different pattern, to that of the original adaptation. A chronic cat preparation with long-term optical reversal of vision has now been developed and shows similar adaptive and recovery changes at low test stimulus amplitudes, but different patterns of adaptive response at high amplitudes. An adaptive neural model employing known vestibulo-ocular pathways is proposed to account for these experimentally observed plastic changes. The model is used to predict the adapted response to patterns of stimulation extending beyond the range of experimental investigation.

Adaptation, Physiological↗
PubMed1979

Application of linear system analysis to the horizontal vestibulo-ocular reflex of the alert rhesus monkey using pseudorandom binary sequence and single frequency sinusoidal stimulation.

Horizontal eye movements of the alert rhesus monkey resulting from both pseudorandom binary sequence (PRBS) and single frequency sinusoidal rotational stimulation were analyzed using a PDP 11/40 computer in order to generate gain, phase, and coherence estimates at discrete frequencies between 0.008 and 1.28 Hz. A computer simulation of vestibular induced eye movements was used to validate our analysis procedures and to determine the effects of digital noise. Frequency domain transfer functions derived from gain and phase estimates revealed that the responses to PRBS stimulation and to single frequency sinusoids were not appreciably different. PRBS testing was accomplished in approximately one third the time required for sinusoidal testing and yielded highly reproducible data. We conclude that PRBS stimulation is a reliable and efficient method for assessing linear system parameters of the horizontal vestibulo-ocular reflex. PRBS testing may be particularly advantageous in studies of vestibulo-oculomotor plasticity in which rapid assessment of alterations in system dynamics is essential.

Animals↗
PubMed1979

Velocity storage in the vestibulo-ocular reflex arc (VOR).

Vestibular and optokinetic nystagmus (OKN) of monkeys were induced by platform and visual surround rotation. Vision prolonged per-rotatory nystagmus and cancelled or reduced post-rotatory nystagmus recorded in darkness. Presumably, activity stored during OKN summed with activity arising in the semicircular canals. The limit of summation was about 120 degrees/s, the level of saturation of optokinetic after-nystagmus (OKAN). OKN and vestibular nystagmus, induced in the same or in opposite directions diminished or enhanced post-rotatory nystagmus up to 120 degrees/s. We postulate that a common storage mechanism is used for producing vestibular nystagmus, OKN, and OKAN. Evidence for this is the similar time course of vestibular nystagmus and OKAN and their summation. In addition, stored activity is lost in a similar way by viewing a stationary surround during either OKAN or vestibular nystagmus (fixation suppression). These responses were modelled using direct pathways and a non-ideal integrator coupled to the visual and peripheral vestibular systems. The direct pathways are responsible for rapid changes in eye velocity while the integrator stores activity and mediates slower changes. The integrator stabilizes eye velocity during whole field rotation and extends the time over which the vestibulo-ocular reflex can compensate for head movement.

Animals↗
PubMed1977

Optokinetic and vestibulo-ocular reflexes in dark-reared rabbits.

Rabbits were raised in complete darkness for 7 months after birth. Eye movements were measured at the end of this period and in the next 3 months of normal light exposure with chronically implanted scleral coils. Horizontal optokinetic nystagmus (OKN) was tested inside a large drum which was rotated at velocities between 0.06 and 60 degrees/sec. Vestibuloocular reflexes (VOR) were elicited by sinusoidal horizontal oscillation on a torsion swing at frequencies between 0.11 and 2.13 Hz and amplitudes up to 10 degrees. At the end of the light-deprived period (with the eyes still covered) a VOR could be elicited consisting of a normal mixture of smooth and saccadic components and normal phase relations, but the amplitude of the smooth (compensatory) component was reduced to about 1/3 of normal control values. At the first exposure to light an OKN could be immediately elicited which was normal in most respects, except for a reduction of the ratio slow phase eye speed/drum speed to about 2/3 of the value in normal controls. The preference of each eye for anterior motion and the quasiconjugate character of nystagmus in monocular stimulation were unaffected. Also the improvement of the VOR by vision was normal. No abnormal habituation or fatigeability were observed. In the next 3 months of normal light exposure about half of the amplitude defects in both systems were restored, largely in the first week. The remaining defects were apparently permanent.

Animals↗
PubMed1978

Vestibulo-ocular reflex from the posterior canal nerve to extraocular motoneurons in the cat.

In the anesthetized cat, the posterior canal nerve (PCN) was stimulated by electric pulses and synaptic responses were recorded intracellularly in the three antagonistic pairs of extraocular motoneurons. Pure reciprocal effects were obtained in the motoneurons innervating the antagonistic pair of ipsilateral oblique muscles and the antagonistic pair of contralateral vertical rectus muscles. These responses consisted of low threshold disynaptic excitatory postsynaptic potentials (EPSPs) in either the contralateral superior oblique (c--SO) (trochlear) or contralateral inferior rectus (c--IR) motoneurons and of disynaptic inhibitory postsynaptic potentials (IPSPs) in either the ipsilateral inferior oblique (i--IO) or ipsilateral superior rectus (i--SR) motoneurons. In addition, disynaptic IPSPs were also found in (i--SO) motoneurons. Mixtures of low threshold (di or trisynaptic) EPSPs and IPSPs were found in all other extraocular motoneurons except for the contralateral lateral rectus (c--LR) motoneurons. These results may afford a basis for the characteristic eye movements induced by vertical canal nerve stimulation.

Animals↗
PubMed1979

A mathematical model of the optokinetic reflex.

The role of the optokinetic reflex (OKR) is that of cooperating with the vestibulo-ocular reflex (VOR) in the task of image stabilization on the retina during head rotations in a stationary visual surround. Since the dynamics of VOR was already well established, it has been possible to make a broad estimation of what the dynamics of OKR should be in order to obtain the performances observed in normal subjects. A mathematical model of OKR has been presented, and the experimental results obtained by Raphan et al. (1977) in the monkey and by Collins et al. (1970) in man were used to validate the model and to obtain a precise estimation of its parameters.

Animals↗
PubMed1979

Downward gaze in monkeys: stimulation and lesion studies.

Ten monkeys were stimulated unilaterally and bilaterally through bipolar electrodes placed stereotactically on each side of the midline under light barbiturate anaesthesia. Bilateral simultaneous stimulation elicited straight downward binocular movements from a core of tissue about 40 mm3 on each side which included the fields of Forel, zona incerta, subthalamic nucleus, oral pole of the red nucleus, fasciculus retroflexus and 'area tegmentalis'. Unilateral stimulation of the same points yielded downward eye movements in only 25 per cent of the instances. Upward deviation of the globes could be elicited by bilateral stimulation of tissue located more caudal, ventral and medial than that from which downward movements were obtained. Bilateral electrolytic lesions within the region outlined above caused significant defects in downward gaze both in saccadic and slow pursuit binocular movements. Passive bending of the head backwards, however, resulted in downward deviation of the globes (oculocephalic reflex). Optokinetic nystagmus and after-nystagmus downward were abolished. Oblique (45 degrees) optokinetic stimulation elicited a perverted response in the horizontal plane. Vestibulo-ocular reflexes elicited by bilateral warm irrigation of both ear canals with the monkey in the erect position, or by turning the animal while lying on one side, caused a strong tonic deviation upward with absence of nystagmus downward. Some of these monkeys showed additional alterations in upward gaze but they were less severe in intensity and duration than those of downward gaze. All eye deviations in the horizontal plane were consistently normal. Recovery occurred in all types of vertical binocular movements except in the rapid motions (saccades and quick phases of nystagmus) below the horizontal meridian. A unilateral lesion had no effect. The minimal damage producing downward gaze defects was about 1.7 mm in diameter, cetred in the prerubral fields, rostral and medial to the red nuclei with minimal involvement of the oral pole of these structures. The nuclei of Cajal, Darkschewitsch and interstitialis of the posterior commissure, as well as the fasciculus retroflexus and the posterior commissure, were spared by this lesion. The so-called rostral interstitial nucleus of the medial longitudinal fasciculus and the nucleus campi Foreli appear to be destroyed. These structures are known to receive an input from the paramedian pontine reticular formation and project on to the oculomotor nerve nucleus. These results demonstrate that the prerubral fields contain structures which are critical for rapid eye movements downward, and therefore an isolated downward gaze palsy is a strong indicator of a bilateral lesion of this zone. The findings in the few reported cases with this sign and available pathological analysis suggest that our conclusions from the experimental monkey apply to man as well. The concept of bilateral innervation for vertical eye movements is amply confirmed for the downward vectors...

Animals↗
PubMed1978

Clinical and theoretical aspects of head movement dependent oscillopsia (HMDO). A review.

Head movement-dependent oscillopsia (HMDO) with peripheral vestibular, brainstem and cerebellar lesions is reviewed. The differentiation of this kind of oscillopsia is based mainly on clinical grounds. HMDO with bilateral abolition of caloric responses, and in the absence of disease of the central nervous system, is due to bilateral vestibular disease. HMDO in patients with internuclear ophthalmoplegia and other brainstem signs is probably due to a lesion of VOR pathways in or near the medial longitudinal fasciculus. The occurrence of HMDO with ataxia of gait and cerebellar eye movement disorders (rebound nystagmus, flutter-like oscillations), in the absence of brainstem lesions (medial longitudinal fasciculus), is clinical evidence for HMDO due to a cerebellar lesion. An attempt is made to associate the different kinds of oscillopsia with current knowledge of the vestibulo-ocular reflexes.

Animals↗
PubMed1978

Vestibular nucleus neurons relaying excitation from the anterior canal to the oculomotor nucleus.

A morphological approach was undertaken to determine which vestibular nucleus neurons relay excitation from the anterior canal to the IIIrd nucleus. In anesthetized rabbits HRP was iontophoresed into the IIIrd nucleus and cells filled with HRP reaction product (positive cells) searched for within the vestibular nuclear complex. By lesioning the MLF or brachium conjunctivum immediately after iontophoresis it was demonstrated that positive cells in the dorsum of the superior vestibular nucleus are backfilled via their axons which ascend in the brachium conjunctivum. By contrast positive cells in the center of the superior nucleus are backfilled via their axons in the MLF. In electrophysiological experiments in the presence of a severed MLF the anterior canal was selectively stimulated for orthodromic, and the 3rd nucleus stimulated for antidromic, activation of vestibular nucleus neurons. Recording extracellularly with glass microelectrodes filled with fast green FCF the only cells both ortho- and antidromically activated were localized to the dorsum of the superior vestibular nucleus. It is concluded that cells dorsally located in the superior nucleus relay the disynaptic excitatory vestibulo-ocular reflex from the anterior canal to the contralateral 3rd nucleus via their axons which ascend in the brachium conjunctivum.

Animals↗
PubMed1978

A film projecting system as a diagnostic and training technique for eye movements of cerebral palsied children.

Films are presented for tracking on a translucent screen after reflection from a galvanometer driven mirror. A wave function generator produces picture displacements of amplitude and velocity capable of stimulating selectively (or simultaneously) the saccadic and smooth pursuit systems. This audiovisual signal permits prolonged eye movement recording and training sessions because of increased motivation and alertness. Optokinetic and vestibulo-ocular reflexes can also be tested. An infra-red photoelectric device monitors the horizontal component of eye movement. Records provide the necessary information for syndrome definition and training progress evaluation. Preliminary results show the technique to be perfectly suitable for the diagnosis of functional disorders and sensory-motor training of the cerebral palsied child's oculomotor system.

Attention↗