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At least 937 records · Page 52Linked to original sources
PubMed1999

Neural circuits underlying ketamine-induced oculomotor behavior in the rat: 2-deoxyglucose studies.

Time-related changes in oculomotor function and of metabolic activity patterns in selected brain networks, as assessed by the quantitative 2-deoxyglucose technique, were investigated in Long-Evans rats following intraperitoneal administration of a ketamine anesthetic dose. During ketamine-induced anesthesia a nystagmic-like behavior was present, characterized by uni-directional slow ocular drifts with superimposed paroxystic bursts of quick (saccadic-like) eye movements; all quick movements were executed in the horizontal direction, were strictly confined to an ocular hemifield of vision, and were followed by a backward (centripetal) drift. A metabolic hyperactivity was found in the dorso-medial shoulder region of the frontal cortex, corresponding to the rat saccadic cortical generator area, whereas functional activity levels were decreased in cerebellum and in several brainstem regions, including portions of the reticular formation and medial vestibular nuclei, putatively indicated as the locus of the oculomotor neural integrator. Starting 2 h after drug injection, a gradual recovery of oculomotor function occurred, with the disappearance of slow ocular drifts. However, an almost uninterrupted sequence of individual saccades was still present. Significant metabolic increases were found at this time in the cingulate and frontal cortex, basal ganglia, superior colliculus, paramedian reticular formation and oculomotor nuclei, the cerebellar vermis and paraflocculus. In medial vestibular nuclei, metabolic levels were undistinguishable from controls. These results suggest different concentration-dependent actions of ketamine on cortical and subcortical circuits involved in saccade generation and gaze holding. These effects are likely to be related at least in part to antagonism of N-methyl-D-aspartate receptor-mediated functions.

Anesthetics, Dissociative↗
PubMed2002

Vestibulo-ocular, optokinetic and postural function in diabetes mellitus.

We compared vestibulo-ocular reflex, optokinetic reflex and postural function in subjects with insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM), as well as non-diabetic controls. Both IDDM and NIDDM subjects exhibited significant deficits in gaze-holding in darkness (p < 0.05), small changes in vestibulo-ocular reflex (VOR) phase re velocity (p < 0.005) without a change in VOR gain, and a decrease in optokinetic reflex (OKR) slow phase velocity (p < 0.001). In addition, a smaller decrease was found in OKR quick phase amplitude (p < 0.02); postural sway was increased in both diabetic groups (p < 0.05), although this was not specific to the conditions of the Clinical Test of Sensory Interaction and Balance (CTSIB) that test vestibular contributions to postural stability. No differences were found in optokinetic afternystagmus or latency to circularvection. These results suggest that both IDDM and NIDDM are associated with deficits in gaze-holding, VOR and OKR function.

Adult↗
PubMed1989

The prism bar--Prentice and frontal positions.

The prism cover test has been in use for many years for measuring ocular alignment. The measurements obtained are used for both calculating the amount of correction needed in strabismus surgery, and monitoring any change in ocular alignment with recovery from muscle imbalance. Variability may arise from its use in either the frontal position or the Prentice position. Most prism bars used in the United Kingdom are calibrated for use in the Prentice position. Inaccurate results arise when a prism bar is used in a position for which it is not calibrated. The theoretical calculation for adjusting measurements obtained in the frontal position with prisms calibrated for use in the Prentice position was assessed clinically. A new modified equation is proposed incorporating practical aspects of performing the prism cover test. A table of values is included to assist in determining the necessary adjustment, so allowing for a more reliable assessment.

Adolescent↗
PubMed1984

Looking with a paralysed eye: adaptive plasticity of the vestibulo-ocular reflex.

When a patient with a peripheral monocular paresis is forced to look with the paretic eye, head movements induce the sensation of an unstable visual world. The patient behaves as if he had acute bilateral labyrinthine lesions. These symptoms are due to the lack of compensatory ocular movement and the patients complain that the visual objects move in the direction opposite to the head. The patients develop ataxia, nausea, vomiting and past pointing. The symptoms, however, are transient and consistently disappear after approximately 48 hours. The central adaptation to looking and seeing with the paralysed eye is associated with a plastic change of the VOR. This plastic adaptation is probably induced by the large retinal slip produced by the lack of compensatory movement of the eye and can be studied in the normally mobile eye in the dark. The psychophysical adaptation is probably generated by an efferent copy or corollary discharge of the vestibular system to the visual system that cancels the retinal error.

Adult↗
PubMed1998

A neural correlate for vestibulo-ocular reflex suppression during voluntary eye-head gaze shifts.

The vestibulo-ocular reflex (VOR) is classically associated with stabilizing the visual world on the retina by producing an eye movement of equal and opposite amplitude to the motion of the head. Here we have directly measured the efficacy of VOR pathways during voluntary combined eye-head gaze shifts by recording from individual vestibular neurons in monkeys whose heads were unrestrained. We found that the head-velocity signal carried by VOR pathways is reduced during gaze shifts in an amplitude-dependent manner, consistent with results from behavioral studies in humans and monkeys. Our data support the hypothesis that the VOR is not a hard-wired reflex, but rather a pathway that is modulated in a manner that depends on the current gaze strategy.

Animals↗
PubMed2001

Adaptive plasticity of head movement propensity.

Individual humans exhibit differing propensity to move the head in association with saccadic shifts in gaze. We assessed whether this tendency can be modified in normal subjects by either reducing neck mobility with a cervical collar or restricting the field of view using aperture spectacles. We quantified head movement propensity in terms of the range of orbital eccentricity within which the eyes are customarily maintained (customary ocular motor range), and the range of final eye-in-head eccentricity for which a planned saccade is likely to be executed without a concomitant head movement (eye-only range). Three subjects wore rigid collars during waking hours for periods of up to 9 days. We measured customary and eye-only ranges with the collar removed, at various times during the adaptation and recovery periods. Collar adaptation reduced head movement propensity in all three subjects, increasing the average customary ocular range from 27.6 +/- 8.9 degrees (mean +/- SD) to 66.1 +/- 4.5 degrees and the eye-only range from 24.6 +/- 17.0 degrees to 67.6 +/- 7.4 degrees. In two subjects the modifications persisted for weeks following final collar removal. In parallel with the reduction in head movement propensity, all subjects improved in their ability to maintain eccentric gaze, suggesting that neck restriction led to effects at the level of the brainstem. Three subjects were adapted to spectacles, masked to restrict the field of view to approximately 20 degrees. The aperture spectacles were worn for periods of up to 9 days. When tested without the apertures, one subject exhibited a definite increase in head movement propensity; in the other two, the data were equivocal, indicating either a small increase in head movement propensity or no effect. Averaged across subjects, customary ocular motor range decreased from 35.1 +/- 12.8 degrees to 25.4 +/- 13.4 degrees and eye-only range decreased from 35.1 +/- 7.5 degrees to 23.0 +/- 4.0 degrees. The marked difference in the magnitudes of collar- and spectacle-induced changes suggests that the responses to the two restrictive appliances are mediated by different mechanisms. Collar adaptation may involve parametric modulation of circuits mediating reflex recruitment of head movements, while aperture adaptation may primarily reflect substitution of an alternative mode of head control triggered by the presence of the restricted field of view, with only minor parametric modulation of the underlying head recruitment circuit. The enduring effects of restricting neck mobility upon head movement tendencies may relate to the common clinical association between neck injury and persistent dysequilibrium.

Adaptation, Physiological↗
PubMed1996

Timing and amplitude of saccades during predictive saccadic tracking in schizophrenia.

Schizophrenia patients have ocular motor abnormalities. It has been hypothesized that these abnormalities are associated with frontal eye field pathology. If so, schizophrenia patients should have difficulties decreasing saccadic reaction times in response to predictably moving targets. To evaluate the frontal eye field hypothesis, 25 schizophrenic and 26 nonpsychiatric subjects completed predictive saccadic tracking tasks. The groups demonstrated equivalent decreases in saccadic reaction times over consecutive trials. Schizophrenia patients, however, had faster reaction times and shorter amplitude saccades than nonpsychiatric subjects. The shorter amplitude saccades were made regardless of reaction time, perhaps an antipsychotic medication effect. The reaction time results are unlikely to be an effect of treatment with antipsychotic medication and are inconsistent with the hypothesis that schizophrenia patients have frontal eye field pathology.

Adult↗
PubMed1996

The oculocephalic response in the evaluation of the dizzy patient.

The oculocephalic response (OCR) is a simple office maneuver that assesses the vestibulo-ocular reflex (VOR). An abnormal response is manifested clinically as refixation saccades following a rapid horizontal head movement. Because little attention has been given to the OCR in the literature, a prospective study was undertaken with 112 consecutive patients who presented with dizziness and underwent OCR testing followed by caloric evaluation. Agreement was good between the OCR and caloric evaluation (kappa = 0.44). Specificity was quite high (97%); sensitivity was found to be less (39%). Positive (68%) and negative (90%) predictive values of the OCR illustrate that the clinician can often anticipate the results of caloric testing based on this response. This easily performed test of the VOR is a useful tool in the evaluation of the dizzy patient.

Adolescent↗
PubMed1995

Combined action of optokinetic reflex (OKR) and vestibulo-ocular reflex (VOR) in macaque monkey during transient stimulation.

Interaction of vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) was studied in macaque monkeys by recording horizontal eye movements during transient rotations of their heads and/or an optokinetic pattern in space. At low peak velocities of the stimuli (1.25 degrees/s, 10.0 degrees/s) the eyes were rather well stabilized on the optokinetic pattern, independently of whether the head, the pattern, or both were rotated. At higher velocities (40.0 degrees/s), the OKR gain was attenuated and, when combining vestibular and optokinetic stimuli, the eyes became increasingly stabilized in space. The data could be simulated by a computer model previously designed to describe VOR-OKR interaction during sinusoidal rotations. In this model eye stabilization primarily relies on the OKR, while the role of the VOR is to compensate for the limited bandwidth of the OKR.

Animals↗
PubMed1998

[Automobile driving fitness of patients with nystagmus].

BACKGROUND: By law, applicants for driver's licenses not only have to have sufficient vision, but also have to use this sight reliably. The nystagmus patient takes advantage of ocularly induced head turns and other forms of compensation. In the approved test procedures he is deprived of such compensations. MATERIALS AND METHODS: The eye movements of a nystagmus patient were recorded oculographically. He was allowed to use compensatory mechanisms of body posture and movement for stabilization of vision. RESULTS: The nystagmus patient can achieve better visual performance when he is allowed to utilize complex segmental body movements for stabilization of vision. CONCLUSIONS: It is proposed that test procedures for visual performance in traffic be altered as follows: nystagmus and abnormal head postures are admittable if sufficient binocular vision is achieved. The test may use illustrations of traffic situations containing relevant details such as traffic signs. These are to be understood by the test person on triplicate presentation.

Adult↗
PubMed1990

Comparison of vestibulo-ocular reflex (VOR) modification methods in cats.

The vestibulo-ocular reflex (VOR) has been measured and optically modified in several animal species. The VOR gain can be increased optokinetically by rotating the animal's visual surround opposite to the animal's direction of rotation or a VOR increase can result from the use of magnifying lenses. We describe here a comparison of three methods for producing VOR increases in cats: (i) optokinetic drum; (ii) a pair of 2.2 x telescopic lenses; (iii) Fresnel lens goggles. The animals were put through several preliminary calibrations followed by a sequence of VOR modification periods alternating with 10 testing periods. The results of the comparison in 4 cats show that the Fresnel lens system produces a greater and more stable VOR gain increase than the other two methods.

Animals↗
PubMed1998

Disentangling gravitational, environmental, and egocentric reference frames in spatial neglect.

Previous studies in neglect patients using rotation of the body around the roll-axis revealed neglect of visual stimuli not only in the egocentric, body-centered left but also in the environmental left. The latter has been taken as evidence for a gravity-based environment-centered component of neglect occurring independently of the subject's actual body orientation. However, by using visual stimuli in a normally lightened room, the studies confounded the gravitational upright with the visible upright of the surround. Thus, it is possible that the visible upright of the environment may have served the role of the gravitational upright relative to which neglect occurred. The present experiment evaluated the influence of gravity on contralateral neglect when no visual information was presented. In complete darkness, neglect patients' exploratory eye movements were recorded in five experimental conditions: body in normal upright position, body titled 30 degrees to the left and 30 degrees to the right, and body pitched 30 degrees backward and 30 degrees forward. In the upright orientation, the patients with neglect showed a bias of ocular exploration to the ipsilesional right side. In egocentric body coordinates, we found no significant differences between the orientation of the biased search field in the different experimental conditions showing that the search field shifted with the orientation of the body. No significant decrease or enhancement of neglect was observed when body orientation was varied in the different conditions. In conclusion, the present results revealed that the modulation of gravitational forces has no significant influence on the exploratory bias of these patients. When visual information was excluded and only graviceptive information was available, the patients' failure to explore the contralesional part of space appeared purely body-centered. The results argue against a disturbed representation of space in neglect that encodes locations in a gravity-based reference system.

Aged↗
PubMed2003

The human horizontal vestibulo-ocular reflex in response to active and passive head impulses after unilateral vestibular deafferentation.

We studied the compensatory eye movements made by subjects with unilateral vestibular deficits in response to passive (unpredictable, manually generated) and active (predictable, self-generated) head impulses. A typical head impulse is a brief, low-amplitude (15-20 degrees ), high-velocity (150-350 degrees /s), high-acceleration (4000-6000 degrees /s(2)), yaw head-on-trunk rotation. In the initial 75 ms of the response, the vestibulo-ocular reflex gain was significantly higher during active head impulses to both ipsilesional and contralesional sides, than during passive impulses. Mean gains were 0.15 (ipsilesional passive), 0.44 (ipsilesional active), 0.5 (contralesional passive), and 0.76 (contralesional active). Differences between active and passive head impulses were present from near the onset of head rotation. The mechanism for producing this behavior is unclear, but the findings could be related to enhanced sensitivity of second-order neurons during active head impulses. However, even with active movements, there is still a large and statistically significant asymmetry in the eye-movement responses for ipsilesional as opposed to contralesional head rotations. After 75 ms, rapid corrective eye movements often were generated to reduce any remaining gaze error.

Afferent Pathways↗
PubMed1993

Saccade-vestibulo-ocular reflex co-operation and eye-head uncoupling during orientation to flashed target.

1. Eye-head co-ordination in the horizontal plane was studied in four human subjects using two successive flashes in the same direction, either increasing in eccentricity (IE), or decreasing in eccentricity (DE). 2. Results showed that for both conditions, head movements preceded eye movements and were typically longer or followed by a slow gaze movement. This slow movement was due to a vestibulo-ocular reflex gain of less than one. Gaze accuracy was achieved by small head movement adjustments. 3. Gaze movement to an IE stimulus had a staircase pattern, and to a DE stimulus, a pulse-step pattern or one gaze saccade to the final flash eccentricity. 4. In some cases, however, in response to a DE stimulus, the eye and head movements were directed to different displacements (dissociation); i.e. the head movement started towards the first flash eccentricity with a concomitant eye saccade to the second flash eccentricity. When this occurred, gaze movement did not resemble a pulse-step pattern. 5. It is suggested that non-visually orienting gaze is driven mainly by head movement. Eye and head movements can be either tightly coupled or dissociated, depending on the stimulus pattern.

Eye Movements↗
PubMed1999

[From vestibular nystagmus to the transfer function of the vestibulo-ocular reflex].

A new method for the separation of the two phases of the vestibular nystagmus (slow eye velocity and fast eye velocity) is presented. The aim is to calculate the transfer coefficients of the human vestibulo-ocular reflex (VOR). With a combination of thresholds on the eye velocity and the eye acceleration signals, the different phases of fast eye velocity in the vestibular nystagmus can be located with a good accuracy. So this phases which are not of vestibular origin can be eliminated. The dependence of the transfer function and of the coherence function from the values of the thresholds is studied. This study shows that our method is very robust and that the consequence of the systematic errors occurring with the preceding methods, we have used, is a bad estimation of the gain of the VOR. The values of the coherence function we obtained show that the VOR has a linear behaviour within the range of frequencies we studied (0.01-0.5 Hz).

Electronystagmography↗
PubMed1980

Dissociated visual development: electrodiagnostic studies in infants who are 'slow to see'.

Four infants were studied who failed to show any visual interest or following responses in the first three months of life. Although no definite ocular abnormalities were found at the time of presentation, both the parents and their medical advisers initially had serious concerns about the infants' visual prognosis. Initial electroretinograms (ERG) were found to be unequivocally normal, but three of the infants showed absent or impaired cortical visual evoked responses (VER). The fourth infant had an initial VER which was immature. Subsequently, all the infants showed increasing visual responsiveness from three to four months of age and all now have visual behaviour and general development appropriate to their ages. The VERs were repeated after four months of age and all showed normal responses. It is concluded that poor or even absent VER responses in early infancy may not always indicate a poor prognosis for vision. The possible mechanisms of this visual maturational lag are discussed.

Attention↗
PubMed1988

Intraocular pressure changes in secondary positions of gaze in normal subjects and in restrictive ocular motility disorders.

One hundred normal Caucasian eyes and 29 eyes with restrictive disorders of ocular motility were studied in order to delineate intraocular pressure changes in secondary positions of gaze. Applanation tonometry was performed in the primary position and at an angle of 22 degrees. In patients with restrictive syndromes the changes of intraocular pressure in the secondary positions of gaze were significantly higher (p less than 0.0001) than in normal subjects. The range of variation in normal subjects was 0, +3 mmHg for supraduction and -3, +1 mmHg for abduction. Patients with restrictive syndromes showed changes between +1 and +15 mmHg for supraduction and between +3 and +10 mmHg for abduction. Results obtained in the two groups showed the existence of false negatives. This test is thus a practical and useful diagnostic tool, but its results must be evaluated cautiously.

Adolescent↗
PubMedDate not supplied

New neurotological test for detecting cerebellar dysfunction. Vestibulo-ocular reflex changes with horizontal vision-reversal prisms.

Adaptation of the vestibulo-ocular reflex (VOR) was studied in 26 normal subjects and 15 patients with cerebellar lesions, using horizontal vision-reversal prisms. In normal subjects, adaptation of gain after wearing prisms for one hour was approximately 50% of the VOR value in the dark. In contrast to this, patients with cerebellar lesions showed less adaptation, approximately 20% after a one-hour forced adaptation task. These cases showed three different types of abnormalities: 1) high gain before wearing prisms and normal adaptation, 2) high gain before wearing prisms and reduction of adaptation, 3) normal gain and reduction of adaptation. From these results it is suggested that observation of the effect of vision-reversal prisms on the VOR may permit the detection of cerebellar lesions of a type or subtlety which escape established tests.

Adult↗