Phases Of Optokinetic Nystagmus Research Articles

Clinical and functional characteristics of patients with chronic dizziness

Objective. To form a clinical and functional characterization of patients with chronic dizziness. Materials and methods. A single one-stage cohort study of 32 patients with chronic dizziness (CD), among them 26 women and 6 men, mean age - 49 [36.5; 51.5] years, was conducted. Patients were examined by objective neurologic examination, laboratory (general and biochemical blood tests) and instrumental (radiography, magnetic resonance imaging (MRI), ultrasound) methods were used during the study. Barany’s test was also performed, and neuropsychological testing was performed. The data were processed using descriptive statistical methods of the application package “Statistica”, 10.0. Results. During the examination, patients complained of dizziness (100 %) and shakiness when walking (84 %), provoked mainly by intermittent visual stimuli (31 % each). Subjective neurological deficit in patients with CD was caused by kinesthetic sensations of instability (34 %), accompanied by decreased attention and memory (28 %). Objectively, the phase of optokinetic nystagmus in Barany’s test lengthened in the studied group - 190 [170; 225] s and the time of balance retention in Romberg’s pose decreased - 3 [2; 5] s. CD patients were characterized by high personality anxiety - 53 [44; 53] points and autonomic imbalance according to the questionnaire of A.M. Vein - 42 [40; 44] points. We did not reveal a connection of CD with structural anomalies, pathology of brachiocephalic vessels. Conclusion. The clinical and functional status of CD patients was characterized by the absence of focal lesions of the nervous system and a small number of concomitant diseases causing vertigo. At the same time, the patients’ subjective sensations underlying the perception of non-existent stimuli led to impaired maintenance of vertical body position and, in turn, formed an anxiety disorder.

The effect of optokinetic stimulation on orientation of sound lateralization

Conclusions. The current study demonstrates that sound lateralization sensitivity during interaural time difference (ITD) discrimination may be altered by optokinetic (OK) stimulation, and that sound lateralization sensitivity of ITD discrimination may be more susceptible to OK stimulation than that of interaural intensity difference (IID) discrimination. These data suggest that nystagmus or the sensation of self-rotation induced by OK stimulation influences auditory afferent information such as sound lateralization. Objective. Using dichotic sound, the effect of optokinetic stimulation on the orientation of sound lateralization was investigated in humans. Materials and methods. Subjects were studied by testing ITD and IID discrimination during OK stimulation. Results. At 90°/s of the light stripes angular velocity the amplitudes for the ITD discrimination tests during OK stimulation were significantly greater than those either before the beginning of OK stimulation or at 30°/s (p <0.05). No significant difference in the amplitude for the IID discrimination test was observed between the results obtained before and during OK stimulation. During OK stimulation, all subjects felt that their perceptual body axes shifted toward the quick phase of OK nystagmus. In 8 of 12 subjects, the median line of amplitude for the ITD discrimination test shifted to the quick phase side of the OK nystagmus.

Differences in slow phase of optokinetic nystagmus in response to various optokinetic stimuli between albino and pigmented rats

Differences in slow phase of optokinetic nystagmus in response to various optokinetic stimuli between albino and pigmented rats

Optokinetic nystagmus in cats with congenital strabismus.

1. Eye movements were recorded in seven innately esotropic cats during monocular and binocular horizontal optokinetic stimulation, using the search coil technique in five cats and electrooculography in two cats. 2. During closed loop measurements in these strabismic cats, slow phases of optokinetic nystagmus (OKN) were characterized by an overall reduced gain when compared with normal controls. In addition, response gain to monocular nasotemporal stimulation was even more reduced than that to temporonasal stimulation, resulting in an increased asymmetry of closed loop gain. 3. During open loop measurements, eye velocity in strabismic cats was very low at all velocities tested. 4. Differential analysis of the symmetry of OKN revealed that all our strabismic cats had a "good" or more symmetric and a "poor" or more asymmetric eye. In addition, when analyzed separately at individual velocities, the symmetry index of the good eye was fairly constant over the velocity range tested. By contrast, the symmetry index of the poor eye dropped dramatically at higher stimulus velocities. 5. To analyze the relationship of OKN symmetry and cortical physiology, we calculated the ratio between the percentage of neurons driven by one eye in the ipsilateral and the contralateral cortical hemisphere. We found a weak correlation between OKN symmetry and this cortical symmetry index (P < 0.05, analysis of variance). 6. In conclusion, slow eye movements in cats with congenital esotropia are characterized by extremely low gain, especially at higher stimulus velocities. In addition, OKN symmetry during monocular stimulation is decreased. Our data suggest that OKN symmetry is weakly correlated with the proportion of binocular neurons in the visual cortex ipsilateral to the stimulated eye. However, OKN characteristics seem to reflect to a higher degree the response properties of neurons in the pretectal nucleus of the optic tract and the dorsal terminal nucleus of the accessory optic system than properties of neurons in the visual cortex.

Human ocular following responses are plastic: evidence for control by temporal frequency-dependent cortical adaptation.

Optokinetic nystagmus (OKN) induced by wide-field visual stimulation was measured with and without prior adaptation to moving sinusoidal gratings. Under unadapted conditions the mean gains of the slow phases of OKN in the first 500 ms were 0.5-0.8, and the eye velocities and amplitudes had rise times with time constants of 0.1-0.2 s. By contrast, following adaptation to as little as 1 s of image motion, the magnitude of the initial gains fell and the rise times of the velocities and amplitudes increased markedly. The degree of adaptation depended on the adapting temporal frequency, the optimum adaptive frequencies being 1.7-3.4 Hz. In this range of temporal frequencies, the initial gains fell to 0.1-0.3 and the rise times for velocity and amplitude ranged from 0.4 to 7.0 s, depending on the length of the adapting period. Thus the observed changes in the time constant were up to 70-fold. Neither spatial frequency or image velocity had any marked influence on the level of adaptation. The dependence on temporal frequency rather than image velocity suggests that the motion detectors feeding the adaptive system respond to local motion-related changes in luminance. The adaptive effects were direction-selective, showing that this must also be the case for the motion detectors. The adaptive effects were observed both when the drift temporal frequency on the retina was established by artificially maintaining a fixed gaze or when the adapting temporal frequency was induced by retinal slip during OKN. Time constants for recovery from adaptation were similar to motion aftereffects measured by psychophysical and physiological methods. The results suggest a link between cortical motion adaptation and adaptive mechanisms effecting the oculomotor system.

The interstitial nucleus of Cajal of the cat. I. Neurons activity related to vertical eye movements.

Interstitial nucleus of Cajal (INC) neurons activity was studied during vertical optokinetic nystagmus (OKN) and after-nystagmus (OKAN) in awake cats lying on their right side. The activity of one hundred neurons was recorded in the left INC and analysed in relation with the vertical component of OKN and OKAN. The activity of 27 neurons was correlated either to eye position or to both eye velocity and eye position; 18 of these neurons were recorded in their on-direction and their off-direction. The analysis of the 18 neurons showed that the activity of 8 of them was correlated to eye position in the on-direction and in the off-direction and the correlation to eye position was higher than to eye velocity; these neurons are considered as position neurons. Seven other neurons had a higher correlation to eye position that to eye velocity in the on-direction and this relation reversed in the off-direction, these neurons are considered as position-velocity neurons. Thirty two burst-neurons were activated only during quick phases of OKN and OKAN and they were silent during slow phases and periods of fixation. Nine burst neurons had an upward on-direction and 23 neurons a downward on-direction. The eye velocity-average burst frequency (ABF) and quick phase duration-burst duration relationships had low correlations and suggested that INC burst neurons were excitatory premotor neurons. Statistical analysis showed that downward on-direction burst neurons had a higher ABF that upward on-direction burst neurons. Moreover, during OKN and OKAN, the velocity sensitivity of INC burst neurons was the same. The activity of the remaining neurons (41 neurons) was not quantitatively correlated to vertical and horizontal eye movements; they were classified as irregular tonic neurons. This study shows that INC neurons carry an eye position signal which was never reported before. This supports the results of INC lesion studies which showed that INC is involved in the vertical velocity to position integration. Moreover, there is an up versus down asymmetry in the frequency of INC burst neurons.

Human Horizontal Optokinetic Nystagmus Elicited by the Upper Versus the Lower Visual Fields

A 30-deg-high horizontally rotating random-dot display was presented to the central field, and with its more central edge at vertical eccentricities of 0, 2.5, 5, and 10 deg above or below the horizon. Stimulus velocities of 25-100 deg/s and two directions of motion were presented. The mean gain of the slow phases of optokinetic nystagmus (OKN) for five subjects was significantly higher when the stimulus was presented to the lower visual field than when the stimulus was presented to the upper field. This difference was most pronounced when the display was displaced 5 deg from the fovea and moving below 100 deg/s. Our results are consistent with existing psychophysical and physiological evidence for the superiority of the upper retina. In addition, four of the five observors showed significant directional asymmetries.

The fast phase of optokinetic nystagmus in the locust

ABSTRACT. When their visual environment is rotated about them, freely moving locusts make the typical slow (following) and fast (flick back) phases of optokinetic nystagmus. The fast phase was examined and is compared with that of Crustacea and vertebrates. It is unusual in the locust in that it is symmetrical about the body midline. Mechanoreceptors play a significant role in maintaining the fast phase reset function.

Cerebellar role in smooth pursuit movement.

It is generally believed that pursuit eye movements are unaffected by cerebellar cortical atrophy or cerebellectomy. The present study was performed on patients who underwent partial vermis and hemisphere ablations as a result of severe cranial injury or cerebellar tumors. Eye movements were measured by DC electro-oculography. A clear disparity of the slow phase of the optokinetic nystagmus was observed. When eye movements were contralateral to the ablated side the slow phase of optokinetic nystagmus was statistically slower than drum or visual field velocity. It is suggested that the cerebellum network is involved in the mechanisms of the smooth pursuit movement.