Integrator Function in the Oculomotor System Is Dependent on Sensory Context

2005 ◽  
Vol 93 (6) ◽  
pp. 3709-3717 ◽  
Author(s):  
W.W.P. Chan ◽  
H. L. Galiana
Keyword(s):  
Time Constant ◽  
Normal Subjects ◽  
Oculomotor System ◽  
Integration Time ◽  
Vestibuloocular Reflex ◽  
Distributed Network ◽  
Sensory Motor ◽  
Gaze Holding ◽  
Analytical Tools ◽  
Effective Integration

The oculomotor integrator is usually defined by the characteristics of decay in gaze after saccades to flashed targets or after spontaneous gaze shifts in the dark. This property is then presumed fixed and accessed by other ocular reflexes, such as the vestibuloocular reflex (VOR) or pursuit, to shape motoneural signals. An alternate view of this integrator proposes that it relies on a distributed network, which should change its properties with sensory-motor context. Here we demonstrate in 10 normal subjects that the function of integration can vary in an individual with the imposed test. The value of the time constant for the decay of gaze holding in the dark can be significantly different from the effective integration time constant estimated from VOR responses. Hence analytical tools for the study of dynamics in ocular reflexes must allow for nonideal and labile integrator function. The mechanisms underlying such labile integration remain to be explored and may be different in various ocular reflexes (e.g., visual versus vestibular).

scholarly journals Contribution of intravestibular sensory conflict to motion sickness and dizziness in migraine disorders

2016 ◽  
Vol 116 (4) ◽  
pp. 1586-1591 ◽  
Author(s):  
Joanne Wang ◽  
Richard F. Lewis
Keyword(s):  
Motion Sickness ◽  
Semicircular Canals ◽  
Inverse Correlation ◽  
Normal Subjects ◽  
Otolith Organs ◽  
Rotational Axis ◽  
Vestibuloocular Reflex ◽  
Sensory Conflict ◽  
Velocity Signal ◽  
Episodic Vertigo

Migraine is associated with enhanced motion sickness susceptibility and can cause episodic vertigo [vestibular migraine (VM)], but the mechanisms relating migraine to these vestibular symptoms remain uncertain. We tested the hypothesis that the central integration of rotational cues (from the semicircular canals) and gravitational cues (from the otolith organs) is abnormal in migraine patients. A postrotational tilt paradigm generated a conflict between canal cues (which indicate the head is rotating) and otolith cues (which indicate the head is tilted and stationary), and eye movements were measured to quantify two behaviors that are thought to minimize this conflict: suppression and reorientation of the central angular velocity signal, evidenced by attenuation (“dumping”) of the vestibuloocular reflex and shifting of the rotational axis of the vestibuloocular reflex toward the earth vertical. We found that normal and migraine subjects, but not VM patients, displayed an inverse correlation between the extent of dumping and the size of the axis shift such that the net “conflict resolution” mediated through these two mechanisms approached an optimal value and that the residual sensory conflict in VM patients (but not migraine or normal subjects) correlated with motion sickness susceptibility. Our findings suggest that the brain normally controls the dynamic and spatial characteristics of central vestibular signals to minimize intravestibular sensory conflict and that this process is disrupted in VM, which may be responsible for the enhance motion intolerance and episodic vertigo that characterize this disorder.

Long Time-Constant Behavior of the Oculomotor Plant in Barbiturate-Anesthetized Primate

2006 ◽  
Vol 95 (2) ◽  
pp. 774-782 ◽  
Author(s):  
S. Sklavos ◽  
D. M. Dimitrova ◽  
S. J. Goldberg ◽  
J. Porrill ◽  
P. Dean
Keyword(s):  
Time Constant ◽  
Oculomotor System ◽  
Recent Analysis ◽  
Substantial Contribution ◽  
Eccentric Fixation ◽  
Orbital Tissue ◽  
Long Time ◽  
In Series ◽  
Release Data ◽  
S Period

The mechanics of the extraocular muscles and orbital tissue (“oculomotor plant”) can be approximated by a small number of viscoelastic (Voigt) elements in series. Recent analysis of the eye's return from displacement in lightly anesthetized rhesus monkeys has suggested a four-element plant model with time constants (TCs) of ∼0.01, 0.1, 1, and 10 s. To demonstrate directly the presence of long (1,10 s) TC elements and to assess their contribution quantitatively, horizontal eye displacement was induced in Cynomolgus monkeys under deep barbiturate anesthesia that prevented interference from spontaneous eye movements. The displacement was maintained for either a prolonged (30 s) or brief (0.2 s) period before release. Return to resting position took 20–30 s after prolonged displacement but only 1–2 s after brief displacement, consistent with the presence of long TC elements that would only be substantially stretched in the former condition. Quantitative fitting of the release curves after prolonged displacement indicated that the two long TC elements contribute a substantial proportion (∼30%) of the total plant compliance. A model based on the estimated compliance values is shown to account quantitatively both for our release data and for Goldstein and Robinson's data on hysteresis of ocular motoneuron firing rates measured after centripetal saccades following prolonged eccentric fixation. Long time-constant elements in the plant thus make a substantial contribution to some types of eye movement, and their inclusion in plant models can help interpret the firing patterns of single units in the oculomotor system.

scholarly journals An attempt to detect the 327-Mc/s line of galactic deuterium

1959 ◽  
Vol 9 ◽  
pp. 352-354
Author(s):  
R. L. Adgie
Keyword(s):  
Radio Telescope ◽  
Integration Time ◽  
Effective Integration

The previous unsuccessful attempts to detect the 327-Mc/s line of galactic deuterium [1, 2] were limited in sensitivity either by the size of aerial or by the inability to use long integration times with a large fixed aerial. The new observations reported here were made with the 250-foot radio telescope at Jodrell Bank, which can continuously follow a source of radiation; moreover, the effective integration time was improved by using a multi-channel receiver instead of a swept-frequency one.

Slow Cumulative Eye Position to Quantify Optokinetic Afternystagmus

1992 ◽  
Vol 101 (3) ◽  
pp. 255-260 ◽  
Author(s):  
Timothy C. Hain ◽  
Gaurang Patel
Keyword(s):  
Time Constant ◽  
Normal Subjects ◽  
Directional Asymmetry ◽  
Slow Phase ◽  
Velocity Versus ◽  
Eye Position ◽  
Full Field ◽  
Optokinetic Afternystagmus ◽  
Optokinetic Responses ◽  
The Mean

In 30 normal subjects we computed the slow cumulative eye position (SCEP) of optokinetic afternystagmus (OKAN) that followed 60 seconds of full-field optokinetic stimulation at 60°/s. The mean SCEP was 112.8° ± 65.0°. The lower and upper fifth percentile limits for directional preponderance of the SCEP were −38.8% and 44.3%, respectively. The time constant, which we calculated by dividing the SCEP by the initial velocity, was 12.0 ± 7.4 seconds. This value is nearly identical to the time constant obtained from semilogarithmic regression of the decay of OKAN slow-phase velocity versus time. We conclude that the SCEP is a good measure of OKAN and that it reflects the substantial amount of variability and directional asymmetry observed in the optokinetic responses of normal subjects.

I. Manual Quantitative Assessment of Eye-Tracking Patterns

1980 ◽  
Vol 89 (4_suppl2) ◽  
pp. 1-6 ◽  
Author(s):  
Yoshio Umeda
Keyword(s):  
Eye Tracking ◽  
Time Constant ◽  
Quantitative Assessment ◽  
Visual Analysis ◽  
Normal Subjects ◽  
Total Index ◽  
Total Index Total ◽  
Second Period ◽  
Total Indices

Quantitative assessment of the electronystagmogram of the eye-tracking test (eye-tracking pattern) was undertaken in 20 normal subjects and 70 patients with vertigo. The abnormal recordings, contrary to the normal, showed, in varying degrees, remarkable irregularities of eye speed. These irregularities appeared in the form of spikes on the electronystagmogram at the time constant of 0.03 second. We measured the height of the spikes using 40°/sec as a unit and added the units of spikes appearing during a nine-second period to obtain the total index. Total indices ranged from zero (normal) to 40 + (severely abnormal), and their values showed levels of abnormality in the eye-tracking pattern more accurately than the visual analysis in current use.

Cerebellar Disease Alters the Axis of the High-Acceleration Vestibuloocular Reflex

2005 ◽  
Vol 94 (5) ◽  
pp. 3417-3429 ◽  
Author(s):  
Mark F. Walker ◽  
David S. Zee
Keyword(s):  
Head Rotation ◽  
Normal Subjects ◽  
Vestibuloocular Reflex ◽  
Cerebellar Disease ◽  
Characteristic Finding ◽  
High Acceleration ◽  
The Difference ◽  
Head Impulses ◽  
Cross Axis ◽  
Eye Velocity

L. W. Schultheis and D. A. Robinson showed that the axis of the rotational vestibuloocular reflex (RVOR) cannot be altered by visual-vestibular mismatch (“cross-axis adaptation”) when the vestibulocerebellum is lesioned. This suggests that the cerebellum may calibrate the axis of eye velocity of the RVOR under natural conditions. Thus we asked whether patients with cerebellar disease have alterations in the RVOR axis and, if so, what might be the mechanism. We used three-axis scleral coils to record head and eye movements during yaw, pitch, and roll head impulses in 18 patients with cerebellar disease and in a comparison group of eight subjects without neurologic disease. We found distinct shifts of the eye-velocity axis in patients. The characteristic finding was a disconjugate upward eye velocity during yaw. Measured at 70 ms after the onset of head rotation, the median upward gaze velocity was 15% of yaw head velocity for patients and <1% for normal subjects ( P < 0.001). Upward eye velocity was greater in the contralateral (abducting) eye during yaw and in the ipsilateral eye during roll. Patients had a higher gain (eye speed/head speed) for downward than for upward pitch (median ratio of downward to upward gain: 1.3). In patients, upward gaze velocities during both yaw and roll correlated with the difference in anterior (AC) and posterior canal excitations, scaled by the respective pitch gains. Our findings support the hypothesis that upward eye velocity during yaw results from AC excitation, which must normally be suppressed by the intact cerebellum.

Overview of Gaia Multi-Color Photometry

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
Erik Høg
Keyword(s):  
Optical System ◽  
Angular Resolution ◽  
Broad Band ◽  
Integration Time ◽  
High Angular Resolution ◽  
System A ◽  
Astrometric Observation ◽  
Medium Band ◽  
Effective Integration

AbstractGaia will obtain multi-color photometry for astrometric and astrophysical purposes. A photometry in five broad bands and with high angular resolution will be obtained after every astrometric observation of a star, especially for the sake of correcting slight astrometric chromaticity errors of the optical system. A separate smaller telescope will obtain photometry in eleven passbands of medium width designed to serve the astrophysical analysis of the mission results. The medium-band photometry (MBP) has less angular resolution, but much longer effective integration time than the broad-band photometry (BBP).

Optokinetic Afternystagmus in Humans: Normal Values of Amplitude, Time Constant, and Asymmetry

1989 ◽  
Vol 98 (9) ◽  
pp. 741-746 ◽  
Author(s):  
Marina A. J. Tijssen ◽  
Timothy C. Hain ◽  
Chiara S. M. Straathof ◽  
David S. Zee
Keyword(s):  
Time Constant ◽  
Repeated Measures ◽  
Initial Velocity ◽  
Normal Subjects ◽  
Directional Asymmetry ◽  
Intrasubject Variability ◽  
Individual Subject ◽  
Optokinetic Afternystagmus ◽  
Short Period ◽  
Normal Humans

It has been suggested that the appearance of directional asymmetry and/or a reduced time constant of optokinetic afternystagmus (OKAN) might be a clinical index of vestibular imbalance. However, we do not know the limits for OKAN parameters in normal humans. Accordingly, we studied OKAN in 30 normal subjects using a “sampling” method, in which a number of values of OKAN are obtained by turning out the lights periodically during optokinetic stimulation. We found that the initial velocity of OKAN has a large intrasubject variability. Accordingly, if precision is desired so as to obtain 95% confidence that the measured mean of the initial velocity of OKAN is within 25% of the true mean in an individual subject, at least eight measurements of the initial OKAN velocity must be taken. When 12 measurements are made, all subjects had a minimum value of 5°/s initial OKAN, and there was little directional asymmetry (mean of −0.47°/s ± 3.13°/s). The intrasubject variability of the time constant of OKAN was similar to the variability of initial OKAN velocity. However, because it is not possible to obtain repeated measures of the time constant in a short period of time, the time constant of OKAN is less likely to be useful in clinical testing.

Kinematics of the Rotational Vestibuloocular Reflex: Role of the Cerebellum

2007 ◽  
Vol 98 (1) ◽  
pp. 295-302 ◽  
Author(s):  
Mark F. Walker ◽  
Jing Tian ◽  
David S. Zee
Keyword(s):  
Tilt Angle ◽  
Three Dimensional ◽  
Head Rotation ◽  
Normal Subjects ◽  
Eye Position ◽  
Vestibuloocular Reflex ◽  
Gaze Stabilization ◽  
Eye Rotation ◽  
Axis Rotation ◽  
Head Impulses

We studied the effect of cerebellar lesions on the 3-D control of the rotational vestibuloocular reflex (RVOR) to abrupt yaw-axis head rotation. Using search coils, three-dimensional (3-D) eye movements were recorded from nine patients with cerebellar disease and seven normal subjects during brief chair rotations (200°/s2 to 40°/s) and manual head impulses. We determined the amount of eye-position dependent torsion during yaw-axis rotation by calculating the torsional-horizontal eye-velocity axis for each of three vertical eye positions (0°, ±15°) and performing a linear regression to determine the relationship of the 3-D velocity axis to vertical eye position. The slope of this regression is the tilt angle slope. Overall, cerebellar patients showed a clear increase in the tilt angle slope for both chair rotations and head impulses. For chair rotations, the effect was not seen at the onset of head rotation when both patients and normal subjects had nearly head-fixed responses (no eye-position-dependent torsion). Over time, however, both groups showed an increasing tilt-angle slope but to a much greater degree in cerebellar patients. Two important conclusions emerge from these findings: the axis of eye rotation at the onset of head rotation is set to a value close to head-fixed (i.e., optimal for gaze stabilization during head rotation), independent of the cerebellum and once the head rotation is in progress, the cerebellum plays a crucial role in keeping the axis of eye rotation about halfway between head-fixed and that required for Listing's Law to be obeyed.

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