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NASA NTRS1998

Otoconia biogenesis, phylogeny, composition and functional attributes

This work consolidates data about these interesting organic crystals of vertebrate inner ears. It addresses 5 aspects of inner ear otoliths not completely understood to date: 1) embryological data that explains the formation of the crystals, 2) the significance of the organic and the inorganic phase of the otolith and the changing patterns of otoconia formation along the evolutionary tree, 3) otoliths contribution for detecting linear acceleration, 4) the effect that altered gravity and aminoglycosides have on the development and adult shape of the crystals, and the evolutionary significance of a changing shape of the crystals from primitive forms (lamprey) to high vertebrate birds and mammals is discussed, 5) functional attributes of the otolithic organs and morphological modifications of the otoliths by physical and chemical insults are presented with an extensive discussion of the most relevant literature published and available to us.

Non-NASA Center↗

NASA NTRS2016

Functional Responses in Otolith Structures from Micro- to Hyper-Gravity

Vertebrates and invertebrates sense gravito-inertial acceleration by mechanoreceptors in the otolith and statolith organs, respectively. These structures consist of ciliated sensory hair cells surmounted by biomineral grains of calcium carbonate (CaCO3) called oto-orstato-conia. The grains provide mechanical loading of hair cell cilia, and their high density increases sensitivity to acceleration. A widely considered mechanism by which the animal responds to a chronic change in amplitude of gravity is a change in weight lending otoconia. In G, it is argued, the organism counters the loss of gravity by increasing CaCO3 production, thereby increasing otolith mass, as a means to increase system gain. In hypergravity (HG), the converse is argued. Here, we present the results obtained in 3 species exposed both to G and HG. Adult toadfish, Opsanus tau, were exposed to G in 2 short-duration shuttle missions and to 1.24 1.73G centrifugation for 1-32 days; re-adaptation was studied following 1-8 days of 1G. Results show a biphasic pattern in response to 1.73G: initial hypersensitivity, similar to that observed after G exposure, followed by transition to a significant decrease at 16-32 days. Recovery from HG exposure is 4-8 days. Next, we examined directly the responses of statocyst receptors in the land snail after exposure to G on two unmanned Russian Orbital missions and at 1.24G. Similar to vertebrate afferents snail receptors increased their sensitivity to tilt after G exposure, and decrease it after 16-32 days of HG. Two major pieces of information are still needed: vertebrate hair cell response to altered gravity and impact of longer duration exposures on sensory plasticity. To address the latter, we applied electron microscopic techniques to image otoconia mass obtained from 1) mice subjected to 91-days of weightlessness in the Mouse Drawer System (MDS) flown on International Space Station, 2) mice subjected to 91-days of 1.24G centrifugation on ground, and 3) mice flown on 2 short-duration orbital missions. Images indicate a clear restructuring of individual otoconia, suggesting deposition to the outer shell. Images from their HG counterparts indicate the converse - an ablation of the otoconia mass. For shorter duration exposures to weightlessness on 13-day shuttle missions, mice otoconia appear normal. Despite the permanence of 1G in evolution, the animal senses exposure to a novel, non-1G, environment and adaptive mechanisms are initiated - in the short term, compensation is likely confined to the peripheral sensory receptors, the brain or both. For longer exposures structural modifications of the endorgan may also result. Support Contributed By: NASA 03-OBPR-04 and 11-11_Omni_2-0002

Vertebrates↗

NASA NTRS1993

Two-dimensional spatiotemporal coding of linear acceleration in vestibular nuclei neurons

Response properties of vertical (VC) and horizontal (HC) canal/otolith-convergent vestibular nuclei neurons were studied in decerebrate rats during stimulation with sinusoidal linear accelerations (0.2-1.4 Hz) along different directions in the head horizontal plane. A novel characteristic of the majority of tested neurons was the nonzero response often elicited during stimulation along the "null" direction (i.e., the direction perpendicular to the maximum sensitivity vector, Smax). The tuning ratio (Smin gain/Smax gain), a measure of the two-dimensional spatial sensitivity, depended on stimulus frequency. For most vestibular nuclei neurons, the tuning ratio was small at the lowest stimulus frequencies and progressively increased with frequency. Specifically, HC neurons were characterized by a flat Smax gain and an approximately 10-fold increase of Smin gain per frequency decade. Thus, these neurons encode linear acceleration when stimulated along their maximum sensitivity direction, and the rate of change of linear acceleration (jerk) when stimulated along their minimum sensitivity direction. While the Smax vectors were distributed throughout the horizontal plane, the Smin vectors were concentrated mainly ipsilaterally with respect to head acceleration and clustered around the naso-occipital head axis. The properties of VC neurons were distinctly different from those of HC cells. The majority of VC cells showed decreasing Smax gains and small, relatively flat, Smin gains as a function of frequency. The Smax vectors were distributed ipsilaterally relative to the induced (apparent) head tilt. In type I anterior or posterior VC neurons, Smax vectors were clustered around the projection of the respective ipsilateral canal plane onto the horizontal head plane. These distinct spatial and temporal properties of HC and VC neurons during linear acceleration are compatible with the spatiotemporal organization of the horizontal and the vertical/torsional ocular responses, respectively, elicited in the rat during linear translation in the horizontal head plane. In addition, the data suggest a spatially and temporally specific and selective otolith/canal convergence. We propose that the central otolith system is organized in canal coordinates such that there is a close alignment between the plane of angular acceleration (canal) sensitivity and the plane of linear acceleration (otolith) sensitivity in otolith/canal-convergent vestibular nuclei neurons.

NASA Discipline Neuroscience↗

NASA NTRS2008

Effect of Vestibular Impairment on Cerebral Blood Flow Response to Dynamic Roll Tilt

Change to upright posture results in reductions in cerebral perfusion pressure due to hydrostatic pressure changes related to gravity. Since vestibular organs, specifically the otoliths, provide information on position relative to gravity, vestibular inputs may assist in adaptation to the upright posture. The goal of this study was to examine the effect of direct vestibular stimulation on cerebral blood flow (CBF). To examine the role of otolith inputs we screened 165 subjects for vestibular function and classified subjects as either normal or impaired based on ocular torsion. Ocular torsion, an indication of otolith function, was assessed during sinusoidal roll tilt of 20 degrees at 0.01 Hz (100 sec per cycle). Subjects with torsion one SD below the mean were classified as impaired while subjects one SD above the mean were considered normal. During one session subjects were placed in a chair that was sinusoidally rotated 25 degrees in the roll plane at five frequencies: 0.25 & 0.125 Hz for 80 sec, 0.0625 Hz for 160 sec and 0.03125 Hz and 0.015625 Hz for 320 sec. During testing, CBF (transcranial Doppler), blood pressure (Finapres), and end tidal CO2 (Puritan Bennet) were measured continuously. Ocular torsion was assessed from infrared images of the eyes. All rotations were done in the dark with subjects fixated on a red LED directly at the center of rotation. In the normal group, dynamic tilt resulted in significant changes in both blood pressure and cerebral blood flow velocity that was related to the frequency of stimulus. In contrast the impaired group did not show similar patterns. As expected normal subjects demonstrated significant ocular torsion that was related to stimulus frequency while impaired subjects had minimal changes. These data suggest that vestibular inputs have direct effects on cerebral blood flow regulation during dynamic tilt. Supported by NASA.

Serrador, J. M.↗

NASA NTRS2000

Otoliths developed in microgravity

Little is known about mechanisms that regulate the development of the otoliths in the gravity-sensing organs. Several reported experiments suggest that the growth of the otoliths is adjusted to produce a test mass of the appropriate weight. If this is the case, larger than normal otoliths would be expected in animals reared in reduced gravity and a reduced mass, relative to 1-g controls, would be expected in animals reared at elevated g. In gastropod mollusks, the gravity-sensing organ is the statocyst, a spherical organ whose wall is made largely of sensory receptor cells with motile cilia facing the lumen. Dense statoconia in the cyst lumen interact with cilia of receptor cells at the bottom of the cyst and action potentials in their axons carry information on direction and magnitude of gravity and linear acceleration. In the marine mollusk, Aplysia californica, larvae reared at 2 to 5-g, the volume of statoconia was reduced in a graded manner, compared to 1-g control animals. In the statocyst of the fresh-water pond snail, Biomphalaria glabrata, reared in space in the Closed Equilibrated Biological Aquatic System (CEBAS), the number and total volume of statoconia was increased approximately 50%, relative to ground-reared controls. Lychakov found the utricular otolith to be 30% larger in space-reared Xenopus, whereas we found the saccular otolith to be significantly larger in newt larvae reared in space. In cichlid fish reared on a centrifuge, the saccular otolith was smaller than in 1-g controls. Here, we demonstrate that the otoliths of late-stage embryos of the swordtail fish, Xiphophorus helleri, reared in space on STS-89 and STS-90 (Neurolab) were significantly larger than those of ground-controls reared in functionally identical hardware.

short duration↗

NASA NTRS1984

Mammalian gravity receptors: Structure and metabolism

High performance liquid chromatography (HPLC) instrumentation was used for amino acid analysis of rat otoconial complexes. The amino acids of otoconial complexes pooled by origin from only 10 rats were analyzed. It is indicated that it should be possible to analyze complexes from only three rats, and perhaps fewer, which means that the method should be applicable to material from space flow rats. It is suggested that the organic otoconial phase is comparable in its complement of acidic amino acids to other calcium carbonate containing materials such as fish otoliths and certain mollusk shells. The organic material is high in acidic amino acids; and the relative proportions of aspirate, glutamate, threonine and serine appear to be similar to those found in neogastropod shells. Its significance to the evolution of biomineralization processes occurring in the animal kingdom is emphasized.

Ross, M.↗

NASA NTRS2003

Early Development of Gravity-Sensing Organs in Microgravity

Most animals have organs that sense gravity. These organs use dense stones (called otoliths or statoconia), which rest on the sensitive hairs of specialized gravity- and motion-sensing cells. The weight of the stones bends the hairs in the direction of gravitational pull. The cells in turn send a coded representation of the gravity or motion stimulus to the central nervous system. Previous experiments, in which the eggs or larvae of a marine mollusk (Aplysia californica, the sea hare) were raised on a centrifuge, demonstrated that the size of the stones (or test mass) was reduced in a graded manner as the gravity field was increased. This suggests that some control mechanism was acting to normalize the weight of the stones. The experiments described here were designed to test the hypothesis that, during their initial development, the mass of the stones is regulated to achieve a desired weight. If this is the case, we would expect a larger-than-normal otolith would develop in animals reared in the weightlessness of space. To test this, freshwater snails and swordtail fish were studied after spaceflight. The snails mated in space, and the stones (statoconia) in their statocysts developed in microgravity. Pre-mated adult female swordtail fish were flown on the Space Shuttle, and the developing larvae were collected after landing. Juvenile fish, where the larval development had taken place on the ground, were also flown. In snails that developed in space, the total volume of statoconia forming the test mass was 50% greater than in size-matched snails reared in functionally identical equipment on the ground. In the swordtail fish, the size of otoliths was compared between ground- and flight-reared larvae of the same size. For later-stage larvae, the growth of the otolith was significantly greater in the flight-reared fish. However, juvenile fish showed no significant difference in otolith size between flight- and ground-reared fish. Thus, it appears that fish and snails reared in space do produce larger-than-normal otoliths (or their analogs), apparently in an attempt to compensate for the reduced weight of the stones in space. The fish data suggest that there is a critical period during which altered gravity can affect the size of the test mass, since the larval, but not the juvenile, fish showed the changes.

Wiederhold, Michael L.↗

NASA NTRS1999

Low-Frequency Otolith Function in Microgravity: A Re-Evaluation of the Otolith Tilt-Translation Reinterpretation (OTTR) Hypothesis

On Earth, the low-frequency afferent signal from the otoliths encodes head tilt with respect to the gravitational vertical, and the higher frequency components reflect both tilt and linear acceleration of the head. In microgravity, static tilt of the head does not influence otolith output, and the relationship between sensory input from the vestibular organs, and the visual, proprioceptive and somatosensory systems, would be disrupted. Several researchers have proposed that in 0-g this conflict may induce a reinterpretation of all otolith signals by the brain to encode only linear translation (otolith tilt-translation reinterpretation or OTTR). Ocular counter-rolling (OCR) is a low-frequency otolith-mediated reflex, which generates compensatory torsional eye movements (rotation about the visual axis) towards the spatial vertical during static roll tilt with a gain of approximately 10%. Transient linear acceleration and off-axis centrifugation at a constant angular velocity can also generate OCR. According to the OTTR hypothesis, OCR should be reduced in microgravity, and immediately upon return from a 0-g environment. Results to date have been inconclusive. OCR was reduced following the 10 day Spacelab-1 mission in response to leftward roll tilts (28-56% in 3 subjects and unchanged in one subject), and sinusoidal linear oscillations at 0.4 and 0.8 Hz. OCR gain declined 70% in four monkeys following a 14 day COSMOS mission. Following a 30 day MIR mission OCR gain decreased in one astronaut, but increased in two others following a 180 day mission. We have studied the affect of microgravity on low-frequency otolith function as part of a larger study of the interaction of vision and the vestibular system. This experiment (E-047) involved off-axis centrifugation of payload crewmembers and flew aboard the recent Neurolab mission (STS 90). Presented below are preliminary results focusing on perception and the OCR response during both centrifugation and static tilt.

Moore, Steven T.↗

NASA NTRS1985

Mammalian Gravity Receptors: Structure and Metabolism

Calcium metabolism in mammalian gravity receptors is examined. To accomplish this objective it is necessary to study both the mineral deposits of the receptors, the otoconia, and the sensory areas themselves, the saccular and utricular maculas. The main focus was to elucidate the natures of the organic and inorganic phases of the crystalline masses, first in rat otoconia but more recently in otoliths and otoconia of a comparative series of vertebrates. Some of the ultrastructural findings in rat maculas, however, have prompted a more thorough study of the organization of the hair cells and innervation patterns in graviceptors.

Ross, M. D.↗

NASA NTRS1974

Model of human dynamic orientation

The dynamics associated with the perception of orientation were modelled for near-threshold and suprathreshold vestibular stimuli. A model of the information available at the peripheral sensors which was consistent with available neurophysiologic data was developed and served as the basis for the models of the perceptual responses. The central processor was assumed to utilize the information from the peripheral sensors in an optimal (minimum mean square error) manner to produce the perceptual estimates of dynamic orientation. This assumption, coupled with the models of sensory information, determined the form of the model for the central processor. The problem of integrating information from the semi-circular canals and the otoliths to predict the perceptual response to motions which stimulated both organs was studied. A model was developed which was shown to be useful in predicting the perceptual response to multi-sensory stimuli.

Ormsby, C. C.↗

NASA NTRS1992

Development of the gravity-sensing organs in the Japanese red-bellied newt, Cynops pyrrhogaster

Pre-mated adult female newts and fertilized eggs will be flown on the International Microgravity Laboratory-2 flight, schedule for 1994. One objective of the flight will be to observe the influence of microgravity on the development of the gravity-sensing organs in the inner ear. These organs contain sensory hair cells covered by a layer of dense stones (otoliths). Gravity and linear acceleration exert forces on these masses, leading to excitation of the nerve fibers innervating the hair cells. If the production of the otoliths is regulated to reach an optimal weight, their development would be abnormal in microgravity. Ground-based control experiments are reported describing the developmental sequence in which the otoliths and their associated sensory epithelium appear and increase in size. Three-dimensional reconstruction of serial sections through the otic vesicle of newt embryos at stages 31 through 40 demonstrate the first appearance, relative position and growth of the otoliths. In adult newts, the otoconia in the utricle appear similar to mammalian otoconia, which are composed of calcite. The newt saccular otoconia are at least 99% aragonite, as is found in most aquatic species. Reports of experiments in which fertilized frog eggs were flown on a Russian Cosmos mission conclude that the utricular otolith is increased in volume, whereas the saccular otolith maintains normal size, suggesting that at least the utricular weight might be regulated.

Wiederhold, Michael L.↗

NASA NTRS1974

A systems concept of the vestibular organs

A comprehensive model of vestibular organ function is presented. The model is based on an analogy with the inertial guidance systems used in navigation. Three distinct operations are investigated: angular motion sensing, linear motion sensing, and computation. These operations correspond to the semicircular canals, the otoliths, and central processing respectively. It is especially important for both an inertial guidance system and the vestibular organs to distinguish between attitude with respect to the vertical on the one hand, and linear velocity and displacement on the other. The model is applied to various experimental situations and found to be corroborated by them.

Mayne, R.↗

NASA NTRS1999

Oculomotor control of primary eye position discriminates between translation and tilt

We have previously shown that fast phase axis orientation and primary eye position in rhesus monkeys are dynamically controlled by otolith signals during head rotations that involve a reorientation of the head relative to gravity. Because of the inherent ambiguity associated with primary otolith afferent coding of linear accelerations during head translation and tilts, a similar organization might also underlie the vestibulo-ocular reflex (VOR) during translation. The ability of the oculomotor system to correctly distinguish translational accelerations from gravity in the dynamic control of primary eye position has been investigated here by comparing the eye movements elicited by sinusoidal lateral and fore-aft oscillations (0.5 Hz +/- 40 cm, equivalent to +/- 0.4 g) with those during yaw rotations (180 degrees/s) about a vertically tilted axis (23.6 degrees). We found a significant modulation of primary eye position as a function of linear acceleration (gravity) during rotation but not during lateral and fore-aft translation. This modulation was enhanced during the initial phase of rotation when there was concomitant semicircular canal input. These findings suggest that control of primary eye position and fast phase axis orientation in the VOR are based on central vestibular mechanisms that discriminate between gravity and translational head acceleration.

NASA Discipline Neuroscience↗

NASA NTRS1985

Development of otoconia in the embryonic chick (Gallus domesticus)

In the chick (Gallus domesticus) embryo, otoconium formation started first over the macula sacculi around the 4th day of incubation, and a day later over the macula utriculi. It was determined that each otoconium formed as a result of the segmentation of the immature otolithic membrane, and that the calcium responsible for otoconium calcification was incorporated into the organic matrix of each otoconium in the form of small electron-dense granules (20-150 nm in. diameter). The presence of calcium in these granules was confirmed by histochemical staining with osmic-potassium pyroantimonate, by EDTA chelation, and by X-ray micronanalysis under the electron microscope.

Fermin, C. D.↗

NASA NTRS1998

Visually induced adaptation in three-dimensional organization of primate vestibuloocular reflex

The adaptive plasticity of the spatial organization of the vestibuloocular reflex (VOR) has been investigated in intact and canal-plugged primates using 2-h exposure to conflicting visual (optokinetic, OKN) and vestibular rotational stimuli about mutually orthogonal axes (generating torsional VOR + vertical OKN, torsional VOR + horizontal OKN, vertical VOR + horizontal OKN, and horizontal VOR + vertical OKN). Adaptation protocols with 0.5-Hz (+/-18 degrees ) head movements about either an earth-vertical or an earth-horizontal axis induced orthogonal response components as high as 40-70% of those required for ideal adaptation. Orthogonal response gains were highest at the adapting frequency with phase leads present at lower and phase lags present at higher frequencies. Furthermore, the time course of adaptation, as well as orthogonal response dynamics were similar and relatively independent of the particular visual/vestibular stimulus combination. Low-frequency (0. 05 Hz, vestibular stimulus: +/-60 degrees ; optokinetic stimulus: +/-180 degrees ) adaptation protocols with head movements about an earth-vertical axis induced smaller orthogonal response components that did not exceed 20-40% of the head velocity stimulus (i.e., approximately 10% of that required for ideal adaptation). At the same frequency, adaptation with head movements about an earth-horizontal axis generated large orthogonal responses that reached values as high as 100-120% of head velocity after 2 h of adaptation (i.e., approximately 40% of ideal adaptation gains). The particular spatial and temporal response characteristics after low-frequency, earth-horizontal axis adaptation in both intact and canal-plugged animals strongly suggests that the orienting (and perhaps translational) but not inertial (velocity storage) components of the primate otolith-ocular system exhibit spatial adaptability. Due to the particular nested arrangement of the visual and vestibular stimuli, the optic flow pattern exhibited a significant component about the third spatial axis (i.e., orthogonal to the axes of rotation of the head and visual surround) at twice the oscillation frequency. Accordingly, the adapted VOR was characterized consistently by a third response component (orthogonal to both the axes of head and optokinetic drum rotation) at twice the oscillation frequency after earth-horizontal but not after earth-vertical axis 0.05-Hz adaptation. This suggests that the otolith-ocular (but not the semicircular canal-ocular) system can adaptively change its spatial organization at frequencies different from those of the head movement.

Non-NASA Center↗

NASA NTRS1997

Development of Gravity-Sensing Organs in Altered Gravity Conditions: Opposite Conclusions From an Amphibian and a Molluscan Preparation

Several components of the systems animals use to orient to gravity might develop differently in micrograms. If the growth of the "test masses" on which gravity acts (otoliths, in vertebrates, statoliths or statoconia in most invertebrates) is controlled on the basis of their weight, larger otoliths (or their analogs) would be expected to develop in micrograms. The vestibular systems in animals reared in altered gravity have been studied in several species, with varied results being reported. Early Russian reports of Xenopus larvae reared in space indicated no qualitative differences in the vestibular organs, compared to ground-reared controls. A similar lack of differences in Xenopus were reported. The ultricular otolith was 30% larger in space-reared Xenopus. No differences in saccular otolith volume between centrifuged and control adult rats were found. A delay in otoconial development in chick embryos reared at 2 grams on a centrifuge was reported but in a later report, no differences in otolith weight between 2 grams and control chicks were found. Increased optokinetic responses in flight-reared Xenopus tadpoles, suggesting that the animals reared in the absence of gravity made greater relative use of their visual system, rather than the vestibular system, in orienting to a moving stimulus was reported. To test early Japanese newt, CYnops pyrrhogaster, were maintained in orbit for 15 days on the IML-2 mission in 1994. All specimens reached orbit before any otoconia were formed and all major components of the inner ear were formed by the end of the flight. In ground-based studies of he Aplysia statocyst, the volume of the statolith in embryos and the number statoconia in post-metamorphic animals were compared between 1-gram controls and specimens reared at 2 to 5.7 grams.

Wiederhold, Michael L.↗

NASA NTRS1997

Development of gravity-sensing organs in altered gravity

Experiments are described in which the development of the gravity-sensing organs was studied in newt larvae reared in microgravity on the IML-2 mission and in Aplysia embryos and larvae reared on a centrifuge at 1 to 5 g. In Aplysia embryos, the statolith (single dense mass on which gravity and linear acceleration act) was reduced in size in a graded fashion at increasing g. In early post-metamorphic Aplysia or even in isolated statocysts from such animals, the number of statoconia produced is reduced at high g. Newt larvae launched before any of the otoconia were formed and reared for 15 days in microgravity had nearly adult labyrinths at the end of the IML-2 mission. The otoliths of the saccule and utricle were the same size in flight and ground-reared larvae. However, the system of aragonitic otoconia produced in the endolymphatic sac in amphibians was much larger and developed earlier in the flight-reared larvae. At later developmental stages, the aragonitic otoconia enter and fill the saccule. One flight-reared larva was maintained for nine months post-flight and the size of the saccular otolith, as well as the volume of otoconia within the endolymphatic sac, were considerably larger than in age-matched, ground-reared newts. This suggests that rearing in microgravity initiates a process that continues for several months after introduction to 1-g, which greatly increases the volume of otoconia. The flight-reared animal had abnormal posture, pointing its head upward, whereas normal ground-reared newts always keep their head horizontal. This suggests that rearing for even a short period in microgravity can have lasting functional consequences in an animal subsequently reared in 1-g conditions on Earth.

STS-65 Shuttle Project↗

NASA NTRS1991

Modeling the spatiotemporal organization of velocity storage in the vestibuloocular reflex by optokinetic studies

1. A generalized three-dimensional state space model of visual vestibular interaction was developed. Matrix and dynamical system operators associated with inputs from the semicircular canals, otolith velocity estimator, and the visual system have been incorporated into the model, which focus on their relationship to the velocity storage integrator. 2. A relationship was postulated between the eigenvalues and the direction of the eigenvectors of the system matrix and the orientation of the spatial vertical. It was assumed that the system matrix for a tilted position was a composition of two linear transformations of the system matrix for the upright position. One transformation modifies the eigenvalues of the system matrix, whereas another rotates the eigenvectors of the system matrix. The pitch and roll eigenvectors rotate with the head, whereas the yaw axis eigenvector remains approximately spatially invariant. 3. Based on the three-dimensional model, a computational procedure was formulated to identify the eigenvalues and eigenvectors of the system matrix with the use of a modification of the marquardt algorithm. With the use of data obtained from a monkey, it was shown that the three-dimensional behavior of velocity storage cannot be predicted solely in terms of its time constants, i.e., the inverse of its eigenvalues. With the use of the same eigenvalues the data could either be fit or not fit, depending on the eigenvector directions. Therefore, it is necessary to specify eigenvector directions when characterizing velocity storage in three dimensions. 4. Parameters found with the use of the Marquardt algorithm were incorporated into the model. Diagonal matrices in a head coordinate frame were introduced for coupling the visual system to the integrator and to the direct optokinetic pathway. Simulations of optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN) were run. The model predicted the behavior of yaw and pitch OKN and OKAN when the animal is upright. It also predicted the cross-coupling in the side down position. The trajectories in velocity space were also accurately simulated. 5. One of the predictions of the model is that when the stimulus direction is along an eigenvector, the trajectory in velocity space is a straight line. Using the "spectral width" of the residuals from a straight line sequence during OKAN, we developed a methodology to estimate how close the OKAN decay was to an eigenvector trajectory. 6. Thus we have developed a model-based approach for studying and interpreting the response characteristics of velocity storage in three dimensions.(ABSTRACT TRUNCATED AT 400 WORDS).

Non-NASA Center↗