T Raphan

..These data support the postulate that the correlation between vertical canal and otolith units is the critical factor in generating continuous unidirectional horizontal nystagmus during PWR...

..The study indicates that the vestibular system utilizes compensatory and orienting mechanisms to stabilize spatial orientation and gaze during walking and turning...

..Model processes have been related to peripheral and central neural behavior in order to gain insight into the nature of the three-dimensional organization and the controversial questions that are addressed...

..Since lesions that affected ocular pursuit had similar effects on ipsilateral OKN, processing for these two functions is probably closely linked in NOT, as it is elsewhere...

..This association could be an important context for expressing the adapted state of the aVOR gain during vertical head movement...

..The data show that compensatory eye, head, and body movements stabilize gaze during straight walking, while orienting mechanisms direct the eyes, head, and body to tilts of the GIA in space during turning...

..There was no difference between monkey and human cupular time constants from these estimates. It is likely that the human cupular time constant is similar to that of the monkey and shorter than previously thought...

..Promethazine is used to treat motion sickness including Space Adaptation Syndrome, but there is incomplete information about how it affects vestibular and optokinetic responses...

..Pathways through the inferior olive are presumably important for this adaptation...

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..We postulate that spatial orientation of the aVOR plays an important role in aligning gaze with the GIA and in maintaining balance during angular locomotion...

..Horizontal head movements during locomotion occur at the stride frequency of 1 Hz, where the IVOR gain is low. Horizontal eye movements are compensatory for head yaw at all viewing distances and are likely generated by the aVOR...

..07 s. The model accurately predicted responses of the normal and canal-plugged animals at all frequencies. These data show that the central vestibular system does not spatially adapt to losses resulting from canal plugging...

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..The adaptation is tuned by how the weights from otolith input to the canal-otolith-convergent neurons are adapted for a given head orientation...

..Semicircular canal input broadened the band-pass of these orienting reflexes, which would make them more appropriate when compensating for head movement during active motion...

..The purpose of this study was to investigate how reinforcement learning algorithms can assist the user in interacting with the database interface application that has been developed to improve the performance of the system...

..This system opens the possibility for studying eye movements in freely moving monkeys under a wide range of conditions...

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..It is likely that this gravitational dependence optimizes the stability of retinal images during movement in three-dimensional space...

..We found this two-radii model more accurate in estimating the three-dimensional eye positions than the traditional one-radius eye model...

..Because of its short latency, this reflex may be one of the earliest mechanisms to sustain blood pressure upon standing...

..This paper provides examples of ocular orientation generated by static tilt and off-vertical axis rotation in three dimensions and demonstrates specifically how vergence would support vision in the rabbit...

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..Thus, mechanisms in the rabbit increase compensatory eye velocity in the eye that leads into the direction of rotation and enhance binocular vision...

..These behavioral differences support the idea that there is a fundamental difference in the central organization of canal-otolith convergence of the roll and yaw/pitch aVORs...

..We conclude that the alteration in gain of the aVOR always occurs in the context of gravity...

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..Vertical gravity-dependent gain changes were not significantly different before and after surgery, indicating that the nodulus and uvula do not have a critical role in producing them...

..Thus, although pursuit alone does not contribute to visual following at higher frequencies, the interaction of binocular pursuit and the lVOR supported accurate binocular fixation for frequencies up to 3 Hz...

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..This could be realized physiologically by the head interface with the dens and occipital condyles during head oscillation with a contribution of the lower spine to pitch during locomotion...

..We postulate that the inability to control step frequency and adjust swing phase dynamics to slower walking velocities are major causes for the gait impairment in PD...

..These results suggest that the sensory-motor conflict that produces motion sickness involves coding of the spatial vertical by the otolith organs and body tilt receptors and processing of eye velocity through velocity storage...

..This convergence could provide the basis for gravity-dependent eye velocity orientation induced through velocity storage...

..We speculate that the brain may use these low amplitude rotating linear accelerations to generate eye velocities that help to orient gaze when making turns during normal locomotion...

..These findings are further confirmation that these regions of the vestibulo-cerebellum control spatial orientation of the aVOR...

..There were substantial neck and/or otolith-related inputs activating the vertical canal-related neurons in the nerve-sectioned animals, which could have contributed to oculomotor compensation after nerve section...

..These data demonstrate that head orientation to gravity plays an important role in both orienting and tuning the gain of the vertical aVOR...

..These data support the postulates that OVAR generates compensatory eye velocity through activation of velocity storage and that oscillatory components arise predominantly through lVOR orientation mechanisms...

..We conclude that the behavioral state associated with active body motion is necessary to maintain head stability in pitch and roll over the full range of stride/step frequencies encountered during walking...

..Such reorientation of central polarization vectors could provide the basis for changes in perception and eye movements related to prolonged head tilts relative to gravity or in microgravity...

..Similar orientation changes to prolonged exposure to complex motion environments may be responsible for producing post-stimulus motion sickness and/or mal de debarquement...

..At higher frequencies, vergence could also be driven by the linear vestibulo-ocular reflex (lVOR). Thus, vision in one nonmoving eye and the lVOR combine to generate convergence over a wide range of frequencies and viewing distances...

..The findings also raise the possibility that 'artificial gravity' during the Neurolab flight counteracted adaptation of these otolith-ocular responses...

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..These results are similar to those in humans, indicating that the gravity-dependent adaptation of the aVOR is likely to be a common phenomenon across species...

..The lack of effect of baclofen on the aVOR gain suggests that only GABA(A) receptors are utilized in the direct aVOR pathway...

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..In contrast, canal-convergent VO and VPS neurons optimize their response vector orientation to gravity when the head is oriented for prolonged periods...

..These findings indicate that the semicircular canals provide critical low frequency information to maximize the accuracy of stepping and stabilize the head during normal quadrupedal locomotion...

..5 Hz and shifted toward 270 degrees as frequencies were increased to 4 Hz. This study demonstrates that adaptation of COR gain is tuned to a frequency range at which the aVOR is compromised by the canal plugging...

..The otolith and canal inputs superposed when the animals were rotated about roll and pitch axes from an upright position. This insured that these neurons would respond over a broad frequency range from very low to high frequencies...

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..This provides further evidence that motion sickness is generated through velocity storage, not the direct pathway, and suggests that motion sickness susceptibility can be reduced by reducing the aVOR time constant...

..More data is necessary to evaluate this hypothesis, but if it were proven correct, in-flight short-radius centrifugation may help counteract orthostatic intolerance after space flight...

..A metric that computes the location of the tracks relative to the nuclei centers was then implemented. This methodology should be useful for quantifying and automating the procedure by which tracks are localized in anatomical structures...

..Although the response to convection currents dominates the normal response to caloric stimulation, velocity storage probably also contributes to the orientation of eye velocity...

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..Running on a 800 MHz Intel-based Dual Processor Pentium III, with a Matrox frame grabber, the system is capable of processing three-dimensional eye position at a rate of 120 frames/s...

..These studies should help us understand how the lVOR fosters clear vision during locomotion and help diagnose diseases associated with visual stabilization while walking. ..

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..When the study is completed, we will have a quantitative model of how the vestibular system contributes to maintenance of binocular gaze stability while moving. ..

..It should also elucidate the functional role of the velocity storage integrator in generating these movements...