Gaze holding in healthy subjects.

Eccentric gaze in darkness evokes minor centripetal eye drifts in healthy subjects, as cerebellar control sufficiently compensates for the inherent deficiencies of the brainstem gaze-holding network. This behavior is commonly described using a leaky integrator model, which assumes that eye velocity grows linearly with gaze eccentricity. Results from previous studies in patients and healthy subjects suggest caution when this assumption is applied to eye eccentricities larger than 20 degrees.

Effectiveness of systemic high-dose dexamethasone therapy for idiopathic sudden sensorineural hearing loss.

Objective: To evaluate the effectiveness of systemic high-dose dexamethasone therapy for sudden sensorineural hearing loss in comparison to the previous treatment regimen at our clinic with systemic prednisone 100 mg daily for 7 days analyzed in a previous study.

Methods: We conducted a retrospective review of an electronic patient data base of 79 patients with idiopathic sudden sensorineural hearing loss. The standard treatment was orally applied dexamethasone (1st to 3rd day: 40 mg daily, 4th to 6th day: 10 mg daily) in an ambulant setting.

Eye position dependency of nystagmus during constant vestibular stimulation.

Alexander's law, the eye position dependency of nystagmus due to peripheral vestibular lesions, has been hypothesized to occur due to adaptive changes in the brainstem velocity-to-position neural integrator in response to non-reciprocal vestibular stimulation. We investigated whether it develops during passive head rotations that produce constant nystagmus for >35 s. The yaw rotation stimulus consisted of a 1-s acceleration (100°/s(2)), followed by a lower acceleration ramp (starting at 7.

A re-examination of the time constant of the oculomotor neural integrator in human.

We studied the horizontal oculomotor neural integrator in healthy human subjects during gaze holding in darkness. We found large variability among subjects with respect to the estimated time constants and the integrator's null position. We also found that individual subjects could demonstrate significantly nonlinear drift velocities as a function of eye position.

A mechanism for eye position effects on spontaneous nystagmus.

In acute stages of unilateral vestibular deficit, the imbalanced tonic activity on vestibular afferents evokes spontaneous nystagmus. The slow-phase velocity of this nystagmus varies with eye position, such that it is smaller when looking in the direction of slow-phases. The neural mechanism for this behavior is still not understood.

Development of eye position dependency of slow phase velocity during caloric stimulation.

The nystagmus in patients with vestibular disorders often has an eye position dependency, called Alexander's law, where the slow phase velocity is higher with gaze in the fast phase direction compared with gaze in the slow phase direction. Alexander's law has been hypothesized to arise either due to adaptive changes in the velocity-to-position neural integrator, or as a consequence of processing of the vestibular-ocular reflex. We tested whether Alexander's law arises only as a consequence of non-physiologic vestibular stimulation.

A dynamic model for eye-position-dependence of spontaneous nystagmus in acute unilateral vestibular deficit (Alexander's Law).

Spontaneous nystagmus (SN) is a symptom of acute vestibular tone asymmetry. Alexander's Law (AL) states that slow-phase velocity of SN is higher when looking in the direction of fast-phases of nystagmus and lower in the slow-phase direction. Earlier explanations for AL predict that during SN, slow-phase eye velocity is a linear function of eye position, increasing linearly as eye deviates towards the fast-phase direction.

Primate disconjugate eye movements during the horizontal AVOR in darkness and a plausible mechanism.

Disconjugate eye movements during the horizontal angular vestibulo-ocular reflex (AVOR) evoked in response to steps or pulses of head velocity have been previously reported in lateral eyed animals. In this study, we measured binocular responses to sustained sinusoidal and pseudo-random vestibular stimuli in yaw, delivered in darkness, in both human and monkey. The vestibular stimuli used in our experiments had peak velocities in the range of 120-200 degrees /s, frequencies in the range of 0.

Implications of gain modulation in brainstem circuits: VOR control system.

Gain modulation is believed to be a common integration mechanism employed by neurons to combine information from various sources. Although gain fields have been shown to exist in some cortical and subcortical areas of the brain, their existence has not been explored in the brainstem. In the present modeling study, we develop a physiologically relevant simplified model for the angular vestibulo-ocular reflex (VOR) to show that gain modulation could also be the underlying mechanism that modifies VOR function with sensorimotor context (i.

Neural computation in the binocular VOR circuit: a theoretical study.

We present here a bilateral model for the horizontal rotational vestibulo-ocular reflex (VOR) that integrates sigmoidal nonlinearities in the response of VOR interneurons. This model realistically links the systems level approach to the underlying neural mechanisms. It is capable of producing VOR modulations with viewing context using only the efference copies of eye position signals to make novel predictions.

Modulation of vergence during the vestibulo-ocular reflex.

It is commonly believed that during the compensatory slow-phases of the vestibulo-ocular reflex (VOR), eyes move in a perfectly conjugate fashion (i.e. the vergence component is zero).

A nonlinear model for context-dependent modulation of the binocular VOR.

Studies on the behavior of the vestibulo-ocular reflex (VOR) reveal that the monocular reflex gain is adjusted according to target position relative to each eye. In this paper, we present a nonlinear approach in modeling the viewing-context dependency of the slow-phase angular VOR. We show that including appropriate nonlinearities in the responses of premotor neurons in the brainstem is sufficient to account for the online modulation of the VOR with target position.