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

Abstract

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 0.17-0.5 Hz, and durations between 60 and 75 s. Our results show a large vergence component to the AVOR response that systematically modulated with head velocity. We also examined our results for temporal-nasal preponderance in slow eye velocity. Although each subject showed some degree of directional preference, we did not find a systematically greater eye velocity for temporal-nasal direction across all subjects. Here, we present these findings and discuss that at least two possible sources could result in disconjugate eye movements during the horizontal rotational VOR in darkness: peripheral and central mechanisms.

The Horizontal Angular Vestibulo-Ocular Reflex: A Nonlinear Mechanism for Context-Dependent Responses

“…head position is small and negative for positive head velocities and positive for negative head velocities (small slope). This is consistent with the observations reported by [35] for control subjects. However, in the case of left canal plugging (light gray trend), the magnitude of vergence has increased and it's gain re.…”

“…However, binocular recordings of AVOR, delivered in darkness, in both human and monkey [35], show a considerable vergence component that is modulated with head velocity. Khojasteh and Galiana [35] suggested that a possible source for vergence responses in the dark could be a secondary effect of nonlinearities that are needed for modulation with sensori-motor context.…”

Hybrid nonlinear model of the angular vestibulo-ocular reflex

“…Moreover, compared to the pure slow phase model, the peak-to-peak amplitude of the vergence component is smaller in the hybrid model since nystagmus serves to limit non-linear functions to smaller excursions on non-linear surfaces at the premotor level. Contrary to common belief, the AVOR is not purely con- jugate in the dark; binocular recordings during sinusoidal rotations in darkness clearly show a vergence component in the AVOR [12]. Fig.3.C presents both the recorded and simulated vergence component.…”

“…We have also compared our model performance in response to a specific rotation profile ( 180 deg/s at 1/6 Hz) where binocular records are available [12]. Fig.…”

The conjugacy of the vestibulo-ocular reflex evoked by single labyrinth stimulation in awake monkeys

“…In the earlier study, binocular eye position signals were measured by the EOG. Without a rigorous treatment of the EOG signals, it would be difficult to overcome its limitations (nonlinearity and baseline drifts) in order to provide an accurate assessment of the VOR conjugacy (Schlag et al 1983; Khojasteh and Galiana 2009). In the present study, binocular eye position signals were measured using a search coil technique that has high spatial/temporal resolution, and excellent linearity and stability (Robinson 1963).…”