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Seiji Ono, Michael Mustari; Smooth pursuit adaptation in strabismic monkey with developmental esotropia. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1932.
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The smooth pursuit (SP) system is capable of adapting its output to produce optimal tracking of target motion. Short-term adaptation of SP can be produced experimentally using a double-step of target speed (double-step paradigm). Furthermore, we previously demonstrated that microelectrical stimulation (ES) in the pretectal nucleus of the optic tract (NOT) could provide “error” signals to produce SP adaptation (Ono and Mustari 2010). It is known that abnormal binocular vision during infancy leads to disorders including strabismus, which typically produces SP with low gain for temporalward tracking and unity gain during nasalward tracking (nasalward bias) during monocular viewing. In this study, we attempted to determine whether SP adaptation could occur for temporalward tracking in strabismic monkeys using double-step adaptation paradigm and ES of NOT.
First, we used a step-ramp tracking task with two different velocities (adaptation paradigm), where the target begins moving at one speed (10°/s) for first 100 ms and then changes to a lower speed (30°/s) for the remainder of the trial. Typically, 100-200 trials were used to adapt the smooth pursuit gain. Second, we applied brief (200ms) trains of micro-electrical (80µA) stimulation (ES) in one NOT to introduce directional (ipsiversive) error signals at the point in time where a second target speed appears in standard double-step paradigms.
SP adaptation using a double-step paradigm did not occur for temporalward SP in the strabismic monkey during monocular viewing. In contrast, when we applied micro-electrical stimulation in the NOT during the double-step paradigm, initial pursuit eye acceleration (first 100 ms) showed adaptive changes in the temporalward direction.
Our results indicate that ES of NOT, which is thought to provide retinal error signals to produce SP adaptation, could compensate for the asymmetric SP gain in strabismic monkeys. Therefore, we suggest that nasalward bias of SP in esotropic monkeys involves the cortical-NOT and the cerebellum.
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