Neural basis of nystagmus and tracking deficits in visually deprived monkeys.

摘要

Primates perform eye movements that work in conjunction with the visual system. This cooperation is necessary to provide precise direction of the central retina toward visual images. Visual-oculomotor coordination requires visual experience in the early postnatal period to develop normally. If visual stimulation is disrupted in neonates, visually guided eye movements fail to mature normally. This dissertation addresses the neuropathophysiology at the root of abnormal visuomotor behavior and attempts to infer the experiential events that lead to them.;Gaze holding and visually guided tracking are susceptible to developmental injury. Infant monkeys simultaneously deprived of detailed vision in both eyes develop these behaviors abnormally. Gaze holding may become disturbed by latent nystagmus (LN) and tracking can be asymmetric (AT). Prolonged deprivation of vision in one eye then in the other consecutively produces similar deficits. Therefore, the hypothesis was advanced that simultaneity of the eyes' exposure to normal visual stimuli is a critical experience. An alternative idea is that frequent uniocular experience is necessary to normal development, because both preparations used prolonged deprivation of at least one eye. To distinguish these possibilities, daily alternating monocular occlusion (AMO) was used to deprive simultaneous binocular experience without prolonged disuse. We present evidence here that AMO spares gaze-holding mechanisms; simultaneous binocular visual experience is therefore unnecessary for development of gaze stability. We conclude that the necessary factor is high-frequency experience in each eye (period < 4 days). Obstructions lasting longer may result in LN/AT.;We measured the strabismus and mild AT resulting from AMO, and the LN/AT of other deprived animals. We related these to elements of human esotropia syndrome, and conducted neurophysiology experiments to elucidate their etiology. Our investigations into the neuropathophysiology of LN/AT show that deprived animals with LN/AT have abnormal receptive field properties in pretectal nucleus of the optic tract (NOT) units. In AMO-deprived animals lacking LN and strong AT, units in NOT and extrastriate STS were normal with regard to ocular sensitivity and directional sensitivity. Deprived binocular simultaneity apparently spares binocular representations in the extrastriate cortex and NOT. We suggest that gaze stability in AMO-reared animals is supported by binocular signals in extrastriate cortex and pretectum.;We also investigated the role of NOT neurons in pursuit tracking. NOT units were observed during performance of several pursuit tasks. Some NOT neurons may trigger voluntary smooth pursuit as well as involuntary optokinetic responses.