Bbrainstem control of slow ocular drifts during gaze fixation

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During gaze fixation, tiny eye movements, including slow ocular drifts and microsaccades, continuously occur. Even though these eye movements have been known to exist for several decades, both their mechanisms of generation and their impacts on vision, perception, and cognition remain to be heavily under-investigated. During the past ~15 years, research on microsaccades has experienced a significant revival, especially in terms of neural mechanisms, but the mechanisms for slow ocular drifts remain to be a major research frontier. The main goal of our research proposal is to uncover the neural mechanisms for the control of slow ocular drifts at the level of the brainstem. We will investigate the causal role of brainstem omnipause neurons (OPNs) and superior colliculus (SC) in both drift and microsaccade control and coordination. We hypothesize that SC and OPNs engage synergistically such that SC activity provides a position estimate for ocular drifts and OPN activity influences eye velocity. The transformative aspects of our proposal are twofold. First, we will uncover hitherto unknown neurophysiological mechanisms associated with the smallest of eye movements. Second, given that a significant portion of systems neuroscience research with awake, behaving subjects is conducted under gaze fixation conditions, our work will clarify how much of behavioural and neural effects observed in such research may be a function of subliminal oculomotor behaviour. For example, ocular drifts occur incessantly and thus keep translating retinal images. If these eye movements turn out to be centrally controlled and not random, then their occurrence may contribute to the results of a variety of experiments on visual processing. Based on the outcome of our previous work with microsaccades, we anticipate that several classic phenomena in systems neuroscience may likewise eventually be cast in a different, yet intriguing, light as a result of our proposed research on ocular drifts.