Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Neuroscience

Supervisor

Dr. Brian Corneil

Abstract

Humans and non-human primates must precisely align the eyes on an object to view it with high visual acuity. An important role of the oculomotor system is to generate accurate eye movements, such as saccades, toward a target. Given that each eye has only six muscles that rotate the eye in three degrees of freedom, this relatively simple volitional movement has allowed researchers to well-characterize the brain areas involved in their generation. In particular, the midbrain Superior Colliculus (SC), is recognized as having a primary role in the generation of visually-guided saccades via the integration of sensory and cognitive information.

One important source of sensory and cognitive information to the SC is the Frontal Eye Fields (FEF). The role of the FEF and SC in visually-guided saccades has been well-studied using anatomical and functional techniques, but only a handful of studies have investigated how these areas work together to produce saccades. While it is assumed that the FEF exerts its influence on saccade generation though the SC, it remains unknown what happens in the SC when the FEF is suddenly inactivated. To test this prediction, I use the combined approach of FEF cryogenic inactivation and SC neuronal recordings, although it also provides a valuable opportunity to understand how FEF inputs to the SC govern saccade preparation. Nonetheless, it was first necessary to characterize the eye movement deficits following FEF inactivation, as it was unknown how a large and reversible FEF inactivation would influence saccade behaviour, or whether cortical areas influence fixational eye movements (e.g. microsaccades).

Four major results emerged from this thesis. First, FEF inactivation delayed saccade reaction times (SRT) in both directions. Second, FEF inactivation impaired microsaccade generation and also selectively reduced microsaccades following peripheral cues. Third, FEF inactivation decreased visual, cognitive, and saccade-related activity in the ipsilesional SC. Fourth, the delayed onset of saccade-related SC activity best explained SRT increases during FEF inactivation, implicating one mechanism for how FEF inputs govern saccade preparation. Together, these results provide new insights into the FEF's role in saccade and microsaccade behaviour, and how the oculomotor system commits to a saccade.


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