On The Role of the Superior Colliculus in the Control of Visually-Guided Saccades

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Marino, Robert A.
Systems Neuroscience , Sensory to Motor Transformation
The ability to safely react to dangerous situations, or exploit opportunities within a dynamically changing world is fundamental for our survival. In order to respond to such changes in the environment, sensory information must first be received and processed by the nervous system before an appropriate motor response can be planned and executed. However, relatively little is known about how the central nervous system computes such sensory to motor transformations that are so critical for guiding efficient behavior. This thesis explores some of the neural mechanisms that underlie the visuomotor transformations that guide eye movements. Specifically, this thesis studied saccades (rapid eye movements critical for visual orienting in primates) and examined the relationships between visual and motor signals in the primate Superior Colliculus (SC, a midbrain structure located at the nexus between visual input and motor output that is critical for visual orienting). I recorded extracellular action potentials (spikes) from single neurons related to: 1) the appearance of visual saccade targets; 2) saccade planning and preparation; and 3) the execution of precise saccades that orient to visual targets. In this thesis I present four studies that examine the relationships between visual and motor related responses in the SC during visually guided saccades. In chapter 2 I examined the alignment between visual and motor response fields and concluded that they were well aligned. In chapters 3 and 4 I explored how visual responses were modulated by stimulus intensity and how this modulation influenced saccade behavior. I concluded that luminance modulated multiple properties of the visual response including the timing and maximum discharge rate and these changes were highly correlated to changes in saccade latency and metrics. In the fifth chapter I applied some of the knowledge gained from the previous chapters to develop a neural network model of the SC that was capable of simulating saccadic sensory to motor transformations and predict saccadic reaction time. I concluded that saccade latency was strongly dependant on the spatial interactions of visual and saccade related signals in the SC. Together, these findings provide novel insight into the neural mechanisms underlying saccadic sensorimotor transformations.
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