Neural Mechanisms of Stereoscopic Vision

University Of Virginia, Charlottesville VA

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Abstract

Project Summary/Abstract Stereopsis is the perceptual process in which the brain combines and compares the input from the two eyes to reconstruct the three-dimensional visual world. Despite the importance of stereoscopic vision in healthy and diseased conditions, its underlying circuit mechanisms remains poorly understood. Here, tree shrews are used as an animal model for stereopsis research. The tree shrew offers many advantages, such as a highly developed visual system, primate-level selectivity for binocular disparity, and a short reproductive cycle that allows for developmental studies. In Aim 1, the investigators will reveal the spatial organization of disparity selectivity in tree shrew primary visual cortex (V1). Two-photon Ca2+ imaging will be performed to determine the orientation maps in V1 and the disparity selectivity of individual neurons in response to random dot stereograms and dichoptic sinusoidal gratings. Multi-channel electrophysiological recordings will also be conducted and guided by the imaged maps. These experiments will reveal the relationship between disparity tuning and orientation selectivity and the spatial profile of disparity selectivity across layers and cortical maps. Aim 2 will test the hypothesis that inhibitory neurons in tree shrew V1 are sharply tuned to disparity, thereby mediating the orientation-specific recurrent inhibition. This is done by 2-photon Ca2+ imaging using cell type specific viral expression of Ca2+ indicators in inhibitory neurons, and their subtype identity is then revealed ex vivo using fluorescent in situ hybridization. The activity pattern, response dynamics, and disparity tuning of these neurons will be determined. Parallel experiments will be performed in mice using transgenic lines that label specific subtypes of inhibitory neurons. These experiments will reveal whether subtypes of inhibitory neurons show distinct tuning properties to binocular disparity and whether these properties differ between species. Aim 3 will determine the synaptic connectivity of disparity selective neurons in tree shrew and mouse V1, by dendritic imaging in both excitatory and inhibitory neurons. The experimental results in all aims will then guide the implementation of a biologically realistic network model for disparity selectivity, which will then make testable predictions for subsequent experiments. Together, by comparing two species that have different cortical architecture and disparity selectivity, and by combining in vivo experiments and computational modeling, these studies will reveal general principles of stereoscopic vision. Because stereopsis is disrupted in people suffering from amblyopia and strabismus, this project will provide novel insights into the understanding and treatment of these disorders.