Organization and Development of Functional Representations in Visual Cortex

Project Summary/Abstract Establishing how features of the visual world are represented in the activity of cortical circuits, and how these representations are constructed during development, remain fundamental challenges for visual neuroscience and are central to understanding the neural basis of visual perception. A critical function of circuits in primary visual cortex is the integration of the inputs from the two eyes to create a single binocularly aligned representation of stimulus features such as the orientation of edges. This alignment is evident in the responses of individual neurons in visual cortex such that visual stimuli presented to either eye yield highly similar responses, giving rise to our coherent binocular perception of the world which, when disrupted, can lead to a host of symptoms that together are called binocular vision dysfunction. Research from this lab is focused on understanding the developmental mechanisms responsible for the binocularly aligned representation of orientation. This work demonstrates that binocularly aligned responses are not present at the onset of visual experience, emerge after a week of visual experience, and do not emerge in the absence of visual experience. In recent studies, we have determined the functional properties of the synaptic inputs to individual cortical neurons and how these inputs change with experience – leading us to a new hypothesis for the process of binocular alignment. Instead of the classic model of simple convergence of monocular input streams, we think that the highly aligned binocular responses of neurons in layer 2/3 (L2/3) of the visual cortex emerge from experience-driven changes in the functional coherence of monocular and binocular inputs to these neurons from two different sources: feedforward synaptic inputs from layer 4 (L4) and inputs from other L2/3 neurons that are part of a highly interconnected recurrent network. The goal here is to test this hypothesis by determining, for the first time, the distinct functional organization of feedforward and recurrent synaptic inputs to individual L2/3 neurons in experienced animals (Aim 1), comparing this with the organization in the visually naïve state and testing the role of visual experience in these changes (Aim 2), and evaluating the contribution of concurrent changes in the responses of L4 neurons to this process (Aim 3). Together, these experiments should provide a new understanding of the changes in the functional properties and the synaptic organization of feedforward and recurrent circuits that contribute to the rapid experience-driven emergence of the binocularly aligned representation of oriented stimuli in primary visual cortex.