Joseph W. Schumacher, Ph.D. - US grants

Project Summary Neurons in primary sensory regions of neocortex encode stimulus features that are important for perceptual representations of the external world, and the ability to use these representations to guide behavior is critical for survival. Substantial progress has been made in our understanding of how cortical circuits integrate, transform, and encode information as coherent neural representations of sensory features, but understanding the contribution of sensory circuits to behavior is a fundamental challenge for modern neuroscience. This is especially true in primary visual cortex (V1), where active behavioral modulation and long-term learning- related plasticity vary between model organisms, behavioral tasks, and other experimental conditions. The proposed aims of this study are designed to test specific hypotheses about the interaction of highly organized functional cortical architecture with the demands of perceptual tasks. Evidence from population recordings in tree shrew V1 layer 2/3 suggests that neuronal populations are theoretically capable of performing fine discriminations on the order of 10 degrees or less by taking advantage of a fine-scale, orderly progression of orientation preference within a cortical map, and preliminary data confirm that tree shrews themselves are behaviorally capable of such fine discriminations. This proposal will capitalize on the perceptual capacity of the tree shrew to test long standing theoretical questions about the differential contribution of neural populations to coarse and fine discrimination tasks, and will determine whether, and to what extent, learning- related changes in the properties of V1 populations might contribute to enhanced discrimination. To determine if visual processing of functional columnar orientation maps is linked to the behavioral performance of the animal, we will simultaneously use 2-photon imaging of the genetically encoded calcium indicator GCaMP6s over wide regions of V1 layer 2/3 while tree shrews perform coarse or fine discriminations. In addition to their map organization, neurons in layer 2/3 of tree shrew V1 represent the earliest stage of hierarchical cortical processing to encode orientation, and observing this stage of the visual circuit will address long standing questions about the relationship between emerging sensory representations and their causal role in perceptual decision making. Finally, we will address preliminary observations that fine discrimination learning occurs over multiple days of variable performance levels by determining the degree and timescale over which learning related plasticity may shape the response properties of visual cortical neurons to facilitate behavior. Tracking the response properties of layer 2/3 neurons longitudinally as animals progress from performing coarse discriminations to learning finer discriminations will allow us to ask whether the learning of fine orientation discriminations improves neural discrimination performance and where in the orientation preference map corresponding changes in neural responses occurred. Combined, these research aims will assess the link between the response properties of sensory neurons and behavior across multiple timescales to understand the basis for discrimination learning and performance in V1.