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Free keywords:
Animals, Female, Ferrets, Male, Molecular Imaging/methods, Motion Perception/*physiology, Neurons/physiology, Photic Stimulation/methods, Visual Cortex/*physiology
Abstract:
Visual experience plays a critical role in the development of direction-selective responses in ferret visual cortex. In visually naive animals, presentation of a bidirectional "training" stimulus induces rapid increases in the direction-selective responses of single neurons that can be predicted by small but significant direction biases that are present in neighboring neurons at the onset of stimulation. In this study we used in vivo two-photon imaging of calcium signals to further explore the contribution of visual experience to the emergence of direction- selective responses in ferret visual cortex. The first set of experiments was designed to determine whether visual experience is required for the development of the initial neighborhood bias. In animals that were dark-reared until the time of eye opening, we found that individual neurons exhibited weak direction-selective responses accompanied by a reduced but statistically significant neighborhood bias, indicating that both features arise without the need for visual experience. The second set of experiments used a unidirectional training stimulus to assess the relative roles of the neighborhood bias and visual experience in determining the direction preference that cortical neurons acquire during direction training. We found that neurons became more responsive to the trained direction even when they were located in regions of the cortex with an initial neighborhood bias for the direction opposite the training stimulus. Together, these results suggest an adaptive developmental strategy for the elaboration of direction-selective responses, one in which experience-independent mechanisms provide a symmetry-breaking seed for the instructive effects of visual experience.
