Learning is an immensely complicated process for which some of the basic network level principles are not well understood. Characterizing these low-level properties is essential to building accurate models of more complicated learning phenomena. The barn owl auditory localization pathway is a system which is uniquely amenable to the study of such basic principles of learning. This pathway has three properties making it ideal;1) the computations in this pathway are complex, yet well understood (Singheiser, Gutfreund, &Wagner, 2012), providing a solid theoretical framework to operate in, 2) structures in this pathway have distinct and well characterized topographical mapping to the sensory environment (Knudsen &Knudsen, 1983), making it possible to measure learning in a predictable fashion, and 3) systematic misalignment of paired audio-visual experiences (accomplished by rearing with prism-goggles) robustly induces adaptive plasticity in the connections between the presynaptic lateral shell of the central nucleus of the inferior colliculus (ICCls) and the postsynaptic external nucleus of the inferior colliculus (ICX) (Brainard &Knudsen, 1993). Three decades of research in this pathway have yielded a rich understanding of the structural and functional changes that accompany induced plasticity, but the signals which drive this learning are not well understood. The prevailing hypothesis is that learning induced by audio-visual disparity occurs through hebbian-mechanisms (neurons that fire together, wire together) (Bergan &Knudsen, 2009). I will test this by using in vivo multi-electrode recordings from single neurons in the ICCls and ICX of the barn owl localization pathway to measure coincident firing in response to paired audio-visual stimuli. Furthermore it is believed that the deep layers of the optic tectum (OTd) drive plasticity in the adaptive network via connections to the ICX (Gutfreund, 2002). While this theory is supported by anatomical evidence (Luksch, Gauger, &Wagner, 2000), the functional relationship between the OTd and the adaptive auditory localization pathway has not been directly measured. I will use in vivo paired electrode recordings from single units in the ICX and OT while presenting unimodal and plasticity inducing audio/visual stimuli to characterize the functional connections the OTd forms on the ICX. These experiments will be conducted in normal, and prism-goggle adapted owls. The proposed experiments are essential for testing current hypotheses describing how the functional relationships between the ICCls, ICX and OTd give rise to the thoroughly characterized plasticity induced by audio-visual disparity.
There are large holes in our understanding of how changes occur in systems of neurons to result in learning. Unveiling network-level principles of plasticity is essential to for understanding learning disorders and other mental disorders, advancing prosthetics and cross-pollinating computer science. The proposed research uses a well vetted model system, uniquely amenable to probing systems level principles of learning, to fill those holes.
