Effects of V1 feedback on LGN function

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DESCRIPTION (provided by applicant): The long range goal of our research is to understand how thalamic neurons integrate their various feedforward and feedback inputs, and what role these inputs play in the flow of information from retina to cortex through the thalamus. Most of the inputs and synapses in the mammalian lateral geniculate nucleus (LGN) are extraretinal, but the way in which these diverse inputs are integrated to control the flow of visual information from retina to cortex is not understood. In particular, the influence of the descending inputs from the cortex and the perigeniculate nucleus (PGN) on the spatio-temporal properties of receptive fields of LGN relay neurons is unknown. To address this gap in our knowledge, we shall study the temporal and spatial aspects of receptive fields in monkey LGN before and during inactivation of the cortical feedback to the LGN. The dynamical properties will be probed with a double m-sequence stimulation paradigm, which will provide new information about both the linear and non-linear dynamics of these neurons, and will expose the effects that the feedback from V1 has on this dynamical behavior. Our hypothesis is that the corticofugal feedback to the LGN has a significant effect on four specific aspects of LGN function: dynamics, receptive field organization, transmission from retina to cortex and response gain. The proposed studies will furnish new information about the effects of the corticofugal pathway on several important dynamical and spatial parameters of the receptive fields of LGN relay cells. These findings will extend and deepen our understanding of the function of this massive yet elusive neural pathway, and pave the way for realistic modeling of the early stages of the visual system. Because such descending pathways are ubiquitous in the brain, the findings are likely to relevant to other reciprocally connected brain regions.