Functional Organization of Visual Area MT

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DESCRIPTION (provided by applicant): The cerebral cortex consists of numerous, relatively discrete, areas that are specialized for various functions. In the visual system, the connections between these areas are orderly and hierarchical, with relatively more abstract representations of the visual world emerging at higher levels of the hierarchy. In addition, different visual attributes, such as motion and color, are, to a first approximation, processed in separate, parallel "streams." However, the visual system is also characterized by rich sets of interconnections between different processing streams, so that any given area will receive inputs from many other areas. What is the role of the various different inputs in generating the particular response properties of a given set of neurons? We propose to use the middle temporal visual area (MT or V5) as a model system with which to address this question. Because a number of higher-level visual motion computations have been identified in MT neurons, and because the different routes of information flow are reasonably well known, we can begin to dissect the role played by the various inputs in generating more complex receptive field properties. This proposal will focus on the anatomical and functional relationships between cortical and subcortical pathways to MT. A combination of novel anatomical techniques (multi-synaptic, retrograde viral tracers), functional techniques (single unit recording, reversible inactivation, 2-deoxyglucose) and behavior (eye movements) will be used to elucidate the role of the so-called "indirect pathways" in shaping the response properties of MT neurons. The result of these experiments will be a better understanding of the cortical circuitry that gives rise to the receptive field properties of MT neurons and of the role that they play in perception and visually guided behavior. Ultimately, these studies will inform our understanding of the biological basis of mental life, which is critical for the treatment and cure of mental disorders.