This project is aimed at the study of the neural mechanisms underlying processing and temporary storage of visual motion information in primate cortex. We will test the hypothesis that area MT, a mid-level cortical region specialized for the analysis of visual motion, also takes part in short-term retention of this information. We will also determine whether this participation is accomplished by the active connection of MT with neurons in prefrontal cortex, a region widely believed to play a key role in short-term retention of sensory information. To accomplish this goal we will take advantage of the retinotopy of area MT and use a behavioral task in which the monkeys are required to remember the direction of motion presented in one spatial location and compare it with another direction presented at a later time in a different spatial location. This will allow us to separately examine the neural processes that take place during encoding, storage and retrieval/comparison phases of the working memory task. We will use this behavioral paradigm in psychophysical experiments aimed at determining the nature of the remembered stimulus direction. We will also record from single MT neurons during the performance of this task. Furthermore, we will apply microstimulation of physiologically identified directional columns in MT during the period of storage of directional information. The same behavioral task will also be used during recordings from a region in prefrontal cortex, interconnected with area MT, previously shown to play a role in the circuitry sub-serving temporary storage of sensory information. Finally, we will examine the contribution of prefrontal cortex to the activity of MT neurons and to the performance of the working memory task. This will be achieved by reversibly inactivating the relevant region of prefrontal cortex and recording from MT neurons during the performance of the task. These studies will provide new information about the cortical mechanisms underlying the ability to retain information about stimulus motion.
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