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Tremblay, Léon, Jeffrey R. Hollerman, and Wolfram Schultz. Modifications of reward expectation-related neuronal activity during learning in primate striatum. J. Neurophysiol. 80: 964–977, 1998. This study investigated neuronal activity in the anterior striatum while monkeys repeatedly learned to associate new instruction stimuli with known behavioral reactions and reinforcers. In a delayed go-nogo task with several trial types, an initial picture instructed the animal to execute or withhold a reaching movement and to expect a liquid reward or not. During learning, new instruction pictures were presented, and animals guessed and performed one of the trial types according to a trial-and-error strategy. Learning of a large number of pictures resulted in a learning set in which learning took place in a few trials and correct performance exceeded 80% in the first 60–90 trials. About 200 task-related striatal neurons studied in …