The question of how the brain enables one to learn new behavior on the basis of rewarding feedback is one of neuroscience's greatest challenges. Research in recent decades has produced considerable knowledge about the neurocircuitry that controls the muscular aspect of behavior and about brain structures that are involved in the perception of positive stimulation, but the location of a site in the brain where a reward circuit acts on a motor control circuit to change future behavior remains an enigma. The purpose of this project is to analyze the connections of a part of the brain where a reward circuit and a relatively well-understood motor circuit converge to determine its role in the learning of new behaviors. Monkeys will be taught to perform the simple behavior of moving the eyes back and forth between two target spots out of 25 possible spots on a video screen. They will be rewarded with direct brain stimulation for the time-consuming process of finding the correct pair of targets and gazing alternately between the two. The goals of the research are to (1) identify the specific areas in the brain where stimulation is sufficiently rewarding that the animal learns to find and alternate gaze between new targets; (2) identify the specific nerve pathways that pass through those areas to an area in frontal cortex where nerve cells are known to be active during the learning of eye movements; and (3) determine whether treatment of that area with neurochemical agents that temporarily disrupt its function prevents the learning of eye movements to new targets. Two animals have received cranial implants and one was tested sufficiently to demonstrate that it learned rapidly to make eye movements when rewarded by electrical stimulation of the medial dorsal nucleus of the thalamus.
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