To produce meaningful behavior, the brain must link information represented in sensory cortex to motor circuitry involved in the planning and execution of behavior. This linkage requires the integration of sensory cues across time and modality. Our research targets neurons in the association cortex of the parietal and frontal lobes, which are believed to play an essential role in working memory. These neurons discharge for several seconds before gaze is shifted to a remembered location in the visual field. Their response provides a temporal bridge between the spatial cues present in visual cortex and oculomotor circuitry. These neurons also appear to link the representation of visual motion toward a perceptual decision. We have recorded from neurons in the prefrontal cortex of two rhesus monkeys while they judged the direction of motion of a random dot display. We have studied neurons that are thought to play a role in spatial working memory and the planning of eye movements. The majority of these neurons are active when the monkey plans eye movements as a means of communicating its judgment about the direction of motion. Our findings suggest that the prefrontal and parietal cortex plays a role in both eye movement planning and visual processing. Using a reaction time paradigm, we have found that this activity arises before the monkey arrives at a judgment. This is the strongest evidence to date for a neural linkage between sensory processing and a contingent behavior. The experiments have begun to reveal the computations performed by neurons in association cortex, lending novel insight into the neurobiology of cognition and its disorders. We are optimistic that our results will lead to new understanding and treatment of such pernicious disorders as Alzheimer's disease, encephalopathy, and stroke.
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