The noradrenergic locus coeruleus (LC) system has been implicated in several behavioral functions, most notably response to salient sensory events. Recently we found that monkey LC neurons are phasically activated in close temporal relation to, and significantly preceding, behavioral responses in target-detection and forced-choice tasks. However, the function of these responses remains unknown. We hypothesize that the LC system is driven by decision processes that link sensory input to motor output, and that the phasic LC response facilitates the execution of behaviors engaged by the decision. Here we propose a set of behavioral and electrophysiological experiments to delineate the relationship between LC responses and decisions, to examine the role of the orbital frontal cortex in driving decision-related responses in LC, and to test for a causal role of such LC phasic activation in facilitating behavioral responses that have been decided upon. Together, these studies will establish the neurobiological basis in primates for the decision processes investigated in psychological, modeling and imaging studies in other projects of this Center.
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