Locus Coeruleus Vigilance and Stress: Brain Mechanisms of Adaptive Behavioral Responsiveness.

During this project period we made significant strides in understanding the role of the brain nucleus locus coeruleus LC in adaptive behavioral responsiveness. Progress included 1 substantial improvement of techniques to record LC neurons, and to make local microinjections into the LC, in behaving monkeys, 2 analyses of LC responsiveness to target cues during performance of a visual discriminationvigilance task, 3 analyses of changes in tonic LC activity with changes in attentiveness during task performance, 4 characterization of LC activity and behavioral performance during acquisition learning a new cue-contingency during reversal training, v analysis of effects of local pharmacological activation of LC neurons on vigilance performance and attentiveness, 5 development of a neural network model of LC function, and 6 improvement in techniques to retrogradely label afferents to monkey LC. Together, these studies have led to a new hypothesis of LC function, indicating that the LC serves to regulate neuronal and behavioral responsivity across a broad spectrum so as to promote either focused, task-defined performance or states of more labile, scanning attention which are optimal for changing, unpredictable environments.