Role of locus coeruleus in attention and behavioral flexibility

Previous findings have implicated the noradrenergic locus coeruleus (LC) sy stem in functions along the dimension of arousal or attention. It has remai ned uncertain what role this system has in attention, or what mechanisms ma y be involved. We review our recent work examining activity of LC neurons i n monkeys performing a visual discrimination task that requires focused att ention. Results indicate that LC cells exhibit phasic or tonic modes of act ivity, that closely correspond to good or poor performance on this task, re spectively. A computational model was used to simulate these results. This model predicts that alterations in electrotonic coupling among LC cells may produce the different modes of activity and corresponding differences in p erformance. This model also indicates that the phasic mode of LC activity m ay promote focused or selective attention, whereas the tonic mode may produ ce a state of high behavioral flexibility or scanning attentiveness. The im plications of these results for clinical disorders such as attention-defici t hyperactivity disorder stress disorders, and emotional and affective diso rders are discussed. (C) 1999 Society of Biological Psychiatry.