Abstract
Locus ceruleus (LC) neurons are phasically activated at short latencies selectively by target stimuli but not by other task events. This response is easily shifted to the new target cue after reversal training, confirming that these responses are driven by stimulus meaning. Optimal performance has been associated with an intermediate level of tonic LC discharge. In addition, phasic responses to target stimuli occur only during epochs of excellent task performance associated with intermediate tonic LC activity. A computational model of the LC explains the relationship between patterns of LC firing and task performance by changes in electrotonic coupling among LC neurons. Specifically, it demonstrates that an increase in coupling results in greater phasic responses to target but not nontarget cues and also produces lower spontaneous (tonic) activity. This model can predict possibility of modulated electrotonic coupling among LC neurons to be an important factor that regulates LC activity and its role in behavioral performance. This chapter describes recording of such LC neurons in monkeys during performance of a visual discrimination task. This task required animals to stably foveate a central fixation spot on a video monitor.
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