Reward expectation, orientation of attention and locus coeruleus-medial frontal cortex interplay during learning

Regulation of attention and promotion of behavioural flexibility are functions attributed to both the noradrenergic nucleus locus coeruleus (LC) and the prefrontal cortex (PFC). The PFC receives a large innervation from LC and small changes in catecholaminergic activity in PFC profoundly affect cognitive function. It is crucial to the understanding of learning-related plasticity, that the cognitive context driving LC neurons be determined and the relation to activity in PFC be elucidated. To this end simultaneous recordings were made from LC and prelimbic cortex (PL) during an odour-reward association task in the rat. Neuronal activity related to orientation of attention, reward predictability, reward itself, and changes in stimulus reinforcement contingencies, was measured. All LC neurons and a significant proportion of PL neurons were engaged during several aspects of a Go/NoGo task, especially after the signal for trial onset and CS+ presentation. LC activation was, however, more tightly aligned to the behavioural response than to the CS+ 22% of PL neurons were activated during the response-reward delay. This suggests that the activity of both these structures is related to reward anticipation. Finally, LC neurons exhibited rapid plasticity when the reward-contingency was modified. Within-trial response latencies were always shorter in LC than in PL and between-trial response adaptation in LC preceded that in PL by many trials. Identifying such temporal relationships is an essential step toward understanding how neuromodulatory inputs to forebrain networks might promote or permit experience-dependent plasticity in behavioural situations.