The behavioral function of the coeruleocortical system and the hypotheses implicating its role in mediating selective attention and behavioral inhibition to anxiogenic cues are evaluated. The diverse pattern of results produced by lesions induced by 6-hydroxydopamine on a variety of tasks (appetitive conditional discrimination, nonreversal shift, blocking, latent inhibition, distraction, taste aversion, neophobia, and conditioned emotional response) are integrated to achieve a tentative hypothesis of coeruleocortical noradrenergic function.There has been enormous interest in the functions of the nucleus locus coeruleus (LC) and its projections to the cortex via the dorsal noradrenergic bundle (DNAB) from several neurobiological perspectives. Although the nature of the afferents to the LC and the precise organization of the DNAB are still a matter for debate, it is perhaps of some functional significance that a single cell body can give rise to both ascending and descending axons innervating regions as diverse as the neocortex, hippocampus, cerebellum, and spinal cord. These peculiar features of organization suggest, for want of a better term, a rather "general" function whereby messages relayed to at least a proportion of noradrenergic (NA) cell bodies would result in the transmission of information to widespread regions, thereby influencing the special forms of processing occurring there.Although such general considerations imply rather nonspecific functions for the LC, we should like to avoid the temptation of assuming simply that this implies a role in nonspecific processes along the lines of the maintenance of cortical arousal by the reticular formation suggested originally by Hebb, Lindsley, and others. Recent neu-

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