The noradrenergic neurotransmitter system has been implicated in the modulation of attention by electrophysiological, behavioral and functional neuroimaging studies. Pharmacological manipulations of the alpha(2)-adrenoceptor in particular are known to modulate attentional performance in both animals and humans. This effect, however, appears to depend crucially on the underlying level of arousal of the subject being tested. For example, arousing stimuli, such as white noise, can counteract beneficial or deleterious drug effects on performance. In practice, this means that effects of alpha(2)-agonists/antagonists on behavioral or physiological indices of attention are more pronounced when general arousal is relatively low. This overall pattern of effect represents an effect of the noradrenergic alpha(2) system on the interaction between arousal and attention. Functional neuroimaging results suggest the thalamus as one of the key neuroanatomical substrates for this effect.
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