Noradrenergic control of cognition: global attenuation and an interrupt function.

It is hypothesized that tonic central noradrenergic activity provides global attenuation, and this system's phasic reactions support an interrupt function. Under normal conditions, these functions enhance vigilance and orienting. Their absence during REM sleep allow greater spontaneous and associative activity and the merging of separate experiences in dreams. An abnormal diminishing of these functions during waking may result in the lack of control and inattentiveness seen in attention-deficit hyperactivity disorder. On the other hand, excessive noradrenergic activity may facilitate the occurrence of panic attacks as these functions undermine processes which normally moderate anxiety.