Norepinephrine and Neural Interrupts

Experimental data indicate that norepinephrine is critically involved in aspects of vigilance and attention. Previously, we considered the function ofthis neuromodulatory system on a time scale of minutes and longer, and suggested that it signals global uncertainty arising from gross changes in environmental contingencies. However, norepinephrine is also known to be activated phasically by familiar stimuli in welllearned tasks.Here, we extend our uncertainty-based treatment of norepinephrine tothis phasic mode, proposing that it is involved in the detection and reaction to state uncertainty within a task. This role of norepinephrine canbe understood through the metaphor of neural interrupts.