Noradrenergic mechanisms are also implicated in action inhibition. Inhibitors of the norepinephrine transporter have been shown to facilitate action inhibition in the stop signal task in both rats and humans.122, 165–167 Direct injection of atomoxetine or the alpha-2A adrenoceptor agonist guanfacine into the prefrontal cortex is able to alter stop signal inhibition,168 providing evidence that prefrontal norepinephrine regulates response inhibition in this task. Additionally, reversal learning has also been shown to be improved by inhibition of the norepinephrine transporter169, 170 and by stimulation of the alpha-2A adrenoceptor.171
