LAUSR

RATIONALE The effects of atomoxetine (ATO) on response inhibition have been typically examined using the stop signal task (SST) which is however confounded by attentional capture. The right inferior frontal cortex (rIFC) has been implicated in the modulation of ATO on inhibitory control, but a precise characterisation of its role is complicated by its functional inhomogeneity. OBJECTIVES The current study aimed to directly investigate the effect of ATO in the SST using the imaging contrast unconfounded by attentional capture, to test the specific drug actions in functionally dissociable rIFC subregions, and to explore the role of locus coeruleus (LC), the main source of cortical noradrenaline, in mediating the drug effects. METHODS This imaging study investigated the effect of ATO (40 mg) in 18 human participants during a modified SST that unconfounds attention from inhibition. Functional definitions for rIFC subdivisions were adopted in the analyses to isolate attention and inhibition during action cancellation. The LC integrity was measured in vivo using a neuromelanin-sensitive sequence. RESULTS We identified one mechanism of ATO modulation specific to inhibitory control: ATO enhanced activity in pre-supplementary area (pre-SMA) for motor inhibition, and the recruitment of temporoparietal junction (TPJ) and inferior frontal junction (IFJ) for functional integration during response inhibition. Moreover, drug-related behavioural and neural responses correlated with variations in LC integrity. CONCLUSIONS These findings provide a more nuanced and precise understanding of the effects of ATO on specific and domain general aspects of stopping.