The effects of increasing and decreasing striatal dopamine on inhibition of return: a psychopharmacologial investigation

Inhibition of Return (IOR) is the phenomenon of being slower to re-attend to previously attended locations, and is thought to improve the efficiency of attention. Previous studies of dopaminergic disorders indicate that excessive or insufficient dopamine signaling in the striatum of the brain reduces IOR. However, there have been no studies of the direct effects of dopamine depletion on IOR in healthy individuals, or that have compared the effect of dopamine increases and decreases within the same population. Therefore, in the present study, we administered a selective dopamine-2 receptor agonist and antagonist to the same healthy participants (cabergoline and amisulpride, respectively) and measured IOR. We further investigated the effects of dopamine manipulation on the underlying cognitive processes of IOR using event-related potentials. Both increased and decreased striatal dopamine reduced the IOR effect relative to placebo. These results provide evidence for an ‘inverted-U’ relationship between striatal dopamine levels and IOR. This can be explained by the dopamine manipulations altering frontostriatal connections, producing extremes in attentional flexibility and stability to interfere with IOR.